December 18, 2017

04.04.10-Fermi: Einstein Still Rules.

We just can’t seem to get enough of NASA’s Fermi Gamma-Ray Space Telescope. The successor to the late Compton observatory that was de-orbited in 2002, Fermi has already pinpointed over 1,000 discrete gamma-ray sources, five times more than previously known. Now Fermi has also provided a rare test of Einstein’s theories of relativity. Relativity says that all electromagnetic waves (including highly energetic gamma-rays) travel through space at the same cosmic speed of 186,282 miles per second. Being a classical theory, however, what Einstein doesn’t do is meld gravity satisfactorily with the other three fundamental forces; electromagnetism and the strong and weak nuclear forces. Gravity stubbornly refuses to be unified, and such a goal has been the holy grail of physics for over the last half century. An alternative model of gravity at the microscopic scale would say that the nature of space-time is “frothy,” and a predicted effect should be a measureable drag induced on high energy photons. Recently, Fermi had a chance to put this to the test; on May 10th of last year, GRB 090510, a short gamma-ray burst 7.3 billion light years distant, was measured by Fermi’s Large Area Telescope. The verdict; gamma-ray photons varying a by a factor of a million times in energy arrived just nine-tenths of a second apart, far below what would be predicted by “frothy” space… that’s round one for Einstein!