
Does Gravity Travel at the Speed of Light? - ColinWright
http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html
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RuggeroAltair
Steve Carlip used to be my advisor in grad school and his style of writing
shows his beautiful way of explaining (and thinking about) deep questions in
physics.

One think that I believe is important to point out is that this short essay is
focusing on the experimental aspect of the measurement of the speed of
gravity. It gives an explanation on why this is even an intelligent question
to answer and why the answer we commonly accept is that gravity moves at the
speed of light. I will never have better words than him so I won't add
anything to what he said.

What I would like to point out, is that this essay is not talking about
whether or not theoretically would be possible to have a speed of gravity
faster than the speed of light. General relativity and special relativity have
been tested on several aspects, and they pretty much are in agreement with all
experimental constraint. There is no other theory that can explain everything
we see (some theories tend to explain a few things, but not all of them, or
they are too vague).

A theory in which the speed of gravity is faster than the speed of light isn't
unconceivable per se, but no one has been able to write a completely
consistent one yet, mostly because it would have large consequences on what
special and general relativity imply for cosmology and particle physics (and
causality). If gravity moved faster than the speed of light then we'd have to
'fix' a lot of problems coming down to paradoxes and stuff like that.

So take this essay as a way to appreciate how elegant and fine some
experimental questions on gravity (and physics) are.

