Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 6 & 7

1. Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLecture 6 & 7

2. Prep For Today (is now due) – L6 • Reading: • BBBHNM Unit 2 • Pre-Lecture Reading Questions • Unit 1 Revision (if needed): Stage 1 • Unit 2: Stage 1 • End-of-Chapter Quizzes • Chapter 4

3. Prep For Today (is now due) – L7 • Reading: • BBBHNM Unit 2 • Pre-Lecture Reading Questions • Unit 1 Revision (if needed): Rest of Assignment • Unit 2: Rest of Assignment • End-of-Chapter Quizzes • Chapter 4

4. Next Set of Topics: Physics We Need Finished our introduction • Big and small things in the Universe • Evidence and the Scientific Method Next we move on learn some of the physics we need in order to understand why scientists have confidence in the Big Bang Theory

5. Overview of Physics We Need • Cosmology, the big bang and black holes are some of the most interesting things that can be understood • However, to UNDERSTAND them better, and the EVIDENCE for them, we need to learn some physics

6. The Topics • Some stuff we need learn a little about: • Light and Doppler Shifts • Gravity, General Relativity and Dark Matter • Atomic Physics and Quantum Mechanics • Nuclear Physics and Chemistry • Temperature and Thermal Equilibrium • We won’t spend too long on each, just enough to get back to the big picture… • Since there is no perfect way to present them (they all tie into each other) we’ll just start somewhere and get going…

7. Back to the Big Picture Questions we’re trying to answer: • How did the Universe come into being? • How did it evolve into what we know today? • What is the evidence for all of this?

8. Light What we know about the universe comes from multiple places One of the most important is from looking at both outer space and inner space Need to know more about the “light we see”

9. Outline for Light • Light is a wave… • …and a particle • Light is REALLY fast, but does have a finite speed • Doppler effect

10. Part 1: Light is a Wave • The light we see is a “wave”, like waves on an ocean • Best described by it’s wavelength

11. Why do we believe light is a wave? • Water and Sound are also both waves • Does light behave like water or sound? • Can “see” water waves hitting a wall and what happens to them when they hit two small openings in a wall

12. Water waves moving towards a wall You are in the sky looking down at the waves as they go by

13. Why do we believe light is a wave? Shine light from a laser at two small holes in a wall and see what comes out on the wall behind it The waves make patterns on the wall the same way water waves do (Physics 202 & 208)

14. The Wavelength of Light • Shine white light at a prism and it breaks up into its different colors • Each color has a different wavelength which we can measure

15. White Light = Lots of Different Color Photons

16. Light is more than the colors we see You may have thought of Radio Waves and X-rays as different things, but they are just light with different wavelengths

17. Part 2: Light is a particle • What if we look at smaller and smaller “amounts” of light? • The light we see is actually LOTS of particles all moving together • Call these Photons Lots of photons where its bright Very few photons where its dark

18. Another view…

19. The Energy of Particles We can think about Energy in many ways • One way is the “energy of motion” • Kinetic Energy in the language of PHYS 201 and 218 • For a particle (with mass) in motion: • The higher the speed the particle has, the more energy it has • The more mass the particle has (the heavier it is) the more energy it has

20. Clicker Question for Energy Which has more energy? (Which will do more damage to a tree?) 1. A) A Prius moving at 10mi/hr or B) An SUV at 10mi/hr? 2. A) An SUV moving at 10mi/hr or B) An SUV moving with 60mi/hr? 3. A) A Prius moving at 60mi/hr or B) An SUV moving at 10mi/hr? C) Depends on the masses of the Prius and the SUV

21. Photons What do we know about photons? • Photons are a type of particle • Like an electron or proton • Higher energy  smaller wavelength • Has no mass, but does have energy • Aside for those of you who are interested: It has momentum

22. A Particle and a Wave • Actually it’s really more complicated than that • Light is both a wave and a particle… can describe it as either… it has properties of both

23. Part 3: The Speed of Light “Not just a good idea, it’s the law!”

24. Light has a Finite Speed Light has been measured to have a specific speed • 3 x 108 meters per second • 186,000 miles per second • 1 foot per nanosecond • Really FAST • The fastest speed allowed

25. Maxwell’s Theory • 1865: James Clerk Maxwell and others showed light was a wave and calculated its expected speed • Gave the observed speed of light! • Confidence that his theories were correct • We can now measure the speed of light to incredible precision Physics 208 2.99792458 x 108 m/s

26. A Light-Year • Some things are so far away that it’s easier to express their distance in light-years • Light travels at 3 x 108 meters/second and there are p x 107 seconds/year  ~1016 m in a light-year • If a star is a light-year away and it must have taken a year for the light to get to us, we are observing the star the way it was a year ago • If we look at light from something billions of light-years away, we are “observing” things that happened billions of years ago

27. Part 4: The Doppler Effect • 1842: Christian Doppler • What happens to waves when the “thing” creating the waves is moving towards us? • Or we’re moving towards it? Physics 221

28. Example with Sound From a Stationary Car The sound we hear is actually a wave • Sound waves

29. Now the Car is Moving Things coming at us have their waves “scrunched up” Things moving away have their waves “stretched”

30. The Doppler “Effect” for Cars Hears a Lower Pitched Sound Hears a Higher Pitched Sound A car blaring its horn and going past you will give the famous “Eeeeeeee-Yowwwwww” sound

31. What Does This Have to with Light? • Since both sound and light are waves, the Doppler “Effect” applies equally to both • Normally can’t see this effect for light since its wavelength is small and its speed is fast • Can in special cases: • Things need to be moving really fast, like stars and galaxies • Need really good measuring devices like the ones Astronomers have

32. Doppler Effect and Light Red Shift Sees light with a larger wavelength Blue Shift Sees light with a smaller wavelength Galaxy moves to the right 

33. Look at Light from Galaxies • The light from galaxies moving away from us will appear to have longer wavelength light • The light is more Red, or shifted to the Red side of the light spectrum • “Red Shifted” • The light from galaxies moving towards us will appear with shorter wavelength • The light is more Blue, or shifted to the Blue side of the light spectrum • “Blue Shifted”

34. The Doppler Effect in Action Doppler Effect

35. Three Observers What does an object emitting light look like to different observers when it is • Not moving • Moving Doppler Shift

36. Look at some cases Next lets look at three cases where an “explosion” occurs and things expand from that point • I’m stationary and the exploding things are moving away from me (I’m the center of the explosion) • I’m moving along with the exploding things • Same as case 2, but how it would look to me in my reference frame

37. Two Objects Moving Away from Me What it looks like when I’m stationary (or in my reference frame)

38. Two Objects Moving Away From Me What it looks like when I’m moving relative to the objects

39. Same Thing: My Reference Frame Why were these three cases important? Sorry… you’ll have to wait until we look at galaxies sending us light

40. Doppler Effect and Light: Summary Compare the light coming from a car that’s parked and one that’s coming towards you If a car is coming toward you with its lights on • The color of the light changes • The speed of the light does not!

41. Putting It All Together Since stars can be billions of light-years away and are moving quickly we can use the Doppler effect on light to measure the speed and direction of all objects in the night sky (Can also use it to tell us what Stars are made of, but for that we need to learn about quantum mechanics…)

42. Outline for Unit 2: Physics We Need • Light and Doppler Shifts Done • Gravity, General Relativity and Dark MatterNext • Atomic Physics and Quantum Mechanics • Nuclear Physics and Chemistry • Temperature and Thermal Equilibrium

43. Prep For Next Time – L6 • Reading: • Required: BBBHNM Unit 2 • Recommended Reading: • See P3 of http://people.physics.tamu.edu/toback/109/Syllabus.pdf • Pre-Lecture Reading Questions • Unit 1 Revision (if Needed): Stage 2 in CPR due Wednesday before class • Unit 2: Stage 2 due Wednesday before class • End-of-Chapter Quizzes • If we finished Chapter 5 then End-of-Chapter Quiz 5 (else, just through Chapter 4)

44. End of Lecture

45. Clicker Quiz Q: What does it mean for an electron to be "stable?" • It is balanced with exactly one proton • Its orbit ring exists in one plane (no wobble) • It has reached minimum size (10-19 m) • Undisturbed, it can go on living forever and ever • They don't appear to be made of anything smaller

46. Clicker Quiz Which of the following travels the fastest? • Radio waves • Gamma rays • Red light • Blue light • They all move at the same speed

47. Clicker Quiz We observe two objects in space. From other studies, we can tell that object X is emitting infrared light and the object Y is emitting Ultraviolet light. We observe the color of the light object X to be Red and the color of Object Y to be blue. Which statement is true? • X and Y are moving towards us • X and Y are moving away from us • X is moving towards us and Y is moving away from us • X is moving away from us and Y is moving towards us

48. Paper 0, Questions 1-5 • Does the paper make it easy to understand what question is being answered, what the answer is, and how it will be answered? If anyone of those are missing, or if you can't follow the argument, then choose No. If the argument is clear, but not said very well (or is wordy), then you should still give a Yes. If the paper is clear to you, but would not be clear to someone who hasn’t taken the course choose No. Being easy to read isn't a good enough reason to give a Yes. Having a sentence or two that are hard to understand (or poorly written) within a basically clear paper is fine, and can still deserve a Yes if it is otherwise ok. • Are the pieces of evidence clearly and correctly enumerated in the opening paragraph? This includes the electrons going around atoms, the Moon orbiting the Earth, and planets orbiting the Sun. • Does the structure of the paper follow the instructions? Specifically: Is there an introduction paragraph, separate paragraphs discussing evidence, and a conclusion paragraph? If any are missing, choose No. Does the paper directly address the question and make the argument to answer it? If the paper addresses the question and makes an argument (right or wrong) to answer it, choose Yes (we will address the wrongness in a later question). Do not choose No due to a poorly written or confusing introduction. The paper does not need to have only three paragraphs, and the pieces of evidence can be intertwined within them. Do not choose No due to missing evidence or more than three paragraphs. Do not choose No just because evidence is not constrained to these paragraphs. If the paper does not end with a conclusion paragraph, choose No. Do not choose No due to a poorly written or confusing conclusion. • Is the paper generally free of extraneous evidence? If there is any significant evidence that is off topic or an argument that has nothing to do with the topic, choose “No.” If there is significant evidence from outside class, choose No. Do not choose “No” due to evidence that is unnecessary if the evidence is relevant to the topic. • Does the paper only use language and words that can be understood by the average lay-person? If the author uses an acronym, like GR, for general relativity that is ok but only if the acronym is clearly defined. If they use an acronym that isn't defined, then select No. Similarly, just because you saw these words in a high-school science class does not mean they are understood by the average person. The average person on the street would know what an atom is, but not know what a spectral line is.

49. Paper 0, Questions 6-10 • Does the essay use language formal enough to give to a statesman? If the paper uses jokes, slang or other informal language, choose No. Do not choose No due to poor grammar, spelling mistakes, incomplete sentences, or poor sentence structure (we will take off points in a different question for this). Do not choose No due to the use of an acronym, like USA, since it is common usage and not slang. • Is the essay generally free of instances of bad grammar, incomplete sentences or spelling mistakes? If there are more than two minor mistakes, choose No. • Does the paper make clear how and why the evidence presented relates to the argument? If the facts are mentioned but show no clear connection to the argument, then choose No. If the facts are not addressed throughout the paper, then choose No. If it states the data without saying why it is evidence then choose No. • Do the middle (evidence) paragraphs clearly tie into the overall structure? • Does the paper use the scientific method and evidence based decision making? It’s OK if the words “scientific method” and “evidence-based decision making” are not mentioned specifically.

50. Paper 0, Questions 11-15 • Does the essay make it clear what the Scientific Method is and why it is important in this paper? • Does the essay clearly tie together the pieces of evidence using the scientific method in the conclusion? • Does this paper say that the Moon orbits the Earth? • Does the paper mention explicitly that the Earth is much more massive than the Moon, and that it is important to why the Moon orbits the Earth instead of the other way around? If it mentions that the Earth is more massive, and that this is what is important, then this is good enough. If it just says that it is more massive without saying why that is important in some way, then answer No. If it says "bigger" or "larger" (or that the Moon is "smaller") that is good enough. • Does the paper mention that the Earth or the planets orbit the Sun? Either is fine. If neither is mentioned, then give a No.