chapter17_the beginning of time

7/30/2019 Chapter17_the Beginning of Time

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Chapter 17The Beginning of Time


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How far/back in time can we see with our current telescopes?

What is the farthest we could in principle see?

Only until 380,000 years after the beginning


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Our Goals for Learning

What were conditions like in the early universe?

What is the history of the universe according to theBig Bang theory?

17.1 The Big Bang


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What were conditions like in theearly universe?


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Universe

must have

been muchhotter and

denser early

in time
http://localhost/var/www/apps/conversion/tmp/scratch_15/estimate_age_of_universe.htm


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The early

universe must

have beenextremely hot

and dense


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Photons converted into

particle-antiparticle pairs

and vice-versa

E = mc2

Early universe was full of

particles and radiationbecause of its high

temperature


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Today, In the labs we created conditions up to 10-10 seconds

after the Big Bang.

And we have a theory for up to 10-38 seconds after the big bang.

The very instant of creations we do not know how to describe.


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What is the history of the

universe according to the BigBang theory?


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Lets step back:

There are four known forces in universe:

Gravity:

Electromagnetism:it acts among charged particles, in atoms and

molecules, and is responsible for all chemical and biologicalinteractions.

Strong Force:important only on very small distances, binds nuclei

together.

Weak Force:important in nuclear fusion and fission. There are

some particles which interact only through this force (and gravity).

Like neutrinos and WIMPs (dark matter).


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Thought Question

Which of the four forces keeps you from sinking to thecenter of the Earth?

A. Gravity

B. Electromagnetism

C. Strong Force

D. Weak Force


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Thought Question

Which of the four forces keeps you from sinking to thecenter of the Earth?

A. Gravity

B. Electromagnetism

C. Strong Force

D. Weak Force


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Do forces unify at high temperatures? (think about ice, liquidand vapor as just a various states of water)


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Do forces unify at high temperatures?

Yes!

(Electroweak)


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Yes!

(Electroweak)

Maybe

(GUT)


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Yes!

(Electroweak)

Maybe

(GUT)

Who knows?

(String Theory)


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Planck Era

Before Planck time

(~10-43 sec)

Random fluctuation

of

energy/particle/space- we have no theory

of quantum gravity.

At the end of Plank

era, gravity froze out

separated from

other forces.


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GUT Era

Lasts from Planck

time (~10-43 sec) toend of GUT force

(~10-38 sec).

At the end of GUTera strong force

froze out.

There are some theories proposed which link GUT forces. Stillunconfirmed, but at least we have some idea how that could work.


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Since this time, space was field with photons (radiation) and all

elementary particles we know of (electrons, quarks, and their

anti-matter counterparts).

Universe was extremely hot and photons had enough energy to

produce even the heaviest particles (most of these particles do

not exist as free particles today). Particles would then annihilate

back to photonsthe universe consisted of the matter-radiation

sea (soup).


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Electroweak Era

Lasts from (10-38

sec) to end ofelectroweak force

(10-10 sec).After

this instant all

forces becameforever distinct in

the Universe.


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We have direct experimental evidence of the transition from

electroweak force to two separate forces: electromagnetic and

weak. We probed in the lab physics of the Universe when it was

just 10-10 seconds old!

To get a better idea: Temperature at the end of this era (10

15

K)was 100 million times hotter than in the Sun!


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Particle Era

In particle era it became cool

enough so that quarks hadcombined producing protons

and neutrons!

The era ended when universe

became too cold (1012 K) for

photons to produce protons

and neutrons. The total

number of protons and

neutrons (and antiprotons/

antineutrons) was sealed at

that time. Photons were stillproducing electrons, and

neutrinos, and got produced

back by their annihilation


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Universe consisted of protons, neutrons, on one hand, and the

soup of photons producing electrons, neutrinos on the other.

But, amounts of matter (protons/neutrons) and antimatter

(antiprotons/antineutrons) was still nearly equal.

How much anti-matter is left in today's Universe?

If the Universe had exactly the same amount of protons and

antiprotons how would it look like today?


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Era of Nucleo-synthesis

There were roughly 1 extra proton

for every 109 proton-antiprotonpairs!

This era begins with matter

annihilating remaining antimatter

at ~ 0.001 sec.

What was left was universe

containing only matter, as we know

it today!


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After that, pand nbegan to fuse, making He and some deuterium and Li.

This era ended when Universe was 3 minutes old. All elements the Universestarted off with (75% H, 25% He, trace amounts of deuterium and Li) where

made in the first 3 minutes!

The Universe expanded so much by than, that p&n, became to far apart, and

synthesis of nuclei ceased.

Why elements heavier than He did not form in the early Universe?


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Era of Nuclei

After the era of

nucleosynthesis the Universeconsisted ofp, He nuclei and

free electrons.

(no neutral atoms existed yet)

Photons were bouncing off

these charged particles, never

managing to travel long

between collisions (in what

layer of the Sun does the

similar condition exists?)


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Era of Atoms

Universe has cooled enough, at

age of ~ 380,000 years, so that

atomscould form (and photons

had not enough energy to ionize

them again).

The Universe suddenly became

transparent for photons, theydidnt have any free charged

particles to bounce from anymore.

They justflashed through the

Universe, and amazingly enough,

we still can see this photons today.All Universe is bathed in this, so

called, cosmic microwave

background radiation. It arrives

to us from every point in space.


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Era of

Galaxies

Galaxies form at

age ~ 1 billion

years.

We have alreadydiscussed the rest

of the story in the

previous

chapters


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Primary Evidence for Big Bang theory

1) We have detected the leftover radiation

from the Big Bang.

2) The Big Bang theory correctly predicts the

abundance of helium and other light

elements.


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What have we learned? What were conditions like

in the early universe?

The early universe was

filled with radiation and

elementary particles. Itwas so hot and dense that

the energy of radiation

could turn into particles of

matter and antimatter,which then collided and

turned back into radiation.


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What have we learned? What is the

history of theuniverse

according to

the Big Bangtheory?


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17.2 Evidence for the Big Bang


How do we observe the radiation left over from the

Big Bang?

How do the abundances of elements support the Big

Bang?


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How do we observe the radiation

left over fromthe Big Bang?


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The cosmic

microwave

background

the radiation left

over from the

Big Bangwasdetected by

Penzias &

Wilson in 1965.

They noticed that wherever they point their antenna

(designed for satellite communications) to, they get some

unexpected noise, which they tried hard to get rid off. At

the end, they got Nobel Prize, for providing first evidence

for Big Bang theory.
http://localhost/var/www/apps/conversion/tmp/scratch_15/era_nuclei_era_atoms.htm


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Background radiation from Big Bang has been freely

streaming across universe since atoms formed at

temperature ~ 3,000 K: visible/IR
http://localhost/var/www/apps/conversion/tmp/scratch_15/era_nuclei_era_atoms.htm


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Expansion of universe has redshifted thermal

radiation from that time to ~1000 times longer

wavelength: microwaves(part of radio waves)

Background has perfect

thermal radiation

spectrum at temperature

2.73 K

Corresponds to a temperature of2.73 K

the temperature of the night sky.


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CLICK TO PLAY MOVIE
http://localhost/var/www/apps/conversion/tmp/scratch_15/full_sky_in_all_wavelengths.htm


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COBE detected the seeds of future structure formation: the

temperature of universe varies slightly, by only about 0.01%.

These variations indicate that the density of the early universe did

differ from place to placethe seeds of structure formation were

present during the era of nuclei.

( )


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COBE (1993)

WMAP (2003)


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WMAP gives us detailed baby pictures of structure in

the universe


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How do the abundances of

elements supportthe Big Bang?


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Before the Big Bang theory, the fact that Universe contains so

much He was a puzzle. It meant that the Universe was once hotenough for nuclear fusion of H to He to happen, but people did

not know how.

The fact that the temperature of microwave background is 2.73 K,

tells us precisely how hot was the Universe in the distant past and

exactly how much He should have been made. The result, 25%

He, is another success of this theory.


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Abundances of

other light

elements agreewith Big Bang

model having

4.4% of critical

density ofnormal matter

more

evidence for

WIMPS!


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Thought Question

Which of these abundance patterns is an unrealisticchemical composition for a star?

A. 70% H, 28% He, 2% other

B. 95% H, 5% He, less than 0.02% other

C. 75% H, 25% He, less than 0.02% other

D. 72% H, 27% He, 1% other


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Thought Question

Which of these abundance patterns is an unrealisticchemical composition for a star?

A. 70% H, 28% He, 2% other

B. 95% H, 5% He, less than 0.02% other

C. 75% H, 25% He, less than 0.02% other

D. 72% H, 27% He, 1% other


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What have we learned? How do we observe the

radiation left over from the

Big Bang?

Telescopes that can detectmicrowaves allow us to observethe cosmic microwave

backgroundradiation leftover from the Big Bang. Itsspectrum matches thecharacteristics expected of theradiation released at the end of

the era of nuclei, spectacularlyconfirming a key prediction ofthe Big Bang theory.


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What have we learned?

How do the abundances of elements support the

Big Bang?

The Big Bang theory predicts the ratio of protons toneutrons during the era of nucleosynthesis, and from

this predicts that the chemical composition of the

universe should be about 75% hydrogen and 25%

helium (by mass). This matches observations of thecosmic abundances, another spectacular

confirmation of the Big Bang theory.


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17.3 The Big Bang and Inflation


What aspects of the universe were originallyunexplained by the BigBang model?

How does inflation explain these features of the

universe?

How can we test the idea of inflation?


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What is cosmological inflation?

A brief period of exponentially fast expansion of the Universe. Theuniverse expanded from to in just seconds!

Do you know for some other period in which universe was

expanding exponentially fast?

It presumably happened at the end of GUT era. When the strong

force separated, the huge amount of energy was released and it

caused this rapid expansion.The idea (like many others) sounds bizzare, but it is useful

addition to the standard Big Bang theory: it helps solve some

features of Universe unexplained by standard Big Bang model.


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What aspects of the universe

were originally unexplainedby the Big Bang model?


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Mysteries Needing Explanation

1) Where does structure come from? (how diddensity enhancements come about)

2) Why is the overall distribution of matter so

uniform?

3) Why is the density of the universe so close to the

critical density? (it could have been whatever

number and it has exactly this, critical density

value)

Inflation can


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Inflation can

make all the

structure by

stretching tinyquantum ripples

to enormous

size.

These ripples in

density then

become the

seeds for all

structures


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How can microwave temperature be nearly identical on

opposite sides of the sky?
http://localhost/var/www/apps/conversion/tmp/scratch_15/inflation_early_universe.htm


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Regions now on opposite side of the sky were close

together before inflation pushed them far apart
http://localhost/var/www/apps/conversion/tmp/scratch_15/inflation_early_universe.htm


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Overall

geometry of the

universe is

closely related

to total density

of matter &

energy

Density =

Critical

Density >

Critical

Density

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