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# what we know about Time

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I would hope that we could agree that a space-time diagram which cannot include light cannot be correct.

I'll try this way:

On the second diagram at this time frame:

you agreed (was it you?) that point C is the point where the observer sees the light coming from.

So, at this time frame, a scientist-observer living on the red dot will take a pencil and mark a black dot at point C, because it is what he is observing.

If the scientist, at this same time-frame, do the same job for all the objects in the universe he observes the light coming from, he will make a regular space-time diagram with a bunch of C-points upon the diagonal.

That is a space-time diagram: a diagram that represent the coordinates of objects as the scientist-observer observes here & now.

And this diagram will ressemble a lot to the first blue-dot diagram, in which the diagonal is the mark of constancy of SOL but in which the path of a ray of light is not shown.

The path of a ray of light is shown on the second yellow-dot diagram.

Edited by michel123456

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I'll try this way:

On the second diagram at this time frame:

you agreed (was it you?) that point C is the point where the observer sees the light coming from.

I agreed that C is the location of the event of the emission of light. The problem is not the location of point C on the diagram, but the frame number of the animation in which point C is at that location. In one animation you have the black dot and the red dot at the same t coordinate in the same frame. In another animation you have the black dot and the red dot at different t coordinates in the same frame. They cannot both be correct.

Let's also be clear, adding a variable of time in the form of animation to a spacetime diagram is not standard and it does not give standard results. I disagree with the practice entirely, and I believe it is the reason you are having to draw inconsistent diagrams.

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I agreed that C is the location of the event of the emission of light. The problem is not the location of point C on the diagram, but the frame number of the animation in which point C is at that location. In one animation you have the black dot and the red dot at the same t coordinate in the same frame. In another animation you have the black dot and the red dot at different t coordinates in the same frame. They cannot both be correct.

The black dots represent different things, that's why.

Let's also be clear, adding a variable of time in the form of animation to a spacetime diagram is not standard and it does not give standard results. I disagree with the practice entirely, and I believe it is the reason you are having to draw inconsistent diagrams.
That should be your stronger argument. I agree it is weird, but I had no other way at disposal to put in front of your eyes the concept of an object changing coordinates versus your concept of an object extending from one coordinate to another.*

As I stated before:

There is no reason why translation in space (motion) should be so radically different from translation in time (duration). when you move in space, you change coordinates, you don't 'persist" from one point in space to another. The same must be true for time: as duration occurs, you change coordinates, you don't "persist".

* What I can assure you is that it is not necessary to extend from one coordinate to another, all can be explained with a change of coordinates.

Edited by michel123456
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The black dots represent different things, that's why.

I suspect both black dots are meant to represent the same object but that the diagrams function differently.

As I stated before:

There is no reason why translation in space (motion) should be so radically different from translation in time (duration). when you move in space, you change coordinates, you don't 'persist" from one point in space to another. The same must be true for time: as duration occurs, you change coordinates, you don't "persist".

Motion requires two dimensions. We can only talk about motion through space because there is a detectable time dimension. Motion through time would require another time dimension which the frames in your animations provide. Your diagrams have two different "durations" because there is no other way to show or express the motion of a dot through space-time. The distance along the t axis is one variable of duration and the length of the animation (i.e. the number of frames) is another variable of duration.

Only one variable of time is detectable. Motion through space is different from motion through time for that reason alone. Only one of them is measurable.

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If you could rotate the diagram 90 degrees in such a way to see the thin side of the sheet of paper, you would see a ray of light coming from the red dot (which is AT REST) to the black dot (at rest), and the labelling of time given by a clock.

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I suspect both black dots are meant to represent the same object but that the diagrams function differently.

Motion requires two dimensions. We can only talk about motion through space because there is a detectable time dimension. Motion through time would require another time dimension which the frames in your animations provide. Your diagrams have two different "durations" because there is no other way to show or express the motion of a dot through space-time. The distance along the t axis is one variable of duration and the length of the animation (i.e. the number of frames) is another variable of duration.

Only one variable of time is detectable. Motion through space is different from motion through time for that reason alone. Only one of them is measurable.

Bolded mine.

If motion through space is different from motion through time, how is it possible for time & space to be interchangeable according to the observer's FOR ?

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Bolded mine.

If motion through space is different from motion through time, how is it possible for time & space to be interchangeable according to the observer's FOR ?

Space is measured with a ruler and time with a clock. Space and time are mixed between frames when one person measures the distance between events entirely with a ruler (for example) and another measures the distance with some combination of a ruler and clock. In other words, some amount of space in one frame has become some amount of time in another frame.

Your question is if some amount of space in one frame can become some amount of time in another frame then why can't some amount of motion through space in one frame become some amount of motion through time in another. The answer is simply that motion requires two dimensions. Time requires one dimension. Space requires one. Motion requires two. If you mix space and time between frames you are mixing one dimension for another. If you mix motion between frames you are mixing two dimensions with two others. It isn't the same thing.

Does that make sense?

Edited by Iggy
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That makes sense.

But the question is not about the amount. The question is about the properties of the process.

I had this bad feeling today that we disagree on what motion actually is.

When I have a pencil on my desk, then change its place upon the bookshelf on the right, the pencil moved.

In my world view, the pencil changed coordinates in spacetime:

At t=zero it was at coord (0,0,0,0) with spacetime coords (x,y,z,t)

At t=1 it is at coord (1,1,1,1) no matter the units for the sake of simplicity.

If I understand correctly, your interpretation of reality is fundamentally different.

For you, the pencil that was at coord (0,0,0,0) occupies this coordinate once for all. It will never leave this coordinate empty, no other object can occupy this coordinate.

For you, when the pencil moves from (0,0,0,0) to (1,1,1,1), in fact it stretches from one coordinate to the other in the time dimension.

In this view, the change of coordinates of the last number has a totally different meaning than the change of coordinates of the first 3 numbers.

And I wonder if there is any good scientific reason for that.

Edited by michel123456
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I had this bad feeling today that we disagree on what motion actually is.

A dictionary could solve any disagreement.

In my world view, the pencil changed coordinates in spacetime:

At t=zero it was at coord (0,0,0,0) with spacetime coords (x,y,z,t)

At t=1 it is at coord (1,1,1,1) no matter the units for the sake of simplicity.

In an effort to make your argument work you are complicating things greatly.

You have just described regular motion. As t changes, the spatial position of things change. At t=0 the spatial potion of the pencil is 0,0,0. At t=1 the spatial position is 1,1,1. That is good old fashion, regular, motion. A change in spatial position per a change in time. The speed is dx/dt.

With only 4 coordinates the description "the pencil changed coordinates in spacetime" is not right. You could say "the pencil changed coordinates in space".

Regular spacetime diagrams show a change in spatial position with respect to time -- three spatial dimensions and one time dimension. Your animated diagrams show a change in space-time position with respect to an additional variable of time. 4 spacetime dimensions and an additional variable of time.

If I understand correctly, your interpretation of reality is fundamentally different.

For you, the pencil that was at coord (0,0,0,0) occupies this coordinate once for all. It will never leave this coordinate empty, no other object can occupy this coordinate.

If you want to say *first* one object occupies 0,0,0,0 *then* another object occupies 0,0,0,0 you need an additional variable that represents "the first object..." and "the second object..." etc. You've ended up with 5 variables. Your diagrams show 5 variables.

For you, when the pencil moves from (0,0,0,0) to (1,1,1,1)...

Do you know how to graph x=y? Do you think it is a dot moving in the x,y plane or do you think it is a line in the x,y plane?

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(...)

You have just described regular motion. As t changes, the spatial position of things change. At t=0 the spatial potion of the pencil is 0,0,0. At t=1 the spatial position is 1,1,1. That is good old fashion, regular, motion. A change in spatial position per a change in time. The speed is dx/dt.

With only 4 coordinates the description "the pencil changed coordinates in spacetime" is not right. You could say "the pencil changed coordinates in space".

(...)

You got it. You are treating the 4th coordinate differently from the 3 others.

That is my question: why?

If time can be observed as space by some other observer in some other FOR, the t coordinate should be treated equally to the 3 others.

Do you know how to graph x=y? Do you think it is a dot moving in the x,y plane or do you think it is a line in the x,y plane?

x=y is a mathematical description. It can be a lot of things, a trajectory for example.

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You got it. You are treating the 4th coordinate differently from the 3 others.

That is my question: why?

I am treating them differently because they are different. One is time and the other three are space. You don't have 4 spatial coordinates. You have three of space and one of time. Regular motion is defined as a change in space per a change in time.

You aren't addressing the problems of using two variables of time. Particularly, that we can only measure one.

If time can be observed as space by some other observer in some other FOR, the t coordinate should be treated equally to the 3 others.

That is untrue. The spacetime metric recognizes the difference between space and time. It does so by having space and time carry a different sign.

If treating space and time differently were a real objection you would object to measuring one with a ruler and the other with a clock. It isn't a real objection. You're trying to direct the conversation away from yet another problem.

x=y is a mathematical description. It can be a lot of things, a trajectory for example.

I asked specifically if you could graph it as a dot moving in the x-y plane or as a line in the x-y plane. The answer is that it is a line in the x-y plane. As a mathematical description, that is correct. Similarly, a space-time diagram with a metric, for example, of ds=dt-dx shows a line in the x-t plane. If you want to show or consider it to be a dot moving in the x-t plane (like your diagrams do and as your description says) you need another variable of time. That is the correct mathematical description. It is not a matter of opinion.

Edited by Iggy
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(...)time can be observed as space by some other observer in some other FOR, (...)

That is untrue.

Is that untrue?

or will you tell me that the (...) is important.

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Is that untrue?

or will you tell me that the (...) is important.

I didn't use ... so I'm not sure what you mean by that. What you said, and what I quoted, is:

If time can be observed as space by some other observer in some other FOR, the t coordinate should be treated equally to the 3 others.

The conclusion doesn't follow the premise. The metric treats space and time differently (specifically, they carry a different sign) while space and time are 'mixed' between frames.

edit,

In other words, "time can be observed as space by some other observer in some other FOR" can be true while "the t coordinate should be treated equally to the 3 others." is false. For example, in Minkowski space-time "time can be observed as space by some other observer in some other FOR" is true while "the t coordinate should be treated equally to the 3 others" is not true.

Edited by Iggy
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For example, in Minkowski space-time "time can be observed as space by some other observer in some other FOR" is true (...)

That's the 2nd time in this thread that we agree on something, champagne!

while "the t coordinate should be treated equally to the 3 others" is not true.

Just because they have another sign?

As much as I know +1 and -1 are different but not so dramatically that they cannot work together. Like time & space, you can make operations on positive & negative values of objects that have equivalent properties like the integers. The fact that time coordinates have a different sign from the spatial ones does not mean that they don't have the same properties. It simply means that they have another orientation, perpendicular to space. (please correct me if I am wrong)

IMHO if time is rotatable in space, time & space must share the same properties.

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Just because they have another sign?

Yes. That is the most basic mathematical difference. There are others such as spatial distance being measured with a ruler and temporal distance being measured with a clock.

As much as I know +1 and -1 are different but not so dramatically that they cannot work together. Like time & space, you can make operations on positive & negative values of objects that have equivalent properties like the integers. The fact that time coordinates have a different sign from the spatial ones does not mean that they don't have the same properties. It simply means that they have another orientation, perpendicular to space. (please correct me if I am wrong)

If I give you 15 objects and ask you to subtract the number of oranges from the number of apples you simply have to treat oranges and apples differently. They work together (they are both things that can be grouped together into a set of 15) but they are different.

The sign does not affect the orientation.

IMHO if time is rotatable in space, time & space must share the same properties.

Time has different properties from space.

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Is time rotatable in space?

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When a dicussion about Time begins, it usually derails into philosophical blah blah after a post or 2.

I'd like to refrain from the philosophical tentation, and try to concentrate on what we really know about Time from a scientific point of vue only.

For example:

1. we know that motion requires time: nothing can move from one spatial coordinate to another in zero time, it would be a transgression of the Speed Of Light.

2. we know that the rate of time is related to gravity: where gravity is stronger Time flows slower.

3. we know that time has a "direction", commonly called the arrow the time.

4. we know that time is related to causality, and causality is related to c, the Speed Of Light.

5. we know that time is linked to space: time alone has no physical meaning, only the spacetime continuum "exists".

6. we know that time can transform in space, and vice-versa: what is space for an observer may be time for another.

What else do we know about Time? (and please correct me for any error)

Hi michel123456,

We have had such discussions of time and I have found we have much more agreement than differences on this subject.

But, let's discuss our differences so that perspectives might be improved, OK? I'll go in the order that you presented your "knowledge" characteristics of time.

BUT I would like to start with a perspective if you don't mind. Instead of saying "we know," concerning all of these characteristics, I believe it would be better to say that "present theory and perspectives based upon observations assert that": 1,2,3, etc.

1. we know that motion requires time: nothing can move from one spatial coordinate to another in zero time, it would be a transgression of the Speed Of Light.

As to this my preferred definition of time is an "interval of change" which is man made concept with absolutely nothing more to it than its definition, in my opinion. As we discussed before, it is difficult to imagine a change without motion so I think we are in agreement on this point.

2. we know that the rate of time is related to gravity: where gravity is stronger Time flows slower.

Yes. Changes of distance to a gravitational field effects the rate of particle spin and particle decay, as well as the measured passage of time, which are a function of the changes/ motion of matter at a distance from a center of gravity. So we are in agreement.

3. we know that time has a "direction", commonly called the arrow the time.

I'm not too fond of the common terminology of this phrase since I think it is based upon the proposed mathematical use of time rather than the logic of it. I would prefer to say that time can be equated with motion but there is no direction to it such as the idea of time going/moving backwards. So in this way my explanation is a little different perspective, and yours is the presently accepted perspective. Not that I disagree, its only that I think such ideas confuse the understanding of how simple time really might be.

4. we know that time is related to causality, and causality is related to c, the Speed Of Light.

Yes. For change/ motion to occur their must be a motivating force of some kind -- which would be times cause. For atomic matter the primary internal motivator results in atomic spin and atomic particle spin which perpetuates time.

5. we know that time is linked to space: time alone has no physical meaning, only the spacetime continuum "exists".

I would use different wording. I would say that logically time can be linked to space to form a new concept, both logically and mathematically. Since galaxies move relative to each other as well as the background of galaxies, no absolute X,Y, Z coordinates can be determined unless we consider only a point in time where there would be is no motion to consider. For predictions of future events, motions, related forces, and effects, we must add the consequences of time, which mathematically can be accomplished by calculating quantitative time intervals as they relate to motion, hence X,Y,Z, T and the invaluable perspective of spacetime.

6. we know that time can transform in space, and vice-versa: what is space for an observer may be time for another.

Again I would choose different wording without being in disagreement.

Instead I think a preferred perspective is simply that the passage of time has a different rate for different observers having different relative motions to each other, or to the prevailing gravitational fields.

My reasoning for all simply this. The Cartesian coordinate system is also an invented concept for calculation purposes as is time. In my opinion there is no simpler man-made concept that I can think of than time: when defined as: An interval of change (with nothing more to it).

This simplicity is in sharp contrast to the concept of time in quantum physics and related cosmologies.

A prime example I think is Sean Carol's book "From Eternity to Here" -- The Quest for the Ultimate Theory of Time. Sean Carrol is a Senior Research Associate in the Department of Physics at the California Institute of Technology. He is a theoretical cosmologist specializing in dark energy and general relativity.

In Sean Carrol's opinion, which is based upon some current ideas in quantum physics and field theory, time may be such a complicated concept that it might take more than a century to even come up with a valid theory of it.

So from my perspective of time being one of the simplest of quantifiable concepts, to his whereby time is one of the most complicated of all theoretical entities.

Probably the prevailing scientific opinion is that the truth concerning the nature of time lies somewhere in between these two perspectives

As to what else do we know about time?

-- time definition (science related) : the measured or measurable period during which an action, process, or condition exists or continues; a duration;

an interval or continuum of continued progress of existence and events; A non-spatial continuum in which events occur in succession from the past through the present to the future, etc.

-- time is normally defined as a quantifiable interval, unlike a time frame which can be defined as a static condition.

-- the cause of time requires potential energy, and the passage of time involves kinetic energy.

-- time is a mathematical tool.

Deleted Philosophical direct implications and temptations

Edited by pantheory
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Is time rotatable in space?

I'm not sure what that means. Objects rotate in space-time between frames of reference. The rotation corresponds with a change in velocity. Think of a vertical world-line on a space-time diagram. If you show the same world line from a different reference frame it would be a tilted line. A rotated version of what it was before.

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I'm not sure what that means. Objects rotate in space-time between frames of reference. The rotation corresponds with a change in velocity. Think of a vertical world-line on a space-time diagram. If you show the same world line from a different reference frame it would be a tilted line. A rotated version of what it was before.

You understood very well.

I'll take your answer for a yes.

That corresponds to point 6. of the OP

6. we know that time can transform in space, and vice-versa: what is space for an observer may be time for another.

So if you can rotate apples and after rotation they become oranges, what would be your scientific conclusion?

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My conclusion is that time and space have different properties.

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as to the discussion of time...

I would post pictures and text... but the mod here is oppressive so all I can do is...

suggest... you go to this page... scan down to the page on TIME... and consider my thoughts and proposals.

see --> link removed

-Mosheh Thezion

Edited by hypervalent_iodine
Link removed - we don't allow thread advertising either
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So if you can rotate apples and after rotation they become oranges, what would be your scientific conclusion?

My conclusion is that time and space have different properties.

Well, if I saw an apple changing into orange under a simple rotation, I'd say there is something wrong somewhere.

Physics don't behave like a magician, physics don't change apples into oranges just like that.

What could possibly happen is that what I observe as an apple is in fact an orange, or vice-versa, or even that what I observe is a very peculiar fruit.

As an analogy, think of a tetrahedron.

A tetrahedron has 4 faces. But if you look at at it, you can observe only 3 faces. Call the visible faces "Space"(or Apple) and the hidden face "Time" (or Orange). If you rotate the tetrahedron, there will always be a hidden face. And what you observe as Space may be observed as Time by another observer.

The tetrahedron is a single entity, it is not something that 'transforms" into something else. The "transformation" is caused by the difference in position between the observers. The "transformation" is not a magic trick, it is an observational consequence.

IMHO spacetime is a continuumm of 4 dimensions that must share the same properties, like the 4 faces of the tetrahedron. No face is different from the other, only one is always hidden.

If the properties of Time were so dramatically different from Space, no observer in no FOR would call time what I call space.

Of course there is a difference between Space & Time. Space is 3D and Time is 1D. In the terahedron analogy, the 3 visible faces are called "Space" against the only one single hidden face called "time".

So, the properties of 1D Time are not to be compared to 3D Space, but to the 1D equivalent of Space, called Distance.

And if you put "common sense" aside, and compare Time to Distance, you will maybe see that there are similarities.

And from all similarities, the most outstanding is that distance can be measured with a clock.

Edited by michel123456
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michel123456,

Of course there is a difference between Space & Time. Space is 3D and Time is 1D

I think your description of the comparison of space and time is apt, but I think that dimensions are just man's mathematical description of reality. 1D space is a line with two directions. The sum of time seemingly could be characterized in 1D. But the progression of time might better be characterized as a vector which is more restrictive, which I believe may more aptly describe man's invention of the concept of the progression of time in the first place.

//

Edited by pantheory
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Ideal clocks measure time.

False. All clocks measure time, to varying degrees of accuracy and precision. A broken clock is a non-functioning clock and does not functionally measure time. Does only an ideal ruler measure distance?

8. we know that distance is related to time: to more an object is far away, the more he is observed in the past (another consequence of point 1)

9. so we know that if you take a close object, then propulse it far away, you are throwing the object into the past (and not in the future as comonly believed). And that is coherent with point 8. because the object is continuously observable along its path. As the distance increases the object falls into the past.

False. You are confusing the delayed observation of an object with the object itself.

14. we know that time is relative: there is no absolute past. The past as described above is the observer's past, that is the specific past relatively to the guy throwing the ball away.

False. There is no universal past. Causally connected events have a unique ordering allowing for an absolute past. There is no absolute ordering for all events because they're not all causally connected. The thrown baseball is causally connected (and causatively as well if you want to differentiate and if the difference in meaning is what I think it is) to the guy throwing the ball; the event of the guy throwing the ball is in the absolute past of an event of the thrown ball being observed at any point.

I apologize if these answers are wrong or have been covered already; I didn't read all the posts.

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michel123456,

I think your description of the comparison of space and time is apt, but I think that dimensions are just man's mathematical description of reality. 1D space is a line with two directions. The sum of time seemingly could be characterized in 1D. But the progression of time might better be characterized as a vector which is more restrictive, which I believe may more aptly describe man's invention of the concept of the progression of time in the first place.

//

Time is a scalar, not a vector. Time as a vector is speculation (interesting though).

Distance is also a scalar.

(...)False. You are confusing the delayed observation of an object with the object itself.

(...)

Physically, since nothing can go faster than SOL, the delayed observation of the object "is" the object, meaning that in our equations the only thing that physically matters is the delayed observation. The "real" position of the object, wathever that means, is out of physical interactions.

The question I am debating for so long with Iggy is the following:

_do you believe the object is static in spacetime, "existing" all the way long, represented in a spacetime diagram by its world line?

or

_do you believe that the object changed coordinates in spacetime?

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