gravitational waves - Isn't LIGO basically measuring the luminiferous aether?

I am bit confused about this one. I am not very acknowledgeable about gravitational waves and LIGO. But if it is basically a Michelson interferometer and can detect shifts in vacuum, doesn't this means that we detected the luminiferous aether and if not, why? Is there an analogy or direct correlation between gravitational waves and aether?

Answer

How a Michelson Interferometer works

LIGO is indeed a Michelson interferometer, which splits a beam of light in two, sending each new beam towards a mirror in the shape of a giant "L". Mirrors at the end of each arm then reflect the light and send the beams back to the splitter, where they merge back. An interferometer looks to find any changes in the beams. If a gravitational wave passes through the detector, it will appear to change the length of the path traveled by a beam, thus changing the result slightly.¹

The Michelson-Morley experiment did pretty much the same thing. Michelson's idea was that the apparent length should change based on the Earth's supposed movement through the aether. It would take longer for the beam traveling parallel to the Earth's movement through the aether to return than if would for the beam traveling perpendicular to the Earth's movement.

The difference between the experiments

If we detect a gravitational wave, then we can still rule out the luminiferous aether. There are a couple reasons:

• If the aether hypothesis is true, the movement of the Earth through the aether should always be detectable. Conditions stay the same. However, gravitational waves do not regularly travel through Earth at measurable strengths.


• In the Michelson and Morley setup, the Earth is traveling through the aether in one direction, and thus changing the orientation of the interferometer should produce different results. However, gravitational waves can come from any direction, so it is possible to get the same measurement from different waves coming from different directions.

This is, of course, in addition to the fact that spacetime is not the same thing as the aether.

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^{1 For more excellent information, see the LIGO website.}