3 ms·

The confusing thing here is that space time warps in the presence of mass. But no mass is transmitted in a gravity wave. So what is the fabric made of?

• ianburrell 3y ago
  Space is the fabric. Moving electric charges produce electromagnetic waves (light). No charge is transmitted with light, but it can cause charges to move. Space is also the fabric for electromagnetic waves.
• ajuc 3y ago
  When you move mass around - the spacetime curvature responds with light-speed delay. I thought gravitational waves are just that - delayed change of curvature of space-time in response to the mass distribution changing in one place?
• vl 3y ago
  We use words to describe abstractions which try to model reality as we observe it. In case of "space time warps in the presence of mass" it's important to understand that this is just a model. Another way to explain it that there is no space-time per se, only masses (with special case of photon et al) and masses interact. What we mean by space-time is that if there was a tiny mass in this given point, it would experience given force. Or, again, modeled differently, travel along given path. But if there is nothing to interact with, there is no "space-time" per se in this point, after all, it is an abstraction to describe interactions. So, to sum up, masses interact, space-time is an abstraction to conveniently describe how they interact. Gravitational wave is two massive masses rotating and shaking third small mass as a result of distance changes.
• semi-extrinsic 3y ago
  No mass is transmitted in a gravity wave, just the same way that no mass is transmitted when the Sun's gravity pulls on the Earth. And just the same way that no cell phone towers are transmitted when you use your phone. It's entirely correct to say that the electromagnetic field warps in the presence of moving charges, sending out EM waves like in wireless communication. And the EM waves can travel without any medium, even in hard vacuum. What is the electromagnetic field made of?
• evanb 3y ago
  Spacetime warps in the presence of mass, yes. But the full answer is that spacetime warps in the presence of energy/momentum; Einstein's field equations make no mention of mass specifically, except that via E=mc^2 masses are energy. So, once you get a gravitational wave going (by shaking masses) the warping of spacetime itself at one place sources warping for a nearby place which sources warping for a nearby place which ... is what we call a gravitational wave.
  • beders 3y ago
    That would also mean Earth moving around the sun would create such waves?
    • evanb 3y ago
      Indeed it does. But the Earth is so light and the orbit so long that the power emitted is very very low. The sun will explode long before the Earth's orbit will be noticeably modified due to energy loss by gravitational radiation. The distortion effects are not noticeable on experimental scales we have the technology to probe. The mechanism can noticeably modify orbits, however. In fact the first (indirect) observation of gravitational waves was using exactly that effect. https://en.wikipedia.org/wiki/Hulse%E2%80%93Taylor_pulsar https://en.wikipedia.org/wiki/Hulse%E2%80%93Taylor_pulsar