From Forbes.com: It's The Power Of Quantum Mechanics That Allows The Sun To Shine, by Ethan Siegel
The greatest source of concentrated energy in the Universe today is starlight, where the largest single objects in the Universe emit tremendous amounts of power through the smallest of processes: the nuclear fusion of subatomic particles...
How does this happen? Deep inside the hearts of stars — including in our own Sun’s core — light elements are fused together under extreme conditions into heavier ones. At temperatures over about 4 million kelvin and at densities more than ten times that of solid lead, hydrogen nuclei (single protons) can fuse together in a chain reaction to form helium nuclei (two protons and two neutrons), releasing a tremendous amount of energy in the process...
It means that every time the Sun winds up fusing four protons into a helium-4 nucleus, it results in the net release of 28 MeV of energy, which comes about through the mass-energy conversion of Einstein’s E = mc**2.
All told, by looking at the power output of the Sun, we measure that it emits a continuous 4 × 10**26 Watts, which means that inside the Sun’s core, a whopping 4 × 10**38 protons fuse into helium-4 every second.
If you consider that there are some 10**57 particles in the entire Sun, of which a little less than 10% are in the core, this might not sound so far-fetched. After all:
- These particles are moving around with tremendous energies: each proton has a speed of around 500 km/s in the center of the Sun’s core.
- The density is tremendous, and so particle collisions happen extremely frequently: each proton collides with another proton billions of times each second.
- And so it would only take a tiny fraction of these proton-proton interactions resulting in fusion into deuterium — about 1-in-10**28 – to produce the necessary energy of the Sun.
So even though most particles in the Sun don’t have enough
energy to get us there, it would only take a tiny percentage fusing
together to power the Sun as we see it. So we do our calculations, we
calculate how the protons in the Sun’s core have their energy
distributed, and we come up with a number for these proton-proton
collisions with sufficient energy to undergo nuclear fusion.
That number is exactly zero. The electric repulsion between the two positively charged particles is too great for even a single pair of protons to overcome it and fuse together with the energies in the Sun’s core...
The secret is that, at a fundamental level, these atomic nuclei don’t
behave as particles alone, but rather as waves, too. Each proton is a
quantum particle, containing a probability function that describes its
location, enabling the two wavefunctions of interacting particles to
overlap ever so slightly, even when the repulsive electric force would
otherwise keep them entirely apart.
There’s always a chance that these particles can undergo quantum tunneling,
and wind up in a more stable bound state (e.g., deuterium) that causes
the release of this fusion energy, and allows the chain reaction to
proceed. Even though the probability of quantum tunneling is very small
for any particular proton-proton interaction, somewhere on the order of
1-in-10**28, or the same as your odds of winning the Powerball lottery three times in a row, that ultra-rare interaction is enough to explain the entirety of where the Sun’s energy (and almost every star’s energy) comes from...
Full article: http://www.forbes.com/sites/ethansiegel/2015/06/22/its-the-power-of-quantum-mechanics-that-allow-the-sun-to-shine/
A very interesting article! Any physicist out there dares to comment? Does it mean that the secret to fusion on demand (hot or cold) could actually be smart manipulation of the wave properties of interacting particles, to increase the chance (to force) a quantum tunneling effect? [Vlad]
