The Big Bang: Fact or Fiction? The Big Bang vs the Steady State A new perspective? Dr Cormac O’Raifeartaigh

Overview Part I Cosmology The expanding universe The big bang model Relativity and the big bang Part II Predictions of the big bang model The steady-state model Choosing a model A new perspective? Einstein’s biggest blunder

I Cosmology Is it finite? how big is it? Is it eternal? how old is it? How did it begin ? The study of the cosmos Not restricted to science

Greek cosmology The geocentric universe Centre of universe All motion about earth Aristotle (350 BC) Ptolemy (200 AD) Earth motionless Eternal universe

Christian cosmology The geocentric universe Earth is center of the universe Universe has definite beginning and end “In the beginning God created the heaven and the earth” and God said…… and there was light Fused with Greek cosmology for 1000 years

20 th cent technology: the galaxies powerful telescopes photography Edwin Hubble ( ) 1920s: many galaxies Cepheid variables  measurement of distance  other galaxies

The expanding universe Edwin Hubble ( ) Far-away galaxies rushing away at a speed proportional to distance v = H o d 1929: galaxies moving apart

Doppler Effect stars moving away look redder than if stationary frequency of light depends on relative motion of observers Redshift

The origin of the universe rewind Hubble graph universe smaller extremely dense, extremely hot? primeaval atom? Fr Georges Lemaitre Expanding and cooling ever since

Lemaitre: Age of the universe velocity = distance / time but v = H o d hence time = 1 / H o How long since BB? t~ 14 billion yr

The Big Bang model 14 billion years ago, U concentrated in tiny volume primordial explosion of matter, energy, space and time U expanding and cooling ever since Misnomer: singularity problem

Reception (classical) gravity pulls in not out space is fixed time has no beginning Newton What is pushing out? What happened at time zero? How can U be younger than stars? Isaac Newton

Relativity and the Big Bang space and time = spacetime spacetime affected by mass gravity = distortion of spacetime Modern theory of gravity (1916) Einstein (1916) Evidence: orbit of Mercury, bending of starlight Not Kuhnian paradigm shift

Relativity and the Big Bang space-time dynamic? Einstein: static universe Friedmann: expanding universe Einstein vs Lemaitre: Apply Einstein’s gravity to the cosmos gravity vs expansion  1933: Einstein capitulates small community in support of BB

Predictions of Big Bang model √ 1. The expansion of the U 2. Nucleosynthesis 3. The cosmic background radiation 4. Galaxy formation

2. Nucleosynthesis H, He nuclei (1 s) atoms (300,000 yr) U = 75% H, 25% He heavier atoms formed in stars confirmed by Hoyle Georges Gamow (1906 –1968) 1940s: nuclear physics apply to Big Bang model We are made of dead stars

3. Cosmic microwave background radiation from hot origin released when atoms form recombination (300,000 yr) radiation still observable? Alpher, Gamow and Herman BB : superhot superdense beginning low temp, microwave frequency No-one looked (1940s) Forgotten knowledge

Steady-State model (1950s) Expanding universe Consistent with relativity BUT Matter continuously created? Not much matter required Fred Hoyle

Steady-State prediction: eternal U  Continuous creation  Density of U constant  U unchanging, eternal  Most distant galaxies similar ? Falsification

Radio-astronomy (1960s) Ryle: radio sources Most distant galaxies Study density and intensity Density the same at all times? (SS) Different? (BB) Answer: different 3C survey Martin Ryle PULSARS!

BB breakthrough: CMB (1960s) radio-astronomy microwave frequency temperature 3 K Echo of Big Bang! CMB observed: 1965 Penzias and Wilson Gamow ignored

Modern measurements of CMB accurate measurements full spectrum perfect fit with theory COBE satellite (1992)

Cosmic background radiation expected temperature expected frequency perfect blackbody spectrum COBE (1992) Nobel Prize 2006 radiation quite uniform? 1 in 10,000 galaxy formation?

Revised Friedmann universes

Cosmological model 1.Ordinary matter: 4% (astrophysics) 2. Dark matter: 22% (cosmology) 3. Dark energy: 74% (supernova, flatness) How can universe be flat? Astrophysics: Ω m + Ω dm = 0.3 Ω m (0.04) + Ω dm (0.22) + Ω vac (0.74) = 1

Remaining puzzles Particle responsible for inflation? Nature of dark energy? Nature of dark matter? Missing antimatter? Singularity at time zero? Further reading: ANTIMATTER What happened at BB? Something from nothing?