What discoveries of scientists have significantly expanded our understanding of the universe?

Physicists made a great contribution to our understanding of the Universe, proving that time slows down as it moves, and the higher the speed, the stronger, which made them understand that what we see in the sky at that point has long passed. Scientists also noted two horizons in their observations: the first – beyond this horizon, the light has not yet reached our Earth from the appearance of the Universe and we do not see what is behind it, the second is the horizon where the Universe is expanding faster than light and what is behind it we will never we will see (only by moving to another point of observation, let’s say another system or planets). Stephen Hawking made a great contribution by introducing the theory of “Hawking Radiation”, which explained how black holes could “evaporate”. Also, dark matter, which has negative mass and, accordingly, negative gravity, this matter fills the entire Universe evenly and canceling gravity allows the Universe to expand further. Of course, all these are theories and observations, no one “felt” these theories and objects close up, and maybe everything is completely different.