What is time? (Again)

[joigus]

22 minutes ago, michel123456 said:

But this statement puts time as if it was an observer only kind of concept, and I think that time is more than that.

Of course it's more than that. I don't see the "only" bit in my statement about how observers cannot get rid of time in their view of the universe. Volume is also. All observers have volume. That doesn't imply that "volume" is an only-observer kind of concept.

22 minutes ago, michel123456 said:

If gravity is the curvature of Spacetime, it means that spacetime is not only a 4D mathematical concept.

You can formulate gravity in different dimensions. Not only 4. 4 is special as concerns topology, not Einstein's equations. Although going down to fewer dimensions than 4 makes gravity more tractable, or trivial, if you will. In 3 dimensions the Ricci tensor codifies all possible degrees of freedom to deal with gravity. In 2 dimensions the Ricci scalar is enough. And in 1 dim there is no gravity because there can be no intrinsic curvature. But I'm not quite sure what you mean by,

23 minutes ago, michel123456 said:

I say that because I doubt that you can infer gravity from the curvature of a pure 4D mathematical concept (or am I wrong here?)

Can you elaborate?

26 minutes ago, michel123456 said:

Of course, once build, they usually don't flip.

Just like observers.  

1 hour ago, MigL said:

I certainly don't have the required math skills to formulate such a theory, and it can't really be backed by observational evidence, so; but it is an interesting concept I've never introduced it in Speculations

I would distinguish pure speculations as rigid frames of thinking that ignore the basis of generally agreed-upon physics from open-ended lines of reasoning that strive to incorporate what's known and try to grope a bit further. That's what I was trying to do here. I wouldn't be surprised that some of the more adroit users here find some kind of overlapping with what I've said. Although I think disagreement among equally adroit users would be just as likely.

Edited August 9, 2020 by joigus
bad rendering of quote

[michel123456]

1 hour ago, Strange said:

Gravity is purely an effect of the curvature of four-dimensional spacetime. I'm not sure what else you think is required?

What else is required? Particles, interactions, physics. Anything else than pure maths.

[joigus]

9 minutes ago, michel123456 said:

What else is required? Particles, interactions, physics. Anything else than pure maths.

Maths is the language of physics. Common language and diagrams are useful complementary tools. That's just how it is.

Physics cannot be formulated in just words (however philosophically sophisticated) or pictures. It just can't. I'm afraid I must insist on @Strange's question: What else is required?

[studiot]

2 hours ago, Strange said:

Gravity is purely an effect of the curvature of four-dimensional spacetime. I'm not sure what else you think is required?

Mass is not a function of the coordinate system, or the manifold.

[Lan Todak]

20 minutes ago, joigus said:

Physics cannot be formulated in just words (however philosophically sophisticated) or pictures. It just can't.

Yes you can. Just multiply p,h,y,s,i,c and s then you'll get physics 😏😏😏.

[michel123456]

1 hour ago, joigus said:

Maths is the language of physics. Common language and diagrams are useful complementary tools. That's just how it is.

Physics cannot be formulated in just words (however philosophically sophisticated) or pictures. It just can't. I'm afraid I must insist on @Strange's question: What else is required?

We have reached a point of not understanding each other.

Let me try to explain my thinking: imagine a completely empty universe. Nothing.

Now imagine Space (mathematically). Then imagine time (mathematically). Then curve it. Does gravity come out of this model? Or do you have to put something else in this empty model to make time begin to run & gravity arise? What is this thing you have to put in?

 

53 minutes ago, studiot said:

Mass is not a function of the coordinate system, or the manifold.

But if mass is not a function of the manifold then why do we say that gravity is the curve of spacetime?

[Strange]

14 minutes ago, michel123456 said:

Now imagine Space (mathematically). Then imagine time (mathematically). Then curve it. Does gravity come out of this model? Or do you have to put something else in this empty model to make time begin to run & gravity arise? What is this thing you have to put in?

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

15 minutes ago, michel123456 said:

But if mass is not a function of the manifold then why do we say that gravity is the curve of spacetime?

The curvature is a function of the presence of mass (energy)

[studiot]

So we are back to what I said a page or two ago.

If we are going to be able to define time we will have to do so in terms of the properties it possesses and the effects it bestows on other inhabitants of the manifold or receives from them.

Edited August 9, 2020 by studiot

[Strange]

46 minutes ago, Strange said:

The curvature is a function of the presence of mass (energy)

You could go further, maybe, and say that is the definition of mass: something that curves spacetime.

[michel123456]

8 minutes ago, Strange said:

You could go further, maybe, and say that is the definition of mass: something that curves spacetime.

Right.

So if the observer has mass (which he has) he is influencing the manifold he is observing. The manifold is not flat, it is curved.

The observer will measure that gravity will recede its influence in function of the square of the distance.

Time around the observer will recede in function of the distance (not squared).

What else do we know? For example what is the role of space in this game? Is it just a recipient doing nothing?

[studiot]

8 minutes ago, michel123456 said:

What else do we know? For example what is the role of space in this game? Is it just a recipient doing nothing?

Well there's electric charge / polarity

There's chirality / eg handedness of the spatial axes.

There properties to do with matter/antimatter.

Perhaps temperature.

But we are supposed to be singling out time for discussion in this thread.

[drumbo]

Time is very simple. Let t=t_0, and then increment by dt, an infinitesimal amount. Those dt increments are the quanta of time, the smallest amount of time that the universe can discretely have. To prove that these time quanta exist, it is sufficient to know that there is some greatest lower bound, or infinitum amount of time such that if there were to be considered an amount of time any smaller, not a single thing about the state of the universe would change in the passing of that even smaller amount of time, effectively defining a time quanta.

Edited August 9, 2020 by drumbo

[michel123456]

15 minutes ago, michel123456 said:

Time around the observer will recede in function of the distance (not squared).

Sorry, time recedes in the sense that it goes into the past. But amazingly, the ticking of time does not change (as far as I know) in function of distance.

7 minutes ago, studiot said:

Well there's electric charge / polarity

There's chirality / eg handedness of the spatial axes.

There properties to do with matter/antimatter.

Perhaps temperature.

But we are supposed to be singling out time for discussion in this thread.

Trying.

I didn't expect any of that. Interesting anyway.

Concerning space: we know that space is "made up of" (sorry for the informal statement) distance in 3 orthogonal directions.

And we know that there is no negative distance, as there is no negative gravity and no negative time.

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.

Now, if temperature plays a role in all this, I don't know.

[joigus]

2 hours ago, Lan Todak said:

Yes you can.

Very droll.

2 hours ago, michel123456 said:

We have reached a point of not understanding each other.

Is it something I said?

 

2 hours ago, michel123456 said:

Let me try to explain my thinking: imagine a completely empty universe. Nothing.

Don't go there.  

2 hours ago, michel123456 said:

Now imagine Space (mathematically). Then imagine time (mathematically). Then curve it. Does gravity come out of this model? Or do you have to put something else in this empty model to make time begin to run & gravity arise? What is this thing you have to put in?

 

Now seriously. You need something to move through space-time to even start talking about gravity. Even if you just have imaginary points trying to follow the closest-to-a-straight-line trajectories you can find, you do have gravity. But  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.

Edited August 9, 2020 by joigus

[studiot]

20 minutes 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 indeed that is our spacetime.

But space, having three axes had left hand and right hand.
Or alternatively if we have angular coordinates, clockwise and anticlockwise.

Time on the other hand cannot supprt this behaviour on a single axis.

But I do wonder (and this is pure speculation) if the 'arrow of time' has something to do with this (I won't use the word connection since Markus has already bagged another meaning for this word) but that is what I mean.

[drumbo]

22 minutes ago, michel123456 said:

space, time & gravity are somehow 3 inseparable elements

Time only exists in reference to a state of a system. If the state of a system does not change, then there is effectively no passage of time.

[studiot]

5 minutes ago, drumbo said:

Time only exists in reference to a state of a system. If the state of a system does not change, then there is effectively no passage of time.

 

35 minutes ago, drumbo said:

Time is very simple. Let t=t_0, and then increment by dt, an infinitesimal amount. Those dt increments are the quanta of time, the smallest amount of time that the universe can discretely have. To prove that these time quanta exist, it is sufficient to know that there is some greatest lower bound, or infinitum amount of time such that if there were to be considered an amount of time any smaller, not a single thing about the state of the universe would change in the passing of that even smaller amount of time, effectively defining a time quanta.

Neither of these ideas make any sense to me.

Do you have any supporting evidence?

[joigus]

1 minute ago, studiot said:

 

Neither of these ideas make any sense to me.

Do you have any supporting evidence?

Nor to me.

[drumbo]

Just now, studiot said:

 

Neither of these ideas make any sense to me.

Do you have any supporting evidence?

Yes. Consider this thought experiment. Let's say you observed a system, and absolutely nothing changes in the system. Well, that would imply that time might as well have not proceeded in that system at all. This necessarily implies the existence of a time quanta when you consider the infinitesimal limit and the greatest lower bound where you begin to see a change in the system.

[studiot]

1 minute ago, drumbo said:

Yes. Consider this thought experiment. Let's say you observed a system, and absolutely nothing changes in the system. Well, that would imply that time might as well have not proceeded in that system at all. This necessarily implies the existence of a time quanta when you consider the infinitesimal limit and the greatest lower bound where you begin to see a change in the system.

I don't see the connection.

Further the idea of no change over time can be very important.
Take some Uranium atoms and watch them for several hours (days).

Will there be a change and is no change significant?

[drumbo]

1 minute ago, studiot said:

I don't see the connection.

Further the idea of no change over time can be very important.
Take some Uranium atoms and watch them for several hours (days).

Will there be a change and is no change significant?

I mean any  change, even at a subatomic level. An electron changing its position. A bond lengthening or contracting. Subatomic particles spontaneously appearing and colliding a disappearing. Any change in the system at all. If there is no change, time effectively never passed. The time quanta is the minimum amount of time that must pass before something in the state of the universe changes.

[Strange]

6 minutes ago, drumbo said:

This necessarily implies the existence of a time quanta when you consider the infinitesimal limit and the greatest lower bound where you begin to see a change in the system.

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.)

[drumbo]

1 minute 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.)

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?

[Strange]

1 minute ago, drumbo said:

If there is no change, time effectively never passed.

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

8 minutes ago, drumbo said:

The time quanta is the minimum amount of time that must pass before something in the state of the universe changes.

Do you have any evidence for this minimum amount of time?

3 minutes ago, drumbo said:

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?

How do you know space is quantised?

[drumbo]

Just now, Strange said:

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

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.