There are four fundamental physical forces that operate throughout the universe - the strong nuclear, which holds the atomic nucleus together against the force of repulsion of positively charged protons; the weak nuclear, which mediates radioactive decay; the electromagnetic, which is the force between charged particles and/or magnetic poles; and gravity. Of these four, gravity is by far the weakest being 10 to the 40th power times weaker than the electromagnetic force, which is in turn 100 times weaker than the strong nuclear force (which is why the SNF can hold protons together against the force of their mutual repulsion, at least over very short distances).
Gravity is the force with which we are perhaps most familiar, and yet no one really understands much about it. We can measure it and predict its effects, but when it comes to understanding it scientists are at a loss. It is indeed strange, when we think about it, that an object like the earth can somehow pull another object, like your body, without there being any discernable physical connection between them.
This is, however, just one of the mysterious aspects of gravity. New Scientist has a piece in which they briefly outline current thinking on each of the following questions about gravity:
- What is gravity?
- Why does gravity only pull?
- Why is gravity so weak?
- Why is gravity fine-tuned?
- Does life need gravity?
- Can we counter gravity?
- Will we ever have a quantum theory of gravity?
The most interesting to me is #4 but check them all. It's a very interesting article.
RLC