Einstein Still Rules, Says Fermi Telescope Team

by Nancy Atkinson on October 28, 2009

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In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect. The animation below shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet

In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect. The animation below shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet

While the Fermi Space Telescope has mapped the gamma ray sky with unprecedented resolution and sensitivity, it now has been able to take a measurement that has provided rare experimental evidence about the very structure of space and time, unified as space-time. Einstein’s theory of relativity states that all electromagnetic radiation travels through a vacuum at the same speed. Fermi detected two gamma ray photons which varied widely in energy; yet even after traveling 7 billion years, the two different photons arrived almost simultaneously.

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.”

“Physicists would like to replace Einstein’s vision of gravity — as expressed in his relativity theories — with something that handles all fundamental forces,” said Peter Michelson, principal investigator of Fermi’s Large Area Telescope, or LAT, at Stanford University in Palo Alto, Calif. “There are many ideas, but few ways to test them.”

Artist concept of Fermi in space. Credit: NASA

Artist concept of Fermi in space. Credit: NASA


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.

GRB 090510 displayed the fastest observed motions, with ejected matter moving at 99.99995 percent of light speed. The highest energy gamma ray yet seen from a burst — 33.4 billion electron volts or about 13 billion times the energy of visible light — came from September’s GRB 090902B. Last year’s GRB 080916C produced the greatest total energy, equivalent to 9,000 typical supernovae.

More images and videos about the Fermi Space Telescope.

Lead image caption: In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect. The animation below shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet

Source: NASA

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Lawrence B. Crowell October 30, 2009 at 1:13 PM

I have read Susskind, which for me is more interesting for the historical and stroy telling aspects than the physics. The physics I already understand. Lenny Susskind does lay out a decent layman’s case for conservation of information in black holes. Randall’s book I have yet to read.

A good technical book on string theory and black holes is also by Lenny Suskind “An introduction to black holes, information and the string theory revolution,” which you can find at:

http://books.google.com/books?id=cxJCBRUNmVYC&pg=PP3&lpg=PP1#v=onepage&q=&f=false

String theory has its own difficulties of course. In particular the curvature Lagrangian is the standard sqrt{-g} R plus an expansion on this classical background of the form alpha’R^2 + higher orders. The LQG people point to this as a main complaint with string theory. It is an expansion around a background. I do think I have found a way around this problem :-) however. The most general Lorentzian spacetime is the exceptional J^3(O) matrix in 26 dimensions, reduced from 27 with a light cone condition or the “infinite momentum” frame. There are three E_8′s there which under a triality define as well an 8 + 3 = 11 dimensional space, which under this condition is compactified to 10. This has as its automorphism groups F_4 (whose root space is a minimal tessellation in 4 dimensions) and G_2. The G_2 acts as a holonomy of M^7 and its transformations are tied to those of F_4 in a way which reduces gauge-like theory for the gravitational multiplet to an abelian Skyrme theory. The basis elements of the automorphisms are e_a = ?^dagger gamma^a? (gamma^a a Dirac matrix in the Clifford Cl_{7,1}) which defines connection terms according to internal fermion degrees of freedom.

It think these internal fermion degrees of freedom behave as Landau electrons around a quantum critical point. This renormalizes the cosmological constant to a small value.

Cheer LC

Jon Hanford October 30, 2009 at 5:01 PM

What a small world, I already own the 2005 book by Susskind (“An introduction to black holes…”) and could only follow the maths in a few sections. I’ll seek out the other Susskind and Randall books to help get my feet wet in this field. Then maybe I can get through the entire 2005 Susskind book! Thanks again, LC.

Lawrence B. Crowell October 31, 2009 at 4:58 AM

It is too bad this thread has fallen off the first page. If you are interested in an overview Susskind’s “Black Hole Wars” is entertaining.

LC

Alfonso Leon Guillen Gomez November 2, 2009 at 8:50 AM

Why the two different photons did not arrive simultaneously?.
Why the photons of less energy arrived first?.

IVAN3MAN November 2, 2009 at 1:18 PM

@ Alfonso,

The same reason why the sky is blue and not pretty pink! ;-)

Alfonso Leon Guillen Gomez November 3, 2009 at 7:17 PM

Did photons travel to speed c? The difference in energy of a million times is significant? What the outcome would between the higher energy photons of gamma rays and photons of visible light?

pellis November 4, 2009 at 10:26 AM

“Fermi detected two gamma ray photons which varied widely in energy; yet even after traveling 7 billion years, the two different photons arrived almost simultaneously.”

If the article means, literally, *two* photons, then how can they tell that the two photons started from the same (or extremely close) points in spacetime?

Why can they dismiss the possibility that the two photons came from very different points, and merely arrived at the detector at nearly the same time?

DrFlimmer November 4, 2009 at 12:27 PM

@ Alfonso:

Photons ALWAYS travel with the speed of light in vaccum. That does not depend on their energy. The energy only says something about the wavelength and the frequency of the photon.

@ pellis

Detectors in these days are able to say, from which direction the photons came. So this reduces the possibility that those photons arrive at the same time by chance. Still you cannot rule out such a possibility, because there could be two sources close to each other on the plain of the sky. But Fermi looks for gamma ray sources, and those are seldom and only rather strong sources are detectable at all. So you can assume that it is very likely that the source is the same.

Alfonso Leon Guillen Gomez November 4, 2009 at 2:04 PM

According to Quantum Physics standard and Relativity standard in vacuum the photons and the gravitons travel to the speed c, because they do not interact with vacuum. But, in some alternatives theories no, because they interact with vacuum. For example, in 2001, Dimitri Nanopoulos, Nikolaos Mavromatos and John Ellis found a new expression to speed of the photon, depending of their frequency; this is, of their energy. In other alternative theory, the LQG, it says too.

Since 2006, we was expected that GLAST, today Fermy, would show that alternatives theories are false. But, sadly the great day arrived and this does not occurred. However, some readers of the news say that if.

I wrote to distinguished professor Dimitri Nanopoulos and in E-mail, 1 of November 14:38, he said. “No it is not!”.

In my opinion, Fermy detected that two gamma ray photons which varied widely in energy, differing by a million times; yet even after traveling 7 billion years, the two different photons arrived almost simultaneously; and the team of Fermy showed that “to one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules”. Not more!.

pellis November 4, 2009 at 2:52 PM

To Dr Flimmer

Thanks for the clarification – I agree that knowing the direction and high energy of the photons reduces the chance of line of sight coincidence of a second source, but for alternative theories to be ruled out by observation I would hope for more convincing proof, or at least an estimate of the likelihood of the result not being a coincidence, such that the probability might be reduced by successive observations.

I would not throw out LQG just yet…

DrFlimmer November 4, 2009 at 3:08 PM

My knowledge about String Theory, LQG and all that things is far too rudimentary. So I don’t want to judge them, and neither do I want to say something specific.

I still hold to: c is the same. If some other theories are right, we will see that in the future.

Lawrence B. Crowell November 8, 2009 at 5:39 AM

Nanopoulos and co. have tendencies to make some outlandish claims. The photon does not couple to the vacuum state in the same way a photon does in a medium so as to display dispersion. I think this is fairly clear.

LC

Alfonso Leon Guillen Gomez November 9, 2009 at 1:14 PM

To test alternatives theories, in moment only there are two registers on radiation gamma; they are based on very different facts:
- Register of Fermi is based in an phenomenon that Astronomers think is cause of explosion when neutron stars collide , to 7.3 billion light-years away, and with photons possessed energies only differing by a million times.
- The register of Magic is based in a blazar to notable minor distance, that showed an indication of a 4±1 min time delay between the peaks of F(1.2 TeV).

Magic, 3 years after, it uses to probing quantum gravity; result is: “The probability of the zero-delay assumption relative to the one obtained with the ECF estimator is P = 0.026. The observed energy-dependent delay thus is a likely observation, but does not constitute a statistically firm discovery.”.

I think that register Fermi is affected strongly by Universe expansion, changes in density of energy of vacuum; and probably changes in permittivity and permeability. This is much minor in Magic. This will give to speculate. For example, in register Fermi, if photons interact with vacuum in two ways, that is, photon-vacuum and vacuum-photon then can that higher photon travel faster that low photon inside of an unknown lapse?. But, result of carrier is that pair arrived just nine-tenths of a second apart.

Of other hand, I have a great respect to both teams. Team of Magic is compound by a great number of scientists and in the test on quantum gravity also are included the emeritus professors D. Nanopoulos, John Ellis, N. Mavromatos, A. Sakharov, E. Sarkisyan.

Alfonso Leon Guillen Gomez November 9, 2009 at 1:54 PM

warnings: – By F(>1.2 TeV) read F(1.2 TeV).
- By carrier read race.

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