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Richard Feynman, 1918-1988
Welcome back
to 8.033!
Summary of last lecture:
• Atomic physics
• Nuclear physics
Image courtesy of Wikipedia.
Image courtesy of Wikipedia.
122 n
m 103 n
m 97.3
nm95.0 nm 93.8 nm
656 nm486 nm
434 nm410 nm
1875 nm
1282 nm
1094 nm Paschen series (infrared)
n = 5
n = 4
n = 3
n = 2
n = 1
n = 6
Lyman series (ultraviolet)
Balmer series (visible)
Figure by MIT OCW.
E big -> λ small
Image courtesy of Wikipedia.
MIT Course 8.033, Fall 2006, Lecture 13Max Tegmark
Today’s topics:• Particle physics
• The greatest unsolved problems in physics
Particlephysics
CERN particle accelerator
Image courtesy of Wikipedia.
Lin
ear
part
icle
acc
eler
ator
(F
erm
ilab)
Image courtesy of Wikipedia.
How derive curvature radius of particle tracks?
Figure by MIT OCW.
Courtesy of CPEP. Used with permission.
WHY?
The Standard Model Lagrangian
(From T.D. Gutierrez)
L=
Cmbgg OmOlSt
anda
rd m
odel
par
amet
ers:
Cos
mol
ogy
Parti
cle
phys
ics
Required
Optional
C = h = G
= kb = q
e = 1−
Cmbgg OmOl How measure?
Stan
dard
mod
el p
aram
eter
s:C
osm
olog
yPa
rticl
e ph
ysic
s
Required
Optional
Why these values?
Cmbgg OmOl
Cmbgg OmOl
More energy
Less energy
α β γ
Over 22.6 meters, the gravitational redshift is only 5x10-15, but the Mössbauer effectwith the 14.4 keVgγ−ray from iron-57has a high enough resolution to detect that difference.
Harvard Tower Experiment(Pound & Rebka 1960)
Gamma photons launched upward
Gamma photons dropped
57Fe Source
57Fe Source
57Fe Detector
57Fe Detector
22.6 m 22.6 m
Figure by MIT OCW.
Image courtesy of NASA and the ESA.
More energy
Less energy
UNSOLVED
PROBLEMS
• Where do the “constants” come from? Why 3+1 dimensions?
• Is there a quantum gravity TOE? (M-theory? Black hole evaporation?)
• Proton decay?
• SUSY?
• Higgs?
• Neutrino properties?
• Dark energy?
• Dark matter?
• Inflation?
UNSOLVED PROBLEMS:
PREDICTINGPARAMETERS
It's tough to make predictions, especially about the future.
Yogi Berra
Mass of Earth 5.9742×1024 kg
Semimajor axis of Earth’s orbit
149,597,870,691 m
Mass of electron 9.10938188×10-31
kgBohr Radius of Hydrogen atom
5.29177x10-11 m
Parameter status?
Mass of Earth 5.9742×1024 kg
Semimajor axis of Earth’s orbit
149,597,870,691 m
Mass of electron 9.10938188×10-31
kgBohr Radius of Hydrogen atom
5.29177x10-11 m
Parameter status?
EnvironmentalEnvironmental
Fundamental?
Fundamental?
Kepler, Newton
Classical Physics
Landscape + Inflation
Level IV Multiverse?
Effective Laws ("Bylaws", "Initial conditions")
Planets are sphericalOrbits are circular
Initial matter distribution (Aµ, Jµ, ψ, ....)
SU(3)xSU(2)xU(1) symmetryDimensionality of spaceConstants (α, ρ , ...)V
TOE equations
FUNDAMENTAL LAWS
Figure by MIT OCW.
What are the 4 multiverse levels like?
1) Same effective laws of physics, different initial conditions
2) Same fundamental laws of physics, different effective laws
3) Nothing qualitatively new
4) Different fundamental laws of physics
Three little numbers:
R~ 1/mpαβ
M~ mp
Weisskopf 1975Carr & Rees 1979
Atom
AsteroidR~ 1/α1/2β1/2mp
2
M~ α3/2β3/2 /mp2
The Earth
R~1/mp2α1/2β
M~ α3/2 /mp2
Weisskopf 1975Carr & Rees 1979
R~ 1/mp3/2α3/4β
M~ α3/4 /mp1/2
Carr & Rees 1979
Mt. Fuji
M~ 1/mp2
Weisskopf 1975Carr & Rees 1979
Image courtesy of NASA.
R~ α3β /mp3β3/2
M~ α5 /mp3β1/2
Carr & Rees 1979
Image courtesy of Wikipedia.
R~ 1/mp5
M~ 1/mp5
Carr & Rees 1979
The known universe
Cmbgg OmOl
Bas
ed o
n C
arr &
Ree
s 197
9,B
arro
w &
Tip
ler1
986
Inside
black
hole
Below quantum
limit
Cmbgg OmOl
Bas
ed o
n C
arr &
Ree
s 197
9,B
arro
w &
Tip
ler1
986
Inside
black
hole
Below quantum
limit
Fine-tuning? NO!
Figure 4 from Tegmark, “Is `the theory of everything' merely the ultimate ensemble theory?”http://arXiv.org/abs/gr-qc/9704009
Most spectacular fine tunings known:
•Dark energy density
•Higgs VEV
Cmbgg OmOl
Agr
awal
, Bar
r, D
onog
hue
& S
ecke
l199
8, P
RL, 8
0, 1
822
• v/v0<0.5: protons (uud) decay into neutrons (udd)•v/v0<0.8: diproton & dineutron• v/v0=1: we are here• v/v0>2: deuterium unstable• v/v0>5: neutrons (udd) unstable even in nuclei• v/v0>103: protons (uud) decay to Δ++ (uuu)
Effect of Higgs VEV v=246 GeV:
Courtesy of Physics Review Letters. Used with permission.
α+ α →8Be8Be+ α →12C12C+ α →16O
Figure 1 from Oberhummer, Csoto & Schlattl, “Stellar production rates of carbon and its abundance in the universe.” http://arXiv.org/abs/astro-ph/0007178
4 effective spatial dimensions: no stable orbits, no stable atoms(Ehrenfest 1917; Tangherlini 1963)
Figure 6 from Tegmark, “Is `the theory of everything' merely the ultimate ensemble theory?”http://arXiv.org/abs/gr-qc/9702052
Figure 7 from Tegmark, “Is `the theory of everything' merely the ultimate ensemble theory?”http://arXiv.org/abs/gr-qc/9702052