Multiverses

1
Multiverses

• by
• Robert Nemiroff
• Michigan Tech

2
Physics X About This Course

• Officially "Extraordinary Concepts in Physics"
• Being taught for credit at Michigan Tech
• Light on math, heavy on concepts
• Anyone anywhere is welcome
• No textbook required
• Wikipedia, web links, and lectures only
• Find all the lectures with Google at
• "Starship Asterisk" then "Physics X" 
• http//bb.nightskylive.net/asterisk/viewforum.php?
  f39

3
Multiverse Hypotheses

• Initial idea from H. Everett.  Expanded by M.
  Tegmark
•  
• Level 1 Beyond our observable universe
• standard general relativistic universe
• open universe with infinite volume
• universe "started" with infinite volume
• expanded by inflation
• physical laws and constants are the same
• everywhere
• at all times
• identical volume 1010115 meters away

4
Multiverse Hypotheses

• Level 1 Beyond our observable universe
•  
• there are infinitely many exact replicas of you
  reading an exact replica of this slide, right
  now.
• there are also infinitely many nearly exact
  replicas of you doing something slightly
  different, progressing toward a different future

5
Multiverse Hypotheses

• Level II Universes with different physical
  constants
• Chaotic inflationary epochs (for example) may
  create universe bubbles were different rules
  hold.
• Some bubbles are "Level 1" bubbles like our own.
• Cyclic Universes (Wheeler) Closed universes may
  "bounce" with different bubbles formed each
  bounce
• Fecund Universes (Smolin) black hole collapse
  causes new universe to form "inside"
• universes that produce black holes proliferate

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Multiple Histories

•  
• Feynman suggested that when a particle moves from
  A to B, it takes EVERY POSSIBLE PATH.  Each path
  is assigned an "amplitude", which is related to a
  probability.  These amplitudes will interfere,
  however, and only those paths with the greatest
  constructive interference at the end will result
  in the most probable endpoints to see in nature.

7
Multiverse Hypotheses

• Level III Universe Offshoots from Many Worlds
  Interpretation of QM
• every time a quantum measurement is made, every
  possible outcome of that measurement creates a
  parallel universe where that measurement occurs 
• these universes do not interact
• similar to Feynman's multiple histories

8
Multiverse Hypotheses

• Level III differs from Level 1 because
• Level 1 twins reside far across 3D space in time
  and space.  
• theoretically a single photon could pass you and
  your twin.
• Level III twins reside in a disconnected physical
  reality
• theoretically, a single photon could NOT pass you
  and your twin.

9
Multiverse Hypotheses

• Level IV Ultimate Ensemble
• All universes that can be theoretically defined 
• all space-time for ...
• different constants
• different measurements
• differences that humans can't imagine
• So general that there cannot be a Level V

10
Multiverse Hypotheses

• Criticisms
• Most multiverse hypotheses are not falsifiable. 
  There is no present practical test that can
  indicate clearly which one is correct, if any. 
• Multiverse theorists are very sensitive to this
  criticism and are constantly trying to find
  falsifiable claims.
•  
• Multiverse hypthoses are needlessly complex --
  hence they violate Occam's Razor.
• Entire Multiverse theory might be simpler than
  any alternative.