Hey all, I'm one of the authors of the paper Introducing Physical Warp Drives and a Y Combinator alum (YC W'14). This video does a great job explaining our paper and Erik's as there a few misunderstandings in this forum https://youtu.be/PA66ah9b0U4. We all know each other and all have the warp bug as we now have a path; it's just going to be difficult. If you would like to join our warp drive cohort, please email us a bit about yourself and your ideas for warp at create at appliedphysics dot org. Our cohort is composed of PhDs and engineers from several STEM disciplines, we meet weekly and have more papers in the works, perhaps you can join the fun! https://thedebrief.org/new-warp-drive-model-requires-no-exot...
Do you have any thoughts on Lentz's comment that IPWD "made a rush to judgement" on his draft of Hyper-Fast []? Or has anything changed in your assessment between the draft and publication of his paper? (I did not see anything on his blog)
The version accepted in the journal clearly states that superluminal warp drives are physically unachievable because they violate the dominant energy condition. It means that superluminal drives require superluminal matter. This is in agreement with the conclusions in the IPWD paper. However, the version E.Lentz uploaded on arxiv or the press-release did not state this clearly.
In principle, yes, for sure, we could detect it. For example, it would still generate gravity and be uniquely identifiable this way. But then, superluminal matter breaks causality, allows sending signals back in time and, to the best of our knowledge, is unphysical.
The superluminal speed is not an infinite speed, it's just faster than the speed of light, of course, but it called "instant". For example, a photon of light is emitted or absorbed "instantly", which is not true, obviously, because it means infinite speed of transition.
I do not understand how the proposed warp drive could help with moving a ship. It sounds more like a "time dilation device" to shorten the travel time for the crew than a setup to make moving through space actually easier.
I believe spherically symmetric bubbles in subluminal regime are more interesting than any warp drive solutions suggested so far. Firstly, they do not require negative energy. Secondly, the passengers in such bubbles age less by the time they reach any destination compared to other warp drives or conventional rockets. Given that exceeding the speed of light is fundamentally prohibited by physics, I would say that spherically symmetric warp drives are the most interesting warp drive constructions we got so far.
How can you accumulate enough mass to make this possible without destabilizing the entire solar system? Even getting to the Oort Cloud to collect mass outside of our solar system is 3 light years away.
>We all know each other and all have the warp bug as we now have a path
What do you mean by that? Not to be a negative Nancy but the titles of both the paper and the video are a bit click-baity. None of this will be possible in our lifetime, the amounts of energy required are way too large, even if it could be engineered (which I have doubts about). Imo as a society we need to focus on getting off earth and establishing colonies in our own solar system first, before we can even start dreaming about going to other stars.
> society we need to focus on getting off earth...before we can even start dreaming about going to other stars.
How about people who are interested in warp physics study warp physics, and those interested in establishing off-world colonies spend their time on that persuit?
Fair. I certainly didn't mean that they shouldn't be able to study this. To use an analogy my point is more that it's similar to how early hominids "studied" going to the moon when they didn't even know how to make fire yet. It's an interesting idea to think about but was science fiction then, just like warp drives are today. Science fiction doesn't necessarily mean it's unscientific. But we don't know where to get the energy equivalent of 1/10th of the solar mass and somehow put it in a spaceship. It's absolutely not something we can work on solving even in theory right now.
I think what's really interesting about this that most readers seem to overlook is the claims about subluminal warp drive, which is practically realizable in a way that the science-fictional faster-than-light case is not
Any subliminal system that avoids Doppler shifting everything in front of your ship into hard X-rays is going to be a big deal. Also help with micrometeoroids.
Everyone papers over these very real problems like they’ll just get solved. But if you can keep your ship at .05c while moving at .4c relative to your starting point that’ll be a huge deal.
You can, but it's not always respected by the user's device. Mobile devices will usually respect it but desktop browsers will often ignore it and start the video from the beginning.
>desktop browsers will often ignore it and start the video from the beginning.
Is there some data on this, or are you just making it up? It's long been a feature on one of the largest internet sites. I've never not had it work on the desktop, at least on Firefox, Brave, and Chromium on both Mac and Linux.
Many websites use handlers for YouTube links in their comments/messages section that treat it differently that just a hyperlink. For example, if you post a plain YouTube URL to Imgur and someone clicks on it, it won't take them to YouTube.com. It'll open a small pop-up player that strip out any modifiers like the timecode and plays the video from the start. I've also run into this problem trying to share videos with subtitles enabled by default.
For what it's worth, I've had it happen a few times and I use Firefox on a PC. I suspect it's probably more to do with linking variables after the url proper from certain sites, rather than a browser-level complaint.
Baby steps! Every step is worth it. I know the math and science doesn't support me but I'm convinced FTL is possible and that the universe won't die a heat death.
The universe heat death theory makes me think of comics where people extrapolate the data they have while lacking other critical data. https://xkcd.com/605/
Most of the universe is void. Most of the rest is whatever dark matter is. What we consider to be the entirety of material reality is a fraction of a fraction, and out of that, as far as we can tell, Earth has the only life that exists. There's probably more life out there, but if there is, as the Fermi Paradox points out, they're awfully quiet.
I think it's fair to assume that life will have practically zero impact on the universe. Even if the universe was teeming with it, it would be of such little significance at scale that it might as well be a rounding error in reality.
There is merit to your thought process but it could just as easily be that life is the spark that sets off an explosion that irrevecobly changes the universe.
Think of a virus. A handful of specially shaped molecules has permanently changed human society.
What? It does no such thing, it just assumes life doesn't violate the second law of thermodynamics, which seems reasonable considering we've never observed it doing so.
It assumes life is subject to the second law of thermodynamics, which it is.
Avoiding heat death requires a renewable source of negentropy, to bypass the second law. Some sort of perpetual motion machine that you can pump energy out of. E.g. if you could extract work out of the expansion of the universe fast enough to build expansion-work-extractors faster than they decay, and expansion continues indefinitely, then you can avoid heat death.
There is another paper on warp drives that came out around the same time, Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein-Maxwell-Plasma Theory [0].
Wow, is that paper saying what I think it is? Previous papers only found a negative energy requirement (pg. 12) because they only considered interior spaces which could reduce down to a point-like region? That's an extraordinary claim, and, I hate to use the phrase, but "big if true".
> Once the energy requirement is lowered, the space–time signatures of positive-energy solitons may be studied in a laboratory setting using existing or novel methods. ... The highly magnetized energetic and diffuse atmospheric plasma of magnetars may also bea natural place to look for signatures of positive-energy soliton geometries even prior to advances in energy reduction.
It is an important paper. However, it is also important to realise that superluminal solutions introduced there are still prohibited by the laws of physics. Making such superluminal drives is at least as hard as making superluminal matter, which we believe requires infinite amount of energy. In physics, they say that such spacetimes violate the dominant energy condition. The issue is relatively clearly stated in E.Lentz's paper accepted in the journal, but not in his arxiv paper or the press-release.
Very good paper. However, it doesn't overcome the problem of superluminal travel. Rather, one of the problems. There are other remaining fundamental physical issues related to FTL, including the need for superluminal matter, causality violation, the impossibility of accelerating past the speed of light and and a few more. Subluminal warps, instead, can be fully consistent with physics.
I've only gotten a few pages into this, but it looks like their general solutions still require negative energy? Regardless, it's been very interesting to see the development of warp drive theory over the last ~20 years.
Anyone selling "warp drives" that do not go faster than light kind of missed the point of why people are excited about warp drives.
And if the video @gmartire just posted is explaining the paper correctly, this warp drive also doesn't accelerate anything. You have to figure out how to speed up on your own.
I don't really see why anyone would bother doing any of these things. To dilate time better? I'd rather invest the same amount of mass towards a larger engine/fuel so that I can go faster, dilating time further and getting me there sooner.
The FTL part of the warp drive is the useless part. The real obstacle to space exploration is the rocket equation. Going FTL doesn't help if fuel needs still scale quadratically with distance.
Am I correct that the interesting thing about subluminal warp drives is that they do not require working mass for propulsion? So if we had such a warp drive, we could put energy in and get motion out of it, without being subject to the tyranny of the rocket equation?
It seems like this idea is not correct. The authors write in section 5.2: "Warp drives, being inertially moving shells of normal or exotic material, do not have any natural way of changing their velocities. They are just like any other types of inertially moving objects. Similarly, just like for any other massive objects, achieving a certain velocity for a warp drive requires an externally applied force or, more practically, some form of propulsion.", from https://arxiv.org/pdf/2102.06824.pdf#page=17
The tyranny of the rocket equation isn't some fixed property of orbital mechanics, it's a limitation of our method for converting energy from chemical propellants to propulsion. Specific impulse for nuclear rockets designed decades ago (i.e. nuclear lightbulb) is in the thousands, which is enough to reach orbit in a single stage without dumping extraneous mass.
The original Alcubierre drive required the energy equivalent of the mass of Jupiter to create the warp field, with an impossible shortcut in the form of exotic particles with negative mass. The sun burns loses about 6x10^9 kg of mass a second which is the upper limit for the amount of energy a Type I civilization can extract in our solar system. Jupiter's mass is roughly 2x10^27 kg, so assuming there are 4x10^11 stars in our galaxy and our star represents the average, a Type II civilization in our galaxy wouldn't have enough energy to produce a warp field. The drive doesn't just need a little bit of working mass to expel, it needs enough energy/mass to bend space time around it!
The rocket equation doesn’t only apply to chemical energy propulsion - it applies to any propulsion system that conserves momentum and uses reaction mass - which nuclear drives do too.
Chemical rockets are limited in how much energy they can put into the reaction mass (by the energy density of their fuel) and therefore the maximum exhaust velocity they can achieve - which is the input into the rocket equation
But while nuclear rockets get away from the constraint of chemical energy density they still have to operate by putting energy into reaction mass and shooting it out the back to create a momentum change.
And the rocket equation still applies to the reaction mass and its exhaust velocity.
In fact in theory you can build a chemical rocket engine that burns a fuel for heat, then uses that heat to energize some other reaction mass that you eject - it’s just that that is inherently less efficient than using the spent fuel as reaction mass since otherwise you’re needlessly pumping momentum into spent fuel. Far better to throw the exhaust products away as reaction mass.
Ah, my mistake - I thought the "tyranny of the rocket equation" was referring to the rocket equation's consequences on our attempts to reach orbit (i.e. multistage rockets), not the equation in general.
Slight quibble, but the original needed more negative mass than the universe, it was one of the subsequent improvements which reduced it to only Jupiter.
Thank you for the correction! Though, I hope you don't mind that I quibble the quibbler: the original needed more regular mass than the universe - negative mass exotic particles were proposed as a more "practical" alternative, if they exist.
Just a causal reminder that solar sails, beamed propulsion, mag sails, photon rockets, etc are all examples of propulsion methods free from the tyranny of the rocket equation which require no onboard reaction mass. There is really no need for exotic physics if that's all you're looking to accomplish.
If general relativity is an accurate model of gravity then distortions in space-time are caused by mass. Traveling at the speed of light can be shown to require an infinite amount of energy to accomplish for a finite mass. However space-time itself could, according to our current understanding, travel faster than the speed of light.
So if you could 'warp' space around you rather than travel through it, you could go at an arbitrary speed. Unfortunately warping space-time is typically accomplished by large amounts of mass. Hence a large amount of energy. If I remember correctly it also requires we bend space in a way we have never seen nor have any reason to believe is possible to accomplish beyond it being allowed by general relativity. It's quite a pickle.
Without such a device humanity will still populate the galaxy but it'll take hundreds of millions of years. Assuming we don't wipe ourselves out.
Does an Alcubierre warp drive violate causality? From my understanding, it's no different than regular FTL travel, which implies time travel, which implies violation of causality.
To me that would indicate that an Alcubierre warp drive still shouldn't be possible despite the negative energy requirement being lifted.
It did recently occur to me that it's not a hard requirement that FTL be impossible, just that causality not be violated. There may be solutions to FTL where naively they could violate causality, but in practice other effects ensure that no usage of them ever will.
The Atomic Rockets website[0] describes the issue clearly:
Relativity proves that FTL travel is identical to Time travel.
Time travel makes Causality impossible, since it can be used to create paradoxes. Note that to a physicist, it is not enough that time travel never happens to be used to make a paradox. The mere fact it is possible is enough to utterly destroy Causality.
1. So if you have Relativity and FTL, Causality is impossible
2. If you do not have Relativity, then FTL is not Time travel, so you can have Causality.
3. Or more mundanely you can have Relativity and Causality, but no FTL/Time travel
∴ Causality, Relativity, FTL travel: chose any two.
> The Atomic Rockets website[0] describes the issue clearly:
I don't find their description very clear. In particular, they don't even define
- what "faster-than-light" is supposed to mean in a non-relativistic setting (Newtonian mechanics) where there's no such thing as a universal velocity and you're dealing with Galilean velocity transformations.
- what causality is supposed to mean exactly outside the relativistic setting where you have a universal velocity which induces the causal structure.
All in all, their definitions are very inter-dependent, so the "trichotomy" they present as truth doesn't make much sense to begin with. From my POV, they're not even wrong[0].
Moreover, they seem to only consider Special Relativity and completely ignore General Relativity where the speed-of-light bound is only a local bound. Basically, even if what they say were true, it would still not apply to the General Relativistic setting we're looking at here.
> Time travel makes Causality impossible, since it can be used to create paradoxes
This is missing the point though: it's not "optional" per se - it's that naively, if we simply go "what if FTL" then yeah, based on current physics we have a problem.
But the logic doesn't then mean "can't FTL" - it's still "can't have paradoxes". An FTL system, theoretically incapable of creating paradoxes, has no such problems.
An FTL system which prevents you from going faster then light in directions which allow violating causality would be totally fine, provided this was a theoretical restriction: i.e. your FTL engine just plain can't thrust in causality violating vectors, because it encounters some temporal restriction field or similar.
So the problem isn't "FTL is a causality violation", it's FTL without a mechanism to prevent causality violation is probably impossible.
The sci-fi conceit of it being difficult to plot efficient paths through hyperspace or whatever might well be quite a real thing, and simply related to charting causality-allowed courses through FTL-space.
No, it makes the idea that causal sequence and temporal sequence are identical and that the former mapped against the latter can’t have cycles impossible.
Making causality more complex than we'd like to think it is isn't making it impossible.
> Does an Alcubierre warp drive violate causality?
The original Alcubierre metric does not, but that's because it only describes a single "warp bubble" that travels in one direction, never starting or stopping and never turning around.
As soon as you have more than one "warp bubble", or you let a single "warp bubble" turn around, then you will have closed timelike curves, which violate causality.
No, for the original Alcubierre, its warping spacetime around the information and moving that pocket. The ship or information or whatever is still traveling inside the pocket at its normal speed. So while it could be virtually instant (ignoring energy requirements), it wouldn't be time travel. However, I believe you could arrive to your destination and look back and see yourself before you warped - and maybe as you traveled - as the light catches up to you. At least that's my understanding.
No, every FTL construction can be used to violate causality. There’s no way at all around that. Fundamentally it’s a geometric problem — relativity has a hard barrier at light speed, but if you can get past that, there’s nothing at all special about infinite speed. Is the same sort of 4-momentum as standing still, and you can accelerate in any direction from there.
The warp drive in the article is subliminal, though, so it doesn’t have that problem.
I've always had serious trouble understanding why FTL travel will break causality.
Do you know of any good layman-level explanations?
Like, if I FTL from point a to point b, 10 light years apart, in my super duper warp vessel. It takes me, for the sake of argument, 10 minutes to make that journey. Now say I set off a big comms laser at point a, sending a message to point b, before I left. I don't see that laser until 10 years later.
What am I missing? I know I'm missing something, but that seems straightforward to me. It's weird to butt up against that seemingly incomprehensible.
Suppose you set off in a spaceship at 80% of lightspeed, or 0.8c, travelling away from Earth. At this speed, according to relativity, time is slowed to 60% of it's 'usual' value. So for every 10 hours that pass on Earth, only 6 will appear to pass on the spaceship.
However, this is only true from the perspective of someone on Earth. From the point of view of someone on the spaceship, the opposite is true. From their perspective, the spaceship is stationary, and Earth is travelling away from it at 0.8c. Therefore, for every 10 hours that pass on the spaceship, only 6 will appear to pass on Earth.
Suppose there was a way of instantaneously communicating between the two. On Earth, 10 hours into the mission, mission control sends a message to the spaceship. Because of time dilation, the spaceship receives the message only 6 hours into the mission, from their perspective. The spaceship then sends a message back, and due to the same time dilation effect, the message arrives on Earth 3 hours and 36 minutes into the mission (60% of 6 hours). In other words, the reply from the spaceship will arrive 6 hours and 24 minutes before mission control sends the original message.
>On Earth, 10 hours into the mission, mission control sends a message to the spaceship. Because of time dilation, the spaceship receives the message only 6 hours into the mission, from their perspective.
And from their perspective - "for every 10 hours that pass on the spaceship, only 6 will appear to pass on Earth." - the message was sent at 3:36 of the Earth time. They immediately send a response message which immediately arrives at 3:36 of the Earth time from their perspective. No paradox so far.
From Earth's POV - the message is sent at 10 of Earth time which is 6 of the ship's time from the Earth's POV, the reply sent and received immediately at 6 of the ship's time which is 10 of the Earth time from the Earth POV.
From the perspective of someone on Earth, when it's 10:00 on Earth, it's 6:00 on the spaceship.
But from the perspective of someone on the spaceship, when it's 6:00 on the spaceship, it's 3:36 on Earth.
From the ship's reference frame, Earth is in the past; from Earth's reference frame, the ship is in the past. If you have superluminal communication, the Earth can send a message to the ship's past, which can then send a response to Earth's past.
>From the ship's reference frame, Earth is in the past; from Earth's reference frame, the ship is in the past.
no. The "when it's 6:00 on the spaceship, it's 3:36 on Earth" doesn't mean "From the ship's reference frame, Earth is in the past". It is just different speed of time. The 3:36 of "slow time" isn't "less" than ("past" of) the 6:00 of "fast time". Say you have 2 clocks, and took one on a spaceship ride. When brought back it will be showing say 6 why the twin clock which didn't left the Earth would be showing 10 - the ship clock wouldn't be in the "past" as both clocks are on the table in front of you in the "present".
> The "when it's 6:00 on the spaceship, it's 3:36 on Earth" doesn't mean "From the ship's reference frame, Earth is in the past". It is just different speed of time.
It amounts to the same thing. From the perspective of Earth, time travels slower on the ship than on Earth. From the perspective of the ship, time travels faster on the ship than on Earth. Superluminal communication allows you to abuse the difference in reference frames to break causality.
Put it another way: when it's 6 on the ship, what time is it on Earth? It depends who you ask. Mission control would say it's 10. The people on the ship would say 3:36. Both are correct.
> Say you have 2 clocks, and took one on a spaceship ride. When brought back it will be showing say 6 why the twin clock which didn't left the Earth would be showing 10 - the ship clock wouldn't be in the "past" as both clocks are on the table in front of you in the "present".
In your example, the ship needs to change velocity in order to get back to Earth and compare the clocks. The ship is not always at rest in any reference frame; it either needs to stop and turn around, or accelerate to catch a retreating Earth.
It just so happens that in this scenario, whatever reference frame you choose, the ratio between the time on the ship and the time on Earth works out to be the same.
But this changes if the ship doesn't need to alter it's velocity. If the ship is travelling at 0.8c away from Earth, then it's equally valid to say that the Earth is travelling 0.8c away from the ship. It is therefore equally true to say:
* For every 10 hours on Earth, 6 hours pass on the ship
* For every 10 hours on the ship, 6 hours pass on Earth
In some reference frames Earth's time progresses faster than the ship; in other reference frames it progresses slower. If you're able to pass around information between reference frames instantaneously, then you can pass information backward through time.
If you use a mobile phone, you can reply to the second message (by network) before the first message will reach you (by air), so you can break causality and travel back in time!
I'm in the same boat as the person you replied to; breaking causality never made sense to me.
In the case of your explanation, what sticks out to me is the "Suppose their was a way of instantaneously communicating" part - it seems more intuitive to me that the warp bubble would not allow any communication across the threshold, effectively becoming a pocket universe.
The ship you're in isn't what's traveling FTL, though; it's going at normal relativistic speeds. But say both you and Earth have an ansible (a faster-than-light communicator); then you get the problem in the previous comment.
Instantaneous communication makes the numbers easier because you don't have to account for travel time, but causality can be broken with any superluminal form of communication.
If you have a ship with warp speed, then you have superluminal communication, because you can just carry a message on board. Even if you can't communicate inside the warp bubble, as long as you can exit the bubble at some point, then you can travel via warp, pop out, and transmit your message conventionally.
In my earlier example, if the ship and mission control had messenger drones capable of travelling many times faster than light, then the ship's response drone could arrive on Earth before mission control's messenger drone was launched.
Oh wow, this was fascinating! I was vaguely made aware of some of these concepts by a friend who studies quantum physics, but on he's never been able to explain it so "simply" (that's not doing the explanation any justice, it's not simple and some of it still went over my head, but "it clicked").
We see that matter and energy and all their fields and stuff move through time and space continuously. They don't spontaneously relocate themselves a million light-years away, and they don't generally relocate themselves a million years into the past. They trace a continuous path through time and space. (Oh, sure, for individual particles there's some quantum weirdness about exactly where it is along the way, but I think we're dealing with larger systems here?)
Now, physics have told us that space and time are glued together into a four-dimensional spacetime. So pick any two given points in spacetime — in whatever reference frame you like, doesn't matter if you're on Earth or in a space or next to a black hole — and take measurements of the distance between them, and the time between them. Ask yourself, "can some matter or energy travel along a path from the one point in spacetime to the other?" This is what it means to say, "are these points casually connected?" Because causes and effects have physical carriers, and they must move through time and space.
We found experimentally that there is generally a special speed limit — the "speed of light", though other things also are affected by this limit. We also found that this speed is constant in all reference frames. Some reference frames will disagree on how much space and time there is (your usual twin paradoxes and the like) but it all works out so that all observers agree on how much spacetime is between the points. (The mathematical objects for representing spacetime are quaternions, and the space and time vectors are just particular projections of the underlying quaternions, onto a set of measurements for a reference frame. But I don't know how to operate quaternions, and the specifics don't matter here.)
Now here's the thing:
If you are able to go faster than the speed of light (as measured in any reference frame of your choosing) it is geometrically equivalent to the power to go back in time. It doesn't really matter how you go faster, how you connected those two points — teleport there, open wormholes, warp space — there is some reference frame where you have travelled back in time. If you perform your maneuvers right, and take the right path, that reference frame could be Earth.
There's no other barrier: the speed of light itself was the barrier, and you just broke it. And if you have done so successfully, that means that the way cause-and-effect actually happens is ... something weird we only understand poorly.
observers moving relative to each other agree on what “the speed of light” is, but disagree about what “2 x the speed of light” is. Specifically, they disagree about which superluminal trajectories are forward in time vs backwards in time. Therefore, if you have a device that accelerates you to 2x the speed of light, it must accelerate you to 2x the speed of light in your own reference frame. As a result, you can accelerate to .99 c relative to earth using conventional means, activate the device, and then be travelling at 2x the speed of light in the .99c frame, which is backwards in time in the earth frame. You could then stop, turn around, and repeat the procedure to arrive at earth before you left.
The Alcubierre solution avoids this by being symmetrical, so that observers don’t have to agree on which direction is the destination and which is the origin
Does FTL really inevitably mean that, or is that a consequence of saying “no preferred frame of reference” and therefore having e.g. “100c” meaning different things to observers in relative motion?
"No preferred frame of reference" is how the universe fundamentally works - if you remove that, you're looking at a universe that functions differently than our own in a lot of basic ways.
Follow up question: while no preferred frame is obviously the simplest model, is it really impossible to add a preferred frame? e.g. https://youtu.be/6MfJ59lkABY?t=413
Ah, i somehow read the subluminal as superluminal in the abstract and got all excited. But the subluminal restriction makes the paper's findings make more sense.
> I believe you could arrive to your destination and look back and see yourself before you warped - and maybe as you traveled - as the light catches up to you
That does sound like traveling faster than light, but I think there's a reasonable view that makes it not.
Suppose you traveled at some very fast speed around a black hole. It bends space time in such a way that you might, at some point, be able to collect photons that could be reconstructed into an image of you earlier in time.
In short, when space time is flexible and bending, there are paths in which you can see your previous self. An alcubierre drive is a means to bend space time.
I don't know enough to think that violation of causality is not possible. It just just seems very unlikely. I can't imagine how the world would look like if it wasn't the case because of the paradoxes it would imply.
You seem to imply that you think differently. Care to elaborate?
Not the GP, but both the many worlds interpretation and superdeterminism would avoid (the issues of) causality violation, would they not, even in the presence of time travel?
It's kind of exciting that we see phrases like this now. I mean it wasn't that long ago that the idea of a 9 story first stage rocket coming back to land (and fly again) was fantasy.
This is a nice paper. A couple thoughts that I haven’t seen raised yet in the thread:
1) this paper exhibits, for the first time, a continuous family of warp drives which contains Minkowski space (see the end of S.4.3). This means that it is, in principle, possible to turn on/off a warp drive, which is a basic requirement if you ever want to build one.
The next basic feature we need to understand is how/whether warp shells can accelerate/decelerate. No paper in the literature does this yet, afaict. Would be very exciting if Bobrick and Martire can exhibit this in a sequel!
The subluminal application is particularly interesting, because it seems almost feasible. Is there a practical path to meeting these mass/energy requirements though?
Where could we source so much mass? That is far more than the mass of the earth, and surely altering the mass of the sun by 10% would have catastrophic effects.
> physically possible
Does an element exist that is dense enough to compress 10% of the mass of the sun into a 620m sphere? If not, how can the claim that this is physically possible be supported?
there was an article a while back claiming the possibility of Alcubierre drive effects (displacement of space/time) in close proximity to a neutron star that is spinning rapidly.
That sounds like a journalist read a bit about both frame dragging and the Alcubierre metric and had as much wishful thinking as is usually my own personal weakness with all things GR: https://en.wikipedia.org/wiki/Frame-dragging
