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?
Best Answer
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.
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.