Transcript Quantum Theory

Quantum Theory
Black Body Radiation
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/astrono
my/blackbody/bbody.html
It was assumed light could
have any energy.
The math of the theory did
not match the distribution of
wavelengths observed:
Max Planck solved the black
body radiation dilemma
He created an equation that fit
the observed distribution of
radiation.
To do so, he had to assume
that energy came in packets,
called quantum.
Planck’s Constant
Frequency/energy = Planck’s
constant
Planck’s constant (h) is one of
the most important constants
in nature.
(h) = 6.626 x 10-34 joule
seconds
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.
Short wavelengths have larger
quanta (packets of energy) to
knock off electrons.
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.
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).
Very small particles exhibit the
same wave addition and
cancellation characteristics as
waves do.
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.
http://www.youtube.com/watch?v=45KGS
1Ro-sc&NR=1
Schrodinger’s Solution
The orbit of an electron can
only be a whole number
multiple of the electron’s
wavelength.
The orbital is a standing wave
of an electron.
There is no “changing
direction” of the electron.
The electron simply exists in
these locations, without
actually moving from one point
to another.
http://www.youtube.com/watch?v=Fw6dI7
cguCg&feature=related
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.
Electrons materialize from one
location to another without
passing a plane of zero
probability existence.
This is just quantum
weirdness.
Paul Dirac’s improvements of
Schrodinger’s 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 E=mc2.
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.
If we really understood
something, we should know
what will happen and what is
really going on “behind the
scenes”.
http://www.twine.com/item/11wp44xsgxx/youtube-quantum-mechanics-fordummies-electrons-are-weird
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.
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 Planck’s constant divided by
4p.
http://www.youtube.com/watch?v=KT7xJ0t
jB4A
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.
Double slit experiment
The same results are obtained
with light, electrons, or any
other type of “wave”.
http://www.youtube.com/watch
?v=DfPeprQ7oGc
How does the particle going
through the slit “know” that the
other slit exists?
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.
Bell’s 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.
Outside the light cone, signals
or forces from one object must
travel faster than the speed of
light to create the observed
behavior.
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
Quantum mechanics predicts
when it will or will not happen,
and what the probability of the
outcome will be.
http://www.youtube.com/watch
?v=Jh8uZUzuRhk&feature=rel
ated
Collapsing Probability Waves
Quantum mechanics says that
the measurement of a particle,
such as an electron, collapses
the probability wave to a single
event.
With entangled particles, the
measurement of one collapses
both of their probability waves
simultaneously.
Any interaction, human or not,
collapses probability waves.
http://www.youtube.com/watch?v=9lOWZ0
Wv218&feature=related
Quantum Theory and the
Universe
Cause and effect gives way to
probability.
The things you do can
instantaneously affect things
far away (non-local).
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.
The Standard Model
This is the current quantum
theory.
Many new subatomic particles
have been discovered.
There are three families of
particles.
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.
Four Force Particles
Strong force – The gluon holds
the nucleus together.
Weak force – The W and Z
bosons cause radioactivity.
Electromagnetism – The
photon causes light.
Gravity – The graviton is the
cause.
Experiments have established
all force particles except the
graviton.
Gravitons are expected to be
discovered soon.
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.
Everything that happens in the
universe, besides gravity, can
be predicted by the Standard
Model.
Newton’s equations fall out of
Standard Model for normal
conditions.
Particle Behavior
The uncertainty principle
allows for extreme particle
behavior on the subatomic
level.
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.
http://www.youtube.com/watch?v=
6LKjJT7gh9s&feature=related
More Unification
Steven Weinberg and his
colleagues unified the weak
and the electromagnetic
forces.
They won a Nobel Prize for
this work.
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.
A few good web-pages
http://www3.hi.is/~hj/QuantumMechanics/q
uantum.html
http://www-groups.dcs.stand.ac.uk/~history/HistTopics/The_Quantu
m_age_begins.html
http://www.youtube.com/watch?v=yLprHM
q4ZkM&feature=related
http://www.youtube.com/watch?v=XEZtw1
yt8Kc&feature=related
http://www.youtube.com/watch?v=1_HrQV
hgbeo&feature=related
LAC collider
http://www.youtube.com/watch?v=1_HrQV
hgbeo&feature=related
Quark song
http://www.youtube.com/watch?v=U0kXk
WXSXRA&safety_mode=true&persist_saf
ety_mode=1
????? Wild possibilities or
psudoscience?
http://www.youtube.com/watch?v=fLLIkTo
4KLc