Can we see it?

[Spyman]

Hmm, the discussion has developed a lot during the weekend and left me somewhat behind, I must say that mostly I agree with what Iggy says, but we might still disagree about the concept of moving through time, or we are misunderstanding each other, so I will try to clear up that part.

 

First of all Iggy don't seem to quite look at the moving dot concept like me, and further more Iggy is talking a lot about the meaning of representations in the spacetime diagrams, but I am talking about the real world.

 

So question No:1 is if when Iggy only means in spacetime diagrams and when it's about the real world too?

 

If it is only about the use of spacetime diagrams, symbols and representations, then I think Iggy is correct and there is nothing more to discuss.

 

And question No:2 is if Iggy understand what I mean with moving through time or if Iggy thinks of something different?

 

The diagram in Iggy's post #89 shows a different view of moving through time than what I meant, I don't think objects in the past are moving forward in time behind us.

 

I will try to explain my view once more and hopefully Iggy will understand, even though my english don't seem to be powerful enough, I have a hard time finding the correct words even in my own language.

 

In Relativity space and time are considered dimensions that objects are moving through, and when an object moves from point A to point B it's not hard to see that the object is no longer in point A, so if we consider time dimension to be similar to space then it is possible to view time as if an object moves from time A to time B it will no longer be in time A.

 

I am NOT claiming that time is in that way, all I am saying is that we can't verify if it is or not.

 

[EDIT] Found this at Wikipedia:

"Endurantism or endurance theory is a philosophical theory of persistence and identity. According to the endurantist view material objects are persisting three-dimensional individuals wholly present at every moment of their existence. This conception of an individual as always present, is opposed to perdurantism or four dimensionalism which maintains that an object is a series of temporal parts or stages, like the frames of a movie. Some philosophers argue that perdurantism better accommodates the theory of special relativity. The use of "endure" and "perdure" to distinguish two ways in which an object can be thought to persist can be traced to David Lewis."

http://en.wikipedia.org/wiki/Endurantism

 

So question No:3 is if Iggy thinks it is possible to verify by observation how time really is?

 

 

The only difference we would notice are if we used a timemachine to go back and look.

You would think that traveling back in time to see if there is a sun and earth would reveal the truth of this. So, I might go back a couple thousand years and stand next to Cleopatra and find out if the sun and earth are there. That would settle the issue for you. But, how is that different from what Cleopatra saw? Can I not take her word on this?

 

The sun was here yesterday and two thousand years ago and we don't need a time machine to prove it. The consequences of this moving dot idea are shown very clearly in the diagram in my last post. The consequences are incompatible with observation.

Well if the Sun and Earth are not there then certainly Cleopatra will not either, no one is arguing that the Sun did not shine in Cleopatra's time, the question is if time is like a spatial dimension in that way that objects in the past can remain there in that past spacetime location or if they move forward in time.

 

How would our observation differ whether there would be a Sun remaining in the past or not?

 

(Iggy is convinced that objects are "lines".)

The entire physics community is convinced of that. It is explained in the links I've given through the thread. There is a reason a world line is a line. There is a reason Minkowski made it so. Conservation of energy and all of our human observations demand it.

If you are talking about symbols and representations in spacetime diagrams it's fine, but if you are talking about how the science community are looking at time then you are very wrong. There are plenty of views of time, more than the two we are discussing here, several of them are concerned valid by the community.

 

How would the difference wheter the Sun remains in the past or not break conservation laws?

 

I think you are making the jump in believing that the past tangibly exists somewhere, when in reality all we see is the light that has reflected off of what once was.

I have not said and not implied that past events exist somewhere

No you didn't say that but for the sake of the argument, from my point of view you seem to be implying that objects *must* remain in the past, as they where during the event. Which they might very well be, I am only arguing the 'must' part or more precisely whether we can distinguish between if they are or not.

 

And to make it clear, they where evidently there when the events took place, the question is if they still remains there, if we would travel back now.

 

Does that mean that the sun actually "exist" in the past, that's the question, IMO still unanswered.

We can prove that the sun was here yesterday and in the distant past with conservation of energy or Noether's theorem or we can prove it through direct evidence. Blue-green algae was using photosynthesis billions of years ago.

Again, nobody is arguing that we can't prove that the Sun was here yesterday or in the distant past, the question is if the Sun still exists in the past.

 

Can you prove that time behaves in such a way that it is possible for the Sun to continue to exist in the past?

 

Nowhere in the links provided by Iggy there is the sentence "an object is a line". All I read can be interpretated as a trajectory as well. I don't think the concept of trajectory can be confused with the object itself.

But, regardless, either an object's path through spacetime is a curve or a moving dot. I don't know if the universe is really four dimensional in a philosophical sense, but I know that when it is represented that way with a spacetime diagram an object's path cannot be a moving dot. It must be a line or a curve. The two different representations have different observational consequences.

 

In other words, I don't need to argue that "an object is a line", only that it must be represented that way in 4 dimensional spacetime.

I agree with "when it is represented that way with a spacetime diagram an object's path cannot be a moving dot" but we don't know how time is in the real world, object might move through time and leave past locations empty, and that could be represented by moving objects along a path, like a world line.

 

There would not be any differences either in representation nor by obsevation.

 

You have inserted half of your argumentation into mine to prove I am wrong.

Explaining:

In the moving dot interpretation' date=' there is only ONE dot moving through time.[/quote']

In your diagram in post 73 there are two moving dots--a black one and a red one. I don't believe I have misinterpreted your meaning. I believe my diagram follows logically from yours.

Well I do have a different meaning, so your diagram is wrong from my point of view.

 

But, this does reveal the problem. Your diagram has two different kinds of 'before'. The problem is that time is twice represented in the moving dot diagram. The difference from one frame to the next is the advancement of time. The difference from one point along the vertical axis to the next is also the advancement of time. But, time is not a two dimensional construct and can't properly be represented that way to be consistent with observation.

I agree that it's not good to represent time that way, but that doesn't imply that time is a two dimensional construct or that it would not be consistent with observation.

 

How would it be possible to observe such an object, like a timemachine suddenly entering our past?

 

The path of an object (ie particle or material point) through spacetime still must be represented with a line.

This wording I fully agree with.

 

In that diagram the red and black objects can never interact. They could both persist for billions of years in the same location but never would the one be able to touch the other. In reality objects separated by time need only persist for the duration of that separation and they will be able to interact.

Agree with the red and black dot can never interact.

 

But in reality objects is separated by space and need only persist for the duration of the time for signals to traverse that separation and they will be able to interact. If there was an object separated by time like in the diagram, say a timemachine, then we could not observe nor interact with it.

 

My opinion was, and still is, that you are mixing up events and objects. For example, you said a couple posts ago "at least, the first question of this thread has been answered several times. Can we see it? the answer is: NO."

 

If "it" refers to an event inside our past light cone then, no, it may not be directly observable. If "it" refers to mass or an object or a material substance then the answer is "yes" we can see it. We can directly observe it.

 

I think a good example is that we cannot directly observe Neil Armstrong walking on the moon (an event inside our past light cone), but we can see the mass of Neil Armstrong and the mass of the moon. The objects are visible--the past event may not be. By conflating events and objects one could come to the conclusion that mass can hide inside our past light cone or that a pair of massive particles in the same location can never come together and touch. Those are good conclusions for events, but bad conclusions for objects.

I fully agree to this.

 

Believe me, I understand. Your view would be called presentism as opposed to eternalism. But, that's ok. I don't want to argue against presentism or for eternalism, only assure that you diagram spacetime correctly. A moving dot on a spacetime diagram that represents an object is inconsistent with observation regardless of the philosophical arguments.

Here again it sounds like we are in agreement and that you only object to the use of symbols an meanings in a spacetime diagram.

 

So you say

I have not said and not implied that past events exist somewhere

and

"I occupied the center of central park on December 31' date=' 1999 and no other object can occupy the center of central park on December 31, 1999 without having touched me." In other words, if something occupies (0,0,0,1) then that specific place and time is taken.[/quote']

Both statements don't seem to be coherent.

Past events don't exist somewhere (by which I mean some place). They existed at a place and time. I existed in the center of central park on December 31, 1999--a place and time--an event--(x,y,z,t).

 

To say that past tangibility exists somewhere would mean to me that I can currently interact with the past event. But, I don't believe that. I can't affect Neil Armstrong walking on the moon. I have not implied that. Past events are not currently tangible.

Here it sound that you are arguing against me, 'you existed' in a past spacetime location, but the question is do you still exist there or are you here now or are you both there in the past and here in the present?

 

The past spacetime locations could be viewed as still existing but out of our reach, beyond our observable horizon, how could we then decide, if Neil Armstrong is still walking on the Moon in the past?

 

Past events are not currently tangible but the objects involved in the events are observable now - so have they moved from the past or have the past objects somehow managed to duplicate themself into the present?

 

There are two Iggy-events along my world-line and making up my world-line, but that does not imply that there are two Iggies.

But that is not the point, the point is if we would have a timemachine and travel back to the event of a past Iggy event, would there be an Iggy object there, frozen in a timestamp or would that past spacetime location be empty now, since you are here in the present now, creating new events?

 

Remember that all I am claiming is that we can't differentiate which is true or false.

 

No event in our present can cause or affect an event in our past light cone.

I fully agree to this and have nothing further to add to your last post.

Edited April 12, 2010 by Spyman
Adding Quote and Link

[michel123456]

Excellent Spyman.

Iggy, your turn.

[Iggy]

First of all Iggy don't seem to quite look at the moving dot concept like me, and further more Iggy is talking a lot about the meaning of representations in the spacetime diagrams, but I am talking about the real world.

 

So question No:1 is if when Iggy only means in spacetime diagrams and when it's about the real world too?

 

The moving-dot diagram has observational consequences inconsistent with the real world. I'm therefore talking about both the diagram and the real world.

 

The diagram in Iggy's post #89 shows a different view of moving through time than what I meant, I don't think objects in the past are moving forward in time behind us.

 

Ok, but I was responding to the diagram in post #73 which has an object moving forward in time behind us. My diagram followed logically from that diagram.

 

In Relativity space and time are considered dimensions that objects are moving through, and when an object moves from point A to point B it's not hard to see that the object is no longer in point A, so if we consider time dimension to be similar to space then it is possible to view time as if an object moves from time A to time B it will no longer be in time A.

 

That is not how I understand spacetime in relativity, or in physics in general.

It seems like you are imposing two kinds of time on the spacetime continuum. Movement is change in position over change in time (dx/dt). The concept already has time in it. We don't want to make time like the movement of space--we want to make it like space (i.e. position in space is like instant in time and length in space is like duration in time)

 

Here is a normal spacetime diagram:

 

 

It depicts two objects that are first 1.5 meters apart. Over the next second the black object moves to the right at one meter per second and the red object moves to the left at half a meter per second. They collide at T=1 and drift away from each other at the same speed as before for one and a half seconds.

 

What you and Michel are doing is adding another time variable:

 

 

But, I only know one kind of time. You have position in space changing along the time axis and position in spacetime changing with the animation. The biggest problem that I would see is that different observers in different reference frames have a different hypersurface of their present. If only one present exists in each frame of the animation then different reference frames couldn't have different presents. You can see, for example, the diagram in my last post shows two different presents.

 

So question No:3 is if Iggy thinks it is possible to verify by observation how time really is?

 

It seems a little vague. A confirmed theory could, at the least, disprove an ontology of time.

 

Again, nobody is arguing that we can't prove that the Sun was here yesterday or in the distant past, the question is if the Sun still exists in the past.

 

There is only one kind of past and one kind of present (that I know of). In the past the sun was in the past. In the present the sun is in the present. You are essentially asking if the sun is in both times at the same time. But, 'both times at the same time' doesn't make logical sense to me.

 

And to make it clear, they where evidently there when the events took place, the question is if they still remains there, if we would travel back now.

 

If the sun was there yesterday and we traveled back to yesterday then it would be there. Asking if the sun is still there yesterday is like asking if something is currently at yesterday. I have trouble making sense of that because currently implies not-yesterday and yesterday implies not-current. It's like asking if something is alive while it's dead--only if there are two kinds of 'alive' would that be true and I only know the one kind.

 

I know the sun existed yesterday and that on a spacetime diagram it should be there yesterday (lower on the time axis).

 

The past spacetime locations could be viewed as still existing but out of our reach, beyond our observable horizon, how could we then decide, if Neil Armstrong is still walking on the Moon in the past?

 

I think this again shows the difference in our understanding. To me "still walking on the Moon in the past" means "currently walking on the moon in the past, today". It's like saying "Is my Doctor's appointment on May 3rd on May 4th?" It's either on may 3rd or not--I don't understand the additional reference to time.

 

Unless there are two different kinds of time, it seems to be a self-reference paradox.

Edited April 13, 2010 by Iggy

[michel123456]

That is what I mean

 

 

(BTW I don't understand what is the meaning of "time B" .There is only one time. The labelling on the time axis must correspond to the elapsing time as mentioned above, only ~2,5 sec have elapsed (following the labelling), not 5 sec. The diagram is presented in slow motion but that is not so important. The result is great)

 

(editing)

My feeling is that books are unable to present animated gif, that's the reason why you will find your static diagram in 100% of litterature. Basically, both diagrams represent the same thing. The gif is closer to reality IMO.

(end of edit)

 

(...) The biggest problem that I would see is that different observers in different reference frames have a different hypersurface of their present.

 

Yes. I agree that different reference frames have a different hypersurface of their present.

 

If only one present exists in each frame of the animation then different reference frames couldn't have different presents. You can see, for example, the diagram in my last post shows two different presents.

 

I don't understand this part.

Edited April 13, 2010 by michel123456

[Spyman]

First I want to nail this issue, which is my only disagreement with Iggy:

So question No:3 is if Iggy thinks it is possible to verify by observation how time really is?

It seems a little vague. A confirmed theory could, at the least, disprove an ontology of time.

So that we can get rid of statements like this:

The moving-dot diagram has observational consequences inconsistent with the real world.

From my understanding the entire physics community has not so far been able to reach a consensus on how time really is and/or behaves so theories like Endurantism are concerned valid and not yet disproved.

 

Since it is not disproved by science, it clearly can't have 'inconsistent observational consequences'.

 

I want a very clear and precise answer to this one, because if Iggy is making claims that it is possible to disprove Endurantism by observation, then it would need to be backed up with massive evidence.

 

 

----------

 

Then I will also try to explain the view of moving through time further:

 

There is only one kind of past and one kind of present (that I know of). In the past the sun was in the past. In the present the sun is in the present.

and

If the sun was there yesterday and we traveled back to yesterday then it would be there.

I think I understand Iggy's view and don't really disagree with it, it is a valid view that time is like a dimension in which events occur in sequence where objects and events persist like frames in a film strip.

(I will return to this movie analogy later.)

 

 

It seems like you are imposing two kinds of time on the spacetime continuum.

No, I am not, I am trying to explain a different view of time, but I seem to fail miserably...

 

I can only se one time and one space dimension in both these two views:

The only difference I can see is that spacetime is empty before and after the objects in their paths.

 

TimeB counting to 5 seconds, I can't understand at all.

[EDIT] Wait, scratch that, it is supposed to represent the rate of movment through time.

But as I mention further down time does flow with a rate, that is nothing new.

 

 

Movement is change in position over change in time (dx/dt). The concept already has time in it.

But time still has a rate and according to relativity it can change between different observers, so movement from one timestamp to another seems to be able to happen, and at different rates too.

 

[EDIT] Look at this diagram from Wikipedia:

 

 

Note how both the distance of space and rate of time changes.

 

"Changing views of spacetime along the world line of a rapidly accelerating observer

In this animation, the vertical direction indicates time and the horizontal direction indicates distance, the dashed line is the spacetime trajectory ("world line") of an accelerating observer. The small dots are arbitrary events in spacetime that are stationary relative to each other. The events passing the two diagonal lines in the lower half of the picture (the past light cone of the observer) are those that are visible to the observer.

 

The slope of the world line (deviation from being vertical) gives the relative velocity to the observer. Note how the view of spacetime changes when the observer accelerates. In particular, absolute time is a concept not applicable in Lorentzian spacetime: events move up-and-down in the figure depending on the acceleration of the observer."

http://en.wikipedia.org/wiki/Time

 

 

 

You are essentially asking if the sun is in both times at the same time. But, 'both times at the same time' doesn't make logical sense to me.

No, what I was asking is if we went back in time with a timemachine would we find a Sun there frozen in a timestamp or if the past spacetime would be empty as if the Sun would have moved towards the future at a rate of time.

 

Let me put it this way: If time is like a film strip and space are the frames of each picture, then objects could be 'jumping' from frame to frame towards the future and thus leaving the old frames empty. The present is then the frame where the objects is or the frame that is displayed and the future frames is still waiting but empty.

 

If we had a timemachine and went back to a past frame to look, then it could be empty or it could still contain the objects as they where.

 

We are not looking at two timestamps at the same time or proposing two kinds of time.

 

Until I am able to explain this concept of time it's difficult to discuss the differences and compare consequenses of them with you, hopefully the movie analogy will settle this.

 

 

----------

 

The biggest problem that I would see is that different observers in different reference frames have a different hypersurface of their present. If only one present exists in each frame of the animation then different reference frames couldn't have different presents. You can see, for example, the diagram in my last post shows two different presents.

I don't see any more problems with this in the moving through time concept versus the persisting through time concept. Every observer has his own view of reference with his own past/present/future lightcone and while different observers don't agree on either distance in space or rate of time, each of their observations are as valid as another. They might even disagree on the order of events.

 

I would like you to explain more of why you think it would be different problems between the concepts.

Edited April 13, 2010 by Spyman
Adding understanding of TimeB & Spacetime diagram from Wikipedia

[Iggy]

I don't have much time to respond at the moment.

 

(BTW I don't understand what is the meaning of "time B" .There is only one time. The labelling on the time axis must correspond to the elapsing time as mentioned above, only ~2,5 sec have elapsed (following the labelling), not 5 sec.

 

The animation ended up being 5 seconds long. It could have been 2.5, TimeB would still be needed to show the animated movement of the dots. Neither you or Spyman are following why the animation makes for two dimensions of time. I'll try to explain further down.

 

From my understanding the entire physics community has not so far been able to reach a consensus on how time really is and/or behaves so theories like Endurantism are concerned valid and not yet disproved.

 

I'm not interested in proving or disproving the metaphysical or ontological nature of time.

 

The moving-dot diagram has observational consequences inconsistent with the real world.

I want a very clear and precise answer to this one, because if Iggy is making claims that it is possible to disprove Endurantism by observation, then it would need to be backed up with massive evidence.

I've made no "claims that it is possible to disprove Endurantism by observation". You assume that the moving dot diagram is a good representation of Endurantism. That is not the case and that is what I am focusing on.

 

[EDIT] Look at this diagram from Wikipedia:

 

 

Note how both the distance of space and rate of time changes.

 

"Changing views of spacetime along the world line of a rapidly accelerating observer

In this animation, the vertical direction indicates time and the horizontal direction indicates distance, the dashed line is the spacetime trajectory ("world line") of an accelerating observer. The small dots are arbitrary events in spacetime that are stationary relative to each other. The events passing the two diagonal lines in the lower half of the picture (the past light cone of the observer) are those that are visible to the observer.

 

The slope of the world line (deviation from being vertical) gives the relative velocity to the observer. Note how the view of spacetime changes when the observer accelerates. In particular, absolute time is a concept not applicable in Lorentzian spacetime: events move up-and-down in the figure depending on the acceleration of the observer."

http://en.wikipedia.org/wiki/Time

 

Yes, I posted that image earlier. I'm ok with it. Notice the moving dots are events--not objects. They would each have a world-line (like the observer has) which has been omitted to make the image viewable. This is an important distinction

 

I can only se one time and one space dimension in both these two views:

The only difference I can see is that spacetime is empty before and after the objects in their paths.

 

TimeB counting to 5 seconds, I can't understand at all.

 

Right. We should focus on that. In the first image the two objects exist at (x=1.5, TimeA=1.0). That is two dimensional. It has one dimension of time and one of space. Looking at the animation I could ask "is there an object at (x=1.5, TimeA=1.0)?" The answer is: "not always". Sometimes it's there and sometimes it's not. We've added another variable TimeB to show the evolution of the dots through spacetime.

 

In the animated view the objects exist at (x=1.5, TimeA=1.0, TimeB=2), but not at (x=1.5, TimeA=1.0, TimeB=4). I think I confused things making TimeB different numerically from TimeA, but that doesn't really matter. The point is that the animation adds another, additional, factor of time.

 

The way TimeA is made into a space-like dimension can be done with TimeB (in the way that post #85 explains). These Two diagrams show exactly the same data:

 

 

There is something at (x=1.5, TimeA=1.0, TimeB=2), but not at (x=1.5, TimeA=1.0, TimeB=4). Where you say, "The only difference I can see is that spacetime is empty before and after the objects in their paths." the before and after is not the same before and after that TimeA shows. It can't be because the concept is impossible to show in two dimensions:

 

 

You either have to animate this 2D image or add another spatial dimension to show an empty before and after. You've added another dimension of time.

 

Also, the objects in the above diagrams don't follow Newtonian mechanics when colliding which I apologize for.

---

Merged post follows:

Consecutive posts merged

I probably should have started at the beginning.

 

Here is space without time:

 

 

It shows a single dimension. Now we show time in the form of animation:

 

 

And that's how we see the world, at least one dimension of it. The black dot moves twice as fast as the red one. They come together and collide at X=1.5, T=1. We can show the same thing on a spacetime diagram treating time like another spatial dimension:

 

 

Each point on the diagram is a specific place and time--an event. The objects collide, for example, at x=1.5, T=1. It shows the same thing as the animation above, but with time as a space-like dimension.

 

What I insist you are doing with the moving dots through spacetime concept is adding another time parameter:

 

 

Now the objects have two kinds of motion: motion in space over timeA and motion in spacetime over timeB. If we make timeB a space-like dimension like we did for timeA we get:

 

 

Where you say that Cleopatra was there 2,000 years ago, but she may not be there if you could go back in a time machine, you are conveying that she was there in timeA 2,000 years ago, but may not be there in timeB 2,000 years ago.

 

I say there is only one kind of time. If the sun was there yesterday then it was there yesterday. The idea that the sun can simultaneously exist yesterday and today requires as a matter of logic two kinds of time otherwise (simultaneous) [math]\neq[/math] (yesterday and today). On the other hand you can logically have (simultaneous in timeB) [math]=[/math] (yesterday and today in timeA).

Edited April 13, 2010 by Iggy
Consecutive posts merged.

[michel123456]

Iggy.

We have touched a sensible point.

 

As you proposed, lets go right from the beginning.

You have posted the following diagram:

 

 

Could you please make another such diagram, representing the same situation adding time only in the graphic (without motion).

 

Thanks.

[Iggy]

Iggy.

We have touched a sensible point.

 

As you proposed, lets go right from the beginning.

You have posted the following diagram:

 

 

Could you please make another such diagram, representing the same situation adding time only in the graphic (without motion).

 

Thanks.

 

I'm not exactly sure what you're asking. I would guess you want the objects not to move, but to have the time axis. I can do that, but I should point out that the objects in the previous pic were not moving because there was no time (essentially, they were moving but without a time parameter there was no way to show it). These will be motionless because they really aren't moving.

 

The first is as an animation and the second is as a spacetime diagram:

 

Is that what you're looking for?

[michel123456]

 

Is that what you're looking for?

 

yes. The spacetime diagram will do.

 

Since you say that the object is a line, can you show where is the mass of object Black?

[Iggy]

where is the mass of object Black?

 

With the black object.

---

Merged post follows:

Consecutive posts merged

I'm sorry that was glib.

 

Mass actually curves spacetime. It mostly curves time in the weak field limit. So, in a naive sense (or diagramed naively) if the black object has mass then this happens:

 

 

The world-line of a nearby observer follows the inertial path of spacetime and accelerates toward the black object. We should probably stay away from general relativity and curved spacetime though.

Edited April 14, 2010 by Iggy
Consecutive posts merged.

[Spyman]

From my understanding the entire physics community has not so far been able to reach a consensus on how time really is and/or behaves so theories like Endurantism are concerned valid and not yet disproved.

I'm not interested in proving or disproving the metaphysical or ontological nature of time.

The moving-dot diagram has observational consequences inconsistent with the real world.

I want a very clear and precise answer to this one, because if Iggy is making claims that it is possible to disprove Endurantism by observation, then it would need to be backed up with massive evidence.

I've made no "claims that it is possible to disprove Endurantism by observation". You assume that the moving dot diagram is a good representation of Endurantism. That is not the case and that is what I am focusing on.

Well Iggy, I don't think that was a good answer, you are still avoiding the main point of the question.

 

You seem to claim that it would be possible to by observation differentiate whether objects travel through spacetime or persist through spacetime and from my understanding that is inconsistent with the current scientific view. I don't care if a diagram of model X is good or bad at representating theory Y and I think I made that clear too in previous posts.

 

Either you agree that it is not possible or you need to explain a possible experiment where the results will falsify or validate how time really acts.

[michel123456]

With the black object.

 

Hm.

 

So when we estimate the mass of an object (the quantity of matter), are we estimating the amount of matter distributed along the black line ?

[Iggy]

...if Iggy is making claims that it is possible to disprove Endurantism by observation' date=' then it would need to be backed up with massive evidence.[/quote']

...I've made no "claims that it is possible to disprove Endurantism by observation"...

Well Iggy, I don't think that was a good answer

 

I'm sorry, but I think your premise was mistaken.

 

you are still avoiding the main point of the question.

 

Not at all. I just think there are differences between 1) endurantism versus perdurantism and 2) representing objects as moving dots in spacetime versus representing objects as world-lines in spacetime. I wouldn't want to argue against a strawman, so I thought it best to express clearly that I'm talking #2

 

You seem to claim that it would be possible to by observation differentiate whether objects travel through spacetime or persist through spacetime and from my understanding that is inconsistent with the current scientific view.

 

Correct. If you accept four dimensional spacetime as the correct representation--or, I should should probably say--If you represent the world with four dimensional spacetime then an object (as it is typically defined) must take on the form of a line rather than something discontinuous in order to agree with observation.

 

The idea of a moving object through spacetime could work with Galilean relativity, but not with special relativity. It could work with classical mechanics in Galilean spacetime, but not with relativistic mechanics in Minkowski spacetime.

 

The reason for this is slightly involved and given your lack of response to the bulk of my last post I should address this before getting into it:

 

I don't care if a diagram of model X is good or bad at representating theory Y and I think I made that clear too in previous posts.

 

Either you agree that it is not possible or you need to explain a possible experiment where the results will falsify or validate how time really acts.

 

I have no interest in proving or disproving the metaphysical or ontological nature of time. I can demonstrate that this:

 

In Relativity space and time are considered dimensions that objects are moving through, and when an object moves from point A to point B it's not hard to see that the object is no longer in point A, so if we consider time dimension to be similar to space then it is possible to view time as if an object moves from time A to time B it will no longer be in time A.

 

is inconsistent with observation. In doing so I will not be "falsifying or validating how time really acts", I'll be showing that a certain model of spacetime (the one you and Michel have described) is inconsistent with special relativity and its confirmed experimental results.

 

 

Ok then, the moving-object-through-spacetime concept:

 

 

I think we can agree that the black object and the red object share a present--that is to say, they are both always in the present. According to this view, nothing exists that is not in their present. Looking at a diagram drawn by Roger Penrose,

 

 

Each sheet is a moment of time--a present instant. As you've put it, we need to prove that the sheets above and below the present are not empty. This wouldn't be possible in Galilean relativity because with a Galilean transformation the sheets are skewed like a deck of cards:

 

 

So, whatever observer's reference frame we're talking about, there is never any disagreement between them about the content of the present they are occupying. They never interact with the one above or below.

 

The consequences of this are Newtonian mechanics. We'll focus on one: the speed of light is not invariant. Not every observer agrees on the speed of light.

 

In order to preserve the speed of light we use Minkowski spacetime. Two observers with relative velocity who flash a beacon of light when they are co-located must both stay at the center of the sphere of light as it propagates away from them. This works in spacetime because the present instant for different inertial observers shifts out of eachother's present:

 

 

The blue and red sheets are the present instant of that observer. Each is skewed into the past and future of the other. The colorado.edu webpage explains:http://casa.colorado.edu/~ajsh/sr/centre.html. If you click next at the bottom of the page it shows an experiment where light interacts with mirrors that are not all in the same present. This is how the speed of light is preserved as an invariant in four dimensional spacetime essentially confirming that things exist for one observer which are in the past and future of the other observer.

 

The usual representation of objects as world-lines in Minkowski spacetime is therefore confirmed by the experimental success of special relativity.

 

 

So when we estimate the mass of an object (the quantity of matter), are we estimating the amount of matter distributed along the black line ?

 

No, the quantity of matter shouldn't change over time. The density in a four dimensional volume would be a density of events--I should think.

[toastywombel]

This is a very interesting conversation, I refrain on commenting further because I have not read the entire thing, but this is what a really love about SFN, when it comes down to it. Talkin' 'bout spacetime, photons, theoretical physics, advanced geometry, and all that other good jazz.

 

Haven't read what your talking about Iggy, but those diagrams looks mean!

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I know this,

 

No, the quantity of matter shouldn't change over time. The density in a four dimensional volume would be a density of events--I should think.

It is good to note over enough time all matter breaks down and decays. But that is probably off topic. So ignore that.

Edited April 15, 2010 by toastywombel
Consecutive posts merged.

[michel123456]

Iggy, you have drawned the fish.*

 

*french slang. You have put too much (correct) information.

 

You wrote

No, the quantity of matter shouldn't change over time.

 

I suppose it is thus not a big deal to draw mass upon your spacetime diagram.

 

Can you do that?

 

-------------------------------------

 

From the site you provided, I see the moving dot, don't you see it?

 

Maybe it is still confusing, because the past trajectory of the dot is showed as a bold line (a LINE you will say, I hear your voice from the other side of the Atlantic Ocean, or is it coming from East?)

 

And here are 2 moving dots

 

Here there is no bold line for the past.

 

 

from http://casa.colorado.edu/~ajsh/sr/simultaneous.html

 

P.S., don't forget my question. Thanks

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(...)I have not read the entire thing, but (...)

 

Shame on you.

Edited April 15, 2010 by michel123456
Consecutive posts merged.

[Iggy]

Iggy, you have drawned the fish.*

 

*french slang. You have put too much (correct) information.

 

Noyer le poisson, non. Enfoncer des portes ouvertes, oui.

 

I suppose it is thus not a big deal to draw mass upon your spacetime diagram.

 

A massive object curves spacetime like I showed a few posts up. It mostly curves time. That way inertial particles accelerate toward it.

 

From the site you provided, I see the moving dot, don't you see it?

 

 

Yes, we've come full circle. They are events--the moving dot. The animation shows subsequent events. The two objects would be the lines. Also, the world-lines for the mirrors (the green circle) have been omitted otherwise the diagram would be impossible to understand.

 

Maybe it is still confusing, because the past trajectory of the dot is showed as a bold line (a LINE you will say, I hear your voice from the other side of the Atlantic Ocean, or is it coming from East?)

 

Yes. The line represents the observer and everything that happens on the line is some event in the history of that observer.

 

What I was going for might be better shown here:

 

 

from ned wright's tutorial. In Galilean relativity everything exist in one present--one horizontal slice. But, in special relativity (the image on the right) the two observers have two different present instants, each in the past and future of the other. So, we can't say that everything in the present is all that exists--not in Minkowski spacetime with more than one reference frame.

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Haven't read what your talking about Iggy, but those diagrams looks mean!

 

Thank you. I didn't draw the last few, but I'm all for taking credit

[michel123456]

Again.

 

 

Where is the mass?

 

I made an attempt some posts ago:

 

[Spyman]

I'm sorry, but I think your premise was mistaken.

I am sorry too Iggy, because I didn't think it would be this hard to reach an understanding, our communication fails miserably and it has reached ridiculous proportions. I would have hoped that we had gone beyond this part by now so we could have an interesting discussion about different models and implications from relativity, but until I am able to interpret you correctly it would only be a waste of time to continue further.

 

You made a very long and hefty reply and after reading it several times, sleeping on it and then reading it again, I can only come to the conclusion that you successfully manages to dance around the subject, occasionally touching it but never truly step out from the shadows into the light and express clearly whether you agree or disagree to the following statement:

 

"The entire physics community has not so far been able to reach a consensus on how time really acts. We are not able, with current knowledge and technology, to by direct observation or by logic conclusions from verified theories distinguish whether objects persists through spacetime or travel through spacetime in the real world."

 

You have to either agree or disagree, you can't have it both ways and you can't have it half way either.

(Note that I do not mention any specific models or representations in the above statement.)

 

 

...given your lack of response to the bulk of my last post...

I think you have a good argument that might put constrains on some models but since we don't manage to pass step one there is no point in commenting on something that probably belong in step three or four...

Edited April 16, 2010 by Spyman
Correcting bad wording

[Cap'n Refsmmat]

Again.

 

 

Where is the mass?

Why does there need to be mass on a space-time diagram?

 

You could add a third dimension of mass and make the bars thick, but they'll be uniformly thick throughout unless there's some sort of nuclear reaction occurring.

 

The space-time diagram is no more complicated than, say, this graph:

 

 

where the x-axis is time (pretend that's not negative) and the y-axis is height, and saying "this represents a ball I threw up in the air."

[michel123456]

Why does there need to be mass on a space-time diagram?

 

You could add a third dimension of mass and make the bars thick, but they'll be uniformly thick throughout unless there's some sort of nuclear reaction occurring.

 

Yes. Thick lines.

 

We have 3 possibilities:

 

A. Lines

 

If you give thickness to the lines, it corresponds to Iggy's point of vue. That means there is mass in the past. At each infinitely small slice of time corresponds a quantity of matter. A huuuuuge quantity of matter from which we can observe directly only a little slice. That small little quantity is the one used in all equations of physics. The rest is ignored.

 

B. moving dots#1

 

If you don't give thickness to the lines, but give thickness to the dot, it is Spyman's (I guess) point of vue. There is no mass in the past: what we are observing is accurately what it is. Point.

 

C. moving dots#2

 

The moving dot interpretation is exactly the same as motion in space: when mass leaves a coordinates for another, the new coordinate is occupied, the old one is empty.

Empty means that leaves place for another (hypothetical) mass. Which in this case is not observable. So that there is full room in spacetime for unobservable hypothetical mass. Not allowed in the Line concept, because in the line concept the coordinate is already occupied.

 

To speak frankly, the line concept looks to me outrageously wrong. I cannot understand how mass magicaly duplicates at each infinitely small frame of time. It looks to me like creation of energy from nowhere, just due to the flow of time. Totally unacceptable.

[Cap'n Refsmmat]

Why does there have to be duplicated mass? All the chart says is that at time t, there was a given mass in existence. That is true, because at that time we could have measured it and found that mass. At any other point in time, we can also measure the mass and record it. If you mark the mass as existing at only one point in time, than someone reading the graph will go "I wonder what the mass was back at t=0.5", look, and find nothing, concluding that there was no object at all at that time. But there was.

 

You don't have to interpret it to mean "that mass still exists in the past", whatever the hell that's supposed to mean. You interpret it to mean "at time t, there was mass."

 

Suppose I graph an object's velocity over time. I don't say that at t=1, the object still has a velocity, even though that time's in the past -- so it's moving while frozen in time. I say that the object had that velocity at that time.

[michel123456]

When you insert the concept of "an object is a line", what you are doing is duplicating its mass. You cannot draw a diagram with the line-concept without expanding the mass of the object all along the time line. When you draw it black on white, you see that.

 

(editing)

You don't have to interpret it to mean "that mass still exists in the past", whatever the hell that's supposed to mean. You interpret it to mean "at time t, there was mass."

That is the moving dot concept.

 

(end of editing)

 

 

 

On the other hand I'd like to avoid discussions about what our understanding of time supposes, like "the object was there", a.s.o. I prefer begin with the diagram and then drive some conclusion.

 

From now on, the only conclusion I could extract is that some events placed upon the diagram are not directly observable. An example of such event is our own past. Our own world-line is not directly observable from our point of vue. This is not something you cannot understand from simple thinking, but looking at the diagram.

 

Now I am trying to extract some more information.

[Cap'n Refsmmat]

When you insert the concept of "an object is a line", what you are doing is duplicating its mass.

 

What you are saying is that its mass has existed throughout time. A space-time diagram shows the object at different points in time. Now, if you want a diagram that only shows what you can perceive at this instant, it's wrong, but that's not its purpose.

[michel123456]

What you are saying is that its mass has existed throughout time. A space-time diagram shows the object at different points in time. Now, if you want a diagram that only shows what you can perceive at this instant, it's wrong, but that's not its purpose.

 

Emphasis mine.

It looks to me you are a moving-dot adept.

I believe you are right.

[Cap'n Refsmmat]

Nope. What I'm saying is that the lines represent object throughout time. The moving dot makes sense if you want to show what the world looked like from one perspective, but there's a time axis on the graph for a reason.

 

Or, more pointedly, what's the point of a time axis on a graph if you insist on only showing the object at one time? The time axis is there to show what the object did in the past.