What is Time?

[koti]

7 minutes ago, swansont said:

Was that because you couldn't explain it properly?

I'm sure that did play a role too. 

9 minutes ago, swansont said:

Really?

Not that it adds too much merit to this discussion but yes, I think that the requirement of having a certain level of knowledge to understand difficult problems and the ability to explain difficult problems are not necessarily related.

[Strange]

25 minutes ago, geordief said:

What buildings would they be? Buildings housing telescopes or scientific experiments? 

Large ones!  Some long bridges for example. 

[michel123456]

I am afraid we are heading out of topic.

I don't think that the union between time & space has any relation with big or small.

From a conceptual point of vue, the distance between my eye and my computer display is spacetime. I mean, it is not distance-only. My ruler has a length in spacetime. It has not a length separated from time. Somehow, Time is also part of my ruler.

What I see around me, the objects in the room, are in spacetime.

Under this concept, time is visible exactly the same way as distance is.

 

[geordief]

58 minutes ago, michel123456 said:

I am afraid we are heading out of topic.

I don't think that the union between time & space has any relation with big or small.

From a conceptual point of vue, the distance between my eye and my computer display is spacetime. I mean, it is not distance-only. My ruler has a length in spacetime. It has not a length separated from time. Somehow, Time is also part of my ruler.

What I see around me, the objects in the room, are in spacetime.

Under this concept, time is visible exactly the same way as distance is.

 

I see it that way too, but it is simpler for practical purposes (when distances ,either spatial or temporal) are small  to "round off" any calculations and treat space and time as separate and independent variables.

 

Strange has surprised me to learn that spacetime curvature can actually come into play in very long structures but I am comfortable with that.  

[Strange]

1 hour ago, michel123456 said:

My ruler has a length in spacetime

Well, length is a single spatial dimension. But the ruler does exist as a world-line in 4D space-time.

47 minutes ago, geordief said:

Strange has surprised me to learn that spacetime curvature can actually come into play in very long structures but I am comfortable with that.  

No, I meant the curvature of the Earth affects the construction of large structures. Sorry if that wasn't clear.

Edited March 21, 2018 by Strange

[Tub]

Just out of interest, the smallest interval of time ever measured is 12 Attoseconds.   https://en.wikipedia.org/wiki/Attosecond

[Knight of Steel]

While the 4th dimension, a brane copying itself, is a popular view of time; it's based on finite space. You only need a plane that copies itself as it folds to create the illusion of depth to produce the effect of time if it's vertically infinite. Time gets created when the horizontally copied layers of the folding plane (viewed from the flat side) get themselves copied by larger folds in the plane that are of a higher order of magnitude. In that framework, time is the third dimension, not the 4th.

Edited March 21, 2018 by Knight of Steel

[swansont]

4 hours ago, koti said:

I'm sure that did play a role too. 

Not that it adds too much merit to this discussion but yes, I think that the requirement of having a certain level of knowledge to understand difficult problems and the ability to explain difficult problems are not necessarily related.

Then why did your explanation ability only "play a role"? What else is there?

[studiot]

17 minutes ago, Tub said:

Just out of interest, the smallest interval of time ever measured is 12 Attoseconds.   https://en.wikipedia.org/wiki/Attosecond

I note you said time interval, which is good.

Time itself is never measured.

All measurements of time are measurements of time difference.

In space, of course, all measurements of 'length' are also measurements of difference.

 

This reflects the fact that there is no such thing as absolute time or absolute difference.

 

However if we consider the third fundamental dimension of Physics - mass measurements are not of mass difference, they are of mass itself.

 

Edited March 21, 2018 by studiot

[geordief]

13 minutes ago, studiot said:

I note you said time interval, which is good.

Time itself is never measured.

All measurements of time are measurements of time difference.

In space, of course, all measurements of 'length' are also measurements of difference.

 

This reflects the fact that there is no such thing as absolute time or absolute difference.

 

However if we consider the third fundamental dimension of Physics - mass measurements are not of mass difference, they are of mass itself.

 

Interesting .Any flesh on that bone?

[koti]

1 hour ago, swansont said:

Then why did your explanation ability only "play a role"? What else is there?

The other persons ability (or lack of it) to let go of his/her misconceptions. 

If you want to undermine my abilities to teach I suggest you open a thread on it. 

[swansont]

39 minutes ago, koti said:

The other persons ability (or lack of it) to let go of his/her misconceptions. 

But you said that has nothing to do with it. 

39 minutes ago, koti said:

If you want to undermine my abilities to teach I suggest you open a thread on it. 

That's not it. It's the disconnect of the two elements I mentioned and you claim aren't connected.

[koti]

17 minutes ago, swansont said:

But you said that has nothing to do with it. 

With what?

Quote

That's not it. It's the disconnect of the two elements I mentioned and you claim aren't connected.

Which elements?

[swansont]

1 hour ago, koti said:

With what?

Which elements?

That some level of prior understanding is necessary (element 1) in order for someone to successfully explain complex concepts to them (element 2)

 

[koti]

1 hour ago, swansont said:

That some level of prior understanding is necessary (element 1) in order for someone to successfully explain complex concepts to them (element 2)

 

This is very obvious and I would never claim otherwise. I’d have to be mentally incapable of any rational thought to claim otherwise. I don’t know exactly which part of what I said in this thread you misunderstood to come to a conclusion that I would suggest that someone without any knowledge on a subject is capable of explaining anything on that subject to the other person but if its this:

9 hours ago, koti said:

I think that the requirement of having a certain level of knowledge to understand difficult problems and the ability to explain difficult problems are not necessarily related.

it means that a person1 with a high level of knowledge on a certain subject may not necessarily possess the skills to convey that knowledge effectively to person2. In simple words: You can be very knowledgeable and suck at explaining things to other people.

I hope I cleared this up. 

Edited March 21, 2018 by koti

[michel123456]

13 hours ago, geordief said:

Interesting .Any flesh on that bone?

Good question.

15 hours ago, geordief said:

I see it that way too, but it is simpler for practical purposes (when distances ,either spatial or temporal) are small  to "round off" any calculations and treat space and time as separate and independent variables.

Maybe that is the mistake. We are so used to make the separation that we cannot put in our head at which moment you must do the union. In fact the union is always there.

 

For example:

 

What is between us and the objects in the picture?

It is distance, because the objects are far away.

And it is time, because it is the image of the objects as they were thousand years ago.

So we see the objects different (smaller) because of  distance and also different (younger) because of time.

If you take a spacecraft and travel toward these objects, you will observe them changing (getting bigger) and evolving (getting older). At some point you may reach them and make the observation that the objects are not there anymore .

But that does not happen because we are talking about stars. It happens also for close objects. It is intrinsic. The phenomenon does not start when distance gets big. The phenomenon is always there. In such a way that if you look around you, everything you see is located both in space & in time. And one should make the remark that everything around you is at a positive distance and at a negative time (in the past). There is no object at negative distance and at positive time (in the future). Which shows that time & space are irreversibly interconnected.

[geordief]

50 minutes ago, michel123456 said:

Good question.

Maybe that is the mistake. We are so used to make the separation that we cannot put in our head at which moment you must do the union. In fact the union is always there.

 

For example:

 

What is between us and the objects in the picture?

It is distance, because the objects are far away.

And it is time, because it is the image of the objects as they were thousand years ago.

So we see the objects different (smaller) because of  distance and also different (younger) because of time.

If you take a spacecraft and travel toward these objects, you will observe them changing (getting bigger) and evolving (getting older). At some point you may reach them and make the observation that the objects are not there anymore .

But that does not happen because we are talking about stars. It happens also for close objects. It is intrinsic. The phenomenon does not start when distance gets big. The phenomenon is always there. In such a way that if you look around you, everything you see is located both in space & in time. And one should make the remark that everything around you is at a positive distance and at a negative time (in the past). There is no object at negative distance and at positive time (in the future). Which shows that time & space are irreversibly interconnected.

I don't think there is any disagreement .Spacetime  is indeed a more fundamental understanding  than space and time  viewed separately  but both are models and one is free to choose one or the other for convenience.

Any model that works and fits the context  is fine and yes the union of space and time can be assumed at small spatial or temporal intervals (But not necessarily  when dealing with "singularities " it seems)

Edited March 22, 2018 by geordief

[swansont]

10 hours ago, koti said:

This is very obvious and I would never claim otherwise.

But you did, or at least appeared to. But it's clear now that you missed something.

Quote

I’d have to be mentally incapable of any rational thought to claim otherwise. I don’t know exactly which part of what I said in this thread you misunderstood to come to a conclusion that I would suggest that someone without any knowledge on a subject is capable of explaining anything on that subject to the other person but if its this:

No, that's not the issue. 

The explainer has the skill, the recipient must have the background. They are both necessary, and are not independent. 

Quote

it means that a person1 with a high level of knowledge on a certain subject may not necessarily possess the skills to convey that knowledge effectively to person2. In simple words: You can be very knowledgeable and suck at explaining things to other people.

I hope I cleared this up. 

You've obviously missed the point here. My post quoting Feynman was about the recipient of the explanation having sufficient understanding of the basics, without which advanced topics will be inaccessible to them, regardless of the skill of the explainer.

[koti]

22 minutes ago, swansont said:

But you did, or at least appeared to. But it's clear now that you missed something.

No, that's not the issue. 

The explainer has the skill, the recipient must have the background. They are both necessary, and are not independent. 

You've obviously missed the point here. My post quoting Feynman was about the recipient of the explanation having sufficient understanding of the basics, without which advanced topics will be inaccessible to them, regardless of the skill of the explainer.

I don’t think I missed anything. I haven’t commented on your Feynman quote (which I agree with btw) so I don’t see why you would bring this up. What we’re having here is a missunderstanding due to your initial (I hope) missconception about what I think. I don’t see a point in continuing this as we both seem to agree. Why keep this going? 

[studiot]

2 hours ago, michel123456 said:

What is between us and the objects in the picture?

It is distance, because the objects are far away.

And it is time, because it is the image of the objects as they were thousand years ago.

So we see the objects different (smaller) because of  distance and also different (younger) because of time.

If you take a spacecraft and travel toward these objects, you will observe them changing (getting bigger) and evolving (getting older). At some point you may reach them and make the observation that the objects are not there anymore .

 

Have you been reading Eddington's "Space Time and Gravitation"  ?

A very readable account of relativity, old but still good.

 

2 hours ago, michel123456 said:

Good question.

 

I'm not sure what was unclear about my comment, but since two members have asked would someone like to tell me?

 

Take measuement of length.

 

What do you mean by length?

It is the difference in 'distance' between two distinct points.

But points in what ?

Take your galaxy that is no longer there when you arrive.

What is the 'distance to it' ?

Distance has meaning unless you measure both endpoints at the same time.
This is of no consequence over the length of a 1 metre ruler, but for the travelling twin to Alpha Centauri it is a significant question as I asked in that recent thread.

So time is intimately involved with emasurement of distance.

So how do we measure time?

Well take the travelling twin again.

He measures it by difference between the reading on his clock when he starts and when he arrives.
Or the delightful story of his cigar in Eddinton's book.

But, of course, he has to know when he has arrived.

For which he has to know the distance he has travelled and how does he do that?

But mass and temperature are fundamental physical quantities that we do not (need to) measure by difference.

 

[swansont]

26 minutes ago, koti said:

I don’t think I missed anything. I haven’t commented on your Feynman quote (which I agree with btw) so I don’t see why you would bring this up. 

"What swansont said about having to have knowledge to understand complex problems is ofcourse right. "

The quote was part of what I said. They were directly related.

26 minutes ago, koti said:

What we’re having here is a missunderstanding due to your initial (I hope) missconception about what I think. I don’t see a point in continuing this as we both seem to agree. Why keep this going? 

You say we agree but also say things that are obviously incorrect. But yes, if you say we are in agreement, let it drop.

[koti]

5 minutes ago, swansont said:

"What swansont said about having to have knowledge to understand complex problems is ofcourse right. "

The quote was part of what I said. They were directly related.

You say we agree but also say things that are obviously incorrect. But yes, if you say we are in agreement, let it drop.

The lack of relation I mentioned was between level of knowledge and skills to explain, I thought its clear by now. 

[michel123456]

17 minutes ago, studiot said:

 

Have you been reading Eddington's "Space Time and Gravitation"  ?

A very readable account of relativity, old but still good.

 

 

I'm not sure what was unclear about my comment, but since two members have asked would someone like to tell me?

 

Take measuement of length.

 

What do you mean by length?

It is the difference in 'distance' between two distinct points.

But points in what ?

Take your galaxy that is no longer there when you arrive.

What is the 'distance to it' ?

Distance has meaning unless you measure both endpoints at the same time.
This is of no consequence over the length of a 1 metre ruler, but for the travelling twin to Alpha Centauri it is a significant question as I asked in that recent thread.

So time is intimately involved with emasurement of distance.

So how do we measure time?

Well take the travelling twin again.

He measures it by difference between the reading on his clock when he starts and when he arrives.
Or the delightful story of his cigar in Eddinton's book.

But, of course, he has to know when he has arrived.

For which he has to know the distance he has travelled and how does he do that?

But mass and temperature are fundamental physical quantities that we do not (need to) measure by difference.

 

Nothing was unclear. It is interesting that some instances are relative and some are constant. The most peculiar is SOL which is both relative and constant. Which raise questions about mass.

 

[studiot]

34 minutes ago, michel123456 said:

Nothing was unclear. It is interesting that some instances are relative and some are constant. The most peculiar is SOL which is both relative and constant. Which raise questions about mass.

 

 

What questions?

I am fond of saying that despite our best efforts to categorise and pigeonhole things, we are often outsmarted by the diversity of Nature.

[geordief]

10 minutes ago, studiot said:

 

What questions?

Same here (as michel123456)  . "Interesting" was approbatory ,not trying to find any flaw.

Your phrase "the third fundamental dimension of Physics" was new to me. and "interesting" .It is not obvious to me why mass differences should not have the same relevance as spatio-temporal differences (because of my level of familiarity,certainly)