Billions and billions. Carl Sagan used to say that a lot. He used that expression to make a point and it worked. But was his point valid?
The billions and billions Carl referred to were stars. Yes, there are indeed billions and billions of them. His argument went on to say that because there are so many stars, billions and billions, there must be planets, and therefore, life out there in great numbers.
You've probably heard of a "Black Hole". Black holes form (we think) when big stars burn out, expand, and then collapse. There is so much stuff crammed into such a small space that the gravitational pull is incredible. In fact, the pull is so strong, nothing, not even light can escape from a black hole. Thus the name.
As you approach a black hole, the pull gets stronger and stronger....and there is a place, a line ... >>full
Let's start with a simple idea. In physics, we know that all objects with mass have a gravitational pull on other objects with mass. We know that the bigger the mass, the greater the pull. And, the closer to an object you are, the greater that pull.
If you are in a space ship far from earth, earth will exert very little pull on your tiny craft. But as you get closer, earth's gravity will begin ... >>full
