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I understand that time has effects and that time can be slowed by gravity and such but I dont understand what time realy is. Gravity is the bending of space and time but what is time? What causes time?
quantum physics is physicsTime perception is an interesting subject. Not sure if it ties into physics though... Quantum physics maybe?
Regarding the definition of time...
We can define a coordinate system in Newtonian mechanics, SR and GR as a function [itex]x:M\rightarrow\mathbb R^4[/itex], where M is spacetime, and then define "coordinate time" as a component of that function. In SR and GR it's also necessary to define "proper time", which is the integral of [itex]\sqrt{-g_{\mu\nu}dx^\mu dx^\nu}[/itex] along a curve.
That takes care of the definitions in the mathematical models used in these three theories, but the theories must still include postulates that tell us how these things are related to what clock's measure. In Newtonian mechanics, clocks measure coordinate time. In SR and GR, a clock measures the proper time of the curve that represents its motion.
Time is certainly more than that mathematical expression, but any answer to the question of what time "is", will always be in the form of a mathematical model and a set of instructions about how to use that model to make predictions about the real world. The best answer we have so far is the one provided by general relativity. The relevant "instruction about how to use the model to make predictions" says that what a clock measures is the proper time of the curve that represents the clock's motion. I don't think anyone has a better answer than that at this time.
Note that two definitions of time are needed. First we have to define time in a mathematical model (in this case as a certain integral), and then we have to define it operationally (as "what a clock measures"). Then we postulate how the two are related.
I feel the thermodynamic definition of time is to narrow, yes entropy increases and we can't un-crack an egg but I think the fact that processes that are exactly the same will increase in entropy at different rates according to the same observer. Take an atomic clock on earth take one exactly the same and send it spinning around the earth as fast as you can. Few years later grab the one spinning around the earth and put it next to the one sitting in your lab and ...they are different. Same processes same "time" from the observers point of view different change in entropy.The direction of Time is shown in thermodynamics by the increase in entropy..
that's my two cents