Cosmology

• Olber’s Paradox• Big Bang • Development of the Universe

Olber’s Paradox

Why is the night sky dark?

Newton believed universe was infinite in space & time.

If the universe contains an infinite number of uniformly distributed stars:

1)The collective brightness received should make sky bright.

2) Every line of sight should eventually lead to the surface of a star

3) Every point in the sky should be as bright as the surface of a star.

Apparent b drops with/d2, but surface A increases with d2, if stars uniformly distributed, the distance cancels – all equally bright.

Olber’s Paradox w mathplay from 1:53 (4:30 min)

• http://www.youtube.com/watch?v=0USMjYfkRxs

http://www.youtube.com/watch?v=gxJ4M7tyLRE

Minute Physics Olber’s 4 min

Big Bang Resolves paradox.

•Universe not infinite in space or time.

•Stars not uniformly scattered.

• Universe too young for light to have

reached us yet.

•Universe expanding.

Big Bang Model

• Space Time & Laws of Physics born from a singularity ~14-15 BYA.

• Space time expanding.

If all galaxies are moving away:

• Light from stars is red shifted into the IR region (we would not see it)

Big Bang Model Evidence

• Einstein’s general relativity also contradicts static universe – he tried to introduce cosmic constant!

• See Doppler Red Shift.

• Explains Olber’s paradox.

• Cosmic Background Radiation.

Cosmic Background Radiation CSBR.

• There is microwave radiation in the universe coming from all directions.

• From Wein’s law can find T of peak radiation ~ 3 K.

• Universe behaves as black body at 3K. Gas laws suggest universe would be that T if cooled by expansion for 14-15 BY.

Evidence Big Bang

http://www.youtube.com/watch?v=uyCkADmNdNo

Future of the universe

• Closed – big crunch. Gravity slowing expansion.

• Open – expansion continues. Not enough matter to overcome expansion.

• Flat – expansion slows almost to v = 0.

Outcome depends amount of mass

Critical density o amt mass needed to stop expansion.

Appears we have too little mass but not all mass is visable.

Only 10% of mass needed to stop expansion is observed so – open

universe.

• Dark matter - mass cannot be seen. No interaction with light. Affects rotational speed of galaxies.

•MACHOS - Brown & Black dwarfs–Massive compact halo objects.

•WIMPS – neutrinos–Weakly interacting massive particles.

Dark Matter Dark Energy

http://www.youtube.com/watch?v=rLmcbjLVPKc

International Research Projectoutline goals.

• http://www.spaceref.com/news/viewpr.html?pid=30109

• Herschel • http://sci.esa.int/science-e/www/object/

index.cfm?fobjectid=32136