We've spent a lot of time talking about
the matter that makes up our universe,
but were things always this way or is
there more to the story?
In this video, we'll investigate what we know about the formation of the universe,
a theory we call the Big Bang, and we'll talk about some of the evidence that has led us to form this theory.
So the first thing you should know is that the Big Bang begins with a mystery.
We think time and space
emerged from a single point,
but since space has no meaning at this stage and time doesn't yet exist,
it's rather hard to get our heads around the start.
Up until the first 10 to the minus 43 seconds of the universe's existence then,
a time interval we call Planck time,
we have to wave a little white flag and
claim ignorance because the laws of
physics as we know them do not yet apply.
What we do know is this: the universe is incredibly hot and it's expanding quite quickly.
As it expands, and as more time passes,
the universe cools.
On this diagram here I'm going to go through
the different time periods since the Big
Bang and what we know about each of them.
So as I said, at T equals 0, that's when
the Big Bang begins. We don't know why or how.
From 10 to the minus 43 seconds to
10 to the minus 35 seconds, we believe
all the fundamental forces, except gravitation,
act as a single "Grand Unified" force.
From 10 to the minus 35
seconds to 10 to the minus 10 seconds,
the strong force separates from the
electro weak force,
then the electromagnetic and weak forces
separate.
Quarks, leptons and their antiparticles are created.
From 10 to the minus 10 seconds to 10 the minus 5 seconds, the universe consists of
a hot mix of quarks, gluons, leptons and photons.
In this incredibly hot soup, quarks and gluons were only weakly bound, so quarks could float around freely in
space, without the constraints they typically suffer today.
From 10 to the minus 5 seconds to 3 minutes, as the universe continued to cool,
quarks and gluons began to form hadrons.
Matter and antimatter began to
annihilate, leaving a slight excess of matter in its wake.
This excess of matter
is what forms our universe.
From 3 minutes to 10 to the 5 years,
nucleosynthesis began.
This is the process where protons and neutrons join to form atomic nuclei.
The lightest nuclei, deuterons, isotopes of
helium and lithium, were formed.
10 to the 5 years to today, electrons began to orbit atomic nuclei in order to form atoms,
and for the first time the universe was not full of free electrons.
Now, these electrons scattered light and other electromagnetic waves pretty readily so,
up until this point, the universe has
been pretty opaque.
When this change occurs, all of a sudden the universe is transparent to electromagnetic waves, and
light begins to have the ability to
travel long distances, without interacting with anything.
During this time, matter also clumps together to form stars, planets and galaxies,
and today, the temperature of the universe is a cool three Kelvin.
So you can see how this
theory, which we call the standard cosmology,
neatly leads to the standard
model as we know it today.
The four forces and the subsequent evolution of matter, as the temperature of the universe cools,
is consistent with our
picture of what matter is and how it interacts.
But what evidence is there to
support this theory, and what questions
does this theory leave unanswered?
Let's have a look at what we do know.
This idea that the universe is expanding is
something that we've known about for quite a while.
In the late 1920s, Edwin Hubble first showed that the universe was expanding using
astronomical observations.
His findings led to Hubble's law, which states that the speed at which distant galaxies move away from us
is approximately proportional to
their distance from the earth.
More recently, Brian Schmidt, Saul
Perlmutter and Adam Rice won the Nobel Prize in
Physics for work using
observations of supernovae - that's
massive explosions of stars that mark
the end of their lives - showing that the
expansion of the universe is accelerating.
So, they won their Nobel Prize in 2011 for the work they did on this in the 1990s.
In terms of what we actually see out in the universe, our understanding of galaxies and large-scale
structure formation is ongoing work.
Astronomers have been observing and
classifying galaxies and large-scale
structures in our universe at various
stages in their lives.
In order to understand how these structures are formed, one really good example of a mission um aimed at this
is the Hubble telescope mission.
This was launched in 1990 into orbit around Earth and it's been sending back observations of distant galaxies
for more than 25 years.
This has allowed researchers to peer back in time to galaxies more than 13.4 light-years from Earth.
So, effectively these researchers are
looking at a galaxy as it was,
not too long after the start of the universe. And by looking at galaxies at various stages of their life cycle,
and various distances from Earth,
they're able to actually get a pretty good picture
of how galaxies are formed.
Now, the next evidence that we have has to do with the stage where all of a sudden atoms were formed and free
electrons no longer rendered the
universe opaque.
At the point when atoms were formed, the universe became transparent to electromagnetic radiation
and the cosmic radiation that remains
today has essentially travelled through
space freely, from that point in time on.
Now, this radiation is cooled as the universes continue to expand.
Because of this, the radiation, which is known today as the Cosmic Microwave Background,
bears signatures at this point in our universe's history.
And here's a picture of what this radiation looks like, from a NASA mission known as WMAP.
One other set of observations that has contributed to our understanding of Big Bang nucleosynthesis, or the
formation of those light elements in the early stages of the universe, also comes from astronomy.
Astronomers have been studying
the composition of the universe for a long time now.
They know elements can be produced in one of two ways, either via the Big Bang or via
nuclear reactions happening in stars.
The Big Bang is thought to account for most of the abundance of the light elements in the universe,
and that's simply based on our understanding of what nuclear reactions are possible within stars.
By measuring the abundances of these elements in the universe, we've been able to confirm
that our theory of Big Bang nucleosynthesis is largely consistent with observation.
Basically, the abundances that we observe and the
abundances we predict with Big
Bang nucleosynthesis theory match up pretty well.
Now, if we want to test our
understanding of the Big Bang at periods even earlier
than this, we actually can no longer rely on observation out into the universe.
We can't directly observe
signs of the early hot soup of quarks and gluons and
other particles, that are thought to have occurred in the early universe, but back on earth we've been using
accelerators like the LHC at CERN or RHIC at Brookhaven National Lab in the US,
to produce and study a state of matter called quark-gluon plasma.
So, this is a state of matter that is hot enough, has enough energy, where the quarks and gluons
are not tightly bound together, but are instead floating in that kind of hot soup,
like they would have been in
this particular time in the universe's formation.
In the next video we'll learn
more about an experiment at one of these accelerators,
the LHC at CERN, and get a
glimpse of how major particle physics
experiments are carried out today
