because those are the things we see but the only reason these big structures

exist is because of the nature of nothingness - empty space. But to

understand why we have to go back to the beginning. The very beginning. The big bang.

You know, I always thought that in the Big Bang the observable universe

started as a point and then just expanded steadily more or less to the

point that we're at today but that's not actually how it happened.

There were four different phases in the universe's expansion. To start it was expanding

steadily but then after just a tiny fraction of a second the expansion just

blew up and the whole universe increased in size by like ten to the twenty six

times in a very short period of time and that period is known as inflation and

then just as abruptly as it began inflation stopped and after that the

universe continued expanding but at a decreasing rate so the expansion of the

universe was actually slowing down which is exactly what you expect if the

universe is full of massive objects that gravitationally attract each other

but then about five or six billion years ago the expansion of the universe

started speeding up again and this is thought to be caused by dark energy,

an energy tied to space. So before that time there was enough matter, the matter

density was high enough, that it was pulling everything back together slowing

down the expansion but once the universe reached a critical size

well then there was enough dark energy to start pushing things apart and that

is the phase that we're still in the expansion of the universe is accelerating.

Now, this story doesn't really explain the formation of galaxies

until you tie in the nature of nothingness

now ordinarily we think of everything around us as made of particles of atoms

and electrons but our best theories of physics are actually field theories that

say all these particles should be seen as just excitations in fields.

The word "field" always gets me because it makes me think of... well, fields.

but a field is just something that has a value everywhere in space.

So every subatomic particle has its own field: an electron field, an up quark field,

a down quark field, a neutrino field, and so on...

And anywhere there's an excitation in this field

that is some energy in the field

well that is where we will observe particles. So out in completely empty

space where the values for all of these fields are basically zero.

but here's the thing

it's impossible to make a field perfectly flat and 0.

You cannot take a quantum field and make it completely quiet.

It's the Heisenberg uncertainty principle.

It says you can't take a particle and pinpoint it to exactly zero energy

likewise you can't take a quantum field and make it exactly flat everywhere.

Now, this is important because ordinarily these fluctuations are really really

tiny and they only affect subatomic processes but during that period of

inflation the universe expanded in size so rapidly and so incredibly that those

tiny fluctuations got blown up to the scale of the observable universe

Now, without them we think the matter distribution in the universe would have

been completely homogeneous completely uniform and that means the gravitational

force on any object in the universe would have been the same in all

directions which means nothing would ever have collapsed into the big

structures that we see today but thanks to these fluctuations there were

slightly denser and less dense regions and of course the denser regions had

stronger gravitational fields so they pulled in the matter from around them

and that clumped together the matter into huge gas clouds that would go on to be

the galaxies that contain the stars and the planets and the things we know today

you can actually see the imprint of these quantum fluctuations in the

leftover radiation from the Big Bang the cosmic microwave background radiation

the quantum fluctuations in the fields were amplified to big classical fluctuations

in the density of

matter from place to place and those fluctuations in the density of matter show up

in the universe today as temperature differences in the cosmic background

radiation and ultimately in things like stars and planets and galaxies

I think it is incredible that without these fluctuations in the vacuum these tiny

insignificant things that we take for granted our universe might really

contain nothing. Nothing of interest anyway...

Speaking of vacuum

this episode was supported in part by Dyson who sent me their 360 eye vacuuming robot

it's got this little camera on the top that can see 360 degrees around it now

it uses that vision plus some complex math and trigonometry to work out its

location precisely and to figure out where it's cleaned already and where it

still needs to clean it actually makes a map that you can see on your phone using

the dyson app and you can use that app also to control the vacuum or to

schedule it even when you're not at home so I for one welcome robots taking over

the housework you want to find out more you can click the link in the

description so i want to thank Dyson for supporting me and I want to thank my

patreon supporters and of course you for watching