Can we see it?

[Iggy]

the lines are simply missing

Indeed they are.

In both cases, the Spacetimed Universe is full of matter (objects) from which we can see only a tiny part: the dots at the intersection of the light-cone in the first diagram.

 

Lines don't hide inside past light cones and mass must be represented with lines. Yes, only a tiny fraction of past events are currently observable. No, it does not follow that a tiny fraction of the mass responsible for those events is currently observable. The reason it does not follow is because an event is not an object.

 

The mass is what you call "directly observable" because its world line intersects the past light cone of the observer. We are not seeing the mass as it exists today, but we can see it.

[Spyman]

Hm. i don't get it.

On a space-time diagram, how do you represent an object? (by differenciation with an event)

Well Michel, I get a feeling that you are stubbornly not listening...

 

 

If that is your point of vue, you must be confident with this (the lines being the objects & the events being the dots)

 

Draw the world lines for both the events X and Y in your picture and you will clearly see that both the objects involved in both the events are visible from Earth in present time.

 

Why is this so hard for you to do or understand ?

 

 

Which is not basically different with the next one (the lines are simply missing, you can draw the objects-lines at will following the one or other theory)

 

 

In both cases, the Spacetimed Universe is full of matter (objects) from which we can see only a tiny part: the dots at the intersection of the light-cone in the first diagram.

If you accept that the points are simply events and draw the world lines for all of them, like you say it can be done, it will be clear that each and every one of the objects involved in the events will have a world line that cross the lightcone for Earth and thus every single one of the objects are visible from Earth.

 

 

What is wrong with this?

IMO you have made a picture of a Universe filled with events and claim that every event is a separate object which is false.

(Some of the 'events' are also placed in the future indicating a deterministic view of the Universe.)

[michel123456]

Spyman.

I am not trying to propose my interpretation.

I am trying to understand yours.

 

Draw the world lines for both the events X and Y in your picture and you will clearly see that both the objects involved in both the events are visible from Earth in present time.

 

Why is this so hard for you to do or understand ?

I got that.

I hope in respond that you agree that we cannot observe the majority of the EVENTS around us.

 

On the other hand:

If an object IS a LINE in the diagram, I understand that the object must be a continuum through time. The object exists in the past as in the present.

It is different from a moving dot.

 

IMO you have made a picture of a Universe filled with events and claim that every event is a separate object which is false.

(Some of the 'events' are also placed in the future indicating a deterministic view of the Universe.)

 

I didn't say they are separate objects. I said the life-lines that connect the events depend on some theory. And I said all those events that are not upon our light-cone are not observable by us.

It is difficult to avoid putting events in the future. If I didn't, I had obtained a diagram ending at the present line. And I am not comfortable anymore to construct a diagram with an absolute universal present.

I would be very interested to see a diagram representing your point of vue.

Edited March 26, 2010 by michel123456

[Astroreeper]

No!

[Iggy]

On the other hand:

If an object IS a LINE in the diagram, I understand that the object must be a continuum through time. The object exists in the past as in the present.

It is different from a moving dot.

 

Right. You can also think of the observer (yourself) as always existing here and now which means the events are the moving dots. As the observer moves through time their view of the events of the universe changes. An example--an event on the moon is about a second old when we see it. The event moves from the observer's present to their past and intersects the past light cone of the observer when it is about a second old. The moon is always visible in the observer's here and now (the moon's world line always intersects the observer's past light cone), but this single event is only visible when it intersects (when it is a second old from this observer's perspective). I'll try to show.

 

 

And I am not comfortable anymore to construct a diagram with an absolute universal present.

 

I know what you mean. If there are two observers with relative velocity then the location of events in space time is different between them, or you could think of a single observer accelerating. The location of events in space time and even the order that they happen will change for the observer. A wikipedia diagram shows (http://en.wikipedia.org/wiki/File:Lorentz_transform_of_world_line.gif) The diagram is like the one I just drew where the observer's here and now stays in the same place on the image as time moves along (the center).

 

 

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.

 

Compare this to the absolute time apparent in Image:

Galilean transform of world line.gif

.

http://en.wikipedia.org/wiki/File:Lorentz_transform_of_world_line.gif

 

I hope this is insightful rather than confusing things.

Edited March 27, 2010 by Iggy

[michel123456]

Spyman, what is your opinion?

[Spyman]

Spyman, what is your opinion?

I seem to be in very good agreement with Iggy, but I will try to respond with my own words.

 

 

I hope in respond that you agree that we cannot observe the majority of the EVENTS around us.

Yes, from all of the events that did happen in the past to every possible event that may occur in the future, we are today only able to directly observe a very tiny part of events.

 

On the other hand:

If an object IS a LINE in the diagram, I understand that the object must be a continuum through time. The object exists in the past as in the present.

It is different from a moving dot.

No, I prefer to view the world lines as the path of the objects which they follow as they travel through time, from the past towards the future, precisely like "moving dots", but keep in mind that the dots placed in spactime diagrams represent fixed events when the objects are in those locations and not the objects themself.

 

Personally I don't think objects are like a long spear penetrating time from past to the future or that the original object leaves a separated or duplicated thing, that stays behind, still existing in the past when the object itself continues towards the future.

 

I didn't say they are separate objects.

You said and I quote: "...the Spacetimed Universe is full of matter (objects) from which we can see only a tiny part...", which I interpret as each dot in the picture is a separate object. If you instead had said something like: "...the Spacetime is filled with events...", I would not have objected.

 

And I said all those events that are not upon our light-cone are not observable by us.

But I am trying to explain that every object involved in all those events have crossed our lightcone and are thus observable by us today, but at different locations in the past.

 

It is difficult to avoid putting events in the future.

IMHO there is nothing wrong with a deterministic view, it's not totally ruled out yet and the only other option we have right now, a randomized future, also have a future filled with events.

 

And I am not comfortable anymore to construct a diagram with an absolute universal present.

I don't think putting a present line in a spacetime diagram from the frame of Earth is the same as proposing an absolute universal present. Observers in different frames might disagree with our view, but in our frame it's valid to have a present line between the past and the future.

[michel123456]

Vety constructive post Spyman.

 

Generally, and after 2 days of thinking, I agree with you. I made some wrong statements. I was over-enthusiast after realizing that there are plenty of events that are not observable. You are right, we are talking about non observable events of observable objects.

 

You wrote that you are in agreement with Iggy, but I see a great difference between your point of vues. Iggy talks about objects as lines in a continuum, you are talking about moving dots. I think the 2 options are not compatible. One must be right, the other must be wrong. The physics cannot be the same for the 2 concepts.

_In the Moving Dot concept, mass is compacted in present time. There is no existence outside, neither in the future or in the past.

_In the line concept, mass is multiplied by time (what is MT?).

_In the Moving Dot concept, if you go back in time at the old Earth's coordinates, you will find nothing, because the Earth will not be there anymore.(wrong?)

_In the Line concept, if you go back in time, you will find the Earth existing in the past.

So, which is wrong, which is right?

[Airbrush]

I never understood what you all are talkin about. But you sound like you know what you are saying. Have fun, or clue us in with common English.

[Spyman]

I think the 2 options are not compatible. One must be right, the other must be wrong. The physics cannot be the same for the 2 concepts.

Why, how can we differentiate between those two options, without a time machine ?

 

Propose we have an alien spaceship crossing paths with Earth, but they lag behind us in time by 10 seconds, can we send signals to them in our past or can they send signals to us in their future ?

 

 

So, which is wrong, which is right?

If we are unable to interact with hypothetical objects then they might be there but their presence are unphysical, making the question more philosophical than scientific.

 

I already told you my personal view, you on the other hand will have to make your own decision.

Edited March 30, 2010 by Spyman

[michel123456]

You cannot answer positively.

Neither do I.

Anyone else?

[Spyman]

You cannot answer positively.

Neither do I.

Anyone else?

Huh ?!? I challenged your position with a very straight forward question, you either have to show us how it is possible to communicate with someone in the past and in the future, or accept that both the two presented concepts of time are valid, since we are not able to theoretically observe or physically measure any difference.

 

You can't just brush off my reply because it is not a positively enough answer for you and then ask for someone else to give you another answer that you might like better...

[michel123456]

Huh ?!? I challenged your position with a very straight forward question, you either have to show us how it is possible to communicate with someone in the past and in the future, or accept that both the two presented concepts of time are valid, since we are not able to theoretically observe or physically measure any difference.

 

You can't just brush off my reply because it is not a positively enough answer for you and then ask for someone else to give you another answer that you might like better...

 

Sorry. Misunderstanding. It was not meant to insult anybody, certainly not you.

I am not challenging anyone, and I don't want to be challenged. My only interest is to better understand. I really don't care if I am wrong 100 times, I just want to understand even if I have to wait for try Nr.101.

 

I don't think it is possible to go in the past make an inspection to control which concept is valid.

 

I simply can not consider that both concepts are valid. Either there are moving dots, either there are lines. Which is right?

I believe that your statement "since we are not able to theoretically observe or physically measure any difference" is not accurate. There must be some way.

[Spyman]

I simply can not consider that both concepts are valid. Either there are moving dots, either there are lines. Which is right?

I believe that your statement "since we are not able to theoretically observe or physically measure any difference" is not accurate. There must be some way.

You think that it is possible to distinguish whether objects old locations are still at present time occupied with the same objects or if the objects has physically moved to present time effectively leaving the old locations empty.

 

I asked you twice to SHOW US HOW that would be possible without a time machine, but the only thing you are telling us is that you belive "there must be some way", which doesn't give us much to discuss does it ?

[michel123456]

Let' s try. Step by step.

 

What happen in the future is out of reach of physics, and generally what is not observable escape physics.

As much as I can understand, the laws of physics apply only on the diagonals in the diagram. Right?

[Spyman]

No, physical laws applies everywhere and everytime.

[michel123456]

No, physical laws applies everywhere and everytime.

 

So you tell me how physical law can reach an unobservable object in the past.

 

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

 

Sorry, wrong statement.

 

 

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

 

Re-trying.

All interactions that travel at C are observed as interactions acting upon objects placed upon the diagonals of the diagram. Each singular element (event, object) has his own diagonals, the entire surface of the diagram is full of diagonals originating from all the possible elements (events) of the diagram.

Is that more correct?

Edited March 31, 2010 by michel123456

[Spyman]

Ok, nothing new yet, continue...

[michel123456]

In the diagram provided by Iggy

 

 

We are at point D: we are in relation through some interaction (EM, gravity) with B. We cannot see event A but B can (could) see it. The event B (as we see it today) is (was) in relation through the same interactions with event A (that we cannot see today).

 

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

 

Now it's getting a little more complicated:

 

using again Iggy's diagram, with some additions (I hope its not copyrighted)

 

Edited April 1, 2010 by michel123456

[Spyman]

Waiting for you to explain the purpose of the added events...

[michel123456]

I crashed.

In this diagram ,as I see it, there is no interaction as I understood the concept till now.

 

_D & E are simultanate & there is no possible connection between them.

The same counts for F & B.

On the other side, looking at the diagonals &

Considering that the flow of time goes from down to up, we have:

 

_B has sent a signal (information, action, force) to D

_reversely, D can sent no signal to B

_F has sent a signal on E

_and E has no possibility to send a signal to F.

 

So there is no proper interaction, but one-way actions from different events positionned in different coordinates in spacetime.

 

I need to think further on this.

---

Merged post follows:

Consecutive posts merged

After a few thinking, this may not be a problem if we consider that mass does not change in time. And that corresponds to what we are observing: mass does not change as time elapses. It is another way to say that D and F are the same object, and that B and E are another single object. But that does not resolve the question: is the life-line of D "existing" in the past, or is D a moving dot?

 

I have introduced mass in the diagram.

To do so, I made a perpendicular line at D, representing graphically the amount of mass. To see this line (D,D1), I have to turn the diagram and see it tridimensionnaly.

Like this:

 

From point F, I drawed the same amount of mass: it is line F,F1.

 

Upon the life-line of D, there are plenty of such lines forming the square F,F1,D1,D,F.

 

Because the gap F,D is time, and the gap F,F1 is mass, we can deduce that the surface of the square is equal to Mass times Time.

 

It is MT, encountered for the second time in this forum for those who know.

 

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

 

This representation of MT is just a way to materialize the life-line.

 

Then I imagined a moving object coming from the past, sended a long time ago by planet B towards D. It is object X in the following diagram.

 

 

If MT is constantly existing, the trajectory of the moving object will in each case encounter MT surface. There will be in any case a crash point.

I think it is not what we are observing.

I think the trajectory of X most of the times miss the target, because mosts objects X may come at the correct spatial coordinates of D, but at the wrong time, and miss D. In other words there is not always a crash point.

Subsequently I tend to conclude that objects are not "lines", but "moving dots".

Edited April 3, 2010 by michel123456
Consecutive posts merged.

[Atomicfool]

About your discussions on time future and past.... A being on a body 2 million LY away from earth will be able to see wat took place on earth 2 million light years ago... ( not taking into consideration the minor details) so he will be able to LOOK into the past. this does NOT mean he is IN the past. The time frame is the same it is the communication that is slow. the being will not be able to communicate with our past as even if his mean of communication travels at the speed of light it will reach us at our present time.

[michel123456]

About your discussions on time future and past.... A being on a body 2 million LY away from earth will be able to see wat took place on earth 2 million light years ago... ( not taking into consideration the minor details) so he will be able to LOOK into the past. this does NOT mean he is IN the past. The time frame is the same it is the communication that is slow. the being will not be able to communicate with our past as even if his mean of communication travels at the speed of light it will reach us at our present time.

 

I agree. The same delay applies on interactions between the 2 objects.

---

Merged post follows:

Consecutive posts merged

I made a little gif to see the actual motion of such an object X of my previous diagram. I am still wondering if such a thing exist or is possible...

[Iggy]

It is another way to say that D and F are the same object, and that B and E are another single object.

 

No, B and E are not objects--they are events. We've been over this. Objects are lines on a spacetime diagram.

 

But that does not resolve the question: is the life-line of D "existing" in the past, or is D a moving dot?

 

It's not "life-line" it's "world-line". The world line of the object accompanying D exists in the past, present, and the future. Noether's theorem demands it. An object is not a dot--moving or otherwise. An object is a line. An event is a dot. An object persists in space, an event does not.

 

If MT is constantly existing, the trajectory of the moving object will in each case encounter MT surface. There will be in any case a crash point.

 

Correct. If ever two objects share the same space they will be touching. Your diagram only has one spatial dimension which means any time two lines cross the objects have essentially crashed into each other (assuming the both objects are in the same place in the other two spatial dimensions). If you were to add another spatial dimension it would make more sense:

 

http://evankeane.files.wordpress.com/2007/04/world_line.png

 

In this case two objects that share the same X and Y coordinate (regardless of what time it happens) will be touching (again, assuming they share the same Z coordinate).

 

I think it is not what we are observing.

I think the trajectory of X most of the times miss the target, because mosts objects X may come at the correct spatial coordinates of D, but at the wrong time, and miss D. In other words there is not always a crash point.

Subsequently I tend to conclude that objects are not "lines", but "moving dots".

 

That is not correct. The meteor that hit earth and wiped out the dinosaurs shared the same x, y, and z spatial position as earth--that it happened some time ago doesn't mean the objects missed one another.

 

As I said very early on in this thread--all of your confusion is stemming from your tendency to think of objects as dots on a space time diagram. That is not correct.

[michel123456]

As I said very early on in this thread--all of your confusion is stemming from your tendency to think of objects as dots on a space time diagram. That is not correct.

 

 

I am not convinced.

 

Iggy said "The world line of the object accompanying D exists in the past, present, and the future. Noether's theorem demands it. An object is not a dot--moving or otherwise. An object is a line."

 

Lets consider Iggy is right & objects are lines. As a matter of consequence I suppose then that , if objects "exist" in the past, they have mass "in the past" 9otherwise, what would be the meaning of the word "exist". In this case, there is a huge amount of mass hidden in the past (& the future), represented by the MT surface in the diagram

 

 

Right?