The Big Bang The Big Bang theory is

The Big Bang • The Big Bang theory is part of cosmology • Cosmology deals with the origins and large -scale structure of the Universe This is totally unrelated to evolution! • Theory of Evolution is part of biology • Biology is the study of living organisms

What we know • Things we don’t yet know: – The exact composition of the Universe – The nature of dark matter – What happened during the first second? – Are we alone in the Universe? • Things we can never know: – What happened before the big bang? – Why does the Universe exist?

Evidence for an old Universe • Nearby Universe – Variable stars • Variable stars can be seen up to 50 M light years away • Minimum age of Universe > 50 million yrs – Oldest visible stars • Some very low-mass stars in globular clusters are 13 Gyr old • Based on well-established stellar models – White dwarf cooling times • The oldest white dwarfs have been cooling for 13 Gyr • Based on very well understood cooling laws • Cosmological arguments – Most distant discovered supernova = 6 B light years – Directly measuring expansion speed • Hubble constant gives us an age estimate – Based on matter, energy densities of Universe – Value is slightly under 14 billion years • All these methods agree very well at ~14 billion years

Homogeneity • Why is the Universe so homogeneous? – It seems very similar wherever you look • Cosmological models predict this • Computational simulations show structure arose • Early Universe inhomogeneity can be seen in the Cosmic Microwave Background Fluctuations in the cosmic microwave background, measured by the COBE satellite (1989 -1992). The fluctuations are exaggerated in the image: they are actually less than one part in 100, 000!

Sir Fred Hoyle • Famous Astronomer (1915 – 2001) • Worked on stellar nucleosynthesis – Formation of various heavy elements within stars • Converted from atheism to theism – His justification was the ‘fine tuning problem’ • (see later slide) Was wrong on pretty much everything after this point – Rejected the Big Bang (and coined the phrase as a joke) – Rejected naturalistic explanations for abiogenesis • He believed that life originated in space and was carried on comets – Later rejected natural selection as a mechanism for evolution – Supported the (now disproved) ‘steady state hypothesis’ • Claiming that the Universe didn’t begin, but has always existed in a steady state • ‘Hoyle’s Fallacy’ – The common misunderstanding that evolution is a random process

Fine Tuning • The Universe has (probably) 25 fundamental constants • Even a tiny change in some of them would be disastrous – The Universe could not have existed in its current state • Why are they so well tuned? Does this prove a god did it? – No, of course not – For a start, how could a god exist without being ‘in’ some Universe with its own parameters that needed tuning? – This is just the ‘no first cause’ fallacy • Several explanations (none very satisfactory) : – Parallel Universes – Anthropic principle – Fundamental parameters do seem to change over time • Bottom line: We don’t know, but we’re looking

Redshift is Unreliable? • Arp (1967), Burbidge (1969) etc. • Claimed “Quasars seem statistically more common near galaxies that are close to us” • Shouldn’t be the case if they are all very distant • Results based on very poor data and bad statistics • This has since been rejected • • We now know of 10, 000 s of quasars We see no statistical correlation with nearby galaxies Most quasars are not associated with visible galaxies at all Those that are, seem to have accurate redshift values • Galianni et al (2005) • Quasar in a galaxy of much lower redshift? • May be caused by the ejection of quasar from the galaxy • We genuinely don’t know the solution • Note: • The publication of these works and the consequent debate completely destroys the Creationist argument that papers that disagree with the status quo are suppressed!

Varying speed of light • Prof João Magueijo – Cosmologist, Imperial College, London • Suggests ‘c’ was much larger in the early Universe • An alternative to ‘inflationary’ models • What effect would that have on distances? – None – it deals with the very early Universe – So. L is definitely constant back to very high redshifts • Note that this cancels fine-tuning arguments! – If ‘c’ could vary hugely then perhaps all parameters somehow settled down on present-day values? – Highly speculative