1. The Planck Era
At the grand unified scale, gravity is weaker than the other forces
But getting stronger as energy increases!
At a temperature of about 1031 K, it is as strong as the others
Maybe all forces are unified!
This scale is called the “Planck Scale”
A theory unifying all forces is called a “Theory of Everything”
We don’t know what it would look like
We have lots of candidates
String theory, Loop quantum gravity, etc.
t = s
T = 1031 K
Planck Era
Inflation
GUT
Electroweak
p/n freezeout
Nucleosynthesis
Recombination
First structure
Today

2. What Came Before the Big Bang?
t < s
T ~ 1031 K
No one knows
One possibility: Eternal/Chaotic Inflation
Inflation went on forever, and is still going on
One small pocket escaped and became “our universe”
Other pockets escaped and became others
My guess:
Space and time was created in the big bang
Time becomes quantum uncertain
“Before” becomes meaningless
Planck Era
Inflation
GUT
Electroweak
p/n freezeout
Nucleosynthesis
Recombination
First structure
Today

3. What is the Nature of Dark Matter?
We don’t know, but there are always kooks who try to guess

4. What is the Nature of Dark Energy?
We don’t know, but there are always kooks who try to guess

5. Multiple Universes What Do We Mean? Scientific Speculation!
Some of these ideas are unproven or controversial
But they are taken seriously by at least some scientists
What do we mean by multiple Universes?
The Universe is the totality of existence that we are aware of or can be aware of us
If there are places that are real, but we can’t see them, they are other Universes

6. Reasons to Believe in Multiple Universes
Universe might be infinite or very large
In a big enough universe, anything can happen
Completely separate universes may appear spontaneously
If our universe came from nothing, why not others?
Many Worlds Interpretation of quantum mechanics
If correct, then everything happens

7. The Horizon 90 Gly Q. 115: Horizon Size
The Universe has, apparently, a finite age: 13.8 Gy
Nothing moves faster than light
Naively, nothing can affect us more than 13.8 Gly away
Because it was travelling in a smaller universe, it can actually go farther, about 45 Gly
The volume of space withing 45 Gly is our horizon
Sometimes called the visible universe
Effectively, it’s our universe
90 Gly
Q. 115: Horizon Size

8. A Big Universe is Many Universes
Different parts of the Universe are cut off from each other
If the Universe is infinite, there are infinitely many Universes

9. Spontaneous Creation of the Universe
The universe we see could be created out of nothingness
Quantum Cosmology
The universe could be a bubble of order amidst a Universe of chaos
Chaotic Inflation
Not all bubbles need have the same properties
Different physical laws
Different numbers of dimensions?

10. Quantum Mechanics and Probability
In the everyday world, we think of probability as expressing our ignorance ? 5

11. Copenhagen Interpretation of Q. M.
Some processes are inherently quantum uncertain
All possibilities actually occur
Until a measurement occurs ?
Q. 116: Copenhagen Interpretation of Quantum Mechanics 5

12. Many Worlds Interpretation of Q. M.
All possibilities actually occur
Even after a measurement occurs
In many cases, the different possibilities become so disconnected, they effectively become separated universes ?
We are only cognizant of one 1 2 3 4 5 6

13. Do People Take This Seriously?
Many famous physicists, and a lot of obscure ones, believe in the Many Worlds Interpretation
Murray Gell-Mann
Steven Weinberg
Stephen Hawking
Richard Feynman
That One

14. Life in the Universe What We Want to Know
There is intelligent life on Earth
Could it have happened elsewhere?
Alien Spacecraft/UFO’s?
Evidence is unconvincing
Can we calculate probabilities? No
Drake’s Equation is a way to estimate how many intelligent civilizations (besides ours) are in the galaxy

15. Q. 117: What Life Doesn’t Need
Drake’s Equation
N = R* fP nPM fl fi L
N = number of civilizations in our galaxy
R* = rate at which solar-type stars form
fP = fraction of those stars with planets
nPM= number of suitable planets and moons
fl = probability of getting life
fi = probability of life evolving intelligence
L = lifetime of intelligent species
Q. 117: What Life Doesn’t Need