astro 113 week11 - Physics & Astronomy

© Dr. Joseph E. Pesce, Ph.D.

Astronomy 113Dr. Joseph E. Pesce, Ph.D.

The Big Bang & Matter


Cosmology³The study of the origins, structure, and

evolution of the universe³Key moments:

²Einstein General Theory of Relativity²Hubble’s observation of expanding universe

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Olber’s Paradox³A simple question: Why is the sky at night

dark?

³Everything is the same for a long way in all directions

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You are here


Assumptions³Assumption: the universe is infinitely big³Assumption: the universe is infinitely old³Assumption: the universe is uniform

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Olber’s Paradox³If the universe is infinitely large and uniform,

why is the night sky not bright?

³Every sight line will eventually hit a star

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You are here


The Answer³The universe can’t be infinitely large and old

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DefinitionsCosmological Principle:³Universe is Isotropic & Homogenous³We are not in a special placeIsotropic: the universe is the same in all

directions³There’s no preferred directionHomogenous: At the largest scales, the

universe is uniform; pretty much the same everywhere; same physical concepts apply

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Expansion & Big BangHubble’s Law: vr = Ho * D

³Universe expanding so must have been smaller, more dense in past

³George Gamow proposes an initial explosion:The Big Bang

³ 1/Ho gives age of universe = 13.74 Billion years old (confirmed independently)

³ Redshift: space stretches as photon flies through it = stretching redshift

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Expansion & Big BangHubble’s Law: vr = Ho * D

³Demonstration

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Alternate Theories

³Steady State Model of Fred Hoyle, Herman Bondi, and Tom Gold

³Universe infinitely big and old, expands forever, matter constantly being created

²Coming from jets in AGN (in some views)

³Big Bang ironically name by Hoyle

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Evidence for Big Bang

³Roll time back: universe begins as an extremely hot (1012 K) singularity

³High-energy radiation field³As universe expands, radiation cools³Radiation should permeate entire universe,

even today³Cosmic Microwave Background (CMB)

radiation

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Detection of CMB³Arno Penzias & Robert

Wilson, Bell Labs (Nobel Prize)

³CMB at 2.74K³Isotropic and smooth

Consistent with Big Bang but NOT Steady State

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Detection of CMB17-14


Isotropy Problem

³To be as smooth as the CMB is, the parts of the universe had to �communicate� with each other

³But universe is too big for this to be possible

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13 Billion ly

26 Billion ly© Dr. Joseph E. Pesce, Ph.D.

Inflation

³Solution to Isotropy problem is inflation

³10-35 seconds after Big Bang, universe expanded 1050 orders of magnitude (atom to grapefruit)²The inflationary epoch²Somewhat strange, but related to dark energy

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Unification of Forces

³Four fundamental forces today²Gravitation (dominant today, but VERY weak.

Operates over larger scales than others)²Electro-magnetic²Strong nuclear (holds protons & neutrons together)²Weak nuclear (important in radioactive decay)

³Were combined into one at beginning²During �Planck time� (0 – 10-43 seconds after BB)

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Post Big Bang Timeline

³�Planck time� (0 – 10-43 seconds after BB)³10-43 s (T=1032 K): Gravity �freezes� out³10-35 s (T=1027 K): Strong force �freezes� out³10-35 -10-24 s: Inflation of universe by 1050

³10-12 s (T=1015 K): EM/Weak forces separate³10-6 s (T=1013 K): Protons & neutrons can exist

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Matter/Antimatter

Pair Production Pair Annihilation³For T < 1s: matter/antimatter co-exist³There should be equal matter and antimatter,

annihilating each other. But not the case³1 EXTRA particle of matter for every billion

particles of antimatter³Good for us!

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Timeline Continues³T = 1 – 3 minutes: nuclei form, destroyed by

gamma-rays³After T = 3 minutes, Temp too cool for fuse

nuclei²H, He, Li, Be formed

³T < 300,000 years: atoms ionized by photons; only nuclei survive: RADIATION DOMINATED

³T > 300,000 years: atoms can form: MATTER DOMINATED UNIVERSE (still more radiation than matter)

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Decoupling³T=300,000 years Transition called: Decoupling

(Temp = 3,000)³T < 300,000 yrs: plasma only³T > 300,000 yrs: H atoms form, universe

becomes transparent²�Era of Recombination�²CMB is �Fossil� of this period²We can’t �see� further back in time (prior universe is

opaque)

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Structures³Then what?

²Stars form²Galaxies form

q Where do blackholescome in?

³All happens very soon after decoupling

³Galaxies seem to be made up of small pieces

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Energy Budget of Universe17-24


Age of the Universe

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³Related to Hubble’s Constant (1/H ~ age)

² Must be at least 10,000 yrs old (tree rings)² Must be at least 200 million yrs old (Cepheid light

travel time)² Must be at least 4.6 billion yrs old (meteor dates)² Must be at least 10 billion yrs old (redshifts of

quasars; globular cluster ages)

³Measured – accurately and with multiple methods – as: 13.74 billion years old


Thank You!


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astro 113 week11 - Physics & Astronomy