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#44958 08/23/12 10:42 PM
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Bill Offline OP
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Phys.org has a report on some research concerning the granularity of space; Spacetime: A smoother brew than we knew.

Observing photons from a gamma ray burst that arrived at the same time the researchers decided that they should not have arrived so close together after coming 7 billion light years, if the universe is granular at the Planck length (approximately 1.6 * 10^35 meters). The Planck length granularity should have scattered them so that they arrived at different times.

Probably not a definitive measurement, there will be people who disagree with them, but if their findings are upheld it will have a significant influence on quantum gravity research.

Bill Gill


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Thanks, Bill, very interesting. This is something that's long puzzled me: Why should any theory of quantum gravity be based on an assumption that space is granular at the Planck length? I'm not suggesting that's it's assumed without reason - I just don't know what the reason is. Sure, we are reliably informed that directly measuring a smaller length would be impossible - but why should that impose a boundary on physical reality?


"Time is what prevents everything from happening at once" - John Wheeler
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I'm not familiar with all of the steps they went through to reach this conclusion, but I think the basic idea is that they know energy is quantized, so why shouldn't space and time also be quantized? It is just one of those things that looks as though it ought to follow a pattern. So if space is quantized then what is the size of the space quantum? The Planck length just happens to be a handy size to start with. And of course for time the Planck time would be a handy size.

Bill Gill


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You got is spot on Bill it looks like it should but it is far from a science fact.

The most authoritive science on gravity being GR is completely linear.

Quantum gravity is one attempt to merge quantum mechanics with GR/SR the logic being something quantized fine enough can look linear like diagonal lines on your computer graphics screen which when you look closely are pixel quantized jaggies.

There are not many ways a quantized thing and a linear thing can merge assuming both are correct.

I should add that there was also a great deal of excitement when quantum electrodynamics (probably the most accurate and tested theory in science) was found to actually contained special relativity seamlessly within it. The only real conflict between SR and QM is the weird state of entanglement.

I should say there are stalwarts that agree that SR and QM give the same answer but QM is quantizing time for no apparent reason and QM time isn't even real time its a parameter. So they give the same answer but no idea as to why and you end up using Feynman's explaination "shut up and calculate".

So lets say that the merger of QM and SR remains topical to science from time to time.

Last edited by Orac; 08/24/12 02:14 PM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.

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