Martin Hendry- Why are we here?

8/3/2019 Martin Hendry- Why are we here?

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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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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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Cloudy skies are common!


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They stay at home


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They stay at home

and surf the net


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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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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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Jupiters are rare


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Jupiters are rare


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If the Universe isso big, and soold, and so finelybalanced tosupport life likeus, why are we

seeminglyalone?....


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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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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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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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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.



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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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Martin Hendry- Why are we here?