John Preskill

A short time ago, an American airplane dropped one bomb on Hiroshima and destroyed its usefulness to the enemy.

That bomb has more power than 20,000 tons of TNT.

With this bomb, we have now added a new and revolutionary increase in destruction.

I remember being in New York with my mother in a restaurant right after, immediately after.

I would see people building a bridge and I would say they don't understand.

I really believe that it was senseless to make anything because it would all be destroyed very soon anyway.

I'm John Preskill.

I am the Richard P. Feynman Professor of Theoretical Physics at the California Institute of Technology.

So picture this diagram.

There are these two lines, both with arrows on them.

And then there's a line connecting the two.

So it looks like one rung of a ladder.

And the line going across is the wiggly line.

That's the photon that's being emitted by one particle and absorbed by the other.

Now, we could have more photons.

So now add another rung to the ladder.

Now we've got the one line with an arrow on it, solid line, let's say, going up.

And now another line with the arrow going down.

That's the electron and the positron.

Now there are two rungs.