[Certhas]

I take your bunch of molecules ("physical manifestation") and squash them into a black hole. Now they have been turned into an aspect of the structure of space and time ("a measurement or perspective").

So no, space and time are not "measurements/perspectives" that are fundamentally distinct from "a bunch of molecules".

[joslin01]

Ok so you change the situation drastically by squashing them into a black hole, something nobody really understands, and tell me coffee and time are interchangeable. Right.

Also I never said space was measurement/perspective, I said time was. You believe what you want to believe, but maybe stick to a single scenario in the future. I'll say it again, a cup of coffee just sitting there is distinct from time.

[Certhas]

Ok one thing at a time.

I did not say they are interchangable, I said if one is an illusion, so is the other.

I also claimed that your notion of "physical manifestation" is not a meaningful distinction. Or at least, it's not easy to make it into a meaningful distinction that is compatible with what we know about the laws of physics.

It iis incorrect to claim that nobody really understands black holes. There are aspects of them that we don't understand, but we understand fairly well how a massive amount of coffee would turn into a black hole (a structure in space and time).

Also space and time are really not on different epistemological or ontological footing anymore.

We also should distinguish a particular instance of coffee and the concept of coffee itself, just as we should distinguish a particular time interval from the overall notion of time. A time interval then is a chunk of metric between two endpoints that would be marked, for example, by molecules doing something like ticking. It's a relative configuration of gravitational and matter fields.

Your concrete cup of coffee is likewise a configuration of matter and gravitational fields. Ontologically they really aren't that different if you take general relativity seriously.

Your perspective seems to be somewhat pre GR. Sort of Kantian: Time is not a category of reality but a category of our perception of reality. The work of Rovelli et.al. is two steps further. In GR time no longer has a distinguished foundational meaning in (and in that way it is like coffee). It's constructed from physical fields that describe its structure. The thermal time hypothesis goes one step further by making the "time field" (which is the metric, which is the gravitational field) be emergent. It's not the only theory to do so. Jacobsons GR from black hole entropy is conceptually similar.

[ben_w]

While I agree that was a poor example for much the same reasons, I think I have a much better comparison:

Duration is as much a measurement/perspective as displacement, this is an observation which led to Special Relatively. If time can be called an illusion, so can position.

[SiempreViernes]

If duration is a simple displacement between two points in another direction of space then you are right, the two are equivalent: you have then also accepted that time does not flow and lacks intrinsic direction for it is precisely these properties that separates "time" from "space".

Time flows and is irreversible, this is what makes it special, and it is the denying that the flow and irreversibility are inherent properties of time that constitutes "dispelling the illusion".

In other words, saying that "time is an illusion" is saying "time is just like space".

[ben_w]

> Time flows

In what sense? Normally people use that word in a sentence such as “time flows like water”, but water is made of discrete molecules and has momentum, which doesn’t generally ever sound like the subsequent sentence, whatever that happened to be at the — ah ha — time.

> and is irreversible

The funny thing is, thermodynamics is the only law of physics which say that and last I checked nobody knew (or agreed) why, as thermodynamics is inevitable from the other laws but the other laws don’t imply a direction for time.

Of course, there’s also the difference of it acting like imaginary (sqrt(-1)) space…

[goatlover]

> The funny thing is, thermodynamics is the only law of physics which say that and last I checked nobody knew (or agreed) why, as thermodynamics is inevitable from the other laws but the other laws don’t imply a direction for time.

There's also cosmology, which says there has to be a direction to time because of how the universe turned out as a result of the Big Bang, inflation, and everything that followed.

[SiempreViernes]

Look, I'm just listing the properties ascribed to time that sets it apart from distance, not taking a position as to their correctness or how accurate the similes are. If you are ready to accept the timeless unchanging universe that's fine by me, just acknowledge that is what you argue for.

[ben_w]

Calling it “timeless and unchanging” is as incorrect as calling it “x-axis-less and dζ/dx is always exactly zero for all possible variables ζ“.

I think you need to be precise with language for this sort of thing, and avoid similies everywhere, or you’ll run into the same sort of problems quantum physicists have with “observations collapse the wave function” being misunderstood as “conscious minds collapse the wave function”.

[Certhas]

We need precision here. The intuitive notion of time that you start from has a lot of structure.

The question is where does this structure originate? Is there a fundamental thing "time" that has direction, irreversibility, a moment of now, memory of the past?

It doesn't appear so. Instead it seems that most of these properties emerge for complex systems.

If the universe was a box of gas there would be none of the above. So we conclude that time direction, memory, irreversibility, etc... are features of particular configurations of matter that we experience. A universe with the same laws of physics but without these features is conceivable, so they are not fundamental.

[joslin01]

I guess I don't see the equivalence. Time very much depends upon duration and the terms might as well be synonymous. Does space depend upon displacement? If we froze a single instance of space & time, we would see a universe sitting still. Space and all its fillings would still be there but would time? I believe it quite bold to call space time and time space just because duration and displacement seem similar.

[ben_w]

You’re calling one dimension special because if you remove it you don’t get to use the special words you use for that dimension.

If updown was a special named dimension and you took a single 2-space+1-time slice of the universe at fixed radius from the Earth, your argument wouldn’t really be different, only words and phrases like “sitting still”, which is inherently about the dimension being removed, because it’s convenient for us.

And that’s ignoring questions like “can particles have momentum if there is no time?” which might actually be important in the unlikely event that I understand what a black hole’s singularly does to time.

[joslin01]

I think what you're saying is fair and I realize it might be pushing it to remove the dimension of time to articulate my position.

Regarding the last question, if I understood forces correctly, it's that they remain in motion until an equal or greater force stops them right? Why do we need time for that out of curiosity?

[ben_w]

Thanks. Velocity is the derivative of position with regard to time. Does it exist if there is no time? It might be that momentum is the fundamental thing and velocity is just a consequence of it. Or not, I don’t know.

Momentum has a direct influence on Einstein field equations, and I don’t know enough maths to follow GR (just two A-levels) so I have no idea if that “direct” influence is still present at a no-more-future boundary condition.

My insufficient maths skills are, amongst other things, why I don’t trust my understanding that a black hole singularity really is a no-more-future boundary condition.

[haZard_OS]

Don't you think the concept of "motion" presupposes time? For that matter, every verb in existence presupposes time.

A fascinating book on this topic is "Philosophy in the Flesh" by George Lakoff:

https://amzn.to/2vCkS9s

[TuringTest]

> If we froze a single instance of space & time, we would see a universe sitting still.

I don't believe that mental experiment proves what you think. If you freeze time, there wouldn't be anyone that could make observations. You might as well choose one fixed point in the universe, eliminating space considerations, and think about its whole story from the beginning to the end of time; that would be as real as a frozen universe.

I think of reality as a goo of vibrating stuff, encompassing all matter and energy. Matter creates space, and the vibrations of change create time.

[jhayward]

The problem you may be having is there is no separate thing called 'space'. There is only 'spacetime'.

[SiempreViernes]

Uh, so you have a reliable theory for the insides of a black hole? Or how do you know what happened inside the black hole?

In any case, the cup distorted spacetime even when it wasn't big enough to form a event horizon, so that it still does it after being squashed proves nothing for the issue at hand.

[Certhas]

Yeah. I do. It's called general relativity. It doesn't tell me what happens at the singularity, but it's valid for the vast majority of the interior of a large black hole.