Let us now complete our inquiry into the early universe with even a little more
speculative things. First something about general particular
physics lore. The strengths of different interactions
change with energy. And one of the basic paradigms is that
the sufficiently high energies, different interactions become one.
For example, the electromagnetic interaction and the nuclear weak force
become unified at energies corresponding to temperatures about 10 to 16 degrees.
And that has been actually experimentally proven.
Similarly, it is believed that electroweak interaction and strong play
force will become unified at energies of the order of 10^28 degrees kelvin, which
corresponds to about 10^-35 seconds after the big bang.
And then, to extend this, and this is purely speculative, those interactions
become unified with gravity, at the plank time, 10^-43 seconds.
Now, moving forward, forward in time, the grand unified interaction, splits, and
that corresponds, to face transitions in the early universe.
One of which, could be driving the inflation.
So the temperatures of 10^28 degrees, there is electroweak interaction and a
strong nuclear force. At temperatures at less than about 10^15
degrees electromagnetic and weak interactions split.
This is the part that, that's been actually probed by accelerators.
Deeper in the past we believed that electroweak interactions, strong nuclear
force adjoined in what's called the Grand Unified Theories which are actually are
not entirely complete, but they're reasonably strong theoretical background.
And there are good reasons to believe that that's what actually happens.
This is many orders of magnitude higher energies than what we can probe in
terrestrial particle accelerators so in some sense, the early universe is our
only means of actually testing these theories by seeing what they predict.
It is possible, but, by no means certain, that it was this particular phase
transition that splits the strong force from electroweak interaction that's
responsible for driving the inflation. Now, let's look at another important fact
in the universe. And that is that, there is a lot more
matter than there is antimatter. Early on people thought that there could
be a symmetry, but there was simply no trace of substantial amounts of
antimatter in the universe. We would have seen much more in terms of
annihilation radiation and so on. Also, people who look for cosmic rays
look hard to see what is the balance between Particles and anti particles and
all of the anti particles that have been seen so far, can be easily explained
through normal interactions. So the universe is predominantly made out
of matter. Which.
Anti matter being a negligible fraction there of.
How did that come about. This leads us into the topic of Cosmic
Baryogenesis. The worded protons and neutrons come from
as opposed to the equal numbers of anti protons and anti neutrons.
Theoretical ground for this was actually laid by great Soviet physicist Andrei
Sakharov as early 1967. He came up with three conditions that
need to be satisfied for this to work. First, Baryon number, which we think is
conserved, must be violated. And, we do not have any experimental
evidence for this. But it's not impossible.
It has been predicted by a number of more modern theories, it just hasn't been
observed yet. Second, there has to be charge and charge
parity violation. For those of you familiar with basic
concepts in particle physics, you know what that means, that the reversals of
charge or reversals of charge and parity of spins can make Arrow of time, glide
away. This has actually been experimentally
demonstrated as early as the 1960s. And finally, there has to be some
departure from thermal equilibrium. And the expansion of the universe
provides a natural way to do this. Since universe expands, the time is not
homogeneous. There is a difference between 1 direction
of time and the other, and that's what provides the necessary condition.
So nowadays most people believe that something like this was indeed
responsible for establishing the asymmetry between matter and anti-matter.
Note, in the early universe, that could have been vast amounts of antimatter.
It just annihilated and what's left, the small fraction that's left is regular
matter. Finally, let's talk about Planck Units.
This is a system of units devised by Max Planck in 1899.
Prior to relativity and prior to quantum theory.
He asked a simple question. Meters and seconds and such are simply
human conventions, are there actually natural units, that he can derive from,
say universal contants, such as Newton's gravity constant, or speed of light, or
Planck's constant. And indeed, they are.
Shown here combinations of such fundamental physical constants that yield
elementary units of time, or length, or mass.
And so for the time it's 10^-43 seconds and this is called Planck time.
For space is about 10^-33 centimeters, that's called the Planck length.
And for mass, it's about 10^-5 grams, which is called the Planck mass.
Similarly, you can derive units for other physical quantities.
And then there are derived units. In any case, the advantage of planck
units is that, indeed. They do not depend on any arbitrary
conventions. They really are given by the constants of
nature. But that doesn't necessarily mean that
they're somehow magical. We use them.
As limiting units for quantum gravity say but we don't really know.
And they may or may not be entirely relevant.
Nevertheless, they're a useful set of units to consider when thinking about
very early universe. So as we approach the Planck era our
knowledge breaks down. We do not yet have a working quantum
theory of gravity. Not for the lack of trying.
Many smart theorists have been working on this for a long time.
And today we have String theory or M-theory or Branes and things like that.
It's fair to say that none of those have yet produced a convincing unifying theory
that will unify quantum physics in gravity.
Nevertheless there are prospects that that might happen.
There are also theoretical attempts to think what was this implied beyond the
Big Bang. One of the interesting theories is the so
called Ekpyrotic cosmology, which essentially states that colliding branes,
which are essentially multi-dimensional supernova particles, can dissipate enough
energy to create all of the mass energy in the universe.
There's also the concept of the String Landscape, saying that there about 10^500
different universes. Each of which could have different
physical constants and different laws of nature.
Needless to say this is completely speculative at this point.
In either case the early universe certainly provides a high-energy physics
laboratory at levels that will never be achievable on this planet.
And so the unification of high-energy physics, particle physics and cosmology
is likely to get even stronger. Next, we will talk about the contents of
the universe.