Relativistic Spaceship
dmytry.github.io
dmytry.github.io
If you pick an acceleration equal to the acceleration we experience on Earth (aka 1g, aka ~9.8m/s^2), you hit relativistic speeds (speeds at which you need to take into account the effects of relativity to do anything) surprisingly fast. On the order of hundreds of days. So, it is not really a matter of safe acceleration on a long space trip. Instead you have to worry about the actual speed you are traveling at—even though space is very empty, there are still atoms floating around out there, and you’ll be moving at very high speeds relative to them, leading to interesting collisions.
That's the other big punchline in relativity: There's no one "actual speed" because that implies that there is a single "important" frame of reference wherein those atoms are floating around waiting to be hit by a spaceship.
I guess you'd notice a change in light frequency based on the light in front/behind. Redder behind, bluer in front.
Edit: supposedly we can measure our speed compared to the cosmic microwave background which is fairly uniform, which gives us a value of 400 to 800km/s relative to the CMB: https://www.researchgate.net/post/How_can_we_practically_mea...
The light in question is not uniform like white noise; the spectral power distribution has relatively light and dark lines in them as a result of the physics of the bright sources and intervening gas and dust. Those features also get redshifted.
If one is moving relative to the sun, one would pay attention to the sun's Fraunhofer lines <https://physics.weber.edu/palen/clearinghouse/labs/Solarspec...>, which would be Doppler shifted to different wavelengths. These lines also appear in reflected light from bodies in the solar system; if you were flying towards Pluto you would see a corresponding blueshift of the reflected Fraunhofer lines (plus some additional structure related to the chemistry of Pluto; it has some luminescence, as does our moon, as do the leaves of plants, and luminescence tends to impinge on the narrower Fraunhofer lines).
Indeed, measuring the Doppler shifts of multiple known-chemistry light sources is a useful technique in navigation of spacecraft within our solar system; it can in principle do better than precision measurement of angles to multiple light sources.
The spectral distortions of the CMB are certainly interesting, but it's hard to imagine their utility for spacecraft navigation within the Milky Way, rather than helping to physical cosmologists understand why there even is a Milky Way.
In the solar system we have kind-of the opposite problem: in order to get reliable anisotropy data of the Milky Way, probes like WMAP need excellent almanac data for the ephemeris of Jupiter (it's a bright reflector of sunlight and its cloud-tops at ~70 kPa are ~22 GHz microwave-bright; I gather other outer planets are used too, but the details are beyond me) to check its 22-GHz-band detection of the CMB Doppler shift in the directions it looks.
So, say you're on earth and you measure the speed of light... you find that it's c (~3x10^8 m/s).
Now you get on a spaceship and accelerate to 0.5c with respect to earth, and you measure the speed of light relative to your spaceship... still c!
In this way, you can't really define a reference frame with a speed "the same as the speed of light". And if you try, you'll run into nasty infinities in all your equations that will cause them to blow up and stop being useful.
How is there a speed limit at all, if that’s the case? You can accelerate to 0.5c and then toss an apple out the window and say you’re moving at the speed of an apple tossed out of the window, relative to the apple. You have all of c available as headroom again? You can accelerate up to 0.5c again, relative to the apple you tossed out the window?
I am imagining you will say that it will seem like this is what is happening to folks in the spaceship, but what’s really happening is that time is slowing for the spaceship and it’s passengers, and that they still can’t reach c. Fine. But c relative to what? There is no absolute c because there are no truly fixed points, so c relative to what?
> A comoving observer is the only observer who will perceive the universe, including the cosmic microwave background radiation, to be isotropic. Non-comoving observers will see regions of the sky systematically blue-shifted or red-shifted. Thus isotropy, particularly isotropy of the cosmic microwave background radiation, defines a special local frame of reference called the comoving frame. The velocity of an observer relative to the local comoving frame is called the peculiar velocity of the observer.
From https://en.wikipedia.org/wiki/Comoving_and_proper_distances#...
Yes you can. You can even do it with 0.6c for both those speeds.
it's either "relative to any observer." or "relative to any inertial reference frame". no matter where you go (on the ship, on a planet you pass by, on another ship) you will never see the apple travel as fast as the photons coming out of your flashlight. Depending on where the observer is, they will see the apple accelerate to 0.5c (if they are aboard the ship) or they will see it gain mass (or rather, see you throw it more slowly as if it had gained mass), contract in the direction it's thrown, and slow down (due to time dilation...relative to the moving frame).
The case I don't know how to answer is two apples thrown at each other, each with a speed greater than 0.5c.
Suppose there is a starting point A from which your ship is moving away from. At the same time, a photon is shot out from A. You can take the distance traversed between A and the ship as D1, and the distance traversed by the photon as D2. Then your "percentage of C" is D1/D2.
How can you get the distance D2? I'm not sure. I guess we have to pretend it's also a ship that is traveling at C that can emit information to us (also at C :p )
As long as one is working with covariant descriptions of matter, taking a notion like a photon's "affine time" or similar for a classical electromagnetic wave into (signed) momentum imparted to some object on a timelike path (such an object will have rest mass) is straightforward. The justifications mainly originate with Newman & Penrose in the early 1960s.
Here's a nice (and very fresh -- it's an incomplete draft) technical note that details one use of the Newman-Penrose formalism in the flat spacetime of Special Relativity. Note the extract from Chandrasekhar's 1983 textbook in section 7.3 (the author sources from a 1998 reprinted edition). <https://astromontgeron.fr/SR-Penrose.pdf> (PDF). The observations in §7.7 and §7.9 would be enough for me, if I hadn't already internalized the ideas further below.
I'll raise a couple of important and noncontroversial points from Jacques Fric's note: a photon -- whose frequency is proportional to its momentum -- oscillates some number of times along its null path lending a useful affine parametrization of the geodesic (photon motion is for all practical purposes always geodesic) that takes into account the spacetime curvature along the geodesic. Deploying the NP formalism in such a situation gives a nice analogy between motion through curved spacetime and motion through a refractive medium. And finally, covariant results in the NP coordinate system are readily interconvertible with covariant results in Minkowski coordinates.
Coordinate systems built along null geodesics -- typically lightlike Fermi-normal coordinates (FNC) -- also find applications in generalizations of the Jacobi equation, geodesic deviation, conjugate points, and so forth.
Now a step back to your comment. Null-basis FNC approaches let one calculate the momentum of a massless force carrier at any point along its evolution from p_{emited} to p_{observed}, and find cosmological applications (redshift of an astrophysical megamaser, the Lyman-alpha forest, etc) and microscopic ones (for the latter see ref [1] at <https://physics.stackexchange.com/questions/62488/local-iner...>). In reading that stack exchange answer you'll want to know that 'Penrose showed that any [Einsteinian] spacetime [...] has a limit which is a plane wave, which can be thought of as a "first order approximation" to the spacetime along a null geodesic.' (from <https://link.springer.com/referenceworkentry/10.1007/1-4020-...>).
Pointing to references rooted in string theory and supersymmetry are not endorsements of those families of microscopic theories; they're just the most accessible examples of the practical use of lightlike FNCs for small locally relativistic systems.
So, not a logical absurdity, not useless, and not even especially uncommon.
It's the inertial frame of reference that makes the cosmic microwave background look most uniform. See https://en.wikipedia.org/wiki/Comoving_and_proper_distances#...
> A comoving observer is the only observer who will perceive the universe, including the cosmic microwave background radiation, to be isotropic. Non-comoving observers will see regions of the sky systematically blue-shifted or red-shifted. Thus isotropy, particularly isotropy of the cosmic microwave background radiation, defines a special local frame of reference called the comoving frame. The velocity of an observer relative to the local comoving frame is called the peculiar velocity of the observer.
There is the occasional weird exception though: https://en.wikipedia.org/wiki/Oh-My-God_particle
By the laws of physics, yes. But most of the stuff in our universe, and definitely in our galaxy, tends to move roughly at the same speed.
See https://en.wikipedia.org/wiki/Comoving_and_proper_distances#...
It's kind of funny that the actual big punchline is that light speed matters at all. There would be no meme of "reaching lightspeed" without relativity, despite that meme originating from relativity specifically mentioning lightspeed as something you can't reach.
[0] https://en.wikipedia.org/wiki/The_Songs_of_Distant_Earth
Though I can't say much without giving away spoilers.
A great read if you are a sci-fi fan!
I have read two of the three body books, but I wasn't aware of a sequel to project hail mary, would be very excited if that's the case!
It was just recommended to me by someone, but I'm usually into sci-fi, stuff like Greg Egan.
I really enjoyed it, but maybe I would have been disappointed if I was expecting more of a mind melter!
yes, the writing was annoying in parts (especially the Earth flashbacks). What I liked about it was 1) if you don't know anything about it (I didn't even read the back cover) the surprises evolve nicely; and most importantly, 2) it was a story of humans cooperating with another species rather than either subjugating or resisting subjugation
I hadn't read any Andy Weir before, but someone recommended it to me so just started reading.
My favorite is probably Permutation City, followed by Diaspora. His stuff can get heavy though.
If you are charging full speed ahead into its center, you are going against just about everything, including energetic particles no doubt coming the from the crowded center of the galaxy.
I’d never seen “a hundred atoms per cubic meter”, but it’s always been my intuition that, without some quite interesting shielding, you couldn’t make it anywhere near the speed of light. And on the other hand, I’ve seen claims that “space is really big” as you mentioned; but that claim has always seemed dubious.
Outside galaxies you have better chances of surviving high speeds. The intergalactic medium is only 1-10 particles per cubic meter in the web of gas we call the warm–hot intergalactic medium, and possibly less outside of that.
I guess Hitchhikers guide to the galaxy building space highways destroying everything in the way could be more than a gag after all.
It's not that bad. With currently known science, your fuel would most likely be hydrogen so you can run a fusion reactor.
The rocket equation tells you that most of your starship by mass would be fuel, if you want to go fast.
Of all the stuff on your ship that's not fuel, you'd probably need quite a bit of water for survival needs.
So you would make your spaceship relatively long and thin (to maximize internal volume for a given frontal area), and you would store your fuel (and water) in front of you to serve as exactly that shield.
Even if no, it would mean your shield will be gradually consumed. Not sure this is the best idea.
That's basically free shielding: you have to carry the fuel around anyway, so you might as well put it to good use. If you run a nuclear fusion reactor, you won't really lose much of the mass of your fuel, unless you want to. Eg you could use the helium you produce as the reaction mass for your ion drive. (I haven't done the numbers to see how the required mass per second for your ion drive compares to the helium mass per second a nuclear fusion reactor would spit out.)
Because it's a free shield, you don't really get to complain about your shield being gradually consumed.
Of course, you can have some extra shielding further inside. You would keep your water forward of your people, but behind your fuel. So your water would not bear the brunt.
Hydrogen doesn't really get all that radioactive: you can use chemical means to remove any helium or so you might accidentally produce; and hydrogen's isotopes are both pretty short lived and relatively easy to separate. (At least much easier than eg enriching uranium.)
Your water and food is also only a very small fraction of the overall mass of your rocket: as always, the vast majority is made up of fuel.
And you are entirely wrong about the isotopes of hydrogen. Tritium is highly radioactive, with a half life of ~12 years. And it is not just hard, but virtually impossible to isolate tritium out of water. So if any tritium forms (which is an extremely common by-product of any fusion reactions which might happen, and the most common decay product of heavier hydrogen isotopes), it will render your water quite poisonous for human consumption, virtually irrevocably.
On the contrary, it's quite easy to do if there is any significant fraction of tritium present. The proportional mass difference of ³H vs. ¹H is x3, which alters the chemistry enough to make separation easy. You can use fractional distillation or electrolysis even for ²H — even mere hobbyists involved in the DIY fusion reactor scene sometimes extract deuterium from water this way, tritium would be easier.
Depending on your fusion reactor, you might actually highly value any tritium produced, instead of seeing it as a nuisance.
> Your fuel still gets consumed, so you still can't rely on your fuel as the main form of shielding. Towards the end of your journey, your rocket is approximately 0% fuel. And at the point of highest speed, before you start decelerating, it is roughly 50% fuel.
With a nuclear engine you make a difference between fuel and propellant. When you fuse your hydrogen into helium, you still have the helium afterwards.
I haven't run the numbers to see how your fuel consumption would compare to your propellant consumption for a reasonable fusion powered rocket. Though I suspect that you also need oodles of propellant, given how the rocket equation works.
For the first part of your journey you could rely on passive shielding via your propellant. For the latter part, you could use more costly active shielding like a big magnetic field or ablative shields in front of your main rocket etc.
Basically, you would still want to use your propellant as free shielding as much as possible.
It's sort of funny, but dozens or hundreds of orders of magnitude below, the same sort of dynamics are at work in air-breathing ramjets. The impact velocity of the medium is starting to tell, and the exhaust velocity isn't particularly more energetic than what's threatening to ionize the air around your leading edges.
[1] Well, aside from the fact you're exceeding the average velocity of your exhaust mass
I'm not sure what you mean by electromagnetism being near-frozen? Doesn't electromagnetism also travel at the speed of light?
A cubic lightyear is about 8.468e+50 liters, and butter weighs 911 g/L, giving the mass of a cubic lightyear of butter to be 7.714348e+50, whose Schwarzchild radius is about 121,103,293 lightyears, about 100x smaller than the radius of the known universe.
... maybe it is? Hear my pet theory out.
Extrapolating backwards from the expansion of our universe, the Big Bang model posits a hyperdense state that exceeds black hole levels originating from a singularity, yet it's thought that somehow it did not collapse back, handwaving it as "physics as we know it did not apply".
But maybe physics as we know it does apply. Notably physics as we know it does not imply a specific direction for the arrow of time.
So our universe might very well be a black hole, but we have time backwards compared to the usual way we think of black holes: what we think of as the origin of time and space is what we think of as the irremediable end of time and space in a black hole.
radius of universe = 4.4 * 10^23 km (47b ly)
mass required to have schwarzschild radius of 4.4 * 10^23 km = 2.96 * 10^53 kg
Surely we are still discovering the implications of these numbers being so close.
I like your time-reversed black hole framing, thanks for that.
https://www.wolframalpha.com/input?i2d=true&i=+schwarzschild +radius+of+mass+of+the+universe
https://www.wolframalpha.com/input?i=radius+of+universe
https://www.wolframalpha.com/input?i2d=true&i=+schwarzschild +radius+of+2.96*Power%5B10%2C53%5D+kg
Before ANGRY KEYBOARD SOUNDS commence, I'm not saying we don't know what mass is, I'm saying fundamentals. I.e., why is mass. What causes it to come into being? Bulk entanglement, i.e., a function of probability or "mass as destiny"? Tiny signals? Lots of rubber sheeting? Etc.
Ok.
> a black hole, but we have time backwards compared to the usual way we think of black holes
Observations of our universe are straightforwardly understood -- and predicted -- by laying matter fields on an expanding Robertson-Walker metric. The same observations are not at all easy to understand by laying matter fields on a time-reversed Oppenheimer-Snyder-like black hole metric.
The first thing you run into is that at the largest scales (i.e., where the solid angles subtended by galaxy clusters are small for observers like us) visible matter is arranged roughly isotropically and roughly homogeneously: we detect typical spiral galaxies (and more importantly various atomic line transitions associated with them, like the <https://en.wikipedia.org/wiki/Lyman-alpha_forest>) at all sorts of redshifts.
Your homework would be to generate lightlike geodesics that can reproduce these observations at any time in a black-hole-like metric. If you can do that at for a single spacelike slice of your black hole, you then would want to work on evolving that slice using e.g. the <https://en.wikipedia.org/wiki/Initial_value_formulation_(gen...>.
Just scratching the surface of how you would go about doing that would be an interesting research project for a layperson. Among other things, you would end up learning a lot more about what's in your second paragraph, and likely develop an idea about how much work is involved in writing down even a simple "pet theory" of physical cosomology that accords with observational data. Or at least you'd have a better idea of what observational data there is that needs to be accounted for. You'd also confront all sorts of open questions about the interiors of black holes where there is significant matter; that would be timely given the recent preprint by Roy Kerr at <https://arxiv.org/abs/2312.00841>.
The mass of ordinary matter in the universe is 2×10^53 kilograms, which would have a Schwarzchild radius of 31.39 billion light years. The explanation from popular science communicators on this topic have never satisfied me.
Your maths is correct for one cubic light year of butter. Proxima Centauri is 4.247 light years away, and that gives such a cube of water[0] a mass of 6.468×10^52 kilograms[1], which would have a Schwarzchild radius of 10.15 billion light years.
[0] At STP, which isn't realistic at all
[1] Close enough; I think it was Brian Cox who once joked that in cosmology it is standard practice to approximate π as 1.
Now, since the universe doesn't appear to be a blackhole, we assume there's an equal amount of stuff outside of it pulling it back into flatness.
The hoop conjecture doesn't apply in a small region of a very homogenous universe
Thus I would've expected the radius of the black hole to be necessarily smaller than the dimensions of the butter cube.
However, I now realize my mistake - in examples like squashing mount Everest or earth or a neutron star into a black hole, we're starting with masses that are stable/in equilibrium. This would not be the case for a cubic light year of butter!
Further, it looks like the radius is directly proportional to the mass. Given that mass grows cubic with respect to dimension, it's expected the radius of the black hole would eventually outgrow the cube of butter if made sufficiently large...
The vacuum in solar space is around 10^7 atoms per cubic metre; the vacuum of interstellar space is around 10^6 atoms per cubic metre; and the vacuum of intergalactic space is around 1 atom per cubic metre.
I wonder if you could capture that energy and use it to generate thrust.
Most of the energy is coming from your thrust so it'd be a lossy process however if you're able to capture all of the energy then there won't be anything left to damage the ship.
(I'm asking genuinely here. My analogy might be wrong because it's too classical!)
There are a few engineering difficulties with the idea but it makes for some good SF stories...
[1] The momentum vector just completely flattens almost any other physical characteristic. I'm not sure there's even enough time for nuclear fusion to take place.
But then there's e=mc^2, so if the stuff you're running into is the fuel source for your fusion engine (could be a fission engine, but unlikely you'll run into heavy atoms like Uranium or Plutonium) then you have an unlimited source of energy...
So maybe sort of? Running into things slows you down, but then you capture that mass and release the energy out of it to go faster... because of the nature of e=mc^2 you'll usually get more energy out of something if you convert its mass than what you lose by running into that mass.
The issue is that the energy for that explosion comes from the slowing down of your ship, so it doesn’t work.
For the same reason that the power of an atomic bomb does not depend on how fast you smash the sections together - it depends on how much mass is converted to energy in the resulting reaction.
It's particles that make things radioactive, mostly neutrons as they aren't repelled by the nucleus and thus have a much easier time getting in. And while it would be hard to construct a shield out of it helium is effectively immune to becoming radioactive under neutron bombardment. And while lead isn't immune the reaction sequence produces nothing that won't be contained by the lead and it self-regenerates, enough bombardment returns it to where it started.
The thing is, you need to be going implausibly fast to have a proton have a fastball level of energy. Even at .99999999 C, a hydrogen atom still has less than a microjoule of energy. You need a lot of 9's to get up to 340 joules.
1/sqrt(1-(0.99999999)^2) * (1 atomic mass unit * (speed of light)^2
1.05529895 × 10-6 joulesApparently bullets are about an order of magnitude more energetic than baseballs (800J vs 80J) so I guess I could try to build my intuition based on being shot ~2 billion times a second instead. A kiloton of TNT is 4GJ, so it’s also like a 500 kiloton bomb going off every second.
Dropping 5e5kg of rock into the worlds biggest dumpster truck at 10m/s yields 25MJ of chaos so it’s also like a parking lot of 80,000 of those being filled with a continuous stream of rubble. That’s probably the best analogy given that we’re talking about machinery — your spaceship needs to have the build resilience of tens of thousands of dumpster trucks but condensed into the cross sectional area of a dinner table.
Funnily, my first reaction to this comparison is that it makes it seem more plausible to me that this is possible. After all, a Star Destroyer can take gigaton level hits!
But the problem with that is Star Destroyers are fictional.
I've been spending too much time on spacebattles.com.
Galaxy filaments are big.
Extreme geek caution: I've been running a Star Wars pen and paper RPG since . . oh dear. . 2015, in an ancient simulationist[1] game system, and the only way I've been able to make anything consistent is dialing everything down to WW2 levels. 7.62x5X, .50 BMG, 46 cm/45 Type 94 capital ship weapons. All except for exceptional plot items, like lightsabers and doomsday weapons, which behave . . well, they're magic. Sensors are likewise pretty primitive, enhanced with canon exotics like Kronau radiation, so engagement ranges are (relatively) piddling, hostiles zip by each other all the time. Electronics and technology in general must be barely understood by literally anyone, with the powerful assemblies - hyperdrive cores, droid motivators, repulsorlift "sand" - being exotics, possibly xenotechnology from the deep past mined by xenoarchaeologists[2], but hooked together by varying degrees of "competent 1950s electrician".
In short, it's a fantasy setting with guns that players get excited about. And a community of worldbuilders that is, let's not dice words here, insane. That second point is huge if you're not 24 or otherwise gifted with a combination of hubris and spare time.
[1] All the kids today with their streamlined narrative-focused games! Seriously, though, I get it. The physics simulationist in me that brings me to HERO System says more about me as a person than my players.
[2] Archaeology a much more valuable degree in the Star Wars universe.
SFB is 1900-1945 naval warfare, but themed with every plot point from TOS and TAS and probably some novels too, so has the Kzinti, Tholian webs, Klingon stasis field generators, and two distinct weapons where the TV series uses just photon torpedoes.
In the 90s, the show Special Relativity’s Funniest Home Videos would often have guys getting hit in the crotch 20B times with a baseball. Honestly, it never gets old.
How large is one of those, even? I much prefer to work with perfectly spherical Olympic swimming pools.
My nephew is Californian and I gave him one for his sixth birthday. Mine felt a bit lighter so we did an experiment over Zoom together to measure the density. He’s certainly a bit young for that — “it’s the same size but yours is heavier” — but there’s no harm in influencing them from an early age.
Of relevance to your comment: I made a point of doing it in grams and millimetres.
I'm not even sure about warp drives. Bending spacetime one way means it has to squish back the other way. The energy released might not affect the ship - possibly - but I'd be surprised if it didn't affect the spacetime it had just passed through.
Some kind of new physics might make all of this possible, but - by definition - we have no idea what that might be.
If the practical limits of rocket technology don't allow life to much beyond their own solar system then given the vastness of space that would be a good reason why we don't see any evidence of intergalactic civilisations or large feats of engineering. All other explanations for why the universe seems to lifeless seem to rely on elaborate hypotheticals like us being an early civilisation, us being extremely lucky/improbable in other ways, or that alien life is anti-social. But it always seemed to me that the best explanation is probably just that such things are not possible.
I mean there's a chance there's some new physics out there, but you'd think if there was star wars level tech out there (warp drives, etc) then something out there would have built one already and would rather quickly spread outwards...
- Without needing to make it to the closest star, we have big problems here. If we solve those problems before we leave our solar system, we may be changed beyond recognition. We may not be biological any longer, for example, or at least not forcibly so, and traveling as solid matter may seem silly to our future descendants.
- We don't understand well enough the nature of reality. For all we know, our machines and organisms made of atoms and molecules may be, by far, more inefficient and wasteful than an equivalent process at some other layer or scale. Like somebody who discovers themselves living inside a match box in a forgotten attic, we may decide to move to the more spacious main floor of the castle.
- A variation of the above: maybe space-time itself is something we use inefficiently. It could be that a way to stop being troubled by the slow speed of light is by lowering our own "life" speed, increasing our volume to span entire solar systems, and decrease our density so much that your ancestors would confuse us with sparse interstellar matter. Or, at the opposite end, it could be that we find a way to move our entire future civilization to a cubic centimeter of space and a few microseconds that feel like eons.
Now let's take a much more reasonable speed like 10% the speed of light. Assuming the 100 protons per cubic meter figure above, each square metre of ship now only needs to dissipate 2.27 mW of energy. 10% the speed of light is enough time to reach Alpha Centauri within a single lifetime (42 years). And fast enough to visit every part of the galaxy in less than a million years. We could even imagine generational ships travelling at 1% the speed of light (now the energy dissipation demands are 2.25 μW per square metre of ship surface). That's still under 10 million years to colonise the entire galaxy.
If intelligent life is abundant in the galaxy then I don't think the speed of spaceships at least offers a fundamentally insurmountable technical challenge for that life to spread everywhere.
Or if we shape the field into a buzzard ramjet then you actually take advantage of the interstellar material for fuel.
(1) https://sciencing.com/magnetic-properties-hydrogen-7648446.h...
Until he starts solving cosmological problems . . I sort of felt like the truth of the matter should have been more ambiguous than was presented. More Shining, less Friday the 13th.
I remember the premise being far superior to the film, but maybe the novel is worth a look.
...until you stop, releasing all of that mass as a gargantuan amount of energy at your landing site.
So not only do you need “exotic” matter with negative mass to bend spacetime into a warp bubble, the bubble itself creates so much radiation that spacetime is flattened back out again.
If the thrust is high enough, a tenth of a G to 1.5 maybe, the ship has to "stand up" on the thrusting engine in the same manner as a building must stand up over it's footprint, supporting itself against the force of (artifical) gravity.
If it's higher thrust (as the human meatsacks are suspended in a fluid they've also swallowed ??) then the ship has to look even more like a heavy load brutilist building.
1. https://www.sciencedirect.com/science/article/pii/S009457652...
Wikipedia says that intergalactic space contains less than one hydrogen atom per cubic meter; and that most of the baryonic matter in intergalactic space consists of hydrogen and helium atoms. If I've understood it correctly...
But if you're trying to avoid self-propulsion and want to launch from Earth, say, even a 200kg craft, anywhere "close to the speed of light", then that will most probably require a significant enough amount of force to knock the planet out of orbit.
If you can apply small force over a long time, that will get you up to speed, too.
Someone did the math in the thread, and suggested that a constant 1g of acceleration would get you to the centre of the galaxy in 20 years (as measured by the clocks traveling on your spaceships). 1g of acceleration for 200kg is about 1962 Newton.
(This back of the envelope calculation assumes you have eg someone fire a laser at your ship to give you the energy you need. If you need to bring your own fuel, the rocket equation increases the total mass needed. But the same principle still applies: something like an ion drive has very little force, even if the top speed it can reach can be enormous.)
Shooting just enough mass at very high velocity is not much different than shooting a lot more mass at lower velocity, in terms of force.
Exactly. You try accelerating 200kg up to anywhere close to the speed of light (say 80%). That is a lot of force.
Technically even photons can exert force on objects, but they have such a small mass that it's a difficult effect to observe.
Wait, hang on, we have access to an appreciable-chunk of the world's knowledge at our fingertips...
https://en.wikipedia.org/wiki/Photon - "Photons are massless[...]In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p[...]Current commonly accepted physical theories imply or assume the photon to be strictly massless"
In more recent times, it has been seen as easier to use just one concept of mass, and to redefine momentum entirely. So, photons have a mass of 0, and we don't need to specify "rest mass". But they do have momentum.
Opening comment said that you'd need absurd amounts of mass to accelerate a person to near light speed.
I said that the velocity of ejecting that mass mattered. That if you could push out mass at speed of light, you'd need a lot less mass.
Not that you'd push out the same mass at speed of light. Or that you could arbitrarily push things out at speed of light. Sheesh.
Of course that .06 m/s velocity change would be near instant, so bad things would happen. Probably a humanity-ending but not life-ending disaster. Global tsunamis and incredibly large tectonic changes, for sure. Imagine the entire water column of the marianas trench jumping up in the air and slamming into the ground below.
If the energy was transferred at a single point, it'll be the worst extinction event ever (4000x worse than chicxulub) but I'd bet single-celled and maybe even some multicellular life would survive. Anything bigger than a mouse is fucked, though.
Just need to build a parabolic reflector on one side of it and point it towards the opposite direction where we want to go. When the reflector shoots to far from the same, tilt the reflectors, drop down closer to the Sun by gravity, tilt them back, do it again.
We could be going places in a few billion years!
Btw, the sun is also an extremely inefficient engine. With a bit of extra engineering we could probably scoop up hydrogen from the sun, and 'burn' it much more efficiently.
Of course…even if that was possible, it’s conjectured that the colonists already at your destination won’t appreciate you boiling the atmosphere when you hit them with blue shifted radiation.
https://www.universetoday.com/93882/warp-drives-may-come-wit...
They implied they avoided that because warping into a gravity well would cause some vague catastrophe.
Of course, the real reason was far more sinister: it’s way more dramatic to slowly creep up on the planet while listening to the captain’s log monologue to start the episode.
So you would never accidentally warp inside a planet.
Our gaze into the heavens is much better at spotting stars than their dark orbiting bodies, and we have fingers left over from one hand counting the number of observation platforms observing deep space from above our shimmering atmosphere.
The sun contains roughly 99.8% of the mass of the solar system, and is by far the largest object in it. But you wouldn't hit the sun randomly either. Space is just so damn large.
The distance from the sun to Pluto is about 5.9 billion km. The radius of the sun is about 696,340 km. The ratio of radii is about 8,473. Cube that to get the ratio of volumes, and you get 608,263,848,559 for the ratio of volume in a sphere out to Pluto vs volume of the sun.
(Doing the numbers, I'm actually surprised: I had expected the ratio of radii to be bigger than 8,473. But I'm not surprised that the sun barely takes up any space.)
Arguably, the entire heliosphere is part of the Sun's atmosphere, and it reaches well beyond Pluto. If I were in a relativistic spaceship, I think I'd want to apply the brakes well before slamming into the heliosphere.
What do you call the heliosphere of a star that isn't the Sun? The stellosphere?
"Stellosphere" is wrong, because "stella" is Latin, and "sphere" is from Greek. It should be "asterosphere", but that's a word I've never seen nor heard.
If we're still talking about Star Trek, then on a solar scale those ships can stop on a dime. They're not going to hit an unmapped planet while putting around.
Given that Star Trek's impulse drives are already traveling at up to around 0.9c, parking somewhere between the earth and the moon (which is about 1 light-second out), the ratio of space to volume of earth becomes 219,648.
That ratio growth with the cube of the distance to the planet.
Even if you can make it, even though it's theoretically possible that the warp bubble could move through space faster than the speed of light, it's a separate and completely open question as to how you might actually get it to move that fast to begin with.
There's a general principle known as Jon's Law (not sure where the name comes from) that any powerful space drive is by definition a weapon of mass destruction.
You see this in The Expanse when incredibly powerful fusion torchship rockets (a major part of the Expanse 'verse) are attached to asteroids and these are used to kinetically bombard inner planets. The results are far worse than a nuclear attack, from kinetic energy alone.
Anything capable of traveling close to the speed of light would be "death star" level planet killer. We're talking smashing through the crust and boiling off the atmosphere or if it were massive maybe even fragmenting the planet. Obviously anything even wilder like an Alcubierre Drive would be likewise. Anything capable of going to the stars within a human lifetime could annihilate worlds.
Even present-day chemical rockets could be pretty destructive. Get something massive that won't burn up (like a rod of tungsten) up to interplanetary velocities and you can approach the yield of a small tactical nuke from just kinetic energy. This has been studied at least on paper by militaries. I think the phrase "rods from God" was used by DARPA at one point for the rod of tungsten idea.
This is glossed over in the vast majority of space sci-fi. Nobody even asks in Star Trek what happens if you point the Enterprise at a planet and say "warp 9, engage!" I'm guessing it would go poorly for the Enterprise but even worse for the planet.
(Be warned: it's a deep hole)
Casual Interstellar Travel:
Most hyperdrives just need to be Neptune’s distance from a star to work - two light hours; the Q-II needs to be five - Pluto’s! This means it can get you from any given human world in Known Space to any other in no more than eleven hours, but also no less than ten hours for any world outside the system.
There’s no intermediate setting. With most hyperdrives, a pilot can leave the helm unattended most of the time. If one does so in a Q-II for more than two minutes, they’re almost certain to crash into a star. It doesn't have an on-off switch, either, it has a grip that has to be kept or the drive turns off.
Also known as the Kzinti Lesson, from Larry Niven's Known Space series. I've not read where in that series this term is first introduced, but they're somewhere in all that.
> Obviously anything even wilder like an Alcubierre Drive would be likewise
Not yet known; the original Alcubierre Drive is a toy model that demonstrates the point, but has so many problems with it that, as is, it definitely won't work.
Something else along similar lines that does work? The only thing it won't act like when it hits something, is like being hit by normal matter that's actually moving at the speed of light, because if it did it would also be an infinite free energy source.
I'm thinking of the Lensmen series--the stardrive ejects non-interacting particles and thus doesn't tear things up. And since it's inertialess you can't use it to accelerate an impactor. However, you can go grab something that's already moving how you want, slap an inertialess drive on it and reposition it so that when the drive is turned off it's heading for your target. When it's a planet you fling around that can be pretty dangerous. And when it's a FTL planet (everything is Newtonian, this doesn't cause issues other than for the crew--can't allow one atom of native matter into your ship, can't use one atom from your ship in the drive on the planet) the results are spectacular.
(Note that they also have normal reaction drives in the Lensmen universe--the stardrive will get you to your objective but you still need to match velocities with it. And that does tear things up and we see it's use as a weapon, although not against a peer-class opponent.)
Of course, that energy didn't come for free: if the rod came from earth, your rockets have to provide the energy.
Also known as "Project Thor", it was devised by Jerry Pournelle before he became a science fiction author. More on various iterations of the concept can be found in Wikipedia:
Edit: to be slightly more pedantic, the right form that still remains true with relativity is F = dp/dt, i.e. the force the spaceship would exert is equal to its change in momentum.
I thought these weapons were real and deployed. Specifically, I understand that hypersonic missiles don't really need an explosive warhead; a hypersonic tungsten rod would make a bigger explosion than any conventional warhead.
The "rods from God" concept is the idea of creating an artificial meteorite as a weapon that comes in from space. These may or may not already exist, but if they do they'd be secret and would probably violate some treaties.
Assuming you're going somewhere, you can use atmospheres and gravity to slow down. Decelerating should take less time than accelerating in practical contexts.
The places people talk about travelling to tend to have atmospheres and gravity, yes.
You can tolerate 2G for hours, particularly if everyone's oriented eyeballs in. That said, both aerobraking and gravity assists are intermittent accleerations.
It's still a lot of energy you can bleed off, particularly if you're aiming for a system with gas giants. I'm not suggesting one only rely on passive deceleration. But especially given it's fuel saved at the very end of the journey, fuel you no longer need to accelerate and decelerate for the entire duration of the trip, the savings could be sizeable.
trying to decelerate by "braking" anywhere close to a gravitionally significant mass sounds like a guarantee to total destruction from the impact of "stuff" (even individual photons).
You decelerate from 0.9C to 50 km/s conventionally, more if you can aerobrake or line up multiple slingshots, and that last 0.00001% with gravity assist.
It saves you more than that in fuel, because the fuel you'd have used on that last bit of deceleration needed to be accelerated and decelerated the entire way from 0 to 0.9C back to close to zero.
I read a paper on the topic a few years back. My recollection is that once you go faster than about 0.3c it becomes impossible to shed heat faster than you gain it from collisions with Helium. I'll try to dig it up.
You could change the distribution of the forces at best but I'm not sure whether that could be enough...
Radiation hazard of relativistic space flight https://arxiv.org/abs/physics/0610030
You don't see a problem with trying to accelerate with two exhaust streams at 180º to each other?
You'd probably move your rocket engine over to the other side (or have both a front and back engine in the first place).
Most of the mass of your spaceship will be fuel (like 90%+). You can use that as shielding.
It's not a coincidence that the original post relativistic spaceship doesn't even bother considering larger accelerations than 0.1g, since achieving even that is a wild assumption.
Keep in mind that when talking about long-distance journeys in space under any sort of constant acceleration, the numbers are generally in thousandths of 1G.
And who's covering the great expense of building these generational colony ships and training their only inhabitants, only to have them zip away never to be heard from again? (With no benefit other than believing there's a slight chance we've succeeded in making our species multi-plantary)?
(Btw, I share your intuition that the number of people willing to sign up for a one-way trip to the stars, or even just Mars, is fairly low. However, if you already look at people who are dedicated enough to become astronauts, I suspect the additional filter of asking for one-way-trip volunteers for a mission to the stars isn't all that severe. My purely speculative guess is that at least 10-20% of current astronauts would be willing to sign up.)
Astronauts seem to me to have a higher propensity for kookiness than the general population. You may be right.
For context, the most powerful chemical rockets peak around 450s-530s. A nuclear rocket of the sort we can build today would be more than twice that value, and super-efficient ion thrusters can have IspS in the tens of thousands of seconds.
But we're talking about an engine with a specific impulse measured in decades, and as far as anyone knows that means having catastrophic amounts of antimatter. I don't think plucky explorers on a one-way trip are going to have access to a small moon's worth of antimatter, and if they did, imagine how many more interesting things they could do with it than fly to nowhere?
Like what?
We're talking about a truly incomprehensible amount of energy, not just to carry the rocket and its own fuel, but the tens of thousands of kg of water and food for even a modest compliment of people.
18 years is a LONG time after all.
Assuming a straight line and assuming 1G is your max acceleration: you accelerate for 10 years, reach your maximum velocity then flip and do the same thing in the other direction. You'll reach your destination with 0 velocity.
After the first time it happens people in the future can start to expect a human from the past to keep visiting every so often.
Do you mean accelerate at 9.8 m/s^2 ?
There exists nothing, even theoretically that you can put on the spaceship to get you that 1G continuous acceleration.
I don't remember exactly what is the maximum achievable delta V but if I remember well it is not a high portion of the speed of light, more like 60% of speed of light. And that assuming you have crazy things like carry a small black hole with you and use it to convert mass into energy at 40% efficiency.
you could tell them when they overtake you due to incessant obsolescence
At this point, only white dwarfs, neutron stars, and various stellar remnants remain. Galaxies have dissipated, and stars like our Sun are a distant memory. (If any still exist to remember them. Which is, I'll add, not out of the question. Life can cling to structures built around black holes, white dwarfs, etc., and extract energy from those bodies for a very long time.) We're a long, long way from "heat death" -- from the Universe becoming an undifferentiated entropic sea of particles -- but it is already a very different place.
Puts things in perspective.
Going back to your original point it's a little different than sending him to the end of the universe, they sent him forward in time, but they actually had no idea how far or where there were sending him.
If something can be "killed" by a dude with an axe, it ain't a world-ending superpower for me. I get that Alduin could harass the known world by eating people or burn down villages if left unchecked, but "end of the world" for me is kinda different scale.
The one time it was used as a punishment it was not sending them to the end of time, but leaving them in the now while everyone else jumped ahead.
It's used by the (free) game "A Slower Speed of Light". http://gamelab.mit.edu/games/a-slower-speed-of-light/
There's a more practical idea in nature: become a seed. It's how living things traverse vast distances and overcome intractable resource constraints during transit.
Compact oneself into an inert crystalized form, aim rocket, launch, wait. All you've gotta do is prevent chemical/structural breakdown for a few millennia or eons. Upon arrival to destination, have a machine turn-on and reconstitute the body and voila, you're there, all refreshed and ready to explore and virtually no time has passed.
Of course to do that one would have had to master biology, or maybe skip biology entirely and opt to copy oneself into a machine format, but that is likely easier than travelling at a sizeable fraction of c?
Could any somewhat-plausible technologies (fusion etc) get us to that point? I don't know how to do relatavistic maths, but it seems that directly converting mass to energy and ignoring relatavistic effects requires 50 000kg to accelerate 100 000 kg (with a constant relationship, as the C^2 cancels out) to the speed of light.
Nuclear thermal or nuclear pulse propulsion. No fusion needed.
You’d need kilotons of nuclear fuel and a 10^3 fuel ratio. But that’s plausible.
The economically-plausible answer is antimatter, where the ratio stays in the single digits and starts permitting deceleration. But I wouldn’t call that technologically plausible at this time.
The best nuclear thermal, gas core, would give you 7000 seconds[0]. A "dusty plasma" rocket (suspend the nuclear fuel in dust form in a magnetic field) might get 100,000 seconds, or just over a day of accelerating at 1g.
[0] for the benefit of non-space nerds: the unit of measure is "lb-force seconds per lb-mass of fuel", which is kinda like "seconds at 1g" if the fuel is a very small fraction of the total mass, which it really won't be in a practical rocket.
I think you mean “a very large fraction of the total mass”… generally the best efficiency comes if your fuel mass fraction is high, as it means there is little overhead of things in your spacecraft of things that are not fuel (the mass of the engine, etc)
If you have 1 gram of fuel and a 1 ton payload and that fuel has 1e6 seconds of Isp, you can accelerate the ship for 1 second at 9.8m/s/s.
If you have 1 ton of fuel and a 1 gram payload and the same fuel and burn at 1 gram/second, the first second is mostly spent accelerating the fuel, which means you're no longer able to just approximate the Isp as "seconds at 1g" in a nice linear fashion — it starts off at 1 gee in this example, but ends up at 10^6 gee in the last moment, a million seconds later.
The rocket equation kills you. A reasonable fusion rocket would require an enormous (like an entire planet worth) to continuously accelerate to relativistic speeds. Antimatter drives are the only option and still require large amounts of reaction mass since have to absorb the energy to throw it out the back, or use a laser.
[1] https://www.sciencedirect.com/science/article/pii/S009457652...
It's a similar story for solar sails, unfortunately, though progress is being made in that area. Personally, I think that's the only realistic way of interstellar travel given our current knowledge of physics and engineering.
> we estimate the neutral hydrogen density in the unperturbed local interstellar medium of 0.195 ± 0.033 cm−3 https://iopscience.iop.org/article/10.3847/1538-4357/abb80a
You need a hydrogen 'scoop' and fusion. If you can accelerate to 0.01c, you can collect enough hydrogen for 1000 MW fusion power from 32 km2 (6 km diameter) scoop area. Faster you fly, more you get. You can accelerate until interstellar particles start to do real damage.
As an SF writer, it's pretty interesting, though, to think of the weird shapes a society would take when your astronauts are outliving entire civilizations. I imagine a sort of neo-Polynesian culture, with travellers never quite knowing how the place will look if they ever come back that way.
I think the lasers would also need ~10,000 years of fuel, as opposed to ~10 years of fuel if you could somehow figure out how to carry it. But the energy to sustain in either case is probably measured in Dyson spheres, or some fraction of all energy in the universe pretty quickly too.
I could see the light spacecraft with their matter-antimatter engines laying down "lightways", like railroads in the old west. Once a lightway is established, then it's much less of a big deal to get from system to system. Apart from the tens of thousands of years in subjective time, of course.
I guess this all depends on how you define simultaneity. Say I got on a relativistic rocket traveling near c and colonized Planet X in 10 years ship time and say 20,000 years Earth time. I put up my TV antenna as soon as I land, and I'd still be receiving Earth transmissions from approximately 10 years after I left, no? So even though civilization is long gone from Earth's point of view, from my point of view, I can keep up with the latest news as if I were still living there. So from my point of view I did not outlive anything.
If I were to go back, yes, everything would be gone.
I was thinking of this being the first half of the twin paradox, but perhaps for the apparent "time gap" in the spacetime diagram to appear, it's necessary for the traveling twin to turn and head back towards Earth quickly to shift simultaneity plane back in the other direction.
If you traveled at the speed of light then you'd be at the planet in 0 time your time, and you would arrive with the first of the broadcasts over those 20k years. So once on the planet you'd get to watch all 20k years of broadcasts.
If you traveled at 1/2 the speed of light (not focusing on your dilation for the moment), then you'd still beat 50% of the transmissions and have 10k earth years of broadcasts to watch.
I think the question is what % of the speed of light is a gamma factor of 20k/10 = 2000. That's something like 99.9999999% of the speed of light.
Meaning you would get there before 99.99999% of the broadcasts had arrived and you'd be able to watch just about all of them in real time over the next (just less than) 20k years.
Assuming those two planets are roughly in the same reference frame, the only way 20k years could pass on earth w.r.t. your arrival is if the destination planet is 20k light years away.
If the destination planet is moving relativistically away from earth at an appreciable percentage of the speed of light then I couldn't say what the math would be. Maybe still the same, maybe not.
We don’t know how to use all the reaction products for thrust [1].
[1] https://en.m.wikipedia.org/wiki/Electron–positron_annihilati...
I love that someone wrote and published a serious paper where the end design involved first stage thrust of 550 million ft-lbs and the total ship weighs something like 17 million metric tons and if I'm reading page 26 correctly, the payload on the ship has to be 7,500 kilometers from the ignition source to survive.
https://www.relativitycalculator.com/images/relativistic_pho...
I'm unsure if the resulting efficienty is 60% however, not all of the energy produced in the anilation is converted to "stuff" that is useful for thrust.
As a bonus, they even talk about the radar-absorbing coating not being perfect, and being able to detect the stealth ship as an object a few Kelvin above the background radiation when they pumped their radar into it.
https://www.projectrho.com/public_html/rocket/spacewardetect...
The main characters also manage to find a stealth ship after coming across coordinates to it - it was parked and completely offline (and unmanned) in the orbit of a small asteroid, which would further obscure any signature it might give off.
First off you have to remember that when a ship turns it's engine on it's going to be visible effectively to the entire solar system unless there is a planet or something in the way. We already have the capability that we would notice a ship moving in the asteroid belt from Earth and in the Expanse it's going to be even higher. So everyone already will have known when you turned your engines on and can run the calculations to see where you are while you are coasting, so even within the confines of the fiction that shouldn't work.
But let's ignore that and say that for some reason no one was looking when you turned your engines on. Assuming your ship is somehow running with all systems off it's going to be roughly 300 C hotter then the vacuum around it, even with a heatsink like you mention (and a heatsink that can store that heat for months is also unrealistic) you're going to be sticking out like a sore thumb to any infa-red. You're just too hot.
They'd need refuels every stop though. Like with early coal fired steamers back in the day.
I got a funny feeling that without much better genetic muckety muck, the hard limit will be the human organism itself. Someone will get to the stars = if we don't screw everything up - but the someone won't be human, or maybe nothing like human.
[1] I know in emergencies they pull mad g, but it doesn't seem like something they keep up for long. Would still burn through their deuterium in no time though.
[2] Like, within an order of magnitude or two.
This makes me think of the Quen Ho in Vernoe Vinge's "Zones of Thought" universe.
https://en.wikipedia.org/wiki/Tau_Zero
Classic hard sci-fi. A colony ship’s Bussard ramjet has a glitch, and it cannot stop accelerating—and basically forever, given time dilation.
Spin, a novel by Robert Charles Wilson, touches on this from a planetary perspective. Quite the interesting read, though I won't say more here for fear of spoilers.
https://ia600704.us.archive.org/view_archive.php?archive=/24...
"A one-way interstellar flyby probe mission uses a 1000 kg (1-metric-ton), 3.6-km-diam. lightsail accelerated at 0.36 m/s2 by a 65-GW laser system to 11% of the speed of light (0.11 c), flying by a Centauri after 40 years of travel. "
"...The third mission uses a three-stage sail for a roundtrip manned exploration of e Eridani at 10.8 light years distance."
[1] https://www.statista.com/statistics/267358/world-installed-p...
If this relation is really true, I am somewhat shocked - us burning 1/30th of the suns energy output, can that really be true..?? If so, scary. And also 'illuminating' concerning how unsustainable what we are doing is..?
I do hope my numbers are off.
https://phys.org/news/2011-10-vast-amounts-solar-energy-eart...
Unless we use space-based systems instead, which would make that a kind of power requirement trivial, ignoring the costs of course ;)
Taking the US as an example: depending on who you ask, we could generate enough power for the US with somewhere between 10000 square miles (Elon math) and 21250 square miles (pretty common number given by multiple other sources) of PV.
That is about a fifth of the state of Nevada. A lot of PV, to be sure, but far from beyond hope.
And that assumes nothing but PV, which is unrealistic. We capture a bunch of the sun's energy as wind and rain.
The power output or luminosity of the Sun is 3.8 x 10^26 W
Bottom line: do NOT rely on figures provided by generative models. The chance of them being completely wrong seems to be alarmingly high.
And even beyond that, you either witness the ships leaving and never hear back or you embark on one and comeback to whatever Earth is in thousands of years from now.
Quoting Wikipedia, GPS “must account for the gravitational redshift in its timing system, and physicists have analyzed timing data from the GPS to confirm other tests. When the first satellite was launched, some engineers resisted the prediction that a noticeable gravitational time dilation would occur, so the first satellite was launched without the clock adjustment that was later built into subsequent satellites. It showed the predicted shift of 38 microseconds per day. This rate of discrepancy is sufficient to substantially impair function of GPS within hours if not accounted for.”
After an observed 12 years of constant 1g acceleration, you will be 113,000 lightyears from your point of departure, which is enough distance to cross from earth to the opposite side of our galaxy.
Of course, you are now traveling at 99.999999996% of the speed of light. If you actually wanted to stop at the other side of the galaxy to take a look around, you would need to turn around at the halfway point to decelerate, which roughly doubles the travel time.
As for the energy used to accelerate from 0C to 0.009C compared to 0.99C to 0.999C, I'm not sure. I know the time taken (from an external reference frame) changes, but part of me suspects the total energy stays the same and the difference in time taken is caused entirely by time dilation. However, I suspect I might be messing up reference frames, I don't actually know the equations.
https://en.wikipedia.org/wiki/Tau_Zero
which has to be one of the most epic sci-fi novels ever since it is about a starship that gets its brakes damaged in a crash so their answer to every problem they face is to go faster!
At many points it reminded me of The Freeze Frame Revolution, by Peter Watts (https://tachyonpublications.com/product/freeze-frame-revolut...), which was also quite good in a similar way, if perhaps a bit darker.
I expected relativity to play a role, but the time dilation the crew experienced was on a _far_ grander scale than I imagined. The book also left me thinking of favorite time travel/relativity classics like Interstellar and, going back, Star Trek IV: The Voyage Home (my favorite Star Trek movie).
Apparently, it takes just over two lines of "9"s on a 1920px display for this to happen. The speed wraps back around to zero, and the world time becomes NaN as an added bonus for (nearly) breaking the laws of physics.
I love this unit of measurement.
For the comments saying we "just" need to maintain a 1G acceleration, should point out that as the ship approaches the speed of light, its mass increases [0].
And as the mass increases, so does the thrust required to maintain that acceleration. So that engine better be able to tap into some magical energy source, otherwise it can't maintain the acceleration at the higher speeds. :)
[0] https://en.wikipedia.org/wiki/Mass_in_special_relativity#Rel...
Edit: this interpretation may not be entirely accurate (comments below).
> even though near the speed of light, more and more of that energy goes into higher mass and slower time?
This to me does not sound very different from saying the (relativistic) mass to be accelerated is larger, and is what's stopping a 1G (or any constant) acceleration to be maintained to bring the ship to the speed of light.
The concept may have been an overly simplified pedagogical tool though that I need to upgrade from. (I'll keep the comment chain intact since it's educational to me).
If, for example, we consider the speed of your ship from the point of view of someone left on earth, then your ship should appear heavier from that person's perspective as you accelerate. But from your point of view, you still weigh the same, and so does your ship. In fact, you would see earth going through the dramatic "weight gain".
This video does a good job talking about the issue: https://www.youtube.com/watch?v=6HlCfwEduqA
This is the first time I see "xyz is not supported", which both helps me understand what's wrong and lets me switch to a popular browser to see the content. And the site works and looks great there (on mobile)! Thanks OP :)
I am now in the galaxy NGC 300, very similar to the Milky Way.
Everyone I ever knew is gone.
I am sad and alone.
I'd love to find a reference for it as I found that surprising too.
The original motivation was, can one make a game with relativistic spaceships, conceptually speaking? The issue is that if a player calls another player IRL it'll be like instantaneous communication... In flat spacetime, though contradictory to its postulates, one can choose a preferred frame of reference, say the planets, and allow instantaneous communication within that plane, not leading to any inconsistencies in a game, I think. Curved spacetime doesn't admit a notion of simultaneity, so that's completely out, no black holes in a game :( Never really got to the point of modelling multiple ships though, the life caught up. So it's just a single ship on the website for the moment.
This is a relativistic spaceflight simulator which shows what it would look like if you were on a spaceship traveling close to the speed of light. It is loosely based on my original code from 2012 implementing relativistic effects in my game The Polynomial.
I know (enough) about the math and physics, the energy required, etc. to logically understand how "impossible" it might be.
My brain still rebels and to some extent, wants to believe.
It's fun to think that this is the closest we could ever come to time travel. I hope someday somebody actually gets to experience this.
What happens if I keep maximum acceleration and pitch up 90deg? The software seems to keep flying on the original vector. Is this a bug or is it intended to be a simulation of how light would behave under those circumstances?
And here I'd observe that the acceleration value is measured in the local system where time slows down relative to the observer's system, while the speed is measured in the observer's system (naturaly, my speed relative to me is always zero).
Sure, from the observer's system (home planet "stationary" the speed is measured from) it can't go faster than c... but that's where I don't think it's accurate. From the flyer's perspective, if you're close to c (as viewed from home) and suddenly accelerate at a 90deg angle, that shouldn't bleed off your speed forward, or be limited by your speed forward. Only from the distant viewer's perspective would those two velocities combined max out at c. From your perspective they wouldn't.
Wait what? That's not true right? All the light we see is concentrated in one point but it's not really the big bang that we see, it's an illusion, is that correct?
Yes, that's the microwave background being blueshifted, but why is it growing across the screen? Shouldn't the angle that's blueshifted be less and less as you go faster? At lower speeds we do see the starbow effect, passing stars going down the spectrum as the angle increases.
And what becomes of the stars as you're going fast enough? Yes, most of the energy is shifted out of view but don't stars emit some at such low energies?
The tool does not deal with gravitation. We know that our local patch of the Milky Way (out to a few hundred lightyears) is full of kHz-Hz waves (LIGO, Virgo et al.), and nHz waves (pulsar timing arrays). Known sources at these frequencies are extragalactic, so there will be lots of these waves outside the Milky Way too. At significant boosts, these gravitational waves will impose visual distortions. The "twinkling" that pulsar timing arrays detect over the course of many months would be detectable over the course of much shorter periods of ship time.
Gravitational microlensing is likely to create uncomfortably hot spots (low-energy caustics from our usual point of view) for an ultraboosted spaceship.
We also strongly suspect there are lots and lots of black holes massive enough to impose a significant gravitational redshift on background light from the early universe, releasing far IR radiation from near the photon sphere (note, this isn't Hawking radiation, just delayed and redshifted background) that an ultraboosted observer should be able to spot.
(Work in this area is usually about considering what an ultraboosted massive particle does as it passes a massive observer. For example, in the 1970s the Aichelburg-Sexl ultraboost tried to capture what a neutral cosmic ray would do -- gravitationally -- to a spherical gas cloud along its path. In essence there is an exchange of momentum: the ultraboosted particle loses some, and small parts of the gas cloud gains some. Increasing the mass and structural complexity of the ultraboosted observer inevitably runs into inelasticities. That admits a hand-wavy expectation that even below the threshold at which subatomic physics of the ship becomes relevant, the ultraboosted spaceship is liable to become so very hot that its thermal spectrum masks practically all the light from everything ahead of it.)
As you raised in your final question, there is good reason to believe there is plenty of very deep IR electromagnetic radiation out there from all sorts of sources. Most models of cosmic inflation will produce gravitational and electromagnetic radiation with all manner of wavelengths, many of which are stretched to cosmological lengths. We don't really have a good view of any of that because presently we can't yet make a sufficiently cold ultra-long-wavelength (sub-30 MHz; cf. FARSIDE, LCRT, GO-LoW) detector and don't even have good ideas about how to look at astrophysical sources below kHz. There's probably lots of bodies (e.g. magnetic interactions with exoplanet atmospheres and gas clouds) that will become optically bright as the CMBR is blueshifted out of the range of human vision.
The visualization also does not offer up a physical observer who would feel variations in the galactic magnetic field (cf. the Sokolov-Ternov effect with enough "nines"), the cosmic neutrino background, and two-photon physics from ultraboosted CMBR and starlight interacting with the observer's photon shock front.
The visualization is pretty, it captures some gross aspects of being relativistically boosted, but as many scattered threads in the discussion discuss, it's probably not a useful hint about what one of our descendants might experience if somehow they could reach "a few nines".
You won’t feel the acceleration ;) nor the light intensity of the higher velocities (luckily).
Years are passing in seconds in this websites simulation, if you were experiencing it all in "real time" everything would appear pretty much stationary for quite a while.
Even at like 95% the speed of light, you're talking about years of time required to move between stars - nothing will appear to change much day to day until you actually get close to one of them.
https://en.m.wikipedia.org/wiki/A_Slower_Speed_of_Light
I also found this render (and game!) that show off some aspects of relativistic spaceflight. https://youtu.be/Ix1XlxF66Zk?si=8HzDH3U-CRM-erRB
I think the technical limit might be moot, better question might be how strong of a stomach you have, geometry gets pretty wacky near c
Even though we can perceive the "depth" of the stars through motion in this simulation, every star is still going to look equally far away, because their positions won't change between the left and right eyes. The same way we can't perceive the sun as further away than the moon -- depth perception merely tells us they're both "max far away".
You could always introduce depth perception by faking your eyes to be light-years apart, but of course that's not how it would really be in the spaceship...
It's not very clear where our black hole in the center of the milky way is taking us though.
Don’t they mean the CMB?
Similarly, the CMB is energy from the Big Bang as last scattered ~380,000 years later. IMO, that’s the Big Bang, but reasonable people can obviously disagree.
Or as an astrophysicist said ~”You can refer to the Big Bang as the first instant or a fairly arbitrary period after that initial event. The universe cooling down enough for matter is just as reasonable an end as the universe cooling down for atoms.”
At constant speed when a distant star first appears it moves directly away from the center point. When accelerating distant stars first move toward the center point then move away.
If you constantly increase the acceleration you can hold a star that is not at the center point stationary for a while, which is totally not something I would have expected.
I'd like to see something like this except instead of a seemingly random assortment of stars the stars are on a regular grid, connected by glowing filaments along the grid lines. That would make it easier to see what the heck is going on.
What does y represent?
Will the universe also say "You Win" when you hit the speed of light?