Grayson Hugh’s song says, “Time
is Like a River.” This simile describes time as we laypeople experience it,
anticipated events arrive and slip into the past.
Time is the causality law
that compels events to play out in sequential order. As Ray Cummings wrote in
his 1922 science fiction novel The Girl
in the Golden Atom, “Time is what keeps everything from happening at once.”
Time ticks once, and only forward, with every link in the chains of causality.
Seldom do any two physicists
agree when debating the definition of time. A lot of definitions have merit but
the science of physics has no single standard.
Einstein suggested that the sharp
difference humans perceive between past, present, and future may only be an
illusion. But, if that were true, life forms too small to suffer from
illusions, such as tiny bacteria, could not have internal clocks (circadian
rhythms). This oft-cited opinion was actually part of a consolation letter to a
friend who had lost a loved one and can therefore not be taken as a
cosmological definition of time.
Is time the fourth dimension?
Time is a dimension only in the sense that it can be represented by a series of
values and treated like one in math. Technically any series of measurements of
the same thing constitute a dimension. Representing time as a dimension is one
way to make it useful but says little about what time actually is. Time would certainly be meaningless without
distance or space in which to happen (t=d/s).
Theorist Brian Greene wrote,
“Just as we think of all of space being out there, we should think of all of
time being out there too.” If he’s correct, then past present and future are pages
in the book of time as legitimately as here
and there are pages in the book of
space. (The Illusion of Time, PBS, 8 Nov 2011)
But, if time is like a book, why
can’t we “see” future pages as easily as past pages in our memories? And, why
can’t we navigate time as we do the pages of space? Why can’t choices made on one
page change the outcome of prior pages? In other words, why don’t future events
affect the past as easily as past ones affect future ones? Greene’s view of
time doesn’t make sense.
God sees the past because He has
total recall. And He sees the future because reality is deterministic for an
omniscient being. It is morally dangerous to go down the rabbit hole of
thinking that the future already exists because, if it did, there’d be no point
in striving to make it better with today’s choices! Choice followed by
consequence is central to God’s plan of happiness.
Time’s actually more like a sea
with waves of dominoes toppling into each other. And, just as there is a limit
to how fast dominoes can fall, there is a limit to how fast any causal chain of
events can play out as observed from any particular reference frame. It’s
commonly called “the speed of light” but more appropriately called “the cosmic
speed limit” or simply c for celeritas, Latin for speed – the speed of
causality. All massless particles can hit this speed. Time is the
unfolding of physical causality within the cosmic speed limit.
Time existed as soon as the
universe had mass. Since time is causality, it started when something happened.
Time is something happening! The Big
Bang was something happening. It’s like fire happening when something’s
burning.
The perception of time is
dependent on the observer’s frame of reference but that doesn’t mean it’s an
illusion. Observers may perceive light as taking time to cross a distance from
point A to point B but a massless photon experiences points A and B
simultaneously. Time and space require a reference frame that photons do not
have. If there is no mass, there are no reference frames, so space and time are
undefined.