Natural Science Forum / Physics / Research / May 2005

I'm looking at Wald's book on QFT in curved spacetime. In section 4.6 he
talks about the definition of the stress-energy tensor. It is defined by
a product of two field operators at the same spacetime point. Since the
field operators are actually operator valued distributions, this ...

There is a posting about this topic:
Length of wavetrain of a single phot
<http://www.lns.cornell.edu/spr/1999-03/msg0015180.html> =20
"How do I calculate the number of photons in a given wavepacket coming

Dear Members,
In Late Sakurai's " Modern Quantum Mechanics", in the description of
Stern-Gerlach experiment, you read "Because the atom as a whole is very
HEAVY, we expect that the CLASSICAL CONCEPT of trajectory can be

Dear Members,
why the square matrix representation of an observable operator A is
diagonal?
cheers,

Dear Members,
On p.18 of Sakurai's "Modern Quantum Mechanics" we read " ...
by asserting that the whole ket space is spanned by the eigenkets of A,
the eigenkets of A must therefore form a complete set by *Construction*

Suppose we discretize a scalar field \phi on a finite lattice and
quantize it. How do we set boundary conditions for the discrete field
operators? Specifying \hat\phi_i = 0 breaks the canonical commutation
relations. Do we set the conditions on the expectation values,

Dear Members,
why in Stern-Gerlach experiment, one of the poles should have a very
sharp edge?
regards,

i've been looking into the NIST site on their standard expression of the
time:
     http://tf.nist.gov/pubs/bulletin/leapsecond.htm
this brings me back several decades when i was a young ham radio operator

Dear Friends,
We now that's a problem when we work in Quantum Mechanics with
Relativity. It's like a paradoxal situation that one works only if the
influences of the other is not near of it.

Also available at http://math.ucr.edu/home/baez/week215.html
April 15, 2005
This Week's Finds in Mathematical Physics - Week 215
John Baez    

The Physics FAQ has a page on Olbers paradox at
http://math.ucr.edu/home/baez/physics/Relativity/GR/olbers.html
As far as it goes the FAQ is OK, but there is another
possibility which is totally ignored. Although the old

This might sound like a science fiction, but Nottingham scientists can
control the amount of gravity a body experiences. They have recently
demonstrated for the first time how mixtures of oxygen and nitrogen in
the liquid and gaseous states provide sufficient buoyancy to levitate a

There was an experiment in which a beam of photons was split and
detectors placed in the two paths.  Few simulateous detections were
found.
My question is: shouldn't the Uncertainty Principle obscure the

For a Lagrangina, we can perform the one loop calculations and
renormalization to get the one loop results. If we have the one-loop
effective potential, can we perform tree level calculations with this
potential to get the same loop results in the original theory?

I always here how, under rotation, a spin 1/2 particle doesn't return to
its origin state until the rotation angle is 4\pi. Mathematically this
is no problem for me being just some facts stemming from the 2-forld
cover of the Lorentz group, but what does this rotation mean ...