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How does a Gravitational wave create ripple in the fabric of space, if space itself is an empty and it is made-up of nothing. Through out my academic life in school, I was told that space is made-up of nothing.

If so, then in which medium waves travel?

If they do indeed travel in "nothing", how is that possible?

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    $\begingroup$ Perhaps the same medium as electromagnetic waves ? $\endgroup$
    – ProfRob
    Nov 7 '19 at 20:51
  • $\begingroup$ How about Higgs field? $\endgroup$
    – Kornpob Bhirombhakdi
    Nov 7 '19 at 22:21
  • $\begingroup$ btw, I thought this site is not for debatable question? $\endgroup$
    – Kornpob Bhirombhakdi
    Nov 7 '19 at 22:25
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Well, space isn't really nothing.

Empty space (properly spacetime), also called the vacuum, is pretty complicated in modern physics. All of the fields, like the electromagnetic field and the electron/Dirac field, are there whether or not there are any particles (photons or electrons). The particles are vibrations of the fields – or to put it another way, they're vibrations of the vacuum.

Although people tend to say that gravity is different from everything else, it isn't really very different. The vacuum has a "shape", and it can vibrate in various ways. Some of the vibrational modes are gravitational waves. Others correspond to electrons, photons, etc. The details are complicated but the idea is simple.

The vacuum is different from an ordinary wave medium in some ways. Most importantly, it doesn't have a state of motion: you can't detect a "vacuum wind" or "vacuum current" resulting from moving through the vacuum. But if you keep that imporant caveat in mind, then the analogies of a "fabric of spacetime" or of gravitational waves as waves on the surface of the ocean are not so inaccurate.

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  • $\begingroup$ Gravity bends the space, isn't it? So, you mean to say that in actuality what it bends is photo and electrons, electromagnetic waves, etc.surrounded by celestial objects? I still don't get it. I have little knowledge about space being not entirely empty. But, normally Gravity bends the space and gravitational waves propagates the phenomenon of bending space further. So, if something is bend then space must be having its own properties. $\endgroup$
    – Ubi hatt
    Nov 8 '19 at 16:04
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    $\begingroup$ @Ubihatt - The vacuum has properties even though it is devoid of matter. One of its properties is its geometry (or metric), which defines how particles and fields propagate through the vacuum. This geometry varies from place to place under the influence of gravitational mass, which arises from either matter or energy. Changes to the geometry of the vacuum represent a change in the potential energy there, which itself effects the local geometry, so with the right sort of change in the distribution of mass you can have a propagating wave that carries energy. $\endgroup$
    – antlersoft
    Nov 9 '19 at 3:25
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    $\begingroup$ tl;dr The vacuum itself is the medium; the property that is oscillating as the wave propagates is the local geometry. $\endgroup$
    – antlersoft
    Nov 9 '19 at 3:27

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