Iggy

That isn't my decision. This is your model of spacetime. That certainly is an incompatibility. If Marion is the red dot according to one person and the black dot according to another person while both people are correct, and she can only be one dot, then your model is inconsistent with itself. It gives two answers, both of which are correct, only one of which can be correct. That means it is internally inconsistent, and since we are in the physics forum it is enough to say that the inconsistency falsifies the model. Marion can't be both: only one dot the black and red dot depending on perspective Do you have any suggestions for fixing the problem? It sounds like you are suggesting that every diagram have only one person on it -- suggesting that I remove Paul from the diagram. That way no two observers will ever be 'superimposed' onto the same diagram. In other words, if your model works when only one observer is diagrammed, it sounds like your solution is to only ever diagram one observer. If the universe only had one observer then this would be a reasonable solution, but it doesn't and it clearly isn't. Do you have any solution to propose?

I see a number of your comments trying to explain why your diagram and your spacetime interpretation isn't working the way you've previously explained, but I also know the things you're saying are false and I feel the need to correct them. Both Marion and Paul are in the same frame of reference. Both exist at the same time. Both are property placed on the same diagram. If Paul identifies the red dot as Marion then everyone in that diagram needs to agree that the dot is Marion. This is the way that every spacetime diagram has ever been made, and you have given no reason for this one to be different. If Paul determines that Marion was at 0,0,0,12:00:09 because he sees her there, it is impossible for Marion not to have been there. The red dot carries the same label regardless of who determines what it is. If your model of spacetime is different (only one observer's observations in any given diagram count), then the diagram has no usefulness. Spacetime diagrams also show multiple frames of reference and allow one to relate observations made in one frame to observations made in another although that isn't necessary or relevant for this example. For example, Marion's proper time between 12:00:09 and 12:00:10 can be calculatee by any observer in a diagram and they would all get the same correct answer. I therefore wonder if you are dissembling to try and cover the problem with your spacetime interpretation. The x axis means "light-seconds from earth". Marion is at zero light-seconds from earth because she is on earth. Paul is at -1 light-seconds on the diagram because he is 1 light-second to Earth's left. I can't re-label Paul putting him somewhere that he doesn't exist. He is at -1,0,0,12:00:10. I can only move him on the diagram if I move him in real life Putting 2 observers on a diagram is not bad mixing. It isn't mixing at all. Paul is at -1,0,0,12:00:10 . That is his space-time position. That is where he goes on the space-time diagram. He is an observer. He has a past light cone. And, he makes observations. If you have some problem with what he sees then that is a problem with your interpretation of spacetime. You can't deny that he belongs in his spacetime coordinates or that he does what he would do in real life -- make observations. In real life he would also compare his obsrvations with Marion, so we can't deny him that opportunity. When I previously said that multiple dots represent the same object I was met with a lot of resistance. I said, in fact, that a multitude of dots making up the world-line are one and the same objects. Do you agree now? You're saying that two of the dots are the same object. Can I assume that more are (if there were more observers for example) as well? Please keep in mind after all this -- I'm working off your assumption that objects are dots that move through spacetime. I'm accepting your premise for the purpose of discussion.

I understand that Paul can't see the black dot. I also understand that Marion can't directly see (by line of sight) the red dot. Those things are not what I'm asking. I'm trying to determine what the red dot in your model is. You keep saying that it is Marion ("Marion in red"), but earlier you said that the one thing the red dot couldn't be is Marion. I'm not asking how many dots at x=0 Paul can observe at 12:00:10... or how many dots any observer can observe at any spatial location at any time. I'm just trying to figure out, according to your model of spacetime, how do we label the red dot? From your interpretation and statements: we know Paul can identify it because it is on his past light cone, we know it isn't Marion because she can't be more than one dot, and we know it is an object because objects are dots in your model. If your model of spacetime works there should be a reasonable answer. How do we label the red dot? In that post I said Marion is at 0,0,0,12:00:10. Paul is one light second left of Marion. He is at -1,0,0,12:00:10. That is where he is in the real world and that is where he is in the diagram. I don't know what you mean by "origin" and I don't know why you are saying to put him there.

I thought the red dot wasn't Marion. Now you say it is. Could you clarify? I've never heard such a thing. What do you mean by "origin"?

That's right, I previously said Marion was at x=0, y=0, z=0, t=12:00:10 Here then: Again, I'm working off of your premise. I'm using your interpretation of spacetime. So far you have not been able to tell me what the red dot is, but you are sure it is not Marion. Marion's friend is one light second away. What does he see when he looks toward Marion? 1) does he see the red dot? 2) how does he identify it?

Yes. Agree. Yes. You are understanding very well. Good to hear. Is this diagram correct? Marion is the dot at t=12:00:10. The triangle is her light cone so she can't see the red dot (one second behind her in the -t direction). Is this correct or should I change it?

Remember, I am accepting your premise that we are dots moving through spacetime. If you have to rely on a straw man about being frozen in time 1 second ago, you are making a straw man of your own model. It sounds like you aren't sure what to put on the spacetime diagram one second lower in the time dimension. If I may make a suggestion (based entirely on your model) -- if a person (let's say Marion) is a dot moving through spacetime then there is one thing for sure which cannot be one second in the -t direction from Marion, and that is Marion herself. Do you agree? If I am represented by a dot moving through spacetime then I can't be at both 12:00:10 and 12:00:09. If I were at both then I wouldn't be a dot. Is that a correct interpretation of your model? If not then could you please tell me where I've gone wrong.

We agree Who's got the champagne! You are expressing yourself fine. I understand very well. Let me accept your premise, and make the assumption about moving through time with you and ask... When you are at the spacetime coordinate x=0, y=0, z=0, t=12:00:10 (twelve o'clock, zero minutes, 10 seconds), what is at x=0, y=0, z=0, t=12:00:09? In other words, what is one second behind you in the time dimension?

I'm not sure what "progress in time" means, but I never said it. This image shows a skateboarder occupying three different spatial locations at the same time. Objects (point particles specifically) don't occupy different spatial locations simultaneously, and I certainly never said or implied that they do. I never said or implied anything close to that. If you are willing to believe that the sun didn't exist in the same spot yesterday at noon and the day before at noon then nothing anybody could say would convince you that you are misunderstanding. If you can disregard the existence of the sun then you can disregard arguments against your view. There simply is no point of evidence that would mean you have to change your mind... so I'm not sure the point in conversing.

If all the orange lines on a world line have the same height in the mass dimension then mass is conserved, correct. The usual definition of "object" corresponds directly to a world line on a space time diagram, yes. Mass is a property of objects, correct. Again, mass can be a property of objects and related to events... just like... wet can be a property of water and related to swimming. Do you *really* not understand? Yes, it is the mass of the object or objects intersecting that event. It is the height of the rectangle. So what? Please, show me where I said the sum of the orange lines or apologize. I am moving through time at infinite seconds per meter and this somehow implies that I either had mass in 2000 or 2001? I don't think so. I think you mean something entirely different when you say "an object moves through time".

If mass persists, the past universe *was* (you've GOT to stop mixing your tenses) filled with what is now old mass. no, it is the equivalent of conservation of mass or saying that mass has time symmetry, neither of which are technically correct but good enough for the purpose of this conversation. I haven't read the thread and I would be afraid of pulling those quotes out of context. If "MT" has units kg*t then it doesn't have a name. I don't think any of the classical quantities like force, acceleration, energy, power, etc... have units where time is in the numerator.

Objects move how fast through time? You didn't ask a question. You listed three non-contradictory sentences and put 5 question marks after them. Answer this: Wait a moment: I thought you have said wet is connected to water. Now you say wet is connected to swimming. But you also say that swimming isn't an object????? How do you want me not to be confused? Wet is a property of water. Swimming is related to water. Mass is a property of objects. Events are related to objects. There is no contradiction. If you are confused -- I'm clearly unsuited to alleviating your confusion. Edit, Apologies... Of course mass persists. Do you think the earth will have no mass tomorrow? To persist means to continue to exist. Mass is a property of objects and objects persist. We've covered this persistently.

Yes. Mass is a property of objects and events are related to objects. Does it confuse you that not everything related to a barn is a horse? I don't think you're confused.

Events don't persist. Objects do. The height of each orange line is the mass present at each of those events. The height of the green square is the mass of the object that intersected each of those events. How does one measure the speed of an object "moving through time"?

I didn't. A space-time coordinate is an event. Mass can exist at an event by way of an object intersecting that event. That doesn't make the event an object any more than having cat food in my pantry makes me a cat.

I still use those. Oh! I thought we were looking for phrases where the etiology's been left in the lurch. Things we say, but don't really know why they mean what they mean... humm.. shiver me timbers I must be three sheets to the wind

en géométrie dans l'espace, c'est une projection telle que la droite et le plan — quels que soient leurs rôles respectifs — sont perpendiculaires. http://fr.wikipedia.org/wiki/Projection_orthogonale On your diagram the plane is the green square and the line is the t axis. See the definition above. That is not a new question. What is the "speed of time" is a dubious question that arises in fora at regular interval. Again, I didn't ask the speed of time. You said object move through time. I asked how fast they move through time. How does one measure the speed of such a movement? No, the mass of the object is just the height of the green square. The mass axis is properly labeled. The height of a rectangle is the same as the height of a point on its base line. It really is just that simple.

High and dry, bought the farm... kicked the bucket.

No doubt, but more often they're found wanting in different texts. Funny how that goes.

You've already agreed, you find the height of a line projected into a surface the same way you find the height of a point projected into a line. You've already agreed. You don't find the height of a square by multiplying length and width just because the square makes a surface. It is as simple as geometry gets. The height of a surface is not a surface area. C'est pas un travail de romain. I don't know what else to say. No! You said objects move through time. I asked how fast. If you can't measure it that should tell you something. I asked if the sun could have existed on march 1st and march 2nd. Your answer is that two suns cannot exist on march 1st. Do you see the disconnect? I wouldn't call science a model, and I've never heard of a scientific model saying the things you're saying, but perhaps you can show me one? I wouldn't say that objects persisting in time is quite my idea. It would be widely considered common sense. In fact, you say the same thing, The object persisted in time means what you just said.

Then, hopefully, you see what I mean? If a world line is an object and that line is projected into the mass dimension, that doesn't imply that the mass changes over time. Does it move one day per day, two days per day, or three days per day? How fast does it move in time? If this is a meaningful concept then certainly we can measure it. The sun can't be in the same spot yesterday and today? I could swear otherwise. The sun either existed on march 1st or march 2nd... it can't be both...? Is there a working model that would demonstrate?

:-D So I understand you correctly... if I draw a rectangle in the mass-time plane where mass is the width (the x axis) and time is the height (the y axis), to find the width of the rectangle I only need to measure it at one point? That doesn't imply that only that one point has width? The width of the whole rectangle can be the width of just that one point? If so... What does this mean:

assuming you mean to measure from the base to the top, which point (or points) do I measure to find the height of the rectangle? Remember, we want to height of the whole rectangle... not just the height of one point.

straightforward. i'm not trying to trick you. You pick up a rectangle. How do you find its height? I don't think you would measure both sides and divide their product.

I understand you perfectly. You are expressing yourself well and I get exactly where you're coming from. A point in space. Not a point in space-time. The reason I said point particle was to be clear we would have a surface in the mass dimension and not a volume... if you look back at the post you'll see that was my line of thought. How then do you find the height of a rectangle? This is the fourth time I've asked. Please.