Natural Science Forum / Physics / Research / December 2004

Time for a new thread;), I'm reading Bjorken and Drell recently, and
it mentioned the equation of motion obtained by substitute the
relative expression of energe H = (p^2 + m^2)^1/2 by operators:
i dW(x)/dx = (-d^2/dx^2 + m^2)^1/2 W(x)

Thank you for your answer. Yes, I think you are right. The center of
gravity is probably the correct notion here. However, I still have
confused ideas on the subject. What I'm trying to understand is which
point is it, in an extended object in a (classical) gravity field,

I would appreciate if somebody knowledgeable in electron transport in
metals would help me answer the following question:
Consider a bulk metal at 0K with no defects or impurities. The only
sources of scattering of the electrons in metals are phonons, defects,

E=mc^2
and...
E^2=m^2*c^4
... are only different if there is a physical meaning to negative mass

Hi there, i am currently conducting a research on the ethical issues
regarding the field of nanotechnologies. I would like to hear from
potential experts as well as public views on whether nanotechnology
research and development brings more advantage than disadvantage with

It seems my view of the measurement of the hubble 'constant' is faulty.
I was under the impression that:
1) Distances were measured by a standard candle.
2) Redshifts were measured.

While it is well known that Feynman path integrals form a class of
solutions to the Schwinger-Dyson equations, they most definitely aren't
the most general solution.
Let me give an example:

In general, quantum systems don't decohere into mixtures of energy
eigenstates.  Sometimes it's position eigenstates, sometimes some
other basis.  I've heard the term "master equation" used in connection
with determining which is the preferred basis for a given system.  Can

Perhaps an absolutely trivial exercise, but for some reason I don't
come up with this simple problem when I have to prove it analytically.
Immagine a an extended (regular or irregular) body immersed in a
gravitational force field (not necessarily that produced by a

Recently I'm reading Streater and Wightman's "PCT, spin and
statistics, and all that". In Chapter 3, they proved that the
assumption of a definite transformation law for all the fields of a
field theory uniquely fixes the corresponding transformation on the

Photons are commonly drawn at angles other than 45 degrees in Feynman
diagrams. But photons are moving at speed c only at 45 degrees in those
diagrams. To quote Feynman "...there is also an amplitude for light to
go faster (or slower) than the conventional speed of light. You Found

The problem of quantizating of gravity can basically be stated like
this:
General Relativity, which is based on special Relativity, which exists
to make Newtonian mechanics agree with Maxwell's equations, needs to

Can the speed of light be viewed as a unitless factor?  We already
define meters in terms of seconds and the speed of light.  Couldn't we
define meters as c*i*seconds in all physical constants (where c is
unitless)?  We use "i" when solving many equations, so I don't see why

What is time?
I do not understand the concept of time in physics. It seems to me
that someone (Einstein?) said that if one could go faster than light,
one could go back in time. Now here is my doubt:

I've read about the Casimir effect and was wondering if it plays a
part in the confinement of protons and/or quarks in an atomic nucleus
as they are extremely close to each other.  Could anyone run a
calculation to estimate the force of this effect if any?