1. Einstein’s Universe Dr Martin Hendry Dept of Physics and Astronomy,
University of Glasgow

2. Isaac Newton
Albert Einstein

3. Isaac Newton
Albert Einstein

4. Isaac Newton
Galileo Galilei

5. How do things move?…. Aristotle’s Theory:
Objects move only as long as we apply a force to them
Falling bodies fall at a constant rate
Heavy bodies fall faster than light ones

6. v How do things move?…. Aristotle’s Theory: Galileo’s Experiment:
Objects move only as long as we apply a force to them
Falling bodies fall at a constant rate
Heavy bodies fall faster than light ones
Galileo’s Experiment:
Objects keep moving after we stop applying a force (if no friction)
Falling bodies accelerate as they fall
Heavy bodies fall at the same rate as light ones

7. How do things move?…. Aristotle’s Theory: Galileo’s Experiment:
Objects move only as long as we apply a force to them
Falling bodies fall at a constant rate
Heavy bodies fall faster than light ones
Galileo’s Experiment:
Objects keep moving after we stop applying a force (if no friction)
Falling bodies accelerate as they fall
Heavy bodies fall at the same rate as light ones

8. v How do things move?…. a r Aristotle’s Theory: Galileo’s Experiment:
Objects move only as long as we apply a force to them
Falling bodies fall at a constant rate
Heavy bodies fall faster than light ones
Galileo’s Experiment:
Objects keep moving after we stop applying a force (if no friction)
Falling bodies accelerate as they fall
Heavy bodies fall at the same rate as light ones

9. Apollo 15 astronaut David Scott

10. How do things move?….
Newton built on Galileo’s work and proposed 3 laws of motion:
A body moves in a straight line unless acted on by some force

11. How do things move?….
Newton built on Galileo’s work and proposed 3 laws of motion:
A body moves in a straight line unless acted on by some force
The acceleration of a body is proportional to the force on it
F = ma

12. How do things move?….
Newton built on Galileo’s work and proposed 3 laws of motion:
A body moves in a straight line unless acted on by some force
The acceleration of a body is proportional to the force on it
F = ma
To every action there is an equal and opposite reaction

13. Isaac Newton:
1642 – 1727 AD
The Principia:

14. Moon’s orbit
Newton worked out that the Moon feels a ‘circular’ force which balances gravity
Earth

15. Classical Physics: “All the World’s A Stage”
Newton’s physics assumes absolute space and time.
Working out how things look to different observers follows simple rules, in different reference frames

16. Classical Physics: “All the World’s A Stage”
Newton’s physics assumes absolute space and time.
Working out how things look to different observers follows simple rules, in different reference frames

17. Classical Physics: “All the World’s A Stage”
Newton’s physics assumes absolute space and time.
Working out how things look to different observers follows simple rules, in different reference frames

18. Classical Physics: “All the World’s A Stage”
Newton’s physics assumes absolute space and time.
Working out how things look to different observers follows simple rules, in different reference frames
The laws of physics are the same for everyone, everywhere!

19. Classical Physics: Maxwell’s theory of light
Light is a wave – electromagnetic radiation

20. Classical Physics: Maxwell’s theory of light
Light is a wave – electromagnetic radiation
Maxwell’s Equations imply
Speed of light = 300,000 km/s

21. Classical Physics: Maxwell’s theory of light
Light is a wave – electromagnetic radiation
Maxwell’s Equations imply
Speed of light = 300,000 km/s
But how did light propagate?……

22. Through the Ether?… Light from a distant star Earth in January Sun
Earth in July

23. 50mph
50mph
In Newton’s picture, the relative speed of the two trains is = 100mph

24. 50mph

25. 50mph
Speed of light relative to the ground faster than speed of light relative to the train

26. Through the Ether?… Light from distant stars Ether drift
Michelson and Morley devised an experiment to measure the speed of light coming from different directions

27. The Michelson and Morley Experiment would try to measure the “Ether Drift” by timing different light beams – like swimmers on a fast-flowing river
River flow

28. The Michelson and Morley Experiment would try to measure the “Ether Drift” by timing different light beams – like swimmers on a fast-flowing river . C
River flow . . A B

30. The Michelson and Morley Experiment would try to measure the “Ether Drift” by timing different light beams – like swimmers on a fast-flowing river . C
River flow
They detected absolutely no Ether Drift. Something weird was going on.
Light was not following Newton’s rules . . A B

31. Special Relativity: 1905
“Maxwell’s Equations of Electromagnetism are the same for all observers, regardless of their relative motion”

32. There must be no ether, and so no ether drift
Special Relativity: 1905
Implies the speed of light must be constant, measured to be the same by any two observers, regardless of their relative motion”
There must be no ether, and so no ether drift

33. Special Relativity: 1905
Implies the speed of light must be constant, measured to be the same by any two observers, regardless of their relative motion”
This abolished completely Newton’s idea that space and time were absolute

34. h
Train carriage
Let’s try to see why!

35. Let’s try to see why! h Train carriage
Torch beam reflected off roof of carriage h
Train carriage
Let’s try to see why!

36. Distance = speed x time h Train carriage
Torch beam reflected off roof of carriage h
Train carriage

37. 2h = c x tc Distance = speed x time h Train carriage
Torch beam reflected off roof of carriage h
Train carriage
2h = c x tc

38. Now viewed from the platform…

39. Now viewed from the platform…

40. Now viewed from the platform…

41. Now viewed from the platform…

42. Now viewed from the platform…

43. Now viewed from the platform…

44. Now viewed from the platform…

45. Now viewed from the platform…

46. Now viewed from the platform…
Let’s call the time measured on the platform tP

47. Now viewed from the platform…
Let’s call the time measured on the platform tP

48. Now viewed from the platform…
Let’s call the time measured on the platform tP

49. Now viewed from the platform…
v tP
The base of this triangle is v tP

50. v tP Now viewed from the platform…
This is an isosceles triangle, so it’s made up of two equal right angled triangles

51. Now viewed from the platform…
This is an isosceles triangle, so it’s made up of two equal right angled triangles

52. Now viewed from the platform…
This is an isosceles triangle, so it’s made up of two equal right angled triangles

53. Let’s look at this triangle. What’s the length of its base?

54. Let’s look at this triangle. What’s the length of its base?1
v tP 2
Let’s look at this triangle.
What’s the length of its base?

55. 1
v tP 2
What about its height?

56. h
Train carriage

57. h 1
v tP 2
What about its height?

58. h 1
v tP 2
2h = c x tc
Remember:

59. 2h = c x tc Distance = speed x time h Train carriage
Torch beam reflected off roof of carriage h
Train carriage
2h = c x tc

60. 1
c tc 2 1
v tP 2
2h = c x tc
Remember:

61. If both observers measure the same speed of light, c…1
c tc 2 1
v tP 2
If both observers measure the same speed of light, c…

62. If both observers measure the same speed of light, c…
Total distance = c x tP
ctS 1 2
vtm 1 2
If both observers measure the same speed of light, c…

63. If both observers measure the same speed of light, c…1
c tc 1
c tP 2 2 1
v tP 2
If both observers measure the same speed of light, c…

64. c tP c tc v tP (ctP)2 = (vtP)2 + (ctc)2 Using Pythagoras’ theorem, 1 1

65. 1
c tc 1
c tP 2 2 1
v tP 2
tc = tP
( v2 c2)

66. We need to think about a unified spacetime
It appears that time is running more slowly on the moving train!!
We need to think about a unified spacetime
tc = tP
( v2 c2)

67. Evidence for Time Dilation
Cosmic Ray
Evidence for Time Dilation
Slow moving muons, would never reach sea level…
Muons
but v = 0.999c, so muon lifetime appears to us to be greatly extended
60km
Sea level

68. 300,000 kms-1 Einstein’s Relativity
The speed of light is the ultimate speed limit in the Universe

69. Just as special relativity shows that space and time are inextricably connected, so too are energy and momentum

70. Just as special relativity shows that space and time are inextricably connected, so too are energy and momentum
Particles have a particular rest mass, which is the mass you would measure if the particle is at rest

71. Mass and energy are equivalent
Just as special relativity shows that space and time are inextricably connected, so too are energy and momentum
Particles have a particular rest mass, which is the mass you would measure if the particle is at rest
Mass and energy are equivalent
E = mc2

72. E = mc Hydrogen fusion – fuelling a star’s nuclear furnace 2
H = Hydrogen
He = Helium
E = mc 2

73. What about accelerated observers?
Einstein’s Relativity
What about accelerated observers?
How does gravity fit into this?
General Relativity: 1916

74. Isaac Newton:
1642 – 1727 AD
The Principia:

75. But how does the Moon know to orbit the Earth?
Moon’s orbit
But how does the Moon know to orbit the Earth?
How does gravity act at a distance across space?
Earth

76. Gravity in Einstein’s Universe
Gravity and acceleration are equivalent
Gravity is not a force acting through space and time, but the result of mass (and energy) warping spacetime itself

77. Gravity in Einstein’s Universe
“Spacetime tells matter how to move, and matter tells spacetime how to curve”

78. v Gravity in Einstein’s Universe
Differences between Newton’s and Einstein’s gravity predictions are tiny, but can be detected in the Solar System – and Einstein always wins!

79. v Gravity in Einstein’s Universe 1. Precession of orbits –
observed for Mercury,
matching GR prediction

80. v Gravity in Einstein’s Universe 1. Precession of orbits –
observed for Mercury,
matching GR prediction
2. Bending of light close
to the Sun – visible
during total eclipse,
measured in 1919

81. v Gravity in Einstein’s Universe 1. Precession of orbits –
observed for Mercury,
matching GR prediction
2. Bending of light close
to the Sun – visible
during total eclipse,
measured in 1919

82. v Gravity in Einstein’s Universe 1. Precession of orbits –
observed for Mercury,
matching GR prediction
2. Bending of light close
to the Sun – visible
during total eclipse,
measured in 1919

83. Gravity in Einstein’s Universe
A ‘Black Hole’ warps spacetime so much that even light can’t escape

86. Gravity in Einstein’s Universe
Close to a rotating black hole,
spacetime does very strange things:
Closed timelike loops are possible
Inside a black hole there may be a wormhole which could allow Faster than Light travel and communication
(but how do we open a wormhole?…)

87. Gravity in Einstein’s Universe

89. Einstein’s Greatest Blunder?…
What is driving the cosmic acceleration?…
Dark Energy
Einstein’s Greatest Blunder?…

90. To hold open wormholes?…
Could we use
Dark Energy
To hold open wormholes?…

91. Well, it works in Star Trek DS9!!

92. Grand Unification Theories
“The generalisation of the theory of gravitation has occupied me unceasingly since 1916”
Einstein, 1952