• Question: As gravity is similar to dark-matter where we cannot see it, but dark-matter has a cause and effect on gravity itself and visible matter. So therefore is not gravity the effect from cause of dark-matter, which leads to the question, what is dark-matter?

    Asked by Ryan Gunning to Heather, Helen, Hugh, Jane, Julian on 11 Nov 2014.
    • Photo: Julian Onions

      Julian Onions answered on 11 Nov 2014:

      Gravity is a force caused by any mass. We know there seems to be a lot of mass missing for the amount of gravity we see acting in our galaxy, so we call this missing mass dark matter. There are several other reasons why we believe dark matter exists.
      So its the gravity that this extra dark matter (which outweighs regular matter by about 5 to 1) that holds things together and makes galaxies form in the first place.

      So dark matter was invented to explain the missing mass we seem to see, but it also fits into a number of other theories too – so currently seems to be the best bet. There are still other competing theories, but they struggle somewhat to answer the questions as well as dark matter does.

    • Photo: Hugh Osborn

      Hugh Osborn answered on 11 Nov 2014:

      So, gravity is just a force between objects with mass. We do not directly see it because it is an effect two particles have on space rather than, say, a new particle itself (in the same way two bar magnets stick together but there is no identifiable ‘thing’ between them).

      But you’re right, we know Dark Matter exists because of the gravitational effect is has on normal matter (like galaxies) and on light itself. From these observations of Dark Matter, though, we have a pretty good idea that it is some new mysterious form of matter (rather than, say, a different way of thinking about gravity). What, exactly, this matter might be is still open for debate.

      Most scientists think we should be able to directly detect particles of Dark Matter here on Earth, despite how little they seem to interact with other particles and light. There are a handful of experiments currently looking for them. I think it is only a matter of time before they do, and we can finally shine some light on what Dark Matter actually is.

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