Question

How do scientists know that dark matter exists? A. It absorbs radio waves. B. It emits electromagnetic radiation. C. It exerts a gravitational pull on other matter. D. It blocks the light coming from other objects.

Answer 1

Scientists cannot directly observe dark matter, but they know it exists by C, the way it exerts a gravitational pull on other matter. Most of the cosmic entities like galaxies do not have enough observable matter within them to logically exist, i.e. the amount of matter they have can’t hold the galaxy together. These large bodies that can’t exist by the laws of nature somehow do, and thus the concept of dark matter and energy supports both the concept, and the galaxy itself, in a sort of way (humor intended). :)