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Disclaimer: I have this doubt due to lack of knowledge, please clear my doubt without closing it or keeping it on hold. my doubt could be silly but please clarify the doubt.

So my knowledge of gravitational waves is just ripples in the space time fabric and that is what most people believe. But can't it be just some vibration in space not the fabric. I mean let's take the example of small metal pepsi tin kept on a plastic table. If we hit hard on the table, the tin will fall down due to vibrations which traversed through the table. Another example could be small plastic ball floating on water and a large speaker submerged in water just below the ball. When we play music in the speaker at a high volume it starts vibrating the water and sound waves traverse through the water and vibrate the ball above. In all these cases the waves need a medium to travel. But EM waves are an exception right?

So can't gravitational wave be just a vibration which travels through the vacuum without any medium like light and not a vibration caused in the space time fabric. Why do we tell that it is a disturbance in the fabric of space time?

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For a vibration to exist, something has to vibrate. In the water vibrations it is water molecules. In light it is electric and magnetic fields that vibrate.

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In gravitational waves it is the space itself that changes , (x,y,z,t) between points becomes larger and smaller and the wave is seen as a distortion of the ring of partilces, the image is of one wavelength passing.

The mainstream gravitational theory is General Relativity which assumes that what we called gravitational field is an effect on the space time fabric created by the presence energy and masses. The space itself is constructed by the existence of these. Gravitational waves arose from the solutions of the differential equations of general relativity for specific boundary conditions. The "medium" you are looking for is space time itself.

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  • $\begingroup$ can it be the vibration of gravitational fields? $\endgroup$
    – Bhavesh
    Commented Apr 20, 2017 at 6:31
  • $\begingroup$ in general relativity there are no gravitational fields, just space distortions. this has been verified up to now by a lot of measurements, that the classical gravitational theory is not exact. In the classical picture it will be the gravitational field the way for classical electromagnetism it is the magnetic and electric field, except in Newtonian gravitation there are no gravitational waves, because the field is transmitted instantaneously. When and if gravity is quantized, there is a graviton the equivalent of the photon traveling with velocity c. $\endgroup$
    – anna v
    Commented Apr 20, 2017 at 8:03
  • $\begingroup$ While I agree with most of your answer, I am puzzled by the last sentence. Surely a vibration is a change of something with time. How can space-time change with time? Is this some kind of an approximative statement? In other words, would it not be more rigorous to state that gravitational waves are vibrations of the fabric of space (not spacetime)? If not what does vibration of spacetime fabric mean? $\endgroup$
    – chris
    Commented Feb 28, 2021 at 12:36
  • $\begingroup$ @chris The four dimensional space is such that the solutions could be seen as functions of time, but also as functions of space . it is complicated, for example .hal.archives-ouvertes.fr/hal-02334349/document $\endgroup$
    – anna v
    Commented Feb 28, 2021 at 14:37

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