1. How bizarre is our universe?
Start with the Big Bang

2. GUT Era
lasts from Planck time (~10-43 sec) to end of GUT force (~10-38 sec). At that point, inflation occurs as the strong forces separates from gravity & releases energy (first kinetic, then thermal)

3. Recall that forces unify at high temperatures
Four known forces
in universe:
Strong Force
Electromagnetism
Weak Force
Gravity
Separation of GUT force into
strong force + electroweak force releases energy

4. Four separate forces today (t=13.75 billion years after Big Bang)
Particle with mass? Affected by gravity.
Particle with ‘colour charge’? Affected by strong force.
Particle with ‘flavour charge’? Affected by weak force.
Particle with electric charge? Affected by electromagnetic force.
(The above is a simplification, but useful.)

5. Three separate forces at t<10-30 seconds after Big Bang
Particle with mass? Affected by gravity.
Particle with ‘colour charge’? Affected by strong force.
Particle with flavour or electric charge? Affected by electroweak force.

6. Two separate forces at t<10-38 seconds after Big Bang
Particle with mass? Affected by gravity.
Particle with colour, flavour or electric charge? Affected by GUT force.

7. Only one force (we think) at t<10-43 seconds after Big Bang
Particle with mass, colour, flavour or electric charge? Affected by quantum gravity force.

8. Future of the Universe: Let 1 millisecond represent 1 billion years
1 msec – runaway greenhouse effect on Earth
0.1 second – only 1 galaxy in observable universe
1 second – no more stars form
10 seconds – all stars have stopped fusion
2 minutes – all solar systems have been disrupted
120 days – all stars have been ejected from galaxies
32,000 years – all orbits decayed via gravity waves
100 trillion years – protons have all decayed

9. Future of the Universe:
Now let 1 second represent 100 trillion years
1 second – protons have all decayed
100 trillion years – stellar-mass black holes start evaporating
Now let 1/100 trillionth of a second represent 100 trillion years
1 second – stellar-mass black holes start evaporating
100 trillion years – all black holes have evaporated
…that’s how long years is.
Universe is cold, dark, nearly empty.

10. Hawking radiation & black hole evaporation
If nothing escapes a black hole, how can it evaporate?
By quantum fluctuations…

11. Quantum fluctuations
On the smallest possible scales, the universe doesn’t play by “normal” rules.
Particle/antiparticle pairs can appear & disappear, if they last for a short enough time
electron-positron pairs can last for seconds
proton-antiproton pairs have higher mass-energy and can last for only seconds (at most)
So on extremely small scales, the amount of energy in existence at one time in one spot fluctuates

12. Hawking radiation & black hole evaporation
If nothing escapes a black hole, how can it evaporate?
Quantum fluctuations are stronger when gravity is stronger, and the smallest black holes have the strongest gravity at their event horizons
So what happens if a particle and antiparticle both appear near the event horizon of a black hole, but one falls in and one flies away?

13. Hawking radiation & black hole evaporation
If nothing escapes a black hole, how can it evaporate?
Quantum fluctuations are stronger when gravity is stronger, and the smallest black holes have the strongest gravity at their event horizons
So what happens if a particle and antiparticle both appear near the event horizon of a black hole, but one falls in and one flies away?
Then from our point of view, the black hole has emitted a particle (or antiparticle) and has lost mass!
So black holes should eventually evaporate, and the smallest ones (e.g., from LHC) will evaporate first.

14. Dark energy and the fate of our universe
100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

15. Dark energy and the fate of our universe
100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection
Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:

16. Dark energy and the fate of our universe
100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection
Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:
Big Rip: happens if dark energy is a ‘phantom’ energy which grows stronger with time and rips apart planets, molecules, nuclei, nucleons.

17. Dark energy and the fate of our universe
100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection
Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:
Big Rip: ‘phantom’ energy grows stronger with time and rips apart planets, molecules, nuclei, nucleons.
‘Standard’ dark energy yields accelerating universe but no big rip: vacuum energy is constant with time

18. Dark energy and the fate of our universe
100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection
Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:
Big Rip: ‘phantom’ energy grows stronger with time and rips apart planets, molecules, nuclei, nucleons.
‘Standard’ dark energy yields accelerating universe but no big rip: vacuum energy is constant with time
Decaying dark energy: acceleration stops, reverses?

19. Dark energy and the fate of our universe
100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection
Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:
Big Rip: ‘phantom’ energy grows stronger with time and rips apart planets, molecules, nuclei, nucleons.
‘Standard’ dark energy yields accelerating universe but no big rip: vacuum energy is constant with time
Decaying dark energy: acceleration stops, reverses?
Won’t know fate of universe for sure until we understand dark energy. (If then!)

20. So much for the end of the universe: the universe seems to go from Big Bang to Big Whimper. But what about the beginning? What caused the Big Bang?

21. What caused the Big Bang?
Currently (always?), science runs out of answers to “why?” questions at this point.
But cosmologists have lots of ideas!

22. What caused the Big Bang?
Currently (always?), science runs out of answers to “why?” questions at this point.
But cosmologists have lots of ideas!
Conservation of energy: The universe’s positive kinetic & mass-energy plus its negative potential energy (gravitational, electroweak, and strong-force) can sum to zero.

23. What caused the Big Bang?
Currently (always?), science runs out of answers to “why?” questions at this point.
But cosmologists have lots of ideas!
Conservation of energy: The universe’s positive kinetic & mass-energy plus its negative potential energy (gravitational, electroweak, and strong- force) can sum to zero.
Superstrings: the current leading contender to deepen our understanding of the Big Bang, etc.
Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny, ‘rolled up’ space dimensions)

24. A two-dimensional cylinder looks like a 1-dimensional line if the width of the cylinder is much smaller than its length

25. With 6 or 7 dimensions, you get weirder geometric shapes, but the idea is the same:

26. A point in spacetime would not be t,x,y,z but t,x,y,z,a,b,c,d,e,f & maybe g

27. What caused the Big Bang?
Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)

28. What caused the Big Bang?
Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)
Superstring theory might unify gravity and quantum mechanics. In this theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)

29. What caused the Big Bang?
Superstring theory might unify gravity and quantum mechanics. In this theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)
Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)
M-theory (M for membrane, a 2-D string) predicts 11 dimensions, with the 11th spanned only by gravity

30. What caused the Big Bang?
Superstring theory might unify gravity and quantum mechanics. In this theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)
Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)
M-theory (M for membrane, a 2-D string) predicts 11 dimensions, with the 11th spanned only by gravity
Big Bang caused by (mem)branes colliding in that 11th dimension? Cyclic Big Bangs?

31. What caused the Big Bang?
Did the Big Bang occur as a quantum fluctuation in another universe?

32. Quantum energy fluctuations = quantum mass fluctuations = quantum spacetime fluctuations

33. What caused the Big Bang?
Did the Big Bang occur as a quantum fluctuation in another universe?
…or did the universe create itself? (Quantum fluctuations at the Planck length might be able to create a wormhole through which energy travels back in time seconds to create the spacetime!)

34. Wormhole in spacetime

35. What caused the Big Bang?
We don’t know! (Yet…)

36. Just how bizarre is our universe?
The Multiverse: if our universe is finite, there might be other universes beyond it (separated by regions of eternal inflation)

37. Duplicate universes?
If our universe (or the multiverse) is infinite, then any part of it must eventually repeat itself.
The consequences may argue against universe/multiverse being infinite!
No communication between island universes, however.

38. Just how bizarre is our universe?
Regardless of whether our universe is finite or infinite, quantum mechanics might allow parallel universes to exist.
Such universe might overlap with ours yet be impossible for us to perceive!

39. Is any of this testable?

40. Is any of this testable? Yes!
(Though not all of it, and not easily)
Analogs to Hawking radiation exist (e.g., high acceleration substitutes for strong gravity)
Patterns in CMBR constrain amount of inflation, cyclical Big Bang theories, etc.
Quantum gravity theory would aid in understanding both general relativity (wormholes) and quantum mechanics (parallel universes) better
Measuring history of universe’s expansion will tell us more about dark energy (e.g., Big Rip or not)

41. Just how bizarre is our universe?
The Multiverse: regions of eternal inflation separating island universes where inflation stopped?

42. Just how bizarre is our universe?
The Multiverse: regions of eternal inflation separating island universes where inflation stopped?
Weak Anthropic Principle: why are the physical constants of our universe just right to allow stars and planets to form and thus give life a chance to develop?

43. Just how bizarre is our universe?
The Multiverse: regions of eternal inflation separating island universes where inflation stopped?
Weak Anthropic Principle: why are the physical constants of our universe just right to allow stars and planets to form and thus give life a chance to develop? Because by definition, life will develop only in universes that allow life to develop (e.g., that don’t have too much dark energy or dark matter).

44. Just how bizarre is our universe?
The Multiverse: if our universe is finite, there might be other universes beyond it (eternal inflation)
Weak Anthropic Principle: why are the physical constants of our universe just right to allow stars and planets to form and thus give life a chance to develop? Because by definition, life will develop only in universes that allow life to develop (e.g., that don’t have too much dark energy or dark matter).
Only universes that can support life will have life in them wondering why the universe supports life!

45. What have we learned?
• What aspects of the universe were originally unexplained by the Big Bang model?
(1)     The origin of the density enhancements that turned into galaxies and larger structures.
(2)     The overall smoothness of the universe on large scales.
(3) The fact that the actual density of matter is close to the critical density.

46. What have we learned?
How does inflation explain these features of the universe?
(1)     The episode of inflation stretched tiny, random quantum fluctuations to sizes large enough for them to become the density enhancements around which structure later formed.
(2)     The universe is smooth on large scales because, prior to inflation, everything we can observe today was close enough together for temperatures and densities to equalize.
(3) Inflation caused the universe to expand so much that the observable universe appears geometrically flat, implying that its overall density of mass plus energy equals the critical density.

47. What have we learned? • How can we test the idea of inflation?
Models of inflation make specific predictions about the temperature patterns we should observe in the cosmic microwave background. The observed patterns seen in recent observations by microwave telescopes match those predicted by inflation.

48. What have we learned?
• Why is the darkness of the night sky evidence for the Big Bang?
Olbers’ paradox tells us that if the universe were infinite, unchanging, and filled with stars, the sky would be everywhere as bright as the surface of the Sun, and it would not be dark at night. The Big Bang theory solves this paradox by telling us that the night sky is dark because the universe has a finite age, which means we can see only a finite number of stars in the sky.