1. Yo!!! Turn in your labs before class starts.
If it isn’t done, turn in what you have completed
If you turn it in after class starts, you will receive a late grade. 
ALSO. You DID have Bellwork the last 2 days

2. Learning Goals:
4. Complex Knowledge: demonstrations of learning that go aboveand above and beyond what was explicitly taught. 3. Knowledge: meeting the learning goals and expectations. 2. Foundational knowledge: simpler procedures, isolated details, vocabulary. 1. Limited knowledge: know very little details but working toward a higher level.
I will:
understand the properties of different types of galaxies.
understand how the universe came to be what we observe today.
understand how astronomers use astronomical objects (standard candles)
Understand how we use a distance ladder to estimate the size of the universe and to measure large distances in the universe.
understand how astronomers determine the age and size of the universe?.

3. 4/19/16
How can you use Hubble’s Law to determine the age of the Universe?

4. Seniors, Senior, Seniors!!!
We still have a weeks worth of material to cover…..at least!
Cosmology is actually an entire class at the university level
This material IS on your EOC
Therefore, you are responsible to know it
For whatever we don’t get to, it is up to you to look at the PowerPoints, readings and videos that will be on the website
I will try to get through as much as I can today, tomorrow and Friday….this does depend on you quite a bit!

5. Read- FYI: Formation of the Universe

6. Cosmology
What does the darkness of the night sky tell us about the nature of the universe?
As the universe expands, what, if anything, is it expanding into?
Where did the Big Bang take place?
How do we know that the Big Bang was hot?
What was the universe like during its beginning years?
What is “dark energy”? How does the curvature of the universe reveal its presence?
Has the universe always expanded at the same rate?
How reliable is our current understanding of the universe?

7. The universe is expanding

9. The edge-center problem:
Suppose the universe has an edge…
It wouldn’t be an edge to the distribution of matter – it would be an edge to space itself!
You couldn’t just reach past it and feel around…
Seems to violate common sense…
We assume it has no edge
No edge => no center
If the universe is infinite  no center problem.
What if the universe is finite… (more on this in a moment…)

10. What about the beginning (if there is one…)?:
When you look at the night sky, what do you see?
Well… for one thing, it’s dark!
What if the universe were infinitely old, and infinite in extent?
Then no matter where you looked, your eyes would fall on a star/galaxy.
The night sky would be bright
But it isn’t!
This is known as “Olbers’ paradox”

11. Heinrich Wilhelm Olbers
“Olbers’ paradox”
Obviously, the sky’s not this bright. And so we’ve just done a “proof by contradiction” – and shown therefore, the universe is either
(1) not infinitely big
There are lines of sight that don’t end in a star
(2) it is not infinitely old
there are stars who’s light hasn’t had time to reach us yet
(3) The Universe is expanding
So some of the light has been stretched (red-shifted) outside the visible spectrum
Or some combination of the three
Heinrich Wilhelm Olbers

12. “Universe” vs. “observable universe”:
Universe = all that exists;
Observable universe = all that we can “see”
The former could be infinite,
The latter is most definitely finite
The observable universe extends about 14 billion light-years in every direction from the Earth, so you would think ~28 billion light-years in diameter…but
It’s actually about billion light years in each direction (~93 ly in diameter). Why?

13. The Size of the Universe

14. Cosmic expansion: Recall Hubble’s observation in 1929…
Z ~ distance  everything is receding from everything else (on the whole)
The universe is expanding
In reference to the balloon,
where is the edge? The center?
Keep in mind that it’s a 2-D analogy…

15. The BIG BANG: Okay… so the universe is expanding…
What if we trace the expansion backward in time? What would we expect?
Would we reach a “beginning?”
Is there a beginning?
This “beginning” is what cosmologists call the “big bang”

16. If no edge, then no center
So what is this big bang?
If no edge, then no center
The big bang did not happen at some “spot,” it happened everywhere…
…and it is still happening…

17. Here’s a Little “Thought Experiment”
Imagine the entire universe were filled with firecrackers. And at a single moment in cosmic time, every firecracker went off.
What would you hear?
--- one Ginormous ear-splitting “BANG”?
--- or, a continuous ROAR that would never end?

19. The age of the universe:
Okay… if there was a beginning, then we can ask the question, “how old is the universe?”
(Based on what we observe that is…)
For starters, we can use the definition of velocity: v = d / t
In this simple form, we can take the distance between two galaxies & divide by their velocity of recession (from each other) and solve for the time…

20.  14 billion years The Hubble time: Using H0 = 70 km/s/Mpc
Where does 1012 come from?
Units of H0 are km/s/Mpc…
Convert Mpc to km, and then s to years
(you did this in your lab, REMEMBER?!?!)

21. The Hubble length or Hubble distance is a unit of distance in cosmology, defined as cH0−1 — the speed of light multiplied by the Hubble time.
It is equivalent to 4,550 million parsecs or 14.4 billion light years.
(The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.)
The Hubble distance would be the distance between the Earth and the galaxies which are currently receding from us at the speed of light
Will light from these galaxies ever reach us?

22. Second Day of Material
CMBR

23. A side road tour… the CMBR (part I):
1948
Gamov  early universe should be hot & dense
Should radiate as a black body
1949
Alpher and Herman  large redshift would stretch the wavelength into the IR, Microwave, and radio spectrum

24. A side road tour… the CMBR: Part II
CMBR = “cosmic microwave background radiation
Picture it:
1960s,
two physicists (Penzias & Wilson) studying the sky in radio wavelengths,
Their measurements showed a “peculiar noise”
They thought it was bird droppings…
After cleaning the antennae of all the bird poop, the “noise” remained…

25. A side road tour… the CMBR (part III):
Princeton physicist Robert Dicke realized that, with the technology available, we should just now be able to detect this redshifted radiation (the CMBR)…
When Penzias & Wilson heard of Dicke’s work, they realized that’s what they saw!
Still… as scientists, we don’t like to jump to conclusions…
We would like to have other observations confirm or reject this…

26. A side road tour… the CMBR (part IV):
This CMBR should be all over the sky & come from everywhere…
Specifically, theory predicted that it should look like the radiation coming from a black body at a temperature of ~ 3K (in the IR…)
1990,
COBE satellite
Measured black body radiation with a temp. of / K
So the average temperature of space is 2.725K or F

28. A side road tour… the CMBR (part V):
Wait a minute! You’re going to tell me that this “hot big bang” only had a temp. of / K !?!
Keep in mind that it is redshifted by Theory predicted that this stuff was emitted when the universe had cooled to ~ 3000K
More on this tomorrow…

30. Space used to be Orange!