The State of the Multiverse: The String Landscape, the Cosmological Constant, and the Arrow of Time

57 Pages·2012·0.48 MB·English

by  Raphael Bousso

The State of the Multiverse:
The String Landscape, the Cosmological
Constant, and the Arrow of Time
Raphael Bousso
CenterforTheoreticalPhysics
UniversityofCalifornia,Berkeley
Stephen Hawking: 70th Birthday Conference
Cambridge, 6 January 2011
RB & Polchinski, hep-th/0004134; RB, arXiv:1112.3341
The Cosmological Constant Problem
The Landscape of String Theory
Cosmology: Eternal inflation and the Multiverse
The Observed Arrow of Time
The Arrow of Time in Monovacuous Theories
A Landscape with Two Vacua
A Landscape with Four Vacua
The String Landscape
Magnitude of contributions to the vacuum energy
graviton
(a) (b)
(cid:73) Vacuum fluctuations:
SUSY cutoff: → 10−64; Planck scale cutoff: → 1
(cid:73) Effective potentials for scalars:
Electroweak symmetry breaking lowers Λ by approximately
(200 GeV)4 ≈ 10−67.
The cosmological constant problem
(cid:73) Each known contribution is much larger than 10−121 (the
observational upper bound on |Λ| known for decades)
(cid:73) Different contributions can cancel against each other or
against Λ .
Einstein
(cid:73) But why would they do so to a precision better than
10−121?
Why is the vacuum energy so small?
(cid:54)= 0
Why is the energy of the vacuum so small, and why is it
comparable to the matter density in the present era?
Recent observations
Supernovae/CMB/
Large Scale Structure:
Λ ≈ 0.4×10−121
Recent observations
Supernovae/CMB/
Large Scale Structure:
Λ ≈ 0.4×10−121 (cid:54)= 0
Why is the energy of the vacuum so small, and why is it
comparable to the matter density in the present era?
The Cosmological Constant Problem
The Landscape of String Theory
Cosmology: Eternal inflation and the Multiverse
The Observed Arrow of Time
The Arrow of Time in Monovacuous Theories
A Landscape with Two Vacua
A Landscape with Four Vacua
The String Landscape
Many ways to make empty space
Topology and combinatorics
RB&Polchinski(2000)
(cid:73) A six-dimensional manifold contains hundreds of
topological cycles. (Say, 500.)
(cid:73) Suppose each cycle can hold 0 to 9 units of flux
(cid:73) Then there will be 10500 different configurations.
(cid:73) This picture is (so far) supported by detailed constructions
[Kachru,Kallosh,Linde&Trivedi2003;
DenefandDouglas2004;...]
(cid:73) random variable with values
between about -1 and 1
(cid:73) With 10500 vacua, Λ has a
dense spectrum [RB&Polchinski
2000]
(cid:73) Many vacua with |Λ| (cid:46) 10−121
(cid:73) But will those special vacua actually
exist somewhere in the universe?
The spectrum of Λ
Λ
(cid:73) In each vacuum, Λ receives many
1
different large contributions
0
−1