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## Quantum Theory

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Title: Quantum Theory

1
Quantum Theory

2
• Temperature determines the wavelength of emitted
light.
• Red hot mostly red light - 3,000 oC.
• White hot all colors 6,000 oC.
• http//www.egglescliffe.org.uk/physics/astronomy/b
lackbody/bbody.html

3
• It was assumed light could have any energy.
• The math of the theory did not match the
distribution of wavelengths observed

4
Max Planck solved the black body radiation
dilemma
• He created an equation that fit the observed
• To do so, he had to assume that energy came in
packets, called quantum.

5
Plancks Constant
• Frequency/energy Plancks constant
• Plancks constant (h) is one of the most
important constants in nature.
• (h) 6.626 x 10-34 joule seconds

6
Photoelectric Effect
• Certain light beams can knock electrons off of
some metals.
• This was independent of the intensity of the
light beam. (total energy)
• It WAS dependent on the wavelength of the light.

7
• Short wavelengths have larger quanta (packets of
energy) to knock off electrons.

8
(No Transcript)
9
Light particle or wave?
• Light followed the wave equation defined by James
Clark Maxwell.
• Light also seemed to exist as packets, like
particles.
• The particle/wave designation seems invalid for
the subatomic world.

10
Particles are also Waves
• 1923 Louise de Broglie found that matter had
both particle and wavelike properties.
• If E hc/wavelength (from Planck) and E mc2
(from Einstein), than wavelength h/(mass x
velocity).

11
• Very small particles exhibit the same wave
waves do.

12
Niels Bohr Planetary Atom
• Electrons orbit the nucleus in specific circular
orbits.
• Problem a charged particle in acceleration emits
light.
• Changing direction is a type of acceleration, yet
orbiting electrons emitted no light.

13

14
Schrodingers Solution
• The orbit of an electron can only be a whole
number multiple of the electrons wavelength.
• The orbital is a standing wave of an electron.
• There is no changing direction of the electron.

15
• The electron simply exists in these locations,
without actually moving from one point to
another.

16
related

17
Schrodinger wave equations
• Any system can be treated as a wave equation in
quantum mechanics.
• The orbitals of chemistry are solutions to
Schrodinger wave equations.

18
• Electrons materialize from one location to
another without passing a plane of zero
probability existence.
• This is just quantum weirdness.

19
Paul Diracs improvements of Schrodingers wave
equations
• He generalized the equations to relativistic
theory.
• He mathematically explained electron spin with
angular momentum.
• He postulated the existence of antimatter based
on the negative square root of Emc2.

20
Quantum Mechanics gives probabilities
• 1926, Max Born the square of the wave equation
gave the probability of finding the particle in a
given location.
• Many (Einstein) felt that probability was not
good enough.

21
• If we really understood something, we should know
what will happen and what is really going on
behind the scenes.

22
ntum-mechanics-for-dummies-electrons-are-weird

23
Heisenberg Uncertainty Principle
• We cannot know both the velocity and location of
an electron. The more we know about one, the
less we know about the other.
• High energy light gives a better location, but
disrupts the velocity.

24
• Low energy light disturbs the velocity less, but
gives high uncertainty of location. Lower energy
light gives worse resolution.
• The uncertainty of position times the uncertainty
of momentum is greater or equal to Plancks
constant divided by 4p.

25

26
Uncertainty vs. Determinism
• Uncertainty was not just a result of the
crudeness of the instruments, it was a
fundamental law of nature.
• Determinism the idea that you can state the
future if you know everything about the present.
• Einstein favored determinism, but uncertainty was
found to rule.

27
Double slit experiment
• The same results are obtained with light,
electrons, or any other type of wave.
• How does the particle going through the slit
know that the other slit exists?

28
• Since the electron, like all matter, has wave
characteristics, its final location is defined by
the probability given by the square of the wave
equation for the given system it is in.

29
Bells Theorem
• John Bell used a thought experiment and logic to
prove that reality is non-local.
• Non-local means objects are affected by distant
objects and events that cannot reach them with a
force, because they are outside of the light cone.

30
• Outside the light cone, signals or forces from
one object must travel faster than the speed of
light to create the observed behavior.

31
Quantum Entanglement
• When two particles or events affect each other
without any signal or force.
• Determinism, and our common sense, says that this
is totally impossible.
• http//calitreview.com/51

32
• Quantum mechanics predicts when it will or will
not happen, and what the probability of the
outcome will be.
related

33
Collapsing Probability Waves
• Quantum mechanics says that the measurement of a
particle, such as an electron, collapses the
probability wave to a single event.

34
• With entangled particles, the measurement of one
collapses both of their probability waves
simultaneously.
• Any interaction, human or not, collapses
probability waves.

35
related

36
Quantum Theory and the Universe
• Cause and effect gives way to probability.
• The things you do can instantaneously affect
things far away (non-local).

37
• Events can happen without a force or signal to
cause it to happen - the fabric of space allows,
or even causes it to happen.
• Objects do not always have specific properties
until they are interacted with the properties
hang in some sort of limbo.

38
The Standard Model
• This is the current quantum theory.
• Many new subatomic particles have been
discovered.
• There are three families of particles.

39
• Each family contains two of the quarks, an
electron (or one of its cousins), and one of the
neutrinos.
• These are the building blocks of all matter.

40
Four Force Particles
• Strong force The gluon holds the nucleus
together.
• Weak force The W and Z bosons cause
• Electromagnetism The photon causes light.

41
• Gravity The graviton is the cause.
• Experiments have established all force particles
except the graviton.
• Gravitons are expected to be discovered soon.

42
Standard Model Equation
• It uses an input of 19 pieces of information,
which are properties of the force and mass
particles.
• It has been flawless at predicting experimental
outcomes as probabilities.

43
• Everything that happens in the universe, besides
gravity, can be predicted by the Standard Model.
• Newtons equations fall out of Standard Model for
normal conditions.

44
Particle Behavior
• The uncertainty principle allows for extreme
particle behavior on the subatomic level.

45
• There is a trade off between the energy a
particle has and the time it takes to measure
this energy, which allows the energy of a
particle to fluctuate wildly over a very short
duration of time, called the quantum jitters.
• Tunneling is allowed.
related

46
More Unification
• Steven Weinberg and his colleagues unified the
weak and the electromagnetic forces.
• They won a Nobel Prize for this work.

47
Weaknesses of Standard Model
• It explains how nature behaves, but not why it
behaves in the way it does.
• It does not include gravity therefore, it cannot
be a complete theory of the universe.
• Its use is primarily for the subatomic level.

48
A few good web-pages
• http//www3.hi.is/hj/QuantumMechanics/quantum.htm
l
• http//www-groups.dcs.st-and.ac.uk/history/HistTo
pics/The_Quantum_age_begins.html
related
related

49