Say goodbye to Loop Quantum Gravity (sadly)

Andy Capp

Captain Pedantic Utility Belt
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Well, it seems if there is a quantum foam, it's barely there and not foamy at all. It has been the popular belief among physicists lately that at the smallest scales, space is divided into discrete units constantly affected by quantum fluctuations. On the other hand, according to Einstein,

"Such a model would violate Einstein's edict that all electromagnetic radiation -- radio waves, infrared, visible light, X-rays and gamma rays -- travels through a vacuum at the same speed."

Quantum Foam and Loop Quantum Gravity

"Predictions and Tests:"

"Nevertheless, radiation from distant cosmic explosions called gamma-ray bursts might provide a way to test whether the theory of loop quantum gravity is correct. Gamma-ray bursts occur billions of light-years away and emit a huge amount of gamma rays within a short span. According to loop quantum gravity, each photon occupies a region of lines at each instant as it moves through the spin network. The discrete nature of space causes higher-energy gamma rays to travel slightly faster than lower-energy ones. The difference is tiny, but its effect steadily accumulating during the rays' billion-year voyage. If a burst's gamma rays arrive at Earth in slightly different times according to their energy, that would be evidence for loop quantum gravity. The GLAST satellite, which is scheduled to be launched in 2005, will have the required sensitivity for this experiment."

Fermi Telescope Caps First Year With Glimpse of Space-Time

Many approaches to new theories of gravity picture space-time as having a shifting, frothy structure at physical scales trillions of times smaller than an electron. Some models predict that the foamy aspect of space-time will cause higher-energy gamma rays to move slightly more slowly than photons at lower energy.

Such a model would violate Einstein's edict that all electromagnetic radiation -- radio waves, infrared, visible light, X-rays and gamma rays -- travels through a vacuum at the same speed.

On May 10, 2009, Fermi and other satellites detected a so-called short gamma ray burst, designated GRB 090510. Astronomers think this type of explosion happens when neutron stars collide. Ground-based studies show the event took place in a galaxy 7.3 billion light-years away. Of the many gamma ray photons Fermi's LAT detected from the 2.1-second burst, two possessed energies differing by a million times. Yet after traveling some seven billion years, the pair arrived just nine-tenths of a second apart.

"This measurement eliminates any approach to a new theory of gravity that predicts a strong energy dependent change in the speed of light," Michelson said. "To one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules."



I have always favored Loop Quantum Gravity (what little I know of it) over String Theory mainly because it makes testable predictions. Sadly that also it means it can be ruled out at stroke and that is just what has happened.

Einstein wins again. I wonder how this result affects the arguments of those elsewhere on here that rather than a singularity, the Universe began with a bubble, blob, or other non-singular entity. I suspect the result is that those ball-like hypotheses are similarly invalidated by this result. I don't think it rules out branes, but then, I don't think branes rule out big bang cosmology.

I'm happy to hear the comments of trained physicists on this matter. Is there a PhD in the house?
 
This is sherdog.... Not a Mensa forum



I liked that tv show about those 2 dudes time traveling
 
I don't even know what this means...

Basically, it's a serious setback for people trying to unite Relativity and Quantum Mechanics because a large part of these theories is so-called quantized spacetime; they say space is composed of segments rather than being smooth. This new information says they are all wrong or, more likely, will need a total rewiring.
 
I don't think they will ever untie quantum theory and relativity.

They need some fresh stuff.
 
I'm happy to hear the comments of trained physicists on this matter. Is there a PhD in the house?

You've come to the right place bro. Take a seat and one our thousands of theoretical physicists will be with you shortly. I would give my own opinion on the matter but I could only express my thoughts using mathematics that are too complex for the feeble minded non-plats in the forum. But if you insist...My thoughts on the matter are the following.

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i have nothing to contribute but i enjoy reading this stuff. ty
 
You've come to the right place bro. Take a seat and one our thousands of theoretical physicists will be with you shortly. I would give my own opinion on the matter but I could only express my thoughts using mathematics that are too complex for the feeble minded non-plats in the forum. But if you insist...My thoughts on the matter are the following.

main-qimg-7beca9cf6c835bdfeabac3541a778973

So the answer is 42?
 
Apparently you haven't. The thread on how to be a dick is in the War Room.

Really? I came off like a dick in my post? Cause I reread it a few times and it just seems like a bit of banter...at the very worst a failed attempt at humor. Where are you picking up the animosity in my post?
 
Always glad to see these types of articles posted as the internet pulls me to useless time wasting crap.
There are so many hypotheses and theories out there and they are all constantly changing, so I never really anchor myself to anything. I never really got into the quantum foam theory myself, it never felt fluid enough for my tastes.
 
I've taken 2 quantum course and my grad work was in radiation physics and I don't know what it means.

If I were you that would make me very sad. But seriously, it's just, here's what almost all the leading theories about combining Relativity and Quantum Theory say, and here's why almost all of them are wrong.

How much of this is recent? Seems that NASA page was last updated in 2009.

Right, but I hope you will understand and agree that sometimes it takes a while for scientific results to percolate just because there are so many of them coming out all the time. The results are from 2009 but it's the first time I saw them, for example.

I wonder you don't hear much from the scientific community about people changing their field of study (like the fictional Sheldon on BBT) because of this result. To me it seems a little shattering to their ideas that there is no sign of this spacetime lumpyness.

Really? I came off like a dick in my post? Cause I reread it a few times and it just seems like a bit of banter...at the very worst a failed attempt at humor. Where are you picking up the animosity in my post?

Your post implied (to my sarcasm detector) that it was worthless to make such a post on Sherdog and I replied that your post was equally worthless. Just banter.

But I also may have misjudged an attempt at humor for sarcasm so take it FWIW. I might be spending too much time in the War Room myself.

Always glad to see these types of articles posted as the internet pulls me to useless time wasting crap.
There are so many hypotheses and theories out there and they are all constantly changing, so I never really anchor myself to anything. I never really got into the quantum foam theory myself, it never felt fluid enough for my tastes.

Yes, there are a lot of theories but they are mostly variations on a small number of basic assumptions/conditions. The idea of quantized space, i.e. that rather than being totally smooth, space and time are made up of discrete but very tiny chunks, is fundamental to most of these theories. This result sort of gives them a smack down.
 
I don't think they will ever untie quantum theory and relativity.

They need some fresh stuff.

I am not certain, but I am inclined to agree. I think a mathematical revolution of some kind is necessary. Right now the math is so complex that it gets in the way of any fundamental new ideas, I think.
 
Your post implied (to my sarcasm detector) that it was worthless to make such a post on Sherdog and I replied that your post was equally worthless. Just banter.

My sincere apologies if it came off like that. I actually love posts like the OP. I might not be able to wrap my brain around 100% of it (which is actually what I was poking fun at...more of a self deprication at my own ignorance...definitely not to demean your post) Sorry mate!
 
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