How many universes are there, anyway

http://timeandquantummechanics.comMultiverse - Balticon, May 23rd, 2015John Ashmead Anyway?
Just how many universes
are there,

http://timeandquantummechanics.comMultiverse - Balticon, May 23rd, 2015
• Rainbow gravity
• Gravity leaking
into nearby
dimensions
• Miniature black
holes

• The multiverse
today
• The problem of
ﬁne-tuning
• A scientiﬁc
hypothesis?
• What are the odds?

The Multiverse Today
• A brief history of the
multiverse
• The edge of the known
• From the Big Bang to now

A brief history of the
Multiverse
• Eratothenes’s Earth
• Kepler’s Moon
• Galileo’s Jupiter
• Wright’s Galaxies
• Bessel’s Star

• Chief Librarian at
Alexandria at 245 BC
• Sieve of primes
• Beta/Pentathelete
• Camel-Days
• Right order of
magnitude
Eratothenes’
Earth

Kepler’s
Somnium
(1608+)
• Autobiographical
• Revised thru his life
• Copernican theory
• The view from the
moon

• Careful reasoning
• Notebooks
• Time series
• A lot to love here
Galileo & The Moons
of Jupiter(1610)

Wright’s Galaxies
(1750)
• Milky way as galaxy
• Nebulae as galaxies
• An indifferent universe

Bessel’s Star
(1838)

Cosmic
Distance
Ladder
• Parallax (Blue)
• Standard Candles
(Light Orange)
• Supernovae (Red)
• The red shift (Dull
green)

• 30 billion years away
• But only 13.7 billion
years since start?
• Space has been
expanding!

Finite but no edge!
• Finite but no edge
• It’s getting bigger
every minute
• Now is a good time for
observers

Big Bang Theory
(De Luce)
• Only theory with a TV
show
• Robert Grossteste, 1175
- 1253.
• The Big Bang theory is
not about the Big Bang

• Why is the
universe so
ﬂat?
• With matching
temperature
• & curvature?

Too Hot to Shine
• Only ionized
particles
• The
unfortunate
photon no
sooner escapes
from one
particle
• Than it is
absorbed by
another!

Tri-Alpha Process
• Helium
stable
• Beryllium
(next) is
NOT
• But there is
a resonance
with Carbon
• Tunnel thru!

The problem of fine-
tuning
• Just six numbers
• Quantum
ﬂuctuations
• String theory

Anthropic testsCurious when you
think about it that the
universe is perfectly
adapted for
velociraptors
What if there are lots
of universes & we
just got lucky?
I see dinner!

Vulcan Science
Directorate Thinks not
A parallel
universe.
The science
directorate has
examined all these
theories.
They've found no
evidence of
alternate realities.

Quantum
Fluctuations
• Quantum
ﬂuctuations
• Fractals
• Led to universe
• And galaxies

Eternal Inflation
• Parts of the mega
universe suddenly cool
out
• Creating a bubble
universe
• That inﬂates with speciﬁc
values of the fundamental
physical constants

Live, Die, Repeat
• Origin of species
• “Generate & test”
• Galaxies, stars, planets,
& us
• Universes & their
observers
• And theories of the
multiverse, e.g. String
Theory

String theory
• Most popular today
• Gets rid of some
inﬁnities
• Lets us combine
particle physics &
gravity
• 10 dimensions for
superstrings

Compactification

Calabi-Yau Manifolds
• The “extra”
dimensions are
curled up into
complex structures
• Many possible
ways to do this

String-scape
• 10^500
possibilities
• Most are
uninteresting
• A few “Happy
Valleys”

Fringe Science?
• Hot scientists?
• Equations?
• Intense but
puzzled
expressions?
• Fate of the
universe at
stake?

How to think about
WeirdThings
• Testability
• Fruitfulness
• Scope
• Simplicity
• Conservatism

Testability

Cosmological
Microwave Background

Bubble universes

Bubbles in the CMB?
• Nearby
parallel
universe
• Leaves
smudge on
the CMB
• Sister
universes?

Gravitational waves
• Distant
universes
• Remnants of
collisions
• From before
the Big Bang

Fruitfulness
• Gives you something
to look for at small
scales
• And at large
• Can rock the mind
loose from hard-
wired assumptions

Scope
• Largest possible
scope
• See as far as possible
• And then drive
imagination a bit
further than that

Simplicity
• # of hypotheses
• not number of parts, but
the kinds of parts
• is a Calabi-Yau manifold
simple or complex?

Wheeler’s Radical
Conservatism
• The combination of Eternal Inﬂation
& String theory gives the multiverse
as a straight forward prediction
• Gellmann’s totalitarian principle +
the 30 odd constants also imply
multiverse
• And Many Worlds Interpretation
implies that the multiverse a natural
implication of quantum mechanics

The universe whisperer

• Shift your
assumptions to match
those of your target
world
• Absurd
• And profound
Syllogismobile

one universe or many?

Thanks!
• Balticon & Miriam Kelly
• Ferne Welch
• Brenda Welch & Jamie Laird
• Other quasi-willing ears

• Stenger - God & the Multiverse -
2014
• Greene - Hidden Reality - 2011
• Barrow - The Book of Universes -
2011
• Clegg - Before the Big Bang - 2009
• Susskind - The Cosmic Landscape -
2006

How many universes are there, anyway

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