Comments on: Why Does Gravity Wave, And Why Does It Matter?

By: Larry Coleman

Larry Coleman — Sun, 18 Sep 2016 17:38:38 +0000

Right. But as you point out, with SR the field change would not be instantaneous.
The point is that in a universe without GR, but with gravity, it is possible to have gravitational waves. All you need is gravitational fields with mass sources and finite propagation. Yes, GR would have to be replaced with something else, but nature is not only queerer than we suppose….
The observation of gravitational waves is not per se a demonstration of GR, albeit a magnificent achievement with loads of promise.

By: Brian Koberlein

Brian Koberlein — Thu, 15 Sep 2016 14:30:53 +0000

In Newtonian gravity forces are instantaneous, so there would be no waves. You can’t simply treat gravity like an electromagnetic field. Folks have tried and if doesn’t agree with experiments.

By: Larry Coleman

Larry Coleman — Thu, 15 Sep 2016 14:17:50 +0000

Not to diminish the importance of the recent LIGO detection, but you don’t really need General Relativity to have gravitational waves. Without GR, if you were to accelerate a mass, a kink would be produced in the gravitational field lines, and this kink would be propagated through space: a gravitational wave is born.

By: Jpatrick

Jpatrick — Fri, 19 Feb 2016 17:07:43 +0000

Many thanks for this link. The author does a remarkable job of dealing with rather arcane subject matter.

By: Brian Koberlein

Brian Koberlein — Thu, 18 Feb 2016 14:45:52 +0000

Basically LIGO is a Michelson interferometer.

By: Ron

Ron — Wed, 17 Feb 2016 22:55:32 +0000

LIGO detected gravitational waves using an apparatus which was capable measuring very small units of length. Would LIGO be useful as a more accurate Michelson interferometer to better test the wave nature of light at these small dimensions?

https://www.ligo.caltech.edu/page/ligos-ifo

By: Ron

Ron — Wed, 17 Feb 2016 19:00:44 +0000

Could we use Ligo as a Michelson interferometer?

Dark matter is suspected to influence gravitation in the universe and light is curved in space-time. As we now have detected gravity waves in a very small dimension is there still any chance the aether does exist only at these very small dimensions? I’ve always been a medium-minded person when it comes to light though all experiments so far have yet to show it. Now that we have a sensitive-enough interferometer will those experiments be run again?

Or, as I suspect, do I just need to learn relativity in a higher dimension…

By: Brian Koberlein

Brian Koberlein — Wed, 17 Feb 2016 16:02:33 +0000

It's not nearly as simple since gravitational waves are in general nonlinear, but you can see derivations of linear equations here.

By: Jpatrick

Jpatrick — Wed, 17 Feb 2016 15:58:28 +0000

For electromagnetic energy, the energy E of a photon is

E = hν = hc/λ,

Where h is Planck’s constant, c is the speed of light, ν is the frequency, and λ is the wavelength.

Of what form would be the expression for the energy of gravitational waves?

By: Rich B.

Rich B. — Wed, 17 Feb 2016 14:35:56 +0000

Thx. I’ll give your post a careful read!

By: Brian Koberlein

Brian Koberlein — Wed, 17 Feb 2016 14:13:04 +0000

It's the founding idea of general relativity.

By: Rich B.

Rich B. — Wed, 17 Feb 2016 13:28:56 +0000

Excellent post, but this sentence has me puzzled:

“Since all bodies fall at the same rate regardless of their mass, a body floating freely in space must be equivalent to a body falling freely.”

Equivalent in what way? Can someone offer a succinct explanation? Thanks!