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Let us now complete our inquiry into the 
early universe with even a little more 

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speculative things. 
First something about general particular 

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physics lore. 
The strengths of different interactions 

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change with energy. 
And one of the basic paradigms is that 

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the sufficiently high energies, different 
interactions become one. 

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For example, the electromagnetic 
interaction and the nuclear weak force 

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become unified at energies corresponding 
to temperatures about 10 to 16 degrees. 

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And that has been actually experimentally 
proven. 

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Similarly, it is believed that 
electroweak interaction and strong play 

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force will become unified at energies of 
the order of 10^28 degrees kelvin, which 

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corresponds to about 10^-35 seconds after 
the big bang. 

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And then, to extend this, and this is 
purely speculative, those interactions 

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become unified with gravity, at the plank 
time, 10^-43 seconds. 

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Now, moving forward, forward in time, the 
grand unified interaction, splits, and 

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that corresponds, to face transitions in 
the early universe. 

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One of which, could be driving the 
inflation. 

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So the temperatures of 10^28 degrees, 
there is electroweak interaction and a 

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strong nuclear force. 
At temperatures at less than about 10^15 

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degrees electromagnetic and weak 
interactions split. 

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This is the part that, that's been 
actually probed by accelerators. 

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Deeper in the past we believed that 
electroweak interactions, strong nuclear 

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force adjoined in what's called the Grand 
Unified Theories which are actually are 

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not entirely complete, but they're 
reasonably strong theoretical background. 

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And there are good reasons to believe 
that that's what actually happens. 

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This is many orders of magnitude higher 
energies than what we can probe in 

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terrestrial particle accelerators so in 
some sense, the early universe is our 

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only means of actually testing these 
theories by seeing what they predict. 

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It is possible, but, by no means certain, 
that it was this particular phase 

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transition that splits the strong force 
from electroweak interaction that's 

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responsible for driving the inflation. 
Now, let's look at another important fact 

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in the universe. 
And that is that, there is a lot more 

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matter than there is antimatter. 
Early on people thought that there could 

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be a symmetry, but there was simply no 
trace of substantial amounts of 

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antimatter in the universe. 
We would have seen much more in terms of 

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annihilation radiation and so on. 
Also, people who look for cosmic rays 

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look hard to see what is the balance 
between Particles and anti particles and 

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all of the anti particles that have been 
seen so far, can be easily explained 

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through normal interactions. 
So the universe is predominantly made out 

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of matter. 
Which. 

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Anti matter being a negligible fraction 
there of. 

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How did that come about. 
This leads us into the topic of Cosmic 

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Baryogenesis. 
The worded protons and neutrons come from 

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as opposed to the equal numbers of anti 
protons and anti neutrons. 

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Theoretical ground for this was actually 
laid by great Soviet physicist Andrei 

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Sakharov as early 1967. 
He came up with three conditions that 

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need to be satisfied for this to work. 
First, Baryon number, which we think is 

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conserved, must be violated. 
And, we do not have any experimental 

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evidence for this. 
But it's not impossible. 

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It has been predicted by a number of more 
modern theories, it just hasn't been 

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observed yet. 
Second, there has to be charge and charge 

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parity violation. 
For those of you familiar with basic 

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concepts in particle physics, you know 
what that means, that the reversals of 

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charge or reversals of charge and parity 
of spins can make Arrow of time, glide 

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away. 
This has actually been experimentally 

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demonstrated as early as the 1960s. 
And finally, there has to be some 

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departure from thermal equilibrium. 
And the expansion of the universe 

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provides a natural way to do this. 
Since universe expands, the time is not 

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homogeneous. 
There is a difference between 1 direction 

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of time and the other, and that's what 
provides the necessary condition. 

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So nowadays most people believe that 
something like this was indeed 

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responsible for establishing the 
asymmetry between matter and anti-matter. 

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Note, in the early universe, that could 
have been vast amounts of antimatter. 

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It just annihilated and what's left, the 
small fraction that's left is regular 

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matter. 
Finally, let's talk about Planck Units. 

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This is a system of units devised by Max 
Planck in 1899. 

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Prior to relativity and prior to quantum 
theory. 

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He asked a simple question. 
Meters and seconds and such are simply 

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human conventions, are there actually 
natural units, that he can derive from, 

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say universal contants, such as Newton's 
gravity constant, or speed of light, or 

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Planck's constant. 
And indeed, they are. 

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Shown here combinations of such 
fundamental physical constants that yield 

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elementary units of time, or length, or 
mass. 

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And so for the time it's 10^-43 seconds 
and this is called Planck time. 

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For space is about 10^-33 centimeters, 
that's called the Planck length. 

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And for mass, it's about 10^-5 grams, 
which is called the Planck mass. 

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Similarly, you can derive units for other 
physical quantities. 

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And then there are derived units. 
In any case, the advantage of planck 

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units is that, indeed. 
They do not depend on any arbitrary 

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conventions. 
They really are given by the constants of 

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nature. 
But that doesn't necessarily mean that 

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they're somehow magical. 
We use them. 

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As limiting units for quantum gravity say 
but we don't really know. 

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And they may or may not be entirely 
relevant. 

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Nevertheless, they're a useful set of 
units to consider when thinking about 

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very early universe. 
So as we approach the Planck era our 

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knowledge breaks down. 
We do not yet have a working quantum 

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theory of gravity. 
Not for the lack of trying. 

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Many smart theorists have been working on 
this for a long time. 

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And today we have String theory or 
M-theory or Branes and things like that. 

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It's fair to say that none of those have 
yet produced a convincing unifying theory 

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that will unify quantum physics in 
gravity. 

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Nevertheless there are prospects that 
that might happen. 

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There are also theoretical attempts to 
think what was this implied beyond the 

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Big Bang. 
One of the interesting theories is the so 

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called Ekpyrotic cosmology, which 
essentially states that colliding branes, 

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which are essentially multi-dimensional 
supernova particles, can dissipate enough 

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energy to create all of the mass energy 
in the universe. 

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There's also the concept of the String 
Landscape, saying that there about 10^500 

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different universes. 
Each of which could have different 

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physical constants and different laws of 
nature. 

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Needless to say this is completely 
speculative at this point. 

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In either case the early universe 
certainly provides a high-energy physics 

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laboratory at levels that will never be 
achievable on this planet. 

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And so the unification of high-energy 
physics, particle physics and cosmology 

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is likely to get even stronger. 
Next, we will talk about the contents of 

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the universe.