Dark Matter & Dark Energy

16.10 - Understand the significance and possible nature of dark matter and dark energy

16.11 - Understand the difficulties involved in the detection of dark matter and dark energy

Dark matter and dark energy have not been directly observed, although there is some evidence for their existence.

Dark Matter

Scientists have measured the mass of galaxies (by studying the light coming from them and their velocity). It has been found that they are moving faster than they ought to for their mass. This should not be possible within other laws of physics. Their mass should be many times higher.

Scientists believe that there is some invisible matter - dark matter - that cannot be directly observed that can make up over 90% of the matter in galaxies.

Candidates could be dark dust, black holes, brown dwarfs, neutrinos or a new type of object or matter, yet to be observed.

Dark Energy

Dark energy works differently; it appears to be a force that moves galaxies away from each other. The expansion of the Universe since the Big Bang should have slowed down the rate of movement between galaxies. The opposite is happening, however; the rate of movement is increasing. Scientists believe an invisible force – dark energy – is responsible for this.


  • What is the difference between dark matter and dark energy?
  • What kind of matter that we know about could possibly make up what we think might be dark matter?
  • Why do cosmologists believe dark matter and dark energy exist?