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Physics 115
“Physics for FUTURE LEADERS”
Prof. Paul Steinhardt
Princeton in the Nation’s Service
Woodrow Wilson, 1896
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Quantum
Revelation1:
Sometimeslightbehaveslikeawave....
Sometimeslightbehaveslikeaparticle....
Butneverbothatthesametime!
Quantum
Revelation2:
ThesepropertiesdonotapplyONLYtolight!
QuantumRevelation3:
Wecanonlysaywhereanelectron(orphotonor...)PROBABLYIS
F(x)
F(x)
x
x
F2(x)
F2(x)
x
x
The End of Determinism
Individual photon or electron
QuantumRevelation4:
Impossibletodeterminesimultaneouslybothposition
andmomentumofparticlesimultaneouslywithhighprecision
“HeisenbergUncertaintyPrinciple”
. (mv)>h
Δ xΔ
h=6.6x10-34 Joule-s
QuantumRevelation4:
Impossibletodeterminesimultaneouslybothposition
andmomentumofparticlesimultaneouslywithhighprecision
“HeisenbergUncertaintyPrinciple”
. (mv)>h
Δ xΔ
h=6.6x10-34 Joule-s
Note:Somepeoplethinkofthewidthfothewavefunctionasbeingthesize oftheparticle.
Ifso,particlesdonothaveaninherent“size”.Theyarewave-likeandspreadoutaccording
totheir“container”(forces)-- anelectroncanbemicroscopic(withuncertainmomentum)
Orgigantic(withcertainmomentum)
Whydoatomsexist?
Anorbitingelectronisalways
oscillatingbackandforth
Andalwaysaccelerating
QuantumRevelation5:
Quantahavespin&thespincanonlytakediscretevalues
Lightquanta(photons)and1unitofspin(bydefinition)
Quantawith1,2,3,….orzerounitsofspin
liketoclumpinidenticalstates
Electronshave½unitofspin
Quantawith½,3/2,5/2,….unitsofspin
canneverbeinidenticalstates
QuantumRevelation6:
Inmacroscopicobjects,manyquantacanactlike
incoherent combinationofwaves
(e.g.likerandomlymovingelectronsinabaseball
atfinitetemperature)
inwhichcasethebehaviorislikeNewton/Einstein
OR
Coherently,inwhichcasequantumweirdness
Isapparentonvisiblescales
(lasers/superconductors)
QuantumRevelation7:
Electrons(orparticlesorpeople...)canpass
throughsolidwalls??
QuantumRevelation7:
Electrons(orparticlesorpeople...)canpass
throughsolidwalls??
- Electroncanhavewavelikeproperties
QuantumRevelation7:
Electrons(orparticlesorpeople...)canpass
throughsolidwalls??
- Electroncanhavewavelikeproperties
- Wallsarenotsolid:theyaremostlyemptyspace
QuantumRevelation7:
Electrons(orparticlesorpeople...)canpass
throughsolidwalls??
- Electroncanhavewavelikeproperties
- Wallsarenotsolid:theyaremostlyemptyspace
U
238
238
92
92
234
90
Th
Nucleararithmetic:
Totalnumberofnucleonsisconserved: 238=====>234+4
Totalchargeisconserved:
92=====>90+2
CCDs(cameras)
1)Wave-particledualityofphotons
Semi-conductor
2)Wave-particledualityforelectrons
Transistor,light-emittingdiodes(LEDs),cell-phones,ipads,internet…
Quantumcomputers
3)Canonlysaywherequanta
probably are
Quantumcryptography
4)Heisenberguncertaintyprinciple
Lasers&
Superconductors
Tunnelingmicroscope
5&6)Quantumspin/coherence
7)Quantumtunneling
Quantum Revelations
Relativity Revelation