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The Nature of Time


addison
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3 hours ago, studiot said:

My apologies if you have truly not heard of this before.

I have. There's no valid inertial frame of reference for light since light by definition is never at rest, hence my confusion about your reply remains unabated. 

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Speculations about a nature of time pop up quite often in one form or another. But I've never seen those on a nature of space. I wonder, why? What makes time so much more ... mysterious?

Edited by Genady
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2 hours ago, Genady said:

What makes time so much more ... mysterious?

"Ever since St. Augustine, people have wrestled with this, and there are all sorts of things [time] isn't. It isn't a flow of something, because what does it flow past? We use time to measure flow. How could we use time to measure time? We are stuck in it, each of us time travels into the future, one year, every year. None of us to any significant precision does otherwise. If we could travel close to the speed of light, then we could travel further into the future in a given amount of time. It is one of those concepts that is profoundly resistant to a simple definition."

~Carl Sagan

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2 hours ago, Genady said:

Speculations about a nature of time pop up quite often in one form or another. But I've never seen those on a nature of space. I wonder, why? What makes time so much more ... mysterious?

You don’t directly sense it as you do with the dimensions of space (which are sensed with vision)

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35 minutes ago, swansont said:

You don’t directly sense it as you do with the dimensions of space (which are sensed with vision)

Do we directly sense with vision the dimensions of space? Do we see space? How does it look?

We rather see stuff, particularly a lit stuff. We mentally construct a "stage", where the stuff lives. This stage is space. By the behavior of stuff as we move around, we discover that the stage has three dimensions.

I don't see (pardon the pun) that we see space any more than we see time. 

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1 hour ago, Genady said:

Do we directly sense with vision the dimensions of space? Do we see space? How does it look?

We rather see stuff, particularly a lit stuff. We mentally construct a "stage", where the stuff lives. This stage is space. By the behavior of stuff as we move around, we discover that the stage has three dimensions.

I don't see (pardon the pun) that we see space any more than we see time. 

I should have been more clear. We see objects which occupy space. We don’t experience time the same way. 

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5 hours ago, swansont said:

You don’t directly sense it as you do with the dimensions of space (which are sensed with vision)

…which is funny if you think about it, since without time there wouldn’t be any such thing as vision, since EM radiation wouldn’t propagate, eyes wouldn’t perceive, and brains wouldn’t process. So when you visually see an extended object, this feat requires space and time.

I think this discussion is going off on a lot of unnecessary tangents. Really, one only needs to ask how many pieces of information are required to uniquely specify an event in our universe - this is very much an everyday, direct experience kind of question, and requires no philosophical or mathematical acumen. If you want to set up a meeting with someone, you have to give them a place: “Meet me at the statue on Trafalgar Square” (which is a particular location on a 3D grid). But if you leave it at just this - a location on a 3D grid -, the meeting isn’t likely to ever happen, because this is not unique. It applies to Trafalgar Square on 6th June 1967, and it equally applies to Trafalgar Square tomorrow morning at 8am. So to uniquely specify the event in a way that admits no ambiguity, you have to specify an instant in time as well. This can be done in many ways - by reading on a shared clock, as an arbitrary parameter on the statue’s world line, or as a detailed description of a serious of changes starting from some agreed point in the past, or some other way. The main point is that this information is extraneous to the 3D grid, it cannot be reduced to any combination of purely spatial information - to put it simply, spatial information alone is simply not enough to uniquely specify an event in our universe. There’s a reason why we all use maps and calendars in our daily lives, and physics does much the same, and for the same reasons.

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3 hours ago, Markus Hanke said:

…which is funny if you think about it, since without time there wouldn’t be any such thing as vision, since EM radiation wouldn’t propagate, eyes wouldn’t perceive, and brains wouldn’t process. So when you visually see an extended object, this feat requires space and time.

I think this discussion is going off on a lot of unnecessary tangents. Really, one only needs to ask how many pieces of information are required to uniquely specify an event in our universe - this is very much an everyday, direct experience kind of question, and requires no philosophical or mathematical acumen. If you want to set up a meeting with someone, you have to give them a place: “Meet me at the statue on Trafalgar Square” (which is a particular location on a 3D grid). But if you leave it at just this - a location on a 3D grid -, the meeting isn’t likely to ever happen, because this is not unique. It applies to Trafalgar Square on 6th June 1967, and it equally applies to Trafalgar Square tomorrow morning at 8am. So to uniquely specify the event in a way that admits no ambiguity, you have to specify an instant in time as well. This can be done in many ways - by reading on a shared clock, as an arbitrary parameter on the statue’s world line, or as a detailed description of a serious of changes starting from some agreed point in the past, or some other way. The main point is that this information is extraneous to the 3D grid, it cannot be reduced to any combination of purely spatial information - to put it simply, spatial information alone is simply not enough to uniquely specify an event in our universe. There’s a reason why we all use maps and calendars in our daily lives, and physics does much the same, and for the same reasons.

In theory, there's expansion, if one somehow knew exact distances.

 

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4 hours ago, Markus Hanke said:

“Meet me at the statue on Trafalgar Square” (which is a particular location on a 3D grid). But if you leave it at just this - a location on a 3D grid -, the meeting isn’t likely to ever happen, because this is not unique. It applies to Trafalgar Square on 6th June 1967, and it equally applies to Trafalgar Square tomorrow morning at 8am. So to uniquely specify the event in a way that admits no ambiguity, you have to specify an instant in time as well. This can be done in many ways - 

I think one reason many people have difficulty getting their heads around our current concept of measuring time is that it is so abstract. What is it that distinguishes one person's 'tomorrow morning at 8am' from another's? There's very little to cross-correlate with, and if the message came by snail mail then somebody might be waiting a long time before the other shows up.

Compare this with an older, more human kind of clock.

Quote

And Mikloth begat Shimeah. And these also dwelt with their brethren in Jerusalem, over against them. And Ner begat Kish, and Kish begat Saul, and Saul begat Jonathan, and Malchishua, and Abinadab, and Eshbaal. And the son of Jonathan was Meribbaal; and Meribbaal begat Micah. And the sons of Micah were, Pithon, and Melech, and Tarea, and Ahaz. And Ahaz begat Jehoadah; and Jehoadah begat Alemeth, and Azmaveth, and Zimri; and Zimri begat Moza

Granted it lacks the accuracy of a modern atomic clock, but it does have one crucial property that modern time-keeping has lost - an explicit chain of causal links that no observer can dispute. Some might disagree on the exact timing of Eshbaal's tenth birthday, but no one in their right mind would imagine that Moza begat Ner.

There are many other historic examples such as the succession of popes or Egyptian pharoahs.

Perhaps the best modern example of is the geological record with its various epochs, each marked by a distinct global change in environmental conditions, and each subdivided by a detailed succession of marker fossils.

When J B S Haldane answered the query of what might challenge his belief in evolution, his response of "Precambrian Rabbits" appealed not so much to the 500+ million years difference in dating (who can truly comprehend such a non-human time period?), but the obvious dislocation in an established causal chain. 

Edited by sethoflagos
missing word
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On 1/9/2023 at 6:29 AM, Markus Hanke said:

You do not seriously propose that we can just do away with time in all our physics models and expect it to still work out correctly, do you? Surely you can see that this doesn’t work.

Come on, I've repeatedly said that I don't propose that. 

 

On 1/9/2023 at 6:29 AM, Markus Hanke said:

A clock provides an additional degree of freedom that uniquely specifies the evolution of the system.

Yes, but with the clock, you are just comparing like with like. The change in this system amounts to three of the change in that system. 

What I'm arguing is that change is what actually exists, and the accumulation of change is what we experience as the past, and the expected change is what we feel as the future. But both are actually a facet of the present. 

On 1/9/2023 at 6:29 AM, Markus Hanke said:

If all the available dimensions are spatial in nature, and there is no other external information, how will there be “change”?

If there is no change, how will there be time? If everything in the universe froze, a second or a billion years would be no different. 

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10 hours ago, iNow said:

~Carl Sagan

The above quote demonstrates that time is a difficult concept. It does not however describe time as being a more difficult concept than space.

More to the point, Carl Sagan emphasizes difficulties of the physics of time, while @swansont emphasizes biology of our senses:

7 hours ago, swansont said:

We see objects which occupy space. We don’t experience time the same way.

If I understand it correctly, it means that the time concept is more difficult because it is not visual.

I am curious, if blind persons think that space is more 'mysterious' concept than time?

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I still don't understand why the 'block universe' was moved to another thread since such an idea offers one view of the nature of time.

I don't agree with that universe, but rather like the antithesis of it which is Mark Twain's famous statement

Quote

Time is what stops everything happening at once.

 

 

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1 hour ago, studiot said:

I still don't understand why the 'block universe' was moved to another thread since such an idea offers one view of the nature of time.

It wasn’t addison’s proposal, and it’s their thread.

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2 hours ago, Genady said:

I am curious, if blind persons think that space is more 'mysterious' concept than time?

IMO, no. Of course not.

Blind individuals still "experience" space all the time and every day, they just use their motor/muscular cortex more to process that experience whereas sighted people just use their occipital cortex more to process that same information.

The information processing and sense of experience, though, is remarkably similar. Not the same, of course not, but it's just passed through and processed with different cortical machinery.

The experience of time, however? That is there and permanently embedded into the background of everything we do... and interestingly our experience of time itself never really changes in any meaningful way across the entirety of our lives. 

A few nanoseconds of dilation "experienced" relative to those on the ground when traveling on a plane, a few millisecond increases in processing velocity when pumped full of caffeine cortisol and adrenaline, but otherwise our experience of time is consistently unchanging and cringingly unremarkable.

Space is not that way though, nor is space that way for blind individuals who simply use different neural machinery to process movements through and experience of our constantly changing spatial world.

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59 minutes ago, TheVat said:

And space is what stops everything from happening to you.

 

 

Indeed +1

11 hours ago, Markus Hanke said:

I think this discussion is going off on a lot of unnecessary tangents.

 

Agreed. +1 is meant to be about or why it is off topic to talk about some aspects of that nature and not others.

I still don't know what an opening post that looks more like a blog entitled the nature of time

The whole point being that space and time are very different things.
I note that at one point responders generally agree that time is not a 'thing', yet returned to treat it as a 'thing'  - after all if it it not a thing how can it have properties?

"Time is a dimension"

3 hours ago, swansont said:

It wasn’t addison’s proposal, and it’s their thread.

So do we take addison's proposal as an invitation to discuss or what ?

 

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It's hard to see time as more than comparative rates of change.  So many oscillations between energy levels in a cesium atom compared to a defined fraction of the solar day (sun moving from the noon meridian to noon meridian at a specific point in Earth's orbit) compared to number of beta decays in one gram of carbon 14 compared to change in position of bowling ball falling from 127 meters above sea level over downtown Scranton PA compared to change in seconds of arc of sun position from the vernal equinox compared to average follicular hair production in nanometers of elongation in the standard poodle.  Time, abstracted from change, can only be defined in a way that logicians call circular.  I need to review McTaggart on the unreal aspects of time.  IIRC Rovelli references McTaggart's A series and B series concept in his theory of time.

https://link.springer.com/article/10.1007/s10701-019-00312-9

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Just now, studiot said:

So do we take addison's proposal as an invitation to discuss or what ?

That’s supposed to be the focus: inquiring about claims and/or responding with mainstream material that rebut or support them

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53 minutes ago, TheVat said:

And space is what stops everything from happening to you.

Exactly! +1

So, what is the difference that makes "curious minds" so unhappy with time, and not with space, that they feel a need to do something about it, up to and including, to eliminate it completely from the picture?

It doesn't seem to be in our visual sensations, per @iNow's explanation above.

BTW there is a good answer to Carl Sagan's question,

17 hours ago, iNow said:

what does it flow past?

It flows past events.

Anyway.

I think that the difference is numerical, namely in the speed of light which is a very big number, and which separates our perception of time from that of space. As we turn or walk, we observe spatial changes in the environment. On the other hand, it seems that whatever we do, time keeps flowing all by itself. But in fact, it is an optical illusion caused by the speed of light being so different from our everyday speeds. If speed of light were, say, 5mi/h, as soon as we started walking, we would observe temporal changes in the environment. And then, I think, the mystery of time would be no more. Or, at least, it would be no more mysterious than space.

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There are two kinds of measurements.
Absolute, as in temperature, where there is a well defined zero point, and all temps are in relation to it, and, gauge, where the measurement depends on where and how the measurement is made; think of a bird on a 15000 v hydro line, that feels zero potential.

Time, and distance, are not absolute ( as Studiot has mentioned ), and it makes no sense to say this point is 12 km, or this instant is 17 sec.
We specify differences in length with separation, and differences in time with duration.
And just like the bird on the wire, we can set the origin of the separation at r=0 and the origin of the duration with t=0 to ease our calculations.

Similarly, as INow has mentioned, there is no universal now, or universal present, because there cannot be simultaneity.
My 'now' or 'present' differs from the person standing two feet away from me, never mind a galaxy a billion LY away.
My now is your future and someone else's past; how do you argue that only the present, or now, exists but past ans future do not ??

And to all those who think that time is simply an effect of motion, that time is emergent from the three spatial dimensions, I challenge you, as Markus did, ( since GR is our map/model of the real terrain ) to find the Panama Canal on a map of Central America from the 1800s.

 

Question for Markus, Mordred and anyone else who may know...

We have a separation interval between events as a distance, so we convert the time coordinates by multiplying by c to get a 'distance'.
Could we also specify the interval length as a time ( by dividing distances by c ) and would this make any difference whatsoever to GR ?
Would some then argue that time is fundamental, and lengths are emergent ?

Edited by MigL
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8 minutes ago, MigL said:

Could we also specify the interval length as a time ( by dividing distances by c ) and would this make any difference whatsoever to GR ?

Yes, we could, and no, it would not. We also could, and do, work in natural units with c=1, in which case there is no multiplication nor division by c, and units of length and time are the same.

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Yeah, I sort of knew that.
I was trying to make a point; that time  is independant, and not related to length. 
( as someone did, back on pg 3, I believe )

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