Cosmologyand

the Big Bang

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Before 1900, astronomers assumed that the universewas static in size. In fact, astronomers believed thatthe Milky Way Galaxy WAS the entire universe.

Einstein was the first mathematical cosmologist.

His equations showed that the universe mustcollapse under the attraction of gravity.

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Yet, the universe hadn’t collapsed.

Einstein introduced a fudge factor, a sort ofanti-gravity which he called the “cosmologicalconstant” to explain the lack of collapse. Today we call it vacuum energy or dark energy.

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Credit: http://starchild.gsfc.nasa.gov/Images/StarChild/questions/universe_expansion.gif

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In the early 1900’s, Edwin Hubble discoveredthat nebulae are actually galaxies outside ourMilky Way. This increased the radius of ouruniverse by a factor of a million.

Hubble also discovered that all of these galaxiesare receding away from us and from each other.

The universe is expanding. The fabric of spaceitself is stretching.

Credit: www.astroex.org - ESA/ESO’s Astronomy Exercise Series

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About the same time, George LeMaitre, a Catholic priest (!) proposes that the universe has expanded from a “primeval atom”.

LeMaitre convinces Hubble and Einstein that it’s only the relentless expansion of theuniverse from the moment of creation. No cosmological constant is needed. The universe is “coasting”.

Credit: www.amnh.org

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In 1949, Fred Hoyle, astrophysicist and BBCradio program host, derisively coins the phrase “Big Bang”.

Hoyle adamantly supports the steady-state theory.

(Hoyle believes that as the universe expands,new matter is constantly being created to fill the void.)

Why do we even think that a Big Bang mayhave occurred?

What evidence exists for this idea?

Direct evidence: the redshift of all the galaxiesindicates the expansion of the universe.

Direct evidence: the cosmic microwavebackground radiation.

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In 1965, Bob Wilson &Arno Penzias, workingfor Bell Labs in NewJersey, discovered anannoying hiss comingfrom space at microwavewavelengths.

Credit: burro.cwru.edu

The hiss was the static from the left-over heatof the Big Bang.

Credit: www.lbl.govCosmic Background Explorer or COBE www.lbl.gov

In 1989, the CosmicBackground Explorer waslaunched with the purposeof mapping the cosmicmicrowave backgroundradiation.

George Smoot was theprincipal investigator.

Indirect evidence for the B.B.

•Baryonic matter (p+, n0, e-, and us) can be created from energy: E = mc2

•The early universe contained only H, He, and traces of Li and Be, as predicted by B.B. models. The oldest (1st generation) stars contain only these elements.

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Problem• We have many stars, galaxies, etc. to

look at in the universe. Therefore, their history is fairly easy to define.

• We have only one universe, therefore its history is difficult to define.

• We must make assumptions.

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What are the assumptions?

• The same physical laws that operate here and now, operate everywhere and everywhen in the universe.

• (Universality of physical laws.)

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• The universe is homogeneous.

• Matter is spread evenly throughout the universe. There are clumps, but the clumps are much smaller than the universe as a whole.

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Credit: The Wilkinson Microwave Anisotropy Probeon www. burro.cwru.edu

• Space has the same properties in all directions, or, the universe is the same no matter where you look.

• (The universe is isotropic.)• For example, the temp. of the background heat is the same all over the sky to 1 part in 105. The speed of light is the same everywhere.

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• The universe has no identifiable center.

• All directions & points in space are equivalent. (Cosmological Principle)

• As a consequence of this: the Earth does not have a privileged place in the universe.

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Cogito…ergo mundus talis est.

The Anthropic principle challenges this lastassumption.

“We must be prepared to take account ofthe fact that our location (including time)in the universe is necessarily privilegedto the extent of being compatible withour existence as observers.“ Brandon Carter,1973, Krakow symposium honoring Copernicus’ 500th birthday.

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Two things happened in the momentsafter the Big Bang:

•4 forces separated from the original “unified force.”•Elementary particles were created.

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The 4 Forces…

• Gravity – very weak, but operates over infinitely(?) long distances.

• Electromagnetism – strong, but rapidly grows weaker with distance.

• Strong force – the strongest, but only good for about 10-15 meter (the diameter of a proton). Keeps nuclei together.

• Weak force – regulates radioactive (fission) decay. Operates within particles.

• Energy can be created when matter is destroyed – we see this every day in the light from the sun.

• Matter can also be created from energy, when high energy photons collide.

• The more massive the particle, the higher energy (hotter) the photon needs to be.

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…and the Particles

• Particles are always made in pairs

• One matter one antimatter

• Proton anti-proton

• Electron positron

• One of the mysteries of our universe iswhy there’s such an imbalance between the amount of matter and the amount of antimatter.

Time-line of the Inflationary Universe (the Big Bang)

• Supergravity era• First 10-44 seconds 1032 K• Universe is all energy, smaller than an electron.

Only 1 unified force exists initially.• Gravity separates from other 3 forces. (But

how can gravity exist w/o mass?)• What if matter doesn’t produce gravity, but

gravity collects matter, like rain puddling in ahole?

• 10-35 seconds 1028 K

• Universe is still all energy, still smaller than an electron, but 1000x larger than before.

• Strong force separates. This will allow heavier nuclei, like He, to form later.

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Radiation Era

• Up to 10-10 seconds 1015 K• Universe expands fast (1 um)• Electromagnetic & weak forces

separate. The separation of the EMforce will later allow light to shine.

• Energy begins to take a recognizable form (photons).

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Heavy Particle Era

• 10-7 seconds 1014 K

• Universe expands to 1 km in size (@ 30 times the speed of light!)

• High energy photons collide to make quarks, then protons & antiprotons.

• Some matter & antimatter annihilate each other.

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Light Particle Era

• 0.1 second 1012 K• Universe is 1,000,000 km wide and

still expanding at ~30 times “c”.• Photons collide to make electrons

& positrons• Photons are too sluggish to make

any more heavy particles

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Nucleosynthesis Era

• 100 seconds to 10,000 years 1010 K• Universe is 1 LY wide in about 6 days.• Protons & electrons collide to make

neutrons.• Protons & neutrons begin to stick

together – make nuclei of light elements (H, He, Li, Be)

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Matter Era

• 10,000 years to now• Up to present size (>150 billion

LY). Today, we can only observe about 10% of the universe’s width.

• Nuclei & electrons are now slow enough that entire atoms form.

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Matter Era

• Density drops low enough that universe becomes transparent afterabout the first 300,000 years.

• Matter begins to clump into nebulae.

• Stars form, clump to make galaxies.

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About 10 years ago, two University of Californiaresearch groups led by Alex Filippenko and Saul Permutter independently determined that theuniverse’s expansion is accelerating.

Alex FilippenkoU.C. Berkeley

Saul PerlmutterU.C. LawrenceBerkeley Lab

Credit: http://starchild.gsfc.nasa.gov/Images/StarChild/questions/universe_expansion.gif

What does this imply about the ultimate fate of the universe?

Heat death of the universe. Entropy goes to infinity.

The End