the AI won’t suddenly discover how to make energy from nothing or how to travel faster than light
I find it amusing that there are actual mechanisms that “our current understanding of the laws of physics” predict will allow both of these (zero-point energy and alcubierre drives, respectively.)
The Alcubierre drive is an highly speculative idea that would require exotic matter with negative mass, which is not considered possible according to mainstream theories of matter such as the Standard Model and common extensions and variations.
Zero-point energy is a property of quantum systems. According to mainstream quantum mechanics, Zero-point energy can’t be withdrawn to perform physical work (without spending more energy to alter the underlaying physical system).
Among the perpetual motion/free energy crowd, Zero-point energy is a common buzzword, but these people are fringe scientists at the very best, and more commonly just crackpots or outright fraudsters.
The Alcubierre drive is an highly speculative idea that would require exotic matter with negative mass, which is not considered possible according to mainstream theories of matter such as the Standard Model and common extensions and variations.
Zero-point energy is a property of quantum systems. According to mainstream quantum mechanics, Zero-point energy can’t be withdrawn to perform physical work (without spending more energy to alter the underlaying physical system).
Not exactly. ZPE has measurable and, in some cases, exploitable effects. I’m not saying it’ll ever be practical to use it as a power source (except maybe for nanotech) but it can most definitely be used to perform work. For example, the Caismir effect. I note that Wikipedia (which I can’t edit from this library computer) makes this claim, but the citation provided does not; I’m not sure if it’s a simple mistake or someone backing up their citation-less claim with an impressive-sounding source.
Among the perpetual motion/free energy crowd, Zero-point energy is a common buzzword, but these people are fringe scientists at the very best, and more commonly just crackpots or outright fraudsters.
Well yeah, anyone claiming to have an actual working free energy machine is lying or crazy. Just like anyone claiming to have flown to Venus or programmed a GAI. Likewise, anyone claiming to have almost achieved such technology is probably conning you. But that doesn’t mean it’s physically impossible or that it will never be achieved.
Uhm, I’m not a physicist, but that’s a short paper (in letter to the editor format) regarding wormholes, which was published in 1988. The Alcubierre drive was proposed in 1994. Maybe somebody used an FLT drive to go back in time and write the paper :D
Anyway, while I don’t have the expertise to properly evaluate it, the paper looks somewhat handwavy:
… A seemingly plausible scenario entails quantum foam (finite probability amplitudes for a variety of topologies on length scales of order of the Planck-Wheeler length, (Gl’i/c )’I =1.3x10 cm): One can imagine an advanced civilization pulling a wormhole out of the quantum foam and enlarging it to classical size.
One can imagine the Moon being made of cheese, but that doesn’t make it physically plausible.
Not exactly. ZPE has measurable and, in some cases, exploitable effects. I’m not saying it’ll ever be practical to use it as a power source (except maybe for nanotech) but it can most definitely be used to perform work. For example, the Caismir effect. I note that Wikipedia (which I can’t edit from this library computer) makes this claim, but the citation provided does not; I’m not sure if it’s a simple mistake or someone backing up their citation-less claim with an impressive-sounding source.
AFAIK, there are multiple interpretations of the Caismir effect, but in most of them it is maintained that the phenomenon doesn’t violate conservation of energy and can’t be used to extract energy out of the quantum vacuum.
It can, in theory, be used to convert mass to energy directly. Bias quantum foam flux over an event horizon - and this need not be a gravitational event horizon, an optical one ought to work- and one side of the horizon will radiate hawking radiation, and the other will accumulate negative-mass particles. These should promptly annihilate with the first bit of matter they encounter, vanishing back into the foam and clearing the energy debit of the hawking radiation—effectively making the entire system a mass->energy conversion machine. Which does not violate CoE.
AKA: A theoretical way to make a mass-annihilation powered laser amplifier. No way to tell if this is good physics without actually building the setup, but the theory all seems sound.
Eh… Only.. Do not point that lab bench at me, please? The amplification ought to stop when the diamond turns into a plasma cloud..
t can, in theory, be used to convert mass to energy directly. Bias quantum foam flux over an event horizon—and this need not be a gravitational event horizon, an optical one ought to work- and one side of the horizon will radiate hawking radiation, and the other will accumulate negative-mass particles. These should promptly annihilate with the first bit of matter they encounter, vanishing back into the foam and clearing the energy debit of the hawking radiation—effectively making the entire system a mass->energy conversion machine. Which does not violate CoE.
I’m not sure I understand what you mean. Sure, assuming that Hawking radiation exists, you could use a black hole to convert mass to electromagnetic radiation (although the emission power would be exceptioally low for any macroscopic black hole).
That paper seems to be discussing lasers with non-linear optical media.
Anyway, AFAIK, in physics, the term ‘annihilation’ is typically used in the context of matter-antimatter reactions. Both matter and antimatter have positive mass.
The point is that if hawking radiation is a physical phenomenon, then any event horizon should produce it, not just a gravitational one - and the non-linear optical medium forms two optical event horizons, which the laser pulse bounces between, picking up more input from hawking radiation each turn around. Very clever, limit should be the optical properties altering when the diamond sublimes into a fine carbon plasma.
Might be an energy source that makes fusion look like cave men burning dried dung, might be a way to disprove the physicality of hawking radiation, might be a lab demonstration that it exists that cannot be engineered to the point of net energy gain (you have to fire quite powerful lasers into the diamond to set things off. Even if it amplifies the laser pulse a lot, no guarantee you can get enough electricity back out to net positive..) Currently, it is simply an interesting computer simulation.
I’m not sure I understand what you mean. Sure, assuming that Hawking radiation exists, you could use a black hole to convert mass to electromagnetic radiation (although the emission power would be exceptioally low for any macroscopic black hole).
Strictly speaking, you’re completely destroying the mass, but in the process gaining equivalent energy from nowhere. Of course, it balances out in the end.
Uhm, I’m not a physicist, but that’s a short paper (in letter to the editor format) regarding wormholes, which was published in 1988. The Alcubierre drive was proposed in 1994. Maybe somebody used an FLT drive to go back in time and write the paper :D
I understand (I can’t get past the paywall) that it describes how the Caismir effect creates an area that violates the positive energy condition, proving that it’s not a law of physics. This is only part of their more general point (which is time machines, which are, of course, equivalent to FTL drives in any case. Harder to build though.)
Anyway, while I don’t have the expertise to properly evaluate it, the paper looks somewhat handwavy:
The quote is handwavy. Then again, I don’t know much about quantum foam. OTOH, considering their paper concerns a mechanism for holding wormholes open, it’s not an unreasonable proposition (and it’s not the only way to get a wormhole, after all, merely a possible way.)
AFAIK, there are multiple interpretations of the Caismir effect, but in most of them it is maintained that the phenomenon doesn’t violate conservation of energy and can’t be used to extract energy out of the quantum vacuum.
The Caismir effect isn’t the only example. ZPE keeps liquid helium liquid and probably contributes (although it’s not the only contributor) to the expansion of the universe. Conservation of energy simply doesn’t apply on a quantum scale; it’s an emergent property of quantum mechanics, like, say, chairs.
I understand (I can’t get past the paywall) that it describes how the Caismir effect creates an area that violates the positive energy condition, proving that it’s not a law of physics. This is only part of their more general point (which is time machines, which are, of course, equivalent to FTL drives in any case. Harder to build though.)
IIUC, while the Caismir effect has been observed, it is still debated whether it is actually evidence for the vacuum zero-point energy, since the calculations aren’t completely developed and there are other proposed mechanisms.
Anyway, even in the vacuum zero-point energy explanation, the vacuum energy density in the geometrically constrained region is still positive, it is just smaller than the vacuum energy density in the unconstrained empty space. It’s only negative if you arbitrarily consider the energy density of empty space equal to zero.
Without a theory of quantum gravity, the speculative connection between vacuum energy density and gravitational effects (the cosmological constant) is highly debatable: typical attempts at calculating the cosmological constant from vacuum energy yield absurdely high values, while astronomical observations are consistent with a very small strictly positive cosmological constant.
Even if the vacuum energy density generates gravitational effects by influencing the cosmological constant, the lower than average energy densiity of a “Casimir vacuum” is probably not the same thing as the absolutely negative gravitational effect of exotic matter with negative mass, which, IIUC, is required by the Alcubierre drive (I don’t know about wormholes).
And in any case, the Casimir effect can’t be used to extract energy out of nothing: the Casimir forces are attractive or repulsive depending on the geometric configuration. If you use these forces to extract work, the system will eventually transition to a configuration where the attractive and repulsive effects are balanced. You have to pay back the same work you extracted to return the system to the original configuration. You can’t complete a cycle with a net gain.
This is the same problem of most of the proposed perpetual motion contraptions: you can extract work in an one-shot transition, but you have to perform the same work on the system (actually more, once you account for the inevitable thermodynamic losses) to return to the initial configuration.
Just one last technical nitpick, if you don’t mind: Zero-point energy is a property of all quantum systems, and this is essentially uncontroversial. The existence of a quantum vacuum with a positive zero-point energy is considered less certain, but relatively plausible in the mainstream models such as the Standard Model. The idea that is possible to extract work from the zero-point vacuum energy is generally considered wild fringe science speculation/crackpottery/fraud.
Zero-point energy is a property of all quantum systems, and this is essentially uncontroversial. The existence of a quantum vacuum with a positive zero-point energy is considered less certain, but relatively plausible in the mainstream models such as the Standard Model.
I was referring to using it as an energy source, as in the original comment.
The idea that is possible to extract work from the zero-point vacuum energy is generally considered wild fringe science speculation/crackpottery/fraud.
That seems a little strong. Still, it’s certainly impossible with current tech, and there’s no method anyone’s come up with to do it with a higher tech level.
That seems a little strong. Still, it’s certainly impossible with current tech, and there’s no method anyone’s come up with to do it with a higher tech level.
It’s not just matter of technology. Such a feat would most likely require a violation of the principle of conservation of energy. While there are still some unresolved issues with renormalization and general relativity, it is generally believed that conservation of energy applies to the universe. The discovery of a violation of conservation of energy (which would imply that the laws of physics are not invariant under time translation) would be a groundbreaking result.
Wrong link? The abstract (full text is paywalled) says:
It is argued that, if the laws of physics permit an advanced civilization to create and maintain a wormhole in space for interstellar travel, then that wormhole can be converted into a time machine with which causality might be violatable. Whether wormholes can be created and maintained entails deep, ill-understood issues about cosmic censorship, quantum gravity, and quantum field theory, including the question of whether field theory enforces an averaged version of the weak energy condition.
I don’t see any connection to Alcubierre drives. Classic Kip Thorne, though.
Without even pretending to be anything other than an amateur layman in such questions, I found this on arxiv, quote:
We show that for particular choices of the shaping function, the Alcubierre metric in the context
of conformal gravity does not violate the weak energy condition, as was the case of the original
solution. In particular, the resulting warp drive does not require the use of exotic matter.
Therefore, if conformal gravity is a correct extension of general relativity, super-luminal motion
via an Alcubierre metric might be a realistic solution, thus allowing faster-than-light interstellar
travel.
(Lastly, if you’re wondering why I’m replying to you a lot, it’s just because you are a prolific commenter with whom I occasionally disagree.)
Wrong link? The abstract (full text is paywalled) says:
It is argued that, if the laws of physics permit an advanced civilization to create and maintain a wormhole in space for interstellar travel, then that wormhole can be converted into a time machine with which causality might be violatable. Whether wormholes can be created and maintained entails deep, ill-understood issues about cosmic censorship, quantum gravity, and quantum field theory, including the question of whether field theory enforces an averaged version of the weak energy condition.
I don’t see any connection to Alcubierre drives. Classic Kip Thorne, though.
looks embarrassed
I just grabbed a citation from someone talking about how the Caismir effect can be used to create negative energy (in the context of stabilizing wormholes.) I should probably have checked that, I would have found it wasn’t actually in the abstract.
Nevertheless! My point was that negative energy is pretty obviously physically possible, since it’s what predicts the Caismir effect working. (There has been some attempt to claim the CE is actually predicted by some other theories, but that’s not widely accepted.)
I find it amusing that there are actual mechanisms that “our current understanding of the laws of physics” predict will allow both of these
From what I understand it may be closer to say “doesn’t rule out” rather than “predict will allow”. Even that much of a possibility is somewhat mind-blowing.
It’s distance and time which are more malleable; if light travels through a vacuum and arrives in x time, the arrival point is defined as being x distance away from the departure point of the light when it arrives. The Alcubierre drive would (given a couple of facts not in evidence) allow you to change the distance. Light emitted from you at the time of departure would still beat you to the destination.
It’s distance and time which are more malleable; if light travels through a vacuum and arrives in x time, the arrival point is defined as being x distance away from the departure point of the light when it arrives.
Sure, so long as the space being traversed remains consistent. Which it doesn’t (always) given General Relativity. Hence Alcubierre drives.
The Alcubierre drive would (given a couple of facts not in evidence) allow you to change the distance. Light emitted from you at the time of departure would still beat you to the destination.
No, it wouldn’t. The drive in question is described thus:
The Alcubierre drive or Alcubierre metric (See: Metric tensor) is a speculative idea based on a solution of Einstein’s field equations as proposed by Miguel Alcubierre, by which a spacecraft could achieve faster-than-light travel if negative mass existed.
Notice the link there to faster than light travel. That title is a literal description.
For emphasis: This is General and not Special Relativity.
No, it wouldn’t. The drive in question is described thus:
Have you finished reading the paragraph the sentence you quoted comes from? And section “Alcubierre metric” from that article, in particular the fourth sentence?
Have you finished reading the paragraph the sentence you quoted comes from? And section “Alcubierre metric” from that article, in particular the fourth sentence?
Of course I have finished reading the paragraph. As soon as I encountered the notion. Because math that allows what is for most intents and purposes a warp drive within general relativity is freaking awesome. Even if it relies on pesky things like negative mass and ridiculous amounts of energy. Oh, and would utterly obliterate the destination. Still damn cool.
In answer to the presumed (and I hope I’m not misrepresenting you here) rhetorical intent of “The first paragraph demonstrates that your claim is wrong” I would (unsurprisingly) disagree.
The paragraph in question is:
Rather than exceeding the speed of light within its local frame of reference, a spacecraft would traverse distances by contracting space in front of it and expanding space behind it, resulting in effective faster-than-light travel.
And, assuming I can count periods correctly, the fourth sentence in the passage you refer to is:
This method of propulsion does not involve objects in motion at speeds faster than light with respect to the contents of the warp bubble; that is, a light beam within the warp bubble would still always move faster than the ship.
Both of these are precisely correct. And the claim:
Light emitted from you at the time of departure would still beat you to the destination.
Is false. Light continues to be faster than you locally. That is, within the bubble. And the bubble goes faster than the speed of light. Light not inside such a bubble goes at the speed of light. You can get to a destination before that light does. Which is the entire point of a Faster Than Light drive.
I was assuming Decius wasn’t assuming the light doesn’t go through the bubble.
Rather than not assuming that it doesn’t he would need to be actively assuming that it does, or he would have to make a different, more specific claim. And that more specific claim (that applies to light that travels in the the bubble) would not have supported the point Decius was using his claim to make in the context.
What happens when the bubble overtakes light? Per my understanding, virtually all of the light emitted within the bubble in the direction of travel ends up in one front at the front of the bubble, along with all of the light overtaken. All of the matter overtaken accumulates along the edge of the bubble where space warps at their velocity, after experiencing some effects of misunderstood severity when space warps around them (does interstellar atomic H-1 fuse into He-2 when the distance between atoms falls inside the region where the weak force dominates? What happens when a solid chunk of mostly Pb-206 has the distance between multiple atoms is reduced to below the range of the weak force?). What happens when the bubble overtakes the gravity effect of the matter within the bubble?
‘Obliterates the destination’ might be a little bit of an understatement.
after experiencing some effects of misunderstood severity
Do you mean ‘poorly understood’ rather than misunderstood? When talking about using negative mass and enormous energy to warp space itself to travel faster than freaking light. Most with even the most rudimentary grasp would see that the effects are inconceivably severe in relation to such a small object and bubble. Being unable to conceive of the scope or currently not knowing in detail is a very different state of knowledge to misunderstanding. At least, it is difference in epistemic states that seems rather important to me. (A wrong map leads you to walk into quicksand. An known to be incomplete map leads you to watch where you are walking or google up a better one.)
What happens when the bubble overtakes light?
The same thing that happens when I overtake a car. I go around. What I definitely do not do is go around saying “Um, the current definition of speed prohibits FTL motion” because whenever I am racing light I must handicap myself and take the light I am racing along with me for a ride.
I meant “Everything that we currently understand about the phenomenon is almost certainly completely wrong.” That’s after accounting for what we know we don’t know.
How, exactly, do you “go around” a wavefront which is propagating out from you in all directions? I’m still hazy on what the effects of autogravitation would be; once you overtake the light/gravational effect from you, are you accelerated towards your prior location proportionally to your mass and the inverse of the cube of distance from yourself?
Of course, if the travel is at some speed slower than that of light, no self-interaction effects are required. The warp drive doesn’t beat the speed record, it beats the distance record.
Describing a method of travel as “faster than x” when x departs at the same time and arrives before you is the opposite of plain language. Distance and elapsed time between events is already agreed to be not constant even between colocated observers. That is an effect of postulating that light propagates at the same speed for all observers.
If you leave Earth in a spaceship using an alcubierre drive and simultanously have someone emit a radio signal from Mars, reach alpha centauri in half an hour, then observe that same radio signal arrive at alpha centauri after approximately six years of lounging around on an alien planet, then you have beaten that light to your destination. You have traveled faster than light.
Your other questions, about your own gravitational force, I assume need to be answered by an actual expert on general relativity.
What do you mean by “simultanously”? You’ve used it to refer to events which do not occur at the same place.
I think that you’ve shown that the distance between your departure point and Mars is six light years; you’ve done that by moving space around such that the point you departed from is in the vicinity of Alpha Centauri.
Space and time aren’t defined to be static in the way the math I understand requires it to be.
What do you mean by “simultanously”? You’ve used it to refer to events which do not occur at the same place.
The details are not significant. Simultaneously in the rest frame of earth. Whatever. Or send a timing signal from Mars to Earth at the same time as the radio message is emitted toward Alpha Centauri, then leave Earth when you receive the timing signal. You’ll still arrive before the radio message, even though you’ve given it a head start.
I think that you’ve shown that the distance between your departure point and Mars is six light years;
The distance between Earth and Mars is 225 million km on average, or 12.5 light minutes.
If you like, you can send your radio message from the same location as your departure point. First emit a (directional) radio signal from earth toward Alpha Centauri. Then depart in your spaceship, just making sure not to collide with the radio signal on your way there (go a different way, say by taking a pit stop at Vega). You’ll still get there before the light signal.
you’ve done that by moving space around such that the point you departed from is in the vicinity of Alpha Centauri.
In a sense, yes, that is exactly what an alcubierre drive is meant to do. The trajectory that starts at Earth, enters the bubble, sits there a while, exits the bubble and arrives at Alpha Centauri travels “locally” less than six light years. The bubble train might be analogised to a wormhole in that it establishes a shorter path between two otherwise distance places.
But unlike a wormhole, the Alcubierre drive doesn’t require you set up the path and destination in advance (unless Krasnikov is right, and there aren’t any tachyons), and it’s an effect confined to the vicinity—in space and time—of the ship using it. So in all meaningful senses it can reasonably be described as a faster than light drive, as opposed to a bridge, which is what a wormhole is.
That ‘directional radio signal’ is taking a longer path, as noted by the fact that a different directional radio signal (one that went with the traveler) would get there first.
Are you using a Euclidean definition of speed? Part of the insanity is that the payload, inside the bubble, can be at rest relative to the origin and/or destination, despite the distance changing.
Sanity check: before, during, and after the trip, shine a laser continuously ‘forward’, toward the destination. Turn off the bubble well short of arrivial. What pattern of red shifting should the destination expect to see?
Part of the insanity is that the payload, inside the bubble, can be at rest relative to the origin and/or destination, despite the distance changing.
I’m sure it only looks like insanity to people who haven’t studied general relativity.
The point is that an Alcubierre drive lets you get from here to Alpha Centauri (which I now discover is actually 4.4 light years away, since I finally decided to look it up just then) in less than 4.4 years. Whether it does that by temporarily making the distance shorter along a certain path is mostly irrelevant for the purpose of classifying it as a particular kind of starship drive.
The point which started the discussion is that you don’t get to look back and see yourself leave. (probably; I’m not certain how light behaves when there is more than one ‘straight line’ path, of different lengths, to the destination; that seems like is could happen if you took a dogleg around the most direct path.
The radio signal and the ship leave from points that are near each other in the space-time metric. In other words, simultaneous from a reference frame in which they are physically close.
You’ve moved space around, but only for a small local (space-time wise) area; you haven’t permanently moved the two stars closer together.
If the radio signal ever touches the bubble, it arrives before/with the non-light content of the bubble.
You’ve moved space around, but only for a small local (space-time wise) area; you haven’t permanently moved the two stars closer together.
The point of departure is now six years away from points that it was previously nearby.
Imagine a strip of topology rubber running the length of the trip; you start next to one end, but instead of moving along the strip, you compress it in front of you and stretch it behind you.
And in any case, you’ve moved a ‘cylinder’ of spacetime roughly 6 light years long. Just because you’ve expanded just as much as you’ve compacted doesn’t mean you’ve expanded the ‘same’ spacetime that you’ve compacted.
So go around the radio. Or use a laser beam or high energy particle beam (near-c, not c, obviously) if you’re worried about diffraction and aiming or refraction of your bubble.
When you get there and turn off the warp drive, space is now flat. (We’ll assuming no one else is making the journey recently / soon / nearby / whatever.) You’re saying the original point of departure is now near where you ended up. I say that’s a distinction that doesn’t matter, and all that’s relevant is that you were near one star, now you’re near another, and at no time were those stars near each other. And you got there faster than a photon / high energy particle / whatever could have, via the normal route.
What experimental result do you anticipate, that distinguishes between the “original departure point” having moved, versus my assertion that all points in space are distinguishable only by things like what matter / energy is occupying them (and the curvature that results)?
A suffienctly flexible braided rope, fixed to Earth and some point beyond the destination, with a splice in it at the point of departure: the splice will end up at the point of arrival, but the number of braids on either side will remain constant and no tension will be noted at either end.
A lack of time-dialation effects on the transported cargo-an atomic clock that made the round-trip would remain synced with one that didn’t, showing that it hadn’t moved.
I’m saying that the path you took is shorter than the naive one. There is no meaningful discussion of instant distance between two points/objects in general relativity; that’s a holdover from Euclidean geometry with time-variable additions.
Finally, the math.
How, exactly, do you “go around” a wavefront which is propagating out from you in all directions?
I don’t and didn’t say that. It is plausible or even likely that you are not being deliberately disingenuous here or in your recent comments but the effect on my expectation of future replies being sequitur is the same regardless of the cause.
I refer to either my previous comments or to the relevant wikipedia article for any future reference.
Er, I think you were substantially less clear than you seem to think you were.
Let it be known henceforth that for all X (where X includes ‘wavefronts that are propagating out from you in all directions’) when I do not mention X and where a claim of X by myself is actively ruled out by multiplecomments of mine and would be a trivial contradiction of basic physics (well, comparatively basic physics) then I do not claim X.
The “That’s not a straw man, you just aren’t clear” social move is rather flexible, particularly when used in response to even moderately subtle goalpost-shifting. (ie. By default it will be supported and assumed to be pro-social by all those who are not interested or have not been following the context.) Nevertheless, I consider it safe to say that those who read the context and still believe that this comment can be legitimately interpreted as a valid reply to the previous comments is sufficiently poor at keeping concepts distinct as to be way out of their depth when trying to comprehend the implications of novel, probably counterfactual physical phenomena such as Alcubierre drives.
My comment was meant to be a data point that IMO Decius’ misinterpretation of you is not as unjustifiable as you think it is, and I would rather see less indignance if possible, as it makes reading the recent comments section much less fun. I thought this data point would be useful as it is coming from someone not actually involved in the conversation at hand and hence with presumably less motive for social maneuvering. If it gets voted below −2 then I would assume that I’m in a minority that’s not good at understanding your posts.
For the record, the exact sequence of statements that prompted me to say that the issue was lack of clarity as opposed to something else:
What happens when the bubble overtakes light?
The same thing that happens when I overtake a car. I go around.
How, exactly, do you “go around” a wavefront which is propagating out from you in all directions?
I don’t and didn’t say that.
The reasonable interpretation of your “I go around” statement isn’t the one that occurred to me first. Should Decius have spent more than 20 seconds puzzling out a model for you that doesn’t mean something bizarre by that statement? Possibly. Sometimes it’s faster just to ask what the other party meant (Decius could have done a better job of this). Should you have spent more than 20 seconds considering whether that statement had obvious misinterpretations? Possibly. It’s difficult to predict how people will misunderstand one’s own statements.
I thought it was clear that he was saying that he was overtaking something which was traveling in the same direction and going faster than him. I probably read a little bit too much into it, thinking that he was intending to win by driving the bubble in a ‘path’ that went ‘around’ the ‘straight line’ between the start and finish, not distorting any of the space through which the ‘direct’ radiation was traveling. (quotes because the terms aren’t strictly meaningful).
In other words, he was ‘going around’ the light he was beating. I was pointing out that he didn’t just have to go around a ray of a photon, he had to go around a wave expanding in all directions, and that the ‘region’ of ‘compressed space’ would also help that wave arrive at the destination ‘sooner’, regardless of the method used to ‘go around’ it.
I understand recent formulations are better in this regard.
I assume you refer just to the ridiculous amount of energy required being a half dozen orders of magnitude less ridiculous than first calculated? Not that there are actually formulations that don’t require negative mass? or don’t obliterate the destination?
Oh, yeah. They’re smaller, but they still need negative energy and they still obliterate anything directly in front of them—although that’s hardly an impossible drawback.
they still obliterate anything directly in front of them—although that’s hardly an impossible drawback.
Definitely. Especially when it comes to one of the first uses people would consider putting this (or most other) technology toward. No need for a payload!
Travel, on the other hand, is a much looser term. Alcubierre drives, in theory, travel faster than their speed woud suggest by distorting space. Until recently they were merely interesting mathematical curiosities, but recently new variations that allow them to be constructed by a non-godlike tech level have been discovered.
Travel, on the other hand, is a much looser term. Alcubierre drives, in theory, travel faster than their speed via distorting space. Until recently they were merely interesting mathematical curiosities, but recently new variations that allow them to be constructed by a non-godlike tech level have been discovered.
Travel, on the other hand, is a much looser term. Alcubierre drives, in theory, travel faster than their speed would suggest by distorting space. Until recently they were merely interesting mathematical curiosities, but recently new variations that allow them to be constructed by a non-godlike tech level have been discovered.
I find it amusing that there are actual mechanisms that “our current understanding of the laws of physics” predict will allow both of these (zero-point energy and alcubierre drives, respectively.)
The Alcubierre drive is an highly speculative idea that would require exotic matter with negative mass, which is not considered possible according to mainstream theories of matter such as the Standard Model and common extensions and variations.
Zero-point energy is a property of quantum systems. According to mainstream quantum mechanics, Zero-point energy can’t be withdrawn to perform physical work (without spending more energy to alter the underlaying physical system).
Among the perpetual motion/free energy crowd, Zero-point energy is a common buzzword, but these people are fringe scientists at the very best, and more commonly just crackpots or outright fraudsters.
Ah … no.
Not exactly. ZPE has measurable and, in some cases, exploitable effects. I’m not saying it’ll ever be practical to use it as a power source (except maybe for nanotech) but it can most definitely be used to perform work. For example, the Caismir effect. I note that Wikipedia (which I can’t edit from this library computer) makes this claim, but the citation provided does not; I’m not sure if it’s a simple mistake or someone backing up their citation-less claim with an impressive-sounding source.
Well yeah, anyone claiming to have an actual working free energy machine is lying or crazy. Just like anyone claiming to have flown to Venus or programmed a GAI. Likewise, anyone claiming to have almost achieved such technology is probably conning you. But that doesn’t mean it’s physically impossible or that it will never be achieved.
Uhm, I’m not a physicist, but that’s a short paper (in letter to the editor format) regarding wormholes, which was published in 1988. The Alcubierre drive was proposed in 1994. Maybe somebody used an FLT drive to go back in time and write the paper :D
Anyway, while I don’t have the expertise to properly evaluate it, the paper looks somewhat handwavy:
One can imagine the Moon being made of cheese, but that doesn’t make it physically plausible.
AFAIK, there are multiple interpretations of the Caismir effect, but in most of them it is maintained that the phenomenon doesn’t violate conservation of energy and can’t be used to extract energy out of the quantum vacuum.
It can, in theory, be used to convert mass to energy directly. Bias quantum foam flux over an event horizon - and this need not be a gravitational event horizon, an optical one ought to work- and one side of the horizon will radiate hawking radiation, and the other will accumulate negative-mass particles. These should promptly annihilate with the first bit of matter they encounter, vanishing back into the foam and clearing the energy debit of the hawking radiation—effectively making the entire system a mass->energy conversion machine. Which does not violate CoE.
One second.. http://arxiv.org/pdf/1209.4993v1.pdf
AKA: A theoretical way to make a mass-annihilation powered laser amplifier. No way to tell if this is good physics without actually building the setup, but the theory all seems sound.
Eh… Only.. Do not point that lab bench at me, please? The amplification ought to stop when the diamond turns into a plasma cloud..
I’m not sure I understand what you mean. Sure, assuming that Hawking radiation exists, you could use a black hole to convert mass to electromagnetic radiation (although the emission power would be exceptioally low for any macroscopic black hole).
That paper seems to be discussing lasers with non-linear optical media.
Anyway, AFAIK, in physics, the term ‘annihilation’ is typically used in the context of matter-antimatter reactions. Both matter and antimatter have positive mass.
The point is that if hawking radiation is a physical phenomenon, then any event horizon should produce it, not just a gravitational one - and the non-linear optical medium forms two optical event horizons, which the laser pulse bounces between, picking up more input from hawking radiation each turn around. Very clever, limit should be the optical properties altering when the diamond sublimes into a fine carbon plasma.
Might be an energy source that makes fusion look like cave men burning dried dung, might be a way to disprove the physicality of hawking radiation, might be a lab demonstration that it exists that cannot be engineered to the point of net energy gain (you have to fire quite powerful lasers into the diamond to set things off. Even if it amplifies the laser pulse a lot, no guarantee you can get enough electricity back out to net positive..) Currently, it is simply an interesting computer simulation.
Strictly speaking, you’re completely destroying the mass, but in the process gaining equivalent energy from nowhere. Of course, it balances out in the end.
I understand (I can’t get past the paywall) that it describes how the Caismir effect creates an area that violates the positive energy condition, proving that it’s not a law of physics. This is only part of their more general point (which is time machines, which are, of course, equivalent to FTL drives in any case. Harder to build though.)
The quote is handwavy. Then again, I don’t know much about quantum foam. OTOH, considering their paper concerns a mechanism for holding wormholes open, it’s not an unreasonable proposition (and it’s not the only way to get a wormhole, after all, merely a possible way.)
The Caismir effect isn’t the only example. ZPE keeps liquid helium liquid and probably contributes (although it’s not the only contributor) to the expansion of the universe. Conservation of energy simply doesn’t apply on a quantum scale; it’s an emergent property of quantum mechanics, like, say, chairs.
IIUC, while the Caismir effect has been observed, it is still debated whether it is actually evidence for the vacuum zero-point energy, since the calculations aren’t completely developed and there are other proposed mechanisms.
Anyway, even in the vacuum zero-point energy explanation, the vacuum energy density in the geometrically constrained region is still positive, it is just smaller than the vacuum energy density in the unconstrained empty space. It’s only negative if you arbitrarily consider the energy density of empty space equal to zero.
Without a theory of quantum gravity, the speculative connection between vacuum energy density and gravitational effects (the cosmological constant) is highly debatable: typical attempts at calculating the cosmological constant from vacuum energy yield absurdely high values, while astronomical observations are consistent with a very small strictly positive cosmological constant.
Even if the vacuum energy density generates gravitational effects by influencing the cosmological constant, the lower than average energy densiity of a “Casimir vacuum” is probably not the same thing as the absolutely negative gravitational effect of exotic matter with negative mass, which, IIUC, is required by the Alcubierre drive (I don’t know about wormholes).
BTW: I’ve found this post on Physics Forums
EDIT:
And in any case, the Casimir effect can’t be used to extract energy out of nothing: the Casimir forces are attractive or repulsive depending on the geometric configuration. If you use these forces to extract work, the system will eventually transition to a configuration where the attractive and repulsive effects are balanced. You have to pay back the same work you extracted to return the system to the original configuration. You can’t complete a cycle with a net gain.
This is the same problem of most of the proposed perpetual motion contraptions: you can extract work in an one-shot transition, but you have to perform the same work on the system (actually more, once you account for the inevitable thermodynamic losses) to return to the initial configuration.
You know, you’re right. ZPE is far less certain/accepted than Alcubierre drives.
I’m going to go on being amused just the same, though. Those really were unfortununate examples to pick :)
Thanks ;)
Just one last technical nitpick, if you don’t mind: Zero-point energy is a property of all quantum systems, and this is essentially uncontroversial. The existence of a quantum vacuum with a positive zero-point energy is considered less certain, but relatively plausible in the mainstream models such as the Standard Model. The idea that is possible to extract work from the zero-point vacuum energy is generally considered wild fringe science speculation/crackpottery/fraud.
I was referring to using it as an energy source, as in the original comment.
That seems a little strong. Still, it’s certainly impossible with current tech, and there’s no method anyone’s come up with to do it with a higher tech level.
It’s not just matter of technology. Such a feat would most likely require a violation of the principle of conservation of energy. While there are still some unresolved issues with renormalization and general relativity, it is generally believed that conservation of energy applies to the universe. The discovery of a violation of conservation of energy (which would imply that the laws of physics are not invariant under time translation) would be a groundbreaking result.
Wrong link? The abstract (full text is paywalled) says:
I don’t see any connection to Alcubierre drives. Classic Kip Thorne, though.
Without even pretending to be anything other than an amateur layman in such questions, I found this on arxiv, quote:
(Lastly, if you’re wondering why I’m replying to you a lot, it’s just because you are a prolific commenter with whom I occasionally disagree.)
looks embarrassed
I just grabbed a citation from someone talking about how the Caismir effect can be used to create negative energy (in the context of stabilizing wormholes.) I should probably have checked that, I would have found it wasn’t actually in the abstract.
Nevertheless! My point was that negative energy is pretty obviously physically possible, since it’s what predicts the Caismir effect working. (There has been some attempt to claim the CE is actually predicted by some other theories, but that’s not widely accepted.)
From what I understand it may be closer to say “doesn’t rule out” rather than “predict will allow”. Even that much of a possibility is somewhat mind-blowing.
Um, the current definition of speed prohibits FTL motion.
Only locally. And ‘local’ is rather malleable (which is the principle alcubierre drives theoretically rely on).
It’s distance and time which are more malleable; if light travels through a vacuum and arrives in x time, the arrival point is defined as being x distance away from the departure point of the light when it arrives. The Alcubierre drive would (given a couple of facts not in evidence) allow you to change the distance. Light emitted from you at the time of departure would still beat you to the destination.
Sure, so long as the space being traversed remains consistent. Which it doesn’t (always) given General Relativity. Hence Alcubierre drives.
No, it wouldn’t. The drive in question is described thus:
Notice the link there to faster than light travel. That title is a literal description.
For emphasis: This is General and not Special Relativity.
Have you finished reading the paragraph the sentence you quoted comes from? And section “Alcubierre metric” from that article, in particular the fourth sentence?
Of course I have finished reading the paragraph. As soon as I encountered the notion. Because math that allows what is for most intents and purposes a warp drive within general relativity is freaking awesome. Even if it relies on pesky things like negative mass and ridiculous amounts of energy. Oh, and would utterly obliterate the destination. Still damn cool.
In answer to the presumed (and I hope I’m not misrepresenting you here) rhetorical intent of “The first paragraph demonstrates that your claim is wrong” I would (unsurprisingly) disagree.
The paragraph in question is:
And, assuming I can count periods correctly, the fourth sentence in the passage you refer to is:
Both of these are precisely correct. And the claim:
Is false. Light continues to be faster than you locally. That is, within the bubble. And the bubble goes faster than the speed of light. Light not inside such a bubble goes at the speed of light. You can get to a destination before that light does. Which is the entire point of a Faster Than Light drive.
I was assuming Decius wasn’t assuming the light doesn’t go through the bubble.
Rather than not assuming that it doesn’t he would need to be actively assuming that it does, or he would have to make a different, more specific claim. And that more specific claim (that applies to light that travels in the the bubble) would not have supported the point Decius was using his claim to make in the context.
What happens when the bubble overtakes light? Per my understanding, virtually all of the light emitted within the bubble in the direction of travel ends up in one front at the front of the bubble, along with all of the light overtaken. All of the matter overtaken accumulates along the edge of the bubble where space warps at their velocity, after experiencing some effects of misunderstood severity when space warps around them (does interstellar atomic H-1 fuse into He-2 when the distance between atoms falls inside the region where the weak force dominates? What happens when a solid chunk of mostly Pb-206 has the distance between multiple atoms is reduced to below the range of the weak force?). What happens when the bubble overtakes the gravity effect of the matter within the bubble?
‘Obliterates the destination’ might be a little bit of an understatement.
Do you mean ‘poorly understood’ rather than misunderstood? When talking about using negative mass and enormous energy to warp space itself to travel faster than freaking light. Most with even the most rudimentary grasp would see that the effects are inconceivably severe in relation to such a small object and bubble. Being unable to conceive of the scope or currently not knowing in detail is a very different state of knowledge to misunderstanding. At least, it is difference in epistemic states that seems rather important to me. (A wrong map leads you to walk into quicksand. An known to be incomplete map leads you to watch where you are walking or google up a better one.)
The same thing that happens when I overtake a car. I go around. What I definitely do not do is go around saying “Um, the current definition of speed prohibits FTL motion” because whenever I am racing light I must handicap myself and take the light I am racing along with me for a ride.
I meant “Everything that we currently understand about the phenomenon is almost certainly completely wrong.” That’s after accounting for what we know we don’t know.
How, exactly, do you “go around” a wavefront which is propagating out from you in all directions? I’m still hazy on what the effects of autogravitation would be; once you overtake the light/gravational effect from you, are you accelerated towards your prior location proportionally to your mass and the inverse of the cube of distance from yourself?
Of course, if the travel is at some speed slower than that of light, no self-interaction effects are required. The warp drive doesn’t beat the speed record, it beats the distance record.
Describing a method of travel as “faster than x” when x departs at the same time and arrives before you is the opposite of plain language. Distance and elapsed time between events is already agreed to be not constant even between colocated observers. That is an effect of postulating that light propagates at the same speed for all observers.
If you leave Earth in a spaceship using an alcubierre drive and simultanously have someone emit a radio signal from Mars, reach alpha centauri in half an hour, then observe that same radio signal arrive at alpha centauri after approximately six years of lounging around on an alien planet, then you have beaten that light to your destination. You have traveled faster than light.
Your other questions, about your own gravitational force, I assume need to be answered by an actual expert on general relativity.
What do you mean by “simultanously”? You’ve used it to refer to events which do not occur at the same place.
I think that you’ve shown that the distance between your departure point and Mars is six light years; you’ve done that by moving space around such that the point you departed from is in the vicinity of Alpha Centauri.
Space and time aren’t defined to be static in the way the math I understand requires it to be.
The details are not significant. Simultaneously in the rest frame of earth. Whatever. Or send a timing signal from Mars to Earth at the same time as the radio message is emitted toward Alpha Centauri, then leave Earth when you receive the timing signal. You’ll still arrive before the radio message, even though you’ve given it a head start.
The distance between Earth and Mars is 225 million km on average, or 12.5 light minutes.
If you like, you can send your radio message from the same location as your departure point. First emit a (directional) radio signal from earth toward Alpha Centauri. Then depart in your spaceship, just making sure not to collide with the radio signal on your way there (go a different way, say by taking a pit stop at Vega). You’ll still get there before the light signal.
In a sense, yes, that is exactly what an alcubierre drive is meant to do. The trajectory that starts at Earth, enters the bubble, sits there a while, exits the bubble and arrives at Alpha Centauri travels “locally” less than six light years. The bubble train might be analogised to a wormhole in that it establishes a shorter path between two otherwise distance places.
But unlike a wormhole, the Alcubierre drive doesn’t require you set up the path and destination in advance (unless Krasnikov is right, and there aren’t any tachyons), and it’s an effect confined to the vicinity—in space and time—of the ship using it. So in all meaningful senses it can reasonably be described as a faster than light drive, as opposed to a bridge, which is what a wormhole is.
That ‘directional radio signal’ is taking a longer path, as noted by the fact that a different directional radio signal (one that went with the traveler) would get there first.
Are you using a Euclidean definition of speed? Part of the insanity is that the payload, inside the bubble, can be at rest relative to the origin and/or destination, despite the distance changing.
Sanity check: before, during, and after the trip, shine a laser continuously ‘forward’, toward the destination. Turn off the bubble well short of arrivial. What pattern of red shifting should the destination expect to see?
I’m sure it only looks like insanity to people who haven’t studied general relativity.
The point is that an Alcubierre drive lets you get from here to Alpha Centauri (which I now discover is actually 4.4 light years away, since I finally decided to look it up just then) in less than 4.4 years. Whether it does that by temporarily making the distance shorter along a certain path is mostly irrelevant for the purpose of classifying it as a particular kind of starship drive.
The point which started the discussion is that you don’t get to look back and see yourself leave. (probably; I’m not certain how light behaves when there is more than one ‘straight line’ path, of different lengths, to the destination; that seems like is could happen if you took a dogleg around the most direct path.
The radio signal and the ship leave from points that are near each other in the space-time metric. In other words, simultaneous from a reference frame in which they are physically close.
You’ve moved space around, but only for a small local (space-time wise) area; you haven’t permanently moved the two stars closer together.
If the radio signal ever touches the bubble, it arrives before/with the non-light content of the bubble.
The point of departure is now six years away from points that it was previously nearby.
Imagine a strip of topology rubber running the length of the trip; you start next to one end, but instead of moving along the strip, you compress it in front of you and stretch it behind you.
And in any case, you’ve moved a ‘cylinder’ of spacetime roughly 6 light years long. Just because you’ve expanded just as much as you’ve compacted doesn’t mean you’ve expanded the ‘same’ spacetime that you’ve compacted.
So go around the radio. Or use a laser beam or high energy particle beam (near-c, not c, obviously) if you’re worried about diffraction and aiming or refraction of your bubble.
When you get there and turn off the warp drive, space is now flat. (We’ll assuming no one else is making the journey recently / soon / nearby / whatever.) You’re saying the original point of departure is now near where you ended up. I say that’s a distinction that doesn’t matter, and all that’s relevant is that you were near one star, now you’re near another, and at no time were those stars near each other. And you got there faster than a photon / high energy particle / whatever could have, via the normal route.
What experimental result do you anticipate, that distinguishes between the “original departure point” having moved, versus my assertion that all points in space are distinguishable only by things like what matter / energy is occupying them (and the curvature that results)?
A suffienctly flexible braided rope, fixed to Earth and some point beyond the destination, with a splice in it at the point of departure: the splice will end up at the point of arrival, but the number of braids on either side will remain constant and no tension will be noted at either end.
A lack of time-dialation effects on the transported cargo-an atomic clock that made the round-trip would remain synced with one that didn’t, showing that it hadn’t moved.
I’m saying that the path you took is shorter than the naive one. There is no meaningful discussion of instant distance between two points/objects in general relativity; that’s a holdover from Euclidean geometry with time-variable additions. Finally, the math.
I don’t and didn’t say that. It is plausible or even likely that you are not being deliberately disingenuous here or in your recent comments but the effect on my expectation of future replies being sequitur is the same regardless of the cause.
I refer to either my previous comments or to the relevant wikipedia article for any future reference.
Er, I think you were substantially less clear than you seem to think you were.
Let it be known henceforth that for all X (where X includes ‘wavefronts that are propagating out from you in all directions’) when I do not mention X and where a claim of X by myself is actively ruled out by multiple comments of mine and would be a trivial contradiction of basic physics (well, comparatively basic physics) then I do not claim X.
The “That’s not a straw man, you just aren’t clear” social move is rather flexible, particularly when used in response to even moderately subtle goalpost-shifting. (ie. By default it will be supported and assumed to be pro-social by all those who are not interested or have not been following the context.) Nevertheless, I consider it safe to say that those who read the context and still believe that this comment can be legitimately interpreted as a valid reply to the previous comments is sufficiently poor at keeping concepts distinct as to be way out of their depth when trying to comprehend the implications of novel, probably counterfactual physical phenomena such as Alcubierre drives.
My comment was meant to be a data point that IMO Decius’ misinterpretation of you is not as unjustifiable as you think it is, and I would rather see less indignance if possible, as it makes reading the recent comments section much less fun. I thought this data point would be useful as it is coming from someone not actually involved in the conversation at hand and hence with presumably less motive for social maneuvering. If it gets voted below −2 then I would assume that I’m in a minority that’s not good at understanding your posts.
For the record, the exact sequence of statements that prompted me to say that the issue was lack of clarity as opposed to something else:
The reasonable interpretation of your “I go around” statement isn’t the one that occurred to me first. Should Decius have spent more than 20 seconds puzzling out a model for you that doesn’t mean something bizarre by that statement? Possibly. Sometimes it’s faster just to ask what the other party meant (Decius could have done a better job of this). Should you have spent more than 20 seconds considering whether that statement had obvious misinterpretations? Possibly. It’s difficult to predict how people will misunderstand one’s own statements.
I thought it was clear that he was saying that he was overtaking something which was traveling in the same direction and going faster than him. I probably read a little bit too much into it, thinking that he was intending to win by driving the bubble in a ‘path’ that went ‘around’ the ‘straight line’ between the start and finish, not distorting any of the space through which the ‘direct’ radiation was traveling. (quotes because the terms aren’t strictly meaningful).
In other words, he was ‘going around’ the light he was beating. I was pointing out that he didn’t just have to go around a ray of a photon, he had to go around a wave expanding in all directions, and that the ‘region’ of ‘compressed space’ would also help that wave arrive at the destination ‘sooner’, regardless of the method used to ‘go around’ it.
I understand recent formulations are better in this regard.
I assume you refer just to the ridiculous amount of energy required being a half dozen orders of magnitude less ridiculous than first calculated? Not that there are actually formulations that don’t require negative mass? or don’t obliterate the destination?
Oh, yeah. They’re smaller, but they still need negative energy and they still obliterate anything directly in front of them—although that’s hardly an impossible drawback.
Definitely. Especially when it comes to one of the first uses people would consider putting this (or most other) technology toward. No need for a payload!
Travel, on the other hand, is a much looser term. Alcubierre drives, in theory, travel faster than their speed woud suggest by distorting space. Until recently they were merely interesting mathematical curiosities, but recently new variations that allow them to be constructed by a non-godlike tech level have been discovered.
[EDIT: whoops, double-post.]
Travel, on the other hand, is a much looser term. Alcubierre drives, in theory, travel faster than their speed via distorting space. Until recently they were merely interesting mathematical curiosities, but recently new variations that allow them to be constructed by a non-godlike tech level have been discovered.
[EDIT: whoops, double-post.]
Travel, on the other hand, is a much looser term. Alcubierre drives, in theory, travel faster than their speed would suggest by distorting space. Until recently they were merely interesting mathematical curiosities, but recently new variations that allow them to be constructed by a non-godlike tech level have been discovered.