I'm basically duplicating this question, because I'm not satisfied with the answer.

Here's why I'm not satisfied.

If we know that "gravity travels at a finite speed", then it seems obvious that it can cause waves.
You don't need to be a genius like Einstein to figure that out. Sure, you might not be able to write down the equations that model its behavior as Einstein did for general relativity, but the mere prediction of the existence of gravitational waves hardly seems surprising (in fact, seems necessary) when you've already considered the idea that nothing can travel faster than light.

Now, I don't know who first had the idea that gravity might travel at the speed of light, but it sure doesn't seem to have been Einstein. (Wikipedia says Poincaré argued for this idea in 1904?)

Considering these, why do we say Einstein predicated the existence of gravitational waves, and why does it seem like such an extraordinary conclusion? Doesn't it seem like a trivial corrolary of the fact that gravity has finite speed, which had already been experimentally verified? Why were the recent discoveries such a big deal, and why does Einstein get all the credit for it?

Or, is it the case that, e.g., the waves predicted by Einstein somehow behave fundamentally differently from what you would expect from a finite-speed Newtonian gravitational wave?
Am I missing something there?

  • $\begingroup$ Would the newtonian gravitational waves propagate via a local wave equation? That's what really defines a wave, and it is not implied by a simple argument through finite propagation speed. $\endgroup$ – Emilio Pisanty Mar 24 '16 at 23:01
  • $\begingroup$ @EmilioPisanty: What I'm confused about it, though, is this: do I really have to predict the mathematical equation of something in order to make a prediction that it almost certainly exists? For example can't you presumably predict the speed of light is finite through observations without ever calculating what it should be? If I did that in the year 1800, would you not count it as a prediction if I didn't calculate $c$? Why is finding an equation considered part of predicting something's existence? Doesn't it suffice to predict how it should qualitatively behave? $\endgroup$ – Mehrdad Mar 24 '16 at 23:10
  • $\begingroup$ I don't have an answer. But recent observations put both lower and upper bounds on the GW speed. What is interesting is that, observationally, it is still possible to have either smaller than c or larger than c speeds. That is kind of uncomfortable especially regarding the upper bound which is slightly higher than c. If I re-find it, I will share the paper. $\endgroup$ – Benjamin Mar 25 '16 at 0:08
  • $\begingroup$ I can predict that, almost certainly, the singularities predicted by GR do not in fact happen. Does this mean I should get credit for whatever detailed theory demonstrates this? Hint: no. $\endgroup$ – tfb Mar 25 '16 at 0:11
  • $\begingroup$ If you put the formalism into action, I myself will give you ALL the credit and not just part of it. Seriously, If your prediction has some mathemtical (maybe not physical) base, it is worth putting efforts into it. $\endgroup$ – Benjamin Mar 25 '16 at 0:16

Well many things may have been known/predicted earlier, but Einstein put the General Relativity together that is mathematically comprehensive (general). His concept of space(time) was revolutionary. Once curving of space(time) is comprehended, I do not see any problem in understanding it's rippling. However, in Newton's theory, the concept of an interacting medium was not there. In GR, mass/energy, and space(time) do interact.

For the speed - we only know speed of the gravitational waves which is same as speed of light. I do not think we have experimentally proved speed of gravity itself. It is not impossible for speed of gravity and speed of gravitational waves to be different. Einstein certainly deserved credit for gravitational waves, because he introduced space(time) fabric and it's curving, rippling, distorting..

Then, to some small extent, the world also has tendency to give more credit to people/institutions who already have a lot of credit, and vice versa.


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