This isn t science! It s inevitable

Transcription

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4 This isn t science! It s inevitable

5 Makes sense! Why not? I hate it!

6 Party on!

7 Q: Is there more that exists than we can see? Cosmology suggests yes!

8 Outline: The most interesting question isn t whether parallel universes exist, but whether the multiverse has 1, 2, 3 or 4 levels Evidence for parallel universes Reasons to like/dislike multiverses

9 What do we mean by our universe?

10 y

11 y Foreground-cleaned WMAP map from Tegmark, de Oliveira-Costa & Hamilton, astro-ph/ CMB Our universe

12 Level I

13 How big is our space?

14 y Foreground-cleaned WMAP map from Tegmark, de Oliveira-Costa & Hamilton, astro-ph/ CMB Our universe

15 g

16 Multiverse level I: other Hubble volumes beyond our cosmic horizon Giordano Bruno (executed 1600) Ellis & Brundrit 1979, Q.J.R. Astr. Soc. 20, 37 Garriga & Vilenkin 2001, Phys.Rev. D64, Features: Same (effective) laws of physics Different initial conditions For our flat concordance cosmological model: Size of our Hubble volume ~ m, Closest copy of you ~ m Closest 100 lightyear bubble like ours ~ m Closest Hubble volume like ours ~ m

17 Evidence

18 Alan Guth

19 (Figure from Boomerang team)

20 Reichardt et al 2008, arxiv:

21 Ω k movie

22 Level II

23 g

24 Why these values? g MT, Aguirre, Rees & Wilczek 2005 Standard model parameters: Cosmology Particle physics C = h = G = k b = q e = 1

25 Multiverse level 2: other post-inflationary regions (Pics from Andrei Linde) Features: Perhaps different effective laws of physics (physical constants, particles, symmetrics, dimensionality) Perhaps even uncountably infinite (Compare a literally parallel Universe; living on another brane)

26 Level III

27 Multiverse level 3: Everett s many worlds

28 g

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30 Level IV

31 Q: What s the entropy of our universe? A: About bits What does all that information really tell us?

32 10 3 bits

33 How much of this information needs to go on the T-shirt? Very little

34 How much of this information needs to go on the T-shirt? Very little

35 Quantum random number generator based on Stern-Gerlach apparatus: Generic outcome: (Just our address in Hilbert space - not specified on T-shirt)

36 So what does go on the T-shirt? g MT, Aguirre, Rees & Wilczek 2005 Standard model parameters: Cosmology Particle physics C = h = G = k b = q e = 1

37 So what does go on the T-shirt? g The Standard Model Lagrangian L= (From T.D. Gutierrez)

38 Multiverse level 4: other mathematical structures

39 Tegmark 1997, gr-qc/ , Ann. Phys, 270, 151

40 Tegmark 1997, gr-qc/ , Ann. Phys, 270, 151

41 Q: Is all we observe all there is? Our high entropy suggests no!

42 If what we observe requires more bits to describe than 1089 bits? a complete mathematical description of the world 103 bits? then we re in a multiverse! So if you re looking for a simple mathematical TOE, you re looking for a multiverse theory.

43 Which are the 4 multiverse levels? 1) Different Hubble volumes 2) Different post-inflationary regions 3) Different decohered branches of the quantum wavefunction 4) Different mathematical structures

44 Where are the parallel universes? 1) Far away in space 2) Infinitely far away in space 3) Elsewhere in Hilbert space 4) Elsewhere in math space

45 What are the 4 multiverse levels like? 1) Same effective laws of physics, different initial conditions 2) Same fundamental laws of physics, different effective laws ( bylaws ) 3) Nothing qualitatively new 4) Different fundamental laws of physics

46 Evidence

47 PHYSICS OR PHILOSOPHY? Q: Are theories which predict the existence of unobservable parallel universes untestable? A: No, as long as they also make predictions for things we can observe. Example 1: GR predicts black hole interiors? infinite Example 2: Inflation predicts space

48 PHYSICS OR PHILOSOPHY? Q: Are theories which predict the existence of unobservable parallel universes untestable? A: No, as long as they also make predictions for things we can observe. Parallel universes are not a theory, but the prediction of certain theories.

49 How to test/falsify a multiverse theory: Not necessary that rest of ensemble be observable Example: the theory that there s no dark matter

50 Sound too crazy?

51 We re not taking this guy seriously enough

52 The strongest form of the anthropic principle: The Universe must be such that we like it.

53 The strongest form of the anthropic principle: The Universe must be such that we like it.