- Joined
- Aug 20, 2009
- Messages
- 44,689
- Reaction score
- 26,915
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?
"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?