Anthropic Principles, Multiverses

1. Why is the World the Way it
is?The Anthropic Principle
and Fine-Tuning

2. Particle Physics in the 20th Century
• By the 1970s physicists had succeeded in constructing a complete quantum
field theory of particle physics
• The Standard Model
▫ All the fundamental particles with their properties – charge, mass, spin
▫ The fundamental laws of physics
▫ The fundamental constants of nature
• An extraordinarily well confirmed model and theory of particle physics

4. The Physical Constants
There are 26 known fundamental dimensionless physical constants. They
cannot be calculated; they are determined only by measurement.
Standard Model of Particle Physics
• the fine structure constant
• the strong coupling constant
• masses of 6 quarks
• masses of 6 leptons
• mass of the Higgs boson, W boson, Z boson
• 4 parameters of the CKM matrix for describing how quarks oscillate forms
• 4 parameters of PMNS matrix – same thing for neutrinos
Cosmology – general relativity
• The cosmological constant

5. New Questions for Physics
New questions erupted in the late 20th century
• Why do we have the particular particles and
forces in nature that we do?
• Why are the constants what they are?
• Why are the laws what they are?
• What determines the initial conditions?
Many contemporary physicists have attempted
to explain this features of the universe.
The assumption here is that is that the world is contingent. It might have been
different!

6. A New ‘Scene of Inquiry’ in Physics
As our knowledge of the elementary particles and fundamental interactions
grew dramatically during the 20th Century we began to be interested in
questions that are not answered by knowing the laws of physics. One of these
is the question: why are these the laws, rather than other possible laws? If
there are many possible laws, each as logically consistent as those we observe,
what selected the set that are realized in our universe? Another question not
answered by knowing the laws is what selected the initial conditions, at or
near the big bang… It is not enough to know the laws of nature. There must be
explicable reasons for the laws of nature themselves. This demand has a long
precedence in the history of science. It was most clearly articulated by Leibniz
in his Principle of Sufficient Reason
Lee Smolin, ‘The landscape problem’ (2013)

7. Examples of Fine-Tuning
• The observed values of the constants appear to be ‘fine-tuned’ to permit the
formation of matter and subsequently the emergence of life.
• The electromagnetic force is 1039 times stronger than gravity
If they were comparable, stars would have collapsed long before life had a chance to
evolve.
• The cosmological constant has a remarkably low value
If the cosmological constant were >10 times its observed value, the universe would
suffer catastrophic inflation, precluding the formation of stars, and hence life.

8. Examples of Fine-Tuning
• The Strong Force is not quite strong enough to bind the dineutron and the
diproton
If it were, all hydrogen would be converted into helium in the early universe.
Water, as well as long-lived stable stars – both essential for life – would not exist.
• Mass of neutron (1) – Mass of proton (0.99862349) > Mass of electron
(0.00054386734).
If this were not the case, the neutron would be stable, leaving little hydrogen to fuel
the stars.

9. Is this Just a Giant Coincidence?
“If we are to genuinely understand our universe, these relations, between the
structures on large scales and the elementary particles, must be understood as
being something other than coincidence. We must understand how it came to be
that the parameters that govern the elementary particles and their interactions
are tuned and balanced in such a way that a universe of such variety and
complexity arises…
Perhaps before going further we should ask just how probable is it that a universe
created by randomly choosing the parameters will contain stars. Given what we
have already said, it is simple to estimate the probability. The answer, in round
numbers, comes to about one chance in 10299… In my opinion a probability this
tiny is not something we can let go unexplained; we need some rational
explanation of how something this unlikely turned out to be the case.”
P. Davies, The Goldilocks Enigma, Why is the Universe Just Right for Life?, 2006

10. Just Right for Life

11. The Anthropic Principle
In 1974 Brandon Carter hypothesized that the universe anthropic coincidences are part
of the universe's very structure and that chance has nothing to do with it.
• Weak anthropic principle
If our universe weren't hospitable to life, then we wouldn't be here to wonder about
it! As such, there's no sense in asking why. It’s like asking ‘what are the odds that
not one of your ancestors died childless?’
• Strong anthropic principle
The Universe (and hence the fundamental parameters on which it depends) must be
such as to admit the creation of observers within it at some stage.
The anthropic principle has has been applied to several distinct ideas. Cosmologists have
devised more than 30 additional takes on the anthropic principle!

12. The Various Responses
1. Intelligent Design
2. No Explanation Necessary
3. Physical explanations
4. Others

13. 1. Intelligent Design
The view that the universe is created by God and designed to be suitable for life because
the emergence of sentient beings is part of God’s plan.
Advantage
Explains the ‘fine tuning’, bio-friendliness and seems a ‘natural’ explanation for those
who have decided on other grounds that God exists.
Disadvantage
• Conversation stopper
• Says nothing about the why? or how? God did it.
• This is not necessarily the Christian God. If not, who designed the designer?
• Makes the answers to scientific questions depend on a faith about something outside
the domain of rationality – a form of mysticism

14. 2. No Explanation Necessary
There is simply no point or purpose or design to the universe
It’s just a brute fact!
• The universe just is the way it is
• It is not a legitimate scientific question to ask why the universe is the way it is –
because it does not admit of an empirical answer
The fallacy of fine-tuning
• Is it possible that the physical constants could have been different? Yes, but …
• How would you calculate the probability?
• If the constants could take on any value (real numbers), this means that the
probability of our universe is 0 – impossible, not improbable!

15. Other Fallacies of Fine Tuning
• Many discussions of fine-tuning study the effect of
varying the parameters, one at a time.
• Varying several parameters together yields
cosmologies that provide conditions for life
• It is not at all clear that our universe is optimally
fine-tuned for life.
• A slightly negative value of the cosmological constant
would maximize galaxy formation

16. 3. Physical Explanations
Theory of everything; Multiple universes; Evolving laws of physics

17. A Theory of Everything?
• Fine-tuned laws, fundamental constants and boundary conditions will all
be explained as part of a final and unique theory of everything.
• The only consistent fundamental theory of physics uniquely sets the
parameters, resulting in only one possible theory of the universe – ours!
• The world must be the way it is – What appears to be contingent turns out
to be necessary.
• However, for many physicists the dream of a unique ‘final theory’ is
becoming increasingly unlikely – the landscape problem in string theory.

18. Multiple Universes
There are in fact multiple universes, each with a different set of parameters and
laws. These are the number of ‘tries’ that might naturally produce a universe
fined tune for life as is our universe.

19. The Multiverse Hypothesis
• Various cosmological models entail, or are at least consistent with the
existence of many universes. Inflationary cosmology, string theory, etc.
• We find the laws of nature that we find, because those laws are precisely the
ones necessary for us to exist and for us to be able to ponder such a mystery.
• Does this really explain the appearance of ‘fine tuning’ of the universe for
life?
• Is the hypothesis even testable? How would we ever observe other
universes?
• What kind of physical process sets parameters randomly? Is the production
of multiverses fine-tuned?

20. Is This Physics?
Extreme multiverse explanations are therefore reminiscent of theological discussions.
Indeed, invoking an infinity of unseen universes to explain the unusual features of the
one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory
may be dressed up in scientific language, but in essence it requires the same leap of
faith.
Paul Davies, A Brief History of the Multiverse (2003)
As skeptical as I am, I think the contemplation of the multiverse is an excellent
opportunity to reflect on the nature of science and on the ultimate nature of existence:
why we are here? … In looking at this concept, we need an open mind, though not too
open. It is a delicate path to tread. Parallel universes may or may not exist; the case is
unproved. We are going to have to live with that uncertainty. Nothing is wrong with
scientifically based philosophical speculation, which is what multiverse proposals are.
But we should name it for what it is.
George Ellis, Does the Multiverse Really Exist? (2011)

21. Maybe the Laws have Evolved
“To suppose universal laws of nature capable of being apprehended by the
mind and yet having no reason for their special forms, but standing
inexplicable and irrational, is hardly a justifiable position… Now the only
possible way of accounting for the laws of nature, and for uniformity in
general, is to suppose them results of evolution.”
C. S. Peirce, ‘The architecture of theories’, Monist (1891)
“At the beginning of time the laws of Nature were probably very different from
what they are now. Thus, we should consider the laws of Nature as continually
changing with the epoch, instead of as holding uniformly throughout space-
time.”
P. Dirac, ‘The relation between mathematics and physics’. Proc. R. Soc. Edinb. (1939)

22. What Kind of Explanation is This?
“the parameters may actually change in time,
according to some unknown physical processes… it
seems to be … our best hope for a completely rational
explanation.”
L. Smolin, The Life of the Cosmos (1997)
“As Wheeler, Dirac and Pierce understood, laws must
evolve to be explained.”
L. Smolin, ‘The Landscape Problem’ (2013)
Is it possible to give a naturalistic explanation of ‘laws of nature’?

23. Physics on the Fringe?
That string cosmology conference I attended was by far the most surreal
physics event I have been to, a star-studded proceeding involving some of
the most famous names in science... After two days, I couldn't decide if the
atmosphere was more like a children's birthday party or the Mad Hatter's tea
party—in either case, everyone was high... the attitude among the string
cosmologists seemed to be that anything that wasn't logically disallowed
must be out there somewhere. Even things that weren't allowed couldn't be
ruled out, because you never knew when the laws of nature might be bent or
overruled. This wasn't student fantasizing in some late night beer-fuelled
frenzy, it was the leaders of theoretical physics speaking at one of the most
prestigious university campuses in the world.
Margaret Wertheim, Physics on the Fringe: Smoke Rings, Circlons and Alternative
Theories of Everything (2012).

24. Speculative Physics?

25. “Without any explanation of nature’s fine-tunings we will be hard pressed to
answer the ID critics.”
Susskind, New Scientist, December 17, 2005.
“If you don’t want God, you’d better have a Multiverse”
Bernard Carr, ‘Science’s Alternative to an Intelligent Creator: The Multiverse Theory’
“I believe that the transition that science is now undergoing is in part a
necessary process of liberation from the influences of this essentially
religious view of the world… These are all steps towards a more rational and
more complete comprehension of the world based on what we know and less
on myths passed down to us from earlier generations.”
Smolin, The Life of the Cosmos,
The Need for Explanation