When did the clock of the universe start ticking? For decades we’ve believed that 13.8 billion years ago the Big Bang set the universe’s clock in motion. While that’s still the prevailing viewpoint, researchers are now exploring a theory called “rainbow gravity” that, if correct, does away with the Big Bang. In a “rainbow” universe, the clock has been ticking forever.
Behind the scenes of the Big Bang is Einstein’s theory of general relativity. But there’s a problem. Einstein’s theory is at odds with quantum mechanics, the theory of tiny particles. Rainbow gravity was proposed to reconcile the two, and if it were correct, the universe would have no beginning—there is no big treasure at the foot of this “rainbow” because the “rainbow” universe goes back forever.
Why is it called rainbow gravity? Because according to the theory, gravity becomes a cosmological prism that can separate different colors of light. Our eyes can’t see that—when we gaze longingly into the night sky, the stars’ white light appears to have streamed smoothly to our eyes. If rainbow gravity is right though, light’s path through outer-space may be more like the famous Pink Floyd poster, where the different colors become spread apart.
So, why don’t we see rainbow stars? Clara Moskowitz, writing for Scientific American, tells us more:
The effects would usually be tiny, so that we wouldn’t notice the difference in most observations of stars, galaxies and other cosmic phenomena. But with extreme energies, in the case of particles emitted by stellar explosions called gamma-ray bursts, for instance, the change might be detectable. In such situations photons of different wavelengths released by the same gamma-ray burst would reach Earth at slightly different times, after traveling somewhat altered courses through billions of light-years of time and space. “So far we have no conclusive evidence that this is going on,” says Giovanni Amelino-Camelia, a physicist at the Sapienza University of Rome who has researched the possibility of such signals. Modern observatories, however, are just now gaining the sensitivity needed to measure these effects, and should improve in coming years.
Rainbow gravity may just be an illusion, a pretty idea that makes science a bit more colorful. But soon we may find out if we’re living in an infinitely old rainbow universe.