It seems to me there's a bait and switch of sorts that we play on kids. We tell them science can answer their questions about the world, or that they can use science to answer those questions, but it kinda can't. Keep digging and pretty soon you're lost in not-quite-accurate metaphors that may have nothing to do with reality and "we can tell you how it behaves, it's [pages of equations], isn't that good enough?"

It may be (probably is) that "what is this" or "why does it do that" are just meaningless questions, in the sense a child (or adult who hasn't re-calibrated their expectations of what science can tell them) means them. Which is interesting itself, I suppose, but at that point just go study philosophy and art, if that's why you were into science in the first place—and I think it's why everyone at least begins to be interested in science.

[EDIT] in particular it's frightening how fast kids' questions stymie an adult because the adult realizes that they're only a step or two away from "why is there something instead of nothing, and also what is something?" and... good lord, at that point seriously just go become religious or get really into philosophy or something, because you're outta luck, kid, sorry, we don't have any actual answers, just observations about what all this stuff does, but no we can't tell you what "stuff" or "does" are.

Noam Chomsky usually has this point, that the human mind seems limited in its "native understanding" to a mechanistic view of the world - that is the only kind of model that is truly satisfactory to us.

He also points out that, ever since Newton, the dream of mechanistic world was shattered, and with it, any hope that science would help us "make sense of the world" in a truly satisfying sense. Instead, we have become content with modelling the world mathematically and predicting how it will evolve.

Of course, space-time and quantum mechanics have driven additional nails in the coffin of a truly understandable world.

>Of course, space-time and quantum mechanics have driven additional nails in the coffin of a truly understandable world.

I'd think the opposite. The fact the world can work at least as strangely as relativity and quantum mechanics suggest, and we still figured those out as much as we have so far, reassures me in our ability to figure out the world we exist in.

What I meant was: quantum mechanics and relativity have shown that not only is the physical world slightly different from the kind of world our mind can picture (e.g. "mechanistic, but with the universal attraction force"), it is in fact nowhere near our built-in mechanistic model, and we can never hope to build a real intuition about the world.

However, we can still hope to model and predict it more accurately than we would have ever hoped before, so there is that :)

It's also frightening how quickly a philosophy professor can get stymied by a really confident or particularly stupid undergrad. I don't think science or philosophy should claim to answer all questions. Many questions are ambiguous, badly formed, misleading, nonsensical, and I don't think a robust account of knowledge is one that ends with a stack of turtles.

Science cannot answer all of our questions, but it can teach us how to ask better ones.

You might enjoy this one https://en.wikipedia.org/wiki/The_Unreality_of_Time

Yes! I do know this one. And it is very interesting to me.

Watch this video: https://www.youtube.com/watch?v=-6rWqJhDv7M

I myself lean to the Aristotelian definition: count of change.

After all, all our clocks are built on this definition. If there were a lone particle traveling in an infinite universe, it'd be nonsensical to talk about its speed because there'd be nothing to relate the distance traveled to (and no observer). Indeed, whenever we talk about "time" and related quantities like "speed", we always compare the observed object to some other, existing reference.

So I think of the interaction of particles/matter as being something fundamental, whereas "time" is a synthetic human notion.

I too subscribe to the idea of time as change, i.e. if all motion stops -- including the motion of subatomic particles -- it is the same as time stopping.

You have your one immutable[0] particle that is left at the tail end of the heat death of the universe. It's not going anywhere, because there is nowhere to go. It's not doing anything because there's nothing to do. It is a lone observer, with nothing to observe.

Except! There would still be virtual particles creating and annihilating. Let's assume that there is an interval between these events (e.g., they aren't constantly present).

Would Aristotle say that no time passes between events? I would tend to say that time yet passes even during the periods when nothing else exists and nothing is happening.

Let's say the second to last things in the universe were another observer with a clock who could time and observe these virtual particle events, and this observer was able to time these events at a 1 second interval between events (duration of event is irrelevant).

And then that second-to-last observer and the clock suddenly annihilate somehow so that only your immutable particle remains. And the virtual particle events still happen at the same interval period.

Would the time interval between virtual particle events somehow be different without the clock/observer as with the sole immutable particle? That doesn't make sense to me, though I will certainly admit that it could very well be!

Aristotle's idea of time is not fully satisfactory to me, though I can't of course rule it out.

[0] Important! Because if the particle is not immutable, then it is waiting for change, which requires time.

> The Planck time is by many physicists considered to be the shortest possible measurable time interval; however, this is still a matter of debate. [0]

So, if this is true, then does it mean that time does not 'flow', but rather 'chunks'?

[0]: https://en.wikipedia.org/wiki/Planck_time

In a very real sense, we may never know. The problem of natural language is that it doesn't really work all that well for scientific purpose: talking about chunks and flows comes with a human's lifetime's worth of thinking they know what those words imply, and so we don't use them except in popular science articles. Time could be discrete, or it could be continuous, but while in normal life the difference between those two is easily determined, this is not the case in physics at all: in order to say "which of the two it is" you first need to have an idea where the boundary between the two would have to be.

(even at the macro level, a river that moves a specified number of molecules per time unit doesn't "flow", it's technically moving discrete "chunks" of water, we just don't say it's moving chunks of water because no one cares about the "well, technically..." in normal conversation. We know what's meant and what to ignore. Physics doesn't have that luxury)

We have no idea where that boundary can even be found; it would certainly have to be below the Planck length, but we have nothing that allows for that kind of precision. The only thing physics can say right now, and possible even ever can, is that nothing we have at our disposal allows us to conclude time "actually is" discrete. We can come up with mathematical frameworks that assume time is a discrete dimension, but even if those yield super accurate predictions that are then verified through experiment, all that does is confirm that a continuous dimension can be reduced to a discrete one without loss of precision.

This is just wrong. The Planck time is just the time scale when quantum and gravity effects become both equally important. The wikipedia article even says so. It's definitely not some sort of time quantum.

The question I've always had about Planck time is about the "clock". If you and I observe something move and we were able to do so at Planck resolution, would our ticks be synchronized?

Can you phrase that question in a way that takes relativity into account? In particular, what do you mean by ticks being synchronized between two observers, when there's no such thing as objective simultaneity?

Two observers in the same inertial frame can share a clock, can't they?

I believe so. I had assumed you were referring to the general case, sorry about the misunderstanding.

My favorite answer is:

“Time is what the clock measures.”

Can you recommend any good books on the topic?

Not OP, but I just fininshed reading Carlo Rovelli's "The Order of Time" and it helped me figure out some pieces of the puzzle a bit better. High level and divulgatory, not an hard science/math book.

Off the top of my head ->

Carroll, From Eternity to Here - reasonably good and quite accessible.

Coveney, The Arrow of Time - better than average

All of my books are packed away right now for a move, so I'm sorry I can't come up with more. Though that Carroll book is really a decent entry point.