What is relativity physics?
Relativity comes in two (2) parts:
i. In Special Relativity Physics:
a. time depends upon your relative position standing in space
watching the hands of a distant clock;
b. time depends upon your relative velocity;
c. in both a). and b). the doppler effect is central to both;
d. and, due to the upper limit of the finite speed of light, different
relative positions and velocities in space, the unit lengths of a
given measuring rod will either contract or expand upon
viewing: it depends;
ii. In General Relativity Physics:
a. acceleration and gravity are the same phenomenon: hence
mini-gravity fields are created in space whenever there's
acceleration, defined as an increase or decrease in speed as
well as changing direction whether there's a change in speed or not;
b. therefore the closer you are to the earth, the slower will the hands of
your wrist watch move.
GPS (Global Positioning System) depends directly upon both
Special and General Relativity physics equations.
Without these relativity physics equations, GPS would be
What is time?
Time is an accounting for the relative motion of two (2) or more bodies. Imagine this: if there were no bodies, would there still be time? If there were no motion between two (2) or more bodies, would there still be time? A need for time??
How to stop time?
Answer: by stopping all motion. Of bodies. Of subatomic particles. Of everything!!
All of which is an impossibility.
Even if this could be accomplished, it would take an infinite amount of energy. Again, an impossibility.
Which unequivocally demonstrates the philosophic nexus and inherent intimacy between “time” and motion of bodies.
█ Corollary question: How to reverse time?
Answer: by reversing all motion! What went forward, now must be placed into reverse. Hence, reverse time.
Which, again, is an impossibility.
This is also called the “Arrow of Time”.
Which evokes the idea of the entropy of dissipating energy into the void of an unremittingly expanding cosmos.
But, wait, why can't I only stop time just for myself?
Actually, yes. How? Simple. By creating a micro-gravity field all encompassing yourself by twirling exceedingly fast approaching a significant fraction of the speed of light, say 20%.
By doing this you'll be employing Einstein's "Equivalency Principle" for a gravity field being equivalent to acceleration. That is, think about it, when you twirl you're accelerating by definition and by doing so you're actually creating an enveloping, all encompassing, micro-gravitational field which in turn will slow your biologic metabolism and concomitantly slow the time progression of any watch "properly attached" to you - i.e., your wrist watch. That's how.
And, interestingly, you’ll eventually come back to "normal" but younger in finally stopping compared to when you began this entire process!
Finally, by twirling at speeds approaching 20% the speed of light, the outer surface of your body will perform as the event horizon boundary of an artificially created black hole! Yes! And during this entire process your "properly attached" watch will stop at this event horizon boundary, your metabolic aging will certainly significantly slow if not stop completely and you may indeed disappear entirely into a form of pure energy from any external view. Ha, ha!
What is space-time or spacetime?
Spacetime is simply the fact that at each and every position in space, there will be recorded a different gravity potential and hence a different time to an outside observer. Einstein formulated a geometry in order to best manifest a spacetime metric with the speed of light providing a standard metric for measuring distance.
What is matter?
"So matter, as it were, is condensed or frozen light" - David Bohm ( 1917 - 1992, born Jewish - American, Manhattan Project, Israel's Technion )
What is mass?
Mass is a subset of matter possessing extensible substance. The Higgs-Boson ( or "God" ) particle, the discovery of which was announced on July 4th, 2012, provides this substantiation as it traverses thru the still theoretical Higgs field.
What is the event horizon ?
The escape boundary beyond which nothing can escape the black hole.
Do black holes evaporate?
Yes, by the Hawking radiation which postulates that as a particle disappears into the maw of a black hole, it's companion anti-particle by quantum tele-transportation ( or simply transportation ) will escape the black hole event horizon speeding in the opposite direction.
What is the far distant future of the universe?
To expand endlessly at an accelerating pace into the deep, dark void of nothingness of absolute cold and darkness due to the doppler effect for light and an unremitting dark energy pushing the expansion of matter in the cosmos ever further outward. Read: "The Emptiest Place in Space", by Istvan Szapudi, Scientific American, August 2016 for an explanation as to the unseen origin of dark energy.