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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Big Bang, Black Holes, No Math
ASTR/PHYS 109Dr. David TobackLectures 22 & 23
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Was due Today – L23• Reading:
– Unit 5: Was due before class• Pre-Lecture Reading Questions Quiz:
– Unit 5 Quiz: Due before next class• End-of-Chapter Quizzes:
– Chapter 13• Do worksheet on class homepage to help prepare for EOC quizzes
– Does not need to be turned in• Chapter 13 parts A-D & Parts E-F: Due MONDAY before class
– Chapter 14• Chapter 14 Parts A-D: Will assign after that• Chapter 14 Parts E-G: Will assign after that
• Feynman Diagram Drawing Assignment– Quiz to help people get better at them in same folder. Can also do Revisions.– (Feynman Diagram 3)
• Papers– Papers 1 & 2:
• Can submit Revisions at any time. Make sure to do all stages– Paper 3: Due tonight, Wednesday Nov 4th
• Honors Section:– You should have Stage 2 Approved, and be working on Stage 3– Need to hear from you at least once every 7 days
3
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
A Big Bang Occurs… Then What?
Universe goes through a phase of being hot and small
As the universe evolves it gets bigger, older and colder
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
More detail
Photons no longer energetic enough to bust apart protons
Photons no longer energetic enough to bust apart nuclei
Photons no longer energetic enough to bust apart atoms
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
The End of an Era• For the next couple hundred thousand years things don’t change much
• Nuclear processes eventually stop making helium since the Universe gets too big
• Still MUCH too hot for atoms to form–Any formed quickly get busted apart 17
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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The beginning of a new Era• From 200,000-700,000 years the universe expands and cools
• All the nuclei and electrons combine to form atoms–Said differently: Universe cools until the photons in the universe can’t knock all the electrons out of the atoms any more
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Atoms in a Lower Temperature Universe
Proton
Electron
HydrogenAtom
ElectroMagnetic Reaction
At these lower temperatures photons can’t
easily break up atoms
Photon
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Where are we now in the history?
200,000-700,000 yearsPhotons can no longer break apart atoms
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Some Time Passes
The Transition From a Hot Universe to a Cool Universe
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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The Universe at ~700,000 Years Old
• At a temperature of about 3000K photons, on average, can’t knock apart atoms
• Stable atoms can form and most electrons become part of atoms
• The atoms are now free to form into stars and galaxies
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Give this special time in history a nameCall this time
“Recombination” Crappy Word!Atoms are
combining for the first time,
not recombining!
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Atoms in the UniverseEarly Universe A couple hundred
Thousand Years Later These days
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Before and After the Creation of Atoms
Before:Lots of free electrons and protons in the UniversePhotons scatter from
charged particles
After:Protons and electrons
combine to form atoms
Universe becomes transparent for
photons
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Transparent UniverseThe Universe now LOOKS different!• The light (photons) have no free electrons to interact with
• Since all the electrons are in atoms, because of Quantum Mechanics, they largely ignore the photons
• Photons just travel in a straight line Like traveling through glass
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Atoms in the UniverseEarly UniversePhotons bust apart atoms
A couple hundredThousand Years Later
Photons can only excite atoms
These daysUniverse is transparent to photons
Hydrogen
High energy photon
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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A Cartoon… Before Recombination: Photons interact with charged particles Scatter and change directions
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After Recombination: Atoms ignore the photons Photons travel in straight lines forever
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Cosmic Background Radiation• The photons we see in the cosmic background radiation are essentially the photons AFTER they interacted with their last charged particle
• Well… they’ve been traveling for awhile so they’ve changed a bit
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Photons in the UniverseAfter recombination, photons can travel freely through spaceTheir wavelength is only stretched (red shifted) by cosmic expansionObserve most photons as the cosmic background radiation! Also can observe photons emitted from Galaxies a billion years ago (just reaching us now) as being red-shifted
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
A Neutral Universe• After the electrons and protons combine to form atoms the Universe is almost completely neutral i.e., neutrally charged
• Why is this so important? All the particles in the Universe stop attracting each other due to their electric charge– Not completely true, just true outside the atoms
– Basically can ignore electric charge from here on out
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Some Time Passes
The Transition From a “Charged” Universe to a “Neutral” Universe
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Aside on Dark Matter• Dark matter is a BIG part of this story because there is 5 times more mass in the Universe in dark matter than in atoms– Will come back to this in Chapter 15
• However, the story doesn’t change much with Dark Matter since we think it is just another neutral particle
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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A Gravity Dominated Universe• The only thing left is gravity! • The gravitational attraction between massive things ONLY makes them move towards each other through space
• Any single atom would be most attracted to the closest place with lots of mass
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Wait a Half Billion Years• As the years go by, mass clumps together
• By a half a billion years after the bang, most of the mass is in one of a large number of “clumps”
• Huge numbers of these clumps, each becomes part of a galaxy!
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
The Next Few Billion Years
After less than ~0.5 billion years, the first stars form Stars produce heavy elements (“Stellar Cooking”)
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Fast Forward…• Fast forward 13 billion years –Temperature of space is now ~3Kelvin
–Cosmic Background Radiation• We get people…• More on Stellar and Galaxy Formation next
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
Lecture on Chapter 14 now complete
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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Looking Forward
• Finished Unit 4–Evolution of the Universe
• Starting Unit 5–From half a billion years until today
–Big Objects and Black Holes
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Evolution of the UniverseTopic 2: After The First Three Minutes
Big Bang, Black Holes, No Math
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For Next Time – L23• Reading:
– (Unit 5)• Pre-Lecture Reading Questions Quiz:
– Unit 5 Quiz: Due before next class• End-of-Chapter Quizzes:
– Chapter 13• Do worksheet on class homepage to help prepare for EOC quizzes
– Does not need to be turned in• Chapter 13 parts A-D & Parts E-F: Due MONDAY before class
– Chapter 14• Chapter 14 Parts A-D: Will assign after that• Chapter 14 Parts E-G: Will assign after that
• Feynman Diagram Drawing Assignment– Quiz to help people get better at them in same folder. Can also do Revisions.– (Feynman Diagram 3)
• Papers– Papers 1 & 2:
• Can submit Revisions at any time. Make sure to do all stages– Paper 3: Due tonight, Wednesday Nov 4th
• Honors Section:– You should have Stage 2 Approved, and be working on Stage 3– Need to hear from you at least once every 7 days
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