Royal Astronomical Society Public Lecture
2012 May 8
THE ORIGIN OF STRUCTURE IN THE UNIVERSE
Simon Mitton
Department of the History and Philosophy of Science, University of Cambridge
Fellow, St Edmund’s College, Cambridge
Why is there something rather than nothing?
The nature of the universe. What the ancients achieved, and why we should be
impressed
• Plato and Aristotle taught that the heavens can be subjected to rational
enquiry
• The Greek geometers changed the nature of that enquiry forever.
Geometry became the key to understanding the mechanics of the
universe
• Eratosthenes measured the diameter of the Earth
• Hipparchus of Rhodes: first star catalogue (850 stars!); discovered
precession of the equinoxes
• Ptolemy of Alexandria: brings the geocentric model of planetary motion
close to perfection, but at a cost of complexity. Nevertheless it worked for
1400 years. Ptolemy’s Almagest is in the rare books room upstairs.
Newton’s Principia
Thomas Wright puts the Sun as a star at
the center of the Milky Way
William Herschel, discoverer of the universe,
and first cosmologist
M51
Lord
Rosse
1845
The Nature of the Universe the last time we had a Diamond
Jubilee (1897)
Astrophysics was in its infancy. So was
astrophotography.
Mainstream view was that the white nebulae
are members of the Milky Way
Cosmology did not exist
In London professional astronomy was
still dominated by the needs of navigation
and time keeping, as well as star positions
and stellar motion
Step 1 to the First Great
Discovery
Lowell Observatory, Flagstaff,
Arizona Territory
Andromeda Nebula is coming
towards the Milky Way at a
high velocity (blueshift)
Vesto Slipher 1875 – 1969
Andromeda galaxy
Step 1 to the First Great Discovery
By 1917 Slipher discovered that a dozen
nearby galaxies are speeding away from the
Milky Way (redshifted)
What could this mean?
By the mid-1920s the number of redshifts
was ~40
Vest Sipher 1875 – 1969
Step 2 to the First Great
Discovery
In1915 Einstein published the
General Theory of Relativity, a
theory of gravity that includes
the “time” dimension
Arthur Eddington in Cambridge understands that GR can
be used to model the properties and behaviour of the
entire universe
At the Total Eclipse of 1919 Eddington confirms GR, which
henceforth joins the cosmologists’ toolkit
Einstein and Eddington, The Observatories
Step 3 to the First Great Discovery
1923-24. Georges Lemaître joins
Eddington in Cambridge. They work
together on models of the universe
1924 Lemaître the theorist goes to the
other Cambridge to work at Harvard and
MIT. He meets observers Slipher and also
Edwin Hubble, with both of whom he
discusses model universes
Step 4 to the First Great Discovery
At Mount Wilson in the 1920s Hubble
measures the distances to nearby
galaxies for which velocities are
available (almost all of them from
Slipher). His truly great triumph was
getting the distance to the Andromeda
Nebula, proving beyond doubt that it
was a great galaxy
Hubble soon noticed a correlation: the larger the
redshift (velocity of recession), the greater the
distance to the galaxies
The First Great Discovery:
Speed away from us
The universe is expanding
Distance from us
Step 5 to the First Great Discovery
1927 Lemaître has an explanation for Hubble’s results.
Publishes in 1927 a paper on the expansion of the
universe in which he demonstrates that the model is
an allowed solution to Einstein’s GR equations
Einstein regards this as preposterous but Eddington
supports
1930 Lemaître speaks on the expanding universe at the
RAS, publishes the Primeval Atom concept in Nature,
and the following year has a paper in Monthly Notices
Lemaitre called his model the “Fireworks Universe”. The
moniker “Big Bang came later, in 1948.
1948 – 1964 Cosmologists at war!
Big Bang versus Steady State
Much blood letting in this very room!
Big Bang versus Steady State
Martin Ryle and Fred Hoyle
The great battle between Ryle and Hoyle concerning
cosmology ran from 1948 - 1964. This is fully documented
in my acclaimed biography, available from Amazon or the
publisher,
Fred Hoyle: A Life in Science
By Simon Mitton
Publisher: Cambridge University Press 2011
Online ISBN: 9780511852107
Paperback ISBN: 9780521189477
Subjects: Astronomy: general interest ,
The Second Great Discovery:
the whole universe is filled with
microwaves
1964 This strange radio
telescope accidentally
discovered that the entire sky
emits a weak microwave signal
The microwaves are a form
of heat energy at a very low
temperature
What had been discovered was
heat energy, in the form of
microwaves, released in the Big
Bang
Arno Penzias and Bob Wilson
1978 Nobel Prize Physics
American Astronomical Society Meeting January 1992
2003 – 2008 Better maps of cosmic microwaves
Tell us the age of the universe 13.7 by
Reveal the presence of dark matter and dark energy
Evidence of reverberating sound waves from the Big
Bang (baryon acoustic oscillations)
The second great discovery - the ripples show irregularities
beginning to form right after the Big Bang
HM Queen Elizabeth II catches up on cosmology!
8 May 2007
The distant universe imaged by
the Hubble Space Telescope
The universe: what’s in the pie?
Clusters of galaxies are weighed down by dark matter
Unseen dark matter is ten times more
common than ordinary matter
An enormous ring of dark matter
surrounds a great cluster of galaxies
“Why is there something rather than nothing?”
• The universe grew from a singularity, or quantum fluctuation, at the scale
of the Planck length 10-43 m. The resulting expansion could not have
been infinitely uniform
• The universe went through cosmic inflation 10-36 – 10-33 seconds.
Fluctuations preserved – baryon acoustic oscillations
• The First Three Minutes – origin of light elements. The next 700,000
years – era of recombination
• Fine tuning of the universe: expand too fast -> no structure, too slow ->
collapse under gravity.
• The Goldilocks solution: conditions “just right”. But honey and nice words
do not work in cosmology …
• … Dark matter to the rescue! Amount detected is “just right” to allow
structure to develop via the gravity of dark matter – the visible matter
alone is insufficient
• Let’s see the dark matter simulation
Present distribution of dark matter in the universe
Zooming in on a massive cluster of galaxies
I’ve seen out to the limit of the observable universe and
believe me it’s no better out there than it is here …
Big Bang versus Steady State
Martin Ryle and Fred Hoyle
The great battle between Ryle and Hoyle concerning
cosmology ran from 1948 - 1964. This is fully documented
in my acclaimed biography, available from Amazon or the
publisher,
Fred Hoyle: A Life in Science
By Simon Mitton
Publisher: Cambridge University Press 2011
Online ISBN: 9780511852107
Paperback ISBN: 9780521189477
Subjects: Astronomy: general interest ,
Royal Astronomical Society Book Series
Editor: Simon Mitton
Department of the History and Philosophy of Science, University of Cambridge
Fellow, St Edmund’s College, Cambridge
Forthcoming Book
Taking the Back off the Watch
A Personal Memoir
Mitton, Simon (Ed.)
Jointly published with the Royal Astronomical Society
2012, 2012, XVII, 225 p. 27 illus.
ISBN 978-3-642-27587-6
Enthralling life story of one of the most remarkable
astrophysicists of the second half of the twentieth century who explained
pulsars as rotating neutron stars
With intriguing anecdotes revealing Gold’s scientific curiosity
and deep understanding of physics
Carefully edited by the author of the biography of Sir Fred
Hoyle
With a Foreword by Freeman Dyson
Published under the auspices of the Royal Astronomical
Illustrated with photographs, many never previously published
Thomas Gold (1920-2004) had a curious mind that liked to solve
problems. He was one of the most remarkable astrophysicists in the
second half of the twentieth century, and he attracted controversy
throughout his career. Based on a full-length autobiography left behind
by Thomas Gold, this book was edited by the astrophysicist and historian
of science, Simon Mitton (University of Cambridge).