Conclusion

1
Conclusion
2
Back to Expansion of the Universe

• Either it grows forever
• Or it comes to a standstill
• Or it falls back and collapses (Big crunch)
• In any case Expansion slows down!

Surprise of the year 1998 (Birthday of Dark
Energy) All wrong! It accelerates!
3
Enter The Cosmological Constant

• Usually denoted ?0, it represents a uniform
  pressure which either helps or slows down the
  expansion (depending on its sign)

• Physical origin of ?0 is unclear
• Einsteins biggest blunder or not !
• Appears to be small but not quite zero!
• Particle Physics biggest failure

4
Triple evidence for Dark Energy

• Supernova data
• Large scale structure of the cosmos
• Microwave background

5
Microwave Background Signal from the Big Bang

• Heat from the Big Bang should still be around,
  although red-shifted by the subsequent expansion
• Predicted to be a blackbody spectrum with a
  characteristic temperature of 2.725 Kelvin by
  George Gamow (1948)
• ? Cosmic Microwave Background Radiation (CMB)

6
Discovery of Cosmic Microwave Background
Radiation (CMB)

• Penzias and Wilson (1964)
• Tried to debug their horn antenna
• Couldnt get rid of background noise
• ? Signal from Big Bang
• Very, very isotropic (1 part in 100,000)

7
CMB Heres how it looks like!
Peak as expected from 3 Kelvin warm object
Shape as expected from black body
8
CMB measurements improve
9
Latest Results PLANCK

• Measure fluctuations in microwave background
• Expect typical size of fluctuation of ½ degree
  if universe is flat
• Result
• Universe is flat !

10
Experiment and Theory
Expect accoustic peak at l200 ? There it is!
11
Supernova Data

• Type Ia Supernovae are
• standard candles
• Can calculate distance
• from brightness
• Can measure redshift
• General relativity gives us distance as a
• function of redshift for a given universe
• Supernovae are further away than
• expected for any decelerating (standard)
• universe

12
Pie in the Sky Content of the Universe
5
Dark Energy Dark Matter SM Matter
23
72

• ?We know almost everything about almost nothing!

13
Properties of Dark Energy

• Should be able to explain acceleration of cosmic
  expansion ? acts like a negative pressure
• Must not mess up structure formation or
  nucleosynthesis
• Does not dilute as the universe expands ? will be
  different of content of universe as time goes
  by

14
Threefold Evidence

• Three independent measurements agree
• Universe is flat
• 28 Matter
• 72 dark energy

15
History of the Universe Hot small ? cold big

• before 10-43 s ?????? (Planck Era)
• 10-43 s T1032 K gravity splits from other
  forces
• 10-43 to 10-35 s Grand Unification era
• 10-35 s T1028 K Strong force splits from
  others. Epoch of inflation?
• 10-35 s to 10-10 s Electroweak era
• 10-10 s T1015 K Electromagnetic force splits
  from others
• 10-10 to 10-4 s Quark era
• 10-4 s T1013 K Quarks combine to form protons
  and neutrons
• 10-4 to 500,000 years Radiation era
• 180 s (3 minutes) T109 K Protons and neutrons
  combine to form nuclei (mainly Helium,
  deuterium)
• 500,000 years T3,000 K Nuclei and electrons
  combine to form atoms Decoupling
• 500,000 years to present Matter era

16
History of the universe
17
Thus ends the story of the doubly expanding
universe for now

• Thanks for your attention, patience, persistence,
  and interest!

18
Final Exam

• Comprehensive
• Most questions from Ch. 15-18, some from Ch.
  4-14, few from Ch. E-2 (What we did not cover of
  some of these chapters or sections will NOT be on
  the exam)
• Multiple choice plus some short answer questions
• Please study
• Midterm exams (available on homepage)
• Homework
• Activities
• Textbook
• Powerpoint slides

19
Daily Rising and Setting

• Due to the rotation of the Earth around its axis
• Period of rotation 1 siderial day
  23h56m4.1s
• 1 solar day (Noon to Noon) 24h
• Stars rotate around the North Star Polaris
• Why are these different?

20
Daily and yearly motion intertwined

• Solar vs Siderial Day
• Earth rotates in 23h56m
• also rotates around sun
• ? needs 4 min. to catch up
• Consequence stars rise 4 minutes earlier each
  night (or two hours per month, or 12 hours in ½
  year)

?After 1/2 year we see a completely different sky
at night!
21

• Figure 2 shows a horizon view of what you would
  see when facing south at midnight on the night of
  December 1 in the northern hemisphere. How would
  this view change if you were to look towards
  south at midnight a month earlier?
• a. You would have the same view as on December 1
  because it still is autumn.
• b. Aries would have been in the South because the
  stars rise earlier in the East every day.
• c. Cancer would be in the South because the
  seasons were closer to summer.
• d. Gemini would have been highest in the South
  because the stars set earlier in the West.

22

• Consider Figure 2 again. How would this view
  change if you were to look towards south at 2am,
  i.e. two hours later?
• a. You would have the same view since the Earth
  barely moves around the Sun in two hours.
• b. Aries would be in the South because the stars
  shift by one constellation.
• c. Pisces would be in the South because the stars
  shift a constellation per hour.
• d. Gemini would be highest in the South because
  the Earth rotates 30 degrees in 2 hours.

23

• On December 1, at noon, you are looking toward
  the south and see the Sun among the stars of the
  constellation Scorpius as shown in Figure 1. At 4
  PM that afternoon, where will the Sun be with
  respect to the stars shown in this diagram?
• in the constellation Sagittarius
• in the constellation Scorpius
• in the constellation Libra
• west (right) of Libra

24
Math

• c ? f
• E hf
• T ? 0.0029 m K
• P A s T4
• B L/ (4pd2)
• d 1/p
• F G mM/d2

25
As the wavelength of EM increases

• the frequency increases
• the energy decreases
• the intensity increases
• None of the above

26
Two stars have the same chemical composition,
spectral type, and luminosity class, but one is 5
light years from the Earth and the other is 50
light years from the Earth. The farther star
appears to be

• a) 100 times fainter. b) 10,000 times
  fainter.c) the same brightness since the stars
  are identical. d) None of the above

27
Two stars have the same chemical composition,
spectral type, and luminosity class, but one is
2000 light years from the Earth and the other is
20 light years from the Earth. The farther star
appears to be

• a) 100 times fainter. b) 10,000 times
  fainter.c) the same brightness since the stars
  are identical. d) None of the above

28
Two stars have the same radius, but one has two
times the temperature of the other star. How much
brighter is the hotter star? 4 times 16 times
64 times None of the above  
29
Two stars have the same radius, but one has four
times the temperature of the other star. How much
brighter is the hotter star? 4 times 16 times
64 times None of the above  
30
Two stars have the same temperature, but one has
four times the radius of the other star. How much
brighter is the bigger star? 4 times 16 times
64 times None of the above  
31
Two stars have the same temperature, but one has
four times the radius of the other star. How much
larger is the peak wavelength of the bigger star?
2 times 4 times 16 times None of the above  
32
If the moon would be twice as far away, the force
of gravity exerted by it on the Earth would
Increase 2x Decrease 4x Be the same (Newton
III) None of the above