Beyond Inflation
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Inflation seems to "solve" the Horizon and Oldness-Flatness
Problems
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in the sense that "fine-tuning" is no longer required - or
at least, not so much "fine tuning" is required
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But, we still have the question: how did the Universe start
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In inflation is right, then what came before
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or even, if inflation is wrong, what started the Big Bang
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Implicit in a scientific approach to this problem
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is the assumption that "creation" can be described as a scientific
process
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There is no room for the hand of God, in these attempts to
describe the origin of the Universe
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the "hand of God" doesn't allow experimental or observational
tests
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Of course, these theories of the Origin of the Universe may
be extremely difficult to test
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so they can be criticized as unscientific
Origin of the Universe Theories
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Quantum Gravity
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at extremely high densities and temperatures, Einstein's
theory of gravity is thought to fail
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quantum mechanical effects are expected to become important
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There is, as yet, no working theory of Quantum Gravity
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superstring theory is thought to be the best bet
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Superstring theory would describe not only gravity, but all
of physics
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It is thought to be a good if the only theory that makes
sense is the 1 true Theory of Everything or T.O.E.
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Superstring theory appears to only work in 10 space time
dimensions
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It's good that the theory uniquely specifies the number of
dimensions
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too bad the answer doesn't seem quite right
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figure out some way to "fold up" those extra dimensions
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with Quantum Gravity spacetime is described as "quantum foam"
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in ordinary Quantum Theory, we have virtual particle-antiparticle
pairs being created and then annihilating on short timescales:
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recall that these "quantum fluctuations" are converted to
the small amplitude density fluctuations that serve as seeds for galaxy
formation in the inflation theory.
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With Quantum Gravity, spacetime itself, would be changing
violently on small scales
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Chaotic Inflation
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The Universe begins with "chaos"
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there is a mixture of particles, fields, and some "false
vacuum" material
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in some locations, there "just happens" to be a high energy
density of the "false vacuum" material
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these regions are dominated by strong negative pressure,
so they start an accelerating expansion
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this rapid expansion leaves the other bits of the Universe
behind, and we only have contact with the inflating part
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the Eternally Inflating Universe
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The Big Picture: the Universe is eternally inflating almost
everywhere
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Every now and then, a bit of the Universe stops inflating
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such regions take up a very tiny fraction of the volume of
the whole Universe
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we live in such a place
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there are other "Universes" that we can never communicate
with
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Spontaneous Creation of the Universe from "Nothing"
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"nothing" means a state with no space and no time
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"before" the Universe was created?
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This can only happen if the Universe has 0 total energy
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but large negative gravitational energy can cancel large
positive matter energy
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All such attempts seem to include inflation
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but there's no evidence for any of them
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they might not be testable even in principle
The Anthropic Principle
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The Weak Anthropic Principle
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the existance of intelligent observers should be regarded
as an important "selection effect"
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Example: In the Eternally Inflating
Universe Theory, it might seem to be very unlikely
that we happen to live in the extremely tiny part of the Universe that
is not inflating
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but, that is the only place where observers like ourselves
could evolve
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so it makes sense that we should live in these rare regions
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This is not very controversial
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This allows theories in which there are many different Universes,
but only some are compatible with life
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The Strong Anthropic Principle
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The Universe is "fine-tuned" to allow the existence of life
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In my view, this is not likely to be true
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We don't understand physics, chemistry or biology well enough
to say what things would be like if physics was different
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seems to suggest a purpose - and to be quasi-religious in
nature
Alternatives to the Big Bang
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There are some, but they aren't worth taking very seriously
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there proponents address puzzles with the Big Bang Theory
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but they generally ignore important observations that tend
to contradict them
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Proponents often have "ulterior" motives
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this doesn't make these theories wrong
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but it does suggest that we should be skeptical
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Steady State Theory
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several updated versions have been introduced since the CMBR
was discovered
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proponents are the same ones who promoted the Steady State
Theory in the 1960's.
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proponents think that the support for the Big Bang is partly
religous in nature
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they are still upset about some "alternative cosmologists"
being mistreated in the 1970's