Comments on: Out-Einsteining Einstein

By: Sonny

Sonny — Sun, 10 Dec 2006 02:20:43 +0000

Use Germanium Calthrates (university of Houston) to capture dark matter at cryogenic temperatures. More surface area equates to more particles seen. Gotta slow down the train to see it.

Smokyjinx 2006

By: Sonny

Sonny — Sun, 10 Dec 2006 01:16:27 +0000

Dark matter is exactly that it is dark to the naked eye
Because it is faster than the speed of light and can only be observed through Gravity
As an object approaches the speed of light, it condenses and becomes invisible
Undetectable is more like it. Matter is neither created nor destroyed.
Dark matter can pass through galaxies, because it is moving just past the speed of light.
It is hard to detect light in the dark
Dark matter and light enjoy a dance that to some is like doing the two - step for others the waltz
Just fast enough to be seen by gravitation but not fast enough to be observed without.
So we do see shapes and shadows, without light and dark matter we would not.
The reason dark matter appears slow because of the observation point.
Gravity is a bit more substantial than we thought
A famous man once stumped many with a theory called relativity
Dark matter too will be bent by space we just haven’t seen that effect yet.
I think maybe Einstein was on to something…

Einstein’s theory still holds. It is all relative.

Smokyjinx 2006

By: Rod Hartman

Rod Hartman — Wed, 06 Dec 2006 01:28:55 +0000

I’ve had a thought for quite a while that the universe may expand and contract, rather than expand endlessly - and we wuld never be able to tell which part of the cycle we were in.

In a contracting universe, bodies and matter would be accelerating toward the center of the universe, but bodies further out would be going slower. This would give the appearance that from any observation point, bodies closer to the center would be moving faster - giving the illusion of an expanding universe. And bodies further out would be moving slower - also giving the illusion of an expanding universe.

So as the universe expands, stops, and then collapses on itself we would have have an endless series of “big bangs”. Is this possible??

By: Coast to Coast | Cosmic Variance

Coast to Coast | Cosmic Variance — Sat, 02 Dec 2006 02:37:35 +0000

[…] Out-Einsteining Einstein […]

By: LeisureGuy

LeisureGuy — Sat, 11 Nov 2006 15:12:23 +0000

Hi, Belizean. No, I didn’t listen to the talk. Indeed, I probably would not have understood it. I came across this posting on the Web, and asked the question that’s been bothering me. I figured asking a question was okay, and maybe I’d get an answer.

And indeed I did. Thank you, Collin. I much appreciate the pointer.

By: Shantanu

Shantanu — Fri, 10 Nov 2006 23:52:55 +0000

Sean, what’s the latest story on apsidal motion of DI Hercules and its observed discrepancy with GR? I can’t recall any recent papers on this? Since you have worked on this system ,
could you give a brief overview of what accoridng to you (and also the general
community) is the consensus on this issue?
Thanks

By: Belizean

Belizean — Fri, 10 Nov 2006 17:22:39 +0000

In the linearized theory (which is where talk of “gravitons” makes sense), gravitons couple precisely to their own energy-momentum tensor. Then you notice that such a coupling contributes to the energy-momentum tensor, so you add another term, and start an infinite series, which (as was discovered by a bunch of people in the 60’s) gives you the full nonlinear Einstein equation.

You’re right. Except that the gravity-self interaction contribution to the energy-momentum tensor gets moved over to the left side of the Einstein equations. It is not part of ususal definition of this tensor (which is restricted to the matter contribution).

So when you say that gravitons couple to energy-momentum, you mean that in the broad sense of an energy-momentum tensor augmented by a gravitational-self interaction piece. [This is a just a silly quibble on my part that boils down to whether “energy-momentum” = “standard energy-momentum tensor”.]

By: Sean

Sean — Fri, 10 Nov 2006 15:02:34 +0000

andy.s — “tensor-vector-scalar” isn’t a new kind of mathematical beast; it just refers to the fact that the theory includes a dynamical tensor field, a vector field, and a scalar field.

By: Sean

Sean — Fri, 10 Nov 2006 14:11:38 +0000

In the linearized theory (which is where talk of “gravitons” makes sense), gravitons couple precisely to their own energy-momentum tensor. Then you notice that such a coupling contributes to the energy-momentum tensor, so you add another term, and start an infinite series, which (as was discovered by a bunch of people in the 60’s) gives you the full nonlinear Einstein equation.

By: Belizean

Belizean — Fri, 10 Nov 2006 05:12:04 +0000

It’s the energy-momentum tensor that the gravitons couple to, not the metric. You’re right, coupling to the metric is automatic. Gravitons are just small perturbations of the metric around a smooth classical solution.

Gravitons, unlike photons, also couple to their own energy. I suppose you could make this self-coupling look as though it’s sourced by a stress-energy tensor, but it really isn’t.