welcome back to 8.033! · image courtesy of wikipedia. image courtesy of wikipedia. 122 nm 103 nm...

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