6
$\begingroup$

In most literature I have found, research into the Alcubierre Metric, and Warp Drives seems to be highly focused on the plausibility of superluminal travel.

Today I was thinking to myself that maybe we're asking hard questions before easier ones. After all we built sub-sonic planes before we built supersonic ones.

So are there any solutions to the Alcubierre Metric that are focused on sub-luminal travel. Like in the realm of 0.1x-0.5x the speed of light?

Improve this question
$\endgroup$
11
  • 2
    $\begingroup$ Could such a sub-luminal drive be made without a negative energy density? $\endgroup$
    – mmesser314
    Commented Mar 10, 2023 at 1:27
  • 1
    $\begingroup$ @A.V.S. A sub-luminal warp drive would just be a solution to the Einstein Field Equations, (similar to the Alcubierre Metric) where the warping of space allows for the 'riding' of a warped spacetime. But where v<c. This is a 'Class 1" warp drive in the paper I linked above. Clearly warp drives are not necessary for subluminal travel, but I don't see how that's relevant to my question. $\endgroup$
    – RudyJD
    Commented Mar 13, 2023 at 18:19
  • 1
    $\begingroup$ the warping of space allows for the 'riding' of a warped spacetime… Use of vague, Sci-Fi language does not help, and the paper you cited is not much better in its definitions. Would you consider the metric of a rotating hollow shell written in a frame where it is moving with velocity 0.1c a “warp drive”? (“Rotating” is in order to have nontrivial frame-dragging since Bobrick&Martire seem to be big on that). $\endgroup$
    – A.V.S.
    Commented Mar 14, 2023 at 5:07
  • 2
    $\begingroup$ A.V.S. is right - a warp drive spacetime would normally be defined as one where you can outrun a light beam in a certain sense. If you can't do that then it's unclear what counts as a warp drive and what doesn't. You can construct a subluminal "warp" geometry with no energy at all – that's the point of the principle of relativity. It doesn't generalize to the superluminal case. $\endgroup$
    – benrg
    Commented Mar 14, 2023 at 7:35
  • 1
    $\begingroup$ Interesting... What do you mean that a warp geometry could be constructed without any energy at all? My understanding was that mass (and therefore energy?) is responsible for the warping of spacetime. $\endgroup$
    – RudyJD
    Commented Mar 14, 2023 at 16:42

1 Answer 1

Reset to default
3
$\begingroup$

I will expand my comment in an answer:

$v$ in Alcubierre is an arbitrary function of time, which can be interpreted as the velocity of the warp drive. In particularly it can lead to arbitrary high acceleration, resulting in arbitrary low round trip times in proper time without experiencing time dilation. The latter is a truly coordinate independent statement, which to me is the core feature of a warp. See this answer for more details: Is observing (superluminal) velocity independent of choice of coordinates for asymptotically flat spacetimes?

In any case yes, you can build a completely subluminal Alcubierre drive by always taking longer proper time than a light ray to perform a round trip, but you will still need negative energy.

Improve this answer
$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.