David Kirtley

So fusion is what powers the universe.

Fusion is what happens in stars and it's where the vast amount of energy that even that we use today here on earth comes from the process of fusion.

It also is what powers plants and those plants become oil and those become fossil fuels that then

powers the rest of human civilization for the last hundred years.

And so fusion really underpins a lot of what has enabled us as humans to go forward.

However, ironically, we don't do it actively here on Earth to make electricity yet.

And so fundamentally what fusion is, is taking the most common elements in the universe, hydrogen and lightweight isotopes of hydrogen and helium, and fusing those together to make heavier elements.

In that process, as you combine atomic nuclei and form heavier nuclei, those nuclei are slightly lighter than the sum of the parts.

And that comes from a lot of the details of quantum mechanics and how those fundamental particles combine and interact.

We also talk about the strong nuclear force that holds the atomic nucleuses together as one of the fundamental forces involved in fusion.

But that mass defect...

E equals mc squared, we know from Einstein, is also energy.

And so in that process, a tremendous amount of energy is released.

And the actual reactions, I think, is a lot more interesting than simply it's a little bit lighter and therefore energy is released.

But that's the fundamental process in fusion is you're bringing those lightweight atomic nuclei, those isotopes together.

Fission is the exact opposite, where you're taking the heaviest elements in the universe, uranium, plutonium, things that are so heavy and have so many internal protons and neutrons and electrons that they're barely held together at all.

They're fundamentally unstable or radioactive.

And those elements are very close to falling apart.

And as they do that, if you take a uranium-235 or a plutonium-239 nucleus and you add something new, usually it's a neutron, a subatomic particle that's uncharged, that unstable, that very large nuclei will then break into pieces, many pieces, a whole spectrum of pieces.

But if you add up all of those pieces, they also have slightly less mass.