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Is there really such a thing as dark matter?

Is there really such a thing as dark matter and if so what is it and how do we know it exists?
Zoe from Wiltshire (Age 5-14)

What is dark matter and does it exist?
Vijay Narbad from Norfolk
Age 15-24

What is dark matter?
Rashid C from Greater London (age 5-14)


2 Responses

  1. Zoe,

    Good question. We see dark matter through it’s gravitational effects; it is needed to hold together galaxies, clusters of galaxies and super clusters of galaxies. Alternatively, you could say our law of gravity are wrong, but that would require us to throw away (or tinker with) Einstein’s great work on this and then we would be left with nothing. So, it’s the lesser of two evils to say the universe is full of matter which doesn’t shine, but glues our galaxy together (using Einstein’s law of gravity). We are also not bonkers in believing this as particle physicists can make lots of particles that behave like this, that is they have mass, do not shine but interact through gravity. One is the neutrino for example. This is one of the greatest problems in physics, especially if you now include dark energy (that’s another story!)

  2. Hello Zoe,

    Dark matter does exist! How do we know?

    Astronomers can measure the mass of our sun by looking at how quickly the earth moves in orbit around the sun. The speed of the orbit tells us about the total amount of matter inside the orbit.

    Now, when astronomers look at stars moving in other galaxies (including our own Milky Way galaxy) they find that the amount of matter determined from looking at the speeds of star orbits is much larger than the actual matter that they can see. In fact it’s four to five times as much!

    So, we know there is extra matter there, but we cannot see it – that’s why its called dark matter. We do not know what it is made from. It could be in the form of undiscovered sub atomic particles.

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