Gravity is the curvature of space-time???

Time and 3 dimensional space form 3+1 dimensions. I understand this i.e. given time and 3 dimension space coordinates you can locate anything including OBL.

But what does physics mean when it says gravity is the curvature of space-time. Can anyone picture and explain what they are on about. I keep thinking of a folded sheet of paper..I dont know why.

Why am I asking this you may wonder but I saw a documentary on the history of the study of the extent of the Universe last night.

 

You keep thinking of a sheet because space and time are often considered to be a 'fabric' like a rubber sheet. Anything with mass warps (or 'curves') the space and time within its vicinity, the bigger the mass, the bigger the depression into the sheet. All the stuff around the mass is literally just following the contours in the “sheet” (eg. In The Moon-Earth system the moon is following the contours in the sheet caused by the earth’s mass). Even the trajectory of a beam of light is warped by the mass being there (The closer to the mass, the more the beam will be "bent". Something like a black hole for instance has such an enormous mass that it literally punches a hole in the sheet. Gravity is actually one of the most poorly understood phenomena in all of modern physics, interesting stuff.

 

I opened this thinking it was going to reference this: http://xkcd.com/895/

 

Wow... Xkcd referenced an actuarial table!
http://xkcd.com/893/

And sorry for taking slightly off topic... Gravity: wouldn't have been discovered if the ground hadnt moved up and collided with that apple.

 

Haha that was great.. wouldn't standard population/assured life tables not apply since astronauts usually have to be supremely fit and would be expected to have lower mortality

 

Thanks I have taken one small step now. I am now now beginning to understand why Einstein is such a genius. After my A'level physics I venerated Newton but now I am beginning to view Einstein in the same breadth. I can not believe how much I have been missing and I say that with pride.

Being reading this article:http://einstein.stanford.edu/SPACETIME/spacetime2.html

 

If anyone is interested in learning more about physics, there are courses on it at the Open University including The relativistic Universe (S383) and The quantum world (SM358). There are also courses in physics and mathematics at MIT OpenCourseWare available free of charge.

 

Fascinating video on the single space-time continuum....http://www.youtube.com/watch?v=MO_Q_f1WgQI