According to modern physicists, if the universe fills with a lot of matter, known as "critical density", then its expansion will cease and collapse upon itself. We do not have enough matter in this universe yet to allow a "big crunch" to happen.

Stephen Hawking and Roger Penrose are the cosmologists who first came up with the possibility of black holes in the universe. Black holes are the end stage of the existence of very large stars which collapse upon themselves when their hydrogen fuel is exhausted.

Cygnus X-1 is believed to be an actual black hole that we are able to see because of a nearby binary star that streams plasma into it.

Some cosmologists theorize that black holes may accelerate matter in the universe to speeds creating energy.

Albert Einstein's special theory of relativity changed the way we think about many of the laws of nature, including the previous law of universal gravitation credited to Sir Isaac Newton.

Einstein proposed that how we see things depends on our frame of reference.

Time is considered as the fourth dimension.

Words that could make you smarter...