Arcadian Functor

occasional meanderings in physics' brave new world

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Marni D. Sheppeard

Thursday, October 29, 2009

LHC Era Begins

As the LHC begins operations, real tests were run on the beam through LHCb. The LHCb RICH detector has also seen its first particle from cosmic rays, as the two rings shown here.

5 Comments:

Blogger CarlBrannen said...

Kea, best evidence yet for the speed of gravity not being c: Searches for gravitational waves from known pulsars with S5 LIGO data. Of course still no observation of gravity waves, but now they admit:

... updated limits on gravitational radiation from the Crab pulsar, where the measured limit is now a factor of seven below the spin-down limit.

That is, they see no gravity waves in violation of general relativity by a factor of 7. What they should do is look for considerably slower pulses. The problem is figuring out just how much slower as this depends on the distance and the speed of gravity.

October 31, 2009 10:53 AM  
Blogger Matti Pitkanen said...

Interesting. My own explanation would be in terms of large Planck constant (see this. Gravitons would come as large hbar quanta with very large energy E= hbar f decaying into bursts of ordinary gravitons. These bursts would be interpreted as noise in GRT based theoretical context.

October 31, 2009 8:06 PM  
Blogger Kea said...

Carl, I don't believe in gravity waves. On the other hand, perhaps there are some observable effects related to characteristic quanta for gravity ... only I can't see how a LIGO type detector would have any hope of seeing them, based as it is on a very naive idea of wave.

November 02, 2009 10:06 AM  
Anonymous Rhys said...

CarlBrannen wrote:
"That is, they see no gravity waves in violation of general relativity by a factor of 7."

That's not what they say, and that's not what they mean. The rate of spin-down gives the total rate of rotational energy loss, and therefore an absolute upper bound on the amount of energy emitted in any given channel. Their results (if robust) imply that gravitational waves carry away only a small fraction of the rotational energy being lost.

Kea wrote:
"Carl, I don't believe in gravity waves."

And I'm sure you have a strong argument to back up such a seemingly bizarre opinion...

November 02, 2009 9:29 PM  
Blogger CarlBrannen said...

Rhys, re "That's not what they say, and that's not what they mean."

Of course not. You have to read what they were saying BEFORE they got the null results, LOL.

Search for Palomba+crab+gravity+wave, for example Beating the Crab pulsar spin-down
and other upper limits: new results
from the LIGO S5 known pulsar
search
.

The above references Palomba 2000, Pulsars ellipticity revised A&A, 354, 163 as having computed a gravity wave production by the Crab Nebula of 1/2.5 of spin down. Since LIGO is at 1/7 of spin down, they missed the verification of GR by about a factor of 3.

Nor is this is the first time the gravity wave people have come up with unexpected null results. The other incident is also documented on Kea's blog and had to do with a GRB.

November 03, 2009 12:07 PM  

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