Think about the universe. The part which you can see (not with naked eyes, of course) is not even 5% of it. The rest is made up of dark matter and dark energy.
Dark matter is invisible to us, but we can infer is existence by examining its gravitational pull towards celestial objects.
What’s Dark Matter?
Dark matter is an invisible form of matter, whose existence we cannot observe, but infer, since it does not interact with light or electromagnetic radiation (Radio waves, gamma rays etc.)
Without it, there would not be enough force to hold galaxies together, since it has been only known to interact with normal matter through gravity thus far. It’s classified as cold, warm or hot in accordance with its velocity.
What’s Dark Energy?
One fine day, astronomers deduced that the universe is expanding. However, what was causing this expansion? Gravity can’t cause the universe to expand : it’s an attractive force.
It’s first appearance came in Einstein’s field equations, where we finally came to a conclusion that even “empty” space has an inherent energy which exerts a repulsive force, causing the universe’s expansion.
A theory suggests that it is a part of a field which evolves over time, suggesting that its energy may change, which may explain certain inconsistencies in data.
Some people are trying to explain this through gravity acting in the opposite direction : a new type indeed.
What if all this is a myth?
If we assume dark matter to not exist, we would be contradicting Newtonian mechanics, and thus we would require a new theory governing objects in motion to explain our observations.
