How can we be Certain that Dark Matter Exists if we Cannot See it or Directly Detect It?

Question

It seems very certain that dark matter exists and that it makes up 26.8% of the Universe today (along with 68.3% Dark Energy and 4.9% Atoms), but how can this be if we cannot see it or directly detect it?

Answer 1

according to the astrophysical observations which shows for example: much more bending expected in lights directions due to the gravity of the stars and galaxies we know. it means we know there are four example 2 galaxies which can bend the light which come from a third and farther galaxy. and the bending to the light due to these 2 galaxies should be X. but the observed bending is much more than X. so there should be something else which cause it to bend more. It is one of the evidences... you can read more in Wiki or others.