EmDrive study officially published
arc.aiaa.org
arc.aiaa.org
A couple more posts about this:
In 1933 von Neumann basically published a proof against the idea of any hidden-variable theory. It took 30 years but Bell then discredited it.
My guess is that a lot of this will get revisited. The outcome of this in the next 10-20 years might be really cheap probes (via reusable launch vehicles like SpaceX is making) that need no propellent to continue onto their merry way for a long time. The current way of doing this would be using solar sails or something along those lines which is not exactly compact.
Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.
Agreed.
> Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.
I'm not sure that actually works. Most use cases are for exploring the outer solar system, or even outside of our solar system. As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.
In space you move in elipses. It's possible to choose an elongated orbit that moves the probe closer and then further from the sun repeatedly and each time it is close to the sun it accelerates forward, moving the "far" side of orbit further away, until it gains enough speed to escape sun gravity.
Or at least it's possible in Kerbal Space Program :)
EDIT: Ok, let's think through the calculus here. Kepler's 2nd law says that the area swept by the line between a planet and the Sun is constant, i.e., r^2 dθ/dt = 2 π a b / P where a and b are the semi-major and semi-minor axes and P is the orbital period. Thus dt / r^2 = P dθ / (2 π a b); and the former is the instantaneous power absorbed. Integrating over an orbit, we get E = P / (a b); or the average power absorbed is proportional to 1 / (a b).
Since the energy of an orbit is determined solely by the semi-major axis a, this means the power absorbed for any given orbital energy is maximized for b ≪ a; so you're right, that highly eccentric orbits are a better way to acquire energy for the purpose of orbital escape. (Subject of course to practical considerations of energy storage -- you'll absorb the most power at exactly the time you don't want to be changing your momentum.)
if you have an efficient insulator, you could absorb an arbitrarily large amount of heat at the perigee, and retain it for the remainder of the orbit.
if you were in a circular orbit, you'd only be able to absorb up to the ambient temp.
Thanks for doing the math. But I'm still confused, I thought you do want to accelerate when near the sun, as that makes the far end of the orbit go further? Again, no math behind, just how it worked in KSP :)
You should trust KSP more than you trust me. :-)
http://www.askamathematician.com/2013/01/q-how-does-the-ober...
By the way, I only know about it because I played KSP a lot ;).
It doesn't just work with orbits and rockets and propellants, it works just as well with an oscillating weight on a spring that you flick with your fingers.
Or maybe it's just a waste of time/money? (I'm not being facetious for the sake of it. See cjensen's comment[1])
The research shown is relatively inexpensive, and can be pulled off with what many labs probably have lying around anyways.
I'm sure it's more a work of love anyways and the guys doing this are probably facing serious headwind for trying 'crazy stuff'.
I would like to think tenure still produces crazy scientists
Crazy stuff becomes an option after one is granted tenure, it doesn't necessarily make one more likely to achieve tenure. On the other hand, theoretical physicists aren't very expensive -- they only need a blackboard and an eraser. Compare that to a philosopher -- much the same but without the eraser.
(Sure, some good researchers turn into cranks later in life[1], but usually in a different -- often unrelated -- field.)
[1] Nobel prize winners often succumb to this, sadly.
https://en.wikipedia.org/wiki/Linus_Pauling#Medical_research...
http://arxiv.org/pdf/1604.03449v1.pdf >McCulloch (2007) has proposed a new model for inertia (MiHsC) that assumes that the inertia of an object is due to the Unruh radiation it sees when it accelerates, radiation which is also subject to a Hubble-scale Casimir effect. In this model only Unruh wavelengths that fit exactly into twice the Hubble diameter are allowed, so that a greater proportion of the waves are disallowed for low accelerations (which see longer Unruh waves) leading to a gradual new loss of inertia as accelerations become tiny. MiHsC modifies the standard inertial mass (m) to a modified one (m_i) as follows: m_i = m (1-(2c^2)/(|a|Θ)) = m (1 - λ/4Θ) (1) where c is the speed of light, Θ is twice the Hubble distance, ’|a|’ is the mag- nitude of the relative acceleration of the object relative to surrounding matter and λ is the peak wavelength of the Unruh radiation it sees. Eq. 1 predicts that for terrestrial accelerations (eg: 9.8m/s2) the second term in the bracket is tiny and standard inertia is recovered, but in low acceleration environments, for example at the edges of galaxies (when a is small and λ is large) the sec- ond term in the bracket becomes larger and the inertial mass decreases in a new way so that MiHsC can explain galaxy rotation without the need for dark matter (McCulloch, 2012) and cosmic acceleration without the need for dark energy (McCulloch, 2007, 2010).
As I understand it McCulloch's requirement that wavelengths fit within the cosmic horizon is an assumption, not a proven logical implication.
Additionally I think a lot of physicists are dismissive because they expect someone who desires to upend mainline theory to at least demonstrate fluency with the mathematics of mainline theory. McCulloch falls short of this.
All that said, I think he's genuine in his pursuit and I've really enjoyed reading his blog over the years.
[1]https://www.reddit.com/r/EmDrive/comments/3hjmtv/my_conversa...
Skepticism is warranted, but the team behind this study seems to be proceeding with a healthy dose of it, and AFAIK they have not made any inappropriate claims. The results so far are interesting, the experiments do not seem terribly expensive, and I see no reason why they shouldn't be followed to their conclusion (which will probably be the discovery of a mundane explanation for the phenomenon that's been observed).
Yes, but nobody's ACTUALLY saying that -- that's just the typical narrative of people-selling-perpetual-motion-machines. (Who, you'll note, have a slightly different agenda.).
What's actually going on is that everybody's saying "this would require New Physics -- hold your horses!"... and the response seems to be "YEAH, BUT WHAT IF?!??!".
Pithy answer to the "what if" challenge: Not good enough.
You asked "Or maybe it's just a waste of time/money?", which is a question for the scientific community, but most of the "WHAT IF?!??!" reactions seem to be coming from the public.
edit: I replied before you edited your post fairly heavily; I think what I said still applies, though.
> You asked "Or maybe it's just a waste of time/money?", which is a question for the scientific community, but most of the "WHAT IF?!??!" reactions seem to be coming from the public.
I really don't understand this. Is this some sort of PoMo response to my original challenge, or...?
My contention is that the public interest may not necessarily have much to do with what the public is interested in. I don't think this a particularly controversial PoV...?
(Though I do have reservations about it, but -- personally -- I've just about given up on even basic scientific literacy. You may be less jaded.)
[1] Readability suffers, but DFW approves "from heaven". I must admit I'm quite DFW-like in that I cannot halt the loop before I write something, so here we are... with massive edits and such.
No worries
> I really don't understand this. Is this some sort of PoMo response to my original challenge, or...?
What's PoMo?
My interpretation of your first comment was that you were questioning whether this research is worth more time and money based on skepticism rooted in scientific knowledge i.e. these "new physics" needed to explain the EmDrive would conflict with a lot of what we currently think of as scientific "fact". Occam's razor, and so on.
My interpretation of your second comment was that you think the "YEAH, BUT WHAT IF?!??!" reactions to this research (generally associated with internet comment sections) are inappropriate and rooted in ignorance of scientific principles (FWIW, I agree with you on that).
I see those as separate concerns. The public is wholly ignorant, and their reaction to the results of this research to date (filtered as they are through awful clickbait articles) should have no bearing either way on whether the research continues. That's the point I was trying to make in my second comment.
> My contention is that the public interest may not necessarily have much to do with what the public is interested in. I don't think this a particularly controversial PoV...?
I don't think so either (and I agree).
PoMo refers to Post Modernism , which is afaiu , "Literary/whatever Theory" that, I think, seems to embrace reletavism
We are currently shooting missiles that cost $800,000 each at people in caves on the other side of the world from boats that cost $4.4 billion dollars each. If anyone can justify that expenditure, I think we can find a small fraction of that money to investigate this further.
http://news.nationalpost.com/news/world/at-800000-per-round-...
However, the justification (OK, a justification) for that action, as part of the war on terror (I believe this is your implication, based on the 'caves' reference) would be that the insured costs of 9/11 were around USD 40 billion [1] (ignoring the unknown intangible additional cost in human life) so spending USD 800000 to kill a terrorist who is planning to perform a similar event is something of a bargain.
But, this sort of logic is flawed to begin with: We spend X on Y, which I disapprove of, therefore we should spend epsilon on Z instead.
[1] https://en.wikipedia.org/wiki/Economic_effects_arising_from_...
http://www.military.com/daily-news/2016/11/22/new-zumwalt-br...
>However, the justification (OK, a justification) for that action, as part of the war on terror (I believe this is your implication, based on the 'caves' reference) would be that the insured costs of 9/11 were around USD 40 billion [1] (ignoring the unknown intangible additional cost in human life) so spending USD 800000 to kill a terrorist who is planning to perform a similar event is something of a bargain.
Except for the fact that that justification is false. We've spent over $5 Trillion fighting the fictional "war on terror" in the 15 years since 9/11 and by every measurable metric there are more "terrorists" (people who would like to attack us) today then there were on 9/11.
http://www.military.com/daily-news/2016/09/13/report-nearly-...
This dwarfs by many orders of magnitudes the total science funding spent by the government since the government was formed. Its absurd to discuss "waste" or "inefficiency" in any context, let alone a tiny expenditure for investigating the EM drive, while ignoring the elephant in the room. The phrase "penny wise pound foolish" applies to that line of thought.
It's in the Panama Canal going from it shipyard to homeport. It isn't yet in service. Apparently the combat systems are not even installed yet. I believe that is what your parent poster means. [1]
[1] http://navaltoday.com/2016/11/22/uss-zumwalt-breaks-down-in-...
It's worth more than any existing or previous theoretical engine. Put this rotating around a center point. Now put 1000s of them. Now we have power generation for outposts in space. The implications of a working EM drive are staggering.
That's another good reason to think it doesn't work.
By special relativity you can't break the momentum conservation principle without breaking the energy conservation principle.
Somehow most people feel more comfortable dismissing the momentum conservation principle, but they are intertwined.
A carousel with Emdrives like the described in the previous comment should be a perpetual mobile and create energy if it's spinning in the right direction. (It will destroy energy in the reverse direction, so be careful.)
[Anyway, I think that the emdrive doesn't work and the conservation of energy and momentum are safe.]
However, any true reactionless thrust is equivalent to a perpetual motion machine, because reactionless thrust drives produce the same acceleration regardless of speed, but the kinetic energy produced by the same acceleration goes up as the speed goes up.
If you accelerate one kg from 0m/s to 1m/s, you impart 0.5joules of energy on it. If you accelerate it from 1m/s to 2m/s, you impart 1.5joules of energy on it. If you accelerate it from 2m/s to 3m/s, you impart 2.5 joules of energy on it, and so on and so on. Each added m/s costs more in energy.
A reactionless drive working in a system with no preferred frame would add the same amount of acceleration for the same amount of cost, regardless of how much energy there already is. This would mean that eventually it would be going fast enough that the added kinetic energy would be more than however much energy it draws in. Then you can build a gigantic carousel that is spinned on the rim and takes energy from the middle and feeds some back in to move it, and now you have perpetual motion.
This is why no real physicist actually thinks that this will be reactionless thrust. However, that does not necessarily mean it's useless. If it, for example, allows you to push against the earth's magnetic field more weight-efficiently than current magnetic propulsion systems, it would be a major win for satellite stationkeeping.
A) Where is that in the paper? Or am I missing something elementary to this?
B) We don't even know if it produces the same level of thrust as speed increases. If it produces the same level of thrust across all speeds, then we have a problem, because as velocity increases, so does mass, and the same level of thrust would produce less acceleration over time, because of the increase in mass. Of course, that may only effect things at relativistic speeds.
Rockets do that too, but they get away with it because they stored the necessary extra energy into the kinetic energy of the fuel.
If there was a reactionless thruster that did, in fact, get less efficient at higher speeds, then that would also be world-shattering physics news, because then you could measure it's performance after accelerating in different directions and eventually get a true rest frame that is privileged over the rest of the reference frames out of it.
That's the implication of the EM Drive. I didn't invent it, it's the very first thing that you think of once you violate the momentum conservation principle. This is why it's unlikely to be true, but at the same time an alchemists dream scenario.
The advantage of the emdrive is that it does not require reaction mass, at the cost of incredibly high power consumption. Unfortunately that makes it not really viable for anything; ion drives are limited by power, not reaction mass, so the emdrive is actually worse because it uses way more in power than it saves in not needing reaction mass.
Since violation of conservation of energy is very unlikely, I'd say that this is a sign that the drive doesn't actually work. Or at least that there is some gotcha that we haven't understood yet.
The EM Drive is an energy reaction engine, rather than a mass reaction engine (if it works as described), so instead of pushing off wake, it uses energy itself to "deepen the fold", as it were, and increase speed (and mass, since the two are exchanged).
That's interesting. I've never considered that the very act of increasing the velocity of the EM Drive would actually increase its mass. Hrm.
And anyway, kinetic energy isn't a conserved quantity. It can be converted into potential energy in a gravity well, or lost entirely in inelastic collisions. Momentum is the quantity that is always conserved, and that is what the emdrive violates directly (though still not in a way that allows for perpetual motion or free power, near as I can tell).
The first internal combustion engines were quite inefficient as well.
1. Details on submarine nuclear reactors are classified, but five minutes' Googling shows that a reasonable guess for their total mass (including shielding) is 1,000 tons. Meanwhile, the entire payload to LEO of the largest rocket ever successfully launched, the Saturn V, is only 155 tons -- and that's for the entire top stage.
2. Submarine nuclear reactors use water for cooling. Water that is not available in space. Cooling would be a huge problem.
So, existing submarine designs are not practical. You'd need to design something from the ground up that is much lighter, and the cooling system would be entirely different and likely more massive, since you don't have all of that free water available to dump heat into. Instead you're talking massive radiators.
But any mission involving humans is likely to carry a large amount of water beyond the crew's personal needs, because it makes such a good radiation shield. So presumably the same water would be used for cooling the reactor.
A 3 MW reactor puts out a hell of a lot of heat, and without the benefit of air-cooling in space, I'm not sure what exactly you would do with all of that waste heat. Consider how massive the space shuttle orbiter's radiators were (they are on the inside of the cargo bay here: http://i.stack.imgur.com/Flgzb.jpg ), and all of that is only capable of shedding waste heat in the amount of ~6 KW! We can put a much more capable reactor into space than we can possibly cool, so we haven't bothered. Cooling is the real problem. The total mass of the radiators and the structure required to support them ends up being way more than the reactor itself.
So for good long distance transportation in space, not only do we need a working, efficient emdrive, but we also need better power generation that is much more efficient from a waste heat perspective. These are really hard problems.
There are several other reactor designs that have been researched over the last half century that can operate in a closed loop with much smaller amounts of nuclear fuel and more manageable radiation emissions. Designs like the nuclear lightbulb, which was researched by United Aircraft Corporation and NASA for almost a decade before the plug on the Mars mission was pulled in the 70s, are much better suited and are what proponents of active nuclear propulsion most often have in mind. Once there is some political will, we have decades old research to start from to build a flight capable nuclear reactor.
You can seed expanding liquid hydrogen in the outer cavity with tungsten nanoparticles which absorb the UV radiation to heat the hydrogen for use as a propellant. You can pump the outer cavity with a UV transparent coolant and line the walls with parabolic photovoltaics (that convert UV instead of visible spectrum) for direct conversion of the black body radiation to electricity. You can theoretically even create a magnetohydrodynamic "turbine" in the outer cavity that is coupled to the spinning nuclear fuel (which can be charged plasma).
You may be thinking of an earlier that was mistakenly called nuclear lightbulb or another design that was lumped into the concept. The variation I have in mind is just as general purpose as any other nuclear reactor, it just uses a lot less fuel and has to actively maintain temperature and pressure to keep the neutron cross section energy high enough to sustain power positive fision.
http://www.ijqf.org/wps/wp-content/uploads/2014/11/Bricmont-...
Non-locality sounds way, way weirder to me than macroscopic decoherence. Stuff like quantum collapse is really an additional, un-falsifiable claim: why the universe would zero-out precisely the stuff that the math says we can't observe?
[1] (https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory)
Could someone kindly explain this thread in conceptually simple terms?
Physics does not seem to operate on conceptually simple terms. Three options, it is simple when approached from some way we have yet to think of. There is some inherent mistake we are making with a huge range of current experiments. Or, as seems most likely the universe operates very differently on different scales making it conceptually difficult to deal with.
Here's a summary, cause talking about this stuff is fun, with the caveat that it won't
Quantum mechanics in its usual interpretations involves some randomness, where a measurement can give multiple results with different probabilities. The interpretations tell us that this is truly random; that the values are not known until you measure them, and then afterwards they are known and true everywhere.
The obvious objection is "hey, maybe the values were there already, but until we measured them we just didn't know what they were". A theory with this property is called a 'hidden variable' theory.
A 'local' hidden variable is one attached to a particle, such as its velocity. If you measured two entangled particles at the same time that are some difference apart, QM shows us that the results of one can be influenced by the results of the other - for example, if you measure one particle as having a positive spin on the Z-axis, the other would have to have a negative spin, in a certain experiment.
Excluding superluminal communication (one particle did not send a message to the other), we might guess: well, one had spin up and the other had spin down to begin with, and we were just measuring them to find out which one was which.
Bell's Theorem [1] proves (in an experimentally verifiable way) that this is not the case. There is no way that local hidden variables can reproduce the results of quantum mechanics. This is one of the most amazing discoveries of the 20th century, in my opinion.
Nonlocal hidden variables still work, which is what Bohmian mechanics is. You're allowed to say "there is a variable accessible to every measurement that determines what the result of a measurement is. In Bohmian mechanics - which is mathematically equivalent to regular QM, just more complex - there is a 'pilot wave' that is computed from the whole configuration of the universe, and then is used to determine what the spin of a particule is.
Basically you get to pick between nondeterminism (randomness) and a global function that influences everything that's much more complicated.
The theory is appealing to many because it avoids non-determinism. It's unappealing because it's strictly more complicated than the interpretations that don't have this extra object, but predicts nothing beyond them. By Occam's razor it's not as good as the simpler interpretations.
It is appealing to people who really don't want to accept the possibility of randomness in the universe, which I have no problem with. Not that it's not worth time investigating it, because it's interesting.
(Some people think it's not worth splitting hairs over interpretations over QM, because they don't provide falsifiable predictions and so this stuff isn't science but philosophy. I disagree with this. Finding that one explanation is simpler than another is finding something, and constitutes, in my opinion, valid evidence for that explanation in a scientific sense.)
"Bohmian mechanics [describes] a 'pilot wave' that is computed from the whole configuration of the universe... a global function that influences everything".
* caveat that it's not enough information to let you make any concrete predictions
Other afterthought: The pilot wave model is definitely not directly compatible with relativity, since it purports to have a function 'defined everywhere' at once, and the concept of 'everywhere at a moment in time' doesn't work in relativity. There are apparently methods of working around this, and they're apparently very complicated.
https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory
In other words, you can say what branches will exist but not with certainty say what you'll see as a result for yourself. By the dictionary definition, isn't that still counterfactual correctness? You'll know what happen in advance, because you can calculate the possibilities.
Is the scientific definition strictly in the perspective of a physical observer?
Bell's Theorem (also called Bell's Inequality) starts with assuming that the universe has locality and counterfactual definiteness and yields and inequality concerning correlations between certain measurements. Experiments later conclusively showed that these inequalities are violated in our universe. So, one of the assumptions of locality or counterfactual definiteness does not hold in the universe we live in. Historically, this result was used to discredit and eliminate a class of theories about quantum mechanics called hidden variable theories -- the idea that quantum mechanics is deterministic, and we just haven't delved deep enough to find out what's determining the behavior of particles.
In my opinion it's most useful to think of Bell's result as a proof by contradiction: there are a bunch of assumptions (implicit and explicit) that go into it, and we're left with a prediction that reality violates. Therefore one of the assumptions is wrong, but we don't know which one, and different interpretations of QM will have different answers to this question. In the context of Bell's Theorem, counterfactual definiteness has a specific definition, and that's from the local perspective of an observer observing from within physics, because Bell's Theorem itself implicitly assumes a single universe and goes from there.
Under the Many-Worlds Interpretation, the result of a measurement is that the observer is split, and different copies of the observer will experience all results. This is the global and deterministic view. The local view is that the observer will see one result or the other, and there is simply no fact of the matter as to why the observer sees this particular result instead of the other.
The Many-Worlds Interpretation has some advantages over other interpretations in that it's local, deterministic, and mathematically the simplest. But it rubs a lot of people's intuitions the wrong way because it posits an unbelievable multitude of copies of what we know of as the universe.
I'm not a physicist, but doesn't classical QM have the problem of the "collapse of the wave function", i.e. "suddenly" Schrödinger's equation does not hold anymore - a problem that the De Broglie-Bohm theory does not have? Shouldn't this be considered as a strong sign against "typical" QM formulations and for the De Broglie-Bohm theory?
I can't speak for De Broglie-Bohm, but it would seem that theory also have a similar strike against it: the math is more complex than the equations QM physicists are familiar with. It's just not the simplest theory that fits the observation.
The obvious alternative is to just stick to the math. Problem is, the simplest math that explains our observations implies a universe that forks all the time. For some reason, possibly the intuition of a unique universe, many people cannot accept that.
Many-worlds - which starts with being a lot more rigorous about what 'measurement' is (entangled yourself with the system in question) is much simpler than either, I think.
My general impression is that Many-Worlds is getting more popular as physicists make precise how entanglement, measurement, and decoherence exactly work. I think it'll supplant Copenhagen as what we teach in intro classes eventually. But this is just my impression from the physics blogs and papers I've read; I'm not a physicist myself.
That sounds as if the universe is passing everything through an RNG monad.
https://www.quantamagazine.org/20140624-fluid-tests-hint-at-...
https://www.quantamagazine.org/20160517-pilot-wave-theory-ga...
Going back to when the original disagreement started, there were a few physicists like Bohm and de Broglie who thought there was more than met the eye going on with discrete particles past a certain size limit. Their theories included a medium, or ether, in which all of this exists. To understand it a bit better, you might want to check out the "two slit experiment". There's one on Youtube that covers doing the experiment with photos, electrons, buckyballs and polarized lasers. Basically, when you understand the experimental results, you understand that matter acts like a wave sometimes and a particle others, even at large scales.
Those waves in the two slit experiment are likely responsible for the forces we're seeing in the EM drive. Also, I'm sure I've left out important bits here, but that's the basic idea.
To the moon!
https://news.ycombinator.com/item?id=12936699
Let me know what you think!
I hadn't expected such a delayed reply! Will get to reading it this afternoon. (:
Quotes: "Components get warmer and the geometry changes slightly due to thermal expansion". "The thermal signal in the vacuum runs was slightly larger than the magnitude of the impulsive signal." "As the aluminum heat sink got warmer, its thermal expansion dominated the shifting center of gravity (CG) of the test article mounted on the torsion pendulum. This CG shift caused the balanced neutral point baseline of the torsion pendulum to shift with the same polarity as the impulsive signal when the test article was mounted in the forward or reverse thrust direction." "The seventh error is outgassing, which has the potential for a false positive from vaporization of surface molecules of the dielectric insert or other nonmetallic surfaces."
Totally not, this is still with 99+ % a measurement error. We really understand theoretical physics pretty well, physicist have repeatedly predict measurement outcomes to a part in a million and less, have predicted particles decades ahead of the experiments discovering them. People really underestimate the power of theoretical physics and if there is a conflict between theory and experiment, it will almost always be the experiment that is wrong.
We also don't know how much it can be scaled or improved.
Yes, but they aren't sure what they're measuring. Remember that science (and Occam's razor) requires us to apply the most pedestrian explanations first, like some overlooked experimental error, not new physics. The "new physics" explanation should be the last possibility considered, not the first.
This similar study comes to a much less encouraging conclusion (the abstract acurately summarizes the study):
https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/...
Occam's razor is a good guide, but it is not a rule the universe is obliged to follow.
It seems to be, actually, because the rule follows straight from probability theory :).
> The point of the experiment is to zero out all pedestrian explanations.
Doesn't mean they did account for all of them. But that's why they're publishing. They've done all they could, they still get the unexpected effect, so it's time for other researchers to try it and at some point we will finally determine whether it's an error or new physics :).
I tend to believe that they measured "something" but that that something has some plain explanation.
It seems that at the time the claims leaked (September) the figure was even "1.2N per MW", but still:
http://www.forbes.com/sites/startswithabang/2016/09/02/nasas...
"For the EMdrive, the device that was tested here, thrust was consistently observed on the device to be between 30-and-50 microNewtons, giving us that 1.2 N/MW figure. But the limits of the measuring device’s threshold was just 10-to-15 microNewtons! In other words, these results may be consistent and interesting, but this isn’t as robust as anyone wants it to be."
Yep. Reminds me of psi. You can set up mechanical radiation-decay powered RNGs with pre-set runs of numbers in pre-registered double-blind experiments with remote audit logs analyzed carefully with permutation tests and randomness test suites, and all of the huge effects claimed by regular people and psychics go away... but you still get on net a slight excess of bit flips in the psi direction. Is psi real? Seems highly unlikely. But what could possibly be left - publication bias, fraud, or what? No one knows. At some point, effects become subtle enough that you just can't believe studies finding it on net - there's some sort of epistemological 'noise threshold' where stuff is happening but you don't know why or can come up with causal explanations.
How can experimental physicists and research groups who have the decade of more experience avoid these traps?
Is that "net" extracted from all published experiments, i.e. in some meta syntheses? And is statistically significance calculated in each individual experiment?
> Is psi real? Seems highly unlikely. But what could possibly be left - publication bias, fraud, or what? No one knows.
Publication bias toward positive results should be detectable via methods such as funnel plots.
If you've looked into these aspects it would make interesting reading.
[1] http://deanradin.com/evidence/evidence.htm [2] http://www.goodreads.com/book/show/319012.The_Conscious_Univ...
You can find excesses in both individual experiments and meta-analyses, IIRC.
> Publication bias toward positive results should be detectable via methods such as funnel plots.
Funnel plots have notoriously low statistical power, it would require only a little publication bias to produce excesses, and asymmetry in a funnel plot can be due to other reasons.
No one knows
It's boring if it doesn't violate momentum conservation.
(Not that I think this is what the EM drive is doing, or that I'd bet on it with anything other than very long odds, but I'm glad someone is looking into it).
Either the EM drive has a unique combination of features that allows efficient creation and separation of particles using electricity, some other unknown quantum effects are present that can convert energy to momentum without an opposite reaction on another particle/field, or there is still a hidden error. Given the scientific knowledge we have today, it's extremely likely to be the latter but that doesn't preclude the possibility that we have discovered something novel.
If you use a particle with mass, the trust/energy ratio is much lower. You have to split some of the energy to create the particles and convert a smaller part to momentum (you must multiply by c or c^2 to get the right units). So creating particles with mass is worse, not better.
If you push a bunch of particles that you have stored, you can get much better result, but it's no more a fuelless drive.
> conservation of momentum, which is just a subset of conservation of energy
This is false. Momentum and energy are two different things, even with mass-energy equivalence. In particular, momentum is a vector while energy is a scalar, and their mass-energy equivalent units (impulse vs energy) are also different.
Also: pair production doesn't necessarily require some amazing quantum device to keep the pair separate.
> There is even some research into using a vibrating "quantum mirror" that forces virtual photons to become real using only energy from quantum fluctuations but that's even more complicated and difficult to engineer.
This is true if you consider conservation of energy to be an engineering problem. Under no scientific theory can you pluck energy from the vacuum.
Your sketch takes as a premise, something that is actually a consequence of conservation laws: the way quantities change under frame-of-reference changes.
You can get both by looking at the least action principle under frame of reference changes and using Noether's theorem, but that's not what your sketch is about.
Fundementality is a different thing, but it's more natural to assume conservation laws and take frame-of-reference equations are a consequence. You can do it the other way (I'm pretty sure, but not 100% sure because my physics math is rusty) but you're still making assumptions, and you still don't have one conservation law following from the other.
In reality, momentum in almost every collision will be converted into other forms of energy such as when intramolecular bonds are broken and materials are deformed in a car accident or when momentum is converted into mass in particle colliders. The elastic collision equations are only useful as a rough approximation precisely because they go out of their way to simplify the energy-momentum equivalence to conservation of kinetic energy just like Newtonian mechanics is a simpler but useful rough approximation of relativity at low energies.
You can't use elastic collisions to reason about energy-momentum equivalence because their most basic assumption is that there is no energy-momentum equivalence.
None of this is correct when you take relativity into account. In relativity, momentum and energy are both parts of a 4-vector, and that 4-vector is conserved. And in natural units, in which c = 1, energy and momentum have the same units. Particle physicists use these units all the time.
What I meant in my original post was that intuition regarding conservation of momentum in classical mechanics may not apply here because as long as the total energy of the system is conserved, the EM drive is free to convert energy to particles and motion because momentum will still be conserved between the drive and the new particles (which is how regular chemical propulsion works). The system experiences a net change in momentum of zero but what matters is that the total energy of the EM drive slowly falls as energy is converted to particles that provide propulsion.
I agree that this would conserve momentum if if were what was happening in the EmDrive. But all of the papers I have read insist that it is not what is happening; no particles are being ejected from the test device; there is no "rocket exhaust".
I don't know that they are specifically looking for any exhaust other than RF emissions (which they say are not observed). If there were in fact an exhaust at some other frequency I don't know that it would be detected. (If such were present it would still be rather unexpected, in my view; there is nowhere near enough energy being pumped into the apparatus to start creating particle-antiparticle pairs, or to trigger any kind of process that would produce UV or X or gamma rays.)
I'm not aware of a physical view for which energy and momentum are the same for the purposes of something like the EmDrive. In particular, you cannot completely turn one into the other by a choice of coordinates, and you cannot mix them by any physical process. And I could be wrong, but I'm 99% sure you need both energy and momentum conservation to get 4-momentum conservation.
No matter your view, conserving the spacelike components of 4-momentum is not "a subset of the conservation of energy". And the truth/falsehood of this view has nothing to do with the "non quantum world". Relativity was an extension of classical electrodynamics before it was anything else.
I'm almost certain you're wrong. The most mathematically precise definition I remember for conservation of 4-momentum only requires that the interaction is invariant to spacetime translations. I don't see how that requires you to conserve both separately from the whole.
> No matter your view, conserving the spacelike components of 4-momentum is not "a subset of the conservation of energy". And the truth/falsehood of this view has nothing to do with the "non quantum world". Relativity was an extension of classical electrodynamics before it was anything else.
That was a poor choice of words on my part. I meant that an understanding of conservation of momentum based in classical mechanics is rather meaningless when talking about a drive that might use energy to create particles. What matters is that the total energy of the system is conserved and I stand by my choice of "subset" because momentum is not independently conserved. Calling conservation of momentum a subset of conservation of energy is not even close to calling energy the same thing as momentum and I have absolutely no clue where you got that idea.
"Conservation" of a 4-vector means its components in a given inertial frame do not change. That entails that, from the viewpoint of a given inertial frame, the total energy and each individual component of the momentum are all conserved separately.
Actually, I'm not 99% sure, I'm 100% sure. It's very easy to imagine a relativistic system where momentum is conserved but energy isn't. Imagine if the universe was made of inelastic billiard balls, with no internal "heat", so every collision just lost energy. But momentum is still conserved.
This won't work. Let's suppose we have just two billiard balls, and that 3-momentum is conserved in the center of mass frame (in which it is by definition zero), but energy in this frame decreases at each collision. (Ignore the fact that this obviously implies that the 4-momentum of the system is not conserved, even though it is undergoing no external interactions.) Now transform into any other inertial frame. You will find that 3-momentum is not conserved either; it has a different nonzero value after a collision than before.
No, it's not. In real life, energy is conserved, so the energy that is lost from kinetic energy in inelastic collisions needs to go somewhere. And whatever receives that energy will also have momentum (even if it doesn't in the center of mass frame, it will in other frames), so it has to be included in the accounting of momentum conservation as well as energy conservation. A relativistic theory that conserves energy as well as 3-momentum (i.e., standard relativity theory) will still conserve both energy and 3-momentum when you change frames, even in inelastic collisions. (In the simplest case, the lost kinetic energy goes into increasing the rest mass of the two billiard balls, by increasing their temperature.)
What you hypothesized was something different: a hypothetical relativistic theory (which obviously does not match our actual world) in which energy is not conserved but 3-momentum is. In such a hypothetical theory, inelastic collisions could take place without the lost kinetic energy going anywhere: it simply disappears. I am simply explaining why such a relativistic theory is not possible: if energy is not conserved, 3-momentum cannot be conserved either (except in one particular frame, the center of mass frame, but that violates the principle of relativity so it is not allowed in a relativistic theory).
You seem to be obsessed about conservation of the magnitude of 4-momentum under Lorentz transformations. It's the whole vector I'm talking about, not the magnitude. and change-of-frame is not a necessary part of conservation laws.
The claim that you can observe conversation in one frame but not another is absurd. The laws are affine; they hold in any frame or none.
In standard relativity, yes. But not in your hypothetical "relativistic system where momentum is conserved but energy isn't". You said such a system was easy to imagine. I simply pointed out that, easy to imagine or not, such a system doesn't work. Nothing that I said about 3-momentum being conserved in one frame but not another applies to standard relativity where the 4-momentum is conserved. It only applies to the hypothetical system that you claimed was easy to imagine. I don't understand why you keep talking as though my comments about 3-momentum being conserved in one frame but not another referred to standard relativity.
> It doesn't "go somewhere".
By "go somewhere" I simply meant energy can get transferred from one part of the system to another. I didn't mean that total energy wasn't conserved (in standard relativity).
> change-of-frame is not a necessary part of conservation laws.
It is in a relativistic theory, since the principle of relativity requires that the laws of physics, including conservation laws, must hold in all frames.
> The claim that you can observe conversation in one frame but not another is absurd.
For standard relativity, of course it is. But not for your hypothetical system.
> The laws are affine; they hold in any frame or none.
This seems to contradict what you said earlier in the same post, that "change of frame is not a necessary part of conservation laws".
All I can say is that momentum conservation is Lorentz invariant in my system, and hence cannot depend on choice of reference frame. The conserved quantity is not invariant, and conserved quantities do not need to be Lorentz invariant, and fact almost always are not. If this confuses you, sorry, but I cannot follow your reasoning anymore.
If by "my system" you mean your hypothetical theory where energy is not conserved but 3-momentum is, I strongly suspect you have not done the math. See below.
> The conserved quantity is not invariant, and conserved quantities do not need to buslye Lorentz invariant, and fact almost always are not. If this confuses you, sorry, but I cannot follow your reasoning anymore.
I understand what you are saying here, but it does not refute what I was saying. You are saying that, for example, in standard relativity, energy is conserved--in a given frame, it stays the same through any series of events--but it is not frame invariant; changing frames changes the energy. I agree with that.
What I am saying is something different: in your hypothetical relativistic theory in which energy is not conserved, then 3-momentum cannot be conserved in any frame other than one particular one (which in my example was the center of mass frame). I am not saying the numerical value of the 3-momentum has to be the same in all frames. I am saying that in all frames but one, the numerical value of the 3-momentum, as evaluated in that frame, is different after an inelastic collision than before, i.e., 3-momentum is not conserved in that frame.
Here is the math backing up that assertion. Suppose 3-momentum is conserved in the center of mass frame. In that frame the 3-momentum is zero. We assume that our system consists of just two billiard balls, each with the same rest mass m. Before the collision, one ball has speed v and the other has speed -v (we can restrict ourselves to one spatial direction). After the collision, one ball has speed w and the other has speed -w, where w < v (because the collision is inelastic). So 3-momentum is zero before and after the collision in this frame, and energy is not conserved--it is smaller after the collision.
Now transform to any other frame. Call the relative velocity of the Lorentz transformation u. Then, in this frame, the speeds of the two balls before the collision are (I am using units where c = 1)
v+' = (u + v)/(1 + uv)
v-' = (u - v)/(1 - uv)
and the speeds after the collision are
w+' = (u + w)/(1 + uw)
w-' = (u - w)/(1 - uw)
Now we evaluate the 3-momentum in this frame. Before the collision, it is
m ( v+'/sqrt(1 - (v+')^2) + v-'/sqrt(1 - (v-')^2) )
After the collision, it is
m ( w+'/sqrt(1 - (w+')^2) + w-'/sqrt(1 - (w-')^2) )
Substituting and straightforward algebra simplifies these to
before = 2mu/sqrt[(1-u^2)(1-v^2)]
after = 2mu/sqrt[(1-u^2)(1-w^2)]
These are obviously not equal, hence 3-momentum is not conserved in this frame. (In standard relativity, where energy is conserved, 3-momentum would be conserved as well; as I mentioned before, the simplest way for that to happen would be for the two billiard balls to heat up, increasing their rest mass. More complicated ways would involve other particles, or the billiard balls emitting radiation, or something like that.)
P0' = 2mu/sqrt[(1-u^2)(1-v^2)]
P1' = 2Mu/sqrt[(1-u^2)(1-w^2)]
But we can simplify this by writing down the total energy before (E0) and after (E1) the collision, in the center of mass frame:
E0 = 2m/sqrt(1-v^2)
E1 = 2M/sqrt(1-w^2)
So we can see that
P0' = E0 (u/sqrt(1-u^2))
P1' = E1 (u/sqrt(1-u^2))
Hence, if E0 > E1, we must also have P0' > P1. In other words, the only reason we happen to have P0 = P1 in the center of mass frame is that being in that frame is equivalent to having u = 0 in the above formulas.
(It is also straightforward to show that if energy is not conserved in the center of mass frame, it is not conserved in any frame. So the Lorentz invariance of the two conservation laws, energy and momentum, cannot be separated--they are inseparably linked.)
You can if you're very patient, have a lot of material, and lucky aim, thanks to the metric expansion of space.
From within a galaxy cluster shoot one end a very very long wire into the central black hole of a galaxy in a distant galaxy to anchor the far parts of the wire, and wind some near part of the wire around the pole of an electrical generator in your galactic cluster.
You won't get much power for a long time by human standards, but you'll get an awful lot of energy (and eventually substantial power give or take divergence in the stress-strain tangent modulus and related quantities) even after the gravitationally anchored far end has receded outside your generator's Hubble volume.
Mining \Lambda dark energy for fun and profit, brought to you by $nabla_\mu T^{\mu\nu} = 0$, where $nabla_mu$ is the covariant derivative. It only takes a large up-front investment that you'll wish you had made billions of years ago.
Honestly, I'm clutching at straws but I can't believe that the only way to create matter from energy is with some complicated device since the existence of the universe seems to say otherwise. As an example, compare our attempts at creating fusion with the 'solutions' that nature has come up with.
> compare our attempts at creating fusion with the 'solutions' that nature has come up with
Well, if you just want to have a nature-like fusion, we've figured that out in the 40s and made it work in the 50s ;).
https://en.wikipedia.org/wiki/Thermonuclear_weapon#History
Our attempts at fusion are now focused on getting useful energy out of it without incinerating everything around the reactor.
My armchair crackpot theory is that's not what's going on here, but some other similar principle is at play. Some other physical law is behaving in a way similar to eddy currents, and the force comes from the field working against itself at a small delta-t
Ever hear of the Luminiferous Aether? From what I can tell, it could explain this phenomenon. Most people consider it an outdated crackpot theory largely because it's at odds with the entirety of quantum theory and the theory of relativity. But, this is the sort of thing that makes you go back to square one and re-consider everything you thought you knew.
* Flawed study. It actually throws something (like, cavity material slowly ablating) or repels of Eddy currents in surroundings;
* It repels of Earth (and the force has either gravitational or magnetic nature); then it's not suitable for deep space propulsion
* A sort of ether actually exists, and it throws that. Though, then there would be some anisotropy showing ether wind; in this case it is suitable to be used in deep space
Just ignore the theoretical explanations. Just imagine that it's something they wrote to avoid the crackpot tag. That explanation doesn't make any sense. Also avoid all the other theoretical explanations, they are also very sloppy.
Just concentrate in the experiments, that is the less sloppy part of these reports.
If they discovered something new, then they can make a working prototype and improve it until it's clear that they are measuring something really new and it's not an experimental error or a misattributed force. They can make foolproof instructions so anyone can make a version in a good enough lab and reproduce the experiment, or sell an experimental setup in Ebay. Then it will "confirmed".
There has been a many famous experiments that were later debunked, like:
* cold fussion https://en.wikipedia.org/wiki/Cold_fusion , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment.
* arsenic in DNA https://en.wikipedia.org/wiki/GFAJ-1 , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment.
If you want success cases, my favorites are:
* the asymmetric disintegration of cobalt in a magnetic field https://en.wikipedia.org/wiki/Wu_experiment , I guess they had some wrong explanation, but the correct explanation was discovered like 20 years later
* high temperature superconductivity https://en.wikipedia.org/wiki/High-temperature_superconducti... IIRC they have some explanation or practical rules, but the correct explanation was discovered like 20 years later
Just concentrate in the experiments, and wait 20 years for a good explanation.
Is that not what this is? Roger Shawyer invented it, but NASA, NWPU and the Dresden University of Technology have all built and verified their own versions to work.
http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083 https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/...
I just read the Wikipedia article about this, and it's clear that the explanation is still not clear :(, so you are right.
If there is an anisotropy in the ether, Sagnac interferometer should catch it.
Why didn't they do a careful analysis of the cavity mass before and afterwards? Or electron microscope analyses of a few points of the outer surface before and afterwards to see if the microscopic topology changed?
Did they rule these out some other way?
The offered explanation model is highly fascinating. I'd appreciate if somebody would chime in with a more understandable version or resources thereto.
Does anyone know what I'm talking about? IIRC it was based on some theoretical work that was done before EmDrive was a thing, and it seemed less hand-wavey to me than simply "conservation of momentum is wrong" or "we're using the quantum vacuum as a tractive medium which is supposed to be impossible but whatever" explanations.
I'm not saying this explanation is right (or wrong, or that the thrust observed in these experiments is or isn't caused by "new physics"); I'm just curious whether anyone knows what I'm talking about and can provide some more context.
edit, found it: https://www.technologyreview.com/s/601299/the-curious-link-b...
Any thoughts?
* A Q-thruster is a thruster which pushes off of the zero point fluctuations in vacuum, which is still not understood.
Quote:
Although the idea of a pilot wave or realist interpretation of quantum mechanics is not the dominant view of physics today (which favors the Copenhagen interpretation), it has seen a strong resurgence of interest over the last decade based on some experimental work pioneered by Couder and Fort [13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a vibrating shallow fluid bath at just the right resonance frequency created a scenario where the bouncing droplet created a wave pattern on the shallow bath that also seemed to guide the droplet along its way. To Couder and Fort, this seemed very similar to the pilot-wave concept just discussed and, in subsequent testing by Couder and others, this macroscopic classical system was able to exhibit characteristics thought to be restricted to the quantum realm. To date, this hydrodynamic pilot-wave analog system has been able to duplicate the double slit experiment findings, tunneling, quantized orbits, and numerous other quantum phenomena. Bush put together two thorough review papers chronicling the experimental work being done in this domain by numerous universities [14,15].
Mathematics will not change, calculation results will not change, but understanding of processes will rise significantly, which may lead to new advances in physics.
If you try to claim, without evidence, that pilot waves predict different behavior than standard quantum mechanics, you might deserve that downvote.
Pilot waves are a mathematical framework, they may be useful mathematical tricks in some cases, but they don't predict new behavior AFAIK.
I've been to talks about Couder et al's work, and the authors don't argue that pilot waves are validated as descriptions of the universe by their work. They do demonstrate a novel macroscopic system that observes the laws of classical mechanics, and under certain circumstances, behavior emerges that is nicely described by the pilot wave equations. This does not mean that pilot waves are somehow a more fundamentally correct description of what's really going on.
However, walking droplets shows that relativistic and quantum effects can be explained in terms of Newtonian physics. For example, just by looking at walking droplet experiment with two slits, I can say that speed of sound in water is constant and it isotropic regardless of speed of particle, because waves around particle are propagating, so water is not moving at all (unless wave is really big, so path to travel will be longer). It is easy to understand. It also explains why Michelson-Morley experiment failed.
It's not constant. It varies by temperature.
This is why you're getting down voted. You're asserting a very minority view in physics as a certainty, while making sweeping statements that contradict a high school physics education.
You are placing way too much weight on youtube videos of excited oil droplet propagation. Your lay understanding of these videos is not equivalent to the consensus of people who dedicate their entire lives to these topics.
> It's not constant. It varies by temperature.
It's worse than that. The relevant speed is (I think) the speed of surface waves, and surface waves in water are really quite complicated.
Also, pilot waves get interesting when more than one particle is involved. Two dancing droples do not act like two noninteracting quantum particles.
[edit: formatting]
Yeah, so when we will have vacuum cooled below 0K, it will confirm existence of ether.
Yes, I asserting very minority view in physics, but I'm able to back it with video of real experiment. It is not a hand waving.
Let be honest. The quick way to check understanding of something is to ask "why?" few times. People, who dedicates their entire lives to relativistic and/or quantum physics, are not able to answer even to single "why?". It's because of orthodox education.
However, they can downvote.
I think you may be rather confused about that video. I've watched what I think is the same video along with many other videos by the same experimenters (presented by the experimenters themselves!).
The waves in the water are not pilot waves. They kind-of-sort-of look like them. With one droplet, you get approximately the behavior that the pilot wave equation would predict, but the interesting bits are missing. If you observe the droplet twice (which you do in the video -- each frame is quite literally an observation), you get behavior that is completely inconsistent with an actual double-slit-experiment particle. If you add a second particle, the whole analogy breaks down: the pilot wave for two 2D particles is a function of five variables (time, x1, y1, x2, and y2), but the water wave is still just a function of three variables (time, x, and y).
But much more importantly, that video is a video of a bouncing water droplet and some surface waves. The droplet is a macroscopic droplet of water, and the waves are waves in a puddle of water. They obey the laws of fluid mechanics. If you grab the droplet while it's bouncing, it'll be gone and the water will still have waves. If you heat it up, it'll boil. If you turn the experiment upside down, everything will fall out and get things wet. Saying that the video proves that pilot waves exist is like saying that the experiments that play with "acoustic black holes" prove that black holes exist.
I think you will face great difficulties in convincing anyone that works in the topic area of this.
> Yes, I asserting very minority view in physics, but I'm able to back it with video of real experiment. It is not a hand waving.
It's clear you do not understand the propagation of acoustically excited droplets are a limited analogy, not a perfect model of QM/QFT. The people doing those experiments would not agree with your statements or characterizations.
> Let be honest. The quick way to check understanding of something is to ask "why?" few times. People, who dedicates their entire lives to relativistic and/or quantum physics, are not able to answer even to single "why?". It's because of orthodox education.
This is willful arrogant ignorance and a gross mischaracterization of the world of physicists. They absolutely address more than "a single why?". You have not put forth the effort necessary to understand the broadly accepted answer, let alone invalidate it.
This is exactly analogous to statistical mechanics (e.g. the ideal gas law) arising from classical Newtonian mechanics when you assume no specific knowledge about gas particles (individual positions or velocities), just aggregate mass and energy.
An experiment that "proves" an extension of pilot wave theory might be, e.g., observing that decay rates of radioactive isotopes are affected by being in a quantum corral or something like that. An experiment that shows there is a more fundamental, and influenceable process underlying phenomenon that the standard interpretation treats as frequentist.
For this reason it could be easily argued that theoretical physicists should be spending more time on pilot wave theory since it is this sort of theory from which future advances would come, vs the standard interpretation which puts up a semantic stop sign and says "proceed no further".
That's a remarkably incorrect statement. Let's see:
* The "standard model" is a quantum field theory and has essentially nothing to do with this discussion.
* Standard quantum mechanism says nothing about frequentist vs Bayesian interpretations of anything.
* Standard quantum mechanism is a deterministic theory, too. Take a look at the Schrödinger equation: it's deterministic.
Determinism is tricky. Suppose you have a particle doing its thing (going through double slits or whatever) and then you measure its position. In standard QM, you have two choices: you use the Born rule (or a fancier version -- I like the POVM formalism) and get a distribution of outcomes and a new post-measurement wavefunction, or you can include the measurement apparatus in your system and you end up with many worlds. In PWT, I think you have two similar choices. You can start with a distribution of your (hidden) initial condition and get an resulting distribution over the outcomes (which will be the same as the Born rule distribution if you calculate it correctly). If you do this, you still need to model decoherence, and I believe it looks at least as artificial as the standard QM case. Alternatively, you could presumably add degrees of freedom and more hidden variables to describe the measurement apparatus and you end up with an IMO extremely messy version of many worlds.
<aside>My personal view is that standard QM with many worlds is the best theory we have. If you start with the many worlds hypothesis and assume that it's totally impractical to devise an experiment that actually detects coherence between large-scale states, you can ignore this coherence, average it out, recover the Born rule, etc, as an approximation. IOW I think that decoherence is a limitation of our ability to build crazy experiments rather than a fundamental property of the universe.</aside>
And if you admit you do, you're at level of photon thrusters at best.
About the previous tests of the same team:
"The testing was done by five NASA employees in a lab devoted to exploring unorthodox propulsion ideas. The team leader is a researcher named Harold “Sonny” White, himself a proponent of ideas about faster-than-light warp drives that most of his colleagues have classified as physically impossible. The lead author is one of White’s Eagleworks teammates, David A. Brady. Calling this group “NASA”—as almost every popular news story has done—is a gross oversimplification."
Maybe, if that 0.05% is used against NASA by claiming it doesn't do its job how it should.
https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physic...
And I believe they actually did a serious job, which is probably why they never found any warp-drive ;-)
NASA pays small amount of money ($50,000 or so) and gives them a room to do experiments. Or at least did in 2011. Eagleworks and their team are not official NASA research. They just have facebook page. Contact attempts trough NASA don't work.
Glenn Research Center offered to replicate the experiment in a hard vacuum if Eagleworks manages to reach 100 µN of thrust.
Contrast this with pressure created via light. Velocities with light don't add that way. Instead there is a red/blue shift in the frequency.
I can't put my finger on how this could work, but it seems there is a discontinuity here between the speed of light being constant in all reference frames and summing velocities to calculate momentum.
Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.
In my initial argument I bring in relativity and the invariant speed of light. What I neglected is everything else in relativity, like lorentz transformations.
I mentioned a discontinuity between invariant speed of light and summing velocities to calculate momentum. The discontinuity is distance. Velocity is distance x time, but under lorentz transformations distance is relative. The discontinuity is resolved if you include length contraction (and time dilation).
Unlike regular matter, waves are propagating through space, by contraction and expanding of a field. Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right?
EM radiation in form of radio-waves can interact with these surrounding waves because of interference. Right?
IMHO, interference between radio-waves and surrounding waves may cause effect similar to used in acoustic levitation.
«Although the idea of a pilot wave or realist interpretation of quantum mechanics is not the dominant view of physics today (which favors the Copenhagen interpretation), it has seen a strong resurgence of interest over the last decade based on some experimental work pioneered by Couder and Fort [13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a vibrating shallow fluid bath at just the right resonance frequency created a scenario where the bouncing droplet created a wave pattern on the shallow bath that also seemed to guide the droplet along its way. To Couder and Fort, this seemed very similar to the pilot-wave concept just discussed and, in subsequent testing by Couder and others, this macroscopic classical system was able to exhibit characteristics thought to be restricted to the quantum realm. To date, this hydrodynamic pilot-wave analog system has been able to duplicate the double slit experiment findings, tunneling, quantized orbits, and numerous other quantum phenomena. Bush put together two thorough review papers chronicling the experimental work being done in this domain by numerous universities [14,15].»
So it makes sense in paper, but does not makes sense at HN?
> You know that X. Right?
> Y. Right?
> Z. Right?
The "You know that" part makes your argument unnecessarily personal, when your comment could just as easily be stated without any reference to the person behind the comment you were responding to.
The "Right?" ending each line is also very patronizing. This sounds like how an adult might talk to a child, walking them through a line of reasoning.
Maybe you did not intend to sound condescending, but you did, and this is no place for that.
(Also, your post is worded as if the pilot wave theory is a fact, when it is actually not even particularly widely accepted. It is one of many interesting views of QM, but certainly not the only one.)
How I should rewrite that text so it will not cause unwanted emotions, but will not look like a dictionary article? Can you help me, please? My level of English is not strong enough to be sure.
PS.
Even when (if) Pilot-Wave theory will be widely accepted, it will be theory, not a fact. :-)
Actually, PWT explains some effects much better than GTR. Moreover, walking droplets shows that relativistic and quantum effects can be described in terms of Newtonian physics, which is much easier to imagine and argue, which may cause significant advance in physics, after almost 100 years of "shut up and calculate".
In the first form you are trying to stipulate facts, and others reading may not agree with those facts. Since you have no reasoning or evidence that you have used to convince yourself that the facts are accurate, the only response to such a stipulation is "I don't believe you" or "that is rubbish", which is often reflected as a down vote here.
Let's look at your first such statement: "Unlike regular matter, waves are propagating through space, by contraction and expanding of a field. Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right?"
I've read a lot of physics paper and had several years of study of it in University, and I don't recall any characterization of electro-magnetic fields as "contracting and expanding". Sure they kind of look like that if you show them on an oscilloscope in the time domain, looking like the waves on the ocean, but in my understanding they they are nothing like pressure waves in their existence.
I am pretty confident your first statement goes against every characterization of EM field theory I've seen, even pilot wave theory. Thus if you are going to start there, you have to explain to how you got there.
The referenced paper shows some good examples of this, the authors know that what they are looking at is disallowed by every existing, mainstream, theory of physics. They are very careful to explain exactly how they did their experiments, the things that affect their observation (thermal expansion, fat fingering the setup) the ways they tried to avoid those confounding factors, and the data they recovered. They don't claim some new theory or some new understanding but they do look at some theories that have been debated in the past which looked promising in terms of having a bearing on the experiment.
So now the hard work for the theoretical physicists is to thoughtfully re-examine the relationships that are called out here, a tapered container, radio frequency energy, and changes in momentum, and then explain them with theory. That explanation has to be consistent with all of the other observed effects and behaviors and include this new effect and behavior, ideally it should predict a still newer effect or behavior so that an additional experiment, one that has not yet been run, would have the outcome they predicted.
Your comments appeared to just want to bring the pilot wave theory back as is. That is fine, except that like the paper here, you need to recognize there are some pretty strong counter arguments that it is not "the" answer and the current quantum mechanical theories answer a lot more questions and have a lot of experimental data backing them up.
You can't just pull this old theory out of storage and say, "Because of this one experiment this is correct and the others are wrong." (and that was how your original comment read to me) You have to say, "Here is this new theory based on the pilot wave conjecture which not only explains this experiment, but all of the experiments that have confirmed quantum mechanics for the last 70 years, starting with the slit up through entangled photon teleportation.
Hold on to this: "Actually, PWT explains some effects much better than GTR.", when you have a theory that explains all effects better than GTR and can explain effects that GTR can't, then you have something (and everyone would be really excited to hear it and understand it). That will also give you the understanding to propose experiments that would demonstrate the predictive power of the theory even if you didn't have the tech to build them yet (for example the Gravity B experiment that showed frame dragging, Einstein predicted it, but couldn't build an experimental apparatus to prove it).
That's easy to answer. A "good" post, one likely to generate light, has many topical references and almost no, or no, first-person ("I") or second-person ("you") pronouns.
A less desirable post, one more likely to generate heat instead of light, has fewer topical references and more first-person and second-person pronouns.
So when composing a forum post, a post to be read by strangers, it's desirable to either remove or edit all constructions that might be taken to describe a distinction between oneself and others.
One could go so far as to write it as an equation:
Forum post Q factor = (topical references) / (1+sum of first-person and second-person pronouns)
The advantage of the equation is that it could hypothetically be automated and added to a forum post editor, so one's score could be seen to rise and fall as the post is typed. The drawback is that it's a classic case of reductionism -- the possibly misguided idea that everything can be reduced to (for example) mathematics.
There's obviously more to quality forum posting than this, but it's at least easy to explain and apply.
Unfortunately, there are too many assholes who would rather just click than talk.
I up-voted your post.
Imagine a particle that can occupy any square of a chess board. The space the particle lives in is then a discrete two dimensional space with eight possible positions in each dimension. The wave function of this particle on the other hand lives in a 64 dimensional complex Hilbert space, one dimension for every possible state of the particle, one for every possible location of the particle. If the particle could additionally either have a charge of plus or minus one unit, then the state space would become 128 dimensional, 64 possible positions times 2 possible charges.
If there is only one particle, you can indeed visualize a probability wave on the chess board indicating the probability of finding the particle on one square or another, but that starts failing once you bring in a second particle. The state space for two particles on a chess board is 4096 dimensional, again one dimension for every possible state, one for every combination of the locations of the first and second particle.
And if the particles are entangled, you can no longer simply visualize the state [of one of the particles] with a probability wave on the chess board because the probability of finding one particle on a specific square may in general depend on the other particle. At best you can integrate over all possible states of the second particle but this will destroy a lot of information contained in the wave function.
Despite that randomness is used in calculations, it is very unlikely that our Universe is random, thus "probability wave" is just mathematical abstraction, disconnected from reality, not a real thing. It just a particle, with concentrated rings of magnetic field around it (like rings of magnetic field around magnets). It moves fast, and it motion is influenced a lot by fluctuations in quantum field, so it is impossible to measure position of a particle precisely, like motion of a single atom in plasma, so random distributions and averages are very helpful in calculation.
PS.
Did you see the famous video? https://www.youtube.com/watch?v=nsaUX48t0w8
Nobody knows whether the universe makes use of randomness or not. Quantum mechanics is essentially deterministic, the evolution of the wave function is described by a unitary operator, the Hamiltonian. Randomness only enters in the Copenhagen interpretation due to the Born rule and the collapse postulate. Note that the unitary evolution of the wave function and wave function collapse are not really compatible. What or who decides whether something constitutes a normal physical process with unitary evolution or whether it is a measurement that leads to the non-unitary collapse of the wave function? So this is definitely an open question whether the universe is deterministic or not.
I don't understand the rest of your comment, from the thing with the magnetic field around particles on, and that again doesn't sound right to me. Especially the uncertainty in the Heisenberg uncertainty relation on the one hand and the uncertainty in the description of a many particle system due to ignorance of the microscopic states on the other hand are of very different nature. The former one is fundamental, the later one is just due to ignorance.
I have seen those videos and they are kind of nice models for simple quantum mechanical systems, but one should really not try to stretch them to far, there is no way those system can accurately model quantum mechanics. They are classical systems and we know from the violation of Bell's inequality that quantum mechanics is not classical, so it is certain that those models will break down at some point.
By the way, IANAP.
I gave you an upvote for persisting in getting corrections/tips from people like 'danbruc and 'lutusp though. Since you were interested in simulation you might enjoy this article (or others on his site) from an actual physicist: http://oyhus.no/QuantumMechanicsForProgrammers.html
PS.
I enjoyed articles about https://en.wikipedia.org/wiki/Amplituhedron .
It's not quite like that. Imagine a particle whose location we don't know, so we're obliged to make an educated guess about where it is. That's the wave interpretation. Later on we actually observe the particle at a specific location. That's the particle interpretation. My point is the wave/particle duality idea doesn't mean there are particles riding waves like miniature surfers -- it's more like making a statement about where a particle is likely to be in advance of observing it, given certain statistical rules.
> Unlike regular matter, waves are propagating through space, by contraction and expanding of a field.
Not necessarily contracting and expanding -- that would be true of a longitudinal wave like sound waves in air, but not an electromagnetic wave in space, which is transverse.
http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/tralon.html
> Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right?
No. See the transverse/longitudinal link's explanation.
Walking droplets demonstration of quantum-like behavior is also done with transverse waves (waves, which are perpendicular to plane of motion of droplet). OK, they are no expanding and contracting, they are rising and falling, thank you for correction.
>> No. See the transverse/longitudinal link's explanation.
> But electron and other particles are actually demonstrating interference patterns, so it is not just interpretation.
Your comment addresses my objection to the idea that matter expands and contracts, not that there are wave phenomena, which is certainly true -- but that wasn't what I commented on.
That's true of the container as a whole, but if you put a delicate torsion balance inside the container, you could see many kinds of apparent anomalies caused by circulating gases at different temperatures. At sufficiently high sensitivity even a vacuum vessel would show some anomalies arising in ordinary physics that would need to be taken into account.
Only for objects with nonzero rest mass traveling at speeds much slower than the speed of light. Which obviously doesn't apply to light itself. When you are talking about light (or about massive particles like electrons traveling at speeds close to the speed of light), you have to use the correct relativistic equations. When you do that, you find that energy and momentum are conserved for light just like anything else.
> Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.
Not according to our best current theories, no. See above.
http://phys.org/news/2016-11-theory-gravity-dark.html
http://www.forbes.com/sites/briankoberlein/2016/11/08/soluti...
I'm in no way qualified to give any technical judgement on Verlinde's paper, but I'm aware that modified theories of gravity have been around for a long time without much success. Of course I'd like it if some elegant theory could be found that fit the evidence better than dark matter, but going by past attempts I'm not anticipating this one will.
In the 3rd step.
The measurement error is stated to be +/- 6 micro-Newtons. However, the difference between force measured at the same power is 30-40 micro-Newtons and the "measurement error" is listed as the +/- error. So if the measurement error is that low then the additional variation is unreliability of the effect itself or a miscalculation of the measurement error.
The tl;dr is that some scientists investigate some fringe technologies that violate the laws of physics and based on some preliminary studies it looks like there could be something. However it's still vastly more likely that the studies are flawed than that we'll have to rewrite the laws of physics.
https://www.eng.fsu.edu/~dommelen/quantum/style_a/physsym.ht...
Newton laws and Noether's theorem has not been changed and they are fundamental
> OTOH, one can hardly say that it violates such laws while we don't know how it works.
The contrary, until we know how it works, it violates fundamental laws of physics
"Extraordinary claims require extraordinary evidence."
I disagree. Even if this actually turns out to be producing thrust due to a reason other than thermal expansion, ablating material, interaction with the Earth's magnetic field, etc., that doesn't mean fundamental laws are wrong. It depends on why it's happening, right? There are...I can't even call them theories...musings that this may simply be an effect which we aren't aware of, but doesn't violate conservation of momentum.
We are so far away from being able to explain why, however, since we first need to determine if this is real and repeatable. I hope that other credible researchers attempt to replicate this.
"NASA’s impossible space engine, the EMdrive, passes peer review -- But that doesn’t mean it actually works as advertised."
"What it means to be peer-reviewed is that an independent scientist who is an expert in the particular field read and reviewed the work undertaken, and found it to be of sufficient quality to be a valuable contribution to the field. It does not mean that the results and conclusion of the paper are necessarily correct, or even the last word on that particular issue."
In short, the paper wasn't so amateurish to be rejected -- it "looks" acceptable enough to be published. But it doesn't mean "verified." It doesn't mean that its claims are even repeatable by anybody else but the author of the paper -- and until that happens, it's just the claim of him.
The same astrophysicist who wrote the previous article also specifies the criteria that have to be fulfilled:
http://www.forbes.com/sites/ethansiegel/2015/05/04/no-nasa-d...
"what I’d demand at minimum:
- A detection of thrust that scaled with input power: the greater the power, the greater the thrust, in a predictable relationship.
- A thrust that was at least many standard deviations above the measurement error.
- An isolated environment, where atmospheric, gravitational and electromagnetic effects were all removed.
- A reproducible setup and a transparent device design, so that other, independent teams can further test and validate the device/investigate the mechanism.
- And finally, a detailed results report with the submission of an accompanying paper to peer review, and acceptance by the journal in question.
What we’ve got, unfortunately, doesn’t meet most of these criteria at all."
Most likely what's happening here is a thermal effect or the machine pushing off the earth's magnetic field. Keep in mind that these things are very difficult to measure due to the tiny amount of thrust they may or may not produce. According to this study 1.2mN was measured, which is about the same amount of force as gravity exerts on 6-7 grains of rice (according to my back-of-the napkin calculation).
If this were real it would be absolutely huge, and destroy just about all of modern physics. It isn't just that we believe in conservation of momentum because we don't know of any way to break it, the equations we're using to describe things don't work without it.
This paper has a number of flaws. For example, the test really needed to be performed inside of a vaccuum to have any credibility at all, and whether that was the case was not made clear.
TL;DR It's most likely bunk, unfortunately, but it would be very revolutionary if true
If I'm not mistaken they did, and the thrust was almost the same than the one in air. No perfect vacuum here, but still.
"Vacuum conditions are provided by two roughing pumps and two high-speed turbopumps, and all vacuum tests are performed at or below 8×10^−6 torr"
"The vacuum test data collected show a consistent performance of 1.2±0.1 mN/kW, which is very close to the average impulsive performance measured in air (also 1.2 mN/kW)"
And then they use a "aggressive slope-filtering level" method (whatever it means) to get 124uN, that is still very small, like 1/10 of a grain of rice.
>What I would say is that the idea that EmDrive violates the laws of conservation of momentum is itself nonsense. Of course it doesn’t. It wouldn’t work if it did. All that EmDrive is a device for exchanging the momentum of the electromagnetic waves going up and down inside it, with the momentum of the thruster as it accelerates. It’s all actually elementary physics.
Edit: Cannae Inc. intends to launch a test with a small satellite. 2017 is so far a guess for launch based on a quick search.
Let's assume we have a spacecraft powered by an energy source with total energy `E` and mass `m`. The EM-drive produces a constant thrust `F` at a constant power `P`.
Kinetic energy of the S/C after time `t`:
Ek = 0.5 * F^2 * t^2 / m
Ek/E = 0.5 * F^2 / P^2 * (E/m)
E/m > 2P/F ~ 1.6 10^6 J/kg
They concluded that the force is excerted by coupling the RF-energy from the outside.
If the system is fully self-contained (driven by a battery physically connected to the cavity) there is no thrust to be measured.
It's very sad to see NASA being involved in such shitty research.
[1] https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/...
I believe they are going to put one of these in space, that'll give a definitive answer.
First you have to completely decouple the cavity from it's surrounding environment - especially the RF-field has to be generated by an apparatus fixed to the cavities frame of reference. Also the power has to come from a source connected to this frame of reference.
For me this is Physics 101.
As otherwise your system is not even closed. You are just neglecting that you are pumping LOTS of energy into an open system that you are measuring while assuming it to be closed -> thus leading to wrong conclusions (measuring a change in impulse in one part of the system)
For me this in line with uBeam and the like.
Whacko-science wherever one looks.
In any case, I am not from TU Dresden and have only a passing acquaintance with Tajmar, but I do agree that credit and recognition is not going where it should in this case.
"The nature of the signals observed is still unclear."
They are, clearly, taking the tack of eliminating all sources of measurement error. But they haven't yet achieved that, and as yet a force remains. It seems perfectly reasonable to assume it will be attributed to measurement error, but that is not yet the case:
" Next steps include better magnetic shielding.... We believe that this is a good education project to track down measurement errors..."
NASA would have had the means to eliminate most of those sources of errors. I wouldn't call these measurement errors though -> the measurement is fine - your setup is the source of error.
But they decided not to follow such a line of research.
And yes, they are right "We believe that this is a good education project to track down measurement errors".
The measurement error being the "thrust" that is due to your experimental setup.
But let them waste some more money, time and reputation and build this in space so they can find out it does not actually work.
> NASA would have had the means to eliminate most of those sources of errors.
Yes. NASA as a whole yes. One group researching something that may or may not bear fruit no.
So it's natural they try to eliminate easier errors first. But (as an example) it's one thing to have a good vacuum, another one to have an excellent vacuum for testing. So first you test on the good vacuum.
Yes i did, usually i just let certain topics pass by me and never comment here.
RF-cavities though are the very core to my line of research, so my acceptance for bs is very low in this regard.
If one wants to convince me of a thrust effect: build a prototype where the power source (a battery for example) and the RF-source are strapped onto the cavity, put the whole setup in a vacuum of your choice (i heard NASA has very nice and !large! facilities) and show me a sustained increase in impulse (just let it rotate for a while)
Okay, but they aren't trying to convince you yet.
They're trying to convince themselves that it's worth spending the resources you describe.
> To definitively rule out any residual concerns about thermal error sources, future test campaigns could employ a test apparatus capable of measuring small torques over much larger angular displacements. For example, a Cavendish balance approach properly designed to allow very large rotation angles such as 90, 180, or even 360 deg will not be susceptible to this type of thermal false positive.
The group has been working five years in their own time in this small laboratory with shoestring budget. White has a day job in NASA and he and others are working with this project in their free time. NASA don't seem to be involved in any other way but "NASA Eagleworks Laboratories" makes it sound like official NASA organization.
To be fair, the authors did enlist Tajmar's paper in the state-of-the-art but they do not discuss despite it being the most relevant prior art.
For anyone who knows a little bit Tajmar, if there was a tiny hint of a possibility that this effect could be real, he would definitely have pursued it; after all, his self-admitted goal is nothing else but to discover the warp-drive... That being said, he is no crackpot and the thoroughness of his article confirms it.
Incidentally, in a similar HN story a couple of days ago I shared my suspicion about spurious contributions from thermal drift, and unsurprisingly I see this was also the number 1 suspect for Tajmar. Beside using thermal barrier to mitigate the problem, he also went from electro-magnetic damping to oil damping and found completely different results. Meanwhile, the Eagleworks guys are still using an EM damper, working right next to a strong EM field source.
That being said, I can understand the over-reaction, it is indeed frustrating to see relatively weak articles making front page because they originate from NASA when earlier, more thorough research did not get any attention because their authors were more careful with their claims.
Mind you, I am not saying the Eagleworks paper should not have been published; any data point is good as long as the experiment is sufficiently described for it to be reproduced or disproved, and in that respect I think it is OK. But very good it is not.
(a) If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one.
(b) As far as I can see, giving up momentum conservation is not a feature that we can simply 'bolt onto' the existing models. It would require a radical rethinking of the very foundations of our current physical models.
So my personal attitude is that extraordinary claims require extraordinary evidence and this paper is not remotely convincing.
This experiment reminds me very much of the faster-than-light neutrinos. The authors of that experiment also seemed careful enough to not overstate their claims but this did not prevent a massive public interest in an ultimately debunked result. I expect the results in this paper to go the same way.
I agree and I'm skeptical myself. But note that models just barely break in this experiment. The deviation from theory (if real) is so small that it's almost unmeasurable. The models might break in a more severe way if extreme conditions are applied in a correct way.
To push back on this kind of thinking a bit, Einstein's breakthrough papers on Brownian motion (which served as evidence of existence of Atoms and Molecules) and the photo electric effect (which demonstrated validity of the Quantum theory of light) were very much "tabletop" effects.
While there's no denying this requires extraordinary proof, I think it's equally important for physicists to prevent themselves being biased by pre-conceived notions.
Yes but they were very well known tabletop effects. What was lacking was the theory to explain them.
What we need now is other physicists to test their own "Q thruster." If no one else detects a thrust, well, fine, chalk it up to weird error and move on. If other people do find a thrust, then we're into "we don't have a theory yet" territory.
Read More: http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36
...well, at least it's better than calculating the theoretical produced thrust by ignoring the axial component of the radiation pressure against the side walls. Which is how tapered resonant cavities like this were supposed to produce thrust when I was in high school.
But, leaving a wake in the vacuum should require that the vacuum exists in some particular reference frame. How's that supposed to work?
Or since the paragraphs immediately before that one discussed the vacuum behaving differently when there's stuff in it, are they just saying that something is being exhausted out the back (which should be visible by some sort of effect on the vacuum?) even if they have no idea what that something might be?
https://hackaday.io/project/5596-em-drive https://hackaday.io/project/10166-flying-an-emdrive
Your typical 100 HP car engine puts out 75.6kW, so you'd need 130 car engines' worth of power to lift a small 1 kg/~2 pound object. Not to mention that the machinery needed to channel/produce that kind of energy would be so heavy that it could not lift itself.
But it's still possibly useful for space travel. Not needing propellant is huge for long-distance space travel.
That said: they don't know why it works. (If it even works, which I strongly strongly strongly doubt.) If they figure out what produces the phenomenon, it's very possible they could get the drive to be way more efficient.
Now, a Newton is the amount of force it takes to hold up an apple (or accelerate it at 1G). So a millinewton would be the amount of force it takes to hold up a blueberry.
Bonus question: The power of the RTG halfes avery 87.7 years. What is the asymptotic speed the spacecraft will reach?
The EMD is simply not applicable to scales where RTGs are used, much as a 5MW maritime diesel turbine is not applicable to swimming motions of a biological cell. The power density of Voyager is a hundred times lower than what an EMD ship would need.
Of course this is considering only the decay of the plutonium and none of the active decay products. I've also disregarded the decrease in mass over time.
[Edited erroneous data for FEEPs and needless rant]
I understand that this is different because the radiation bounces around an enclosed chamber and so momentum wouldn't be conserved, but if the issue is to create propellant-free propulsion, doesn't that already exist (even though it's not practical)?
pressure against what?
the difference with the EM drive's method of propulsion is, that while the article you posted describes a force reacting upon an external, "grey body," as is acceptable with the copenhagen interpretation of quantum mechanics, the EM drive force exhibits a characteristic betrayed by a theoretical pilot wave, which indicates a non-copenhagen interpretation of quantum mechanics, but rather a bohmann version of quantum mechanics, in which the force can act upon itself.
run-on sentence alert.
If you use a photon thruster (aka a laser or a flashlight in the right direction (or a microwave)), then the maximal thrust/energy ratio is at most 1/c = 3.33 nano-Newtons per Watt = 0.0033 uN/W = 0.0033 mN/KW.
Someone compiled here two lists of experiments: http://forum.nasaspaceflight.com/index.php?topic=36313.msg13... http://emdrive.wiki/Experimental_Results
Some of the experiments are few years old, but you can compare the current result with 0.0033 mN/KW. The results in the tables vary from 3x to 200000x the theoretical maximum of a photon thruster. I think that the typical current value is x4000.
It's a theoretical upper bound that is very easy to calculate using special relativity, and it depends on very fundamental laws, not tricky details of the universe.
The theoretical bound is so fundamental, that it's even true if you use a graviton thruster instead of a photon thruster. This example is not totally made up, someone have an alternative impossible massless drive that "push against the far away stars". They claimed also a thrust/energy ratio > 0.0033 mN/KW, so it was also impossible from a theoretical point of view.
Also, for the EmDrive, someone proposed that it emits twin photons that somehow cancel each other, but the pair still carry momentum. That explanation extremely wrong.
https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is...
Conservation of momentum is pretty fundamental.
The interesting part will be to see how this performs when we scale it up in size and stick it in a true space vacuum - it seems based on the experiments done that the amount of thrust scales linearly based on kW/h input, I imagine there are some significant gains to be made in terms of efficiency and cavity design which could well see significant increases in performance.
Then take in to account that the Hall Thruster requires a propellant - this only requires electricity, theoretically with a nuclear reactor on board, you could achieve constant acceleration, instead of our current methods of putting things in to deep space which consist mostly of "Blow up a ton of stuff behind it and then coast along for tens of millions of miles"
I'm not a trained physicist, by the way, so there could be fallacies or inaccuracies here, this is based on my understanding.
I mean I guess it depends on how far back you want to go. The early electronic systems (Collosus, ENIAC, the crazy relay boards and bedsteads in the Newmanry at Bletchley) were all pretty much built expressly to solve practical and immediate problems (breaking ciphers, calculating parameters for nuclear weapons) that would take too long or contain too many errors if done by hand. Babbage got his freak on because of error rates in (IIRC) log tables. My Mesopotamian history is a little rusty, but it's easy to imagine a similar development story for the abacus. (In the sense of 'tool to surpass unaugmented human in speed and accuracy of computation' rather than 'hacking crypto and nuke yields'). But I dunno. Maybe.
[1] ie. nothing working with radiation pressure (solar sails, lasers etc)
> Working mass, also referred to as reaction mass, is a mass against which a system operates in order to produce acceleration. In the case of a rocket, for example, the reaction mass is the fuel shot backwards to provide propulsion. All acceleration requires an exchange of momentum, which can be thought of as the "unit of movement". Momentum is related to mass and velocity, as given by the formula P = mv, where P is the momentum, m the mass, and v the velocity. The velocity of a body is easily changeable, but in most cases the mass is not, which makes it important.
This thruster pushes nothing. It just achieves thrust with only energy. No refueling ever, solar/nuclear energy into movement until you have no more energy.
This violates certain physical laws, but there it is being measured anyways.
There is one other thruster that doesn't need a tank of reaction mass: a photon rocket-- moving yourself around only using radiation pressure. Exhaust speed really is c, but generated thrust is tiny, since photons are pretty light. The resonant cavity thruster is more interesting than a photon rocket, since its thrust is much higher.
If their idea worked, it would be completely new physics.
1. It violates Conservation of Momentum. If the phenomena is real, a large number of basic Physics principles would need to be discarded.
2. It was designed based on certain principles. Those principles have been shown to be wrong. But it works anyway because reasons?
3. The results of each experiment are suspiciously close to the limits of measurement.
There are two choices here: (a) experimental error or (b) profound alteration to fundamental physics. Occam's Razor applies. Also, "extraordinary claims require extraordinary evidence" and this evidence is far from extraordinary.
That this is being published in a journal which does not cover basic physics is not helping.
I guess, the more info is available to the public, the better. Hopefully someone will test it properly. But no way it can be considered as "provably works"
We've been hearing about this for ~1 year at this point, so I'm not sure what you mean.
> I guess, the more info is available to the public, the better.
This is up for debate -- esp. given the whole "fake news" thing and the observation that people basically love echo chambers (as observed in the field of Behavioural Economics).
If, by "info" you mean "actually provable[1] info", then I probably agree.
[1] To some reasonable standard of "proof". Certainly we don't need "mathematical" proof, but we need something better than "a study says". (See: reproducibility crisis[2], the fact that a "study" doesn't require any particular standard of evidence, etc.)
[2] Meta: I wonder if the BE field is itself suffering from a reproducibility crisis? Anyone know?
Not "everything is clear, the case is closed" - that's what I meant
http://emdrive.wiki/Experimental_Results claims that there are six orders of magnitude difference between the lowest detected thrust and the highest detected thrust.
Going from the assumption that some effect actually exists and all the physical principles we have painstakingly tested ten million times over are wrong... Most of these studies are still complete BS, because they don't agree closely enough to be a replication.
Anyway I agree with you, although it has already surpassed initial expectations stronger evidence is required.
Assuming it is not actually violating conservation of momentum, it's pushing off something. Either that something is some part of the apparatus (in which case it's a boring old reaction drive) or else it's something environmental (in which case it's probably not going to work in the very different environment of deep space).
For this thing to be exciting as a drive per se, one of the following must apply:
1. Violates conservation of momentum, and like literally everything we know about physics is wrong.
2. Pushes against some kind of omnipresent ether-like medium, and darn near everything we know about physics is wrong.
3. Pushes against something in the device in some kind of very efficient way (ie accelerates reaction mass to a much higher exit velocity than conventional drives do), in which case why haven't we detected these high energy emissions?
I don't actually think this is true, because measurement error sounds more likely, but unlike conservation of momentum violation it would require only a minor tweak to known physics.
1. A process can convert normal matter to dark matter and at the same time accelerate that dark matter to some absurd speed -- so you can take a small reaction mass with you and use it very efficiently, but you don't have an ultra-efficient weapon system.
2. A process can push against some background medium of dark matter.
But. If there is dark matter in the vicinity of Earth (and while I agree it's "in the same places as ordinary matter," that's at a macroscopic, galactic level), it's unlikely to be at some convenient rest-y-from-human-perspective frame of reference. Which would suggest that the EM drive would work better facing one direction than others. Which is, I think, not congruent with the experimental evidence in front of us.
If we accept for the moment the existence of a pseudo-CDM identical to the concordance CDM except that it can interact with EmDrive microwaves, then the first question must be: why doesn't it interact with astrophysical masers in GMCs, affecting the structure evolution therein? (e.g., if astrophysical microwave hotspots move pseudo-CDM then there will be a bias in the location and age of young stellar objects and H II regions due to the change in energy-density). Some astrophysical megamasers have luminosities on the order of a thousand suns -- that's a lot of watts to shuffle dark matter around in your idea about the EmDrive, and that shuffling will drag dust and gas along with it.
Tweaking CDM into pseudo-CDM without it collapsing gravitationally by radiating photons directly or by colliding with charged particles is probably impossible for any but a tiny fraction of the overall mass-density of the dark matter sector. Collision or direct dissipation removes angular momentum from the particles such that they can fall a little closer to the centre of the galaxy. On a galactic scale, that leads to a much higher total energy density at galactic core at even fairly small fractions of the local energy density.
Avoiding that would require extremely demanding work and likely would have you adding a lot more new particles to the standard model to capture all the additional (broken) symmetries -- and it gets worse the greater the local energy density or equivalently the greater the interaction cross-section you require in order to interact with a physically small device like an EmDrive.
An ether that can be pushed against is also an ether that has a frame of reference, and that frame of reference is unlikely to be one that is extremely favorable to use of the EMDrive as a drive.
An ether that is in some way massless or frame-of-reference-less but still can be pushed against is a fundamental rethinking of physics.
The "Laws of Physics" are our current best way to describe the phenomenon that we see; but they may simply be the best approximations we have given the limited set of our observations. It does not follow that these laws are perfectly correct.
I think of it as a best-fit curve, which does a great job of describing the real curve so long as we have sufficiently accurate samples.
Sometimes I worry that we do not provide enough funding to experiments which fly in the face of our current understanding of Physics, and so skew our sample data towards fitting the curve we are presently comfortable with.
Part of that is confirming that things we expect not to work do not work. We shouldn't fear or avoid testing things simply because they disagree with our understanding, because testing them may confirm our understanding.
But because many thought it did, it's been an incredible uphill battle to get this thing tested; yet throughout tests it shows strange outcomes. Something odd is going on, and perhaps the simple outcome is that we find a better way to perform the tests.
To me, that's a fantastic outcome and I'm dismayed it's taking such a _political_ fight to arrive at it.
Why is it such an uphill battle to engage in actions that have positive outcomes like these, simply because they challenge our core understanding of the world? At the least, we end up better equipped to measure and test future experiments.
Just to get back on track: The point is that we have a huge number of explanations, currently, which are "hard to vary". You need a commensurate amount of "hard to vary" explanations to counter that. That's why it's very hard to overturn e.g. the 2nd Law of Thermoses, erm, Theormodynamics.
[1] I think, from "The Beginning of Infinity"... Actually, I can't remember if he cited anybody else for this idea, but I can say that it's the first place I came across it.
There are a few bits in there that may be hard for the layperson to understand, but I think the overall point is amazingly well made.
https://en.wikipedia.org/wiki/Pioneer_anomaly#Explanation:_t...
It's much easier to produce "some results" then to prove that the researcher didn't fool himself.
Re Pioneer: "once the thermal recoil force is properly accounted for, no anomalous acceleration remains."
Now from the EmDrive paper's conclusion actually confirms that not everything was proved to be "sure" even from the point of view of the authors:
"Although thermal shift was addressed to a degree with this test campaign, future testing efforts should seek to develop testing approaches that are immune to CG shifts from thermal expansion."
Why too much public attention before the whole thing is actually proved can be dangerous:
http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-v...
"When the results of the Cannae Drive prove impossible to validate (as will almost surely happen), it may produce an unjustified cynicism about how NASA has failed us once again."
It's just a very small team "devoted to exploring unorthodox propulsion ideas." "The reality is that space exploration is expensive, difficult, and time-consuming. Therein lies both its challenge and its glory."
> That this is being published in a journal which does not cover basic physics is not helping
AIAA is an extremely reputable journal and society. All the members are extremely familiar with conservation of momentum.
The observation of superluminal photons (later disproved) was published in reputable journals as well.
No scientist took either result very seriously. However, the observation of anomalous results is a result worth of publication and communication to other scientists and engineers.
As a practicing scientist, I can assure you that peer-review does not mean something is 'correct', but that is it not provably false, and that the results may be important to the community.
> 1. It violates Conservation of Momentum. If the phenomena is real, a large number of basic Physics principles would need to be discarded.
According to our current understanding of the system yes, however, it's also plausible that this works via in a non-trivial interaction of general relativity and quantum mechanics. Which is still a very open question, and may not actually be violating conservation of momentum. To state it more correctly, it appears the em drive violates conservation of momentum by all means we currently understand. Given the minuscule amount of thrust it's plausible there could be a unknown quantum effect. One group tested the drive in vacuum which makes it certainly more interesting if there is an actual novel physics interaction.
> 2. It was designed based on certain principles. Those principles have been shown to be wrong. But it works anyway because reasons?
That's a non-sequitur. If there weren't several repeated experiments showing similar results it might be a reasonable caution. However, many of the best scientific discoveries arose in similar mis-comprehensions.
> 3. The results of each experiment are suspiciously close to the limits of measurement.
This is the most problematic portion of the experiments. It's only an order of magnitude smaller thrust per kW than more conventional drives. However, this article at a cursory reading was designed to try various configurations of thrust to check for potential systematic experimental errors in measurement. At this point asking more serious questions would be required rather than a "this doesn't fit into my preconceptions". E.g. explain how the particular experimental design in question could be flawed, in particular, what conditions could cause the null thrust test to not remove systemic measurement.
In short, scientific skepticism doesn't mean incredulity.
It's not a non-sequitur! It's firm evidence they don't understand what is going on and therefore aren't in a position to explain it. The fact that they have found a consistent effect does not mean they found anything interesting, a tiny wiggle very close to the detection range when you put a lot of power into it isn't by itself interesting unless you have a good basis to know it is. Which they DON'T.
Relativity didn't make us discard Newtonian physics though. It just turned out to be a good approximation of something more complex in certain conditions. Similarly, we don't discard the descriptions of macroscopic events when they turn out to be just emergent phenonema, good approximations of complex quantum events at certain scales. Why would this be any different?
> 2. It was designed based on certain principles. Those principles have been shown to be wrong. But it works anyway because reasons?
Those 'reasons' are imo more interesting than whether it really works or not. Sure, the measurements may be off, or the setup of the experiments could be flawed. But until someone can point out exactly why we're measuring what we're measuring, I think it's worth pursuing.
> 3. The results of each experiment are suspiciously close to the limits of measurement.
If nothing else, maybe it will motivate scientists to come up with more exact ways of measuring, or better experimental designs that shield from unintended effects.
I guess my point is, regardless of whether it works as a drive or not, we shouldn't discard it as a hoax or consider its study a waste of time as some scientists seem to do.
It may not be a reasonable argument to claim that it is impossible, but it is a totally fine argument to make that it is insanely unlikely and needs a mountain of evidence before we take the conclusions seriously.
Any evidence can be explained either by the effect or by experimental error. Your prior is how relatively likely these two possibilities are.
If something is "significant" then it is surprising and requires stronger evidence.
Not that it matters. If it works, it already violates conservation of momentum as we currently understand it. That's just as fundamental as conservation of energy.
v(t) = a t / sqrt(1 + a^2 t^2)
Ek = m c^2 / sqrt(1 - v^2/c^2) - m c^2
Ek = (1 - t^2/(1+t^2))^(-1/2)
Proof:
d/dt Ek = t sqrt(1 / (1 + t^2))
= sqrt(t^2 / (1 + t^2))
I've seen claims that the max is the efficiency of a photon rocket, but I haven't seen it backed up with math.
It's certainly not going to take too long before someone puts an EM drive to space to see if it works there too, it's not that expensive to do so when put into context.
They're putting in a fair amount of energy to make this happen.