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Chapter S4Building Blocks of the Universe

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How has the quantum

revolution changed our world?

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The Quantum Realm

Light behaves like particles (photons). Atoms consist mostly of empty space. Electrons in atoms are restricted to

particular energies. The science of this realm is known as

quantum mechanics.

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Quantum Mechanics and

Society Understanding of quantum laws made

possible our high-tech society:

Radios and television Cell phones Computers

Internet

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What have we learned?

How has the quantum revolutionchanged our world? Quantum mechanics has revolutionized

our understanding of particles and forces

and made possible the development ofmodern electronic devices.

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S4.2 Fundamental Particles and

ForcesOur goals for learning: What are the basic properties of

subatomic particles? What are the fundamental building

blocks of matter?

What are the fundamental forces innature?

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What are the basic properties

of subatomic particles?

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Particle Accelerators Much of our

knowledge aboutthe quantum realmcomes particleaccelerators.

Smashing together

high-energyparticles producesshowers of newparticles.

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Properties of Particles

Mass Charge (proton +1, electron -1) Spin

Each type of subatomic particle has acertain amount of angular momentum, as ifit were spinning on its axis.

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Fermions and Bosons

Physicists classify particles into two basictypes, depending on their spin (measured inunits of h /2 ).

Fermions have half-integer spin (1/2, 3/2,5/2 ,). Electrons, protons, neutrons,

Bosons have integer spin (0,1,2 ,). Photons, gluons, intermediate vector

bosons,

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Fundamental Particles

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Orientation of Spin Fermions with spin

of 1/2 have twobasic spin states:up and down.

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What are the fundamental

building blocks of matter?

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Quarks

Protons and neutrons are made of quarks. Up quark (u) has charge +2/3. Down quark (d) has charge -1/3.

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Quarks and Leptons

Six types of quarks: up, down, strange,charmed, top, and bottom.

Leptons are not made of quarks and alsocome in six types. Electron, muon, tauon

Electron neutrino, mu neutrino, tauneutrino

Neutrinos are very light and uncharged.

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The Standard Model

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Matter and Antimatter

Energy of two photons can combine to create aparticle and its antimatter counterpart (pairproduction).

Insert TCP 5e Figure S4.5b

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What are the fundamental

forces in nature?

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Four Forces

Strong Force (holds nuclei together) Exchange particle: gluons

Electromagnetic Force (holds electrons inatoms) Exchange particle: photons

Weak force (mediates nuclear reactions) Exchange particle: weak bosons

Gravity (holds large-scale structures together) Exchange particle: gravitons

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Strength of Forces

Inside nucleus: strong force is 100 times electromagnetic

weak force is 10-5

times electromagneticforce gravity is 10 -43 times electromagnetic

Outside nucleus: Strong and weak forces are unimportant.

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What have we learned? What are the basic properties of

subatomic particles? Charge, mass, and spin

What are the fundamental buildingblocks of matter? Quarks (up, down, strange, charmed, top,

bottom) Leptons (electron, muon, tauon, neutrinos)

What are the fundamental forces innature? Strong, electromagnetic, weak, gravity

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S4.3 Uncertainty and Exclusion in

the Quantum RealmOur goals for learning: What is the uncertainty principle?

What is the exclusion principle?

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What is the uncertainty principle?

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Uncertainty Principle

The more we know about where a particle islocated, the less we can know about itsmomentum, and conversely, the more weknow about its momentum, the less we canknow about its location.

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Position of a Particle In our everyday

experience, aparticle has a well-defined position ateach moment intime.

But in the quantumrealm particles donot have well-defined positions.

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Electrons in Atoms In quantum

mechanics anelectron in an atomdoes not orbit in theusual sense.

We can know only

the probability offinding an electronat a particular spot.

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Electron Waves

On atomic scales, an electron often behavesmore like a wave with a well-defined momentumbut a poorly defined position.

Insert TCP 5e Figure S4.8

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Location and Momentum

Uncertainty

in location

Uncertainty

in momentum

Plancks Constant ( h)/4

=X

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Energy and Time

Uncertainty

in energy

Uncertainty

in timePlancks Constant ( h)/4

=X

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What is the exclusion principle?

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Quantum States

The quantum state of a particle specifies itslocation, momentum, orbital angularmomentum, and spin to the extent allowed bythe uncertainty principle.

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Exclusion Principle

Two fermions of the same type cannotoccupy the same quantum state at the sametime.

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Exclusion in Atoms Two electrons, one

with spin up andthe other with spindown can occupy asingle energy level.

A third electronmust go intoanother energylevel.

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What have we learned? What is the uncertainty principle?

We cannot simultaneously know theprecise value of both a particles positionand its momentum.

We cannot simultaneously know theprecise value of both a particles energyand the time that it has that energy.

What is the exclusion principle? Two fermions cannot occupy the same

quantum state at the same time.

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S4.4 The Quantum Revolution

Our goals for learning: How do the quantum laws affect special

types of stars? How is quantum tunneling crucial to

life on Earth?

How empty is empty space? Do black holes last forever?

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How do the quantum laws

affect special types of stars?

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Thermal Pressure Molecules striking

the walls of aballoon applythermal pressurethat depends onthe temperatureinside the balloon.

Most stars aresupported bythermal pressure.

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Degeneracy Pressure

Laws of quantum mechanics create adifferent form of pressure known asdegeneracy pressure.

Squeezing matter restricts locations of itsparticles, increasing their uncertainty inmomentum.

But two particles cannot be in same quantumstate (including momentum) at same time.

There must be an effect that limits how muchmatter can be compressed degeneracypressure.

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Auditorium Analogy

When the number of quantum states (chairs) ismuch greater than the number of particles(people), its easy to squeeze them into asmaller space.

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Auditorium Analogy

When the number of quantum states (chairs) isnearly the same as the number of particles(people), its hard to squeeze them into asmaller space.

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Degeneracy Pressure in Stars

Electron degeneracy pressure is whatsupports white dwarfs against gravity quantum laws prevent its electrons frombeing squeezed into a smaller space.

Neutron degeneracy pressure is whatsupports neutron stars against gravity quantum laws prevent its neutrons from beingsqueezed into a smaller space.

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Quantum Tunneling Person in jail does

not have enoughenergy to crashthrough the barrier.

Uncertaintyprinciple allowssubatomic particleto tunnel throughbarriers because ofuncertainty inenergy.

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Quantum Tunneling and Life

At the core temperature of the Sun, protonsdo not have enough energy to get closeenough to other protons for fusion(electromagnetic repulsion is too strong).

Quantum tunneling saves the day by allowingprotons to tunnel through the electromagneticenergy barrier.

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How empty is empty space?

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Virtual Particles Uncertainty

principle (in energy& time) allowsproduction ofmatter-antimatterparticle pairs.

But particles mustannihilate in anundetectably shortperiod of time.

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Vacuum Energy According to

quantummechanics, emptyspace (a vacuum)is actually full ofvirtual particle pairspopping in and outof existence.

The combinedenergy of thesepairs is called thevacuum energy.

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Do black holes last forever?

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Virtual Particles near BlackHoles

Particles can beproduced nearblack holes if onemember of a virtualpair falls into theblack hole.

Energy topermanently createother particlecomes out of blackholes mass.

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Hawking Radiation Stephen Hawking

predicted that thisform of particleproduction wouldcause black holesto evaporate overextremely long timeperiods.

Only photons andsubatomic particleswould be left.

h h l d

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What have we learned? How do the quantum laws affect special

types of stars? Quantum laws produce degeneracy

pressure that supports white dwarfs andneutron stars.

How is quantum tunneling crucial tolife on Earth? Uncertainty in energy allows for quantum

tunneling through which fusion happens inSun.

h h l d

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What have we learned? How empty is empty space?

According to quantum laws, virtual pairs ofparticles can pop into existence as long asthe annihilate in an undetectably short timeperiod.

Empty space should be filled with virtualparticles whose combined energy is thevacuum energy.

Do black holes last forever? According to Stephen Hawking, productionof virtual particles near a black hole willeventually cause it to evaporate.