THE YOUNG UNIVERSE

John K. WebbUniversity 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)

O n e o f th e g reat p io n eers o f m o d ern astro n o m y, th e A m ericanastro n o m er E d w in P o w ell H u b b le (1 9 8 9 - 1 9 5 3 ), started o u t b yg ettin g a law d eg ree an d serv in g in W o rld W ar I. H o w ev er, afterp racticin g law fo r o n e y ear, h e d ecid ed to "ch u ck law fo rastro n o m y an d I k n ew th at, ev en if I w ere seco n d rate o r th irdrate, it w as astro n o m y th at m attered ." H e co m p leted a P h .D . th esis o n th e P h o to g rap h ic In v estig atio no f F ain t N eb u lae at th e U n iv ersity o f C h icag o an d th enco n tin u ed h is w o rk at M o u n t W ilso n O b serv ato ry, stu d y in g th efain t p atch es o f lu m in o u s "fo g " o r n eb u lae in th e n ig h t sk y.

U sin g th e larg est telesco p e o f its d ay, a 2 .5 -m reflecto r, h estu d ied A n d ro m ed a an d a n u m b er o f o th er n eb u lae an d p ro v edth at th ey w ere o th er star sy stem s (g alax ies) sim ilar to o u r o w nM ilk y W ay.

H e d ev ised th e classificatio n sch em e fo r g alax ies th at is still inu se to d ay, an d o b tain ed ex ten siv e ev id en ce th at th e law s o fp h y sics o u tsid e th e G alax y are th e sam e as o n E arth - in h is o w nw o rd s: "v erify in g th e p rin cip le o f th e u n ifo rm ity o f n atu re."

In 1 9 2 9 , H u b b le an aly zed th e sp eed s o f recessio n o f a n u m b ero f g alax ies an d sh o w ed th at th e sp eed at w h ich a g alax y m o v esaw ay fro m u s is p ro p o rtio n al to its d istan ce (H u b b le's L aw ).T h is d isco v ery o f th e ex p an d in g u n iv erse m ark ed th e b irth o f th e"B ig B an g T h eo ry," an d is o n e o f th e g reatest triu m p h s o f 2 0 thcen tu ry astro n o m y.

In fact, H u b b le's rem ark ab le d isco v ery co u ld h av e b eenp red icted so m e ten y ears earlier b y n o n e o th er th an A lb ertE in stein . In 1 9 1 7 , E in stein ap p lied h is n ew ly d ev elo p ed G en eralT h eo ry o f R elativ ity to th e p ro b lem o f th e u n iv erse as a w h o le.E in stein w as v ery d istu rb ed to d isco v er th at h is th eo ry p red ictedth at th e u n iv erse co u ld n o t b e static, b u t h ad to eith er ex p an d o rco n tract. E in stein fo u n d th is p red ictio n so u n b eliev ab le th at h ew en t b ack an d m o d ified h is o rig in al th eo ry in o rd er to av o id th isp ro b lem . U p o n learn in g o f H u b b le's d isco v eries, E in stein laterreferred to th is as "th e b ig g est b lu n d er o f m y life."

-E S A B u lletin 5 8

T o v iew a larg er p ictu re o f E d w in H u b b le, click o n th e d iam o n d sh ap edp ictu re in th e h ead er ab o v e.

H S T M ain P ag e

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 WashingtonCommunicated 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.

oH describes the rate at which the Universe is expanding.

THE FACT THAT THE UNIVERSE IS EXPANDING SUGGESTS IT BEGAN WITH A BIG BANG.

dHV o 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 1019 km)

VELOCITY DISTANCE

oH

dHV oimedistance/tVBut

Td

dHTd

o

oHTor 1

AGE OF UNIVERSE

The latest value of is 71 km/s/Mpc

This is an upper limit – correct value is 13.7 Byr…..

oH

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 pitch High pitchLong wavelength Short 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 1.6x109 (5%)• Time of first stars 180 Myr (50%)• Time of MWB 380,000yr (2%)

The Flatness ProblemShould be either exactly equal to 1, or very very far from one. But we measure !1.0

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

5o

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 1050 during the first 10-30 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