(3/31/08) From Big Bang to Black Holes: Part II

The Big Bang
The Evolution of the Universe
Galaxy Formation and Evolution
Dark Matter/Dark Energy
The Big Questions
Future Prospects

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-Basic Forces-

Strong nuclear force - Holds nuclei together: Strength 1, Range 10^-15 m, gluons + nucleons
Electromagnetic Force - Strength 1/137, Range Infinite, photon [mass o] [ spin 1]
Weak - Strength 10^-6, range 10^-18m [0.1% of the diameter of a proton], intermediate vector bosons, W+, W-, Z0,mass > 80 GeV, spin =1
Gravity - Strength 6 * 10^-39, Range Infinite, [potential gravitron particle], mass =0, spin = 2

Cosmological principle - isotropic [large-scale structure looks the same in all directions] and homogenous [general physical properties are the same everywhere]

The universe has no edge and no center

-Hubble Law-
On large scales, galaxies are moving apart, with velocity proportional to distance

There is no center of expansion
Spacetime itself is expanding and carrying the galaxies with it

^ Can tell this via cosmological redshift


Redshift = (wavelength - original wavelngth) / (original wavelength)


Extrapolating backwards w/ Hubble's Law = universe had a beginning [infinitely small and hot] - the cosmic singularity

(Planck's constant t = 1.35*(10^-43) sec

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We should expect thermal radiation from hot gas
Radiation should is blackbody spectrum

Initially, all four forces were equally strong.
Broke off in the following order: gravity, strong force, weak force
Gravity broke off (forze out) within 1 Planck time of Big Bang

First Galaxies - Approx. 1billion years after Big Bang

Bizarre inflationary period - exponential expansion of universe soon after Big Bang

W/O inflationary period, universe would have had to start out relatively large

Infationary period theory - explains lack of magnetic monopoles, horizon problem, flatness problem

Horizon problem: things far enough apart that they didn't come into contact with each other
Flatness problem: near critical energy density (eqiuilibrium point between infinite expansion and infinite compression) - Sphere needed to move from a small size (high arc) to large size (low arc) quickly

Initially, was equilibrium between pair production and annihilation (between regular matter and antimatter). There was a slight shift in favor of regular matter

Then, atomic nuclei were created (a few seconds after the Big Bang). This settled out a few minutes after the Big Bang.

This initial process created hydrogen, helium, lithium and beryllium (along with hydrogen isotope deuterium). Mostly hydrogen/helium.
Other elements were formed via fusion in the center of stars.

As universe expanded, it cooled down, cooled down to a point where atoms formed, and electrons were not allowed to interfere with photons anymore, because they were locked down in atoms

Cosmic Background Radiation was predicted as a 'signature' of the Big Bang.
R. Wilson and A. Penzias won the Nobel Prize for discovering this in 1978


Highly isotropic - intensity of this radiation very similar in all directions
Perfect blackbody spectrum would have a temperature of 2.725 Kelvin

Slight nonuniformity explains the clusters of matter that ended up as galaxies


Spiral galaxies: relatively small nuclear bulge, disk with spiral arms, gas/dust/star formation/young stars
Barred spirals are 2/3 of all spirals; they have elongated nuclei with spiral arms emerging from the ends

Elliptical galaxies: squashed-sphere shape, largely old stars

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Even seemingly empty patches of sky probably contain very distant, faint galaxies
Most galaxies are members of clusters; galaxy clusters themselves are grouped into superclusters [many superclusters have a few dozen clusters spread out over ~40 Mpc]
Superclusters are *not* gravitationally bound

Rich Clusters - >1000 galaxies, ~ 3Mpc diameter, condensed around a giant central galaxy
Poor Clusters - 10-1000 galaxies, more spirals
Isolated galaxies are mostly spirals

Hierarchichal merging - start of cloud og gas, which starts telling out and clumping into discrete entities.
Galaxies were formed this way, and probably solar systems aswell

Star birth comes about relatively early in the universe (0.5 - 1.0 billion years ago)

Dark Energy - 70% of universe
Dark Matter - 25% of universe
Free H, He - 4%
Stars - .5%
Neutrinos - .3%
Heavy Elements - .03%

By the way gravity is behaving, we know there has to be a certain amount of mass, not all of which is visible matter - hence, dark matter

Is dark matter baryonicor nonbaryonic? Most probably nonbaryonic

Gravity should slow down expansion, dark energy should speed up expansion

Current data pointing to expansionary model; we're not sure.