There is no empirical evidence of Time being tangible, concrete or ‘real’ – no evidence at all. Time doesn’t cause anything.
If it has no causal impact, it has no existence, other than in our mind.
If it was real, tangible, we could base hypothesis about its nature on that impact. But there isn’t any. Time is therefore just a word; and hence the definition that we ascribe to it is based simply on our usage and agreed meaning.
And when you break down the words usage, Time has two core, root meanings:
1. Time is the ‘flow’ of change. Time is a non-specific collection of change events, i.e. time is to change what traffic is to vehicles, and
2. Time is the dimension of change. Time is an abstract framework for referencing, indexing and calibrating change (i.e. a ‘dimension’) – i.e. time is to change what temperature is to heat – it is an abstract calibration set of the underlying reality.
For what else other than change is there to indicate time ‘happening’? Without change there is no time. Change is the underlying reality, time is the overlaying abstract.
So that is time – so simple. Mystery solved.
If time is the dimension of change, and space is the dimension of static position, hence space-time is the dimension of dynamic position i.e. motion.
The two universal realities aren’t space and time, but their underlying fundamentals of existence and change – or more directly, matter and energy.
Time might be construed as universal, but change is quantum or reference-frame specific. Time is abstract. Change is the objective reality.
What science needs to focus on is not time but the underlying fundamental – change-events and the relationship between change events; the relationship between the outcome of energy differentials. Einstein was good at relationships.
What is more surprising than having to accept that time is an abstract is the absurdity of ever believing that it wasn’t. The idea that there was something concrete or tangible, that was time, but which not only couldn’t be explained, but that even its possible nature couldn’t be explained (was it meant to be a force, a flow, a current – who knows) is strange. For me the most mysterious thing about time is that it is just a word – so how can we, the authors of the word, have allowed its definition to have run away from us?