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Dr Martin Hendry
Dept of Physics and AstronomyUniversity of Glasgow
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A little old lady at the back of the room
got up and said: What you have told us is
rubbish. The world is really a flat plate
supported on the back of a giant tortoise.
The scientist gave a superior smile before
replying What is the tortoise standing on?
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A little old lady at the back of the room
got up and said: What you have told us is
rubbish. The world is really a flat plate
supported on the back of a giant tortoise.
The scientist gave a superior smile before
replying What is the tortoise standing on?
Youre very clever young man, very
clever, said the old lady. But its turtlesall the way down!
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Science:
The intellectual and practical activityencompassing the systematic study of the
structure and behaviour of the physical
and natural world through observationand experiment
From the New Oxford dictionary
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Bernard Carr
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Bernard Carr
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Bernard Carr
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Bernard Carr
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Two talks in one:
Why are we here?...
Why are we here?...
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Why are we here?...
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Edwin Hubble
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Space is big. You justwon't believe how vastly,
hugely, mind- bogglinglybig it is. I mean, you maythink it's a long way down
the road to the chemist's,but that's just peanuts tospace.
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HubbleHubbles Laws Law
Distant galaxies are moving away from uswith a speed proportional to their distance
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Spacetime is expanding like
the surface of a balloon.
As the balloon expands,
galaxies are carried farther
apart
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How fast is the Universe expanding?
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What is driving the cosmic acceleration?What is driving the cosmic acceleration?
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CMBR: all-sky temperature map from WMAP satellite.
Temperature fluctuations from
~380,000 years after the Big Bang
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CMBR fluctuations, are theseeds of todays galaxies
Galaxies and Cosmology: the Basic Paradigm
Structure we see today was assembledby gravity, causing density fluctuations
in the early Universe (which we see
imprinted on the CMBR) to grow, as thebackground smooth Universe expands
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So what exactly is
this dark energy?...
Einsteinscosmologicalconstant?...
Energy of thequantum vacuum?...
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4%
74%
22%
Dark Energy
Cold Dark
Matter
Atoms
State of the Universe Apr 2008
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4%
74%
22%
State of the Universe Apr 2008
Why does 96% of the Universe consist
of strange matter and energy?
CDM
b
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From Lineweaver (1998)
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Why now?
CDM
Value of
Present-day
Age of theUniverse
Big Bang
0
0.2
0.4
0.6
0.8
1
0 1 2 3
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Hydrogen fusion fuelling a stars nuclear furnace
E = mc 2
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Hydrogen fusion fuelling a stars nuclear furnace
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Why are we here?...
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Why are we (and only we)here?...
If the Universe is so big, andso old, and so finely balanced
to support life like us, whyare we seemingly alone?....
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Why are we (and only we)here?...
If the Universe is so big, andso old, and so finely balanced
to support life like us, whyare we seemingly alone?....
Where is everybody?Where is everybody?Enrico Fermi, 1950
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Where is Everybody?by Stephen Webb
Fifty solutions to the Fermi Paradoxand the problem of extraterrestrial
life:
o They are here
o They exist but have not yet
communicated
o They do not exist
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They are here and are meddling in Human affairsThey are here and are meddling in Human affairs
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They exist but have not yet communicatedThey exist but have not yet communicated
We are Solar chauvinists
Perhaps there are simply
too many other interesting
places to visit?
25000 10000 8000 6000 5000 4000 3000
Surface temperature (K)
O5 B0 A0 F0 G0 K0 M0 M8
Luminosity(Sun=1)
Spectral Type
1
102
104
106
10-2
10-4
-10
-5
0
+5
+10
+15
AbsoluteM
agnitude
. . . . .
. . ..
.
.
.... ...
.
................
.......
.......
......
.... ...
.
..
. ....
.
..
.......
..
...
........
.
. ..
..
..
.......... .
..
....RegulusVega
Sirius A
Altair Sun
Sirius B
Procyon B
BarnardsStar
Procyon A
..
...
.. Aldebaran
Mira
Pollux
Arcturus
Rigel
Deneb
Antares
Betelgeuse
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They exist but have not yet communicatedThey exist but have not yet communicated
Cloudy skies are common!
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They exist but have not yet communicatedThey exist but have not yet communicated
They stay at home
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They exist but have not yet communicatedThey exist but have not yet communicated
They stay at home
and surf the net
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They exist but have not yet communicatedThey exist but have not yet communicated
They are signalling but we dont know how to listen
The Waterhole: strong H and OH emission between1.42 GHz and 1.64 GHz
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They do not existThey do not exist
Perhaps emergence of Life depends on astrophysics
o e.g. carbon-based life may
appear only after peak in
cosmic carbon production
o This peak occurred ~ 7 billion
years ago.
o Still leaves a ~ 3 billion-year
head start for some ETC
o Shouldnt that give plenty of
time to colonise the galaxy?...
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They do not existThey do not exist
Rocky planets are rare
Most exoplanetsfound to date arehot Jupiters:massive planets
close to theirparent star.
This is largely a
selection effect.
K lK l
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KeplerKepler
Launch: Feb 2009
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They do not existThey do not exist
Jupiters are rare
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They do not existThey do not exist
Jupiters are rare
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Why are we (and only we)here?...
If the Universe isso big, and soold, and so finelybalanced tosupport life likeus, why are we
seeminglyalone?....
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Why are we (and only we)here?...
If the Universe isso big, and soold, and so finelybalanced tosupport life likeus, why are we
seeminglyalone?....
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Why are wehere?...Selection effects can address the
fine-tuning of our location within theUniverse.
But what about theglobal properties ofthe Universe?...
Theconstants of nature
Thelaws of nature
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The Anthropic Principle
"Although our situation is not
necessarily central, it is inevitably privilegedto some extent"
Introduced by Brandon Carter (1973).
A reaction to over-zealous use of the
Copernican Principle: we are not at
a special position in the Universe.
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Why are wehere?...Selection effects can address the
fine-tuning of our location within theUniverse.
But what about theglobal properties ofthe Universe?...
Theconstants of nature
Thelaws of nature
Weak
A.P.
StrongA.P
.
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The W.A.P. merely summarises the
idea of selection effects for differentlocations in our Universe.
The S.A.P. requires the existenceof other universes with different
constants / laws of nature.
Th i id t f
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There is a w ide spectrum ofviews on the Anthropic Principle:
Freeman Dyson:
I do not feel like an alien in this
universe. The more I examine theuniverse and the details of itsarchitecture, the more evidence Ifind that the universe in some
sense must have known we werecoming.
Th i id t f
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There is a w ide spectrum ofviews on the Anthropic Principle:
Heinz Pagels:
The influence of the anthropic principle on
contemporary cosmological models has been sterile.It has explained nothing and it has even had anegative influence. I would opt for rejecting theanthropic principle as needless clutter in the
conceptual repertoire of science.
Th i id t f
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There is a w ide spectrum ofviews on the Anthropic Principle:
Brandon Carter:
The anthropic principle is a middle
ground between the primitiveanthropocentrism of the pre-Copernican age and the equallyunjustifiable antithesis that no
place or time in the universe canbe privileged in any way.
Th k M l i
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Three ways to make a Multiverse:
1. Cosmological inflation
2. M-theory / String Landscape
3. Quantum cosmology
Th t k M lti
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Three ways to make a Multiverse:
1. Cosmological inflation
2. M-theory / String Landscape
3. Quantum cosmology
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Three ways to make a Multiverse:
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Three ways to make a Multiverse:
1. Cosmological inflation
2. M-theory / String Landscape
3. Quantum cosmology
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Present Day
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Big Bang
Present Day
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Big Bang
String TheoryString Theory
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Particle representation String representation
Point particles replaced by string loops
Avoids infinities
No unique theory
(Branes in higherdimensions)
MM--TheoryTheory
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yy
More than the 3 spatial dimensionswhich we actually observe.
Our observed spacetime emergesfrom the way in which the extradimensions are compactified.
Calabi-Yau manifold
There could be up to 10500 different compactifications
each with a different set of constants of nature.
We find ourselves in one that is anthropically selected.
Three ways to make a Multiverse:
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Three ways to make a Multiverse:
1. Cosmological inflation
2. M-theory / String Landscape
3. Quantum cosmology
Present Day
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Big Bang
Summary of QM InterpretationsSummary of QM Interpretations
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Summary of QM InterpretationsSummary of QM Interpretations
CopenhagenMany
Worlds
Transactional
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But is it science?....
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But is it science?....
We cant observe the other universes.
How do we test theories?
How do we make predictions?...
Much heated debate on these points.
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Thomas Bayes
(1702 1761 AD)
Steven Weinberg
Ockhams Razor
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Frustra fit per plura, quodfieri potest per pauciora.
It is vain to do with morewhat can be done with less.
William of Ockham
(1288 1348 AD)
Everything else being equal,we favour models which aresimple.
How do we measure the simplicity ofuniverse versus multiverse models?
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Martin Gardner
There is not the slightestshred of evidence that thereis any universe other thanthe one we are in. No
multiverse theory has so farprovided a prediction thatcan be tested. As far as wecan tell, universes are notas plentiful as even twoblackberries
Evolving constants of nature?...
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g
Paul Davies
Lee Smolin
CosmologicalNatural Selection?
But why do we live in thismultiverse?....
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y
Hierarchical picture
Different constants of nature
Different laws of nature
Different mathematical and logical structures
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