The end of cold dark matter?

There have been recent murmurings that Cold Dark Matter (CDM) is in trouble. Dark matter is stuff that is hypothesized to make up a fair chunk (23%-ish) of what is in the universe (as opposed to normal matter – the stuff we ‘see’ and experiment with – which may make up only 5% what’s in the universe). The remaining 72%-ish would be ‘Dark Energy‘  – more bizarre still. 

The key word here is ‘hypothesized’. No-one has seen dark matter – that’s one of the problems with it – being dark it is almost by definition undetectable and so very very hard to research.  The reason it is believed to exist is that, if you look at how galaxies move, there just isn’t enough visible matter to account for it. Well, not according to our best current theories, anyway.  It’s hoped that the Large Hadron Collider will give some evidence for its existence, but, so far, nothing. (Interestingly, the LHC hasn’t given us anything startling at all yet, but that might come with time.)

Now there is some evidence which goes against the current CDM hypothesis. Some computer simulations suggest, that if CDM were true, there would be many more dwarf galaxies close to the Milky Way than there actually are.  So we have the hypothesis, we have a prediction from the hypothesis, and we have data that can test this prediction, and, the hypothesis doesn’t stack up. That’s a neat example of how science works.

Whether this means that CDM is completely off track, or whether it just means a modification of the CDM hypotheses are needed, remains to be seen. If it’s the former, I wouldn’t want to suggest that massive research time over the last 30 years or so has been ‘wasted’. It’s simply science doing its job – testing things so as to determine what’s what with the world and the universe.



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