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The great scientists of history, like Galileo, Newton and Einstein, turned the time in the fundamental pillar of its scientific construction of the reality. But today we still do not understand in depth the nature of time. With the theory of relativity we witness the collapse of the absolute time of Newtonian mechanics and the advent of "counterintuitive" ideas as the "multitude of times". From this theory, the present, past and future are confused in the "now" and are given at once. That is to say, time is there, as the fourth dimension, where events do not "happen" but are printed in the space-time continuum.
The notion that Isaac Newton institled of time.
For Newton, time was like a river, a flow that flowed continuously. In addition, in the Newtonian metaphor it flowed in a regular, uniform, constant and in the same way for all observers.
The majority view, today, is not so much that time flows but we move through a temporal dimension. Thus, the majority notion among physicists is that time is basically geometric. In a universe of four dimensions (3 spatial + 1 temporal), we would all move along a line through it (the tangent vector to that line gives our energy and our momentum). So when I am "still" in my room, in reality, I and the objects at rest regarding me are moving at the speed of light in the direction of time. And according to the theory of relativity we all move at the speed of light in space-time: (1) if you move at the speed of light in time, then you are at rest in space, (2) if You move very fast in space near the speed of light, then your speed in time is slower and you age less (because the speed you have in space and time are "compensated" in some way).
Someone will say that my last paragraph is only a metaphor, but in reality it is more than that. The idea can be formalized with equations and in Minkowski's geometry and what results is a physical theory called: theory of relativity (in which what we observe as space and time depends on the state of movement of the observer).
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Time is one of the last remaining mysteries to man.
Yes i think the same
Much like how we needed to give up determinism when moving from Newtonian mechanics to quantum mechanics, now we need to give up spacetime in order to expand our theories to explain all the mysterious phenomenon we struggle with today. Yes, that means our notions of 3space+1time HAVE TO GO. I would not worry too much about the mysteries of space and time and remain transfixed with questions like "What is time?" because the next layer of truth is way more intricate than that. I am not saying that space and time are wrong in all contexts, our future theories would have to reduce to relativity much like relativity reduces to Newton when you take certain limits. What I am saying is that worrying about the "nature of time" is much like worrying about the waves on a beach when there is a whole ocean to explore.