This is a great video describing the evidence for dark matter and dark energy, courtesy of National Geographic.
1st Evidence for dark matter -Astronomers expected stars near the center of galaxies should travel slower than stars near the outer areas. What astronomers noticed was quite different.
Astronomers noticed that velocities of matter in galaxies rotates at the same velocity, no matter where anything is located. There must be matter present exerting a force on all stars in the galaxies that keeps them travelling at the same speed. It cannot be detected with any forms of known light or radiation. It does not react with visible light, infra-red, ultra-violet, radio waves, etc.
2nd Evidence - gravitational lensing.
Astronomers noticed that light from distant galaxies is bent by the gravity of something with immense mass. The bending of light created lensed, duplicate images of those distant galaxies. Visible matter was calculated to be vastly insufficient to bend light of these distant galaxies. Therefore there must be an immense mass creating the distortion of light from distant galaxies. That something is dark matter.
Dark matter does not react with any type of light so it cannot be seen. We only know it is there because we can see the effects of its gravity.
3) Expanding Universe -Dark Energy
It is estimated that 70% of the universe is composed of dark energy, 25% dark matter and only 5% is composed of everything we can see! The universe is expanding and the rate of expansion increases for galaxies that are farther away than those galaxies that are closer. This expansion is acting in opposition to gravity and dark matter. Something is driving expansion of the universe. It is suspected that Dark Energy is causing the expansion.
We will never completely understand our universe until we understand dark matter and dark energy.
Maddalena Environmental Inc.