Warp drive's best hope dies, as antimatter falls down

I don't think anybody expects a wrap driver to be possible. It's just one of those odd things where the math says something, and it's well work looking at just in case. (Just like negative mass matter is something that nobody expects to exist, but likes to appear on equations here and there.)

That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter?

Even among people who hold out hope that a warp drive is physically possible (as opposed to merely mathematically possible), I don't think anyone ever suggested that antimatter was a candidate for the negative mass required by the equations. It's always been some kind of unobtainium.

Agreed, though also I really appreciate this sort of "obvious" experiment, because the incentives really aren't set up to encourage it and we've been surprised often enough over the centuries that Actually Double Checking is probably something we should do more of.

(there's a parallel here to 'more negative results' and 'more replications')

It always seemed like a reasonable, but still big, assumption that antimatter behaved the same way under gravity. Anti-particles have opposite charge, so maybe it could have made sense that they have opposite "gravitational charge"? But also gravity doesn't have "charge".

So yeah, agreed. A good thing to confirm, even if (especially if) they expected the result to be unexciting.

The author directly addresses this sentiment in the concluding paragraph:

> Although there are physicists who wonder “Why did we even need to do this experiment; we all knew that antimatter has positive mass,” that sentiment is absolutely foolish. We must remember — and I say this as a theoretical physicist myself — that physics is 100% an experimental science. We can be confident in our theory’s predictions only insofar as we can test and measure what it predicts; as soon as we step outside of the realm of what’s been validated by experiment, we run the risk of stepping outside the realm of where our theory is valid. We just learned that Einstein’s general relativity passed another test, the antimatter test, and with it, our greatest science-fiction hope for achieving warp drive has completely evaporated.

And ludicrously energetically expensive.

But that's science proposal writing, isn't it? Propose something that would be ludicrous even if it were physical.

And hilariously useless even if you wave away the costs and catastrophic dangers. Yes, you can have a floor of normal matter and a ceiling of antimatter and produce... like... maybe 0.00001 m/s^2 of gravity?

Doesn't that proposal merely ~halve the amount of mass required?

I'm in an office right now that has a ceiling made out of normal matter (gypsum, fiberglass, steel, and tar, probably a couple thousand kg overhead) and a floor also made out of normal matter (carpet, concrete, iron, silicon, oxygen, and a bunch of other stuff adding up to 6x10^24 kg), which generates artificial gravity at 1g. It happens to be rotating at 1/1440 RPM, but that's only a 0.2% reduction in the acceleration.

Sure, if antimatter caused anti-gravitational forces, you could have achieved the same gravitational acceleration I experience in my office using one 3x10^24 kg sphere of antimatter overhead and one 3x10^24 kg sphere of matter beneath, but that's still not a Starship Enterprise, much less an X-wing, with artificial gravity generators. You're still stuck at:

    F = G x m_matter / r^2 + G x m_antimatter / r^2

    F = 4 x pi / 3 x G x density x radius_matter + 4 x pi / 3 x G x density x radius_antimatter

with planet-sized masses and radii for both.

And I'm not sure that "hilariously" is a sufficient modifier for the danger level when standing in a 3m gap between planet-sized spheres of matter and antimatter.

What about building a circular ship around a micro black hole? Or is that just real gravity and not anti-gravity?

I have never heard of antimatter being used in that way, even in the most off the wall, science illiterate speculation. Usually its as a power source.

The idea was mostly limited to really bad science fiction, the kind that is really a fantasy with science–fictional set dressing.

What are the walls made of? Surely the ceiling must touch normal matter at some point?

how are you so sure that anyone else besides you is actually conscious ? you might be the only conscious being in the universe. the whole universe is yours. you've already traveled the entire thing.

I'm conscious too but that's in my own universe, running in parallel to yours.

the "once consciousness has been digitized" step would have many hurdles of similar complexity to meet before simplistic 21st century manipulation techniques would ever apply.

> and construct bodies onsite at minimal cost.

Once established, perhaps, but microchips aren't easy to build. You'd have to send a lot of infrastructure before you could create AI brains on another planet.

A lot of people seem weirdly aggrieved by the limit of the speed of light. It's not really the reason we can't go to space -- if you had magic energy density you could go to the stars in as little time as you wish, due to relativity. (Weird stuff happens when you try to come back, but nobody ever seems to care about that anyway.)

I think people hear "Einstein said you can't go faster than the speed of light" and think, "Surely I can figure out how to be smarter than Einstein". It appears to be parallel to the ones who get cranky when being told that Newton says you can't make a perpetual motion machine.

I suspect that they don't spend as much time thinking about the brain-in-a-box version is that it opens up too many scenarios that are hard to think about. If you decouple consciousness from bodies, who are you? Why not make multiple copies? Why go anywhere at all, when you could just stick the sensors there?

People really want the cowboys in space, and get aggrieved that somebody told them they can't. So they focus on overcoming a limit that seems like it can be solved just by thinking really hard, and leave the engineering details to the peons with calculators.

Why would you put an AI on another planet? It's easier to transfer images and other data back here for everyone and everything to perceive.

> construct bodies onsite at minimal cost

That requires a bit more than a receiver. You'd have to build a robot factory, which requires energy production which requires mining which requires heavy machinery, which etc.

This is a good argument for transhumanism. People seem to have a problem with the speed of light since without FTL, unmodified humans cannot meaningfully travel interstellar distances - and pop culture entertainment has surreptitiously sold us on this, if only because otherwise the timeframes and types of bodies involved would not be "relatable" anymore for the common types of drama we consume.

> Once consciousness has been digitized, you can beam it at the speed of light to a receiver.

In principle yes, however, the energy required is still dramatic and bandwidth would probably still be a problem. It seems to me the default option would be to physically send non-aging transhumans, or virtualized/uploaded brains, or people in stasis (or a combination of these) using non-relativistic speeds.

> But it is possible with artificial intelligence. Once consciousness has been digitized, you can beam it at the speed of light to a receiver.

That may not remain true. The ability to serialize consciousness does not come for free, it requires extra wiring to carry all information out of the system or to stream it in, which is an intrinsic inefficiency. All other things kept equal, a brain's performance ceiling is higher if you only locally connect the units/neurons that need to be connected and nothing else, but in doing so you give up digitizability. It is entirely possible that future AI, in order to be performant enough, will lose the ability to be transmitted in the way that you describe.

We need to let go of the "Ship full of brave men" meme of space exploration.

It'll have to be robots, probably very small robots, some kind of solar sail / exogenous energy source (or maaaaaybe fusion?), and probably either a copy of some human's consciousness in a machine, or a bunch of fertilized frozen embryos, or both.

And even then only after a lot of gene / tree bombing of the target planet to have any hope of making it liveable.

This is how interstellar travel worked in Altered Carbon.

We don't know for sure that AI would be conscious. Teleporting super intelligent zombies around isn't all that interesting.

Speed of light limit is a big problem though. How do you explore the universe if you can't catch up with it? Even with a googol of human lifeforms running as AI spread out across it in a mesh, it is still expanding too fast!

> Once consciousness has been digitized, you can beam it at the speed of light to a receiver.

You may be interested in Philip K Dick's experiences. He believed himself (and humanity) to be receivers for information being transmitted across space.

https://en.wikipedia.org/wiki/Valis_(novel)

If we're going to imagine breaking the laws of physics and changing our understanding of metaphysics, as a goal.. then moving an object past the speed of light seems to be more likely than identifying what consciousness is, successfully separating it from it's source and then inserting it in a recepticle, across the other side of the universe.

Stupendous amounts of energy would be beneficial to have for literally everything humans do... whether or not we use the tech on space travel.

We have lived (as a species) through cavemen, industrial revolution to the atomic bomb and somehow you're coming to the conclusion that technology progress has to take a weird bend into uploading people to the internet, as if computers havent capped out on that already?

We have never really cared what the universe prefers. We'd still be living 'in harmony with nature' (so to speak) if we genuinely cared what the universe prefers.

I'd rather be the guy who tore up Einstein's map, than some internet electron.

We’ve lost the “best hope”, not all hope.

The author addresses this (in a very condescending way) in the last couple paragraphs. But yes, I tend to agree with you.

The universe is just a matryoshka of recursive couch potatoes eating cheese puffs.

If its intention was to illustrate realistic causal disconnection, Interstellar does a pretty poor job.

What with the causal loops and so on.

Theoretical warp physics -- the real kind, like Alcubierre, not the Wesley Crusher kind -- proposes that a source of negative mass would be critical to the creation of a warp field.

Antimatter as part of an energy storage system for propulsion is still a good idea. They'll just have to look elsewhere for that property, or modify the theory to work on different principles. Eric Lentz is working in that direction and doesn't think negative mass/energy is needed.

Not weird, just irrational. If warp drives were possible, aliens might be traveling to us before we'd invent them. That doesn't seem to be the case. There are a lot of explanations for that, including a few that involve conspiracy theories where this did in fact happen but we are being kept in the dark about it. But the easiest one would be that it hasn't happened because it isn't possible. Faster than light travel not being possible, it's unlikely for there to be a coincidence of any other intelligent species to exist within tens/hundreds of light years of our tiny little corner of the universe exactly at the moment where we hit enlightenment, steam machines, and rocketry in the time frame of about 250 years. Never say never of course but it does sound astronomically unlikely when you put it like that.

In the absence of any nearby aliens to travel to, what exactly is the value of traveling at warp speed to some desolate bit of universe? We'd get nowhere a lot faster is about the most positive thing you could say about that. Most sci-fi is premised on the notion that we're not alone and that there is this wealth of interactions (good and epically bad) to be had on the far side of any worm hole that we travel through at warp speed. But we have zero proof of that nor a way to travel in such a fashion. Or even the confirmation of the possibility of being able to do so. Fantasy and reality are not really aligned here.

To my understanding, the researchers released antimatter particles with detector plates above and below them. The particles started out traveling in random directions. Some of the particles hit the top, some hit the bottom. They saw that more particles hit the bottom than the top.

If the particles had "anti-gravity", they'd be repulsed by the large mass of the earth (instead of attracted), and you'd have expected more to hit the top plate than the bottom plate.

The researchers also added a magnet to the top designed to cancel out the downward force from gravity, and they hit the top and bottom plate at even rates.

> To use an analogy, Let's say I am on the Amazon river (fastest river according to google). You want to detect which way I was swimming. Would you even be able to detect the marginal effects of me swimming upstream relative to the massively more impactful force from the river?

Definitely yes! If you're even a reasonably competent swimmer you should be able to outswim the Amazon and make headway upstream at most points.

I'm not sure what this says about your analogy, but I would think the measurement devices are millions of times more sensitive than needed to detect which way you were swimming.

You're making a very interesting distinction between the experimental result, which is that antimatter follows the same space-time curve as normal matter, and the dashed hope of warp drives, which is that antimatter causes the same space-time curve as normal matter.

However, if antimatter were to create a negative curvature but follow positive curvature, then you would be able to put a lump of normal matter next to a lump of antimatter, connect the two together, and the whole mechanism would spontaneously accelerate forever, breaking the laws of conservation of energy and momentum. For that reason, I think this experiment also gives us high confidence that antimatter causes exactly the same space-time curvature as normal matter, even though we haven't gathered enough antimatter to see it creating a normal space-time curvature. In essence, gravity is symmetrical.

that's quite optimistic. i'd give us fifteen tops

Yeah once Dr Cochrane starts working on it :).

BigThink, ironically, is sponsored by the Charles Koch Foundation.

> Why did they think it would have negative gravitational attraction?

They didn't. There are very strong theoretical reasons (among them, CPT symmetry) to expect antimatter to gravitate normally. But it's still good to actually check.

Wait until you hear about the situation in the middle east... :-(

We truly live in the universe with most boring set of physical laws.

Hard light speed cap, no anti-gravity, entanglement can’t be an information channel, no warp drives. It’s like we got stuck on the “no fun” setting hahaha.

Side note: re-watched ST2 and 3 recently and switched to french audio for a bit for giggles and nostalgia: warp speed got translated to "exponential hyper-atomic".

"Warp Drive" dates back to 1947 (John Barret, "Stellar Snowball") according to sfdictionary.com (a resource I love for this kind of question).

Other phrases like "Space Warp" go back even further (Nat Schachner, "The Son of Redmask", 1935).

Wouldn't it be more interesting to learn real physics instead of made up stuff?

> The controversial scientist Bob Lazar

Lazar was briefly a subcontracted technician at Los Alamos: not a scientist, controversial or otherwise.

What about jump drives in Battlestar Galactica?

Depending on the model, anything from the mass-energy of a few tons to several times the universe.

Apparently a few models work with positive mass, but I'm reading headlines for that, I can't follow field equations.

The Tsar Bomba (5.3YW) managed about 2% of the power output of the Sun (384YW) - admittedly not for very long though...

So Teller's Sundial design was aimed at 10Gt so ~200 times more than the Tsar Bomba as tested.

So Sundial's peak power output would perhaps have been roughly 1RW?

Edit: Maybe you power the Warp drive with a sequence of Sundials.... in a sort of Orion like approach? :-)

Edit2: So about a billion Sundials a second and you're good to go?

Edit3: Usual upper limit of yield per mass is about 6Mt per t - so a Sundial would be about 1500t. So that would be burning about 1.5 Tt of bombs a second?

Honestly, this does sound like an intimidatingly high amount of energy, but look at the progress of computational power since, say, 1973, 50 years ago. If the same advances in physical control of energy had taken place, who knows where we'd be today

That's just a scaling issue.

So what’s going to provide your negative energy density, given it isn’t going to be antimatter now, and that was our best candidate?

Where do you get the energy to move that amount of mass?

People have tossed the idea around, and it makes sense to check, but I’m not aware of anyone who seriously thought it might have negative mass.

I don't think anyone really expected antimatter to produce antigravity, but it had never been tested before so it was worth doing the experiment.

One of the questions in physical cosmology is, "why is there so little antimatter/matter mixing in the cosmos?". We can measure the mixing by looking for the annihilation spectrum (e.g. e+ e- -> 511 keV/c^2, which for distant extragalactic sources should redshift with the expansion of space). We can produce lots of e+ (positrons) and other antimatter here in laboratories, and so have a fair chunk of the total annihilation spectrum. We also have the spectra of lots and lots of galactic objects (stars, neutron stars, and so forth) and spectra from extragalactic events large (neutral hydrogen clouds) to small (supernovae). There is essentially no sign of known matter-antimatter interaction.

Our galaxy and other members of its cluster are, to high confidence, made essentially entirely of matter.

We have not yet totally precluded distant isolated galaxy clusters made essentially of antimatter, but the cosmic ray spectrum (we see lots of particles that originate at cosmological distances) puts increasingly strong constraints on the distribution and density of such galaxies: there aren't many in total, there's no dense blob of them. The oldest galaxies that we can obtain spectra are also closer together, and each non-observation of annihilation spectral lines puts ever-tighter constraints on other old galaxies' antimatter/matter mix. It is fairly safe to bet that there is simply no significant blob of antimatter in the observable universe, and that what antimatter there is comes from nuclear decays and high-energy astrophysical processes, and all of this antimatter quickly annihilates spatially near where it's produced.

However, that raises a trio of questions. (1) Did some process strongly disfavour the production of antimatter in the early universe, when hydrogen and helium was being produced in abundance? (2) if (1) is true, what is the nature of that process, and how could we see it experimentally? (3) if (1) is not true, where did all the antimatter go? There is an inversion of (3) as well: why didn't the disappearing antimatter take all the matter with it too?

The above is the essence of "the missing antimatter problem" or "the matter-antimatter asymmetry problem" or "baryon asymmetry" <https://en.wikipedia.org/wiki/Baryon_asymmetry> (that last name is for technical reasons, including that there are lots of antineutrinos, anti-photons (which are just photons), and (somewhat complicatedly) anti-gluons and antiquarks [endnote 1] in our universe) and there is a substantial academic literature by experimentalists and theorists.

A family of that literature explores the idea of segregation: matter and antimatter had similar abundances but were driven apart by some process in the early universe. The result is that there will be large (observable-universe-size-or-bigger) regions dominated by antimatter, and large regions (like ours) dominated by matter. But what is the nature of the process?

A subfamily exploring that last question considers the possibility that the segregating interaction is gravitational; a sub-sub-family considers that a change of sign of quantum spin can generate a gravitational difference. One approach to this is to treat quantum spin as a generator of the spin tensor in a modification of General Relativity in which the spin tensor generates the torsion tensor. In General Relativity there is no spacetime torsion at all, so in "semiclassical gravity" where one adds quantum fields to General Relativity (e.g. as in Stephen Hawking's famous 1974 "Black hole explosions?") matter and antimatter gravitate identically. Introducing non-vanishing spacetime torsion can change the nature of black holes enough that black hole evaporation could be very different. And if one couples particle spin to torsion, one could distinguish a black hole created by significant antimatter from a black hole created by practically no antimatter, and we would expect that to show up in the spectra of active galactic nuclei (generated by supermassive black holes) and in the gravitational wave detections of black hole mergers and black hole-neutron star collsions.

Apart from the lack of observational support (which one could sidestep by saying that there is basically no antimatter available to large black holes because it was all chased out of the observable universe by spacetime torsion effects), this quantum spin = spacetime torsion approach runs into a number of theoretical problems. The anti-hydrogen experiment that's the subject here adds a further problem that would need solving. Why would antimatter-matter gravitation today work differently from antimatter-matter gravitation in the early universe? If they work the same, then this experiment makes it unlikely that gravitational repulsin from torsion could solve the missing antimatter problem via early segregation.

This antihydrogen result also imperils proposals for theories of quantum gravity wherein quantum spin (other than that of the graviton or its string equivalent) is gravitationally relevant (but not necessarily arising in that family of string theories especially to solve the missing antimatter problem, i.e., "our theory has a gravitational spin-antispin term in the action which we don't mind because maybe it's too small to matter or maybe if it's big at high energies (like in the hot dense early universe) it can solve a big problem like the missing antimatter problem", essentially).

Finally, wikipedia has a so-so page which is at least reasonably accessible and equipped with a good references section: https://en.wikipedia.org/wiki/Gravitational_interaction_of_a...

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[1] https://profmattstrassler.com/articles-and-posts/largehadron...

"The standard shorthand, “the proton is made from two up quarks and one down quark”, is really a statement that the proton has two more up quarks than up antiquarks, and one more down quark than down antiquarks. To make the glib shorthand correct you need to add the phrase “plus zillions of gluons and zillions of quark-antiquark pairs.” Without this phrase, one’s view of the proton is so simplistic that it is not possible to understand the LHC at all." (for which see a later followup, <https://profmattstrassler.com/articles-and-posts/largehadron...>)

We can do a lot of stuff with energy in various forms but gravity is just from mass which is quite difficult to control. Essentially we suck at fission and fusion at meaningful scales and we have a very narrow capability as well. I mean, to destroy mass equivalent to Mars in a short time frame is a cosmically cataclysmic nuke, then to not waste that energy, so you efficiently capture it and recreate the mass elsewhere in one huge fusion reaction. Maybe I talked past you and just daydreamed about Dr Manhattan stuff, maybe what it takes to emit gravity at will at some location, is much more difficult than just redirecting it which I dont have the tools to daydream about.