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As I understand, some parts of Universe really are moving faster than light -- is this expansion something we think we can create artificially?

And if we can do this artificially, could it be done a on very small scale in the near future? Or is it possible that space is already being affected in this way in, say, particle accelerators or during nuclear explosions?

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  • $\begingroup$ en.wikipedia.org/wiki/Alcubierre_drive $\endgroup$
    – DKNguyen
    Commented Sep 19, 2022 at 20:36
  • $\begingroup$ physics.stackexchange.com/questions/119522/… $\endgroup$ Commented Sep 20, 2022 at 15:35
  • $\begingroup$ @AndrewSteane: I am not a physicist but if sending a message faster than light violates causality, anyone can see that a spaceship carrying info reaching Alpha Centauri in under 4 years does send a message FTL. If it does not, not even sure what the utility would be or what it means to travel in this fashion. I do wonder if space expanding FTL allows info to move FTL but I think it probably is understood that it does not. $\endgroup$
    – releseabe
    Commented Sep 20, 2022 at 18:19
  • $\begingroup$ @releseabe The phrase "in under 4 years" is ambiguous. The amount of time passing between two events, for a traveller going from one event to the other, depends on how they make the journey; see twin paradox for more information on this. $\endgroup$ Commented Sep 20, 2022 at 19:25
  • $\begingroup$ @AndrewSteane: my point is, it sounds like someone traveling using the warp drive could reach someplace faster than light does which is sending a signal faster than light which i believe violates causality. $\endgroup$
    – releseabe
    Commented Sep 20, 2022 at 20:55

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Is the kind of physics proposed for "warp drive" related to the way that space really is expanding?

Related, yes, in that both are based on Generated Relativity, but the two are fundamentally different (specifically, they have different units).

As I understand, some parts of [the] Universe really are moving faster than light

well, kind of. Depends on what you mean by "moving": the distance from us to certain places in the universe (as measured now), is increasing faster than the speed of light, yes. But thinking of this as the "speed of the universe's expansion" would be misguided, since this variation of distance cannot be meaningfully interpreted as the "velocity of something" within GR.

But, our model for the expansion of space (ΛCDM cosmology) describes the expansion as being spatially uniform on large enough scales. The typical analogy is to think of dots drawn on an inflating balloon. Each of these dots is stationary, it's the distances among the dots that are increasing. Also, no thing is moving through space at a speed larger than $c$: cosmological expansion is locally compatible with Special Relativity.

So, the meaningful quantity to describe the expansion is not a speed but an expansion rate: something in the form $(\Delta D / D) / \Delta t$, where $D$ is some (large, cosmological) distance, and $\Delta D$ is is variation across a time difference $\Delta t$. Notice that the units of this are [1/time]. This is a somewhat loose description of the Hubble parameter.

is this expansion something we think we can create artificially?

Maybe, in the far future! Surely not with current tools.

And if we can do this artificially, could it be done a on very small scale in the near future?

I'd venture that if we did recreate it artificially it would likely be on small scales compared to the cosmological ones we currently observe expansion at! But this is quite speculative, of course.

Or is it possible that space is already being affected in this way in, say, particle accelerators or during nuclear explosions?

So, if "this way" means FTL then no, with quite good confidence, although people are still looking. If "this way" means to have some general-relativistic effect in particle physics experiments, then still no unfortunately, and we might not see anything of that sort unless we build detectors with much higher energies.

Regarding the warp drive: it is a theoretical construction within GR with the following properties

  • it entails no local violation of the speed of light,
  • it allows one to move arbitrarily fast from A to B, both according to the one moving and to people outside (the latter is the difficult part!),
  • it requires negative energy.

The first thing sounds like what I was writing before, but that's just because it's a GR requirement, and both models are GR-compatible. The second thing is not happening in cosmology! The third thing is what makes this "impossible" (i.e. we don't know of any current materials or techniques to make negative energy in any substantial amount, and you'd need a black hole's worth).

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  • $\begingroup$ maybe a bit picky, but expansion does not have to be 'driven', it can be free-fall. It is just acceleration that has to be driven. $\endgroup$ Commented Sep 19, 2022 at 22:37
  • $\begingroup$ I mean, yes, I guess the point is what "driving" means - by "what is driving the expansion" I just meant the energy density in the universe (since $\rho$ determines $H$)... $\endgroup$ Commented Sep 20, 2022 at 8:42
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    $\begingroup$ It is like the difference between velocity and acceleration. Something "drives" acceleration (or deceleration) but velocity is just velocity (as in Newton's first law). Similarly, expansion is a velocity effect. The universe expands because its initial conditions sent in on an expanding trajectory. It is a change in the rate of expansion which requires some sort of force or cause in the present. As I say, all this is picky; I just felt that a non-expert might get the idea that expansion itself needs some sort of force to drive it forward, which of course it does not. $\endgroup$ Commented Sep 20, 2022 at 10:16
  • $\begingroup$ That's fair, looking at the acceleration $\ddot{a}$ as the "causal" part makes sense. $\endgroup$ Commented Sep 20, 2022 at 10:26
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At the current moment, we don't even know what dark energy is which is the reason the universe expands faster than the speed of light. There is not really a way we could recreate it per se but there are talks about how we can create an effect similar to dark energy which has some kind of "negative energy effect".

There has been talks about how Harold White with his Eagle Works Laboratory has been working on like a potential precursor to the warp drive and might use the Casmir effect to cause some kind of dark energy like effect which could maybe used on warp drives. However, there has not really been any real success and for the moment it is pretty much impossible to harness such a faster than light expansion.

In the end, such a thing has a really low chance of existing but there might be a tiny chance that something might be discovered. Even if it is discovered, harnessing it is very difficult thing to do.

There is not really any other known way to create a faster than speed of light flow of space(maybe aside from black holes).

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    $\begingroup$ Just to say: dark energy and "faster than light" expansion are different things; you can have either without the other. $\endgroup$ Commented Sep 19, 2022 at 20:50
  • $\begingroup$ There is no way the universe can expand faster than the speed of light without the use of dark energy as it is what is causing the accelerated expansion of the universe. Without it, it would be impossible to create a faster than speed of light patch of space. $\endgroup$ Commented Sep 19, 2022 at 21:14
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    $\begingroup$ No, @AndrewSteane is correct. Dark energy is required for accelerating expansion, because otherwise the only long-range interaction is gravitational attraction. Faster-than-light expansion is a consequence of a linear Hubble expansion over large enough distances, and could be observed in a universe without dark energy. $\endgroup$
    – rob
    Commented Sep 19, 2022 at 21:29

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