What's a "stuff" and what's a "dimension." I think attempting to define things so basic to our experience like "time", "space" and my favorite "shape" doesn't lead anywhere. I think these are concepts that cannot be reduced to anything else.

not a dimension. — Bartricks

And yet it can be dealt with as a dimension in mathematics and physics and predict observed results.

yet nothing that is infinitely divisible can exist in reality — Bartricks

Why not? Just curious.

And yet it can be dealt with as a dimension in mathematics and physics and predict observed results. — John Gill

That's consistent with it not being a dimension.

We can note too that if it is a dimension then we would predict that it would be infinitely divisible and would extend infinitely - yet nothing can be like that, and so we now know that treating it 'as if' it were a dimension is merely useful, in much the same way as, for example, taking our sense reports at face value is often useful even though reality may not be as they represent it to be. And we would predict that there would be no fundamental difference between an event's being present, past or future (yet manifestly there is a world of difference).

yet nothing that is infinitely divisible can exist in reality — Bartricks
Why not? Just curious. — John Gill

It is manifest to reason that 2 + 2 = 4 and that if a proposition is true it is not also false, and it is manifest to reason that nothing can actually extend for infinity, or be composed of an actual infinity of parts.

For example, someone who claimed there was a hotel that was full and would remain full even if half the occupants left, is someone we know a priori has said something false. There can be no such place. Yet if actual infinities are permitted, then such a hotel would be possible.

and it is manifest to reason that nothing can actually extend for infinity, or be composed of an actual infinity of parts. — Bartricks

Manifest=clear or obvious to the eye or mind. And does the eye or mind unravel every detail of the universe? If there are features of reality we cannot fathom does that negate their existence? Your hotel example is not terribly convincing, IMO.

Manifest=clear or obvious to the eye or mind. — John Gill

Hmm, no, just as it is clear to sight that there are colours, it is clear to reason - that is, our faculties of reason represent it to be the case - that 2 + 2 = 4 and that this:

1. P
2. Q
3. Therefore P and Q

is valid, and that no proposition that is true is also false, and that no actual infinities exist.

Obviously there is no suggestion here that our reason is an infallible guide to reality, but it is ultimately the only guide we have (such that even establishing that some of what our reason represents to be the case is not, in fact, the case would require appealing to reason).

And does the eye or mind unravel every detail of the universe? If there are features of reality we cannot fathom does that negate their existence? — John Gill

'No' to both. But if our reason - that is, the unprejudiced reason of most of us - tells us that something is not the case, then that is excellent prima facie evidence that it is not the case.

Note too that even those who, for dogmatic reasons, insist that only the reports of the five senses give us insight into anything real, also have to appeal to reason, for it is by reason - not sense - that we recognise that our senses provide us with insight into something.

What's a "stuff" and what's a "dimension." I think attempting to define things so basic to our experience like "time", "space" and my favorite "shape" doesn't lead anywhere. I think these are concepts that cannot be reduced to anything else. — khaled

I think the important distinction would be between substances that are extended and those that are not. Time, to the extent that it is conceived of as a kind of substance, must be being conceived of as being an extended stuff. And it is extended stuff that generates the problems.

What's a "substance"? And what does "Extended" mean? And again what is "Stuff." I think defining these is just as hard as defining time, which is why I don't think this discussion ever goes anywhere.

A substance bears properties. Extended would mean that it occupies some space - that is has volume, shape.

which is why I don't think this discussion ever goes anywhere. — khaled

But I've argued that time is not a substance. If the case is good, then we have gotten somewhere, for now we know that thinking of it that way is a mistake.

Time is what allows you to reflect on the past and plan for the future.

Ah, the great ovdtogt has pronounced.

Time is what allows you to reflect on the past and plan for the future. — ovdtogt

No it isn't. It 'is' the past and the future (and the present). Stop trying to be profound. Time is love on a tricycle. Time is what tomorrow needs to prevent it from being today. No, no, no.

No it isn't. It 'is' the past and the future (and the present). Stop trying to be profound. Time is love on a tricycle. Time is what tomorrow needs to prevent it from being today. No, no, no. — Bartricks

Time is a quality, like the colour blue.

Time is a four-sided simultaneous four day cube unlike the round earth one-day educated stupid the lizard people teach in schools these days.

j/k, time is actually a local entropic anisotropy in the phase space of possible worlds.

By which I mean that time is more like a big ball of wibbly-wobbly, timey-wimey... stuff.

(One of these is not a joke).

Time is a quality, like the colour blue. — ovdtogt

My food looks really time right now

they are all wrong, see op for details.

It is not, I think, a kind of stuff or dimension. This is for numerous reasons. Conceived of as a stuff (or dimension, if dimensions are not stuff), it would be infinitely divisible, yet nothing that is infinitely divisible can exist in reality (yet time does exist, thus it is not a stuff/dimension).

Note too that the past is potentially infinite, as is the future. But if time is a kind of stuff or dimension, then it - the stuff itself - would have to extend infinitely otherwise how could any event in it recede potentially infinitely into the past? Yet nothing that is actually infinite can exist in reality (yet time does exist, thus time is not a stuff).

Finally - and I am not suggesting these exhaust the problems - there would be no fundamental difference between past, present and future. Indeed, there would not really be such properties, only early than and later than and simultaneous-with. But future past and present are essential to time - they 'are' the fundamental temporal properties - and they are radically distinct from each other (thus, time is not a stuff).

Time, then, is not a stuff, not a dimension. — Bartricks

I've given it some thought and...

Motion is a very fundamental phenomenon. In fact every object in the universe is in motion relative to at least one other object. Imagine now a 100 meters race between 3 runners of differing prowess taking place in front of you. Since they're unequal in ability it's plausible and expected too that they will reach the finish line in a specific sequence 1st, 2nd and 3rd. This sequence is true and verifiable through actual first-hand experience.

The question that naturally arises is "how do we make sense of this sequence?" It isn't a spatial sequence because the race is 100 meters for all runners. Ergo, the sequence must exist in something that is not space and this domain where events can be sequenced is called time. This allows us to get a handle on what the sequence in the race means - the 1st runner took less time than the 2nd runner who took less time than the 3rd runner.

This also gives us the classical divisions of time into past, present and future. If we were to focus on the runner who comes 2nd we could call it the present; then the runner who came 1st is in the past and the runner who'll be 3rd is in the future.

Time is a domain in which events can be sequenced into past, present and future. It's very much like space where location can be sequenced into far, midway and near.

We measure time in some unit; the usual ones being seconds, minutes, hours, days, weeks, months and years etc. The most obvious unit of time and hence the first unit to measure time with is the day (24 hrs). However, the day is simply the distance the earth travels in one rotation around its axis. In other words we may reduce time (1 day) to space (the distance covered in one rotation of the earth). This model continues onto all units of time with a second being a specific distance between two marks on an analog watch.

Is it that time is just space (distance) then, with every unit of time being nothing but different distances? Recall the 100 meter race scenario above and we can see that the past, present and future (1st 2nd and 3rd) sequence isn't spatial - 100 meters for all 3 runners. The sequence is real and must be a sequence in some domain of reality and it's this domain, independent of space, we call time.

A measuring rod is divided into arbitrarily defined standard units.
Spatial measurements are made for an object by corresponding locations of the object to the rod.
A clock is a periodic standard event (tick) generator. It allows a measurement of the interval between events of interest in terms of ticks, in addition to an ordering of those events. Time is a human concept of convenience.

Time is a human concept of convenience — sandman

Yet there is a universal speed limit - the speed of light - and speed = distance / time, so it appears that something / some mechanism within the universe must be 'time-aware' else the speed limit could not be enforced - so time seems not just a human concept - it seems to be part of nature.

The OP seems to believe in absolute time. But absolute space is infinitely divisible, so he will have to reject that

(One of these is not a joke). — Pfhorrest

Nope, they all are .. including this one.. lol

I do not dispute that time essentially consists of the properties of present, past and future. But your analysis simply assumes that time is a dimension. The OP provides several reasons for thinking this is a misconception. Those problems have not been addressed.

For instance, can something exist that is infinitely extended? Well, no. For instance, when a position is shown to generate an infinite regress, we consider that a damning indictment of the view. Why? Because we - most of us - recognise that actual infinities cannot exist.

Now consider that any event in the past recedes potentially infinitely further into the past. Well, if we conceive of time as a dimension then the only way it would be possible for an event to recede infinitely into the past is if time itself extends infinitely - yet as just shown, nothing can be like that. Thus time is not a dimension.

Yes, that's correct. Space - conceived of as a dimension or stuff - shares some of the same problems.

As for 'absolute' time - I am not sure what you mean.

No it isn't. We have a concept 'of' time, but time is not a concept. The past, the present and the future are real. It is not by convention that there is a now. There 'is' a now, and we have come up with ways - no doubt confused - to express this.

Flat Earth physics.

Which is worse, bad theology or physics without the mathematics? Neither has a place in this forum.

The question of what time is, is a philosophical one. It is not a question in physics or mathematics.

Time is a human concept of convenience
— sandman

Yet there is a universal speed limit - the speed of light - and speed = distance / time, so it appears that something / some mechanism within the universe must be 'time-aware' else the speed limit could not be enforced - so time seems not just a human concept - it seems to be part of nature. — Devans99

An anti-realist with respect to time, might say that "nothing can travel faster than the speed of light" is a statement about the grammar of special relativity, rather than being a factual statement about the world.

The reason why special relativity 'concludes' that nothing can travel faster than c relative to any inertial frame of reference, is because otherwise causality would be violated by faster-than light objects moving 'backwards' in time to inform the past.

If we could make empirical sense out of this idea of causality being violated, then special relativity could not rule out the possibility of faster-than-light objects. But we cannot make empirical sense out of the idea of causal violations, since it leads to empirical contradictions. Therefore an anti-realist might argue that "faster than light travel" isn't a false proposition but a meaningless sentence. In which case "nothing travels faster than light" is a statement about the language of physics rather than a negative proposition about the world.

For instance, can something exist that is infinitely extended? Well, no. For instance, when a position is shown to generate an infinite regress, we consider that a damning indictment of the view. Why? Because we - most of us - recognise that actual infinities cannot exist. — Bartricks

Thanks for reminding me. All I wanted to do was prove that time is non-spatial, despite its measurement being so and that time isn't some kind a special space. Although it's represented as a 4th dimension in modern physics it is unique enough to deserve separate treatment.

If time can be represented as a dimension then what is time for a 2-dimensional being? Would it view our 3rd spatial dimension as time just like time is a 4th dimension for us? This is a puzzle for me and is beyond my skills to answer but I'll try and explain the issue: Either time is always the fourth dimension for all possible worlds or time is an "extra" dimension added onto whatever spatial dimension a world exists in. The former scenario would mean that all worlds, regardless of how many dimensions they have would consider time always as a fourth dimension. Let's call this situation as T4 time. In the latter view a N-dimensional world would make time as N+1th dimension. Let's call this N+1 time.

If time is N+1 time then time is actually space in a higher dimension accessible to N-dimensional worlds in a limited way in that we can only go from the past, through the present, into the future.

A T4 time situation seems unlikely because there is a sense that time flows in a universal way for all worlds and each world would need to have time added onto their space as an extra dimension.

So, time is probably N+1 time but that leads to time being just space in a higher dimension. Notice though that our freedom, what we can do, is severely limited in the time dimension - we can only move forward. For instance take a ball and roll it on a table. We can roll it back so it retraces its course perfectly to it's starting position but even though the ball moved backwards in space, it can never move backwards in time for time has passed into the future between rolling the ball forwards and rolling it backwards. Another way to see this would be the impossibility of going back to 1945 to witness the end of world war 2.

Some say this irreversibility is due to entropy - that it always increases causes the arrow of time. This is where things get interesting because entropy is a physical-spatial concept. If we could reverse every spatial entity in the right way then the world could travel back in time. Imagine that every event is reversed causally (for simplicity think billiard balls) we could then retrace our step back to, say, 1945 and see the end of WW2. Doesn't this suggest that time is reversible in theory but not in practice due to entropy? This explains the unique nature of the dimension of time insofar as we're concerned.

That means, if entropy didn't behave the way it does, we could access the temporal dimension as easily as we do the 3 dimensions of space. Time then is just space in a higher dimension.

As for infinite regress, I think if we consider time as a higher dimension of space the problem disappears. Nobody will object to space being infinite and if time is simply a higher dimensional space then there should be no problem in it being infinite.

For instance, can something exist that is infinitely extended? Well, no. — Bartricks

Why not? You are making it axiomatic that this cannot happen. Is your axiom true or false? How can you tell?

(time) is not, I think, a kind of stuff or dimension. — Bartricks

Which is to say no more than that you choose to use the word "dimension" in a way quite at odds with how it is used in physics.

You have invented a useless word game.

In which case "nothing travels faster than light" is a statement about the language of physics rather than a negative proposition about the world. — sime

There is a great deal of empirical evidence that the speed of light is a universal constant obeyed by everything in the universe; we have been measuring it for 100s of years and we currently know it within a measurement uncertainty of 4 parts per billion.

Saying the statement "nothing travels faster than light" is about the language of physics seems to me to be equivalent to saying the statement is a natural law - the language of physics is our model of natural laws after all - so I maintain a belief that the natural laws of the universe are time-aware. This suggests time is more than just a human invention.

We can roll it back so it retraces its course perfectly to it's starting position but even though the ball moved backwards in space, it can never move backwards in time for time has passed into the future between rolling the ball forwards and rolling it backwards. — TheMadFool

Theoretically anyway, the ball can end up back where it started in time - you might like to read about:

https://en.wikipedia.org/wiki/Closed_timelike_curve

So if time is best modelled as a dimension, which maybe the case, it seems to be a complex, convoluted, non-linear dimension - bearing in mind the results of SR and GR.

Nobody will object to space being infinite and if time is simply a higher dimensional space then there should be no problem in it being infinite. — TheMadFool

Some people do object - spacetime looks like a creation (see the BB). It's impossible to create anything infinite in size, so therefore spacetime should be finite.