I heard this neat idea on Big Picture Science the other day (a great radio show, by the way, that gets into reasonable discussion of lots of new ideas in science and technology), that life might be a byproduct of quantum mechanics. Something about how the universe acts like a quantum computer... I don't actually fully understand the argument made, but I'm sort of keen on the thought because it reminded me of this issue with fusion in stellar cores.

If you weren't aware, fusion---combining small atoms to make bigger atoms---is what powers stars. Atoms typically repel each other; their nuclei are made up of protons (positive charge) and neutrons (no charge), so they have a net positive charge. When you push the positive sides of two magnets together, they repel each other. Same is true with atomic nuclei. So if you want two atoms to combine into one, you have to push them into each other hard enough to overcome that magnetic force (the "Coulomb barrier"). So the idea is that in the cores of stars, atoms are:

a.) really close together (high pressure)
b.) moving really fast (high temperature)

So theoretically atoms are crashing into each other all the time in stellar cores, and at high speeds, so they should fuse. Right?

Well it turns out that the math doesn't actually work out. Even in the core of the sun (something like 30 million degrees Fahrenheit, ~17 million Celsius), atoms aren't hitting each other hard enough to get over their mutual repulsion. The Coulomb force gets stronger the closer in you get, and at the scales of atomic nuclei, it becomes a losing game (the harder you push, magnetism pushes back harder still). So in classical mechanics, atoms should rarely or never fuse in stars and the sun should be inert.

What's required is, oddly enough, quantum tunneling. Here's the basic idea... in QM, particles are described by probability. This includes their positions in space and time: where they are at any given moment. There are hence places where they are likely to be, and places where they are unlikely to be, and things in between. So now let's say you take two particles that are both likely to be in close proximity to each other (two particles that are close together in space). Now the probability functions that describe their positions in space might overlap---it's not the most likely possibility, but there would be a non-zero probability that both particles are actually in the same place. So sometimes they end up in the same place---one tunnels into the other---and now you've just jumped wholesale over the Coulomb barrier. The two particles fuse.

When you include that probability into the equations, alongside the classical mechanics, you get exactly the right answer for stars. So because the math doesn't work out for just random collisions, you need to invoke quantum tunneling to get fusion to happen in stars.

Maybe then you can see why I like this idea that QM is required for the emergence of life, too. It's another instance of something we know can happen (we are an example of life, so it has emerged on one planet), but that regardless seems like it shouldn't given its inherently low probability. Kind of neat! Maybe these 'quantum biologists' are on to something, here.

Anyway, just thought I'd share. Here's the episode in question, if you want to give it a listen (they discuss quantum computing in general, too): http://radio.seti.org/episodes/quantum-why-we-want-em