1. You!!! Questions for the Lab were due at Midnight
After bellwork, read this:
After reading, answer the
2 Questions in your journal
Please take out your foldable

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.
Cite evidence used to develop and verify the scientific theory of the origin of the universe known as the Big Bang.

3. 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?

6. 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
What if the universe is finite and has an edge…

7. The edge
In the bread, you could say where the center is, because there is an edge…unlike our universe
In reference to the balloon,
where is the edge? The center?
Keep in mind that it’s a 2-D analogy…

8. 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”

9. 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 is an edge)
There are lines of sight that don’t end in a star
(2) it is not infinitely old (there is a beginning)
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

10. 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?

11. This is the light that is constantly reaching us. CMBR
and here?
What is here?
and here?
and here?

12. “Universe” vs. “observable universe”:
Universe = all that exists; could be infinite
Observable universe = all that we can “see;” most definitely finite
Not an edge like we would think of it. Just a place that is too far away for us to see past

13. Okay… so the universe is expanding…we see galaxies move away.
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”

14. 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…

16.  14 billion years The Hubble time: (age of the universe)
Using H0 = 70 km/s/Mpc
 14 billion years
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?!?!)

17. What is the farthest away thing we can see?
The Hubble length or Hubble distance is a unit of distance in cosmology, defined as c · H0−1 — the speed of light multiplied by the Hubble time.
It is equivalent to ~14 billion light years or ~4,550 million parsecs
We can see things that had their light leave 14 billion light years
So we want the observable universe to have a diameter of ~28 billion light-years in diameter

18. EXCEPT.. Scientists know that the universe is expanding.
Thus, while scientists might see a spot that lay ~13.8 billion light-years from Earth at the time of the Big Bang, the universe has continued to expand over its lifetime.
If inflation occurred at a constant rate through the life of the universe, that same spot is 46 billion light years away today!!!
making the diameter of the observable universe a sphere around 92 billion light-years

19. The Size of the Universe

20. Another way to think about this.
Galaxies that are farther from us are moving away faster.
Even farther, even faster
The Hubble distance would be the distance between the Earth and the galaxies which are currently receding from us at the speed of light
Your Exit Ticket….
Will light from these galaxies ever reach us?
Why or why not.

21. Expanding Faster Than Light…EdPuzzle