• Question: what specifically is dark matter and what does it do?

    Asked by Logan F on 3 Oct 2021.
    • Photo: Richard Collins

      Richard Collins answered on 10 Sep 2021:

      “Dark” mostly means “we don’t really know”.

      Both of your questions are some of the very big questions in physics! If you happen to figure it out, you would definitely get a Nobel Prize!

    • Photo: Jacob Maresca

      Jacob Maresca answered on 10 Sep 2021:

      We don’t know what dark matter is, and this is one of the biggest questions in physics today!

      We know that it exists because by studying all of the visible matter in galaxies (stars, gas, dust etc) and adding up the mass, we find that a large fraction of the mass needed to hold the galaxy together is invisible. This is why we call it ‘dark’ matter because it emits no light.

      So dark matter is responsible for holding galaxies together.

    • Photo: Giles Strong

      Giles Strong answered on 10 Sep 2021:

      As Richard and Jacob say, we don’t exactly know what dark matter is. From various experiments and measurements, we estimate that about a quarter of the Universe is made of dark matter, the remaining amount is mostly dark energy (which we also don’t fully understand), and only actually a vary small amount of the Universe (5%) is stuff that you can “see” (planets, stars, and black holes).

      There are several possible explanations for what dark matter is, and a few theories describe particles which could be dark matter candidates (super symmetry, (sterile) neutrinos, primordial black holes, etc.). What we do know, is that it interacts gravitationally, meaning that you have to be really close to it to actually notice it and it can be easy to miss due to all the other interactions that happen.

      Based on this, a lot of experiments try to isolate out all other possible effects by building detectors deep underground, where other interactions are reduced thanks to the vast layers of rock which shield the experiment.

    • Photo: Andrew Hone

      Andrew Hone answered on 13 Sep 2021: last edited 13 Sep 2021 2:28 pm

      We don’t know what dark matter is – it is one of the biggest challenges in modern physics. We infer that it is there because we see its effect via the gravitational field that it exerts on other matter, but we cannot “see” it in the normal sense because it doesn’t absorb/emit visible light or other electromagnetic radiation – that is why it is called “dark”.

      There are four forces that we observe in nature – electromagnetic, weak, strong, and gravitational. Dark matter is something that only seems to interact with ordinary matter via the gravitational force, so it has mass which effects the motion of the stars and galaxies that we can see with telescopes, but apparently is unaffected by any of the other three forces.

      So it is a great mystery!

      Further to the answer by Giles, there is a documentary on Netflix called “The Most Unknown” https://www.netflix.com/gb/title/80222042 which includes a visit to the Gran Sasso lab in Italy, where they are trying to detect dark matter particles underground.

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