To study and encourage popular interest in all branches of Science.

Newsletter April 2003

Dear Member,

Our last lecture meeting this session will be:

ANNUAL GENERAL MEETING on Thursday June 26th at 8.15 pm.

This will start with wine and cheese (2 pp), there will also be a Bring & Buy; please donate generously books, scientific instruments, cameras, tools, pictures and bottles. Bring your gifts at 8 pm if possible to be laid out. The Society's expenses have increased this year and the Council would rather see an increase in donations than in the subscription.

The AGM itself will start at 8.45 and will be followed by a Scientific Entertainment.

The agenda will include the usual reports from Officers and Sections and the Election of Officers and Ordinary Members of Council for the coming year. The Council re-appointed Professor Robert Weale to be President at its meeting on 9th April. Council also proposes the following::
Secretary Julie Atkinson
Treasurer Peter Wallis
Membership Secretary Elisabeth Fischer
Programme Secretary Jim Brightwell
Ordinary Members Brian Bond
(8 maximum) Simon Lang,
Angus McKenzie,
Eric Morgan,
Michael Sabel,
Betty Weale

Council invites further nominations to the above officer posts and ordinary members; such nominees shall be duly proposed and seconded and have agreed to serve if elected.

John Oakes has been nominated by Peter Wallis as an ordinary member, seconded by Elisabeth Fischer.

The British Association for the Advancement of Science (BA). The Council will propose at the AGM that the HSS affiliates to the BA for an experimental period of two years. The BA approached the Society last year when they were considering setting up their own branch organization. They found us, and felt what we offered was in line with their plans, so asked if we would affiliate and offer our facilities to their members. Affiliation would cost 90 per annum, inclusive of three memberships in the BA for those acting as branch liaison officers, though this would be offset by an initial grant of 250, and other HSS members could obtain membership of the BA at a discount. We would advertise BA events to our members and notify BA members in the North London area of ours on an annual basis. We would gain access to the BA's list of speakers and the contacts and experience of other branches. We should gain some kudos and possibly some new blood ourselves. There might be problems to the HSS if too many BA members attended our meetings and forced a move to larger and more expensive accommodation. Some details are still being negotiated and will be reported at the AGM.

The Craters of The Moon

A cold, clear night in Hampstead.
Walking friends back to the tube
we pass the observatory - that demi-hemisphere.

On impulse we detour up to the tiny wooden room.
Inside, two lovers drawn by the light, several scientific types
and us ... the curious intimacy
of strangers staring at stars.

The telescope pokes accusingly through a revolving roof
magnifying one hundred times
not much against the distance
but enough to show the knife-edge of ash-grey moon
against the black circumference of the universe.

Politely - even Jess hushed
we take turns to lift an eye to the skies
then relinquish our place to the next in line
because a big cloud is coming.

We push together, slide the roof around
focus in - on Jupiter: two lines of dust,
on Saturn: its rings a stiff tutu of ice,
a halo slipped down to the angel's round belly
in an infant's Christmas play.

A sudden break in the cloud
so we return to the moon:
cratered, like a child has run its finger through a ball of
still-damp clay
leaving pits and trough
... like God's fingerprint on earth.

This was left in the observatory. Its provenance is not known, but a manuscript note on it reads "Marmalade Season - Katie Campbell, Iron Press, 2003 Jan."

Dark Matter.

Last October the Society received an interesting lecture from Professor Bernard Carr on one of the most intriguing problems in Astronomy - Dark Matter. For more than 50 years astronomers have observed that the rotational velocity of stars on the periphery of spiral galaxies do not reduce with increasing distance as expected if the gravitational mass of the galaxy is that of the observed stars and dust. There appears to be a substantial additional mass extending around a galaxy that we cannot see. More recently, cosmologists have been studying the clusters and super-clusters of galaxies and find a similar situation, that the observed mass is insufficient to explain what holds them together. The majority of astronomers now believe that what we see, the 'baryonic matter', represents only some 5% of the total gravitational mass of the universe, even after allowing for some of it having disappeared into 'black holes'. There are a few who challenge this but can only do so by postulating alterations to Newton's Laws at distant times or low accelerations [1].

Inferring extra mass is all very well, but we need to propose what it is and then detect it. Could it come from the sea of photons? We now have accurate knowledge of the cosmic microwave background which is the legacy of the photons from the 'big bang'. There are plenty of them but it's estimated that they could only contribute less than a hundredth of a percent to the missing mass. The more recent photons of larger energy come from baryonic matter in the stars and are only a small fraction of stellar mass. Another possibility is the neutrino, previously postulated to have zero rest-mass. We now believe them to have some mass, see the next article, but probably not enough. Moreover photons and neutrinos are 'hot dark matter', with velocities at or close to the speed of light. As such they are unable to clump together in a way that could explain the formation of galaxies and clusters.

The best fit to the astronomical observations is some form of 'cold dark matter'; 'cold' to give it a sluggish behaviour and 'dark' because it must have very little interaction, other than gravitational, with itself and baryonic matter. The Standard Model of elementary particles offers us no candidates however, so cosmologists have sought answers from postulated extensions to the Standard Model, for example Supersymmetry. These ideas have thrown up the Z-boson and the neutralino; these are heavy particles, perhaps 100 times the mass of a proton

The hunt is now on to detect such particles, essentially looking for the recoil of an atom if struck by such a particle [2]. In particular the experiments aim at observing the annual variation produced by the orbital velocity of the earth around the sun, which will add or subtract to the sun's velocity around the galaxy. There are some dozen groups working in this field.

But even if the experiments are successful, they only relate to what is thought to be some 25% of the gravitational mass required if the universe is to be 'flat'. On the basis of the observation of an acceleration in the expansion of the universe, cosmologists postulate that the remaining 70% must be 'dark energy'! But that's a story for the future.

Solar Neutrinos.

The April 2003 edition of Scientific American claims in an article by McDonald, Klein and Wark that the solar neutrino problem has now been solved. In 1920 Sir Arthur Eddington suggested that the sun was powered by nuclear fusion, by the transmutation of hydrogen into helium, with the release of the surplus mass as energy. A by-product of such a reaction is the emission of a neutrino. The first experiment to detect them in 1967 by Davis at the University of Pennsylvania found them, but only in about half the numbers predicted. His experiments were confirmed by other groups but no reason for the discrepancy from the prediction was found.

Now, according to the 'Standard Model' of particle physics, neutrinos are mass-less neutral particles in 3 distinct 'flavours': the electron-neutrino, the muon-neutrino and the tau-neutrino, only the first of these being emitted by the sun's fusion reactions. In 1969 Gribov and Pontecorvo proposed that spontaneous 'oscillation' of the neutrinos between the flavours might explain the discrepancy [3]. If they changed during their passage through the sun (2 seconds) or the journey to earth (8 minutes), Davis's detector of only electron-neutrinos could miss many of them.

For many years 'oscillation' was merely a speculation. Now, however, the Sudbury Neutrino Observatory in Ontario, using 1,000 tons of heavy water 2km below the ground has confirmed that the neutrino oscillation does exist; their detector can measure the electron-neutrinos by deuteron absorption and separately the total flux by deuteron break-up. The total flux now agrees, it is claimed, with the solar fusion prediction. Their biggest problems are to discount the cosmic ray muons also detected, using ordinary water around the detector, and natural radio-activity in the materials.

So neutrinos, or at least some of them, have mass.

Ref 1: For example Mordehai Milgrom's Modified Newtonian Dynamics (MOND), Scientific American, August 2002Back

Ref 2: Ref. David B Cline, Scientific American, March 2003. Back

Ref 3: This requires the neutrinos to have some mass and conflicts with the 'Standard Model'. Back

Peter R Wallis

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Last updated by Julie Atkinson   28-Jan-2018