# A silly question about gravitational waves

Alright, so I have been reading about gravitational waves and have a silly question to ask. Suppose, hypothetically, under the right conditions you were standing somewhere on the surface of the Earth and a gravitational wave were to pass through the area of space you were occupying...would you "feel" it? Or rather than standing, suppose you were falling and a gravitational wave passed through that area of space, would you "feel" it? Would you momentarily fall at a faster/slower rate if that were to happen? OR suppose you were in a microgravity environment....if you could feel it, what would it feel like?

Thanks in advance for any responses.

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phinds
Gold Member
2019 Award
Alright, so I have been reading about gravitational waves and have a silly question to ask. Suppose, hypothetically, under the right conditions you were standing somewhere on the surface of the Earth and a gravitational wave were to pass through the area of space you were occupying...would you "feel" it? Or rather than standing, suppose you were falling and a gravitational wave passed through that area of space, would you "feel" it? Would you momentarily fall at a faster/slower rate if that were to happen? OR suppose you were in a microgravity environment....if you could feel it, what would it feel like?

Thanks in advance for any responses.
It's happening to you right now thanks to the moon. The tides on Earth occur due to the moon's gravitational effect on the Earth, so the moon's gravity is affecting you right now. It isn't strong enough for you to notice, but it's there. If there were a gravitational effect, other than the Earth's gravity, that was acting on you strongly enough for you to notice, I believe that would have catastrophic effects on the Earth, but I'm not saying that with any authority.

HallsofIvy
Homework Helper
The question was about gravitational waves, not just the moon's gravitational effect. While gravitational waves are predicted by General Relativity, none have ever been detected.

WannabeNewton
When gravitational waves pass by a congruence of test particles, their effect is to shear and expand the congruence. The usual illustration is to imagine a circular ring of test particles; a gravitational wave that passes by will "stretch" the ring into an ellipse whose major and minor axes will vary sinusoidally as the wave passes by. The thing is that gravitational waves in the linearized approximation are very weak in amplitude. It is quite difficult to directly detect them as noted by Halls but they have been indirectly measured.

cepheid
Staff Emeritus
Gold Member
Gravitational waves are ripples in spacetime. The effect of a gravitational wave passing over you can be illustrated by considering a ring of "test particles" in space. Suppose this ring is initially perfectly circular. As a gravitational wave passes through the point where the ring is, the ring gets stretched into an ellipse, with the long axis alternating between two orthogonal directions. It oscillates between these two states.

Code:
        O O

O     O

O     O

O     O

O O
stretched vertically

O  O  O
O           O
O           O
O  O  O
stretched horizontally
Something like that. I suspect that you would feel absolutely nothing at all, because, from a typical astrophysical source, the expected amplitude of the gravitational waves, as quantified by the strain (fractional change in length) is expected to be something like 10-20. Don't quote me on the number -- I just remember that it is something ridiculously small like that.

phinds