Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time ...Isaac NewtonThings always change, as do we ourselves, in our perceptions, our beliefs, our social life, our mortal frame, the latter ultimately to be with clay compounded, or as a plume of smoke and a heap of ashes dispersed.
We cannot pause or rerun the tape.
Or can we?
After writing what I took to be my definitive view of time, I came across this, an essay by Thibault Damour, a French physicist and specialist in General Relativity, wherein the author states:
The paradigm of the special relativistic upheaval of the usual concept of time is the twin paradox. Let us emphasize that this striking example of time dilation proves that time travel (towards the future) is possible. As a gedanken experiment (if we neglect practicalities such as the technology needed for reaching velocities comparable to the velocity of light, the cost of the fuel and the capacity of the traveller to sustain high accelerations), it shows that a sentient being can jump, “within a minute” (of his experienced time) arbitrarily far in the future, say sixty million years ahead, and see, and be part of, what (will) happen then on Earth. This is a clear way of realizing that the future “already exists” (as we can experience it “in a minute”).So on that view, the future really does "already exists”, while the past continues to exist everlastingly. In fact every instant of time exists, apparently, simultaneously, now, as if set in aspic, in a world where every moment of horror, every seemingly endless geological age, exists, on and on, for ever and ever and ever: the hideous, four-dimensional "block universe." Good God?
"But is that a fact?
The space traveler, with an Earth-bound twin, who returns to Earth "say sixty million years ahead" returns to Earth sixty million years after the death of his Earth-bound twin when the Earth of 60 million years ago is long gone — sixty million Earth years ago, in fact. The travelling twin has not time traveled, he has simply aged well. In fact he has hardly aged at all, but he cannot return to the Earth of his youth because that Earth ceased to exist 60 million years ago.
So no, the Earth of today does not endure for ever, neither has it existed for ever. It exists only for a day. It is possible, however, under the right conditions of gravitation or acceleration for an individual to live very slowly relative to an Earth-bound twin.
This refutes the Newton-Barbour concept of time "flowing uniformly". Time has no reality apart from the events by which it is measured. Thus, in different places, the evolution of like systems, for example the aging of twins, or the ticking of clocks, are not necessarily correlated.
CanSpeccy: The Nature of Physical Reality, Part I: Time
CanSpeccy: The Nature of Physical Reality, Part II: Space