Einstein in A Nutshell
Einstein in A Nutshell
Einstein in A Nutshell
Richard Wolfson
Benjamin F. Wissler Professor of Physics
Middlebury College
Insight Cruises/Scientific American
January 15, 2011
http://newscenter.berkeley.edu/2011/12/05/record-black-holes-bigger-than-our-solar-system/, http://news.discovery.com/space/faster-than-light-speed-neutrinos-re-run-111118.html
Source (all three photos): Clark, Einstein: The Life and Times (Abrams, 1984)
1905: Photons
Relativity Principle?
Physical
Absolute
motion is meaningless
So
is I am at rest
Only statements about relative motion are
meaningful
www.virginia.edu/ims/photogallery/images/rip-tennis-ladies.jpg
www.virginia.edu/ims/photogallery/images/rip-tennis-ladies.jpg
www.virginia.edu/ims/photogallery/images/rip-tennis-ladies.jpg
~1750-1900:
In Einstein s Words
Examples
c
1
c
2
600 mph
70 mph
c
1
c
2
1
c
2
Maybe
Time is Relative
In a frame of reference
in which the light clock
is moving to the right:
Mirror
Light path
is twice this
distance
Light
path
Light source
Shorter path; same speed
LESS TIME
Clock A
Clock A
Clock B1
Clock B2
Star Trip!
0.8c
20 light years
Star Trip!
Who s right?
Both!
B: I m at rest,
A is moving,
so A runs slow
Clock B
Tennis
Space is Relative
12 light years
0.8c
0.8c
12 light years
0.8c
0.8c
Simultaneity is Relative
Who s right?
Both!
B: I m at rest,
A is moving,
so A runs slow
Clock B
Clock A
Clock B1
Clock B2
Clock A
Clock B1
Clock B2
Clock A
Clock B1
B1, B2
NOT synchronized
Clock B2
Clock A
Clock B1
Clock B2
Clock A
Clock B1
Clock B2
Clock A
Clock B2
No Contradiction!
B:
simultaneity is relative!
Free fall,
in gravity
Intergalactic Space
Uniform
motion,
no gravity
Intergalactic Space
At rest
Accelerated
So What s Gravity?
Not the heaviness you feel standing on
That can t be real because it s not there in another
reference frame (in free fall)
Einstein:
Earth
Bending of Light
Star
Sun
Earth
Gravitational Lenses
Quasar
Galaxy
Earth
Distances:
Hubble Space Telescope image from www.antwrp.gsfc.gov/
apod/image/9612/eincross_wht.gif
galaxy: 500 million ly
quasar: 9 billion ly
Hubble Space Telescope image from www.astr.ua.edu/keel/agn/qso2237.htm
A Cosmic Lens
1920s
Astrophysicists,
1998
Final Exam
Whats
a)
b)
c)
d)
e)
Bonus Material:
The Twins Paradox
Star Trip!
0.8c
20 light years
Star Trip!
Star Trip!
Star Trip!
20 light years
Simultaneity is Relative!
Events that are Simultaneous in One
Frame of Reference are Not
Simultaneous in Another Frame!
00
00
0.8c
12 light years
0.8c
16
15
09
12 light years
0.8c
25
41
12 light years
0.8c
25
0.8c
30
50
12 light years
0.8c
34
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