What is dark matter and what is dark energy?
1 Answer
Dark matter and dark energy are theories to explain the motions of stars in galaxies and the expansion of the universe.
Explanation:
Current theories of motion and gravity work well. When observing the motions of stars in galaxies there was a problem. The stars are travelling too fast for gravity to explain. The mass of the visible objects in galaxies is too small by a factor of over five to explain the motion.
Dark matter was theorised to explain the missing mass. Dark matter doesn't interactive via the electromagnetic force so isn't visible. It does however create sufficient gravity to explain the star motion.
The problem is we don't know what dark matter is or even if it exists.
The universe should ultimately collapse due to gravity pulling everything together. Observations of distant supernovae has shown that the universe is expanding.
Dark energy was theorised as something which permeates the fabric of the universe causing it to expand.
Again we don't know what dark energy is or even if it exists.
It may be that our understanding of physics on large scales is wrong. It may be that new physics will eliminate the need for dark matter and dark energy.
Alternatively, if dark matter and dark energy exist we will need to discover new particles. New particles will also require new physics.
