TL;DR: a warp trip will show up on a gravitational detector because the space ship’s mass instantly disappears and later re-appears somewhere else.
There is some interesting foundational research [ALC] into faster than light [FTL] travel, but by everything these theories tell us, the ingredients for such modes of transportation aren’t available in the universe. FTL should be possible because the universe expands [EXP] at speeds greater than that of light, as [EXP] eloquently states: “galaxies that are farther than the Hubble radius, approximately 4.5 gigaparsecs or 14.7 billion light-years, away from us have a recession speed that is faster than the speed of light”.
Since it is unclear whether the material needed for an FTL drive will ever be available, funding research in that direction could be a waste of resources, unless synergies emerge. In the spirit of respecting taxpayer’s money, I think FTL research should try to exploit – and generate – synergies with other fields of research.
FTL research might lie in the intersection of two such fields: the search for extraterrestrial intelligence [SETI] and observation of gravitational waves [LIGO]. If FTL-capable civilisations exist out there, their use of FTL technology should produce observable interactions. Maybe warp drives paint bright orbits into the sky by emitting radiation or their space-bending drives disturb particles in the space ship’s path that emit radiation. But, since we don’t know the mechanism with which an alien FTL works, such direct observations may not be possible.
What we do know, however, is that a warp trip between A and B starts with a mass instantly disappearing from point A and appearing sometimes later at point B. Changing/moving masses produce gravitational waves and the trip should show up as two blips: one when the ship disappears from A and one when it re-appears at B. It is conceivable that the mass is reduced (fuel consumption) during the trip or that there is a gravitational trace along the path of the ship, but the start and end of the trip should show up as two distinct events. Assuming FTL-capable civilisations concentrate their populations in certain parts of the galaxy, just like we live in cities, a spatial concentration of those blips would be a good indication towards someone having invented FTL.
Edit: HN user pavel_lishin points out that the gravitational signal generated by the start end end of a trip might not look like spikes or blips. In case the trip involves long phases of slow acceleration, the signal might indeed not be there.
Edit: HN user sigmoid10 objects that the initial and terminal events might not be detectable (presumably because of sensor sensitivity limits). FTL trips close to our solar system might show up in LIGO data.
[ALC] Alcubierre drive
https://en.wikipedia.org/wiki/Alcubierre_drive
[FTL] Faster than light
https://en.wikipedia.org/wiki/FTL:_Faster_Than_Light
[EXP] Expansion of the universe
https://en.wikipedia.org/wiki/Expansion_of_the_universe
[SETI] Search for extraterrestrial intelligence
https://en.wikipedia.org/wiki/Search_for_extraterrestrial_intelligence
[LIGO] LIGO
https://en.wikipedia.org/wiki/LIGO
George's Techblog 
If we read the signatures from a ftl civilization, and they haven’t already found us, I’d be surprised. Because what are the odds they aren’t expanding out faster than those signatures are reaching? Because what are the odds that there are more than 1 habitable planet in a 100ly radius?
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Research into terrestrial intelligence would be more profitable.
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The only thing I would say to that statement is that sometimes, we should do stuff just to do it. Profit should be the last motivator in evolution and yet it seems to be the first. Profit just like bureaucracy slows everything down
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The best thing is to develop new communication technologies. We know there’s advanced life out there, and they’re talking to each other, but, we haven’t heard them? There must be another was of communicating that we haven’t heard of. Detecting communication signals is the best bet at confirming not only ET, but FTL as well. We’re so fixed on digital RF, and it works great for us so we’ve never tried too hard to replace it, and, we for us to assume any highly advanced being would use RF is hilarious.
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We tend to ridicule those who claim to be clairvoyanty connected to Alien life, but what if…?
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Unless there mode of communication is telepathy they just send words with there mind I mean if they are so advanced that they have developed ftl the idea of them sending there thought light years away with there mind is not far fetched and would be undetectable
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Hmm. No such thing as tachyons.
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” In the spirit of respecting taxpayer’s money” 😆😂🤣
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This is a fascinating idea that we could detect civilizations utilizing FTL jumps. Can’t wait till we build even better GW detectors.
Since we are on fantasy land with FTL technology, what if the technology required to make the jump relies on mass switching? So in order to move 1kg of matter from star A to B you have to transport back the same amount of material you want to transport to B. This might be a way to cloak the trip, but also could be a way this tech works by design 🙂
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If one had to bring mass back, such trips would be very dangerous if stranded in the void. I wonder about a different implication: would such an FTL drive permanently wrap space in the same way cosmic expansion does?
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