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quote:Originally posted by Dan BRelativity ties space and time together (space-time) Mass distorts space time (gravity). You can have empty space.... you cannot have mass without space. Mass does not equal space.
quote:Originally posted by SmeggitThese are just my idle thoughts so please shoot them down at will.  I've thought for a while now that gravity pulls in the direction of the 4th dimension. A simple example being a round planet. The 4th dimension should be perpendicular to our 3 dimensions and if we take a planets surface to be "smooth" then gravity pulls perpendicular to all surfaces. I wonder if gravity is like a magnet under paper moving iron filings around. Mass bends space-time in the direction of the 4th dimension, we try and fall in and like the iron filings we feel the force but cannot move that direction.
quote:Originally posted by Dan BI have a 1st class honors degree in astrophysics and am currently writing my PhD thesis on (basically) the cosmological evolution of supermassive black holes and their host galaxies....hurrah for me 
quote:Originally posted by gsmollinOkay... and I have a PhD from MIT in cosmology. Alan Guth was my advisor. I am currently teaching at the University of Hawaii.
quote:Originally posted by tweenerWow! We're getting some real heavyweights in this forum. It's nice to be acquainted with you guys!
quote:That's a good analogy OmnipotentOne, but as with most analogies, it can only be carried so far. The sheet is like a two dimensional representation of space-time and the lead ball on the sheet causes it to distort. So far so good, but this setup requires that the lead ball be in a gravity field to make the distortion happen. In relativity, the distortion is caused by the mass of the ball and occurs to the 3 dimensional space-time. The moon tries to roll "down" into the gravity well, but it's movement is always trying to send it flying out and to stay in orbit, they just cancel out.