1. ASTR 1020 – May 2 Last Lecture on Thursday – Largely Review per vote
Final Exam: Monday May 8 4:30-7:00pm .
Website

2. Cosmological Principle
Cosmological Principle applied to expanding Euclidean Universe
New matter must be formed of nothing to keep density everywhere the same.
Implies no edge
Whatever that means….

3. Olber’s Paradox If universe is infinite with stars everywhere,
then there an infinite number of stars.
Any line of sight will eventually intersect the
surface of star. Sky would be as bright as the
surface of the Sun.
Well it isn’t. So why not?

4. Universe Must Change Answer to Olber’s Paradox: Universe must change:
Space: ie the stars stop
This was the answer until mid 20th Century
Time: Universe hasn’t always been here, so can’t see forever.
Discovery of Big Bang leads us to this answer.

5. General Relativity GR provided an answer
The presence of matter warps space in on itself.
Space is actually DEFINED by the presence of the matter in it!!!
Solves the edge problem
But geometry is no longer Euclidean

6. Geometry of Universe
Space Curves
in on itself
There’s no path
out!

7. Curved Space Surface of Earth has no end, but it is finite.
There is no “edge” but the volume is finite.

8. Expands and falls back Universe starts as pinprick Expands.
But its below escape velocity.
Hits maximum size.
Then shrinks
The End is the “Big Crunch”

9. Negatively Curved Universe
Its warped so it cannot close back on itself.
Is infinite in extent.

10. Open vs Closed That’s INFINITY Folks!!!
Universe is either open or closed.
If closed: Positive Curvature
Finite Mass
Finite Lifetime
Finite Volume
If open: Negative Curvature
Infinite Mass
Infinite Volume
Infinite Lifetime
That’s INFINITY Folks!!!
Astronomers have prejudice in favor of closed universes.
All measurements have been inconclusive. We live near the edge!

11. Critical Density
Whether Universe is open or closed depends on the average DENSITY of matter.
Above g/cc the universe is closed
Below g/cc the universe is open
We are very close to that density
Coincidence?
rcrit is about 1 atom per liter

12. History and Fate of Universe
Universe is one of these (maybe).

13. Best Guess Size
Diameter of Universe is about 1024 times larger than the part we can see.
That makes the volume 1072 times larger.
But still finite
How big is 1072 ?

14. Heat Death of Universe If universe is open, then it will last forever
But stars will all burn out years
Protons decay 1031 years
Orbits will decay into black holes at center of the galaxies years
Giant black holes evaporate years
Nothing left but redshifting photons

15. More on Infinite Universe
If Cosmological Principle holds and universe is infinite, there’s infinite mass.
Infinite Planets
Infinite Earth-like planets
Infinite planets just like you.
Infinite You’s
Far away: About
meters away

16. The Origin of it All? Good Question
Perhaps a bubble in a hyper-universe
Perhaps its “unknowable”
But it appears Universe started as a very tiny bubble. How small, we don’t know.

17. The “Planck Era”
When quantum fluctuations exceed the radius of the universe our theories are definitely inadequate.
R < 10-35m
t < seconds
Density of Universe > 1093 g/cc
T > 1032 K
Then it starts to expand and cool….

18. The Inflationary Universe
Idea: Vacuum of space-time created with excess energy  folded upon itself
At t=10-37s, T=1028K, starts to relax
From to 10-33s it expands by the creation of new space.
Universe expands from 10-28m to 0.1m
That’s 10cm in 10-33s = 1032m/s v = 3x1023 c !!!

19. How Can It Expand Faster than Light?
Einstein’s Law says nothing can travel faster than light.
Particles in the inflationary universe aren’t traveling.
More space comes into existence between them.
Before inflation could see whole universe.
Since then, can only see a small part.

20. Big! Very, Very Big Because of inflation, universe gets much
bigger  A factor of 1026!
Means now, universe is 1026 times larger
than we can see.
Rvisible = 1026m
Runiverse = 1052m
We are connected to only one part in 1078
of the volume

21. Maps of Microwave Background
The size of lumps and
blobs set before inflation.
Indicate residual gravity from
parts of the universe we can
no longer see.
Strong evidence that inflation
is on the right track.

22. The Annihilation Era
After inflation settles down and resumes normal expansion
So hot that matter and anti-matter are in equilibrium.
For every 100,000,000 antimatter particles, there are 100,000,001 matter particles.
Basic Asymmetry From Planck era is not understood, but it’s why we’re made of matter.

23. .001 Seconds Jump from 10-33s to 10-3s T = 1012K
Neutrons and Protons now have cooled so that can annihilate with anti-neutrons and anti-protons.
Leave mostly photons and an occasional particle of matter.

24. 1 Second
Electrons and Positrons have cooled to point where they are no longer in equilibrium. T=1010K
Create photons.
One matter particle in hundred million is left.
Those are today’s electrons.

25. Era of Nucleosynthesis
T = 109 K
t = 100s
Hydrogen and Helium form from neutrons and protons.
Tiny amounts of Li and Be are created.
No carbon: density too low for triple alpha
This is when the initial elements form

26. The Plasma Era
From 100s to 100,000 years universe is a soup of ionized hydrogen and helium
But its expanding and cooling
Ends at 100,000years when the temperature falls below 3000K.
Hydrogen and Helium nuclei combine with electrons to form neutral atoms
At that moment, universe becomes transparent

27. Sky Aglow
At moment of de-ionization, sky is glowing as blackbody at 3000K (M star)
Photons released are no longer re-absorbed
They travel into the universe and are travelling today
But they redshift.
Now 1000 times longer wavelength than then (makes them microwaves)

28. The Cosmic Microwave Background
Microwave Antenna at Bell Labs – 1965
Penzias and Wilson
Microwaves coming from sky, but not Earth. Uniformly
Predicted as part of a “Big Bang” by Gamov in the early 1950’s
Inescapable proof of the “Big Bang”
Killed all steady state theories
Now we’re studying it.

29. At 100 Million Years No Galaxies yet – or perhaps protogalaxies
Gas mostly smooth through universe
Clumps cause gravitational spots that create even greater density fluctuations.
Size:
Remember: Dark matter dominates

30. Primordial Density Enhancements Grow
Now (12.4Billion years) we have structure
Galaxies and clusters

31. Recap

32. History and Fate of Universe
Universe is one of these (maybe).

33. Dark Energy Expansion of Universe is Accelerating!!!
Implies New Inflationary Era (Why Now?)
Acceleration takes energy

34. New Cosmology 70% of mass is Dark Energy (E=mc2)
25% of mass is Dark Matter
3.5% of mass is in Intergalactic Medium
1.5% of mass is regular matter in galaxies
Together they add to exactly critical density.
We’re right on the edge of open/closed
Universe is either finite and very big, or infinite.