Fusion
Written by John Carl Villanueva
Fusion is one of the beneficial offsprings of Einstein's iconic equation, E=mc2. Central to the equation is the direct relationship between mass and energy. Instead of what used to be a separate principle of conservation of mass and conservation of energy is now a combined conservation of mass and energy. Hang on to that idea while we continue to discuss fusion.
What happens to the total mass of the resulting body when you combine two particles? The total mass will not change, i.e., if the sum of the masses of each separate particle was m1 + m2, then the mass of the final body, say M, should also be equal to that sum. Hence, M = m1 + m2.
That's what would happen in a separate conservation of mass and energy principle. Here's what would happen if we married the two.
If we combined or fused two separate particles, the resulting body would have a mass lighter than the sum of the masses of the separate particles. So where would the missing mass go? It would be released in the form of energy. Let me underline this: the released energy is the missing mass.
That is, without going into the mathematical details, if we do the necessary conversions using E=mc2, add the original masses and energies and compare the sum to the sum of the final masses and energies, both sides will come out equal. Thus, the total mass and energy is conserved.
Notice that c there, which is the speed of light, is a very large quantity. c = 3.0 x 108 m/s. Hence, even with a small amount of m, E can be very large. Thus, the missing mass, though tiny, may be equivalent to a huge amount of energy.
Nuclear fusion, or the fusion of nuclei, happens all the time in the stars. These processes produce elements through nucleosynthesis characterized by large energy releases.
For fusion to readily occur, the reactants must be confined in a region with high temperatures. In massive stars, the confinement is made possible via the immense gravitational forces present there. Here on Earth, the most successful confinement unit so far is the tokamak, a large doughnut shaped container with very powerful magnetic fields.
Since the particles inside are ionized (charged), the helical magnetic field is able to keep them from touching the inner walls of the tokamak. For fusion to occur, the confined nuclei are allowed to collide with one another at very high temperatures.
You can read more about fusion here in Universe Today. Want to know more about nuclear fusion in the stars? How about fusion in the Sun?
There's more about entropy at NASA and Physics World too. Here are a couple of sources there:
Here are two episodes at Astronomy Cast that you might want to check out as well:
Filed under: Astronomy
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