Wow there is SO much here to comment on.
TIME Steve hit it squarely on the head, time is one of the spacial dimensions and DURATION is an excellent way to describe it.
To exist in the Universe something must have Length, Width, and Depth AND it must have a fourth dimension of Duration, i.e. it must endure for a period of time...from one instant to another. That of course does not actually say what time is or why is is unidirectional.
The Laws of Thermodynamics do not answer the question of WHY they merely state what is. SPACE is necessary (Length, width, height) else everything would happen in the same place and TIME (whatever that is) is necessary else everything would happen at once. Clocks, no matter what type do NOT measure time (whatever that is). Clocks count EVENTS. TICK and TOCK are events separated by an interval of time (whatever that is). Since we can only measure these events and not time itself, time will appear to be a constant to any observer within his frame of reference. Since there does not exist an absolute Frame of Reference every ones unique frame is as valid as anyone elses...IT'S ALL RELATIVE you see.
Gravitational fields (which also don't actually exist any more than centrifugal force exists) also affect time. The more intense gravitational field of the sun, for example, causes time to run slower RELATIVE to the flow of time on Earth. Thus within the ultimate field of a Black Hole time would cease to flow, and volume would go to zero that's why it's called a SINGULARITY.
Speed also alters the flow of time. Time slows as speed increases RELATIVE to the slower moving Frame of Reference. The so called Twin Paradox: My twin brother boards a spacecraft and heads to the nearest star at 98% of the speed of light. If I could observe him in flight I would see him moving slower and slower whereas he, observing me, would see me moving faster and faster. On his return he would be much younger than I and I much older than he due to the time differential within our Frames of Reference.
Oh, by the way, Newtonian Physics NEVER actually worked as it was supposed to, there always existed small discrepancies between prediction and experiment. Those discrepancies were chalked up to EXPERIMENTAL ERROR, i.e. the inability to make a fine enough measurement. Experimenters stated that WHEN the ability to measure improved those discrepancies would vanish. Unfortunately as mensuration improved the discrepancies got worse. The Quantum Universe is not Newtonian and can't be made to be so.