The Challengers

Obviously, challenging a theory that has held its own for decades—a theory that is essentially the cornerstone of physics as we know it—is no easy task. The fact that this particular theory was postulated by none other than the Father of Modern Physics makes the challenge even more daunting.

However, that is precisely what several scientists are doing.

In the 1990s, cosmologist and theoretical physicist João Magueijo, in collaboration with astrophysicist Niayesh Afshordi, proposed that the speed of light may have been faster in the very early universe, right after the Big Bang. Yes, they propose that the speed of light may not have always been constant. This is contrary to what Einstein’s theory of general relativity dictates: That the speed of light is, and always has been, the same.

They believe that the violent events following the Big Bang resulted in regions with fluctuating or erratic variations in density, and that these fluctuations were powered by varying speeds of light. These early fluctuations are imprinted on the cosmic microwave background (CMB)—the earliest radiation that fills the universe.

To Prove or Debunk

Now, the theorists published a prediction using a model that they used to pinpoint an exact figure on the spectral index for primordial speed of light: 0.96478. "The theory, which we first proposed in the late-1990s, has now reached a maturity point – it has produced a testable prediction. If observations in the near future do find this number to be accurate, it could lead to a modification of Einstein's theory of gravity," Magueijo says.

"The idea that the speed of light could be variable was radical when first proposed, but with a numerical prediction, it becomes something physicists can actually test. If true, it would mean that the laws of nature were not always the same as they are today."

Magueijo and Afshordi are not alone in rethinking relativity. Quantum physics has always been unpredictable using classical physical assumptions, hinting at a mismatch somehow. Other physicists have echoed their excitement at testing the theory. If this hypothesis turns out to be correct, physics has a lot of rewriting to do.

“We have a model of the universe that embraces the idea there must be new physics at some point,” Magueijo says. “It’s complicated, obviously, but I think ultimately there will be a way of informing quantum gravity from this kind of cosmology.”

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