Transcript Open Questions in Physics

Open Questions in
Physics
Tareq Ahmed
Research Assistant
Physics Department, KFUPM.
7, Jan. 2007
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The job of a theoretical
physicist is to try to find the
right answers for the good
questions.
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Typical Questions
1. Where and what is dark matter?
2. How massive are neutrinos?
3. What are the implications of neutrino mass?
4. What are the origins of mass?
5. Why is gravity so weak?
6. Why is the universe made of matter and not antimatter?
7. Where do ultrahigh-energy cosmic rays come from?
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Outline
• Classical Mechanics
• Quantum Mechanics
• The Theory of Radiation
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Classical Mechanics
• Indeterminate behavior in the collisions
of point particles.
Before
v
After
v
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Before
v
After
v’
θ
θ
v’
Conservation of Kinetic Energy
0.5 m v2= 2*0.5 m v’2
Conservation of linear momentum
m v= 2*m*v’ * cos(θ)
 v'  v / 2
   45
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•Three equations
Conservation of Energy (1)
Conservation of Momentum (2)
•And Four parameters !!
(
v1 ' , v 2 ' ,1 ' , 2 '
)
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The interaction between the particles
have to be included to treat collisions
between point particles. The laws of
classical mechanics alone are not
sufficient.
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Quantum Mechanics
( A theory of observers)
Anyone who is not shocked by quantum
theory has not understood it. -Niels Bohr
I think I can safely say that nobody
understands quantum mechanics. -Richard
Feynman
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The Wavefunction
A reality or a computational tool?

Schrodinger
Wavefunction:
Dirac Spinor
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A single wavefunction of the
Universe!
What is it?
If [quantum theory] is correct, it signifies the end of
physics as a science. Albert Einstein
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The Concept of Superposition
• Any model for the particle (or system)
being in a superposition of different
eigenstates?
  a1 1  a2  2  a3  3  ...
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The Collapse of the
wavefunction
The "spooky action at a distance."
• How does the wavefunction collapse
upon measurement?
  a1 1  a2  2  a3  3  ...
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The theory of quanta can be likened to a medicine that14
cures the disease but kills the patient. Hendrick Kramers
Violation of the conservation of Energy
Conserved or not conserved? This is the question !
•The uncertainty principle allows
conservation of energy to be violated for
a very short period!
hw
hw0
•Photons of frequencies not resonant with
the atomic transition frequencies can still
excite the atom for a very short periods !!
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Quantum Tunneling
How long does a particle take to tunnel through a quantum
barrier?
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Electron positron creation in
vacuum
e
e+
e
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The Nature of Quantum Jumps
Are there quantum jumps ?
"If we have to go on with these damned
quantum jumps, then I'm sorry that I ever got
involved!” E.Schrodinger
• Do there exist phenomena that are truly
spontaneous? Or do all phenomena, when
investigated in depth, turn out to be
deterministic?
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Quantum Mechanics and Randomness
Does Randomness Exist?
• What is the source of randomness in
quantum mechanics?
• Can the world be deterministic but only
our description is indeterminist?
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How does an electron absorb a
photon? Any physical picture?
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Why doesn’t the electron in1s
state fall on the proton?
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The Most Beautiful Experiment
in Physics
"We choose to examine a phenomenon which is
impossible, absolutely impossible, to explain in any classical
way, and which has in it the heart of quantum mechanics.25In
reality, it contains the only mystery.“ R.Feynman
Fundamental Constants in
Physics
How Many?
• What is the number of the truly
fundamental constants
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The identity of particles
Do quarks have a well defined identity?
T he particle:
0
mass :135 MeV
No.of quarks : 2
1
wavefunction :
(uu  dd)
2
•"If you cannot - in the long run - tell everyone what
you have been doing, your doing has been
worthless." - Erwin Schrodinger, Science and
Humanism
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And the result…..
"I don't like it, and I'm sorry I ever had
anything to do with it." - Erwin
Shrodinger, speaking about quantum
mechanics
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The Theory of
Radiation
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Why two fields to describe the force
between moving charges?
• No single expression that describes the
force between two charges in arbitrary
motion.
q1
v1
v2
r
Gauss
q2
What is the nature of magnetic fields?
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The Quantization of the
Electromagnetic Field
H em
1 2 1
 E  H 2
2
2
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How can a constant electric
field be represented in terms of
photons??
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Vacuum Fluctuations
So much fluctuations!!
Is this a beautiful universe?
• Any model better than vacuum fluctuations?
• Each theory has its own vacuum!!
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How Are Photons Produced?
1. Electron Positron Annihilation
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2. Transition between different atomic states
3. Transition between different vibrational
or rotational modes of molecules
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4. Charge acceleration
e.g, Cyclotron radiation
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Any pattern to unify all these
processes?
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Conclusion
Behind it all is surely an idea so
simple, so beautiful, that when we
grasp it - in a decade, a century, or
a millennium - we will all say to
each other, how could it have been
otherwise? How could we have
been so stupid for so long? - John
Archibald Wheeler
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Acknowledgment
I would like to thank Dr. Hucine
Bahlouli, Dr. Abdulaziz Aljalal and
Abdallah Baziyad for their valuable
comments
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Questions