Why classical physics says the sun doesn’t shine

In the first half of the twentieth century, physicists discovered something alarming about the sky. When they looked up, they saw the sun—and it was shining. You see, according to their calculations this was impossible. Their models stated that the sun was not enough energy to shine. Despite their efforts to explain the problem, the numbers were loud, clear, and anything but bright.

First, some background on the sun. Like all stars, the sun converts its mass into energy via nuclear fusion. In short, the gravity of its outer shells heats the core until it can convert hydrogen into helium, producing enough energy to support itself. This process gives off immense radiation, which we perceive as heat and light. I explained how stars work a few weeks ago—click here to learn more.

Our physicists’ problem arose when investigating this fusion. According to their models, two protons had to more or less come into contact before they could fuse. Since like charges repel, this requires a massive amount of energy and a temperature far higher than that of the sun. Either the sun was lying, or physics was wrong.

Fortunately for the physicists (and for everybody else), the following years saw the invention of quantum mechanics and with it a new understanding of subatomic particles. New research found that matter behaves strangely at the subatomic level. Particles act like waves, and waves act like particles. In their most fundamental forms, waves and particles seem to be the same thing. Furthermore, these waves behave probabilistically. At any given moment the “particle” can be at any place on the wave function. We don’t know how or why, but we do know the chances of it appearing in any one place. (I’ve written about how cool the quantum world is as well. Click here to learn more!)

Quantum Tunneling Mechanics Probability Wave Particle Duality Hill Rock Example Graph Weekly Show

While classical physics would require enough energy to push the rock over the top of the hill (make the protons touch), quantum mechanics allows the rock to sometimes “tunnel” through to the other side.

Viewing these protons as waves solves our sun problem through a process known as quantum tunneling. Imagine that instead of particles we are pushing two waves together. We know that the particles are likely to be in the center of the waves, but there is a small chance they can be on the outer fringes. If both protons happen to be on the outer edges of the waves, we can actually get them close enough to fuse without having to push the waves on top of one another. In other words, we do not to spend all that energy to make the protons touch—we can get them close enough so that the waves overlap. Since there are so many atoms in the sun, this unlikely event occurs a massive number of times, allowing our star to shine.

So that’s the mysterious quantum tunneling and how it lets the sun shine. Not so scary, right? Check out the video I’ve included for an awesome visual explanation of how this works. Is this mind-blowing? Still confusing?  Let me know what you think in the comments below. As always, please like, share, or reblog this post if you enjoy it. That small click really helps me out! Be sure to check me out on Twitter and Facebook as well. Thanks for reading! Don’t forget to subscribe for new content every Wednesday! IT’S FREE!

Other related articles:

Weird Quantum Tunneling Enable “Impossible” Space Chemistry (Space.com)

Particles Walk Through Walls While Physicists Watch (LiveScience)

Gian Guidice: Why Our Universe Might Exist on a Knife-Edge (TED)

Three Amazing Facts About the Quantum World

You Are Made of Beautiful Stardust


Comment question of the week

Did you know physicists had so much trouble figuring out why the sun shines? What other famous problems are worth mentioning?


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