How is it possible for a 2 dimensional object to exist in a 3 dimensional world? Even the atoms that make up everything in the universe are 3D. This being the case how can we say that our 3D universe is surrounded by a 4D world we cannot see? I guess what I am saying is if 2D objects cant exist in 3D than how can 3D objects, like our universe, exist in a 4D? ---RedSingularity
If you'd take something (like a sheet of paper) and looked at it from a 90° angle, you wouldn't be able to see that it's actually 3-dimensional, would you? Especially if you didn't have any control at all over it's motion in the third dimension it would be very hard to detect that it actually has a thickness. The "fourth dimension" usually used in physics, time, is a rather tricky one anyway. According to our mathematical theories, it is very much "the same" as our spatial dimensions, yet our intuition tells us completely the opposite. For one, we are moving through time at a constant velocity (well, through space-time at least) so we have hardly any control about where we go in this dimension. If you want to talk about string theory with > 9 dimensions, it becomes an even more complicated story so let me not go there ;)
I don't really follow the answer. It might appear as 2d yes, but he even mentioned the atomic level. You can have an object appear as 2d or a point like particle but the closer you get you eventually see that it is does have thickness. Speaking of strings that is something I don't get, how can a 1D string exist if it has length but no width or other dimensions? I know it can vibrate in 3 dimensional space (as well as calabi yau space or whatever other sets of spacial dimension configurations that might exist) but I still can't picture on the planck length scale viewing the string I'd think it would appear as invisible if it truely had zero thickness.