What happened after the Big Bang?

How did early structure form?

Goals for Today

1) Put the stages of early Universe evolution in order and relate them to early structure formation

2) Distinguish dark energy and inflation, especially with respect to the flatness problem

The Early Universe

first structure already seen in Cosmic Background Radiation (CBR=CMB today) – why not earlier?

Think-Pair-Share 1

A B C D

1) Where is the CBR released?

2) Where does primordial nucleosynthesisoccur?

3) Where is recombination?

4) Where is reionization?

5) Where is the first structure seen to be forming?

How secure is Big Bang Theory?

Go back to 14 years ago…

Neil Tyson, “In Defense of the Big Bang,” Natural History, 1996:

Evidence:Hubble law (caused Einstein to abandon his cosmological constant Λ, why?)

Expanding universe tested by gravitational lenses

Nucleosynthesis predictions

Cosmic microwave background located behind distant galaxy clusters

Cooling of universe tested by radiation near distant galaxies

Concerns:Why is mass density similar to critical density of 1? (Flatness Problem)

Why is the cosmic microwave background so uniform? (Horizon/Isotropy

Problem)

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mFlatness ProblemThe overall gravity of

all the matter+energy

in the Universe causes

an overall curvature.

Ω measures average

density: could be

anything 10-∞ to 10∞

Ω = 0.3 (matter

density) is oddly

close to 1

Too much:

closed

Too little:

open

Just right: flat

Horizon/Isotropy ProblemThe cosmic microwave background is too smooth: areas separated by more than the age of the Universe in light

travel time should not have exactly the same temperature, because they can’t share heat.

All these fluctuations are <2% !

Inflation solves both!

http://universe-review.ca/option2.htm

Alan Guth, inventor of

inflation theory:

“The huge expansion

factor of inflation drives

the Universe toward

flatness for the same

reason that the Earth

appears flat, even

though in is really round.

A small piece of any

curved space, if

magnified sufficiently,

will appear flat.“

Yikes, was that a prediction?

Again, as of 14 years ago…

Neil Tyson, “In Defense of the Big Bang,” Natural History, 1996:

“Inflation's main prediction is that the universe was born with

its mass density equal to the critical value and continues today

to have the critical mass density. Current observations have

recovered anywhere from 20 to 40 percent of the mass

necessary to reach the critical density. Inflation enthusiasts are

fervently looking for the rest.”

Inflation made a new flatness problem:

Ω = 0.3 was too far from 1…

Inflation vs. Dark Energy

• solves original flatness problem

• solves horizon problem• occurred in very earliest

Universe (first 10-32 sec)• key prediction: Universe

should seem perfectly flat

• solves new flatness problem created by inflation (for now…)

• explains accelerating expansion of Universe seen in supernova data

• always there, but only important recently –accelerating expansion

• no predictions yet that can rule out alternative models

Think-Pair-Share 2

Which of the following helps to solve the originalflatness problem, that Ω=0.3 is close to 1 when it could be anything?A)dark energy

B)the Universe having critical densityC)a brief epoch of rapid expansion in the first split second after the Big Bang

D)the quantization of spacetime

Think-Pair-Share 3

Which of the following helps to solve inflation’s flatness problem, that Ω must exactly equal 1?A)dark energy

B)the Universe having critical densityC)a brief epoch of rapid expansion in the first split second after the Big Bang

D)the quantization of spacetime

Think-Pair-Share 4

What do dark energy and inflation have in common?

A)They are two words for the same thing

B)They both describe changes in the expansion rate of the Universe

C)They both occurred soon after the Big Bang

D)They both act like Einstein’s cosmological constant Λ

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Exam Review Sessions:Sunday & Monday Dec. 12 & 13, 4-5:30pm Phillips 277

Final Exam: Dec. 16, 4-6pm usual classroom

Please do class evaluations online!

Contact me if you want to visit a SOAR Telescope observing night in the spring.

Thanks for a fun semester! May your life be filled with wonder!