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.