non-Gaussianity
Non-Gaussianity is a measurement of the
correction from a Gaussian function. A Gaussian function takes the form
of the famous 'bell-shaped' curve and is used in statistics to represent
statistically probable outcomes of an event.
Anisotropy
If something is isotropic it is the same
in all directions. In cosmology the universe is assumed to be isotropic
on large scales (known as the Cosmological Principle). Anisotropy is
the opposite of isotropy and the fluctuations in the CMB data are referred
to anisotropies.
Cosmic Microwave Background
The Cosmic Microwave Background (CMB)
is an electromagnetic radiation filling the entire universe. It was
emitted at the surface of last scattering, when photons were no longer
bound in plasma and free to travel through space. This radiation has
redshifted in time to peak in the microwave part of the electromagnetic
spectrum.
The radiation was discovered in 1965
almost completely by accident by Penzias and Wilson who noticed an
unwanted noise in their radiometer instrument, which they initially
blamed on bird shit! Turns out the CMB had been predicted in work
as early as 1948 by amongst others George Gamow and Ralph Alpher.
Useless trivia: other uses for CMB:
Cash Money Brothas; former Chicago gang
China Motor Bus; bus provider in Hong Kong
Core Mantle Boundary; in Earth Science
Combat Medical Badge; a decoration of the US army
China Merchants Bank.
Big Bang
The Big Bang is a highly successful model
of the universe which states that the entire universe must have once
emerged from a single hot and dense point. This explains the large scale
isotropy visible today and is now supported by substantial experimental
evidence.
COBE
The Cosmic Background Explorer (COBE)
satellite was the first dedicated experiment to measure the CMB radiation.
The two principal investigators, George Smoot and John Mather received
the Nobel Prize in Physics in 2006 for the COBE project. Lauched in
1989, the COBE mission lasted 4 years, during which it confirmed CMB
anisotropy for the first time.
Inflation
Inflation is the era of exponential expansion
following the Big Bang that solved one of its major problems, showing
that the universe could originate from one small, causally-connected
region. The inflationary model, first put forward in 1981 by Alan Guth,
has been redefined over and over, with many different versions vying
to become the definitive inflationary model.
WMAP
The Wilkinson Microwave Anisotropy Probe
(WMAP) was launched by NASA in 2001 and built on the work of COBE by
increasing its resolution and accuracy. The satellite is named after
Dr David Wilkinson, a member of the MAP science team.
Planck Surveyor
The Planck Surveyor will be the next satellite
to measure CMB anisotropy, increasing on the resolution of WMAP. It
is scheduled to return data in 2010. The satellite is named after Max
Planck, a German physicist who was one of the founders of quantum mechanics.
Warm inflation
Warm inflation predicts that inflaton
interactions with surrounding fields during the inflationary period
will result in a friction term in the equations of moton. In this scenario,
the anisotropies seen in the CMB are produced by thermal fluctuations.
It may be possible to distinguish between warm inflation and standard
supercooled inflation models using forthcoming satellite data.
Vacuum
A vacuum is a volume of space with no
matter. A perfect vacuum has not yet been created experimentally. It
has by definition has no temperature (i.e. 0 degrees Kelvin).
Inflaton
The inflaton is the name given to the
scalar field responsible for the inflationary epoch.
CMBFAST
A computer code which produces theoretical
spectra of anisotropies from cosmological models, which can be compared
to CMB data.
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PhD Research:
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| Where:
School of Mathematics
and Statistics, Merz Court, Newcastle University. NE1
7RU. |
| Contact:
c.m.graham@ncl.ac.uk |
|
| Funding:
MyPhD is funded by the Particle Physics & Astronomy
Research Council. |
|
Supervisor:
I am supervised by Professor Ian Moss, who has vast
research experience in Big Bang, inflation and black
hole subjects. Ian was one of Professor Stephen Hawking's
students , whom he worked with on inflationary theories.
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| Overview:
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| My
current research focuses on placing limits on the
predicted non-Gaussianity
of the cosmic microwave
background anisotropies ,
in particular for a model of inflation known as
warm inflation. |
| Since
its discovery in 1965, the Cosmic
Microwave Background CMB) radiation has
allowed cosmology to become more than just
a theoretical subject, and into a precision
science. The CMB confirmed what was already
widely believed; that the Universe started
in a fiery Big
Bang. However, it was the outstanding
discovery of fluctuations in the radiation
by the satellite COBE
in 1992 that was hailed "the greatest
discovery of the century, if not of all time"
by no less than Professor Stephen Hawking. |
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Above:
Predicted CMB fluctuations produced using
the software HEALPIX
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In 1982,
Alan Guth proposed a model of inflation,
a phase of exponential expansion shortly
after the Big Bang. Inflation overcame some
of the biggest problems facing the Big Bang
model but Guth's model wasn't without its
own issues. In the years that followed many
inflationary models were developed, each
with their own twist on the physics of the
expansion. One of the predictions that all
of these models had in common was that the
CMB would be anisotropic, which is exactly
why the COBE results brought so much excitement.
The problem
now facing cosmology is how to use the results
of COBE, and the satellite missions which
followed, to distinguish between models
of inflation. In 2000, the satellite WMAP
returned data with resolution high enough
to begin constraining these models, bringing
with it a mountain of scientific papers.
It is the WMAP data that I use in my research,
although I, like many others, am looking
ahead to exciting times as the ESA Planck
Surveyor promises even higher resolution
data in the coming years.
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| Above:
An artist's impression of the PLANCK surveyor.
Image: ESA |
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| My
own research considers warm
inflation, which predicts that the fluctuations
visible in the CMB are due to thermal, rather than
vacuum
fluctuations, arising from a friction term in the
inflaton
equation of motion, the fundamental equation governing
the inflation process. I make extensive use of the
CMBFAST
software, a powerful program capable of predicting
the fluctuations created by any feasible cosmological
model. |
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Above:
Some results produced by the software CMBFAST
in my own research.
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