No Foam (quantum)

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MarkF
MarkF
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Topic 190710


The "Airy ring" around quasar PKS 1413 135 may eliminate one proposed form of quantum gravity.
I will post a more accessible link if I can find one.
Haven't found any other info: for those without Science online access the author's name is Yee Jack Ng

Chipper Q
Chipper Q
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No Foam (quantum)

Hi Mark. I found this one: "How Foamy is Spacetime?"

Some interesting comments in other threads regarding the implications of not directly detecting GW radiation with LIGO, and I was wondering what reasons there might be for that; as if GW radiation is somehow scattered, absorbed, or otherwise transformed into a different form of energy, by spacetime itself over long distances. If spacetime is discrete, and if the geometry of it is changed in a gravitational field, then might it be heated by this action (as in virtual particles acquire some energy)? Is the expectation for detection of GW with LIGO related to how 'foamy' spacetime is?

MarkF
MarkF
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Hi Chipper Q, thanks for

Hi Chipper Q, thanks for finding and posting the link.

I can't answer you question about why LIGO is showing a null result. Some form of GW should exist given what we know about gravity. I an not concerned yet but that might change if S5 is completed and we still have a null result.

If I understand this article than the quantum courseness is insufficient to seriously disrupt the light from the quasar. I would think the same argument would hold regarding GWs.

Ben Owen
Ben Owen
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Folks, The waves LIGO is

Folks,

The waves LIGO is looking for are very macroscopic in scale. Quantum gravity will not have much effect on them in the modern universe. Quantum gravity undoubtedly affects the shape of the early universe, and some signature of it may be imprinted on the stochastic background of gravitational waves. But it will be tricky detecting that with LIGO because in its frequency band the background from lots of distant "normal" sources (neutron stars etc) is probably louder.

The non-detection of gravitational waves so far isn't a surprise. At the current sensitivity (S5 data run), we have a fighting chance of seeing something in the next couple of years. After that there will be upgrades and it will get much better. If we find nothing in S5, that starts to say something astrophysically interesting about some neutron stars and other things, but doesn't get anyone worried about Einstein's theory not describing gravity well.

Keep on crunching,
Ben

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