I'm very mystified why this is called "news" about warp drives. The article is about an as-yet unpublished and un-peer reviewed paper that describes a general type of spacetime configuration which _might_ go faster than the speed of light. That is cool, but not really something we didn't have before.
Also, any article that ends with a phrase like "while it may look now like you can’t do superluminal warp drives, this is only correct if General Relativity is correct" does not bode well for practical applications of the subject matter. There is also the logical fallacy that it might be the case that GR is incorrect and you still can't do superluminal speeds.
Sabine is very careful about how she defines warp drives in the beginning of the video. A warp drive that is not superluminal is still interesting for other reasons (all reactionless drives are kind of interesting). Also importantly the paper suggests specific mathematical properties of the geometry; namely that they should be flatter in the direction of motion. That is not at all intuitive to me, and certainly not the aesthetics of space ship design in most sci-fi.
We seem to systematically forget that the “shockwave problem” for FTL or even high fractional C travel is that all the light of the stars in front of you is now gamma radiation due to red shifting, and every particle you encounter behaves like cosmic rays. We will cook ourselves and our ships will turn to dust.
A warp drive that lets your local frame feel like .1c while you are actually traveling at .3c would still be a civilization-altering development.
It's news because it's a new paper. Even if the paper might be wrong, it's still news.
Regarding practicality, you may have missed the thesis, which is that warp drives are more practical than previously thought, because the theory allows subliminal warp drives at finite energy, not only superluminal warp drives at unphysical negative energy.
The part about GR is just the stretch part. It's obvious what she means about GR, that our current arguments against superluminal drives are based on General Relativity.
I thought she very clearly explained how this is different from warp drive concepts before, and why this is more interesting. Sure, you could disagree with her on that, but your post reads as if you’re not even aware she addressed those points at all.
Also her explanation of how general relativity works, the equations specifically, is too simplified and not even conceptually correct to be of any use to the reader who wants to understand this deeper . The right hand side is the parametric representation in matrix form of the manifold used. The 'R' is the curvature tensor, which is a in terms of the metric and its derivatives of the entries. Because there are 4 dimensions, a 4x4 metric tensor is used to describe the manifold, and because it is symmetric, there are 10 unique entries and hence 10 equations. These entries are not integers but are parametric equations themselves.
“ Bobrick and Martire show that for the Alcubiere drive you can decrease the amount of energy by seating passengers next to each other instead of behind each other, because the amount of energy required depends on the shape of the bubble. The flatter it is in the direction of travel, the less energy you need”
I don’t buy into the UFO phenomenon hype, but does this mean that a disk shaped “saucer” requires less energy than a craft with an elongated geometry? Wow
I'm wondering if part of the problem with trying to come up with technology which allows us to propel ourselves vast distances "faster than the speed of light", is to do with how we abstract/describe the problem (and the proposed solution) in language.
For example; instead of saying "faster than the speed of light", would the problem not be better described using "faster than the speed of causality" ?
After all, isn't c really just the speed of Causality in a vacuum? (i.e. the time it takes for a beam of light from a source to be detected at, say, a distance of 500,000 kilometres, is basically the rate at which Causality allows that light to get from the emitter to the detector.)
And isn't the speed of Causality, basically like some kind of inertia-like quality of spacetime? (Apologies in advance - I'm trying to describe what's in my head as best I can using... language ;) ) For example - the speed of "light"/Causality through water is slower than the speed of "light"/Causality through a vacuum.
(And mea culpa - I am a layman, trying to make sense of all this in as best a way I can. I'm not sure if what I wrote makes any kind of sense (it does in my head))
Your claim is that we've had trouble coming up with technology going FTL because physicists forget that the speed of light is the same as the speed of causality?
Separating the terms/ideas may actually be useful to address a common misconception you illustrate here. Light does change speed in water, but causality does not
There's an episode of PBS Space Time about this, "The Speed of Light is NOT About Light" [1], which comes pretty close to making the same points you are making.
It might be useful to watch this earlier episode, "Are Space and Time an Illusion?" [2], first.
There is a later episode (or maybe a couple of them) that go into how interactions with the Higgs field make it so things with mass travel slowed than the speed of causality.
To tie back to the warp drive news, they have an episode that would be a good place to start on warp drives, "Is The Alcubierre Warp Drive Possible?" [3]. There's also "Superluminal Time Travel + Time Warp Challenge Answer" [4], and "Will Wormholes Allow Fast Interstellar Travel?" [5]. A non-warp unknown physics drive that comes up a lot also got an episode, "The EM Drive: Fact or Fantasy?" [6].
There is at least one episode covering interstellar travel without using any unknown physics, "5 REAL Possibilities for Interstellar Travel" [7].
The scope of the series is basically anything vaguely connected to astronomy, cosmology, and quantum mechanics, and the episodes are all pretty short (5-12 minutes), so it is a great thing to watch when you've got a short wait for something.
Here's the series home page [8], and their YouTube channel [9]. Also on the PBS streaming app, for those who like to get their physics on their big screen TVs.
I’m as layman as you here but I assume it comes from the line of thought “just because light is contained to only go that fast doesn’t mean matter has to be constrained to only go that fast.”
It’s a natural extension of knowing that humans can’t fly. We need only look up to see that constraint didn’t hold up to the rest of time nearly as well as contemporary humans assumed it would.
How do we know that some immutable property of space/time causes light to travel at the speed it does rather than the other way around where some immutable property of light causes it to be incapable of traveling any faster (the old strap wings to a human and look now it can fly; so strap X to light and look now it can go faster to!)
Again, the extent of my knowledge in this space is from Star Trek not science so please be gentle with my clear level of ignorance.
Any reactionless drive might as well be FTL. The limit to traversing the universe isn't the speed of light it is the rocket equation. As long as you don't mind rather intense time dilation, you can get anywhere as fast as you want with enough fuel and ability to tolerate sustained acceleration. Remember: you can go any speed you can accelerate to, it is everything else that can't go faster than light.
Well, another implicit barrier is human lifetime. Though I suppose if we don't mind massive time dilation, we might not mind thousands of generations passing by during transit.
> Remember: you can go any speed you can accelerate to, it is everything else that can't go faster than light.
You cannot accelerate masses to the speed of light, because if General Relativity holds, you'd require infinite energy to do so.
In addition, every bit of radiation arriving from the direction of travel will be turned into high energy gamma radiation and cook you something fierce real quick; not to mention dust or tiny rocks that would release the energy equivalent of a thermonuclear explosion upon impact.
Since these effects alone will create a practical upper limit to your interstellar travel speed, there's still a huge difference between FTL and reactionless drives. An FTL drive might get you to Proxima Centauri in a month, whereas even the most optimistic subluminal option will take at least a decade.
Ok, so Warp Drives have many technological hurdles to accomplish, but currently all assumptions are on expansion and compression of space-time at faster than light speeds.
Let's say we want to travel in 1 hour to the nearest star 4 light years away. That would require compressing roughly 6.5 billion miles/second of spacetime into this bubble!
All matter in those 6.5 billion miles will be sucked into your passenger area of the warp bubble and decompressed back to Earth spacetime. This would be a weapon of galactic destruction.
But that's not the real issue, how exactly would we be able to warp spacetime faster than light at such large distances? The main engine would have to already be breaking the speed limit as part of its technical specification, which becomes a paradox, trying to use the solution as the foundation.
Find an alternative solution to breaking the speed limit, and we can overcome the paradox.
> All matter in those 6.5 billion miles will be sucked into your passenger area of the warp bubble and decompressed back to Earth spacetime.
This presumes that we're doing the moving all in one big operation, doesn't it?
What if each nanosecond, the warp bubble is moving forward by a small fraction, slipping through without imparting any momentum on the matter it passes by.
It might not let you go FTL, but this would seem to imply that you could get going extremely fast without a reaction mass to perform the acceleration. That alone would make shorter interstellar trips like the one to proxima centauri feasible as far as time goes.
Any technology advanced enough to travel between solar system is advanced enough to destroy them. It's order of magnitude more difficult to make the trip than it is to blow up everything when you get there.
On a side note, I like how The Expanse sidesteps the scientific issues of interstellar travel with alien magic.
On yet another note, I read an unsettling sci-fi/theory about how the expansion of space is perhaps being caused by whatever tech allows interstellar travel in lightspeed-like time. So whatever intelligent species that evolved first may have a monopoly on such tech, while inadvertently altering the fabric of physics to make interstellar travel gradually impossible for any younger species.
> On a side note, I like how The Expanse sidesteps the scientific issues of interstellar travel with alien magic.
I thought the "alien magic" behind the gates technology was the same old K. Thorne wormholes.
> On yet another note, I read an unsettling sci-fi/theory about how the expansion of space is perhaps being caused by whatever tech allows interstellar travel in lightspeed-like time. So whatever intelligent species that evolved first may have a monopoly on such tech, while inadvertently altering the fabric of physics to make interstellar travel gradually impossible for any younger species.
Do you have a link to read more about that? Reminds me of the FTL technology in the books "The Dark Forest" and "Death's End" by Liu Cixin.
> Bobrick and Martire explain that if you want superluminal motion, you need negative energy densities. If you want acceleration, you need to feed energy and momentum into the system. And the only reason the Alcubierre Drive moves faster than the speed of light is that one simply assumed it does. Suddenly it all makes sense!
They’re ultimately saying the Alcubierre Drive can’t go superluminal speeds because negative energy is not real, but it will work just fine if you go slower than the speed of light.
Ok I have a question kinda related about bubbles traveling faster through a medium.
If objects underwater can supercavitate, can objects in the atmosphere also supercavitate and can we have objects orbiting the earth inside the atmosphere?
That's an interesting question. Supercavitating torpedoes take advantage of two effects (a) gas typically is much less viscous than liquid, which reduces drag and (b) if you reduce the pressure enough, liquid turns into gas.
In the atmosphere, you're already in a gas, so there's not an obvious other state of matter that would be advantageous. Furthermore, reducing pressue would certainly reduce drag, but not by orders of magnitude like a phase transition.
But in the spirit of 'yes, and': if you reduced pressure near the skin by A LOT (near vacuum) you might see a dramatically lower drag. Maybe that could be accomplished by ionising the incoming air and then electrostatically repelling it? Who knows. It's fun to speculate though.
So, the biggest question I have about all this eminently theoretical physics video thing is, has anyone ever managed to experimentally demonstrate you can __voluntarily__ bend the brane our reality resides on by any measurable amount, and also demonstrate this causes an actual translation in 3d space? At all? Ever?
Or are we conjecturing what would happen if this was even slightly viable?
We've only very recently managed to experimentally demonstrate that unimaginably huge cataclismic events can make this happen, but, has anyone ever built some device that can make a crease of any significance at all in reality, and do so at will?
The argument is that they're impossible, because they require negative energy (which not only doesn't exist but doesn't make sense), so it's fine.
In the presence of negative energy you can form closed time-like curves in general relativity, which would violate causality, but these are not valid solutions because negative energy is not a thing.
It's just like saying you can travel faster than the speed of light in special relativity, you just need imaginary mass (ie. m^2<0), but mass is unfortunately a real quantity rather than a complex quantity so you can't.
In the latest Star Trek, the starship Discovery runs on spores harvested from shrooms grown onboard. Despite being set in the Captain Pike era, no one ever noticed this up to then :]
Why it's almost as if Star Trek is fiction and the "canon" of a franchise spanning over fifty years of television, film and books has always been fluid and arbitrary.
1 - Your comment isn't about content of the article. I don't use apple hardware or software. There are tons of apple posts, especially about the M1. How would it work out if all the people who aren't part of the apple ecosystem hit every apple story with a "Sheesh, not another apple article! Can't we get something more interesting?"
2 - You are free to submit things you think are interesting. Be the change you want to see, etc.
3 - People who whine about being downvoted tend to get more downvotes
[+] [-] WJW|5 years ago|reply
Also, any article that ends with a phrase like "while it may look now like you can’t do superluminal warp drives, this is only correct if General Relativity is correct" does not bode well for practical applications of the subject matter. There is also the logical fallacy that it might be the case that GR is incorrect and you still can't do superluminal speeds.
[+] [-] dnautics|5 years ago|reply
[+] [-] hinkley|5 years ago|reply
A warp drive that lets your local frame feel like .1c while you are actually traveling at .3c would still be a civilization-altering development.
[+] [-] alisonkisk|5 years ago|reply
Regarding practicality, you may have missed the thesis, which is that warp drives are more practical than previously thought, because the theory allows subliminal warp drives at finite energy, not only superluminal warp drives at unphysical negative energy.
The part about GR is just the stretch part. It's obvious what she means about GR, that our current arguments against superluminal drives are based on General Relativity.
[+] [-] simonh|5 years ago|reply
[+] [-] paulpauper|5 years ago|reply
[+] [-] hdhdurhdhdud|5 years ago|reply
I don’t buy into the UFO phenomenon hype, but does this mean that a disk shaped “saucer” requires less energy than a craft with an elongated geometry? Wow
[+] [-] scarygliders|5 years ago|reply
For example; instead of saying "faster than the speed of light", would the problem not be better described using "faster than the speed of causality" ?
After all, isn't c really just the speed of Causality in a vacuum? (i.e. the time it takes for a beam of light from a source to be detected at, say, a distance of 500,000 kilometres, is basically the rate at which Causality allows that light to get from the emitter to the detector.)
And isn't the speed of Causality, basically like some kind of inertia-like quality of spacetime? (Apologies in advance - I'm trying to describe what's in my head as best I can using... language ;) ) For example - the speed of "light"/Causality through water is slower than the speed of "light"/Causality through a vacuum.
(And mea culpa - I am a layman, trying to make sense of all this in as best a way I can. I'm not sure if what I wrote makes any kind of sense (it does in my head))
[+] [-] whimsicalism|5 years ago|reply
I'm probably misunderstanding what you're saying.
[+] [-] Misdicorl|5 years ago|reply
[+] [-] mybandisbetter|5 years ago|reply
[+] [-] tzs|5 years ago|reply
It might be useful to watch this earlier episode, "Are Space and Time an Illusion?" [2], first.
There is a later episode (or maybe a couple of them) that go into how interactions with the Higgs field make it so things with mass travel slowed than the speed of causality.
To tie back to the warp drive news, they have an episode that would be a good place to start on warp drives, "Is The Alcubierre Warp Drive Possible?" [3]. There's also "Superluminal Time Travel + Time Warp Challenge Answer" [4], and "Will Wormholes Allow Fast Interstellar Travel?" [5]. A non-warp unknown physics drive that comes up a lot also got an episode, "The EM Drive: Fact or Fantasy?" [6].
There is at least one episode covering interstellar travel without using any unknown physics, "5 REAL Possibilities for Interstellar Travel" [7].
The scope of the series is basically anything vaguely connected to astronomy, cosmology, and quantum mechanics, and the episodes are all pretty short (5-12 minutes), so it is a great thing to watch when you've got a short wait for something.
Here's the series home page [8], and their YouTube channel [9]. Also on the PBS streaming app, for those who like to get their physics on their big screen TVs.
[1] https://www.youtube.com/watch?v=msVuCEs8Ydo
[2] https://www.youtube.com/watch?v=YycAzdtUIko
[3] https://www.youtube.com/watch?v=94ed4v_T6YM
[4] https://www.youtube.com/watch?v=HUMGc8hEkpc
[5] https://www.youtube.com/watch?v=ldVDM-v5uz0
[6] https://www.youtube.com/watch?v=hqoo_4wSkdg
[7] https://www.youtube.com/watch?v=EzZGPCyrpSU
[8] https://www.pbs.org/show/pbs-space-time/
[9] https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g
[+] [-] purple-again|5 years ago|reply
It’s a natural extension of knowing that humans can’t fly. We need only look up to see that constraint didn’t hold up to the rest of time nearly as well as contemporary humans assumed it would.
How do we know that some immutable property of space/time causes light to travel at the speed it does rather than the other way around where some immutable property of light causes it to be incapable of traveling any faster (the old strap wings to a human and look now it can fly; so strap X to light and look now it can go faster to!)
Again, the extent of my knowledge in this space is from Star Trek not science so please be gentle with my clear level of ignorance.
[+] [-] Animats|5 years ago|reply
[+] [-] blamestross|5 years ago|reply
[+] [-] progman32|5 years ago|reply
[+] [-] qayxc|5 years ago|reply
You cannot accelerate masses to the speed of light, because if General Relativity holds, you'd require infinite energy to do so.
In addition, every bit of radiation arriving from the direction of travel will be turned into high energy gamma radiation and cook you something fierce real quick; not to mention dust or tiny rocks that would release the energy equivalent of a thermonuclear explosion upon impact.
Since these effects alone will create a practical upper limit to your interstellar travel speed, there's still a huge difference between FTL and reactionless drives. An FTL drive might get you to Proxima Centauri in a month, whereas even the most optimistic subluminal option will take at least a decade.
[+] [-] JoeOfTexas|5 years ago|reply
Let's say we want to travel in 1 hour to the nearest star 4 light years away. That would require compressing roughly 6.5 billion miles/second of spacetime into this bubble!
All matter in those 6.5 billion miles will be sucked into your passenger area of the warp bubble and decompressed back to Earth spacetime. This would be a weapon of galactic destruction.
But that's not the real issue, how exactly would we be able to warp spacetime faster than light at such large distances? The main engine would have to already be breaking the speed limit as part of its technical specification, which becomes a paradox, trying to use the solution as the foundation.
Find an alternative solution to breaking the speed limit, and we can overcome the paradox.
[+] [-] mabbo|5 years ago|reply
This presumes that we're doing the moving all in one big operation, doesn't it?
What if each nanosecond, the warp bubble is moving forward by a small fraction, slipping through without imparting any momentum on the matter it passes by.
[+] [-] simcop2387|5 years ago|reply
[+] [-] jandrese|5 years ago|reply
[+] [-] Razengan|5 years ago|reply
On yet another note, I read an unsettling sci-fi/theory about how the expansion of space is perhaps being caused by whatever tech allows interstellar travel in lightspeed-like time. So whatever intelligent species that evolved first may have a monopoly on such tech, while inadvertently altering the fabric of physics to make interstellar travel gradually impossible for any younger species.
[+] [-] avaldeso|5 years ago|reply
I thought the "alien magic" behind the gates technology was the same old K. Thorne wormholes.
> On yet another note, I read an unsettling sci-fi/theory about how the expansion of space is perhaps being caused by whatever tech allows interstellar travel in lightspeed-like time. So whatever intelligent species that evolved first may have a monopoly on such tech, while inadvertently altering the fabric of physics to make interstellar travel gradually impossible for any younger species.
Do you have a link to read more about that? Reminds me of the FTL technology in the books "The Dark Forest" and "Death's End" by Liu Cixin.
[+] [-] LockAndLol|5 years ago|reply
Uh... what?
[+] [-] ickelbawd|5 years ago|reply
[+] [-] sitkack|5 years ago|reply
If objects underwater can supercavitate, can objects in the atmosphere also supercavitate and can we have objects orbiting the earth inside the atmosphere?
[+] [-] robbmorganf|5 years ago|reply
In the atmosphere, you're already in a gas, so there's not an obvious other state of matter that would be advantageous. Furthermore, reducing pressue would certainly reduce drag, but not by orders of magnitude like a phase transition.
But in the spirit of 'yes, and': if you reduced pressure near the skin by A LOT (near vacuum) you might see a dramatically lower drag. Maybe that could be accomplished by ionising the incoming air and then electrostatically repelling it? Who knows. It's fun to speculate though.
[+] [-] cfv|5 years ago|reply
Or are we conjecturing what would happen if this was even slightly viable?
We've only very recently managed to experimentally demonstrate that unimaginably huge cataclismic events can make this happen, but, has anyone ever built some device that can make a crease of any significance at all in reality, and do so at will?
[+] [-] JumpCrisscross|5 years ago|reply
Bends in spacetime creating measurable effects is how LIGO’s interferometers see gravity waves.
You’re asking for a light bulb when we’ve barely begun grinding lenses for a telescope.
[+] [-] generalizations|5 years ago|reply
[+] [-] Dylan16807|5 years ago|reply
[+] [-] mrfusion|5 years ago|reply
(She mentions she explains it in another video but I couldn’t find it.)
[+] [-] jleahy|5 years ago|reply
In the presence of negative energy you can form closed time-like curves in general relativity, which would violate causality, but these are not valid solutions because negative energy is not a thing.
It's just like saying you can travel faster than the speed of light in special relativity, you just need imaginary mass (ie. m^2<0), but mass is unfortunately a real quantity rather than a complex quantity so you can't.
[+] [-] sgt101|5 years ago|reply
[+] [-] ck2|5 years ago|reply
(a lazy writing device that was a step too far IMHO)
[+] [-] unknown|5 years ago|reply
[deleted]
[+] [-] Stierlitz|5 years ago|reply
[+] [-] edgyquant|5 years ago|reply
[+] [-] krapp|5 years ago|reply
[+] [-] whimsicalism|5 years ago|reply
e: I'm curious what the opinion of professional physicists would be.
[+] [-] tasty_freeze|5 years ago|reply
1 - Your comment isn't about content of the article. I don't use apple hardware or software. There are tons of apple posts, especially about the M1. How would it work out if all the people who aren't part of the apple ecosystem hit every apple story with a "Sheesh, not another apple article! Can't we get something more interesting?"
2 - You are free to submit things you think are interesting. Be the change you want to see, etc.
3 - People who whine about being downvoted tend to get more downvotes
[+] [-] segfaultbuserr|5 years ago|reply
> When disagreeing, please reply to the argument instead of calling names.
> Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.
> Please don't comment about the voting on comments. It never does any good, and it makes boring reading.
[+] [-] WarOnPrivacy|5 years ago|reply
I'm a good audience for her writeup - someone who hasn't deep-dived into FTL for decades.
Maybe it helps I'm not at all familiar with Sabine.
[+] [-] unknown|5 years ago|reply
[deleted]