# Hypothetical - If a gravitational wave was somehow produced on Earth, could its origin be triangulated?

Suppose object X is hidden somewhere on Earth and can, somehow, produce "weak" gravitational waves, that do not cause anything perceivable by people, but can be detected by all gravitational wave sensors on Earth. (I understand it's impossible due to mass issues, but just suppose it happened by a currently unknown phenomena, a detectable gravitational wave was produced on Earth by some not yet developed technology, despite being currently impossible for us.)

QUESTION: Would it be possible to triangulate the location of object X, by analysis of the gravitational waves it produced?

If yes, could you give me a brief description of how it would be done? If not, why not? What would be needed to triangulate this position?

This would be for a short story. It has an impossible element (the wave being produced on Earth), but the reaction to the situation has to be plausible. Thank you for helping. :)

• – Qmechanic May 18 '17 at 15:09
• Qmechanic, thanks, but, as I understand, that's mainly about something that "would happen all the time" or "would be too small to be detected". I'm talking about something out of the ordinary, yet not catastrophic, that could be detected and would draw enough curiosity for researchers to try to spot its origin on Earth. ;) – Anne Mae May 18 '17 at 15:18
• This site is for answering main stream physics questions, not for fantasy and science fiction. – anna v May 18 '17 at 15:49
• I'm into science myself, I'm a molecular biologist, and, for me, thinking and coming up with ideas is always a good exercise, so I wouldn't mind someone asking me weird questions about protein and DNA for fiction. But I'm sorry if I offended those who do not think like me, I might delete the question later. ;) – Anne Mae May 18 '17 at 16:05
• Your question is mainstream. Not the hyphotetical questions are bad, the nonmainstream questions are. – user259412 May 26 '17 at 0:48

Yes it would, though you need at least three detectors so we couldn't do it right now. It would be possible when more GW detectors are commissioned, and indeed more detectors are being built as I type.

The way you do this is by measuring the times the wave arrives at the detectors. Gravitational waves travel at the speed of light, so if for example the wave arrives a microsecond later at detector B than at detector A you know the distance from the source to B must be $300$m greater than the distance from the source to A. That difference of $300$m is the time difference of $1\mu$s multiplied by the speed of light. With enough detectors you can work out where the source is from the different distances to the detectors.

• Would the difference in measured wavelength of the wave at each detector allow us to determine the direction with only two detectors? If the relative orientations of the two detectors are known... or is this line of thinking negated by each detector having orthogonal arms? – Asher May 26 '17 at 3:18
• As of summer 2017 four interferometric gravitational-wave detectors and maybe two bar detectors are producing at least some data and they might have all been running together at some point. Granted, Virgo is still working hard to get to full sensitivity and GEO 600 is too small to fully compete with the others. But if you produce a strong enough signal, maybe at around 900Hz, you should have plenty detectors for triangulation. And since you're hand-waving the signal generation anyway, making it a bit stronger shouldn't be a problem. :) – Emil Jun 2 '17 at 14:06

QUESTION: Would it be possible to triangulate the location of object X, by analysis of the gravitational waves it produced?

Gravitational waves to be detectable, need enormous masses in asymmetric distributions, as for example the gravitational waves detected by the LIGO experiment. "Triangulation" gave an approximate location of the source, with astronomical distances.

No masses at the center of the earth will give detectable gravitational waves, due to the, comparatively with heavenly bodies . very small masses and the weak nature of gravitational interactions.

• Thank you. I understand about the masses and how it would be impossible. I'm not sure I expressed myself well... it's a fictional situation, so it has a "magic" element which is the HOW, but the approach to the situation has to be real. So, suppose LIGO detected another gravitational wave, but this time, "by magic", its origin is on Earth, would it be possible to determine the continent, country, or city of origin, by analysing the wave? – Anne Mae May 18 '17 at 15:32
• It could not be an earth based gravitational wave, i.e. with the general relativity theory of gravity. There are seismic waves used to determine the composition at the center of the earth, and artificial vibrations for locating minerals oil and water but these are not gravitational waves. indiana.edu/~geol105/images/gaia_chapter_3/seismic.htm and earthsky.org/earth/… – anna v May 18 '17 at 15:38
• Thank you very much, Anna. The page about seismics is a really interesting material. :) – Anne Mae May 18 '17 at 15:52