B2 中高級 419 分類 收藏
We take it for granted that our universe contains planets, stars and galaxies
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


星際的起源 (Galaxies From Nothing)

419 分類 收藏
BH 發佈於 2016 年 10 月 6 日    王芊蓁 翻譯    Mandy Lin 審核
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