Feynman vs. Uncertainty Principle

[Frisbieinstein]

Richard P. Feynman, QED, Penguin, 1990, pp. 55-6, and 84:

�I would like to put the uncertainty principle in its historical
place: when the revolutionary ideas of quantum physics were first
coming out, people still tried to understand them in terms of old-
fashioned ideas � But at a certain point the old fashioned ideas would
begin to fail, so a warning was developed that said, in effect, �Your
old-fashioned ideas are no damn good when ��. If you get rid of all
the old-fashioned ideas and instead use the ideas that I�m explaining
in these lectures � adding arrows [arrows = phase amplitudes in the
path integral] for all the ways an event can happen � there is no need
for an uncertainty principle! � on a small scale, such as inside an
atom, the space is so small that there is no main path, no �orbit�;
there are all sorts of ways the electron could go, each with an
amplitude. The phenomenon of interference [by field quanta] becomes
very important ��

--

I have read this book, but a decade or so ago. Feynman said that
instead of the uncertainty principle one could use the principle of
least action combined with his "the particle travels all possible
paths" idea.

I am wondering how Feynman's ideas would apply in the case of Bose-
Einstein condensates. The way I understand this, this is a result of
the uncertainty principle. The momentum of each atom is known as
being very close to zero. So the location must become very
uncertain. I don't see how to do this with the all possible paths
approach. can anyone explain how Feynman would approach this without
the uncertainty principle?

[ben6993]

On Oct 12, 8:06 am, Frisbieinstein <patmpow...@gmail.com> wrote:
<snip>

In a recent strand in sci.physics.foundations, a paper by Armin Nikkhah
Shirazi: A Novel Way of 'Understanding' Quantum Mechanics, has a
reference to videos of lectures in 1979 by Richard Feynman. In these
four videos, Feynman explains QED to a lay audience giving frequent
examples illustrating how probabilities are calculated. Each video is
about 90 minutes.

http://vega.org.uk/video/programme/45
http://vega.org.uk/video/programme/46
http://vega.org.uk/video/programme/47
http://vega.org.uk/video/programme/48

I have watched three of them in the last few days. Being intended for a
lay audience made them especially interesting for me, as a non-
physicist.

I suspect that in a BEC chamber the number of possible paths is greatly
reduced compared to normal space in a laboratory. In a normal space in
a laboratory the probability of a photon arriving at a point is based on
lots of alternative paths with slightly different time durations from
one another. And that should allow a finely graduated probabilities at
that point compared to nearby points. Ie interference effects could
arise that are easily measurable as we can (say) put a screen up to see
the interference bands. But in a BEC chamber, I guess, there are fewer
possible paths. So there are fewer graduations of time differences in
the paths leading to that point, compared to a nearby point. Ie there
should still be interference effects but more like building up a pattern
on a screen one photon at a time. In a normal lab space, more photons
arriving could complete a sharp fringe pattern. But in a BEC, I
speculate that more photons should not build a sharpe fringe pattern as
there are too few paths available. But this may be too naive a view.

[herbert...@gmail.com]

Do you know what the sum of all paths means? Why Feynman used it to
answer two slits.

TreBert