Special Relativity for everyman (or woman) - 3. Time

Time - What is time? Time is, strictly speaking, not a dimension; so much as it is the rational ordering of events; It is an effect, an effect produced by the process of change.

Time is a mysterious amorphous entity whose presence is everywhere, yet its definition has eluded man ever since he started to question his understanding of the world.

So what is time? To determine that, we could start by defining what we know, the Fundamentals of time. And yet, how can we determine the fundamentals of time, without defining what time is?

Newton wrote:

"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 inequable) measure of duration by the means of motion, which is commonly used instead of true time ..."

Which seems to be a very sensible and concrete definition. It is something that agrees well with our own perception. That time flows equably, without regard to anything external, all we can do is to choose the background, or coordinate scale, against which to measure time. We can change the units we measure by, we can change their dimension but time moves inexorably on.

It is said, in a somewhat light-hearted way, that: "Time is what stops everything happening at once"; yet I would venture to declare that it is, in fact, the very opposite, that Time is created because changes don't happen 'in an instant'. Time is an effect of change.

Time Happens. It accumulates.

A Time Interval, is the temporal separation of two Events, that may, or may not, be at the same location.

A System is a set of interacting or interdependent components forming an integrated whole.

Any System has an Absolute time. That is the time measured from the start of that system. It stops at the end of that system. The Universe is one such system, where time began at the Big Bang.

Then time is being created by many systems at the same time, I hear you say, so what happens to it all?

The time created by each system is independent and created in parallel but it can only be measured by comparison to other generated times.

And how is it absolute? Because, whatever scale we use, all times occur at individual points on that timescale.

Because it can only be measured against another time. All times are measured against whatever timescale we choose.

And one time scale, the life of the Universe, encompasses all others. Every event occurs at one individual specific point on that scale.

So again What is time? A good question. For, as I say, it is not easy to determine the fundamentals of time without defining what time is. Let us begin by examining what we do know about this strange entity, that has a presence, but no physical form, yet is described as the fourth dimension.

How do we detect time? How does it interact with the physical world as we know it and with the other three dimensions?

Anything but an instantaneous change (if such a thing is even possible) has a duration. A period of time that lasts from the start of the process of change until the end of that change. Time is the label that we give to the interval between the start and the end of a change, or to the interval between Events.

(Remember; an Event is a specific point in space at a particular instant in time).

Whenever and however we measure time, we are measuring change. How long it takes to change from a 'Before' state to an 'After' state. Time is the Duration of that change.

If there existed a volume of Spacetime, or a unique Spacetime, in which there wes no change: a completely empty vacuum, not affected by any kind of radiation, for example; no time could pass within that volume.

(Think about it; if that space were visited at 1,000 year intervals, as measured by an outside observer, within that space nothing could have changed so, within that space, no time could be measured to have passed).

I believe it is valid therefore, to aver that time is generated by change. Intervals between Events are measured within a global or absolute time that has existed from the Big Bang since which there has been a single ongoing change - the expansion of the Universe.

If we keep two identical clocks, in identical systems, or in the same system, they would keep identical time. Viz. Einsteins First Postulate.

If we imagined them as the finest Swiss mechanical watches, or indeed as atomic clocks, it would mean that when synchronized, they would always read the same time but if one were to be set running slow then the time created by that clock would be less; e.g. it might read 59 secs when the other watch read a full minute. Or it could be stated just as correctly that one watch was running fast, reaching 60 seconds while the other read only 59 seconds. Each would be creating its own local time.

The one thing that we can say is that if two identical clocks keep different times, that the conditions under which those clocks operate are different.

Durations

Time: that constitutes the temporal interval between events.

Event: a location in Spacetime; i.e. a point in space at an instant in time.

Interval:

As Processes progress, so time accumulates.

The past cannot be changed, as it has already happened. To change it every particle of mass or energy would have to returned to its state at that past time.

The present is where we are and it always will be, just where we are.

Future time does not exist, it has yet to be created.

Can time's rate of progression vary?

No, the duration of the processes measured may vary due to the conditions under which those processes operate, OR because of the conditions under which those measurements are made.

Time is an effect created by change; It is no more than a measurement, against a scale.

It is change that has a rate, not time; time is the scale against which a rate of change is measured. To say that time can be fast or slow is to measure time against itself!

Processes may be fast or slow and this may affect the duration of an event; that is the time that has passed between the start and the end of a process, measured against some scale, but that does not mean that more or less time has passed, only how it is measured.

We must not only count the units of time, for the total amount of time measured is also dependent on the magnitude of those units.

Time is absolute. It may be considered to have started with the Big Bang and can, logically, be measured against the expansion of the Universe. Every event has happened at some point in that expansion of the Universe. At some point on a simple, single, straight-line scale. And each point marks how long after the Big-Bang that event occurred. If two events have the same separation from the Big-Bang then they must be simultaneous measured against the life of the Universe! It is as simple as that.

Different observers may perceive Time differently, but that is only because of the conditions under which they measure Time.

If we say that time passes more slowly when observed by a speeding observer, it is the movement of the observer that is affecting the measurement of the time passing, rather than the passage of time. It cannot be the passage of time, for, when measured in the clock's own Frame of Reference, rate that time passing is unchanged; and again, when measured against a wider scope, such as the expanding Universe, the same time will have passed.