# What is time? (Again)

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12 minutes ago, drumbo said:

Any change in the system at all. If there is no change, time effectively never passed

You haven't shown why this claim of yours is true,

(or why  you ignored my example that shows it to be false)

10 minutes ago, Strange said:

Or it implies the non-existence of quanta when you consider that time is continuous and there is no lower bound.

(In other words, your statement is an example of the fallacy of begging the question.)

Good response to my second query to Drumbo over this. +1

I know of no evidence that space is quantised. Although there is much speculation and discussion about that question in Physics, nothing has definitely shown this.

In any event time itself is not quantised in Relativity theory.

Edited by studiot

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2 minutes ago, drumbo said:

But is that not an example of a memory-less process? As far as I know, the prior amount of time which has passed without a decay does not give you any information about when the muon will decay in the future.

Huh? So what. The muon will decay in a few microseconds, even though nothing changes in the meantime. So obviously time passes with no change.

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1 minute ago, Strange said:
4 minutes ago, drumbo said:

But is that not an example of a memory-less process? As far as I know, the prior amount of time which has passed without a decay does not give you any information about when the muon will decay in the future.

Huh? So what. The muon will decay in a few microseconds, even though nothing changes in the meantime. So obviously time passes with no change.

Indeed, but it is worse than that because different observers (including the muon) will measure that amount of time differently.

How does that work with quantisation?

One observer's quantum is another's 1/3 or 0.3 recurring forever quantum ?

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Just now, Strange said:

Huh? So what. The muon will decay in a few microseconds, even though nothing changes in the meantime. So obviously time passes with no change.

If you observed time passing between your observation of the intact muon and its subsequent decay, then that implies a change in the system since you could not perceive the passage of time otherwise, and therefore is not a refutation the existence of the quanta.

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Just now, drumbo said:

If you observed time passing between your observation of the intact muon and its subsequent decay, then that implies a change in the system since you could not perceive the passage of time otherwise, and therefore is not a refutation the existence of the quanta.

I can't see how it has anything to do with quantisation of time, even if it were support for the idea that change is required (which it isn't).

Again, what evidence do you have for the quantisation of time or space?

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5 minutes ago, Strange said:

I can't see how it has anything to do with quantisation of time, even if it were support for the idea that change is required (which it isn't).

Again, what evidence do you have for the quantisation of time or space?

The big bang. If there was no quanta of space, you could just keep compressing everything together more and more. But you can't, you can only fit so much inside of a quanta of space, and that's why there was a big bang.

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Just now, drumbo said:

The big bang. If there was no quanta of space, you could just keep compressing everything together more and more. But you can't, you can only fit so much inside of a quanta of space, and that's why there was a big bang.

That incoherent nonsense is not evidence for anything.

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2 hours ago, Strange said:

If you curve the empty spacetime then you will get gravity. Well, depending how you curve it, I suppose.

IF. . . you can have empty spacetime and our substantialist interpretation of general relativity holds water in the possible absence of quantum fields. Or that it holds at all. Map versus terrain issue here?

30 minutes ago, Strange said:

Take the example of a muon then: no internal structure, nothing to change. And yet it still decays after some time.

Yes, it has the properties that you ascribe to a muon then after some allotted time (certain amount of ticks by physical clocks in nature or in the lab) it changes to have there be other particles with unique relational/monadic properties (mass, charge, spin, etc) but so what we regraded as the muon no longer exists. . . change has occurred due to a difference of properties after a certain number of clock ticks from one of our physical clocks/internal clock has gone by.

32 minutes ago, drumbo said:

Lol muh fallacy. Consider this, if space in quantized, and we know it is, then how could time also not be quantized, since one cannot exist without the other?

As far as I know we do not happen to know that time is quantized or that there should be a benefit mathematically to experimentally show the improvement of moving from a real number line representation abstractly of change to that of the natural numbers.

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1 hour ago, joigus said:

Very droll.

Now seriously. (...)  Gravity can be defined even if there are no sources (energy-momentum tensor). Those are empty space-times. They can be defined theoretically. Out of this context, I don't know what you're talking about.

Please explain. You have a 4D spacetime. How do you end with an interaction like gravity while being empty?

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26 minutes ago, Strange said:

Huh? So what. The muon will decay in a few microseconds, even though nothing changes in the meantime. So obviously time passes with no change.

The universe around it does and eventually the muon as well. Change without time in the Sydney Shoemaker sense doesn't preclude you could have objects that in the presence of change around them retain the same properties (relational/monadic) so that they do not change. Extend your example to a universe without any physical clocks/substantivalist time implied?

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2 minutes ago, The victorious truther said:

IF. . . you can have empty spacetime and our substantialist interpretation of general relativity holds water in the possible absence of quantum fields. Or that it holds at all. Map versus terrain issue here?

You can model empty spacetime. Obviously there is no such thing in our universe.

3 minutes ago, The victorious truther said:

Yes, it has the properties that you ascribe to a muon then after some allotted time (certain amount of ticks by physical clocks in nature or in the lab) it changes to have there be other particles with unique relational/monadic properties (mass, charge, spin, etc) but so what we regraded as the muon no longer exists. . . change has occurred due to a difference of properties after a certain number of clock ticks from one of our physical clocks/internal clock has gone by.

So you are saying that the muon knows when to decay by looking at the lab clock?

3 minutes ago, The victorious truther said:

As far as I know we do not happen to know that time is quantized or that there should be a benefit mathematically to experimentally show the improvement of moving from a real number line representation abstractly of change to that of the natural numbers.

GR only works if space and time are continuous. But then again, we know that GR probably needs to be modified at quantum scales.

Good article on the possibilities here: https://www.forbes.com/sites/startswithabang/2018/06/14/are-space-and-time-quantized-maybe-not-says-science/

1 minute ago, michel123456 said:

Please explain. You have a 4D spacetime. How do you end with an interaction like gravity while being empty?

I guess this (like so many questions) depends how you define "gravity". If you mean something causing masses to move under the effects of other masses, then obviously that does't happen in empty spacetime. But if you use gravity to mean the curvature of spacetime that would cause such movement if mass were present, then it does exist. (This is explored theoretically using "test masses" that have effectively zero mass.)

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1 minute ago, Strange said:

You can model empty spacetime. Obviously there is no such thing in our universe.

Assuming we got the interpretation right.

2 minutes ago, Strange said:

So you are saying that the muon knows when to decay by looking at the lab clock?

No, i'm saying that relationally change occurs around it so that even if you were to regard the decay as purely random and before said decay it retained it's properties monadically in the most perfect sense it isn't in the absence of change (relational/monadic). Never said time or change is casually resulting its decay only that it isn't in the absence of change (system wise - greater universe) nor soon to probabilistically under go one.

4 minutes ago, Strange said:

GR only works if space and time are continuous. But then again, we know that GR probably needs to be modified at quantum scales.

Good article on the possibilities here: https://www.forbes.com/sites/startswithabang/2018/06/14/are-space-and-time-quantized-maybe-not-says-science/

Why thank you.

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I think drumbo is using that other definition of 'change'.

2 hours ago, michel123456 said:

Please explain. You have a 4D spacetime. How do you end with an interaction like gravity while being empty?

The geometry of space-time is the field, even in the absence of any mass.
The 'curving' of space-time, necessarily introduces energy of the field ( such that gravity gravitates ) in an otherwise empty universe.
The introduction of a test mass in that otherwise empty universe will see it move according to that geometric field.

By the same token, the victorious truther is proposing that muons decay, not according to their subjective time, but according to 'external' time/change. Does that mean a muon in an otherwise empty universe will not decay as there are no 'external' changes ???
( his proposal is easily falsified by the fact that time dilation extends a muon' decay time, but, is purely dependent on the muon's subjective speed )

Edited by MigL

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3 hours ago, michel123456 said:

Please explain. You have a 4D spacetime. How do you end with an interaction like gravity while being empty?

Empty means vacuum Einstein equations (T=0). That's what it means. There are solutions to the Einstein field equations that are non-trivial. The matter term is zero. Gravity gravitates, did you know? So gravity itself (curvature) can perturb space time and deviate from the globally constant metric (flat spacetime). You must know these things if you don't want to be involved in a non-ending conversation about words that have a very precise technical meaning.

The vacuum Einstein field equations

$R_{\mu\nu}-\frac{1}{2}Rg_{\mu\nu}=0$

Do not imply, repeat, not imply that:

$g_{\mu\nu}=\left(\begin{array}{cccc} -1 & 0 & 0 & 0\\ 0 & 1 & 0 & 0\\ 0 & 0 & 1 & 0\\ 0 & 0 & 0 & 1 \end{array}\right)$

globally. That's where you're wrong.

Edit: As MigL has said too, sorry I didn't notice. +1

Edit 2: This is because the theory is non-linear. This is getting ridiculous, really. Words have a special meaning. I suppose you're trying to tackle it from philosophy or common language. That's not how it works.

Then there's another non-sensical conversation going on about quantization of time I won't address for obvious reasons. There's a reason why Pauli introduced the words "not even wrong".

3 hours ago, Strange said:

That incoherent nonsense is not evidence for anything.

Exactly. +1

Edited by joigus

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On 8/9/2020 at 9:28 AM, michel123456 said:

Ontology ((the existence of the underlying object) needs time. You cannot "exist" without time. IMHO Time is sooo fundamental that it underlies almost everything.

I think it's perfectly fine if we disagree on this - these being 'just' philosophical speculations This place would be boring and kind of pointless if all of us always agreed on everything.
To me anyway, time is precisely the difference between ontology and epistemology - the latter is a temporal concept, the former isn't. I say ontology does not even need 'space' either.

On 8/9/2020 at 9:36 AM, michel123456 said:

My point is that there is an arrow between the two mathematical statements.

Is there? I don't see one - neither written nor implied.

23 hours ago, joigus said:

I may have misinterpreted you completely, Markus, but something like that is what I thought you were referring to

Yes, that's pretty much what I am trying to say - though I am not sure whether I follow your deduction using the line element. If $$ds^2>0$$ for all spacetime intervals, you'd be in a world that contains neither fermions nor bosons (no notion of massless particles, nor spin), and also no notion of causality; it is doubtful whether there would be any observers in such a world.

21 hours ago, joigus said:

Could conscience be some version of this kind of symmetry breaking? When you are exposed to the concept of spontaneous symmetry breaking, it just blows your mind.

Isn't this circular reasoning? Spontaneous symmetry breaking is a Lorentz-invariant process (right?), so it is already contingent upon the existence of time as we observe it.

18 hours ago, MigL said:

A hot dense universe, at Planck energy, with one unified force undergoes a symmetry break, which separates gravity from the remaining Strongelectroweak force.

The trouble with this is that it relies on the tacit assumption that gravity is a fundamental interaction in the same sense as the other three interactions, and thus can be unified in terms of some overarching quantum field theory (which then includes a mechanism for spontaneous symmetry breaking). I think we need to be careful not to take this for granted - such an assumption is a hypothesis at best, and, in my mind at least, dubious at best.

12 hours ago, michel123456 said:

So, what I am trying to say is that time does not go alone. Time & space are intertwined in such a way that the entire body (the manifold) can curve. And the fact that the curve is obtained by mass means (to me) that space, time & gravity are somehow 3 inseparable elements.

Yes, that's right - this is why we talk about spacetime.
Note however that mass isn't the only source of gravity - any form of energy-momentum has a gravitational effect. Furthermore, gravity is also self-interacting, so you can - at least in principle - come up with topological constructs that are held together purely by their own gravitational self-interactions, in the complete absence of any source of energy-momentum. So you can have completely empty spacetime, which nonetheless is gravitationally non-trivial.

11 hours ago, The victorious truther said:

IF. . . you can have empty spacetime and our substantialist interpretation of general relativity holds water in the possible absence of quantum fields. Or that it holds at all. Map versus terrain issue here?

Well, GR is a purely classical theory, so it "knows" nothing about quantum fields. So far as GR is concerned, given a small region of spacetime, there is either energy-momentum, or there is a vacuum - which then means a completely empty region. The important thing to remember is that the absence of energy-momentum in some region does not necessarily imply a flat spacetime.

11 hours ago, michel123456 said:

Please explain. You have a 4D spacetime. How do you end with an interaction like gravity while being empty?

Gravity is non-linear, so the gravitational field couples to itself. Mathematically, you can have completely empty spacetime - entire universes that are completely empty -, and yet non-trivial gravitational dynamics. These are valid solutions to the Einstein equations. Whether they are physically realisable in our universe is another matter. But even in our universe, you obviously have gravitational influences in the exterior vacuum outside of distant sources, so the principle still holds. I should mention here again (because this is really important) that the GR field equations are a purely local constraint.

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4 hours ago, Markus Hanke said:

Yes, that's pretty much what I am trying to say - though I am not sure whether I follow your deduction using the line element. If ds2>0 for all spacetime intervals, you'd be in a world that contains neither fermions nor bosons (no notion of massless particles, nor spin), and also no notion of causality; it is doubtful whether there would be any observers in such a world.

I understand your objection. The clarification is in one subtle self-correction I made about one of my statements that deserves to have been overlooked on account of my sloppiness. Here it is:

On 7/27/2020 at 12:21 PM, joigus said:

Edit 2: The metric should be defined on the f's, not the x's. So it'd be,

ds2=gijdfidfj

where the f's are the dynamical variables, not involving t explicitly. It's classical mechanics I'm talking about, with trajectories qi(t), then it'd be ds2=gijdqidqj

When you have a system of fields, the trajectories would be configurations of your fields. So you would have a trajectory in field space.

With propagating fields it probably wouldn't work, but with topological fields I'm reasonably sure it would (topological fields are highly constrained). In a way, they would work much as coordinates do. I can develop the point in case you're interested, but won't press it otherwise.

4 hours ago, Markus Hanke said:

Isn't this circular reasoning? Spontaneous symmetry breaking is a Lorentz-invariant process (right?), so it is already contingent upon the existence of time as we observe it.

Yes. But circular reasoning is not a death sentence for a fledgling idea for a theory. IMHO, tautologies are necessary to start formulating a theory. Let me explain.

Galilean relativity principle:

What is an inertial system? One in which Newton's laws are satisfied.

Where are Newton's laws satisfied? Only in inertial systems.

Get out of the tautology: Identify as legitimate forces only those that can be attached to physical sources (densities). Those cannot be globally removed by re-framings.

You're left with forces that can't be globally removed by re-framing and leave out those that can: ficticious forces.

Mass and force

What is mass?: ratio between force and acceleration

What is force?: mass times acceleration

Get out of the tautology: force (in most interesting cases) is a universal function of position (and perhaps velocity in a very special way as a pseudo vector)

I have this (maybe not general enough, etc.) intuition that all good theories start with a tautology and then make auxiliary assumptions to get out of it and make them productive.

I don't know what you think about that. But your points are certainly well taken. And very sharp, as usual. +1

Edited by joigus
minor correction

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7 hours ago, Markus Hanke said:

Well, GR is a purely classical theory, so it "knows" nothing about quantum fields. So far as GR is concerned, given a small region of spacetime, there is either energy-momentum, or there is a vacuum - which then means a completely empty region. The important thing to remember is that the absence of energy-momentum in some region does not necessarily imply a flat spacetime.

As far as that interpretation goes but this depends on whether you identify spacetime as distinct from matter and its configurations (classical substantivalism), that it cannot exist in the absence of matter with its accompanying configurations (relationism), or that matter is fully identified with a specific spacetime region so an empty spacetime is basically a spacetime devoid of quantum field looking spacetime configurations (super-substantivalism).

You can even speculate whether it would mean anything for there to be spacetime without matter in GR without resorting to having to construct a new theory but newly analyze it again. In that arxiv article, while I cannot fully vouch for its veracity, presents the intriguing possibility that even in a universe thinly distributed with matter you could still get back a spacetime that was geometrically Minkowskian. We are assuming that spacetime could take on background inherent geometries independent of the mass distribution (as there isn't any supposed matter) in the empty spacetime.

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One of the most important lessons of modern physics is that there is no simple way to define vacuum, or empty space-time. In GR "vacuum" is filled with structure, or has room for it. So is QFT's "vacuum". Whether that's pointing to an important philosophical statement or not, I do not know.

Is our notion of an empty scenario inconsistent in itself, or does it resist a simple definition? May be.

But the theories are correct in every other single instance. Maybe they're trying to tell us something.

Edited by joigus

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4 hours ago, joigus said:

One of the most important lessons of modern physics is that there is no simple way to define vacuum, or empty space-time. In GR "vacuum" is filled with structure, or has room for it. So is QFT's "vacuum". Whether that's pointing to an important philosophical statement or not, I do not know.

Is our notion of an empty scenario inconsistent in itself, or does it resist a simple definition? May be.

But the theories are correct in every other single instance. Maybe they're trying to tell us something.

Does this hold water? Space is a function of what's in it otherwise it can't exist... a bit like energy can't exist on its own because it's e a function of something.

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That's a good question. Maybe the mental operation of removing everything (stars, galaxies, black holes, etc.) does not ultimately make any real sense. It wouldn't be that surprising to me. The thing is that when you get to a sufficiently sophisticated formulation of the physics, and you remove the things (the terms in the equations) that you can identify with the "contents" of space-time, it just doesn't give you a flat, featureless, inanimate thing, so to speak. I gives you something that's not what you would expect.

Does that hold water? I don't know. But it holds whatever it is that it holds.

Maybe it's the idea of removing everything that doesn't hold water, and we have to accept that we've been very naive all over again, in a very unexpected way.

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