ok i was reading an article the other day and i'm quite new to the world of physics, so i came accross this statement "dense mass curves space-time". What does this mean and can anyone give me an accurate descirption of space-time because i fail to see how it can be curved. By the way the dense mass was a reference to black holes. thnx

The concept of gravity can be represented by two "charges" which attract each other. The charges are, of course, the masses of the two objects. Any two massive objects experience a force that pulls them together. This is a simple picture. Space is a stage, and masses are the actors. The masses do the pulling, and space is just the arena in which we watch them pull.

Another way to think of gravity is to think that space itself is curved, and that massive bodies move through the curved space along the straighest possible lines. These straightest possible lines are then the trajectories of baseballs and so on. In this model, two masses don't pull on each other. Space is no longer a static stage on which we watch the actors act; space itself causes the masses to experience a "force" towards one another. The force isn't "real," just like the force you feel when you're pressed against the inside of a car making a sharp turn isn't real. The force you feel is your own body, which wants to follow the straightest possible path through space, clashing with the car, which is being forced via friction to move around the turn.

Mass tells space how to curve, and curved space tells mass how to move. The curvature of space can be demonstrated by the deflection of light around massive bodies; light has no mass, and shouldn't be bothered by a massive body -- unless space itself is curved, and everything, even massless particles, do the same thing.

It's difficult to imagine three-dimensional space as being curved, so it's common to use a lower-dimensional analogy. Imagine a flat, rubber sheet, suspended at the edges, but free to deform in the middle. Imagine putting a bowling ball on the rubber sheet. It deforms from being a two-dimensional plane into being a curved object having three dimensions. Many of the same effects we see with gravity (baseballs going up and coming down in parabolae, orbits, etc.) can be seen by rolling ball bearings around in the indentation caused by the bowling ball.

Now, real three-dimensional space is curved into a fourth dimension -- and this fourth dimension ends up being time. This is an almost maniacal proposition -- and it leads to all sorts of strange effects which are all together called "general relativity." Despite its odd premise, the theory is experimentally correct to a precision of several parts per billion. The three dimensions of space are curved in fourth dimension, time, by mass.

This leads to the weirdnesses you'll hear about: time slows down in gravitational fields, for example.

- Warren

All this caused by selecting light speed to each observer being the same. This makes time a variable. This warps my mind that anyone could come up with this.