Parallel Universes The Possibility of Alternate Realities

What’s the basic idea? • We have discussed many different models of the universe • Some of these have some observational validation. • If true, these models actually predict the existence of alternate universes. • There are currently 4 different types and they are NOT mutually exclusive!

The ‘80’s Universe • One answer to Olber’s paradox – a finite but unbounded universe • Predicts that on the largest scales we would see evidence of curvature • WMAP observations – no curvature out to the largest scales – space is

flat

• Matter doesn’t get diluted out – implies galaxies “forever”

Multiverse I – The Infinite Universe – Beyond our Cosmic Horizon • We live in an observable universe that has a light travel time of 13.7 billion years • Inflation means that the real universe is much larger but we can’t observe it • If space is flat, as observations seem to indicate, does it just end somewhere? • Laws of physics are the same everywhere but the initial conditions (eg concentration of matter) may not be.

The Set-up • At the time of the annihilation of antimatter, the universe had a certain number of particles and was at a certain temperature • Quantum physics gives a volume of space that can contain this, but it is finite. • If so, then conditions must eventually repeat • What does this mean?

The Implications - Doppelgänger • There are an infinite number of repeating universes • You are a rock star in one • You are an NFL quarterback in another • You are a lowly college student in yet another – oh, sorry that’s this one! • Every possibility that can exist MUST EXIST in an infinite universe

Weirder Implications • Infinite number of universes means infinite number of alien civilizations with the capability of creating an artificial universe • Artificial universes become more likely than real ones • Higher likelihood that you live in an artificial universe created by superior beings! • Basic evidence for this possibility: WMAP data

• Chaotic eternal inflation –large scale - different bubbles of space emerge with different initial conditions; vacuum does not decay to ground state – vacuum energy drives bubble formation • Different number of dimensions • Different values for physical constants • Basic laws of physics are still the same, they just operate on parameters of different value, eg the force of gravity or the mass of the electron • Evidence: inflation and fine-tuning

What’s so appealing about this? • The anthropic principle – why is the universe so exquisitely fine-tuned for our existence? Now we don’t have to worry – ALL POSSIBLE VALUES for physical parameters exist, just in different universes

Level 3 – Quantum Many Worlds • Derived from quantum mechanics • The uncertainty principle again • The universe keeps branching at every quantum decision point • Evidence: laws of quantum mechanics

Your universe

The Other universes

How is this different? • It is different in that all of these realities occur in the SAME SPACE, just in other “dimensions” • It is the SAME in the sense that all the same realities exist here that would exist in the level one universe – ergodicity • This now provides an alternate view of the concept of time!

Level 4 – Other Mathematical Structures - The Laws are different too! • eg classical universe without QM • Gravity goes by the cube of the distance (or the 2,000,000,000,000,000,000 power!) • Time is quantized • Evidence: the uncanny ability of mathematics to solve problems

Does Occam have a problem with all this? • The simplest solution is usually the correct one! • Occam loves it because every mathematical structure that can exist does and we don’t have to invoke ad hoc reasons why our special universe, with a certain value for all the parameters and a certain set of laws, exists AND OTHERS DO NOT!