michel123456

O.K. But still the amount of distance is not so important for the concept. We never observe more distant galaxies closer to each other. i mean, when distance increases, time increases too. So the further we look in the past, the more far away is the galaxy. The concept is the same with or without expansion. There is never a situation where more ancient galaxies on diametrically opposite sides of our observable universe are closer to each other. --------------------------------- The past is sread out around us. as much we look into the past, the more the sphere of the observable universe gets large. We never observe ancient galaxies getting close & closer to each other.

What I see is this: I see 2 circles representing your head. The one was in the past, the other is in the present. Both represent the same object as time passes by. Can we agree on this?

Then you are obtuse. I am afraid you are blinded by your convictions. I'll try otherwise: How many circles do you see in the drawing?

It is difficult to me to understand that because it goes against what we observe. What we observe are galaxies further and further away from each other as much as we look in the past. Don't you realize that?

How many "you" do you see in this diagram? I see at least two. in fact an infinity of "yous" in the interval. The diagram gives the impression that there is a "you' at all time stamps, that all coordinates x,t are inexorably occupied by "you". It is a completely different concept from motion. I believe it is wrong. IMHO the diagram describes a path.

Exactly. 1D. You wrote 1D Time is 1D In a spacetime diagram, the events that you observe as simultanate are along the diagonal. IOW simultaneity between your head and your feet is something that spreads through time.It does not mean that head and feet are at the same time. It is physically impossible to observe what is at the same time because all informations travel at velocity equal or less than C. ------------------------------------ Here, if I understand correctly ACG52's comment And here from MigL

My question is the following: You look at the West and observe far away galaxies 12 billion years from us. You look at the East and observe far away galaxies again. As much you look in the past the more the galaxies are far away from each other (the West from the East) And suddenly the BBT tells us that the West and East galaxies, instead of being diametrically far away from each other, were together. That is difficult to swallow.

And what is the relation between space and time? Following the learnings of Relativity?

Motion. It just as if you wanted to explain motion. When an object is here, it is not there. It goes from here to there. It changes coordinate. Why is it so difficult conceptualize the same thing for time? ----------------- When an object moves in space it does not duplicate. The same concept should apply for time. And it is not metaphysics.

Because there is a distance between your head and your feet. No, I disagree. If an object is extended in space it must obligatory extend in time. ONLY a point particle could be considered as not extending in time.

Yes I understand that. You are correct, in real world there is no superposition.The diagram has been made to explain an impossible situation. The grotesque arises when one consider that instead of sliding in time, the objects somehow "continues to exist" in the past. Some even consider that the object already exists in the future. My diagram show this situation, which provoques a superposition that we do not observe. So the diagram is wrong, there is no superposition. Which means that the object moves through time exactly as it moves through space. An object leaves a set of coordinates and go to another set of coordinates. That is my point.

I don't speak about the life of the object. In the diagram, the object, at any instant, has an extent in time just as all objects have an extent in space. For example, at T=0, say my head is at T=0 and my feet are at T=minus1.

This is what I mean. In the following there is no space, only Time. The object is supposed to have extents in time, IOW it is not a point on the time line.

But time has a single dimension, you are correct. Your comment bothered me. I was thinking: 1D is represented by a line. When there is no space represented, an object can be drawn as a point on the time line. If (if) the object had extent in time, it should be represented as a segment upon the line. In this case, When the segment travels upon the line, there is superposition and I am correct. When one dimension of space is added then to the diagram becomes a space-time diagram. If the object has extent in time, then it should be represented as a segment diagonal to the time line. When the segment travels along the time line, there is no superposition and I am wrong.(I mean even in the case the first "if" s correct. When the second dimension of space is added then the diagram becomes complicated. If the object has extent in time, then it should be represented as a surface (the surface of a cone). When the surface travels along the time line there is no superposition and I am wrong again. When the third dimension of space is added then the diagram becomes impossible to be drawn on a sheet of paper. Anyway: If the object has extent in time, then it should be represented as a volume. That is not a surprise. When the volume travels along the time line there is finally a superposition and I am right. So the question is whether objects that take a certain volume have also a certain extent in time. Objects like cats, planets and galaxies.

The BB happened (also) here.

I like your comment. I hope you understand the difference between your interpretation of a cat that changes coordinates with this Strange comment: The first interpretation is a change of coordinates. The second interpretation is like an extruded cat.

It may also be an IP address issue. Your system look like being configured with a continuously changing IP address. Look in the instruction manual of your modem.

How does time behave then? Are there multiple cats along the time line? Or is there only one single cat traveling through time and space? I don't understand why it is so difficult to answer this question. When it comes to space only, everyone agrees on what motion is: it is a change of coordinates. But when it comes to time, then everything changes and people are ready to believe that objects do not change coordinates in time, instead they believe that objects remain on their coordinates. I find that absolutely grotesque.

How does time work then? MigL believes that there are many cats along the time line, if I understand clearly his point. Is that the way time works?

Your guess is right. Because a cat is an object that extends in space (about 30cm) it also extends in time. If your cat "remains in time" then you can calculate that under a specific time interval, the 2 cats should be superposing. Pzkpfw's cat is at the BBQ at 1pm. One nanosecond after 1pm you must have 2 cats superposing each other. The same way as the 2 Earths at 2 time stamps in my diagram. Is that possible?

Do you realize how empty is spacetime if one agrees with me? If I say that the coordinates x=0,y=0,z=0,T=0 contain the Earth it means that coordinates x=0,y=0,z=0,T=-2000000 do NOT contain the Earth. And if coordinates x=0,y=0,z=0,T=-2000000 do contain the Earth then coordinates x=0,y=0,z=0,T=0 do NOT contain the Earth It is not metaphysical. Because if I am correct, there is a lot (a lot) of coordinates able to contain materials that we are unable to observe. And in this case, the universe has much much more than that we can see.

Am I?

Now please correct me: The experiment shows that the Earth 2,5 sec ago was the same object that it is today, but at another position in spacetime. That is kind of trivial. It simply says that the Earth has moved. The experiment does not show whether there "exist" in the past another "past-earth" at T=0. In fact. it shows that such an hypothetical "T0-past-earth" does not exist because it would superpose to today's Earth. And since we don't see such a superposition happening, it must mean that the "T0-past-earth" does not exist. What happened is that the Earth changed coordinates in spacetime. Again, it sounds trivial but it is not.

Provided that the screen is perpendicular to the beam, i suppose. Does the following diagram depicts roughly the situation?

So the Moon & Earth are almost acting like a single object. I see also that the reflectors on the Moon are not parallel to the surface (they are not horizontal on the Moon) http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment#mediaviewer/File:ALSEP_AS14-67-9386.jpg http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment#mediaviewer/File:Apollo_11_Lunar_Laser_Ranging_Experiment.jpg