THE YOUNG UNIVERSE John K. Webb University of New South Wales Sydney, Australia

Part 1 Why do we think the universe began with a ?

Several fundamental observations and theoretical facts suggest that there was a  The Universe is expanding (Hubble’s Law)  We are “bathed” in a microwave background radiation, most readily interpreted as the cooled relic radiation of the Big Bang  The night sky is dark (Olber’s paradox)  The observed abundances of light elements (eg. He, Li, D, Be) agree incredibly well with, and were predicted by, detailed calculations  The Big Bang was essentially “predicted” by Einstein’s General Relativity, which passes every observational test and provides a fundamental, physically meaningful, description of the world  Many other independent observations are all most readily interpreted within the framework of the Big Bang (eg. quasars, galaxy clustering, distant supernovae and star formation rates, chemical evolution, distant radio sources, gamma-ray bursts)

1916: Einstein predicted a static universe (his “biggest blunder”). 1929: Hubble discovered the expansion of the Universe

Christian Huygens (b1629 Holland). In astronomy, he was the first person to: " measure the size of another planet " speculate Venus is covered in clouds " sketch the surface of Mars and determine its rotation period (roughly 24 hours) " recognize the true nature of Saturn's rings " observe Titan, the largest moon of Saturn " provide a reasonable estimate for the distance to nearest stars. He also believed in the existence of life on planets around other stars... And wrote a book about it…...in 1690! Huygens’ believed light conveys energy from one place to another through waves - like waves in the ocean carry mechanical energy.

You can see the wave nature of light (and how a spectrum is formed) very simply for yourself. All you need is candles and fingers (or pencils)! This is a great demo! You just need to do it properly: 1. Squeeze 2 fingers together so no light can pass between them and place them about 1” in front of one eye (close the other). 2. Now look at a candle light (or some other point source or narrow source of light) through your fingers. Open them up only a tiny bit, so you can JUST see light. Can you see the `diffraction bands’? This is analogous to taking the spectrum of a galaxy with a “spectrograph” on a telescope.

The discovery of the expansion of the Universe (figure from Hubble’s 1929 paper)

From the Proceedings of the National Academy of Sciences Volume 15 : March 15, 1929 : Number 3 A RELATION BETWEEN DISTANCE AND RADIAL VELOCITY AMONG EXTRA-GALACTIC NEBULAE By Edwin Hubble Mount Wilson Observatory, Carnegie Institution of Washington Communicated January 17, 1929 Determinations of the motion of the sun with respect to the extra-galactic nebulae have involved a term of several hundred kilometers which appears to be variable. Explanations of this paradox have been sought in a correlation between apparent radial velocities and distances, but so far the results have not been convincing. The present paper is a re-examination of the question, based on only those nebular distances which are believed to be fairly reliable.

 describes the rate at which the Universe is expanding. THE FACT THAT THE UNIVERSE IS EXPANDING SUGGESTS IT BEGAN WITH A BIG BANG. is called HUBBLE’S CONSTANT and it’s value is about 71 km/s/Mpc (Mpc = Megaparsec, a million parsecs, which is about 3 x km) VELOCITY  DISTANCE

AGE OF UNIVERSE The latest value of is 71 km/s/Mpc  This is an upper limit – correct value is 13.7 Byr….. HUBBLE’S LAW  THE AGE OF THE UNIVERSE T = 14.4 billion years

View from galaxy A A B

View from galaxy B A B

Galaxies don’t move THROUGH space. Space ITSELF expands!

Hubble law tells us : the Universe ….. Has no centre Will get emptier in the future Was denser in the past  its youth was very different Was “all together” ~14 Byr ago  it was “born” in a Big Bang

“open space” “closed space”

Part 2 The

Part 3

Flat, 4% atoms Flat, 8% atoms Closed, by 150% Low pitchHigh pitch Long wavelengthShort wavelength

Properties from the CMB Age of Universe 13.7 Byr (2%) Atoms 4.4% (9%) Dark matter 23% (15%) Dark energy 73% (5%) Flatness 1.02 (2%) Hubble constant (km/s/Mpc) 71 (6%) Photon/proton ratio 1.6x10 9 (5%) Time of first stars 180 Myr (50%) Time of MWB 380,000yr (2%)

The Flatness Problem Should be either exactly equal to 1, or very very far from one. But we measure ! The Horizon Problem Regions on the sky separated by more than a few degrees can never have been in “causal contact”. Why then are the physical characteristics so similar?

The Horizon Problem 5o5o

Regions on the sky separated by more than a few degrees can never have been in “causal contact”. Why then are the physical characteristics so similar? The size of the Universe increases by a factor of during the first seconds of its existence!! Varying speed of light?

Part 4

HDF

For the first time in the history of humanity, new technology provides detailed views of the early universe. We can almost see back to the beginning of time, and have now developed a profound understanding of the birth and evolution of the universe. But there’s much more work left to do! Conclusion