The speed of light has always been considered the limiting factor for interstellar transportation. For example, the closest star to us is Proxima Centauri, about 4.25 light-years away. The fastest spacecraft we’ve ever been able to build is the now-in-space Parker Solar Probe, which should eventually attain a top speed of 450,000 mph. Even at that high speed, it would take the solar probe about 6,633 years to reach our nearest neighbor (https://theconversation.com/warp-drives-physicists-give-chances-of-faster-than-light-space-travel-a-boost-157391#:).
Of course, it’s easy to exceed the speed of light in science fiction. The popular TV show “Star Trek” and all its incarnations used warp drive. The physics behind this method is to compress space in front of a spacecraft while expanding spacetime behind it.
Would that even be possible? The article “Warp Drives: Physicists Give Chances of Faster-Than-Light Space Travel a Boost” at the website The Conversation (as cited above) explains how Mexican theoretical physicist Miguel Alcubierre showed In 1994 that compressing spacetime in front of the spaceship while expanding it behind was mathematically possible within the laws of General Relativity. But unfortunately there is another complication — Alcubierre’s method of compressing spacetime requires negative energy or negative mass.
But let’s suspend disbelief a moment and assume an advanced civilization has perfected warp drive. How would we know?
This brings me to the article that caught my eye in the first place — “One of the World’s Largest Lasers Could Be Used to Detect Alien Warp Drives” by Ben Turner. Our species now has the Laser Interferometer Gravitational-Wave Observatory (LIGO) which can look for space-time ripples. Scientists think alien spacecraft traveling at high speeds, or pushed along by warp drives, would produce detectible vibrations. Again, it’s complicated — to be detected by LIGO, an alien ship would have to weigh about the same as the planet Jupiter, travel at one-tenth the speed of light, and be within 326,000 light-years of Earth.
But considering the progression of science in the last 100 years and the theoretical abilities of alien lifeforms, who knows? In any event, it’s a fun subject to think about.
For the complete explanation, Mr. Turner’s article is at https://www.livescience.com/ligo-to-detect-alien-spaceships?.