The Big Bang

The Big Bang: Fact or Fiction?

The Big Bang debateA new perspective?Dr Cormac ORaifeartaigh CosmologyIs it finite? how big is it?

Is it eternal? how old is it?

How did it begin?

The study of the cosmosNot science?Greek cosmologyThe geocentric universe

Centre of universeAll motion about earthAristotle (350 BC)

Ptolemy (200 AD) Earth motionlessEternal universe33 reasons gravity caused by suns mass

Newton (1642-1727) planet orbits due to gravityNewtons cosmology

Eternal, infinite universe attractive force

space, time fixedParadoxes? 20th cent astronomy: the galaxiespowerful telescopesphotographyEdwin Hubble (1889-1958)

1920s: many galaxies Cepheid variables stellar distances other galaxies

The expanding universe

Edwin Hubble (1889-1958)Far-away galaxies rushing away at a speed proportional to distancev = Hod1929: galaxies moving apart

Note: Doppler Effect

frequency of light depends on relative motion of observersRedshiftControversy?The origin of the universerewind Hubble graph

universe smaller in the past

extremely dense, extremely hot?

primeaval atom?

Fr Georges Lemaitre Expanding and cooling ever sinceLemaitre: Age of the universevelocity = distance / time but v = Ho d hence time = 1 / Ho

How long since BB? t~ 14 billion yrCo-produced model?Wrong estimate at first Reception (classical): nonsense! 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 NewtonReception: general relativity 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 starlightNote: not Kuhnian paradigm shiftReception (relativity): nonsense!space-time dynamic?Einstein: static universe (1917)Friedmann: expanding universe

Einstein vs Lemaitre:Apply Einsteins gravity to the cosmosgravity vs expansion1933: Einstein capitulates relativity supports BBsmall community only: pedagogyThe Big Bang model14 billion years ago, U concentrated in tiny volume

primordial explosion of matter, energy, space and time

U expanding and cooling ever since

Misnomer: singularity problemNot acceptedPredictions of Big Bang model1. The expansion of the U

2. Nucleosynthesis

3. The cosmic background radiation

1940s: nuclear physics

H, He nuclei (1 s) atoms (300,000 yr)

U = 75% H, 25% Heheavier atoms formed in starsconfirmed by HoyleGeorges Gamow (1906 1968)

nuclear fission nuclear fusion apply to Big Bang modelno impactBB prediction 3: microwave background

radiation from hot origin

released when atoms form recombination (300,000 yr)

radiation still observable?Alpher, Gamow and Herman

BB : superhot superdense beginninglow temp, microwave frequencyNo-one looked (1940s)Forgotten knowledgeInstead: steady-state model (1950s)New attack on BB

Expanding universe

Consistent with relativity BUTNo beginning

Matter continuously created

Fred Hoyle

Co-produced model?Deviation?Large impactSteady-State prediction: eternal U Continuous creation

Density of matter constant

U unchanging, eternal

Distant galaxies similar to present?

Youngest galaxies similar to present?

Falsification possibleAnswer: radio-astronomy (1960s)Ryle: radio sources Study most distant galaxiesStudy density and intensity

Density the same at all times? (SS)Or different? (BB)Answer: different

Cambridge3C survey

Martin RylePULSARS!Blow for SSRadio-astronomy: CMB (1965) radio-astronomy

microwave frequency

temperature 3 K

Echo of Big Bang!CMB observed accidentally

Penzias and WilsonGamow ignoredModern measurements of CMB

accurate measurements full spectrum perfect fit with theoryCOBE 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?Cosmology TodayCosmic inflation (CMB)

Dark energy (CMB)

What happened at BB? Quantum gravity

Singularity at time zero?

Strong evidence for relativity Black holes, GPS

Hawking theorems

Revised Friedmann universesSummaryEvidence for BB model (expanding U 1929)Accepted by relativists (1933)Resisted by physics community

New avenues of evidence for BB (1948,49)Ignored by physics communityRise of rival SS model (1950)

Defeat of SS model (radiogalaxies, 1960)New evidence for BB (CMB 1965)Model gradually accepted (1968..)Latest: cyclic universe?