Dr Martin Hendry Dept of Physics and Astronomy University of Glasgow

Transcription

1 Dr Martin Hendry Dept of Physics and Astronomy University of Glasgow

2 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?

3 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? You re very clever young man, very clever, said the old lady. But it s turtles all the way down!

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5 Science: The intellectual and practical activity encompassing the systematic study of the structure and behaviour of the physical and natural world through observation and experiment From the New Oxford dictionary

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7 Bernard Carr

8 Bernard Carr

9 Bernard Carr

10 Bernard Carr

11 Two talks in one: Why are we here?... Why are we here?...

12 Why are we here?...

13 Edwin Hubble

14 Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

15 Hubble s s Law Distant galaxies are moving away from us with a speed proportional to their distance

16 Spacetime is expanding like the surface of a balloon. As the balloon expands, galaxies are carried farther apart

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18 How fast is the Universe expanding?

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20 What is driving the cosmic acceleration?

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23 CMBR: all-sky temperature map from WMAP satellite. Temperature fluctuations from ~380,000 years after the Big Bang

24 Galaxies and Cosmology: the Basic Paradigm CMBR fluctuations, are the seeds of today s galaxies Structure we see today was assembled by gravity, causing density fluctuations in the early Universe (which we see imprinted on the CMBR) to grow, as the background smooth Universe expands

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27 So what exactly is this dark energy?... Einstein s cosmological constant?... Energy of the quantum vacuum?...

28 State of the Universe Apr % 22% Atoms Cold Dark Matter Dark Energy 74%

29 State of the Universe Apr % 22% Ω b Ω CDM Why does 96% of the Ω Universe consist of strange matter and energy? Λ 74%

30 From Lineweaver (1998)

31 Value of 1 Ω Ω Λ Ω CDM Why now? Big Bang Present-day Age of the Universe

32 Hydrogen fusion fuelling a star s nuclear furnace E = mc 2

33 Hydrogen fusion fuelling a star s nuclear furnace

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35 Why are we here?...

36 Why are we (and only we) here?... If the Universe is so big, and so old, and so finely balanced to support life like us, why are we seemingly alone?...

37 Why are we (and only we) here?... If the Universe is so big, and so old, and so finely balanced to support life like us, why are we seemingly alone?... Where is everybody? Enrico Fermi, 1950

38 Where is Everybody? by Stephen Webb Fifty solutions to the Fermi Paradox and the problem of extraterrestrial life: o They are here o They exist but have not yet communicated o They do not exist

39 They are here and are meddling in Human affairs

40 They exist but have not yet communicated We are Solar chauvinists Perhaps there are simply too many other interesting places to visit? Luminosity (Sun=1) Surface temperature (K) Deneb..... Rigel Betelgeuse.... Antares Arcturus Regulus Vega Sirius A Mira Pollux Procyon A.. Altair. Sun Sirius B Procyon B O5 B0 A0 F0 G0 K0 M0 M8 Spectral Type.. Aldebaran Barnard s Star Absolute Magnitude

41 They exist but have not yet communicated Cloudy skies are common!

42 They exist but have not yet communicated They stay at home

43 They exist but have not yet communicated They stay at home and surf the net

44 They exist but have not yet communicated They are signalling but we don t know how to listen The Waterhole : strong H and OH emission between 1.42 GHz and 1.64 GHz

45 They 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 Shouldn t that give plenty of time to colonise the galaxy?...

46 They do not exist Rocky planets are rare Most exoplanets found to date are hot Jupiters : massive planets close to their parent star. This is largely a selection effect.

47 Launch: Feb 2009 Kepler

48 They do not exist Jupiters are rare

49 They do not exist Jupiters are rare

50 Why are we (and only we) here?... If the Universe is so big, and so old, and so finely balanced to support life like us, why are we seemingly alone?...

51 Why are we (and only we) here?... If the Universe is so big, and so old, and so finely balanced to support life like us, why are we seemingly alone?...

52 Why are we here?... Selection effects can address the fine-tuning of our location within the Universe. But what about the global properties of the Universe?... The constants of nature The laws of nature

53 The Anthropic Principle 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. "Although our situation is not necessarily central, it is inevitably privileged to some extent"

54 Why are we here?... Weak A.P. Selection effects can address the fine-tuning of our location within the Universe. But what about the global properties of the Universe?... Strong A.P. The constants of nature The laws of nature

55 The W.A.P. merely summarises the idea of selection effects for different locations in our Universe. The S.A.P. requires the existence of other universes with different constants / laws of nature.

56 There is a wide spectrum of views on the Anthropic Principle: Freeman Dyson: I do not feel like an alien in this universe. The more I examine the universe and the details of its architecture, the more evidence I find that the universe in some sense must have known we were coming.

57 There is a wide spectrum of views 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 a negative influence. I would opt for rejecting the anthropic principle as needless clutter in the conceptual repertoire of science.

58 There is a wide spectrum of views on the Anthropic Principle: Brandon Carter: The anthropic principle is a middle ground between the primitive anthropocentrism of the pre- Copernican age and the equally unjustifiable antithesis that no place or time in the universe can be privileged in any way.

59 Three ways to make a Multiverse: 1. Cosmological inflation 2. M-theory / String Landscape 3. Quantum cosmology

60 Three ways to make a Multiverse: 1. Cosmological inflation 2. M-theory / String Landscape 3. Quantum cosmology

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63 Three ways to make a Multiverse: 1. Cosmological inflation 2. M-theory / String Landscape 3. Quantum cosmology

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65 Present Day Big Bang

66 Present Day Big Bang

67 String Theory Point particles replaced by string loops Avoids infinities No unique theory (Branes in higher dimensions) Particle representation String representation

68 M-Theory More than the 3 spatial dimensions which we actually observe. Our observed spacetime emerges from the way in which the extra dimensions are compactified. Calabi-Yau manifold There could be up to different compactifications each with a different set of constants of nature. We find ourselves in one that is anthropically selected.

69 Three ways to make a Multiverse: 1. Cosmological inflation 2. M-theory / String Landscape 3. Quantum cosmology

70 Present Day Big Bang

71 Summary of QM Interpretations Copenhagen Many Worlds Transactional

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73 But is it science?... We can t observe the other universes. How do we test theories? How do we make predictions?... Much heated debate on these points.

74 Steven Weinberg Thomas Bayes ( AD)

75 Ockham s Razor Frustra fit per plura, quod fieri potest per pauciora. It is vain to do with more what can be done with less. William of Ockham ( AD) Everything else being equal, we favour models which are simple. How do we measure the simplicity of universe versus multiverse models?

76 Martin Gardner There is not the slightest shred of evidence that there is any universe other than the one we are in. No multiverse theory has so far provided a prediction that can be tested. As far as we can tell, universes are not as plentiful as even two blackberries

77 Evolving constants of nature?... Lee Smolin Paul Davies Cosmological Natural Selection?

78 But why do we live in this multiverse?... Hierarchical picture Different constants of nature Different laws of nature Different mathematical and logical structures

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