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

Newsletter December 2003

Dear Member,

On behalf of the Council, I send you Christmas Greetings.

HSS Lecture Meetings in the Crypt Room at St John's Church, 8.15 pm.

December 11th Sea Level Change, Old and New by Professor Michael Tooley of Durham University.

January 22nd Machine Minds, What do they tell us about the real thing? By Professor Igor Aleksander of Imperial College.

February 19th Dinobirds by Dr Angela Milner of the Natural History Museum.


Doug Daniels

It was, I believe, Iain Nicholson who, at a lecture to the H.S.S, some years ago, described the Universe as "rather like a pint of beer", the froth on the top representing all the matter that we can see and the greater volume of the 'beer' beneath, representing the 'Missing Mass' - the major constituent of the Universe that we cannot see. That oblique reference to the product of the brewers' art may now be even more appropriate. Was it not the purveyors of that well known brew - Guinness, who described their product as 'Dark Energy'? It now seems that 'Dark Energy' is the new 'force majeure' in cosmology.

If we accept the standard model of an expanding Universe created from an initial hot 'Big Bang' and we can determine the rate of expansion, we should be able to calculate its approximate age and deduce a pattern for its evolution and ultimate fate. There are three possible outcomes:

(1) The Universe will continue to expand forever as predicted in the 'Open Universe' model. In the course of time, with increasing entropy, the stars will eventually use up all their fuel, cool, fade and die in accordance with the laws of thermodynamics. Such a Universe is described as having 'negative curvature', it is usually depicted as a 'saddle shape' on which parallel lines diverge.

(2) It will stop expanding at some point as predicted by the 'Closed Universe' model and then possibly begin to contract again back to its point of origin to end in a 'Big Crunch'. This model is harder to swallow as it involves a reversal of the 'Arrow of Time' and is not consistent with the laws of thermodynamics. Described as having 'positive curvature', this model can be visualised as a sphere on which parallel lines converge.

(3) It will remain more or less 'Flat', a condition where the expansion rate of the Universe is equal to its escape velocity. Visualised as a flat plane, parallel lines will always remain parallel, so this model at least conforms to the principals of Euclidean geometry.

In the theory of General Relativity, Einstein states that "Matter tells space how to curve" and whether the Universe is 'Open', 'Closed' or 'Flat,' depends upon the 'Mean Density' of matter and energy. If this density exceeds an amount known as the 'Critical Density', the Universe will be 'Closed', if less it will be 'Open'. If equal, it will be 'Flat'.

To determine which of these three models is correct, it would help if we knew the total mass of the Universe. It is here that we run into difficulty. Observations of the behaviour of galaxies in galactic clusters, for example, indicate an overall mass for the cluster as much as ten times that of the luminous matter which we are able to see. This differential has been described as the 'Missing Mass.' It has been suggested that the 'Missing Mass' could be accounted for by the presence of dark matter and that this might exist in two possible varieties: 'Cold Dark Matter' and 'Hot Dark Matter'.

Cold Dark Matter may exist in the form of exotic elementary particles called WIMPS, short for Weakly Interacting Massive Particles, particles that interact only weakly with radiation and matter. Early in the history of the Universe, such particles may have clumped together to begin to build the framework for the formation of larger structures like galaxies.

Hot Dark Matter particles are believed to possess large random velocities and could include such particles as neutrinos, if they actually possessed a small mass. These particles would predominate during the decoupling era of matter and radiation and would build large scale structures first which would ultimately fragment to form clusters of galaxies. Such theories for an evolution of a Universe modelled on the existence of either hot or cold dark matter remain unproven.

Some of the 'Missing Mass' might be accounted for by less exotic materials. Cold dwarf stars, dead stellar remnants, neutron stars and black holes, are examples of objects called 'MACHO's' - Massive Astrophysical Compact Halo Objects, believed to exist in a vast roughly spherical halo surrounding our galaxy and, by inference, other galaxies as well. It has been postulated that as much as 90% of a galaxy's mass might consist of such material in the halo.

In whatever form it exists, there can now be no doubt that the Universe contains far more dark matter than luminous matter and there is evidence that the total density is still less than 30% of the 'Critical Density' required for a 'Closed Universe.'

Recent detailed examination of the Cosmic Microwave Background (CMB) in 2001 by the Wilkinson Microwave Anisotropy Probe (WMAP), has indicated a new composition and age for the Universe. WMAP has plotted temperature fluctuations in the CMB down to one millionth of a degree. These fluctuations are a kind of 'fossil record' of density fluctuations that existed in the early Universe just 380,000 years after the initial 'Big Bang'. Observed as irregular patches they vary in size according to the curvature of space. Experiments carried out by WMAP seem to indicate that the Universe is in fact 'Flat' i.e. it has zero curvature and is 13.7 billion years old. It appears to be composed of 4% Baryonic Matter (the atoms which make up everything), 23% Dark Matter and 73% Dark Energy.

So what is this 'Dark Energy' that now appears to dominate our Universe? At this juncture, it is safe to say 'nobody knows!' But there is evidence from another source to suggest that it does actually exist - from a recent observation of a type 1a Supernova.

Type 1a Supernovae occur when a White Dwarf, which is part of a binary star system, draws off material from its companion star and in so doing increases its mass to a critical level. At this point it is destroyed in a violent explosion of energy. As there is a close relationship between the mass and luminosity of such stars when they become Supernovae, it is possible to determine their distance from observations of their observed and predicted luminosities. Such events occur from time to time in distant galaxies and therefore the distance of the galaxy itself can be calculated. As the mean density and curvature of space will affect the relationship between the red shift and brightness of such Supernova outbursts, observations of such events can provide valuable information on the rate of expansion of the Universe. Recent examination of the red shift and luminosity of a type 1a Supernova in a very distant galaxy, the furthest so far observed, seem to indicate that the expansion rate of the Universe is increasing and not as we might expect, decreasing with time. It is as if some repulsive force is at work acting against gravity. It must be borne in mind that this conclusion is derived from a single observation, but its conclusion is, nevertheless, supported by the results obtained from WMAP.

When the concept of an expanding universe was first proposed, it did not appeal at all to Albert Einstein, so he suggested a force to keep the Universe static, building it in to his field equations. He called this mathematical proposition the 'Cosmological Constant', a force acting against gravity. Later, when observations proved the expansion of the Universe to be an irrefutable fact, Einstein admitted that his Cosmological Constant was the 'biggest blunder' that he had ever made! It now seems that such a force might exist after all but not quite as Einstein had envisaged it. Far from holding the Universe static, Dark Energy is actually causing it to expand at an increasing rate.

At this moment we know next to nothing about Dark Energy, except for the fact that it appears to currently pervade the Universe. This may not always have been the case, as in the early history of the Universe gravity would have slowed down the expansion. Later on when the energy density of matter and radiation fell below that of Dark Energy, possibly when the Universe was just half its present age, Dark Energy took control and begin to accelerate the expansion of the Universe. Investigating this 'Dark Side' of the Universe is the new challenge for cosmologists.

Junk DNA?

By Peter Wallis

It was 50 years ago that the discovery of the double helix was announced and it has been in this year that the 'Human Genome Project' announced the completion of the "final draft" of the DNA sequence for Homo sapiens. Until now the work of the scientists has concentrated on the genes, those sections of the DNA that encode proteins, regarded as the basis of heredity and the 'blueprint' of all life.

The central dogma so far has been that DNA makes messenger-RNA, RNA makes protein and proteins do all the biological work. They do this through their ability to twist themselves into intricate three-dimensional shapes; some form muscles and organs, others become enzymes to catalyse, metabolise or signal. The number of genes that code for proteins in human DNA is estimated to be about 25,000 [1], but this represents only 1 or2% of the total DNA sequence, estimated to be 3 billion units long. Oddly enough, the number of genes in different organisms does not appear to correspond closely to the complexity of the organism; rice plants have more than humans, 30,000!

In 'higher' organisms, such as humans, there are extensive sequences which do not code for proteins, some separate from the genes and called "junk DNA" and others inside genes and called "introns" which are spliced out in the transcription process. It appears that the amount of all these corresponds more closely with the complexity of the organism. Previously ignoring them as contributors to inheritance, scientists are now recognising that some of these additional sequences have a part to play; they may not code for a protein, but are transcribed into RNA which can alter the behaviour of cells. This was discovered from studies of the genome of mice, but a team of scientists at the National Human Genome Research Institute has recently compared excerpts from the genomes of pigs, humans, dogs, rats and 7 other species and found that many of them appear with only minor changes in many species ; this is a strong indication that they contribute to evolutionary fitness.

Biologists are now turning to studies of 'active' RNA. One form is called "anti-sense RNA". This is made from the complementary DNA strand that sits opposite a DNA-coding gene on the double helix. This is usually not transcribed into RNA and biologists think of it as a back-up copy which can be used by the cell to repair damage to the gene. However, while the gene is producing a sensible RNA message, its alter ego can produce an anti-sense RNA with a complementary sequence; if this meets its pal, they can form a double-stranded ladder which interferes with the intended protein manufacture. Until recently, this was thought to occur only in plants and bacteria, but it has now been shown to occur in humans. It is thought that these interact with another part of the cell's machinery, the "RNA interference machinery", which chops up double-stranded RNA; this helps to protect against viruses which penetrate the cell in that form

Another form of active RNA is "microRNA", first observed in roundworms, as short non-coding RNAs that fold back on themselves like hairpins. They appear to originate from the 'introns' that are snipped out from the gene before the messenger RNA can be generated to code for a protein. Together with the interference machinery, they can control other genes.

There is a great deal more to learn about the genome, and we have clearly been wrong to speak so disparagingly about "Junk DNA".

Ref 1: Dr Ewan Birney of the European Bio-informatics Institute at Royal Society lecture on 4th Dec 2003 Back

Henry Wildey 1913 - 2003.

We are very sorry to announce the death of our Vice-President Henry Wildey, just hours after celebrating his 90th birthday. One of the oldest members of the Society, his contribution to it is immense; he was Astronomical Secretary from 1946 to 1988. He was active all his life in the field of Astronomy and the manufacture of astronomical instruments for both amateurs and professionals. He enjoyed wide interests in opera and in Egyptology.

A fuller obituary written by Doug Daniels is to be found on the Society's website and will be in the journal of the British Astronomical Association.


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