Every high school physics student can ramble this off by memory: According to Albert Einstein’s Theory of General Relativity, the speed of light is always the same; therefore the laws of physics exist and behave the same everywhere in the universe.

For a pair of physicists, that century-old notion simply reads: Challenge Accepted. João Magueijo from Imperial College London and Niayesh Afshordi of the Perimeter Institute in Canada proposed a new experiment proving Einstein wrong and demonstrating that the speed of light actually isn’t a constant. The pair thinks light may have moved faster in the past, around the time of Big Bang, and that it’s actually slowed down since.

The speed of light is an idea that scientists have pondered since the time of Aristotle, but it was Einstein who really gave this concept context for the modern era of physics with his infamous Theory of General Relativity. The assumption that the speed of light is a constant has been a proximal way to also assume the universe operates uniformly.

If the speed of light isn’t constant, however, it throws even the most basic laws of physics into question.

Magueijo and Afshordi think the speed of light might have been different in an infant universe that exhibited a more lumpy density. Historically, this was explained by inflation theory the universe rapidly expanded before slowing down and normalizing out to its current rate of growth. But if the speed of light was affected by this lumpiness, then perhaps it hasn’t been able to reach the edges of the ever-expanding universe and smooth things over yet.

The pair think the speed of light used to be faster than it is today and helped bridge the fringes of the universe with the insides. As the universe evened out and became more homogenous, the speed of light dropped. But if the edges of the universe are still composed of clumped up densities, they could facilitate a faster-than-expected speed of light.

This is all pretty fascinating, but it raises the more critical question: Should we even care? If Einstein is wrong, and the speed of light isn’t a constant, what exactly would that have to do with what we know about the universe?

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In practical terms, obviously, this means nothing. The speed of light, where we are in the universe, will be basically the same for as long as the human species exists. We are nowhere near the point where we can develop modes of travel that rival the speed of light (although we are trying).

If that ever happens, then we might have reason to better understand the speed of light. If we master interstellar travel, that would give humans the operate to travel out to regions of the universe that possess lumpy densities. If we have spaceships that can move at the speed of light or even faster, then we’ll need to know what might happen to them should we venture out to those places where the laws of physics as we know them no longer function as we know them.

And that raises perhaps the most important ramification behind a variable speed of light. It throws everything we know about the physical world into disarray. If our most basic natural laws suddenly have exceptions, then everything has an exception, doesn’t it? Scientific research may feel like it has amounted to very little.

But a complete upheaval of our knowledge of physics would be equal parts fascinating and discouraging. Yes, we should care if Einstein was wrong about the speed of light, because the effects on how we investigate physics might not even be comprehensible to us at this point in time. And all this speculation is moot if Magueijo’s and Afshordi’s experiment can’t support their hypothesis. We’ll have to wait impatiently to see exactly what the pair find. They might be totally wrong. But if they’re not, the scientific community will have to come to grips with a world they actually know nothing about.

Photos via Flickr / Domiriel

Neel is a science and tech journalist from New York City, reporting on everything from brain-eating amoebas to space lasers used to zap debris out of orbit, for places like Popular Science and WIRED. He's addicted to black coffee, old pinball machines, and terrible dive bars.