4-D Spacetime Reality

We live in a 4-D spacetime reality. Spacetime is the combination of space and time that makes up the "fabric" of our universe. People disagree about measurements of time and space because we all look at the same thing from different perspectives. General relativity tells us that gravity is caused by curving in the spacetime by the mass of objects. This means that time runs more slowly the stronger the gravitational field, referred to as gravitational time dilation. Note the green rings. They represent flat spacetime, but they are curved due to the mass of the earth. This changes the rate at which time moves and causes gravity to exist. This can actually be seen in light coming from other objects. The light bends around massive objects as
This is called gravitational lensing. General relativity also tells about gravitational waves, ripples in spacetime caused by moving objects, like waves on water caused by a moving boat.

Special relativity is different, based on the idea that space and time are not absolute, it fluctuates. Space and time are not totally independent but are apart of a single entity. It states that motion at a constant velocity is always relative, but it is less evident when gravity and acceleration are involved. The equivalence principle allows us to treat motion as relative because it tells us that the effects of gravity are equivalent to the effects of acceleration. In other words, Einstein's special theory of relativity is based on the idea of reference frames. A reference frame is simply "where a person (or other observer) happens to be standing". You, at this moment, are probably sitting at your computer. That is your current reference frame. You feel like you are stationary, even though you know the earth is revolving on its axis and orbiting around the sun. Here is an important fact about reference frames: There is no such