Big Bang, Black Holes, No Math ASTR/PHYS 109 Dr. David Toback Lecture 26 & 27

1. Big Bang, Black Holes, No MathASTR/PHYS 109Dr. David TobackLecture 26 & 27 Early Times & Fate of the Universe Topic 1: Possibilities

2. Was due today– L26 • Reading: • Already due • Pre-Lecture Reading Questions: • Already due • Can do make ups in CPR. Instructions at http://people.physics.tamu.edu/toback/109/Question_Guideline_109_CPR.pdf • Will need to submit 4 questions, and do the entire CPR assignment to get credit • End-of-Chapter Quizzes: • All end-of-chapter quizzes are due by 11:55PM of Monday December 2nd. This includes AMS-2 • Papers: • Paper 3: Working on recent re-grade requests • Paper 3 Revision: Text due tomorrow before 4:10PM. Rest of assignment. Monday before 4:10PM • Paper 4: Text due tomorrow before 4:10PM. Rest of assignment. Monday before 4:10PM Early Times & Fate of the Universe Topic 1: Possibilities

3. Honors Papers • Due Wednesday at 11:55PM on eCampus Early Times & Fate of the Universe Topic 1: Possibilities

4. Course Evaluations Course evaluations will be done online: • You should have gotten an email about this already The Fall 2013 evaluation period will: • Begin on Wednesday November 27th at 8AM • Ends on Friday December 13th at 5PM • Please do them… won’t take long Early Times & Fate of the Universe Topic 1: Possibilities

5. Unit 6 Going back in time and going forward in time Before the first millionth of a second and the Fate of the Universe Early Times & Fate of the Universe Topic 1: Possibilities

6. Outline of Unit 6 • Possible Fates of the Universe, Dark Matter and Dark Energy • Particle Physics, Dark Matter and the Very Early Universe • Inflation Today Early Times & Fate of the Universe Topic 1: Possibilities

7. Caveats While the data is VERY powerful, some of the details I will show are not fully “proven” or understood Still need data to tell us about the theory, and theory to tell us about the data New data and theoretical advances have recently changed our understanding of the Universe Early Times & Fate of the Universe Topic 1: Possibilities

8. The Fate of our Universe Will the Universe continue expanding forever? • That depends, mostly, on a few things: • How fast is it expanding now • How much STUFF there is in the Universe • How big it is now • Are the laws of physics really understood? Early Times & Fate of the Universe Topic 1: Possibilities

9. Why the first three are so important • Gravity is trying to pull space-time back together again • Attractive force • Either it’s strong enough to pull the universe back together again, or it isn’t Early Times & Fate of the Universe Topic 1: Possibilities

10. What about that last issue? • Dark Energy fits into this story, but it is an effect that only impacts on the largest scales • Takes 10 billion years and HUGE distance scales to have ANY effect • Start by discussing gravity first, then come back to it • Kinda like when we did the expanding universe Early Times & Fate of the Universe Topic 1: Possibilities

11. Gravity: Three Possibilities There are basically three possibilities Use an analogy… Shooting a bullet into the air at the surface of the Earth Early Times & Fate of the Universe Topic 1: Possibilities

12. Possibility 1: Small Speed Universe ends in a Big Crunch • If the bullet is shot up with a small speed, gravity will eventually stop it and it will fall back to the Earth • Can think of the gun shooting the bullet as an explosion (our big bang) • If the “Bang” is too small, all the stuff in the Universe will eventually all fall back together as the space-time collapses on itself… like a giant black hole Early Times & Fate of the Universe Topic 1: Possibilities

13. Continue the analogy… It’s a balance between the speed of the bullet and the density of the object the bullet is trying to leave Does the bullet have a speed below the escape velocity? Early Times & Fate of the Universe Topic 1: Possibilities

14. A bullet has a speed smaller than the escape velocity Early Times & Fate of the Universe Topic 1: Possibilities

15. The Sun

16. Possibility 2: Big Speed Universe expands forever If the bullet has a speed greater than the escape velocity, gravity will not be strong enough to pull it back • Will keep on going away from the Earth forever • Like launching a rocket into outer space but using a slingshot, not thrusters that keep firing Early Times & Fate of the Universe Topic 1: Possibilities

17. Early Times & Fate of the Universe Topic 1: Possibilities

18. The Moon has a “small” escape Velocity

19. To infinity and beyond • As the bullet gets further and further from the moon the gravitational attraction gets smaller and smaller… It still slows the bullet down, but less and less… • Eventually, the attraction is so small (since they are so far away from each other) that the bullet effectively moves off into space at the same speed forever Early Times & Fate of the Universe Topic 1: Possibilities

20. Possibility 3: In between • It will approach zero speed as it gets farther from the Earth • It’s true that it can orbit the Earth it has just the right speed, but that’s not what we are talking about here… Early Times & Fate of the Universe Topic 1: Possibilities

21. Back to the Universe • Since there is a lot of mass in the Universe, if were expanding slowly enough the force of gravity would cause it to eventually stop expanding and then start contracting again • Even with a large speed today gravity might force it to stop expanding and then contract Early Times & Fate of the Universe Topic 1: Possibilities

22. Look at it the Other Way Since we can observe the speed of the expansion of the Universe we ask the question the other way “Is the density of the universe big enough to make the Universe contract again? Collapse back on itself? A Big Crunch?” Does it have a “critical” density? Early Times & Fate of the Universe Topic 1: Possibilities

23. Summary: 3 Possibilities • Over the critical density: Collapse (an anti-big bang, or a Big Crunch) • Under the critical mass: Expanding forever, but slows down and eventually hits a constant speed • Exactly critical mass: Eventually stops expanding just barely enough… Speeds get smaller and smaller, although never quite reaches zero Early Times & Fate of the Universe Topic 1: Possibilities

24. Look at all three together Early Times & Fate of the Universe Topic 1: Possibilities

25. A Universe Ending in a Big Crunch • Remember this is only an analogy  There is no center or edge of the Universe Early Times & Fate of the Universe Topic 1: Possibilities

26. A Universe That Expands Forever Early Times & Fate of the Universe Topic 1: Possibilities

27. Critical Density Early Times & Fate of the Universe Topic 1: Possibilities

28. Well? • Which universe do we live in? • Need to know the present rate of expansion and the density of the universe Early Times & Fate of the Universe Topic 1: Possibilities

29. Measure Both • Can measure the speed of expansion fairly accurately • What Hubble originally measured • What do we know about the density of the Universe? • Add up the mass of all the stars we can see • Add in all the stuff between the stars (hydrogen and helium gas) • This density is about 5% of the critical density • Dark Matter makes up about 23% Early Times & Fate of the Universe Topic 1: Possibilities

30. Below the Critical Density? • The naïve scientist would conclude that we “must” be in a Universe that would expand forever • Is this right? • How could we check this? • Any evidence we’re missing something? Early Times & Fate of the Universe Topic 1: Possibilities

31. Other Ways? Are there other ways to predict the Fate of the Universe? Early Times & Fate of the Universe Topic 1: Possibilities

32. The Data Measure the Density of the Universe from the Cosmic Background Radiation Early Times & Fate of the Universe Topic 1: Possibilities

33. The Cosmic Background Radiation 0 Look at the size of the spots Early Times & Fate of the Universe Topic 1: Possibilities

34. Look at the Spots We know what the size of the spots should be back during recombination, but we can ask how much the light was lensed as it moved through space Big Crunch Critical Density Expands Forever Early Times & Fate of the Universe Topic 1: Possibilities

35. Computer Simulations 0 Big Crunch Critical Density Expands Forever Early Times & Fate of the Universe Topic 1: Possibilities

36. Which Universe Do We Live In? 0 Big Crunch Critical Expand Forever? Looks like a Universe with the Critical Density The Data Early Times & Fate of the Universe Topic 1: Possibilities

37. Summarizing the Data • Speed of far-away galaxies moving away from us gives us the speed of expansion fairly accurately • The measured density of the “known matter and dark matter” is about is about 28% of the critical density • The background radiation says the density is consistent with being 100% of the critical density Something is inconsistent… Early Times & Fate of the Universe Topic 1: Possibilities

38. How do we tell which is right? • Looking at distant galaxies shows that the Universe is expanding • Since there is lots of mass in the Universe, the expansion should be slowing down • Like a ball thrown up into the air, it should slow down • Question: Is it slowing down like a Universe with 28% of the critical mass or 100% of the critical mass? Early Times & Fate of The Universe Topic 5: Dark Energy

39. How do we measure the deceleration? 0 • Look at Supernovae since they are REALLY bright for about a month so we can see them from far away • We believe we understand these explosions really well Early Times & Fate of The Universe Topic 5: Dark Energy

40. Measuring the “Deceleration” of the Universe 0 • Can use the brightness of Supernova to tell how far they are away • Can use spectral lines to tell how fast they are moving Early Times & Fate of The Universe Topic 5: Dark Energy

41. What Does the Data Say? 0 • The most distant things in the Universe are further away than we think they should be • The Universe doesn’t appear to be slowing down, it’s speeding up! • Accelerating! • It’s like there was an explosion and then something CONTINUES to force the stuff further apart • Throw a ball into the air and the ball speeds up!??! Early Times & Fate of The Universe Topic 5: Dark Energy

42. The Accelerating Universe Early Times & Fate of The Universe Topic 5: Dark Energy

43. What the ??? • Is there some Force that that is pushing things apart faster? • Gravity, as we know it, only attracts… Give it a name: Dark Energy Early Times & Fate of The Universe Topic 5: Dark Energy

44. Why do we call it Dark Energy? • Can’t see it • Call it Dark • Doesn’t seem to interact gravitationally  Not mass or matter, but is forcing the Universe apart so it has energy (E=mc2). Not Dark Matter • From the acceleration can measure how much energy must be “doing the forcing” ~72% of the critical density Early Times & Fate of The Universe Topic 5: Dark Energy

45. Dark Energy and Dark Matter related? • Not clear dark matter and dark energy have anything to do with each other • Just because we use the word DARK for both doesn’t mean we know how they are related • Probably IS something fundamental that is similar, but we don’t know enough about either so say anything useful yet Early Times & Fate of the Universe Topic 1: Possibilities

46. It all adds up! • Add up all the mass/energy in the Universe • Atoms account for ~5% • Dark Matter is about 5 times more mass in a galaxy than atoms  ~23% • Dark Energy is about ~72% Cosmic Background Radiation says the Universe has 100% of the critical density Early Times & Fate of The Universe Topic 5: Dark Energy

47. The Evolution and Fate of the Universe We don’t know the nature of Dark Energy Lots of possible Fates… but it looks like we’ll expand forever… and it could get REALLY cold! Dark Energy overcomes the deceleration of Gravity about 6 billion years ago, Universe starts accelerating Deceleration due to Gravity for the first 6 billion years Dark Energy Makes the Universe Accelerate (keep expanding Faster and faster) Early Times & Fate of The Universe Topic 5: Dar Energy

48. Lots of Questions How will we figure out the fate of the Universe? Need to know the Nature of Dark Energy What is Dark Energy? We don’t know yet… Just starting to have ideas.. Early Times & Fate of The Universe Topic 5: Dark Energy This result was so important that it was awarded the Nobel Prize for 2012

49. Prep for Next time – L26 • Reading: • Already due • Pre-Lecture Reading Questions: • Already due. If you want to do a make up, you need to email me • End-of-Chapter Quizzes: • All end-of-chapter quizzes are due by 11:55PM of Monday December 2nd. This includes AMS-2 • Papers: • Paper 3: Working on recent re-grade requests • Paper 3 Revision: Text due Monday before class • Paper 4: Text due Monday before class

50. End of Lecture Early Times & Fate of the Universe Topic 1: Possibilities