Iggy

Movement is already represented in this static spacetime diagram, The black object moves relative to the red one. It moves in space over time. The two objects interact at T=1. If they were thrown at T=0 toward each other then we would say that the T=0 events caused the T=1 event. Two points in spacetime are connected (hence information about the one is available to the other) if they are connected by the world-line of a material particle. The existence of the world-line means that there is a causal relationship between the points. See: time-like interval. The x,y,and z dimensions show location in space. The t dimension shows location in time. Since "movement" is a change in spatial location over a change in time it is already encoded on a static spacetime diagram. To have things moving through spacetime is to show two different kinds of motion. To have the coordinate (x,y,z,t) take on two different values would require another coordinate: (x,y,z,t,t2) so that x,y,z and t can change in t2. This, for example, That needs three coordinates (one of space and two of time). An object is at (x=1.5, tA=1, tB=2) but not at (x=1.5, tA=1, tB=3). Take a look at this website: http://dev.physicslab.org/Document.aspx?doctype=5&filename=Kinematics_ConstantVelocityPositionTimeGraphs1.xml It gives this diagram, asking these questions: which is at rest which is traveling slowly in a positive direction which is traveling quickly in a negative direction which is traveling fast in a positive direction The static diagram already represents the concept that we understand as movement or motion or change. Four spatial dimensions is not exactly the same as spacetime. An event at T1 can cause an event at T2 if an object (or a massless particle) intersects them both. In order for things to move through space you must add time. It is a parameter that allows motion through space. In order for things to move through spacetime you must add another dimension of time. It would be a parameter that allows motion through spacetime.

Yes, but a Protestant could quote Jesus from John (eg 3:16) just as meaningfully as a Catholic could quote him from Matthew. Very well informed and respected theologians have debated the topic for a very long time. I don't think Jesus' opinion is so easily and decisively proven.

Paul and Peter had completely different views regarding whether the Law should be follow. There's a good wiki summary in: Judaizers: In the Early Church Statements like these seem mutually exclusive to me, Paul: "For we maintain that a man is justified by faith apart from observing the law." Ro. 3:28 James: "You see that a person is justified by what he does and not by faith alone." James 2:24 Who could say what Jesus actually taught.

Why not? Why can't an event at T=1 cause an event at T=2? Try reading: http://en.wikipedia.org/wiki/Spacetime While time is space-like in spacetime there are still some distinctions between the two. The most obvious is that space is measured with a measuring tape and time is measured with a clock. There are some others.

No, the word "event" has a precise definition which predates spacetime diagrams. The word doesn't come from the unusual circumstance of animation not yet being available. The word means "a specific place at a specific time". An "instant" on a spacetime diagram is a single coordinate along the t axis. A "duration" is a range of coordinates along the t axis. This is true in a 'static' spacetime diagram in a book or an animated one. Incorrect. They show three dimensional dynamics in time. By introducing the idea of objects moving through spacetime you are imposing another dimension of time on spacetime. You fail to understand how these diagrams show the same thing: Animating the second image would add another dimension of time. No, the word "event" has exactly the same meaning. Yes.

By definition, an event is a specific place at a specific time. By the definition of coordinate, a dot on a spacetime diagram is a specific place at a specific time. What I said is simply true by definition. People have issues with it because it is not correct. Motion is change in position over change in time. On a spacetime diagram motion is depicted by run over rise, or tilt. Like wikipedia shows: I think you would benefit from reading that wikipedia article, Trivial examples of spacetime curves Three different world lines representing travel at different constant speeds. t is time and x distance. A curve that consists of a horizontal line segment (a line at constant coordinate time), may represent a rod in spacetime and would not be a world line in the proper sense. The parameter traces the length of the rod. A line at constant space coordinate (a vertical line in the convention adopted above) may represent a particle at rest (or a stationary observer). A tilted line represents a particle with a constant coordinate speed (constant change in space coordinate with increasing time coordinate). The more the line is tilted from the vertical, the larger the speed. Two world lines that start out separately and then intersect, signify a collision or "encounter." Two world lines starting at the same event in spacetime, each following its own path afterwards, may represent the decay of a particle in to two others or the emission of one particle by another. World lines of a particle and an observer may be interconnected with the world line of a photon (the path of light) and form a diagram which depicts the emission of a photon by a particle which is subsequently observed by the observer (or absorbed by another particle). http://en.wikipedia.org/wiki/World_line Spacetime does not make motion in time like motion in space--that's a mistaken understanding. Spacetime makes the dimension of time like the dimension of space. Motion then becomes geometric. A line tilted Δx/cΔt on the diagram represents an object moving through space with the speed Δx/cΔt.

On the premise that the younger looking person was always the virgin I got 76% "You got 16 of the 21 people correct, and you did better recognizing the virginity of guys. Overall, you guessed better than 95% of all test takers. "

Unfortunately, rwalters21 forgot that he posted here

You didn't respond to the main point everyone is saying. You say that the speed of light is different in different inertial reference frames. Special relativity says that the speed of light is the same in any inertial reference frame. There is no debate. Experiments (like the Michelson-Morley experiment) have shown that the speed of light is the same in different reference frames. If you say it, it doesn't make it true. Experiments (like the Hafele-Keating experiment) show conclusively that clocks in different reference frames run at different rates. The bullet is not traveling c, so it will have a different velocity relative to and measured by people in different reference frames. Light will have the same velocity relative to and measured by anyone in any inertial reference frame. If a train is moving away from you at velocity u and a person with a gun on that train shoots a bullet or a laser beam toward you and the person on the train measures the velocity of the bullet or laser beam relative to himself/herself at v, then you will measure the velocity of the bullet or laser beam relative to yourself at w: [math]w=\frac{u-v}{1-\dfrac{uv}{c^2}}[/math] The answer will be negative because the bullet or laser beam is moving toward you.

This diagram: would be ok if we added world-lines and recognized that the dots (the moving things) are events--an object at a specific time: Otherwise, why is there a time axis? Empty of directly observable events, yes. Not empty of objects. Looking through a telescope, you will not see Neil Armstrong walking on the moon. That event is inside our past light cone. This does not mean that Neil Armstrong and the moon cannot be observed. They are objects, we can observe them today, and objects cannot hide inside a past light cone. You are thinking that objects move though spacetime in the same way that objects move through space. That interpretation is unusual and requires two different variables of time--one for the object's movement through space and another for the object's movement through spacetime. Movement is change in distance divided by change in time. It requires time. I'm not aware of any philosophy that has such an interpretation of spacetime. It should be clear that your concept has two different kinds of yesterday. 1) yesterday that has an earth and 2) yesterday that has no earth. If there is an earth tomorrow then instantly traveling to tomorrow you would find an earth. This is possible using relativity. If you traveled near the speed of light for roughly one light-day (about 10^10 kilometers) then you would near-instantly arrive at earth's tomorrow. The earth would still be here otherwise conservation laws would have a big problem. If there is only one kind of time then "still exists in the past" is not a logical statement. In the past the object exists in the past. In the present the object exists in the present. To say that the object simultaneously exists in the past and present is a contradiction in term.

I think you see the problem clearly. The way spacetime diagrams are understood and used in science, the red dot marks one point in the history of the earth. To be exact, it is how the earth was two days before the present. The physics community calls them events because the dot not only represents the earth, but the earth at a specific time. The red dot that the moon is seeing is the earth as it was in the past. If the black dots were supposed to be the location of the objects in the present then they would be out of place. But, they are supposed to be the location of events in the history of that object. In particular, they mark the event where light is emitted from that objects which earth sees now. And, the events are right where they should be. Yes, exactly. They mark where the airplane was previously in time. That's why there is a time axis on a spacetime diagram--to show where things were--to show what they were doing at all different times--the whole history of the object. What we see is an event in the history of the object. Correct. There was something there. It is understood that it is not there in the present. By the time we see/hear it, it has moved on to somewhere else. The event is in the past--lower than the observer on the spacetime diagram. It's not a problem if you understand that the black dots mark where the objects were (not are).

Ok. No trouble, mate. I'll also post this: to represent, like you said: "On the 5th of January, the light coming from the black dots have reached us. That's now, every day." So that the black dot is understood to be now. It is understood to be the present, like us moving through time. If you are doing a new diagram my biggest recommendation would be that a single day not have two different-looking past light cones. For example, on January 3rd black sees something different from what red sees on January 3rd: It would make more sense if the past light cone of black on Jan. 3rd were the same as the past light cone of red on Jan. 3rd. Otherwise, it is hard to explain how the universe looks two different ways from the same location on the same day. In other words: the way we observe the universe today should be the same as we remember it looking two days from now.

I understand what you're saying. Certainly I agree that the dots along the light cone represent what the observer at the apex sees. All I'm looking for is if the time axis is labeled right. Did I label it the way you meant for it to be understood, or is there another way that I can label it?

Michel, would you label your time axis like this? Maybe not with those specific dates, but that's the idea, yes? Red and black are moving through time?

That's fine. Let's say that the red and black observers are astronomers looking out of their telescopes separated by a few years. So, presumably they should see the same things--the same stars, the same galaxies--that type of thing. So, why do their light cones look so different? Shouldn't the same things, the same objects, be intersecting them both? Maybe if you drew world-lines it would be a bit easier to understand.

You see only the events on the surface of your past light cone. I think you've agreed that objects, or mass, cannot hide inside your past light cone. An object that was in your past light cone will have intersected it at some point in the past.

Noyer le poisson, non. Enfoncer des portes ouvertes, oui. A massive object curves spacetime like I showed a few posts up. It mostly curves time. That way inertial particles accelerate toward 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. 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. Merged post follows: Consecutive posts merged Thank you. I didn't draw the last few, but I'm all for taking credit

Well Iggy, I don't think that was a good answer I'm sorry, but I think your premise was mistaken. 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 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 have no interest in proving or disproving the metaphysical or ontological nature of time. I can demonstrate that this: 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. 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.

With the black object. Merged post follows: Consecutive posts mergedI'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.

I like the way fish don't notice the hook. I don't like the way deer wait for the headlights to make the first move. I like being startled by thunder and the sound rain makes on the roof. I don't like my dog's reaction to either. I like bees because they dance and make honey. I don't like people who insist that if the bees go extinct it'll just be a matter of hours before the ecosystem self-destructs in apocalyptic starvation collapsing the food chain, turning the oceans red with blood, vaporizing rain forests at the speed of sound, and leaving no chance of human survival. Also, there would be a terrible shortage of honey. I like dolphins because they’re very intelligent and cute to boot, and they occasionally save people from sharks. But, I don’t like that they also occasionally try to rape people, because, you know, no means no. Speaking of dolphins, I also really like killer whales (orca). They are majestic, intelligent, and have a whole lot of personality. I don’t like our human tendency to hold them in captivity in tiny pools and make them perform tricks for food. It's really quite rude. Overall and in general, I like life on earth. I give it a B- graded on the intergalactic curve of class M planets (planet rankings are on display at your local planning department in Alpha Centauri). Unfortunately, a good deal of the less-than-fantastic aspects that I personally notice come from humanity. But, a good deal of the truly inspiring aspects do too.

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?

I don't have much time to respond at the moment. 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. I'm not interested in proving or disproving the metaphysical or ontological nature of time. 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. 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 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 mergedI 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).

The moving-dot diagram has observational consequences inconsistent with the real world. I'm therefore talking about both the diagram and the real world. 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. 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. It seems a little vague. A confirmed theory could, at the least, disprove an ontology of time. 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. 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). 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.

Lets slightly disagree on this:-). We are constantly interacting with past event. Yes, we are causally connected to past events in our past light cone. Clearly, they can affect us now. For example, Neil Armstrong walking on the moon has affected the way I write this sentence. Any event where ct > x (where t is time before my present and x is distance from my location) can potentially affect me here and now. We cannot, on the other hand, affect any event outside our future light cone and certainly not any event inside our past light cone which is what I was meaning to convey--that we can't affect the event in question. Certainly the events we observe existed in our past. Yes. Every sufficiently old star in Neil's observable universe could conceivably affect him while walking on the moon because they all intersect his past light cone. The moon event could likewise affect any star inside his cosmological event horizon. If the universe is matter or radiation dominated this would include the whole universe (more than just the observable universe). If the future evolution of the universe is dominated by the cosmological constant then it would include only the part of the universe bound by Neil's cosmological event horizon. But, I was referring specifically to my present. No event in my present can affect the Neil Armstrong event. The past is not tangible in that sense. It cannot be changed. I was not trying to imply anything about the event's affect on us, only that we (and any other event in our present) cannot affect the event. There may be a different observer out there in our present for whom Neil Armstrong walking on the moon is in their present, like would happen here: But, they cannot affect the event. No event in our present can cause or affect an event in our past light cone. Like I've shown, while a trajectory in space can be diagrammed with a moving dot, an object's path through spacetime cannot. Two kinds of diagrams have been mistakenly combined into a kind of spacetime diagram which you will find nowhere in scientific literature that has observational consequences which have been demonstrated false. A world-line is a well established scientific concept and using it doesn't amount to mixing up trajectories and objects. Yes, I agree, that is usually true in astronomy. You would have to make exceptions where the index of refraction of the medium is greater than unity (like light traveling through air) or where something is observed by some other means than light (like the observations of a bat or a submarine) as those examples would always observe events inside their past light cone. But, for the purposes of astronomy I absolutely agree--we observe the events on the surface of our past light cone.

Right. So, Tutankhamun accomplishes what the red dot never can. 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. If the sun is five billion years old then an object 50 million years ago could not occupy the center of the sun's location without touching it. I understand. A world-line is just what happens when time is made a dimension and diagrammed with space. Since the object exists at each point along the time axis a point object represented as a dot in three dimensional space becomes a series of dots making up a line in spacetime. Minkowski introduced the idea in 1908. The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality... A point of space at a point of time, that is, a system of values, x, y, z, t, I will call a world-point. The multiplicity of all thinkable x, y, z, t systems of values we will christen the world... Not to leave a yawning void anywhere, we will imagine that everywhere and everywhen there is something perceptible. To avoid saying "matter" or "electricity" I will use for this something the word "substance". We fix our attention on the substantial point which is at the world-point x, y, z, t, and imagine that we are able to recognize this substantial point at any other time. Let the variations dx, dy, dz of the space co-ordinates of this substantial point correspond to a time element dt. Then we obtain, as an image, so to speak, of the everlasting career of the substantial point, a curve in the world, a world-line, the points of which can be referred unequivocally to the parameter t from -∞ to +∞. The whole universe is seen to resolve itself into similar world-lines, and I would fain anticipate myself by saying that in my opinion physical laws might find their most perfect expression as reciprocal relations between these world-lines. http://www.spacetimesociety.org/minkowski.html 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. 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. and 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. Ok, but again, Iggy reading a post is an event. Iggy getting drunk in central park in 1999 is an event. An event is a single place and time, an x, y, z, t, a dot on a space-time diagram. 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. Since an object is represented with a world-line, saying that there are two objects (e.g. two Iggies) would imply that there are two world-lines--not a single world-line with multiple events. A world-line is, itself, a sequence of events. Neil Armstrong experiencing the moon is an event--one of many that make up the history of that Neil Armstrong object. I should apologize, I meant to keep this post short and not drag out any disagreement. I failed miserably and ended up rambling. Sorry.