We may be able to spot enormous alien spacecraft by the gravitational waves they would create. Gravitational waves are ripples in space-time formed when a massive object moves around, so if there are any extraterrestrials driving gigantic spacecraft around our galaxy, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US could potentially detect them.
Gianni Martire at , a research institute in New York, and his colleagues calculated how large such a craft would have to be, and how fast it would have to move, to create a gravitational wave big enough for LIGO to spot. They found that the craft would have to be about the mass of Jupiter, travelling at about one-tenth the speed of light 鈥� that is nearly 30,000 kilometres per second, faster than any star astronomers have discovered.
They found that LIGO could spot such a craft if it travelled within about 326,000 light years of Earth, and more sensitive planned gravitational wave detectors could extend that distance even further.
Advertisement
鈥淲ith trillions of stars out there, you鈥檙e telling me that one doesn鈥檛 have aliens that haven鈥檛 done this? Just one? I think the odds are in our favour,鈥� says Martire. 鈥淚 wouldn鈥檛 want to be on the team figuring out how to build a Jupiter-sized spacecraft, but the odds aren鈥檛 zero.鈥�
This could also work for crafts using warp drives, theoretical engines that move by creating their own wrinkles in space-time. 鈥淭here鈥檚 no way in hell we could detect a craft so far away in other ways, even if it鈥檚 as big as Jupiter,鈥� says Martire. 鈥淭he LIGO folks and the SETI [Search for Extraterrestrial Intelligence] folks should be best friends.鈥�
But even though it is clear that extraordinarily massive spacecraft and warp drives should create gravitational waves, other researchers have expressed scepticism that we will ever be able to actually detect them.
鈥淭his is well and fine in principle, it鈥檚 just that I am surprised they find the result to be in the sensitivity range of LIGO,鈥� says at the Munich Center for Mathematical Philosophy in Germany. 鈥淚f the spacecraft was actually Jupiter, which is pretty close, maybe we鈥檇 actually be able to measure it, but if it was much further away, probably not.鈥�
Even if we were to detect gravitational waves from a massive, fast-moving object, it would be difficult to discern whether it was an alien spacecraft or a natural phenomenon. It could be easier for warp drives because of the unique way they are expected to affect the gravitational field around them. 鈥淗ow do you know the difference between a comet and the starship Enterprise? You can tell between a rock and a warp drive the same way you can tell whether a jet ski went past or a boat,鈥� says Martire. 鈥淭hey both create waves, but they have a particular signature in their wake.鈥�
There is no downside in checking for an outlandishly enormous spacecraft in LIGO data, says Hossenfelder. 鈥淚t鈥檚 there, it鈥檚 collected already and freely available, I don鈥檛 see why not,鈥� she says. 鈥淚鈥檓 just not that excited about the idea that they鈥檒l actually find anything.鈥�
But if they do, even if it isn鈥檛 an alien spacecraft but simply a huge object moving far faster than we expect anything that big to go, it would be an important find. 鈥淓ven if it鈥檚 not aliens, it鈥檇 be something new,鈥� says Martire. 鈥淚t would be exciting no matter what it is.鈥�
Reference:
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
