Dig that reverb (Image: Henning Dalhoff/Getty)

HEAR that? Echoes bouncing around the universe might be carrying messages from shortly after the big bang.

The earliest light in the universe is more than 13 billion years old, its photons dating back to an era when plasma generated in the big bang cooled enough to let light through. These photons carry information about the state of the early universe, but have been growing ever fainter. Now they form the cosmic microwave background, a low-level sea of radiation permeating the universe.

Eduardo Martín-Martínez of the University of Waterloo in Ontario, Canada, and his colleagues think they have found another, better-preserved source of clues about the very early universe. They calculated that events which produce photons – such as an atom releasing energy – also create certain echoes in the electromagnetic field, the very field which forms the basis of light.


To test how these could carry information, the team imagined someone in the early universe sending a message into the distant future by creating a series of echoes and using them to encode a string of 0s and 1s. These echoes travel slower than light but do not fade, meaning they can carry more information than photons over large distances (arxiv.org/abs/1501.01650).

They imagined someone in the early universe sending a message of 0s and 1s into the distant future

“We prove how an intelligent entity can use this phenomenon to transmit much more information than just plainly sending a radio signal,” says Martín-Martínez. Of course, it’s pretty unlikely that intelligent aliens from the distant past are trying to signal us in this way, but the principle means it could be worthwhile for cosmologists to look out for these echoes.

“Information about background signals from the early universe will also be propagated through this echo,” he says. The challenge is to figure out precisely what form the echoes will take and how to build receivers that can pick them up.

Avi Loeb of Harvard University says it’s an interesting idea, but still quite theoretical. “The authors need to give specific examples of observables that would show their effect,” he says.

This article appeared in print under the headline “Ancient echoes speak to us from the big bang”