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From: kosower@harvard.UUCP (David A. Kosower)
Newsgroups: net.physics
Subject: "Fifth" force.
Message-ID: <621@harvard.UUCP>
Date: Thu, 16-Jan-86 19:07:30 EST
Article-I.D.: harvard.621
Posted: Thu Jan 16 19:07:30 1986
Date-Received: Sat, 18-Jan-86 08:17:09 EST
Organization: Aiken Comp Lab, Harvard
Lines: 94


    There might possibly be a "fifth force", or sixth force, or
all sorts of other strange things we can't yet measure, but in my
opinion (and the opinion of others around here), none are revealed
by the article of Fishbach et al. which appeared in the January 6
issue of Physical Review Letters.  As I will detail below, the
article is so hopelessly riddled with errors that the only sensible
thing at the moment is to pay no attention to it at all.  Don't
be misled by the eagerness with which the popular media have latched
onto the story; NOTHING has been discovered yet.

    The article refers to three different experiments: a set of
measurements by an Australian geophysicist of the gravitational
constant in an mine Down Under;  the old Eotvos (spelling with
accents: E\"otv\"os) torsion-balance experiment;  and kaon
experiments at Fermilab.  The authors claim that (a) all three
experiments show unexplained anomalies (b) these anomalies can
be explained in terms of a new force, similar in nature to
electromagnetism, but much weaker (indeed, weaker than
gravity), and coupling to a different kind of charge, which
they dub ``hypercharge''.  The first of these claims is dubious,
and the second is incorrect.

    The first thing that struck me, upon reading the article, is
that the geophysical data they quote show an effect only at one
standard deviation; with two-standard deviation error bars, the
effect disappears.  Normally, three or four standard deviations'
significance are necessary before anyone will take the data seriously.

    Upon closer examination, the paper reveals itself to be internally
inconsistent; the magnitude of the effect supposedly indicated by geophysical
experiments is 20 times smaller than that indicated by their re-analysis of
the old Eotvos experiment.  This discrepancy is NOT going to be explained by
local variations in the Earth's composition or any of the approximations they
have made in modelling the shape of the earth; one might believe a factor 
of 2, but not 20.  If the geophysical data give the right order of magnitude,
then the error bars in Eotvos's data must be larger than he indicated (which
there is reason to believe anyway), and NO effect at all can be extracted
from the his data.

    Fishbach et al. also choose to disregard a later experiment by
J. Renner (performed in the early 30's; the last Eotvos experiment
was done in 1909).  Renner did his statistical analysis incorrectly;
but once one corrects for this (as R. Dicke has done), there is no
reason to believe the Eotvos experiment more than the Renner one.
The reason they disregard the Renner experiment is obvious, however,
once one plots his data: the later experiment is consistent with
absence of any effect, and not consistent with the existence of
a "fifth" force as supposedly seen in Eotvos's data.

   The really damning thing about their re-analysis of the Eotvos
experiment, however, is the fact that the data indicate an effect of the
OPPOSITE sign, i.e. attractive, if they indicate any effect at all!
As a plot in the article shows, the total acceleration of an object
towards the Earth INCREASES as the baryon number (which is the same as
``hypercharge'' for ordinary matter) per unit mass increases.  
But a repulsive force would have the opposite effect, since the Earth
contains lots of baryons.  So the factor of 20 aluded to earlier isn't
merely 20, it's -20!

    None of us have bothered to look in detail at the supposed
"anomalous" effects in the kaon system; but I for one doubt the
effect they claim to be seeing is a genuine anomaly.

   The idea of this particular kind of "fifth" force is an old one, 
first proposed in 1964 by Bernstein, Cabibbo, and Lee to explain
a then-new observation of certain kinds of rare kaon decays (they
are actually due to the violation of time-reversal invariance).
It didn't last long; Weinberg quickly showed that as originally
proposed, the idea was completely inconsistent with particle-physics
data.  It was then deservedly discarded, until ``resurrected'' on
extremely shaky grounds by Fishbach et al.

    All in all, it's unfortunate that the popular media (NY Times,
Time magazine) have lent so much exposure to proposals of such
dubious merit.  To say that these proposals have "jolted physics",
as Bob Alpert (alpert@chovax.DEC) read in the Jan. 12 issue of
the Philadelphia Enquirer is just plain silly.

    To those who are interested in more details on Eotvos-type experiments,
I recommend two articles by R. Dicke.  One, in the December 1964 issue
of Scientific American, is a gentle, non-technical introduction, while
the other, in an issue of Annals of Physics from the same year, is
more technical, and goes into great depths about the sources of noise
and error one has to worry about in experiments of this sort.  The
experiments are quite difficult, which is undoubtedly one reason they
have not been repeated more frequently in the last 50 years.

    I should note that although many of the above observations were
made by others here (Andrew Cohen, Sidney Coleman, Sheldon Glashow, 
Aneesh Manohar, Greg Moore), any inaccuracies are due solely to me.

                                  David A. Kosower
                                  kosower@harvard.Harvard.Edu