Beyond Inflation

Inflation seems to "solve" the Horizon and Oldness-Flatness Problems

in the sense that "fine-tuning" is no longer required - or at least, not so much "fine tuning" is required

But, we still have the question: how did the Universe start

In inflation is right, then what came before
or even, if inflation is wrong, what started the Big Bang

Implicit in a scientific approach to this problem

is the assumption that "creation" can be described as a scientific process
There is no room for the hand of God, in these attempts to describe the origin of the Universe

the "hand of God" doesn't allow experimental or observational tests

Of course, these theories of the Origin of the Universe may be extremely difficult to test

so they can be criticized as unscientific

Origin of the Universe Theories

Quantum Gravity

at extremely high densities and temperatures, Einstein's theory of gravity is thought to fail
quantum mechanical effects are expected to become important
There is, as yet, no working theory of Quantum Gravity

superstring theory is thought to be the best bet
Superstring theory would describe not only gravity, but all of physics

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.
Superstring theory appears to only work in 10 space time dimensions

It's good that the theory uniquely specifies the number of dimensions
too bad the answer doesn't seem quite right
figure out some way to "fold up" those extra dimensions

with Quantum Gravity spacetime is described as "quantum foam"

in ordinary Quantum Theory, we have virtual particle-antiparticle pairs being created and then annihilating on short timescales:

recall that these "quantum fluctuations" are converted to the small amplitude density fluctuations that serve as seeds for galaxy formation in the inflation theory.
With Quantum Gravity, spacetime itself, would be changing violently on small scales

Chaotic Inflation

The Universe begins with "chaos"

there is a mixture of particles, fields, and some "false vacuum" material
in some locations, there "just happens" to be a high energy density of the "false vacuum" material
these regions are dominated by strong negative pressure, so they start an accelerating expansion
this rapid expansion leaves the other bits of the Universe behind, and we only have contact with the inflating part

the Eternally Inflating Universe

The Big Picture: the Universe is eternally inflating almost everywhere
Every now and then, a bit of the Universe stops inflating

such regions take up a very tiny fraction of the volume of the whole Universe
we live in such a place
there are other "Universes" that we can never communicate with

Spontaneous Creation of the Universe from "Nothing"

"nothing" means a state with no space and no time

"before" the Universe was created?

This can only happen if the Universe has 0 total energy

but large negative gravitational energy can cancel large positive matter energy

All such attempts seem to include inflation

but there's no evidence for any of them
they might not be testable even in principle

The Anthropic Principle

The Weak Anthropic Principle

the existance of intelligent observers should be regarded as an important "selection effect"
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

but, that is the only place where observers like ourselves could evolve
so it makes sense that we should live in these rare regions

This is not very controversial
This allows theories in which there are many different Universes, but only some are compatible with life

The Strong Anthropic Principle

The Universe is "fine-tuned" to allow the existence of life

In my view, this is not likely to be true
We don't understand physics, chemistry or biology well enough to say what things would be like if physics was different

seems to suggest a purpose - and to be quasi-religious in nature

Alternatives to the Big Bang

There are some, but they aren't worth taking very seriously

there proponents address puzzles with the Big Bang Theory
but they generally ignore important observations that tend to contradict them

Proponents often have "ulterior" motives

this doesn't make these theories wrong
but it does suggest that we should be skeptical

Steady State Theory

several updated versions have been introduced since the CMBR was discovered
proponents are the same ones who promoted the Steady State Theory in the 1960's.
proponents think that the support for the Big Bang is partly religous in nature
they are still upset about some "alternative cosmologists" being mistreated in the 1970's