Mysterious Radio Signals Now Used to Test Einstein’s Equivalence Principle

This new method is ten to one-hundred times more accurate.

Have you ever felt the desire to test one of the basic principles underlying Einstein's theory of General Relativity?  Yeah, me neither, but now scientists have discovered a new way that is ten to one-hundred times better than previous testing methods.

Previous methods used gamma-ray bursts, but this new method uses rare radio signals from space known as Fast Radio Bursts (FRBs).  FRBs are blasts of energy that last only milliseconds, and until now, only about a dozen FRBs have been detected on Earth.  Researchers are not exactly sure what causes these mysterious radio signals, but evidence points to them being generated beyond our Milky Way Galaxy.

Currently, advanced radio-signal observatories are being planned and built in hopes to analyze many more observations of FRBs.  “With abundant observational information in the future, we can gain a better understanding of the physical nature of Fast Radio Bursts,” said Peter Mészáros, Professor of Physics at Penn State and the senior author of the paper.

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This new method will most likely lead to discovering the origin of FRBs, and according to Mészáros, “If Fast Radio Bursts are proven to originate outside the Milky Way Galaxy, and if their distances can be measured accurately, they will be a new powerful tool for testing Einstein's Equivalence Principle and for extending the tested energy range down to radio-band frequencies.”

Einstein’s Equivalence Principle states that any two photons of different frequencies, emitted at the same from the exact same source and traveling through the same gravitational fields, should arrive at Earth at exactly the same time.   This means the researchers are going to measure, in time, how two different frequency photons arrive at Earth — testing how closely they obey Einstein’s Equivalence Principle.  This concept is illustrated in the image below.

photo credit: Purple Mountain Observatory, Chinese Academy of Sciences

So far, Mészáros and his team have analyzed less than a dozen detected FRBs, and preliminary results point to its accuracy being one or two orders of magnitude better than previous results based on gamma ray bursts.  “Our analysis using radio frequencies shows that the Einstein Equivalence Principle is obeyed to one part in a hundred million,” Mészáros said.  “This result is a significant tribute to Einstein's theory, on the hundredth anniversary of its first formulation.”