Goal: To understand the history of the universe especially the

beginning

Objectives:1) To learn about the beginning of the Big

bang!2) To explore the Big bang to recombination

3) To explore Recombination until start of galaxies

4) To explore the timeline of the start of Galaxies to us

5) To examine The future6) To learn about The end of the universe

Big Bang!

• We saw last week that the big bang was the universe starting from roughly a point.

• We saw some of the evidence of why we know this to be the case.

• We didn’t give details on the first 380,000 years though.

• So, lets go back in time 13.7 billion years and see what the first 380,000 years of our universe were like.

The beginning of the Universe!

• Time starts with the Planck Era.• This “Era” lasted for the first 10-43 seconds

of our universe’s life (temperature was about 1032 K).

• Imagine our entire universe in a region of space much smaller than a proton.

• Note all the universe is pure energy at this point. No mass or matter – just energy.

• What would this be like?

Planck Era

• The truth is we have no idea of what happened in the first moments of our universe.

• Our only way to guess is by examining quantum mechanics.

• Quantum says that there is always an uncertainty in position.

• So, if there is a shift in the position of energy (and gravity is an attraction of energy) then there is a shift in gravity.

• So, you can get slight clumping of energy even at the start of the universe!

• Other than that – your guess is as good as mine.

How did it start?

• Again, we have no idea.

• There are ideas out there such as string theory (now called M theory), multiverse theory, and a few others.

• You are welcome to believe whatever you want in this first 10-43 seconds.

• (Thus the Big Bang model does not overthrow religion).

The GUT Era

• There are 4 fundamental forces in nature:• Gravity• Strong Force• Weak Force• Electromagnetic Force

• During the Planck Era we think these forces were all combined into 1.

• During the GUT Era gravity separated itself from the other 3 forces.

Reign of GUT

• GUT lasted until the temperature fell below 1029 K (the temperature range that the 3 forces stay merged).

• This Era lasted until 10-38 seconds after the Big Bang.

• However, we do not know much else about this era.

• The one thing we do have an idea of is that at the end of this era the Strong force split from the GUT force.

• This split would have released a lot of energy – enough to greatly expand the universe!

Need for inflation

• When the key economic indicators – err wait, wrong inflation.

• There is a slight problem with the big bang as I have stated it so far.

• If we look out today we see two things about the universe:

• It is homogeneous and isotropic.• Homogeneous means is that the universe is fairly

smoothly distributed and it looks pretty much the same in all directions.

• Isotropic means that the universe is about the same temperature everywhere.

• This is a problem. Tiny fluxuations (as I have told it so far) should have created a LOT of structure to the universe – a lot more than we currently see.

What is inflation?

• Inflation was a brief period of time (10-33 seconds) when the universe expanded at an insane rate.

• This smoothed out the universe as any perturbation would have been made a lot smaller.

• Regions of space the size of the nucleus of an atom would have been blown up to the size of our solar system in this short timeframe!

Electroweak Era

• Inflation occurred during the very first part of this era.

• Here the electromagnetic and weak forces were still combined.

• This era lasted for 10-10 s (leaving the temperature of the universe at 1015 K).

• At the end all 4 forces separated.

Contents of Electroweak era

• During this period we don’t yet have elements.• We do have elemental particles such as quarks,

electrons, and photons.• However at the temperature and density of the

universe at this point they would quickly collide with other particles (and antiparticles) which would turn them back into energy.

• This has been tested in the lab! This is the first era of the universe we can actually test the conditions of.

The Particle Era

• In this era photons dominated as it was still very hot (a trillion degrees at the end).

• This era lasted until the universe was 0.001 seconds old.

• The photons in this era started to build to strange forms of matter such as quarks.

• Unlike the era before the quarks were able to survive.

Matter!

• These quarks formed into protons and neutrons by the end of the era.

• The end of the era is when the temperature was too low to make protons from pure energy.

• Problem: In this period you should have equal #s of quarks and anti quarks, which means equal #s of protons and anti protons.

• However, today we see almost all regular matter and very little anti matter – how could this be?

Not equal

• It is likely that while close to balance the production of matter to antimatter was slightly unbalanced for whatever reason.

• If we examine the # of photons we can gain an insight into the difference. If matter/anti matter were exact we would have all photons. If there were twice as many protons and anti protons then there would be 2 photons (for each pair that collides) and 1 remaining proton for each set.

• In our universe photons outnumber protons by a billion to 1.

• Therefore, there were about 1 billion and 1 protons per 1 billion anti protons.

• This gives us the matter that we have still today.

Era of Nucleosynthesis

• Before this point the temperature was so high that if protons collided that they would destroy each other, and anything bigger than a single proton really didn’t stand a chance.

• Once the temperatures dipped below a trillion K this was no longer the case.

• You can now have fusion!

What can we form?

• We start with all Hydrogen.

• Some of this fuses into Helium because of the high temperatures and densities.

• However, many of this is broken back down due to the same reasons.

• The universe is expanding and cooling.

• This makes the rate of fusion slow quickly.

• The fusion process only lasts 5 minutes.

End of Nucleosynthesis

• After 5 minutes temperatures were still a billion degrees, but the densities are now too low for fusion and fusion shut off.

• So, what is the biggest atom we have at the end of this era?

• A) Oxygen

• B) Carbon

• C) Iron

• D) none of the above

No metals

• We get NO metals from this era! • All the metals (including the ones in our bodies)

were all formed in the cores of stars in the next 13.7 billion years.

• We are star stuff!• The resulting breakdown is:• Hydrogen (90% by #, 75% mass)• Helium (10% by #, 25% by mass)• Trace amounts of Deuterium and Lithium

(maybe some very trace amounts of Boron and Beryllium).

• Nothing else!

Era of Nuclei

• We don’t quite have “atoms” yet. • The temperatures are so high that you have nuclei and

electrons (plasma).• There is a lot of light being emitted, but since all the

electrons are free they can absorb ANY photon. • So, all the light emitted during this period of the universe

(and there was a lot of light back them) was all absorbed or scattered.

• Photons bounced very quickly, much like deep in the sun today.

• This era ended 380,000 years ago when the universe was 3000 K.

Recombination

• As was talked about last week there reached a point in time when the electrons could FINALLY join back up with the protons to form full atoms.

• When this happened a photon was emitted.• This photon was now free to traverse the

universe without being absorbed.• This created the cosmic microwave background

(CMB) – which is the OLDEST light we can see.

COBE map of CMB

WMAP• Differences show us structure of early

universe. Differences are 0.0002 K

Raw images…

• Have to eliminated galaxy and doppler shifts…

How tell us stuff?

What we learn

• We know from galaxies and galaxy clusters that 80% of all mass is dark matter.

• However, the cosmic microwave background tells us that most of the ENERGY in our universe is NOT in mass form!

• 22% of the energy in our universe is in the form of dark matter.

• ONLY 4% is the type of matter we can see!• 74% of the energy of our universe is Dark

Energy

Dark Energy

• Dark Energy is an unknown energy that is pushing outwards.

• The implications of this will be talked about in the next period.

Dark Ages!

• For the next billion or so years not much happened.

• Gas slowly fell into smaller regions, but stars and galaxies were not yet ready to form.

Stars and galaxies

• 1 billion years after the big bang the first stars formed.

• Also, the first galaxies formed.

• What are the first stars like?

Population III stars

• The first stars were Population III stars.

• Population III stars are stars with no metals – only H and He.

• These stars could not use the CNO cycle.

• Also, these stars would have had to be very large (hundreds of solar masses).

• Therefore, they would not have lived very long.

Pop III dies

• Very quickly (few million years) the Pop III stars died!

• In the last leg of their life they would have created all the elements up to iron.

• The deaths of these stars would have spread enough metals throughout the newly forming galaxies to form the Population II stars – the next generation.

• Also, you form (somehow) supermassive black holes in the cores of galaxies.

• However, no Pop III star has ever been observed.

Far side of the universe

• We are now in the regime that we can start to observe objects.

• The first are quasars.

• We also observe other brief but massively bright events.

Supernovae

• Two supernova we can observe are Type Ia (death of a white dwarf) and some Type II (death of normal star).

• When a White Dwarf merges with another white dwarf or accretes more than 1.44 solar masses (the mass electrons can no longer hold the star up) gravity wins!

• The core of the white dwarf starts to collapse. • This raises the temperature of the core.• Eventually you will be able to fuse Oxygen!• Once that happens though, the white dwarf is a bomb

and it detonates (there is nothing to stop the burning, and it cannot expand).

Supernovae

• Since they all die at about the same mass and size, Type Ia’s are so close to being exact that they are called “standard candles”.

• From their brightness we can get an idea of their distances from us.

• However…

Brightness issue

• Type Ia supernovae don’t seem to be as bright as we expect when far away.

• The reason is that the expansion of the universe is NOT constant (remember that dark energy)!

• In the earliest eras of our universe expansion slowed down a little because gravity had a bigger effect (smaller area of universe).

• However, at some point gravity stopped winning out and the rate of expansion has INCREASED!

• So, the light has traveled further than we expected it to for a given age.

Type II Supernova

• We see a similar result from Type II although that one is harder to normalize as each star has a different mass and composition.

Hypernovae and Gamma Ray Bursts

• What really big stars die, their cores fall into a black hole!

• There is no bouncing off a surface and exploding most the star into space.

• The black hole will create a jet of ultra high energy photons called Gamma Rays that they will beam clear across the universe.

• Gamma Ray Bursts are the most energetic bursts in the universe (not counting the big bang) and are very bright even from 12 billion light years away!

Age of Galaxies

• The next 12.7 billion years to today is the age of galaxies.

• We can observe galaxies directly as well as observe what fractions of the universe are ionized vs unionized (from the Quasar’s Lyman-Alpha forests).

• Galaxies merge, form clusters, voids open up, and stars are constantly formed.

• Somewhere in here – 4.5 billion years ago – our sun was formed.

• That brings us to know with humankind looking back in time to try to figure out how it all started.

Conclusion

• The universe has had a very interesting history – for what we can determine.

• However, there is still a lot we don’t understand (and a lot of problems unsolved that I have not mentioned).

• This is why cosmology is one of the hot topics in astronomy currently and probably will continue to be so for at least the next decade.