Most of Our Universe is Missing

Notes from the BBC Presentation for the Melbourne Philosophy Forum, Feb 1, 2009

Required Viewing: BBC Horizon, "Most of Our Universe Is Missing"

Programme Summary available at:

1.0 Dark Matter, Dark Energy and Philosophy

1.1 The importance of Dark Matter, apart from being a hypothetical expansion in the field of cosmology, is also a philosophical one. In addition to the ontological characteristics (i.e., it expands our notions of being and existence) it also illustrates the rational epistemological approach used by the scientific method.

1.2 Dark Matter is hypothetical matter; it has never been observed directly (as it appears to be a mass that is not made of atoms), but its existence is inferred by gravitational effects.

1.3 Dark Energy is an expansion to the hypothesis of Dark Matter that is used to explain the observation that the universe is expanding at an accelerating rate. In an expanding universe density (and the density dark matter) declines - but the density of dark energy is nearly unchanged.

2.0 Proof By Inference

2.1 Gravity is the attraction that matter has for each other. Galileo's experiments showed, contrary to Aristotle's assertions, that gravity applies equally to all objects regardless of weight. Note that Galileo, philosophically, made a constative statement, verified through correspondence with external reality. Newton expanded this to the more mathematically precise inverse square law of gravity ("the forces which keep the planets in their orbs must be reciprocally as the squares of their distances from the centers about which they revolve") which applies universally for non-relativistic calculations. Newton's law predicted the existence of Neptune on the movement of Uranus.

2.2 Slight anomalies in Newton's theory could not be explained until 1915 with Einstein's Theory of General Relativity where the effects of gravity are expressed as curves in the spacetime continuum. General relativity was used to explain Mercury's discrepencies from Newton's law, time delay of light, gravitational radition through observation of binary pulsars, and the expansion of the universe. There are several variant and alternative theories of gravity, the most challenging being quantum gravity.

2.3 In 1975 Vera Rubin noted that stars in spiral galaxies orbited at the same speed as those in the galatic centre. This was contrary to Newton's prediction on non-relativistic mass. The alternative was that a significant amount of "dark matter" would be found in the dark galatic halo. In 2005 astronomers from Cardiff University claimed to discover an entire galaxy made of dark matter (VIRGOHI21); "seen" with radio frequency observations.

2.4 In 1997 Saul Perlmutter noted that not only were galaxies moving away from each other, they were doing so at greater and greater speeds. "Cosmic acceleration", as it has become known, has been confirmed by several other observations.

2.5 An alternative explanation, proposed by Jacob Bekenstein, is that dark matter does not exist. Rather he has modified Newton's law of universal gravitation to one which uses variable gravitational fields known as Tensor-vector-scalar gravity.

2.6 However these alternative explanations are weakened by computer simulations from Durham University which strongly correlate with the results of Wilkinson Microwave Anisotropy Probe surveys. By measuring the temperature of the Big Bang's radiant heat the composition, age and shape of the universe can be determined.

2.7 According to WMAP, the current content of the universe is 72% Dark Energy, 23% Dark Matter and 4.6% Atoms. Approximately 13.7 billion years ago - when the universe was a "mere" 380,000 years old, the content was 63% Dark Matter, 15% Photons, 12% Atoms, and 10% Neutrinos.

3.0 The Scientific Method

3.1 The cosmological study of Dark Matter provides some interesting insights into the scientific method. Firstly, a status quo of knowledge exists which is used to explain an existing state of affairs. As anomalous results, based on attempting to match theory to observations, increase alternative explanations are sought. The strength of these alternative explanations depend on their capacity to be tested (verification principle), and their capacity to explain the anomalous data (confirmation principle).