I saw this vid on youtube about FTL travel and a lot of people missed the point:
I felt I had to explain the main principles (due to some viewers not understanding it right) as well as some guesses on how to achieve the desired effect:
Quote:
"Travelling" at 10 times the speed of light in this manner does not break Einsteins theory of relativity regarding the speed of light since the ship itself doesn't move fast in itself, it moves the space around it instead. We already know that stars and galaxies that have left our hubble-horizon are moving away from us in speeds faster than light and thus we'll never receive any photons from anything outside that horizon. An allegory that has been used before is that we take a photon just on the other side of the border of our planets hubble-horizon. As it travels towards us the room itself is expanding faster than light and the room in which the photon is travelling in is actually stretching out faster than the photon can move.
That's the idea behind this warp bubble. Instead of using kinetic energy we reshape the space to shrink the distance in front of us and expand the distance behind us.
Or an even easier analogy: Imagine two people stretching out a very stretchable rubber-ribbon on which you put a toy car that you can pull with a string. If they stretch out the rubber-ribbon faster than the car is pulled the car will have longer and longer to roll. If the opposite happens, ie. the people stretching the rubber-ribbon moves towards each other the car won't have to move fast at all to reach the end of the track since the distance of the track will become shorter.
ps. I should add that when it comes to "room" and "space" or "space time" they are not interchangeable, they have different meanings. When the room expands it stretches out space time. There may be areas of room without any space time. Obviously that "area" is truly a void and won't be "real" as far as we're concerned until space time has spread into that "void". In space time we have matter and energy (well, two sides of the same coin) that can move within it. In the room, space time takes the place of matter and energy.
To actually fold/compress-expand space time we need a LOT of mass or a way to "simulate" mass with enormous amount of pressure and energy. We may be able to use vacuum energy or zero point energy to exploit the Lamb shift effect, ideas from the Casimir effect or the "Vacuum catastrophe" (use wiki) to manipulate the room though.
Obviously it would become easier if we could actually affect the room in which the space time continuum exists, then we could "move" at arbitrary speeds (we wouldn't actually "move" in any kind of kinetic way, we would cut-n-paste our very local space time to a different part of the room).
This is based on general relativity and modern quantum gravity theories seem to point that wormholes and Alcubierre ("warp") drive described above are in fact not possible.
However quantum gravity is a very new field with no widely accepted theory and no experimental evidence due to incredibly small scales. For those interested, quantum gravity theory is supposed to be the connection between general relativity and quantum mechanics.
But even if this is theoretically possible I would say it's an grand overstatement that it's nearing possibility, as the mass required is so incredible that we are nowhere near achieving it. (Lowest estimates go from mass of Jupiter, and highest go to mass of observable universe or even negative mass)
More potentially interesting talks (second one less so since there's not much concrete information about quantum gravity yet):
Warp drive:
Fuck that, if its not possible on macroscopic scales we have to convert a civilization to nano/femtomachines and once they're out on the other side we can start mining for resources and re-assemble.
I am hard pressed to see how this is even based on GR. GR has special relativity as a solution both on really small scales but also on large scales if space is mostly empty. So lets take this nice FTL buble flying through empty space. Zoom out and choose an observer observing the vast expanse of empty space in front and behind the buble. The buble would look like it moves back in time, hence it doesn't obey special relativity. That is bad.
But don't wormholes have pretty much the same problem and they are also consistent with general relativity (and yes, this drive has been mathematically proven to be consistent with Einsteins field equations judging from all that I have read)? I cannot imagine what the observer would see, but I doubt it's anything we can intuitively understand.
But don't wormholes have pretty much the same problem and they are also consistent with general relativity (and yes, this drive has been mathematically proven to be consistent with Einsteins field equations judging from all that I have read)? I cannot imagine what the observer would see, but I doubt it's anything we can intuitively understand.
If you know STR and GR it's actually quite intuitive
There is a thing in GR called closed timelike curves (ctc), if you draw a space-time diagram, and you can draw a ctc, that basically means that you could go back in time, because you'd just go over and over and over on the same path, always returning to the same point in space-time you started from.
In your everyday life you always move forward in time (a thing called causality - cause and effect thing), you can stay in one place, but you cannot stand still in time (yet?).
By allowing ctc you could loop back to where you started originally, basically going back in time, since you come to same time you started (you go towards future, but end up going from the past towards present and so on).
This metric Alcubierre proposed allows ctc, and that's something nature doesn't like.
His drive works theoretically, but from today's standpoint is really not manageable...
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson
chiv wrote:
thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found.
STR = special theory of relativity, and yeah CTC is closed timelike curve (I think I put that down in post ).
The main problem of GR these days is that you cannot test quantum gravity. You have string theory which in itself has several ways of explaining the quantum gravity, you also have holographic theory, that may or may not use string theory to try to shed some light on the quantum side, but both still aren't testable (there is anti de-Sitter/Condensed matter theory that could be testable on the condensed matter side, but I haven't really looked at the details, that's some hardcore stuff ). Also loop quantum gravity that hasn't been proved as well (strings theory biggest rival iirc)...
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson
chiv wrote:
thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found.
But don't wormholes have pretty much the same problem and they are also consistent with general relativity (and yes, this drive has been mathematically proven to be consistent with Einsteins field equations judging from all that I have read)?
I think the wormholes have the same problem really. In the case of a wormhole I guess the problem is sort of overcome by the fact that they are dynamically unstable as far as I know. But then apparently this drive is as well unless we allow for negative energy density. Which again is forbidden by varies energy conditions.
dingo_d wrote:
The main problem of GR these days is that you cannot test quantum gravity.
It is a bit harsh to say it is a problem when a theory can not be used to predict phenomenon never observed
But don't wormholes have pretty much the same problem and they are also consistent with general relativity (and yes, this drive has been mathematically proven to be consistent with Einsteins field equations judging from all that I have read)?
I think the wormholes have the same problem really. In the case of a wormhole I guess the problem is sort of overcome by the fact that they are dynamically unstable as far as I know. But then apparently this drive is as well unless we allow for negative energy density. Which again is forbidden by varies energy conditions.
dingo_d wrote:
The main problem of GR these days is that you cannot test quantum gravity.
It is a bit harsh to say it is a problem when a theory can not be used to predict phenomenon never observed
Ok, we'll call it a quirk
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson
chiv wrote:
thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found.
So this died a quick death with a curious lack of responses from Frant . Maybe to get a better idea of what works and what does not work with the alcubierre metric we could try and see if it is possible to work through the actual article. Would any one be interested in trying that? ( it is free on arxiv).
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)
. Maybe to get a better idea of what works and what does not work with the alcubierre metric we could try and see if it is possible to work through the actual article. Would any one be interested in trying that? ( it is free on arxiv).
