[General] Casimir and van der Waals

[Andrew Meulenberg]

Dear John W,

Re: Van der Waals and Casimir.

I know that you didn't have space for the whole story and I do not think it
rare that two different models describing the same mechanism turn out to be
identical (e.g. Heisenberg &  Schrodinger representations); nevertheless,
it is a very interesting story. I do not know enough about either Casimir
or vdW mechanisms to see thru the details, but Martin's comment about the
zeroth-order approximation of the material addressed one of my questions.
How did dielectrics compare with conducting plates (e.g. just sequentially
reversing orientation of 1st surface mirrors after comparing blanks and
double-sided mirrors)? I might think that test could provide a 1st order
effect. The next step in this direction would be to change the environments
to one better known. What happens in the two models and experiment (with
the 1st surface mirror sequence) when the external environment is dominated
by introduction of mono-energetic light from a laser? I believe this is a
case where the two models would also differ.

David's suggestion of testing spin (and other dynamic) effects is good, but
more difficult to implement.

I don't have time to look into these details, but I would also love to have
a quick look at conclusions from a recent survey source more definitive
than Wikipedia. However, that source does compare the more-narrowly-defined
vdW & Casimir effects as "The *London*-van der Waals forces are related to
the Casimir effect for dielectric media, the former being the *microscopic*
description of the latter bulk property."

Andrew
_________________________________________

Right ....

Van der Waals and Casimir.

There are hundreds of published, peer reviewed, papers out there purporting
to have measured the Casimir force. I have not read all of them and some of
them may well be right. Many of these are "me too" papers confirming
someone else's results. Others are papers showing an agreement between the
forces measured and the calculations for the Casimir force.

So why, then, do I think that most of these guys have been wasting their
time?

That is down to a couple of friends of mine Philipp Steinmann and John
Weaver (cheers)- as well as many other excellent people in nanoelectronics
in Glasgow who made the experiment possible in the first place.  I'll copy
this to Philipp for comment - though he now works in another field. It also
comes from, for me, to some understanding of the basic physics due (partly)
to an excellent collaboration with Casimir himself many years ago.

The Glasgow guys are seriously excellent set of experimental physicists -
with the proper integrity to see things for what they truly are. Casimir
was a pleasure to meet and work with. One of the smartest people it has
been my pleasure to interact with.

Yes, indeed, the van der Waals force dependence depends on the
configuration, as you say David. So does the Casimir force.

John Weaver, Philipp and others, considered measuring the Casimir force
using their atomic force microscope (AFM), one of the best in the world at
the time. I'm telling you - these guys are good. Easy experiment - plenty
of sensitivity - direct measurement -no messing around. Just do it. Indeed,
the experiment showed, as have countless others,  a force as predicted by
Casimir. Job done? no!

What about other possible forces such as the Van der Waals force?

I think it was Philipp who did most of the work here (corrections guys?).
He calculated it and found it was virtually the same as the Casimir force,
with the same dependence and the same constants.

Consider, for a moment, the two scenarios ...

One, Casimir. Two parallel mirrors in a vacuum. Excluded QM modes.

Two. vd Waals. Two parallel conductors in a vacuum. Electron wave-function
overlaps.

Oh dear: mirrors are conductors ...

Think about it: it is the same physical problem. Different boundary
conditions. Same answer.

Surprise?

These guys had the integrity to drop this at that point. Qudos.  Question
is, can one trust others to do as good a job?

Now, any paper on "measuring the Casimir force" had, for me, better do a
damn good job on the van der Waals force as well. There may be such a paper
now. This was not the case for the first few dozen I looked at though.
Phillipp? John? anyone else?  Please let me know.

Regards, John W (the other one).
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