Because the word Time has two distinct, core meanings:-
And Time 1 could be said to measure Time 2.
Hence Time seems self-referencing. But isn’t really. Time 1 and Time 2 are different (abstract) nouns.
Time is how we reference change; it is both the dimension of change (e.g. ‘per hour’) and the collective ‘flow’ of change (a non-specific collective like Traffic is to vehicles).
One word, two distinct contexts, both referencing change and change-events.
Dimensions and collective nouns are both abstract nouns. Abstract nouns only exist in our collective minds (some say ‘illusion’, I wouldn’t call Traffic an illusion).
The tangible underlying reality is change and change-events. Zillions of quantum and compund change-events. From the universe expanding, earth spinning, your heart beating , atoms vibrating to quarks decaying – change (of which motion, spatial change, is one subset).
So Time is abstract, change is real.
And change is reference-frame specific (not universal as people misunderstand Time to be).
The ONLY empirical evidence of Time is change / change events (look around you – earth spinning, you breathing, quarks decaying – all change event series). Change can be quantum or compound, depending on your reference-frame. Time represents TWO distinct contexts of change:
1.The calibration of change (i.e. the dimension of change – hence ‘rate’ e.g. miles PER HOUR – the calibration of change of position aka motion) i.e. Time is to change what temperature is to heat, a dimension/calibration set. Temperature is abstract, heat is real, Time is abstract, change is real; and
2. Time is the collective ‘flow’ of change. Time is to change-events what ‘River’ is to water molecules – a collective term. But, fundamentally the word River is an abstract collective, water molecules are real. Time is a collective abstract, change-events are real – Time, the ‘flow’ of change.
Time, one word, two distinct meaning, both reference change.
So Time is abstract, it wasn’t created; but change occurs due to energy differential.
Does Time exist? Does a river exist or just a collection of water molecules?
Er, no. And the answer lies in your question.
In the first part of your question you very rightly call Time the flow of change.
But in the second part you revert to talking about time flow.
Fundamentally all there is is quantum change-events. They are the tangible reality. Time is merely the (non-specific) collective word for all that change.
Let me give you another example of a non-specific collective word. Traffic is the non-specific collective word for vehicles. We talk of traffic moving, slowing, stopping etc. Yet traffic merely references the underlying reality which is individual vehicles. Individual vehicles are the underlying reality. Vehicles move, starts, stop.Traffic is merely a collective noun.Traffic only ‘flows’ as the aggregate/ average speed of the underlying individual vehicles.
So too Time. Time is merely the collective noun for the underlying reality of change-events. .
So the first half of your question encompasses that understanding, i.e. that it is individual change-events that matter.
But the second half reverts to expressing Time as a tangible entity itself. Fundamentally its not. Its the individual quantum change events that are the reality.
Sir,
Time (in this context) is a measurement framework, calibrated in standard units (e.g. hours). It calibrates change (hence ’rate’) So, yes, Time is constant. It is also reference-frame specific.
Space too (in this context) is also a measurement framework, calibrated in standard units (eg miles). It calibrates relative position.
Spacetime hence calibrates changing position ie. Constant Motion (constant because all calibrations are reference-frame specific). It is calibrated in miles per hour.
Spacetime-time calibrates constant acceleration eg miles per hour per hour.
Spacetime-time-time calibrates constantly changing acceleration. Miles per hour per hour per hour.
And so on.
That makes spacetime complex.
What is Time? 