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Why Is the Speed of Light So Slow?
Einstein's theory of special relativity sets of the speed of light, 186,000 miles per second (300 million meters per second). But some scientists are exploring the possibility that this cosmic speed limit changes.
Credit: Iscatel | Shutterstock

In 2015, a team of Scottish scientists announced they had found a way to slow the speed of light. By sending photons through a special mask, the researchers altered their shape. In this malformed state, these infinitesimal particles of light traveled slower than normal photons.

The difference in speed was almost imperceptible, but the accomplishment itself was stunning! At 299,792,458 meters per second, the speed of light has stood as an unbreakable, unchangeable speed limit. No longer.

But why would anybody want to slow down the speed of light? After all, it's already slow enough!

As strange as that assertion may seem to humans accustomed to traveling a mere 70 miles per hour on the highway, it makes a lot of sense on a cosmic scale. Consider this: If the observable Universe was reduced to the size of planet Earth, traversing the Milky Way Galaxy would be roughly equivalent to walking three houses down the block to visit your neighbor. And yet, traveling at the cosmic speed limit of our smaller, Earth-size universe, that short jaunt would take 100,000 years!

This example showcases just how tediously slow exploring the galaxy would be for a ship traveling at the speed of light. Such a journey would span more than a hundred human generations!

Even if you don't consider humanity's self-centered wish for interstellar light-speed travel and instead think about photons dashing across our solar system, the speed of light still seems positively sluggish. As astrophysicist Brian Koberlein calculated, it takes 45 minutes for light from the Sun to reach Jupiter, and five hours for it to reach Pluto.

And of course, when gazing at the sky with the naked eye, we're viewing some stars as they were more than 4,000 years in the past -- that's how long it takes their light to reach us!

So now that we've ascertained that light is not fast but rather is excruciatingly slow, we can now turn to a more pressing and difficult matter: Why?

Theoretical physicists can muse and cosmologists can measure, but all their learned tinkering currently leads back to an inescapable answer: Because.

Theoretical physicist Gennaro Tedesco provided a slightly more satisfying version:

The universe is made such that photons propagate with that velocity, there is no reason why it should be so, but it is just the way it is. Physics does not explain why things are what they are, rather it explains how to make predictions by using proven models.

Okay, so like in much of theoretical physics, the answer is effectively a non-answer, and we're still stuck in a slow universe.

To salvage this situation, let's examine a scenario where light is much faster. What would existence be like if, say, the speed of light was boosted by a factor of 1,000? Steve Jones explored the hypothetical. A light-speed vessel could cross the Milky Way in less than a century! A trip to Alpha Centauri, home to a potentially habitable planet, would take fewer than two days! Computers and networks would run faster thanks to enhanced optical speeds! We might be more likely to receive signals from extraterrestrials!

But – and this is a big but – the Sun would burn a million times hotter. We'd be cooked.

So you better learn to love our finely tuned speed of light, however slothlike it may be. If it were any faster, life on Planet Earth might not exist.

Originally published on RealClearScience.