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Announcements. Exam 3 is next time: Thursday April 11. Format will be 7 MC’s and 4 SA’s (out of 7). Covers chapters 7 – 11. Sample questions are posted. Additional sample essays for Chapter 11 have also been posted. The stuff covered today will not be on the exam. Olber’s Paradox.

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Announcements
Announcements

  • Exam 3 is next time: Thursday April 11. Format will be 7 MC’s and 4 SA’s (out of 7). Covers chapters 7 – 11. Sample questions are posted. Additional sample essays for Chapter 11 have also been posted.

  • The stuff covered today will not be on the exam


Olber s paradox
Olber’s Paradox

Why is the night sky dark?


The cosmic background radiation
The Cosmic Background Radiation

First detected by Arno Penzias and Robert Wilson



They discovered a persistent noise
They discovered a persistent “noise” Milky Way in the microwave

The “noise” came from all directions so it had to be receiver based. The even cleaned out the horn of pigeon droppings and other debris but it wouldn’t go away


James peebles at princeton was trying to measure the cbr
James Peebles, at Princeton, was trying to measure the CBR Milky Way in the microwave

Robert Dicke, who originally built the receiver Penzias and Wilson were using, was working with Peeples and others

Peebles had predicted a CBR based on a calculations of a cyclic universe


Penzias and wilson only measured the cbr at one wavelength 7 35cm
Penzias and Wilson only measured the CBR at one wavelength: 7.35cm

Most of the CBR is in the infrared region which is difficult to measure from the Earth’s surface




A closer look reveals fluctuations in the background radiation at the one part in 100 000 level
A closer look reveals fluctuations in the background radiation at the one part in 100,000 level


The discovery of the CBR killed the Steady State Model by proving the existence of a hot early universe

There were many other problems with the Steady State model but the CBR was the final nail in the coffin.


Where did all this come from
Where did all this come from? proving the existence of a hot early universe



Nucleosynthesis in the early universe
Nucleosynthesis in the early couldn’t make enough Heliumuniverse

Early calculations by George Gamow, Ralph Alpher and Robert Herman started with neutrons which decayed into protons then fused to make everything else. They predicted a cosmic background at 5 Kelvin.


The stability gap was a problem for theories that made everything in the early universe
The “stability Gap” was a problem for theories that made everything in the early universe

Note the extremely low levels of Beryllium, Lithium and Boron around the “stability gap”.


The answer was that both theories were correct
The answer was that both theories were correct everything in the early universe

Big Bang nucleosynthesis makes most of the helium. Stars make everything beyond helium. Only in stellar cores is the density of Beryllium high enough to get past the stability gap.


The early universe
The Early Universe everything in the early universe

What was the universe like before the CBR? How about before nucleosynthesis? How far back can we go if we can’t see anything farther than this?


Matter density decreases differently than energy density
Matter density decreases differently than energy density everything in the early universe

This term is due to the decrease in energy from the expansion of space



Solving the friedmann equation for an energy dominated universe
Solving the Friedmann equation for an energy dominated universe

Energy decreases as 1/R4 so

But energy density is proportional to T4 so


At the extremely high density of the early universe, the density term dominates the Friedmann equation


Putting it all together gives a simple relationship between time and size
Putting it all together gives a simple relationship between time and size

During the energy dominated era, the universe expands as the square root of time



What was a universe dominated by energy like
What was a universe dominated by energy like? gets and the hotter it gets

Virtual particles of all types of elementary particles were popping in and out of existence everywhere


If only particle antiparticle pairs are produced there would not be any matter in the universe
If only particle-antiparticle pairs are produced there would not be any matter in the universe

There must have been particle production processes that did not conserve baryon number




Some fields are easy to picture
Some fields are easy to picture fields

The photon is the exchange particle for the electromagnetic field




Before the planck time 10 43 seconds we know nothing
Before the Planck time (10 fields-43 seconds) we know nothing

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