1. 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

2. 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

3. The Horizon 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

4. 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

5. 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?

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

7. Copenhagen Interpretation of Q. M.
Some processes are inherently quantum uncertain
All possibilities actually occur
Until a measurement occurs ? 5

8. 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

9. 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