Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLecture 15
Overview • Finished: The Exploding Universe • This Time: Expansion of Space-Time and General Relativity • After That: Photons and Hydrogen in the Universe
Outline • General Relativity and Expanding Space-Time • Expanding Space and Red-Shifts
Recapping the Data Galaxies are moving away from us, faster if they are further away AND moving the SAME WAY same way in ALL DIRECTIONS Simple-but-wrong explanation: We are the center of an explosion!
Is this right? Only consistent this data if we’re at the center of the Universe and not moving Not consistent with other data Need a better explanation!
General Relativity to the Rescue • Space-time can change • E.g. Mass causes it to curve and stretch • What if space-time is expanding?
Expanding Space 0 Analogy: A loaf of raisin bread where the dough is rising and expanding, taking the raisins with it
Balloon Analogy • Our Universe doesn’t have any over all curvature, but thinking of Space-Time like the SURFACE of a balloon is something you can try at home • Balloon is a two dimensional example/analogy • There is no inside, space IS just the surface • As space-time expands, the distance between any two spots increases, but there is no spot ON THE SURFACE that is the center of the expansion
Expanding Space http://bigbang.physics.tamu.edu/Figures/StolenAnimations/originredshifts2.swf
The Expanding Universe 0 It’s not just galaxies moving through space Space is expanding, carrying the galaxies along!
Galaxies Moving in Space • Space is like a river carrying boats along • Line is like the speed of the river • Stuff above the line • Galaxies that are moving “away” from us in space • Stuff below the line • Galaxies moving “towards” us
Velocity? How does this explain why things are moving FASTER the further away they are? As the radius of the balloon increases, the farther apart the spots on the balloon, the faster they will be moving apart
More on Expanding Space-Time and Raisin Bread Distance http://bigbang.physics.tamu.edu/Figures/StolenAnimations/RaisinBread.swf
Photons in Expanding Space-Time • Since space is so empty, light from 10 billion years ago can reach us just fine • What happens to photons as they travel in the Universe? • The wavelength gets stretched as space expands The wavelength gets longer
What do photons look like in Expanding Space-Time? A distant galaxy emits a short wavelength photon towards our galaxy billions of years ago The Grid shows space
Space-Time Expands The expansion of space-time stretches the photon to longer wavelengths as it travels The Grid is bigger now
Space-Time Expands More The farther the photon has to travel, the more it is stretched Still bigger
How We Observe It When the photon arrives at our galaxy we see it with a larger wavelength The bigger the distance the more red-shifted it has become! Even bigger as time goes by
Red Shifts in an Expanding Universe http://bigbang.physics.tamu.edu/Figures/StolenAnimations/originredshifts1.swf
Expanding Space-Time • Explains all the data (and more in next Chapter) • Note: Implies that the Universe look the same to “everyone” in the Universe “everywhere” • Call this the Cosmological Principle
No Center of the Universe? I’m the center of expansion! Everyone moves away from me! • Nowhere on the surface can be called the center • No “center” of the Universe • Everywhere can be considered the center • Yes… As we’ve always known, Aggieland IS the center of the Universe • There is no “Before” the Big Bang • Space and time come into existence together No! I’m the center of expansion! Everyone moves away from me!
How big IS the Universe? We can’t really know how big the Universe is, since all we can see is back a certain distance in TIME
Next… Move to more evidence we live in an expanding space-time by looking at photons and hydrogen in the Universe
For Next Time– L15 • Next week is Spring Break. Meet again Monday March 17 • Reading: • Unit 3 • Pre-Lecture Reading Questions: • Unit 3 Revision in CPR (if desired): Stage 1 • End-of-Chapter Quizzes: • Chapter 10 & 11 • Papers: • Paper 1: • Revision (if desired): Stage 1 due Friday, Stage 2 due Monday March 17 by 11:55PM • Paper 2: • Stage 1 due THURSDAY at 5:45 • Stage 2 due Monday March 17 by 11:55PM
Full set of Readings So Far • Required: • BBBHNM: Chaps. 1-12 • Recommended: • TFTM: Chaps. 1-3 • BHOT: Chaps. 1-7, 9 and 11 (117-122) • SHU: Chaps. 1-3, 4(77-86), 5(95-104), 6, 7 (up-to-page 153) • TOE: Chaps. 1 & 2
Early Universe Universe Some Time Later E E C C D D B B A A Clicker Question Which of the following is the best ranking for the speeds (from fastest to slowest) at which galaxies A, C, and D would be moving away from an observer in galaxy B? • A > C > D • D > A > C • C > D > A • D > C > A
Clicker Question Are the Earth and Sun moving away from each other since space-time is expanding? • Yes. It is just a matter of time before the Earth will leave the Sun's orbit. • Yes, but the gravitational attraction between the two keeps them at the same distance • No, because the Sun is big enough to prevent space-time from expanding locally • No, because the only thing that matters is that the Earth is attracted to the Sun
Clicker Question Let's say I have two galaxies in space and they are exactly stationary relative to each other. What will happen next? • Since they are so massive that they will attract each other by gravity and start moving towards each other. • Since space-time is expanding, the distance between them will grow as space-time expands so they will start moving away from each other. • It depends on the overall distance between them.
Clicker Question If space-time is expanding, is our galaxy expanding? • Yes. Everything in the universe is moving away from everything else. • No. It isn't expanding because the gravitational attraction of masses pulls the galaxy back together again
Clicker Question If space-time is expanding, are atoms expanding? • Yes. Everything in the universe is moving away from everything else. • No, they aren't expanding because the electric charge attraction and quantum mechanics keep the atoms the same size in space
Clicker Question For the most distant galaxies, which is true? • Most of the red-shift of their spectral lines is because they are moving very fast through space • Most of the red-shift of their spectral lines is because space is expanding
Prep for next time – L17 • Reading: • BBBHNM: 13 • Pre-Lecture Reading Questions: • Chapter 13 • End of Chapter Quizzes: • Chapter 11 (if we finished 11, if not, just 10) • Papers: • Paper 0 Revision: Was due before class. Let us know if you think you were mis-graded • Paper 1: Still working on re-grades. • Paper 1 Revision: If you want to do a revision, due Wednesday before class. • Paper 2: Calibrations/Reviews are due Wednesday before class • Honors Paper: Stage 0 approval required
Prep for Today (Is now due) – L15 • Reading: • BBBHNM 12 • Reading questions: • Chapter 12 • End-of-Chapter Quizzes: • Chapter 10 • Paper Stuff • Paper 2: CPR Calibrations and reviews due today
Was due before Class – L17 • Reading: • BBBHNM: 12 • Pre-Lecture Reading Questions: • Chapter 12 • End of Chapter Quizzes: • Chapter 10 • Papers: • Paper 0 Revision: Was due before class. Let us know if you think you were mis-graded • Paper 1: Still working on re-grades. • Paper 1 Revision: If you want to do a revision, due Wednesday before class. • Paper 2: Calibrations/Reviews are due Wednesday before class • Honors Paper: Stage 0 approval required
Prep For Next Time – L7 • Note: May change depending on how far we get in lecture • Reading: • BBBHNM: All reading through Chapter 13 • Reading Questions: • All reading questions through 13 • eLearning Quizzes: • If we finished Chapter 11 then end-of-chapter quiz 11 (else just through Chapter 10) • Papers: • Paper 2 calibrations and reviews due before class on Tuesday
Prep for Next Time – P14 • Reading: • BBBHNM 12 • Reading questions: • Chapter 12 • End-of-Chapter Quizzes: • If we finished Chapter 11 then end-of-chapter quiz 11 (else just 10) • Papers: • Text was due Yesterday at 5:45PM • Calibrations/Reviews due Monday March 19
Prep for Next Time – P15 • Reading: • BBBHNM 12 • Reading questions: • Chapter 12 • End-of-Chapter Quizzes: • If we finished Chapter 11 then end-of-chapter quiz 11 (else just 10) • Paper Stuff • Paper 2: CPR Calibrations and reviews due today
Prep for Today (Is now due) – L14 • Reading: • BBBHNM 11 • Reading questions: • Chapter 11 • End-of-Chapter Quizzes: • Chapter 9 • Paper Stuff • Paper 1 Revision: CPR due Fri 6PM • Paper 2 Submission: Wed 4PM in CPR
Frequently Asked Question Page • I have created a new webpage on the main course page • http://faculty.physics.tamu.edu/toback/109/109FAQ.shtml • I’ve tried to take all the questions I keep getting and put answers to them there • Please read it and send fixes, comments, questions and requests for additions • In the future, you might check there if you have a question about the course before emailing • If it’s there, I’ll probably point you there in the first place
Paper 2 Revisions • Will allow Paper 2 revisions • I was REALLY pleased by some of the great papers • Then again, some really weren’t good • If you are not going to submit a good paper, then we aren’t going to give you a chance to revise • If you aren’t doing well with calibrations, we expect you to ask for help
Final Note General Relativity doesn’t really explain WHY this expansion occurs, but expanding space is perfectly allowed Thus, the expansion could occur since its only SPACE that is expanding
Our Best Understanding • Thus, either we believe we’re at the center of an explosion or take seriously the idea that we’re part of an expanding Space-Time • More evidence that we’re part of an expanding space-time?
What if we Think about it Differently Maybe it just “looks” like we’re at the center of the Universe and not moving Could this be true? Could be, but what’s the reason it looks like we’re at the center?
The Cosmological Principle At any given time the Universe ought to look the same to observers in all typical galaxies and in whatever directions they look • In other words, the universe should look the same no matter where you look at it from • There IS no center
Advantage of this way of thinking No longer need to live in a special place in the Universe If this idea is true, then the Universe looks essentially the same for ANY OTHER OBSERVER any where else in the Universe • Can’t check this…
No center or edge of the Universe? 0 2-dimensional analogy: Ant that can only walk on the surface of a sphere: Surface is finite, but has no edge For a creature living on the sphere, having no sense of the third dimension, there’s no center (on the sphere!): All points are equal Alternative: Any point on the surface can be defined as the center of a coordinate system
??? • Do we REALLY believe we’re the center of the Universe AND not moving? • A better explanation?