3A03 – GR and Cosmology

Ralph Pudritz

Dept. of Physics & Astronomy

McMaster University

Hubble Space Telescope – time machine

This telescope has enabled our deepest probe at optical wavelengths, of the cosmos – the Hubble “deep field”.

Looking back in time – galaxies long ago

This image, consists entirely of galaxies. Very faint ones are at cosmological distances:-smaller and “blotchier” than galaxies at present.-Evidence for for galactic evolution over cosmic time.

Mapping where galaxies are – “large scale structure”

Da Costa et al (1994)

(Center for Astrophysics survey )

- 9,325 galaxies shown

- The largest structure yet seen: the “Great Wall”.

Coma - cluster of galaxies

THE EXPANDING UNIVESE Edwin Hubble:

1889 - 1953

At the 48 inch on Mt. Palomar

Cepheid variable stars – measuring distances to other galaxies

Hubble Diagram (1929): galaxies move apart!

Galaxies move away from us - the same for observers in any other galaxy…

Albert Einstein – General Relativity

Fate of the universe - depends on how dense it is…

Geometry of the universe in four dimensions….

Closed Universe Critical Open Universe

(sphere) (flat) (saddle)

Discovery of microwave radiation – blackbody at 2.7o K

COBE satellite – mapping the CMBR

COBE map: temperature of universe 2.735 deg above absolute zero - image shows slight “dipole” Dpppler shift, picking out our direction of motion

Cosmic Microwave Background Radiation - temperature fluctuations (one part in 105 )

Inflation – making the universe flat

Cosmic Microwave background radiation is surprisingly smooth – universe probably “inflated” incredibly rapidly from one tiny little region.

The expanding, cooling universe

THE ORIGINS OF STRUCTRE IN THE UNIVERSE

How did galaxies form?

- Density fluctuations infinitesimal in size, originate from quantum fluctuations in spacetime soon after the Big Bang.

- These are seen in fluctuations in CMBR – baby photo of galaxies!