Low energy, fantastic range

From HDE in another topic, I learned gravitational waves have an intensity which is inverse proportional to distance, not square distance, like in electromagnetic fields..


Because of this, the gravitational wave energy becomes spread over a giant distances and their amplitude is extremely small.

Now suppose future detectors of gravitational waves will be very sensitive. I was thinking of using an array of highly sensitive gravitational wave detectors in orbit around a planet, as a long range sensor for ships that make use of artificial gravity, or Alcubierre drives.


An approximate direction to the ships is known

Important thing to keep in mind for this question: we know where to look, the direction: we know in what region of space these aliens are to be expected. So far, they were not particularly hostile to Earth, but we would like to know their capabilities. Distance to earth of the alien ships can be anywhere between 26 and 200 light years.

The source of the gravitational wave used for this

For our detector array, there is a suitable and regular gravitational wave, coming from that direction. The source of this GW is an imminent neutron star collision, which is in progress ca 600,000 light years behind our observation region, as seen from Earth. We expect to be able to use this constellation for about 100 years, before they collide.


Interference patterns

I wonder if an "obstacle" such as an Alcubierre drive, could cause a ripple in the gravitational waves, which could be found invoking interference patterns, like it happens in the water, when you put 2 sticks and disturb the surface.

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Alternative method: the bending of light

(thanks @ChristopherJamesHuff for the feedback..)

The linear artificial gravity and the Alcumbiere drive introduce excessive gradients in space time, which could be detected using other means. When the field required for the drive has enough range, it could be detected using the same methods applied for exo-planets: find a disturbance in the starlight characteristic for sudden ST-gradients, like like gravitational lensing. We've chosen to invest in the GW array, because 1) we don't know if these ships emit EM radiation, and 2) whether these ships will be be parked anywhere near a star.

Question: is it plausible that a ship invoking a space time distortion may form characteristic interference patterns in gravitational waves, that can be detected by my array ?


Answers I'll vote for would explain how artificial gravity or other space-time irregularities would disturb gravitational waves, or not. The best answer would make me replace a tag.. I'd like this question to become science-based, now it is not.

Note 1: the goal of my detector is to find out if FTL or Alcubierre drives or artificial gravity can exist, if it is in use anywhere within our Milky Way, say 100 thousand light years. My sensor has no space-war or defensive purpose. EDIT: You may assume we know in what direction to look.

Note 2: science based frame challenges are very welcome ! When gravitational waves e.g. can't do interference patterns of any kind, please correct me.

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    $\begingroup$ Remember, this will tell you where they WERE, not where they ARE. $\endgroup$ Commented Feb 12, 2022 at 3:53
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    $\begingroup$ I love this idea, but aren't you still constrained to information traveling no faster than the speed of light? If so, the only practical detection might be within one's own solar system (unless you're SETI, they'd take this in a heartbeat). $\endgroup$
    – JBH
    Commented Feb 12, 2022 at 6:34
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    $\begingroup$ @JoinJBHonCodidact clear, this can't be used for defense, they would be here when we see them, when their Alcubierre drive works properly. $\endgroup$
    – Goodies
    Commented Feb 12, 2022 at 11:16
  • $\begingroup$ @JustinThymetheSecond yes that is relevant, but we know - about, only a direction - where they are, we want to find out more about their technology, the above is related to an earlier question worldbuilding.stackexchange.com/questions/220922/… $\endgroup$
    – Goodies
    Commented Feb 12, 2022 at 11:17
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    $\begingroup$ The biggest problem that gravity wave detectors have is the ambient noise level. There is so much going on with gravity waves that LIGO needed special signal processing to even detect anything. When I looked at the raw data, I was surprised that they could even find any signal in that much noise. There have been other teams processing the data and suggesting that other events were hidden in the noise. A ship would easily disappear into the noise. $\endgroup$
    – David R
    Commented Feb 12, 2022 at 15:42

3 Answers 3


Gravitational waves and electromagnetic waves traveling through a gravitational field would behave basically identically in terms of lensing, Shapiro delay, etc. Both are just waves traveling at c through curved spacetime. The gravitational waves are themselves curved spacetime, but to a minuscule degree when speaking of ambient gravitational radiation from sources at astronomical distances.

So, given similar sources, any detection of warp drives or artificial gravity by lensing or other effects could likely be replicated exactly with electromagnetic antennas.

Worse, there are very few gravitational wave sources, and they are all very low frequency, so any instruments will have to be similarly huge to match them, and so will any disturbances you wish to detect. In electromagnetic radiation, there is a thoroughly-studied cosmic microwave background that reaches peak intensity at a wavelength of 1.9 mm, and a sky full of near-black-body stars, interstellar clouds of gas absorbing or emitting with sharp spectral lines, etc. There is far more signal to work with, and the shorter wavelengths will reveal smaller targets or provide a more detailed view of those targets, as well as improving sensitivity to small disturbances.

Gravitational sensors would be more useful for detecting the emissions produced by such ships, which are likely to be quite distinct from any natural ones. They could also provide information on objects that can't be seen electromagnetically due to obstructing dust clouds, though this seems unlikely to be relevant.

  • $\begingroup$ Aha +1 thx for the answer.. "Gravitational sensors would be more useful for detecting the emissions produced by such ships, which are likely to be quite distinct from any natural ones" I am also looking for these! if the ship would produce gravity waves itself, that would be very nice, because the GW from behind would not be needed. Btw I still don't understand how light or radio waves from 26 light years distance would be affected in such a way, that the result can be observed. The ship must be huge, and you'd still need a light source behind the ship, to see distortion, or lensing. $\endgroup$
    – Goodies
    Commented Feb 13, 2022 at 22:07
  • $\begingroup$ @Goodies you have precisely the same illumination problem with gravitational radiation, except the available sources are dim and few and your detectors are less sensitive. As unlikely as it is with EM, it's even less likely with gravitational radiation. $\endgroup$ Commented Feb 14, 2022 at 0:24
  • $\begingroup$ I have changed the opening question yesterday to clarify, also what the source is and how long it will last. Comments were taken into account, also yours. $\endgroup$
    – Goodies
    Commented Feb 14, 2022 at 7:18
  • $\begingroup$ I acknowledged this answer, it does not make my topic scientific, but it yielded an idea for my story... deviating gravitational waves - or pulses - could origin from the ship's Alcubierre drive itself. I think I can use that idea. It also solves the source-problem. In my original plan I need a steady field of gravitational waves, above answer circumvents that. $\endgroup$
    – Goodies
    Commented Feb 20, 2022 at 9:47

Not practically.

Need many sensors to determine if patterns

To reconstruct a pattern you need a matrix/array of sensors. The example given, the 'Hartmann wavefront sensor' is backed by sensing devices that are millions of 1d sensors packed into a 2d array.

So to be able to create an image that makes it clear the patterns that may exist many sensors are needed ideally in 2d or 3d configurations. Each sensor to be one pixel of an image.

How many pixels do you need to clearly determine there is a pattern? Depends on what is attempted to be observed. What frequency, what resolution. It can be assumed that spaceships have less impact then stellar object mergers. My guess Is that millions of LIGO detectors scattered throughout the solar system would be needed to get good resolution of patterns.

Gravity-Radar (gravdar?)

Same idea as radar just with gravity. Much more practical then checking interference patterns.

To merely detect signal source magnitude and direction would require far fewer devices. Perhaps on the order of a dozen sensors. A few on earth plus a few at the L4, L5 points. This would assume they are large enough to be sensitive enough to detect smaller signals. Bare minimum would be three but large sensors in space with separation would allow for much better resolution both in detecting weak signals and for determining angle.

This is already being done. The array just needs to have bigger sensors that are not earthbound to be able to detect something like ships.

Military applications:

Sensor array. High resolution. Enough said.

  • $\begingroup$ "My guess Is that millions of LIGO detectors scattered throughout the solar system would be needed to get good resolution of patterns" No problem, my sensor array could be upscaled to let the gravitational wave detectors reside in solar orbit.. Technology level is science fiction, say 23th century. The array could even be launched into a galactic orbit, if needed. I just wonder if the principle would work. $\endgroup$
    – Goodies
    Commented Feb 12, 2022 at 3:11
  • $\begingroup$ Will you take a check? $\endgroup$
    – Mazura
    Commented Feb 12, 2022 at 8:41


The best warp drive paper I've seen lately comes from the Heisenberg lab at the Swiss Federal Institute of Technology. She says a warp drive could be constructed with just 1/10000 the energy obtainable by converting the sun to pure energy, though this might be improvable by a factor of, say, 10³⁰.

The energy requirement as described, if converted to gravitational waves, is not all that much less than is dissipated in a black hole merger. So if the aliens can't tune their drive well, you might see it. If, of course, they do better than that ... well, keep watching the skies!

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    $\begingroup$ Alien ships may roam around consuming stars (or DM), no problem. Thanks for your answer & PDF $\endgroup$
    – Goodies
    Commented Feb 11, 2022 at 23:49

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