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Suppose we grant a 1 time scientific miracle for exotic matter to power Alcubierra wrap drive, then could two such drives communicate with each other? The drive discharges exotic matter particles around the spaceship and caused a massive distortion of spacetime, could the spaceship still communicate with outside world where the distortion gets attenuated and is barely noticeable. Communication can be in the form of electromagnetic waves or gravitational wave, I have a chasing scene and a kamikaze scene. The chasing scene shows a superior drive catching up to the other drive and the kamikaze scene is where both drives meet in a awe inspiring dramatic head on collision. If the answer is a radio silence then I will not need the scenes anymore.

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    $\begingroup$ Interesting question, +1, I don't see a solid frame challenge yet.. but I think your above idea is problematic.. WHEN would a gravitational wave, or electromagnetic field reach the other ship ? Both propagate slower (=c) than the ships travel (>c). there must be other detectors involved, or spacetime shape itself. $\endgroup$
    – Goodies
    Commented Mar 11, 2022 at 9:05

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No need to use radio or any medium

Suppose your ship has an Alcubierre drive. Its propulsion is based on a space time warp. The ship will deform space time in its vicinity, to be able to travel faster than light, it manages to deform surrounding space time so the ship will cross more of it per time unit. It takes shortcuts, it gets detached from space time, translated..

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Range of influence

The scale of above picture is far off reality.The range of space time deformation can't be anywhere near to the ship, its gravitational field (gradient, or the exotic matter, as you like) would destroy it. The range of space time bending must be considerable, multiple AE's around the ship, when fully unfolded (interstellar) An Alcumbierre drive cannot start full power anywhere near an inhabited planet, its gravitational waves would deform it.

Kamikaze or chase

In a kamikaze (approach) the travel speed of both ships will increase ! On distances of multiple AE's, the drives would find extra space time deviation and accellerate, because the forward deviations in space time caused by the ships enhance eachother! Same sign! I wonder if a real "Kamikaze" would even be possible, or the move can be controlled on the kamikazing ship. The probability of an actual collision at FTL speed is quite small and may invoke time paradoxes (?)

When a chase happens, there could be another issue. The two ships cannot be anywhere near each other, the gradient on the back will be opposite.. the Alcumbierre drive will partially compensate that bump, with energy loss.. and both ships would decellerate. Sign is opposite!

The other ship is very aware of your presence, instantly

Now suppose.. in more peacefull circumstances.. you have another ship, also with Alcubierre drive.. the deformation of space time caused by your ship is instant, and it must be added to the existing shape of space time. That counts for both ships. Therefore, the other ship will know exactly where you are, and what your vector of travel is. It will need that information, to accurately adjust its own space time deformation. Other ships know your travel plan in detail.. and they can adjust their field to your presence, you need to adjust your field to theirs. These adjustments need to happen high speed, instantly, and full automatic.

For communication, an Alcubierre drive has a separate frequency modulation option

Deformations will occur instantly, everywhere in space time. All the Alcubierre drive needs to do for "communication", is to provide some high frequency modulation component.. and use its field generator to transfer information, as an additional deformation in space time. As it happens instantly, that is how Alcubierre ships can communicate instantly. The modulation (information) itself cannot be fast, but a sound channel, say 16kHz sampling, or 38 kBaud digital information transfer may be feasible. Say 2-5 telephone connections, or 200 sensor channels..

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  • $\begingroup$ I'm not sure how instant the propagation of the space-time distortion would be. $\endgroup$
    – Monty Wild
    Commented Mar 11, 2022 at 15:15
  • $\begingroup$ @MontyWild an Alcubierre drive is supposed to travel faster than light speed. So its field/ST deviation (shape) should also propagate forward, traveling along with the ship, faster than light speed. In terms of the opener's interpretation, the exotic matter will manifest (materialize) instantly, in a Newtonian way. This is not a science-based question, Alcubierre drives are counter-intuitive if you follow Einstein's limits. Gravitation travels at light speed. But I don't want to bother an SF-story with a frame challenge. $\endgroup$
    – Goodies
    Commented Mar 11, 2022 at 15:49
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An Alcubierre drive distorts the fabric of space-time in order to move a pocket of space-time and its contents. However, neither the ship nor its bubble of space-time moves, so while the ship and its warp bubble moves relative to other objects, at any instant, it is also stationary.

Additionally, while the drive fields cause a positive distortion in front of the ship and a negative distortion behind the ship, these distortions are no different to a gravity field save that the front field is positive, and the rear field is negative. The fields need not be so strong that they become an artificial black hole and white hole.

Given these facts, it can then be seen that electromagnetic radiation would be able to both enter and leave the warp bubble. The ship would be visible within its bubble, if only briefly to a stationary observer,

As radio waves are a variety of electromagnetic radiation, if an Alcubierre warp ship is emitting radio transmissions, they will escape the warp bubble, and could be detected from another Alcubierre warp ship.

The positive and negative gravity fields of the warp ship may cause gravitic lensing, but they won't prevent detection, and neither will the drive cause red- or blue- shift.

If a receiver is aboard another warp-ship, as long as the receiving ship is behind the transmitting ship, detection would be possible.

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  • $\begingroup$ Lensing is not your only concern. Did you take into account the EM message should traverse over warped space time, between the ships ? Couldn't that take longer ? $\endgroup$
    – Goodies
    Commented Mar 11, 2022 at 16:00

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