• Question: what is dark matter ? ,and if it composes about 95% of the mass of the Universe, and we have no idea of what it is, how do we sense its existense?

    Asked by bilallatif to Emma, Jimmy, Janet, Niall, Simon on 12 Mar 2013.
    • Photo: Niall Crawford

      Niall Crawford answered on 12 Mar 2013:

      Not too sure, I know that it is difficult to detect, and that the only evidence for it is its effect on other matter.

      Maybe Jimmy can answer this?

    • Photo: James Holloway

      James Holloway answered on 12 Mar 2013:

      The answer to ‘What is dark matter’ is:
      We don’t really know!

      We know a fey key things about it:
      1) It dosn’t give off light and it doesn’t reflect light (that is why its dark)
      2) It does attract things to it with gravity (that is why its matter)
      3) It could be all around us now, in our living room and it would pass straight through us (this is related to it not giving off light strangely)

      How do we know its there?
      We see its effects on the stars and galaxies. Galaxies are billions of stars in a disk shape, turning slowly around the centre. When we count the stars in a galaxy we can work out how much stuff there is in that galaxy. It turns out the more stuff there is in a galaxy – the faster it spins.

      Some clever person did the maths and found out that galaxies were spinning much faster than they should be. After lots of thinking and debate scientists realised that there must be more stuff (matter) in the galaxy that just the bright stars we see – we call it dark matter.

      So we know its there because we see its effect (like the wind blowing trees), but we haven’t seen it directly.

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