Page 14 - Perimeter Institute 2012 Annual Report

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research
Cosmologists at Perimeter Institute are working to pin down the constituents and history
of our universe and the rules governing its origin and evolution. They look for solutions to
some of physics’ most enduring problems at length scales and energies that could never be
matched in an earth-bound lab. Cosmology also connects deeply with other areas of research
at Perimeter Institute, including particle physics, quantum gravity, quantum fields and strings,
and strong gravity.
Between the last crunch
and the first bang
What happened before the big bang? It depends on whom you
ask.
The common idea is that the big bang singularity was the
beginning of space and time – nothing happened
before
the big
bang because time itself did not exist until the big bang. However,
to explain the structure of the universe we actually observe, this
model relies on inflation – that is, a brief period of hyper-expansion
in the universe’s first trillionth of a trillionth of a trillionth of a second,
during which the large-scale structure of the universe was set.
Inflation comes with a set of problems – enough problems to
prompt the development of alternative ideas.
One alternative idea, developed by
Perimeter Distinguished
Visiting Research Chair Paul J. Steinhardt
and
Perimeter
Director Neil Turok
, is called cyclical cosmology. In the cyclic
model, the big bang is actually a bounce: a transition from an
earlier contracting universe to the present expanding one. There
have been bang-crunch-bang-crunch models before, but in this
model, the cycles are interlinked. In fact, in this model, the large-
scale structure of our universe was set during a phase of slow
contraction before the big bang – in the previous version of the
universe, as it were.
The biggest open questions in the cyclic model are about the
bounce itself – the transition from crunch to bang. This year,
Turok and collaborators developed a new possibility for how
this bounce might have happened. Before this, research had
considered two possibilities: that the contracting universe (or,
technically, its cosmic scale factor) might shrink to zero during
the big crunch and then expand into the big bang, or that it
might shrink to some small but non-zero size. The new model
involves an antigravity phase between the big crunch and the big
bang. This antigravity phase would help explain the origin of the
expansion in the big bang.
The result may be useful for the construction of complete bouncing
cosmologies like the cyclic model.
Looking for lithium
The oldest stars don’t contain as much lithium as they should.
It’s called the lithium shortfall and it’s a major hole in an otherwise
highly successful model of big bang nucleosynthesis, which
Cosmology