Welcome back everyone.
So we've talked about the Planck era and we talked the inflationary epoch and now
we want to talk we're still very much in the early history of the universe.
Before a second essentially has elapsed but
important things are happening and in particular
we want to talk about the idea
of phase transitions occurring in the early universe.
So what is a phase transition?
We all have experience of this is when we take liquid water, right?
Which you know, you can take water and you can pour it into a cup and
you can pour it into another cup and
it takes whatever you know, shape the container has.
But then you put it into a, your freezer and you go away for a
while and then you come back, and now suddenly you've got a chunk of ice.
So the water has gone from a phase transition.
From being a liquid state to the, the solid state.
And of course if I took that solid state and put it in a in a boiler.
Then what would happen is the solid would turn back into a liquid.
So the movement
from one phase to another is what is called a phase transition.
And it's clearly associated with temperature.
So the universe actually is doing the same thing.
because we have to understand that the
temperature in the universe is dropping with time.
As the universe expands, its temperature is dropping and we're going to get phase
transitions like, you know, the analogy of going from a liquid to a solid.
Things are going to change as that temperature drops.
So one of the first things that's going to happen is what we believe
is, is that early in the universe the four forces of the universe were actually one.
There was one grand unified force, only
one force operating, and as the universe cooled,
that force broke out into, at various times
into the four forces that we see today.
And it didn't all ha, all, didn't all happen at once, and the one thing
that we know about is that the electromagnetic
force, and the weak force, if your temperature
is high enough, those will merge in to one.
So, there must have been a time when all four forces were together, and then
the strong force and weak, electro weak force must have separated out.
Actually of course gravity must have separated
out, but we don't understand that at all.
But we do certainly understand, we've already
in our particle accelerators come to understand
the electroweak force and how the electroweak
force splits out into the electromagnetic and
weak force.
And so at around when the universe was about 10 to the minus 12 seconds, and had
a temperature of 10 to the 15 degrees K