Nishan C J

This is a very fundamental question that you have asked, and quite simply, we don't definitively know. General Relativity gives us a 3+1 classical field theory, where there are 3 dimensions of space and 1 dimension of time(x,y,z-direction, and time). Superstring theory, on the other hand, gives us a 10+1 quantum gravity theory with ten dimensions of space and one dimension of time. The dimensions of space other than x, y, and z dimensions are 'compact' dimensions.

A simple way to think of a compact dimension is to think about looking at a far off traffic light. It appears two dimensional when you're far away, but as you get closer and closer, you see that it is 3 dimensional. Similarly, these compact dimensions are so tiny that they are not possible to be detected by today's experiments, and I am hoping that they do find them in the near future.

I hope that answers your question.

This confusion might arise due to the rewording of newton's first law into a more understandable form. What newton's first law states are that there exists an inertial frame either at rest or moving at a constant velocity, in which the said body that we are considering is at rest. Dynamical laws will remain the same in all such inertial frames. Now if you bring acceleration into the picture, you get non-inertial frames. Dynamical laws do not stay the same in all non-inertial frames of motion(centrifugal force is an example of this). We use the first law to define inertial frames, and the second to set non-inertial frames.

The question you have posted above is a fundamental postulate of Einstein's special relativity, which is that there exists a maximum speed limit in this universe. It will be constant in all reference frames. On preliminary inspection, this speed ends up being the speed of light. This fact that the speed of light is constant in all frames ensures the fact that there is no particular reference frame, and that the laws of physics are the same in all reference frames. Please refer to Chapter One of Robert Resnick's book on Special Relativity.