It's never wrong to confirm by experiment, but there was never really any doubt among professional physicists that antimatter falls down. Similar doubts are expressed about the feasibility of the warp drive by Alcubierre himself: https://twitter.com/malcubierre/status/362011821277839360
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.
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.
Not a big assumption at all. Gravity is believed to be a property of space as opposed to a property of matter. That is, a satellite orbiting around the Earth is really going in a straight line but space is curved.
Seen that way it’s just insane that any kind of matter could fall up. See
If you treat GR as a gauge theory, and plug local Poincare symmetry into Noether's theorem, the corresponding conserved current and charge you get out are the stress-energy tensor and 4-momentum. It's not exactly the same situation as typical examples of gauge theories, since you need to impose some extra geometric conditions to pick out the Einstein field equations, but I think it's close enough that 4-momentum could reasonably be called gravitational charge.
If antimater particles were time reversed then I could see how they could have negative energy and thus antigravity. That's not at all how any observed particles behave though.
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?
>That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter?
Yes. There was recently a few papers published showing that a static warp field is mathematically possible without negative energy. However, the field doesn't move or impart acceleration on its own. The best you can do is drag the warp field behind your ship with normal thrusters. Such a field seems to be pretty useless right now, but maybe that research will lead to something else in a few years
I always liked the neat dodge of hyperspace proposed by Larry Niven. Idea was that humans never noticed it in their experiments, because they always ran their tests on Earth, too close to a gravity well, where it resolved to a singularity. At this point I believe the hands on the other foot. It's not the speed of light - but causality itself - that's not allowed to be broken by the universe.
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.
"Why do we need to measure the speed of light coming from a moving source. We all know that the velocity of all objects compounds with the velocity of their emitter"
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')
>Also dying with this measurement is another sci-fi hope: artificial gravity that works without rotation or acceleration. If antimatter truly anti-gravitated, then simply by building a spacecraft’s floor out of normal matter and its ceiling out of antimatter, we could create a spacecraft that had its own built-in, automatic system for artificial gravity.
I've never heard this idea, but that sounds hilariously dangerous.
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.
How big as mass? After some calculations on a slide rule:
> “I’m almost afraid to answer. You would need a good sized asteroid, of lead, to get anywhere at all.”
> “Asteroids have been moved before this.“
> “Yes, but what is to hold it up? No, Chief, there is no conceivable source of power, or means of applying it, that would enable you to hang a big planetoid over a particular spot on the Earth’s surface and keep it there.”
But wait, what about something dense, like core material from a dwarf star?
> “All we would need for that would be a ship capable of going light-years in a few days, some way to mine the interior of a star, and a new space-time theory.”
> “Oh, well, skip it."
Oh, yeah. In this space-age future where people can travel across the Solar System, they also use punched cards.
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?
Ludicrous barely begins to describe the idea. It would have to be a mass on the order of magnitude of a moon that you would have to a) create and b) carry with you so that you would feel some gravity. Why not just build a rotating ring instead? No one in scifi was even entertaining this idea afaik.
Note: armchair reply, I don't know enough astro whatnots to substantiate this take:
That implies that you can actually move the black hole; a black hole producing 1G requires it to be as heavy (or, to have as much attraction) as the earth itself. It would be a lot more compact - a black hole as heavy as the earth is about the size of a ping pong ball - but if my intuition is correct, would require as much force to move as it would to move the earth.
I know there are a lot of hopes for warp travel, but doesn't it make more sense to decouple (most of) space travel from moving matter?
To do this you need to decouple consciousness from bodies, which isn't possible with humans given that our consciousness grows along with our brains and everyone's structures are unique. But it is possible with artificial intelligence. Once consciousness has been digitized, you can beam it at the speed of light to a receiver.
You still need to physically install the receiver somewhere, which is why I said only most of space travel could be non-physical. But once that receiver is in place, you can beam information to it and construct bodies onsite at minimal cost.
This just seems like the kind of space travel the universe prefers, since it minimizes action. Energy is for travel, and matter is for staying put.
The stupendous amounts of energy required for warp travel just seem wasteful, when instead of adapting the universe to life we could adapt life to the universe.
> 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.
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.
Agreed. Thing is we can still have our cowboys in space. The solar system is insanely huge and can be traversed in human time scales with technology based on known physics. The baseline world of The Expanse (minus the alien stuff) is entirely feasible.
Interstellar travel is entirely possible too as long as you are okay with it being effectively a one way trip. Suspended animation is probably possible; we can do it to some animals and individual organs. So you go to sleep for a very long time and wake up in another star system. It would make the most sense to send a bunch of robots to build yourself a settlement first. Or alternatively send sentient AI which would find it much easier than humans to simply turn itself off for the duration of the trip.
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.
A very believable theory is that this is how life on earth started - another ancient civilization shooting the building blocks of life everywhere and hoping something sticks. (panspermia?)
But while this is cute, given the inexorable passage of time and entropy, any evidence that life was planted by ancient aliens has long gone. If it was e.g. a spaceship or meteor, it's been swallowed up by the earth and into the mantle by now.
Unless there's a new source - like aliens making contact - it will remain unknowable.
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.
> 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.
Because other's express things that I in my wildest dreams couldn't have imagined.
I think solipsism dies when epistemic humility comes into the picture.
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.
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.
I'm not sure how we can verify that empirically. Current LLM AI will hallucinate about the feelings it "has" and argue why it is a person, but only because it was trained on human language. The more human we make something seem, the more we blur the line until we might have a day where people upload their consciousness permanently without knowing if "they" will wake up inside the computer or just some copy of themselves that answers all the "don't kill me, I'm a real person" questions will wake up in the computer.
Human software is still intrinsically tied to human hardware, so this seems like it would be far easier to create zombies than true humans, even if the checksum matches after an interstellar transmission.
Well can you prove you're conscious? I'm just gonna assume you're not otherwise. That's the kind of benefit of the doubt we'll be giving AI apparently.
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.
Driving on Mars is incredibly slow in part because the signal has to get to and from us for every decision. And if communication is blocked for any reasons, the vehicle is stuck.
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.
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.
I was a Traveller once, then I suffered a qbit flip in transmission the checksums couldn't compensate for. Now, I just love Coca-Cola brand Mango Fantastic soda, and hunting indigents for sport!
The whole article feels like a strawman, I wasn't aware anyone was presuming antimatter could lead to the negative energy required for the warp drive metrics...
Antimatter is not negative mass or energy. The experiment verifying it falls down wasn't surprising
At this rate it is going to be easier to simply emulate the entire universe (aka Devs) and just travel virtually around space-time that way. Then we can just stay home and eat cheese puffs.
Even mathematically it doesn’t make any sense: we would need to go to a causally disconnected region of spacetime to be able to go faster than the speed of light, but that’s just not feasible. Once you go to that causally disconnected region of spacetime, the only outcome is to go to a singular point in space (even though you can go back and forth in time, theoretically at least) : if that sounds familiar to you, it’s because it is well represented into the movie «interstellar» and indeed he goes to a region causally disconnected to ours: a black hole.
Readit News
The technical term is exotic matter. I think a better name would be Goshwoodentbeeneetium.
https://en.wikipedia.org/wiki/Exotic_matter
Like with voltages. One can be positive or negative if you swap "ground".
So yeah, agreed. A good thing to confirm, even if (especially if) they expected the result to be unexciting.
Seen that way it’s just insane that any kind of matter could fall up. See
https://en.wikipedia.org/wiki/Equivalence_principle
anti-matter falling up would be as crazy as superluminal neutrinos (which I have to admit I almost want to believe)
If you treat GR as a gauge theory, and plug local Poincare symmetry into Noether's theorem, the corresponding conserved current and charge you get out are the stress-energy tensor and 4-momentum. It's not exactly the same situation as typical examples of gauge theories, since you need to impose some extra geometric conditions to pick out the Einstein field equations, but I think it's close enough that 4-momentum could reasonably be called gravitational charge.
That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter?
Yes. There was recently a few papers published showing that a static warp field is mathematically possible without negative energy. However, the field doesn't move or impart acceleration on its own. The best you can do is drag the warp field behind your ship with normal thrusters. Such a field seems to be pretty useless right now, but maybe that research will lead to something else in a few years
> 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.
"Why do we need to measure the speed of light coming from a moving source. We all know that the velocity of all objects compounds with the velocity of their emitter"
(there's a parallel here to 'more negative results' and 'more replications')
Dead Comment
I've never heard this idea, but that sounds hilariously dangerous.
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:
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.
How big as mass? After some calculations on a slide rule:
> “I’m almost afraid to answer. You would need a good sized asteroid, of lead, to get anywhere at all.”
> “Asteroids have been moved before this.“
> “Yes, but what is to hold it up? No, Chief, there is no conceivable source of power, or means of applying it, that would enable you to hang a big planetoid over a particular spot on the Earth’s surface and keep it there.”
But wait, what about something dense, like core material from a dwarf star?
> “All we would need for that would be a ship capable of going light-years in a few days, some way to mine the interior of a star, and a new space-time theory.”
> “Oh, well, skip it."
Oh, yeah. In this space-age future where people can travel across the Solar System, they also use punched cards.
But that's science proposal writing, isn't it? Propose something that would be ludicrous even if it were physical.
That implies that you can actually move the black hole; a black hole producing 1G requires it to be as heavy (or, to have as much attraction) as the earth itself. It would be a lot more compact - a black hole as heavy as the earth is about the size of a ping pong ball - but if my intuition is correct, would require as much force to move as it would to move the earth.
To do this you need to decouple consciousness from bodies, which isn't possible with humans given that our consciousness grows along with our brains and everyone's structures are unique. But it is possible with artificial intelligence. Once consciousness has been digitized, you can beam it at the speed of light to a receiver.
You still need to physically install the receiver somewhere, which is why I said only most of space travel could be non-physical. But once that receiver is in place, you can beam information to it and construct bodies onsite at minimal cost.
This just seems like the kind of space travel the universe prefers, since it minimizes action. Energy is for travel, and matter is for staying put.
The stupendous amounts of energy required for warp travel just seem wasteful, when instead of adapting the universe to life we could adapt life to the universe.
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.
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.
Interstellar travel is entirely possible too as long as you are okay with it being effectively a one way trip. Suspended animation is probably possible; we can do it to some animals and individual organs. So you go to sleep for a very long time and wake up in another star system. It would make the most sense to send a bunch of robots to build yourself a settlement first. Or alternatively send sentient AI which would find it much easier than humans to simply turn itself off for the duration of the trip.
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.
But while this is cute, given the inexorable passage of time and entropy, any evidence that life was planted by ancient aliens has long gone. If it was e.g. a spaceship or meteor, it's been swallowed up by the earth and into the mantle by now.
Unless there's a new source - like aliens making contact - it will remain unknowable.
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.
Because other's express things that I in my wildest dreams couldn't have imagined.
I think solipsism dies when epistemic humility comes into the picture.
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)
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.
I'm not sure how we can verify that empirically. Current LLM AI will hallucinate about the feelings it "has" and argue why it is a person, but only because it was trained on human language. The more human we make something seem, the more we blur the line until we might have a day where people upload their consciousness permanently without knowing if "they" will wake up inside the computer or just some copy of themselves that answers all the "don't kill me, I'm a real person" questions will wake up in the computer.
Human software is still intrinsically tied to human hardware, so this seems like it would be far easier to create zombies than true humans, even if the checksum matches after an interstellar transmission.
> 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.
Driving on Mars is incredibly slow in part because the signal has to get to and from us for every decision. And if communication is blocked for any reasons, the vehicle is stuck.
AI on Mars fixes both problems.
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.
> 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.
That's a good point. Something about "never underestimate the bandwidth of a U-Haul carrying a bunch of tape drives."
https://news.ycombinator.com/item?id=37679584 ("Observation of the effect of gravity on the motion of antimatter (nature.com)"; 68 comments)
Antimatter is not negative mass or energy. The experiment verifying it falls down wasn't surprising
What with the causal loops and so on.