Physics team finds new constraints on how lumpy space-time can be

January 11, 2012 by Bob Yirka, weblog
Image credit: NASA/Sonoma State University/Aurore Simonnet

( -- Robert Nemiroff and his colleagues at Michigan Technological University will be discussing new constraints on the so-called lumpiness of space-time at this year’s meeting of the American Astronomical Society.

Nemiroff, also known for his Astronomy Pick of the Day site, has been studying that have been traveling through space for several billion years following a γ-ray burst that was recorded back in 1989. Called GRB 090510A, the burst let loose high energy photons that have been traveling through space at the speed of light; two of them are of special interest to physicists because they are believed to have left the same place at exactly the same time, which would seem to make them arrive here at exactly the same time as well. But, they won’t, due to the lumpiness of space-time and the long distance they have traveled.

In the abstract for the presentation, the authors suggest that because a high-energy time scale for the photons detected from the gamma-ray burst have been found, a new upper limit is in place on the dependence of energy on speed and light as it’s dispersed across the universe.

Studies of high energy photons traveling through space have already shown there are differences in actual speeds recorded, though they are very, very small; seven parts in a billion trillion, according to a previous study done by researchers at Yale. Because of this and other studied phenomenon, various researchers have theorized that space-time isn’t actually continues as it appears, but is instead made up of very, very tiny elements that are almost unbelievably small, on the order of a 10-35 (the Planck length). In such theories, photons that have the highest amount of energy also have wavelengths that are near to the Planck length. This makes them more apt to intermingle with so-called “lumps” which slows them down. The amount of slowdown is obviously very tiny, but as the photons travel so far for so long, the effect is amplified.

In their study, Nemiroff et al, find due to measured differences in the arrival time of the two photons, that new constraints are in effect that impact the lump size of space-time. Because of this, the lumpiness of space-time only becomes meaningful when things are roughly 1/500 the Planck length, which could, obviously, put some limits on quantum gravity theories.

Explore further: Gamma Ray Delay May Be Sign of 'New Physics'

More information: Nemiroff, R. J., Connolly, R., & Holmes, J. A New Limit on Lorentz Invariance and Chromatic Dispersion Across the Universe from GRB 090510A (American Astronomical Society, 2011)

A high-energy, fast-variability time scale for Fermi-detected gamma-ray burst GRB 090510A is found that creates a new strictest upper limit on the energy dependence of the speed and dispersion of light across the universe. In particular, evidence is presented for variability at or below Δ t = 0.00136 for super-GeV photons, a factor of 10 more limiting than any time scale previously claimed for a GRB at GeV energies, including a previous limit reported by Abdo et al (2008). This variability derives from the duration of three separate closely-arriving photon groups prominent only in photon data above 1 GeV. One pulse pair has an energy difference of Δ E >/~ 23.5 GeV. Coupled with a redshift of z >/~ 0.897, the resulting limits on the differential speed of light and Lorentz invariance were found for a concordance cosmology. It was found that Δ c / c < 6.09 x 10-21, a limit consistent with, but slightly stronger than, a previous limit found for a GRB by Schaefer in 1999. Given a generic dispersion relation across the universe where the time delay is proportional to the photon energy to the first power, the variability translates into a dispersion strength of k1 < 1.38 x 10-5 sec Gpc-1 GeV-1. This limit results in an upper bound on dispersive effects created, for example, by dark energy, dark matter, or the spacetime foam of quantum gravity. This dispersion constraint also results in the most stringent lower limit yet claimed for the onset energy scale of quantum gravity: MQG c2 > 7.43 x 1021 GeV.

via Nature

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5 / 5 (2) Jan 11, 2012
Their lower bound is in accord with that found 1 yr ago by Laurent etal, http://www.physor...ein.html
They see Gamma ray dispersion at an incredible Mqg ~ 10^32 Gev, 14 decades higher than the Planck mass.
1 / 5 (2) Jan 11, 2012
IMHO, this also fits a momentum dependent interaction with gravity. The quantum packet's probability as massive virtual particles alters the path integral. This would imply a tiny frequency dependence on the angle of lensing events.
1 / 5 (10) Jan 11, 2012
In AWT the high energy gamma ray bursts are actually dispersed a way more, than it corresponds the above limit - their photons are moving collectively as a single vortex/soliton, being tied with their own gravity field, thus reaching far longer distance without attenuation. http://aetherwave...rsy.html

1 / 5 (4) Jan 12, 2012
Called GRB 090510A, the burst let loose high energy photons that have been traveling through space at the speed of light; two of them are of special interest to physicists because they are believed to have left the same place at exactly the same time, which would seem to make them arrive here at exactly the same time as well.

Comment: Photons move in space (quantum vacuum) only not in space-time which is merely a math model. Time is a numerical order of photon motion. In the Block Universe model time is a numerical order of change, see more at: http://www.spacel...lativity
1 / 5 (4) Jan 12, 2012
The spacetime doesn't exist.
1 / 5 (3) Jan 12, 2012
Photons move in space (quantum vacuum) only not in space-time, The spacetime doesn't exist.
Why not, why yes...
What that would imply? The ideas without testable predictions are infalsifiable. The unfalsifiable predictions are just a belief, the spreading of belief is propaganda. http://imgs.xkcd....eory.png
1 / 5 (5) Jan 12, 2012
space-time does not exist as time is related to change not to space......time is numerical order of change in space.
2.6 / 5 (5) Jan 12, 2012
I see, another Oliver Manuel - just in atemporal form. The reasoning and conclusions aren't important, the ideas are. After all, what else to expect from deniers of the causality arrow...
not rated yet Jan 12, 2012
presumably all these results are consistent with 0 dispersion.
4 / 5 (4) Jan 13, 2012
time is numerical order of change in space.
Change is a numerical order of time. The math works if you use time. It won't if you use change. So your idea is pure crap and completely worthless. You can't make any predictions with your idea. Worse than The String Hypothesis. It isn't even worth saying it isn't even wrong.

Your posts on this are still bad philosophy and still not science. Your evasions of questions are still Crank standard behavior.

I still pity your students.

5 / 5 (4) Jan 14, 2012
This article sure brings in the kooks.
1 / 5 (1) Jan 17, 2012
Photons move in space (quantum vacuum) only not in space-time which is merely a math model.
So how do you express the uncertainty principle in terms of change in energy delta E?
1 / 5 (1) Jan 19, 2012
"they are believed to have left the same place at exactly the same time," in which case it seems like they would have travelled over the same path of lumps. So maybe they mean they travelled the same distance and therefore should have arrived at the same time.

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