Flamsteed Astronomy Society

Successes and Problems of Big Bang Cosmology

— Prof Michael Joyce, September 23, 2005

The current standard model suggests there is 5 times as much dark matter as ordinary matter in the Universe.  There is a great deal of experimental research under way to detect hot and cold dark matter, so far without success.   The only evidence for the existence of dark matter is its gravitational influence believed seen in the large-scale structures and also in the rotational velocity of stars in outlying regions of galaxies.  Outlying stars are orbiting their galaxies much faster than can be explained by Newton’s law and the observed mass of the galaxy. (Some scientists do postulate a modification to Newton’s law, called MOND, Modified Newtonian Dynamics, to explain this).

The second area of difficulty concerns the ‘accelerating Universe’.  Since 1998 supernovae studies seem to indicate that these objects are farther away than can be explained by the present theory.  The Universe may be in a phase of accelerating expansion — the expansion is speeding-up rather than slowing as would be otherwise predicted.   Such acceleration is addressed in the ‘ Lambda CDM’ model which has to introduce a cosmological constant in the form of ‘dark energy’ which is repelling matter and pushing the Universe apart faster.

Lambda CDM postulates the structure of mass and energy in a ’flat’ Universe as 5% ordinary baryonic matter, 25% cold dark matter, and 75% ‘dark energy’.

 

In conclusion —

The ‘standard’ Big Bang Cosmology model has had remarkable success in predicting the existence and nature of the CMB cosmic microwave background, and the abundances of the elements formed in nucleosynthesis during the Big Bang.

However, observational data especially during the last 10 years has challenged the theory.  Recent observations can only be addressed by postulating the existence of so-far undetected forms of matter and energy called dark matter and dark energy.   We are unsure if these notions are helpful or are just ‘parameters for the failure of our understanding’ much like the luminiferous aether of the 19th Century.  In particular —

What and where is dark matter?

Is dark energy a valid concept?  What is it?

Where do the large-scale fluctuations come from?  Why so?

Is the Universe ‘flat’?  Why?  Is ‘Inflation’ a valid cosmological concept?

How do ‘seed fluctuations’ develop into the LSS seen today?  Our simulations break down as the fluctuations amplify.

Is our concept of dark matter valid?  We are making very complex assumptions which fit the data only very approximately.  Dark matter as postulated would not actually cluster in the way observed.

Professor Joyce offered no answers to these questions. Clearly he is anticipating an interesting 10-year career at least!

 

“Cosmologists are often in error but never in doubt” — Lev Landau

Cosmologists and their predecessors have always worked at the very frontier of reliable observational data and often beyond it.  Our knowledge has progressed by interaction and leapfrogging between the theorists and the observationalists, each provoking the other and pushing at the boundaries of understanding.

Today the history of science tells us mostly about the development of the successful theories, not the blind alleys although there have been plenty of those.  Scientists have always been reluctant to abandon theories that had previously been useful, even when they seemed fatally flawed.  We smile now at Ptolemy’s epicycles and Tycho’s hybrid solar system, but even Copernicus was wedded to the perfect circle.  How much thought and experimental energy was lavished on the luminiferous aether?  

Which of today’s confident ideas have really been born of poor, lacking, or misinterpreted data, fuelled by imagination and wishful thinking, only to be consigned to the dustbin of history?

 

MRD 25/9/05

(picture Mike Dryland)

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