michel123456

1 minute ago, michel123456 said:

Do you disappear from the previous 5 photographs ???

No.

Where are the photographs? Are they in the past? or are they in your hands? Are the photographs the same thing as the event? Or are they a record?

12 minutes ago, MigL said:

OK, now you've defined motion.
How about the rest of the terms you use ?

Using Eise's example...
You sit in a chair at 13:00h and I take a photograph.
You still sit in the chair at 13:01 and I take another photograph.
You still sit in the chair at 13:02 and I take another photograph.
You still sit in the chair at 13:03 and I take another photograph.
You still sit in the chair at 13:04 and I take another photograph.

At 13:05 you get up and move away from the chair and I take a photograph of an empty chair.

You have moved, and according to you, vacated all pre-'now' time co-ordinates.
Do you disappear from the previous 5 photographs ???
( and for bonus marks, why not )

That is the wrong question. Think better.

1 minute ago, michel123456 said:

You have moved, and according to you, vacated all pre-'now' time co-ordinates.

Yes.

On 2/26/2020 at 4:45 PM, Eise said:

'Moving' means (continuous?) change of coordinates. So if an object changes its space coordinates, we classically say it moves: movement is movement in space.

But the time coordinate also changes: at the beginning of the movement it was 13:00h, when it stopped it was 13:05h. So the object does indeed move in time. The only way that this does not fit the conventional meaning of 'movement' is that even if we do not change our space coordinates, we still move in time (even more so, according to SR). E.g. if I sit still in my chair from 13:00h to 13:05h, I 'moved' in time, but not in space.

So what is wrong is the kind of expressions as 'time flies like an arrow': no, we fly through time.

I am asking everybody here to digest what Eise wrote here above.

And to get firmly in mind what motion is. It is a displacement in space and in time. A displacement. And not a copy.

If you digest the displacement, well, drive your conclusions by yourself.

You may get a glimpse of the universe.

2 hours ago, MigL said:

Being gone from the SPACE co-ordinate, at THIS time co-ordinate, does not mean that they are gone from previous time co-ordinates when they were  at that space co-ordinate.

Forget 'flying' , 'moving' and 'footpaths' through time.
Think of events ( people, balls, whatever ) describing a worldline through spacetime.
This worldline persists, or is a line with all points along its length occupied, as long as the event persists.
If I talk about Michel and say that he is 2 feet tall, that makes no sense, yet saying Michel was two feet tall when he was 2 years old does. Saying a ball is a molten piece of plastic does not make sense, but saying it was a molten piece of plastic before it was formed, does. Events, like people and balls, need 4 dimensions to locate them in space-time, and you can't argue we are 3dimensional, simply because that is all you see, as that is an incomplete description, and ambiguous.

Further, each event has a specific 'now' which is not common to any other event.
This 'now' is a light-cone, a window of causality if you will, that moves forward through the time dimension, and does so according to certain constraints imposed by relative differences in space-time curvature, or relative motion through space
This 'now' or window of causality is what actually 'moves'.
Us people, the ball, or any other event, does not 'move' at all; events already occupy all points along their worldline, past, present and future, as long as they persist.

You realize that it is not what Eise was describing, do you?

you are describing what is presented in the video, where what is moving is this "now", the slot as I call it. At least you admit that "something' is moving in time, I hope you realize that. You don't have solely a Block Universe, you have "something" (the slot, the "window of causality") that moves. It means that you are accepting some kind of change in time, and not only a frozen 4D entity in which nothing happens.

Well, because everything is relative, instead of a slot that is scanning a frozen 4D Block Universe, try to imagine a slot that is still & objects that slide in time. Doesn't that give the same apparent result?

11 minutes ago, Eise said:

OK. Except that I must also be careful with my words

And sometimes I read what I want to read instead of reading what is written.

34 minutes ago, Eise said:

1 hour ago, michel123456 said:

Julius Caesar & Napoleon are dead, they are not "persisting" in time, in another dimension. They are gone.

Of course.

If you agree that they are gone, doesn't that mean that their spacetime coordinates are vacant? How else would you translate the "they are gone".?

50 minutes ago, Eise said:

Sorry. Still friends? 😟

🙂 Sure. Educated disagreement is fine.

50 minutes ago, Eise said:

Well, I think that is a kind of definition of an object: something that persists in time and space. Compare with an explosion. This is a very short event, and part of its essence is that it is a (huge) change. It is essentially a process, concentrated around some narrow spacetime coordinates. But e.g. a ball persists in existing in spacetime. It can change space coordinates when travelling in time, but is still identifiable as the same ball: on one side because of its own properties (it is red, plastic, and 20 cm in diameter, with some scratches made by Tony yesterday), and on the other side by its continuity in spacetime: it follows an uninterrupted path through spacetime (except at the moments of it being made, resp. destroyed).

Yes, it follows an uninterrupted path through spacetime.

The word "persist" is disturbing me.

It looks like you are accepting that objects "move" into time along a path & also accept that the object persits in time.

I am afraid you have to choose the one or the other, these are incompatible statements.

37 minutes ago, Eise said:

No! When you were at the mall at t = 1, and today at t = 100 you are at home, it is still true that you were at the mall at t = 1. In a spacetime diagram time is depicted as a space coordinate. If I have the (magic) bird's view on 4D-spacetime, the question "where is Michel now" makes no sense: the Superbird does not know what 'now' means: for him you are the complete line. But you can ask the bird where Michel was at t = 1, or t = 100. Those questions make sense from the 4D perspective. 

Yes, the path is history carved into stone. You cannot change it. I do not disagree on that. But it remains a path. Julius Caesar & Napoleon are dead, they are not "persisting" in time, in another dimension. They are gone.

Oh sorry, maybe are you using the word "persist" to say that the object does not vanish in present time?

I had the wrong understanding that you believe that objects are persisting in the past.

I am confused.

25 minutes ago, swansont said:

If you can't access the coordinates, I don't see how they are "free"

If an event happened at x1, y1, z1, t1 in some frame of reference, those will always be the coordinates for that event. That set of coordinates is not "free".

If you can't access the coordinates then you cannot change what happened then. We agree. But that doesn't mean that there is something there, or that there isn't. We simply don't know. We are assuming (guessing).

4 hours ago, michel123456 said:

My understanding is that the points that form this line are mutually exclusive. If I am at t=100, I am not anywhere else. If I am at t=2, I am not at t=3. The physical entity is only one point of the line. The whole line is a path.

Quoting myself: am I wrong saying that?

Note: in the quote you can replace the word "if" with the word"when" and it becomes:

My understanding is that the points that form this line are mutually exclusive. When I am at t=100, I am not anywhere else. When I am at t=2, I am not at t=3. The physical entity is only one point of the line. The whole line is a path.

2 hours ago, Eise said:

What is 'flying' in time is one and same object, persisting in time.

Oh, what a disappointment. I thought we were on the same stance when you posted:

22 hours ago, Eise said:

Objects can overlap in time, because at the moment t + 1 the object is not at t anymore, so there is nothing there to overlap with. 2 Objects cannot be at the same place at the same time, but they can perfectly at different times. A spacetime diagram is a diagram of events, not of objects. And as a diagram it is just a simplified model of what is going on. You confuse the model with reality.

Now you seem to support the idea that objects are 4D entities when you say that they persist in time.

You said:

4 minutes ago, michel123456 said:

A spacetime diagram is a diagram of events, not of objects

5 hours ago, MigL said:

Since a line is composed of multiple points ( or events ), no point is vacated when he 'moves' to the next moment in time.

My understanding is that the points that form this line are mutually exclusive. If I am at t=100, I am not anywhere else. If I am at t=2, I am not at t=3. The physical entity is only one point of the line. The whole line is a path.

If "flying" in time is so much different from "moving" in space, how can we compute mathematical theories where the one rotates to become the other? Is it possible that "flying" in time corresponds to Copy? When we all know that a move in space is a ... move.

19 minutes ago, MigL said:

Why not ?

You can occupy only a single space co-ordinate at a specific time.
Or you can be at a specific  place different times.
But you're not understanding the concept of space-time.

If you were at a specific location at a specific time ( say at the mall by your house, yesterday at 1 pm ), you will always be there at that time.
The next day your location for the previous day at 1 pm will NOT have changed ( or else you'd remember it differently ).
The next year, or 50 years from now, you will still be at that location, yesterday at 1 pm.

See, that is the difference between you and me (and Eise).

You are supporting the concept that objects are 4D. That I am extending in time from my birth till my death. Eise said that no, spacetime is full of events, not objects. You are saying that spacetime is full of objects. You are disagreeing with the concept of 3D entities "flying" in time. You prefer the concept where entities are "extruded" in time.

30 minutes ago, swansont said:

It makes no sense to say you aren't there anymore, referring to a 4-d coordinate — you are giving two pieces of information about the time. It only makes sense of you use a 3D coordinate.  

Events are probably what we have to refer to.

My point is: since we all agree (do we?) that we "fly" in time, each one of us occupies only one single spacetime coordinate, objects are not 4D extending back & forward in time.

If you are in the present, you are not in the past (anymore) and you are not in the future (yet)

As a consequence, if we are using only one set of coordinates, then the other sets are free.

And not to say that the signal of the event is spreading at c all around, leaving the coordinate completely empty. What all observers will agree with is the signal that they will receive from the event.

15 minutes ago, swansont said:

I'm not sure what you mean by coordinates being "empty"

I am not there anymore. There is no object at this spacetime coordinate. There is only an event: Michel was there.

15 minutes ago, swansont said:

Is there some interpretation of time where changing the past is possible?

No. As far as i see it, even in my interpretation, there is no physical way to change our own past. It is not observable and not reachable.

But the question is still there: If we are "flying" along the time dimension, if the spacetime diagram describes what I call a path, what Eise calls "process", then does that mean that our past coordinates are empty? And that all our future coordinates are empty also? Or are they full, as presented by the Block Universe concept.

From what I understand from Eise's post, the past & the future are full of events. Objects belong solely to the present. Am I correct in this or am I putting words in his mouth?

50 minutes ago, Eise said:

No, because these footprints are in space, not in spacetime. I can assure you, when your spacial- and time-coordinates are the same as that of the dog, this is a Minkowski-depiction of you colliding with the dog. The dogs steps crossing yours in your example means that the dog passed your spacial coordinates at a later point in time. Again you do as if time is just a 4^th space-dimension. It is not.

I firmly believe that the concept of time is more close to that of space than is commonly assumed. There is no reason it would be fundamentally different otherwise how would it be possible for time to change into distance & reversely.

50 minutes ago, Eise said:

I mean what everybody means with 'process', see above.

'Moving' means (continuous?) change of coordinates. So if an object changes its space coordinates, we classically say it moves: movement is movement in space.

But the time coordinate also changes: at the beginning of the movement it was 13:00h, when it stopped it was 13:05h. So the object does indeed move in time. The only way that this does not fit the conventional meaning of 'movement' is that even if we do not change our space coordinates, we still move in time (even more so, according to SR). E.g. if I sit still in my chair from 13:00h to 13:05h, I 'moved' in time, but not in space.

So what is wrong is the kind of expressions as 'time flies like an arrow': no, we fly through time.

This is history, for the 1st time I agree 100% with someone here.

So, if we are "flying" through time, doesn't that mean that our past coordinates are free? And our future are free also?

1 hour ago, Eise said:

If I make a graph of the path that an object takes in time, what does 'the imprint exists' even mean? Just do it: make a graph of the movement of some particle. And? Does the imprint disappear? To say it more realistically: if I was in the shop yesterday evening, was I not there anymore today, now I am not there anymore? (Careful, do not blow your head...). Of course: it is still true that I was in the shop yesterday evening, so if I want to make a spacetime diagram of my life, I certainly will add the event 'me in the shop yesterday evening'. The idea of an imprint 'truly existing' makes no sense.

It makes sense exactly as the footsteps in the snow. There can be a dog following me and his steps cross mines. However this crossing will not have changed my past.

After reading your comment twice, maybe do you agree with the "path" concept.

1 hour ago, Eise said:

No, of course not. Objects can overlap in time, because at the moment t + 1 the object is not at t anymore, so there is nothing there to overlap with. 2 Objects cannot be at the same place at the same time, but they can perfectly at different times. A spacetime diagram is a diagram of events, not of objects. And as a diagram it is just a simplified model of what is going on. You confuse the model with reality.

Well I assumed that conventional thinking is that the objects are 4D entities, represented with segments on the diagram.

1 hour ago, Eise said:

You, as an object, are not smeared out over time, But as a process (i.e. a continuous line of events), you are. 

By "process", what do you mean? As if you agreed that objects are "moving" in time.

10 hours ago, MigL said:

Yet, you have an 'extent' in the x dimension, probably about 0.5 m ( width, depending on whether you regularly do shoulder presses).
An 'extent' in the y dimension of about 1.75 m ( height, maybe less; are Greek or French people short like us Italians ? ).
And an 'extent' in the z dimension of about 0.3 m ( depth, depending of course, on how much you like to eat ).

So why would you have no 'extent' in the t dimension, instead of a 82 year line ( lifetime ), and be constrained to only one co-ordinate ?

We do have an extent in time as objects. Because we have dimensions in xyz we also have a dimension in t, but it is limited to an extremely small figure because c is very large. For example my hand at ~50cm of my eyes is slightly back in time (the same way that we are observing planets back in time).

But this extent in time does not cover my entire existence. If it did, for an extemely small time-lag, there would be an overlap of 2 Michel123456's.

If you take an object large enough, like the Earth, diameter 12740 km, after a 0,04 sec (if my calculation is correct) there would be an overlap with the "Earth-extended-behind-in-time". We do not observe such a thing.

Anyway, since we have already an extent in time as objects we cannot have a 2nd kind of extent in time.

1 hour ago, dimreepr said:

Do you?

It's called space-time for a reason...

 

 

I even understand the counter argument of what I am saying.

The counter argument is that I have introduced change in the 4D universe which means that I have introduced time in time.

But that is also the way the video is presented. The slot moves upward in the 4D continuum. And that have annoyed nobody here.

10 hours ago, MigL said:

Why would you vacate a previous time co-ordinate; you were 'there' ( then ? ), and we both remember it.

10 hours ago, MigL said:

A higher dimensional space always intersects a lower dimensional space in the lower dimension.
For example.
A two dimensional plane intersects a one dimensional space in a line ( one dimensional ).
A three dimensional space intersects a two dimensional space in an area.
( take a 3D pencil and punch it through a 2D sheet of paper, the intersection is a circular area; easiest to visualize )

Similarly, if we are 4D in extent, then we intersect the 3D 'now' in a volume.
It is this volume that you consider our 'selves' ( not the points on your 2D graph and videos ), but actually we extend in the time dimension along a world line.
Why would you vacate a previous time co-ordinate; you were 'there' ( then ? ), and we both remember it.
And we also occupy future positions along the world line, according to the Block Universe.
Our 'now' cross section just hasn't gotten 'there' ( then ? ) yet.

I really can't explain it any better than that

I understand.

But, to me, we don't "also occupy future positions", and we don't "extend in the time dimension along a world line".

We cannot both be in the past, the present & the future, these are mutually exclusive situations. If you choose a position at a past coordinate, you are there and nowhere else. if you choose a position in present time, you are not in the past. And you are not in the future. To me, 3D objects are not  4D entities reduced by 1 dimension. 3D objects are what they are: 3D. Simply they travel through a dimension we call time.

In this concept, Time is simply an extra dimension, Time does nothing, Time is a kind of empty receptacle exactly as Space is.

Time doesn't "pass by". Objects change position in Time.

When I say that they "change position", I mean exactly as objects change position in space. They do not copy themselves from one position to the other.

Quote

Why would you vacate a previous time co-ordinate; you were 'there' ( then ? ), and we both remember it.

Yes we remember it, we have a photograph of the event, we even have it recorded and carved into stone. But does that mean that the event is frozen forever at some coordinate in time? A coordinate we have currently no access to? Just because it is physically impossible to change our past doesn't mean that we are stuck there.

Yes the path exists, the picture of the event is here in present time, I can look at it, and the marble stone is also here in present time. And if the stone is here now then it is physically impossible to be in the past or the future. There are no 3 stones. There is only one, and it is in the present.

If a new event happens in our past (although seemingly impossible under current understanding), this "new-old" event will not make any change to the picture nor to the stone. Because the picture & the stone are not there (anymore). They have traveled together with us in present time. 

The video

9 hours ago, MigL said:

Again, I ask, what simultaneity.
You ( and the video ) base your argument on a tenuous concept, which is an approximation.

The simultaneity of events as observed by the observer. I see today a star exploding. This star may have exploded a long time ago but I see it now. The slot is this  now.

3 hours ago, MigL said:

So, I have to ask, Michel, do you agree with the slot video ?

The slot yes.

But not the image when you remove the sheet & show the B.U.

Not to say that the comment at the end of the video shows the embarrassing situation that occurs with the B.U. concept: the future is already there, and in order to avoid the "already existing future" one has to invoke quantum fluctuations (as an ex machina explanation).

let me explain once again:

IF (if) you can accept that objects travel through time (that objects change time coordinates), you may also see that the slot in the sheet is unnecessary. My point is that simply objects move in time exactly as they move in space. they change position, they do not copy themselves. They progress from down to up. Objects are not "extruded" through time. Objects are not 4D. Objects are 3D entities that travel in a 4D continuum. Sure you can show the path of this object in 4D, but it will be a path, not a 4D object. The same as your footpath in the snow. At each instant you are somewhere at a specific point of the path, you are not extended all along your footsteps.

4 hours ago, dimreepr said:

Well, you certainly didn't elaborate, but in answer to your question: It was there, according to my eyes, and now it's not... 🙄 

Right. It is not. If you get the concept of the vanishing path, you may also get the concept of the empty future. The situation resumes to an empty universe behind us & an empty universe in front of us. The unique things that exist are the ones that travel with us in time enhanced by the slot in the video.

4 hours ago, MigL said:

Do you somewhat understand relativity Michel ?

Maybe yes. Maybe no. I am often surprised with the many possible interpretations of this Theory.

4 hours ago, MigL said:

The imprint may 'vanish' for one observer, but it does not for another.
Your now is NOT the same as another observer's now.
And your past is NOT the same as another observer's past.

The block universe is common to all observers; there is no 'outside' , nor 'preferred', vantage point.
But every observer 'experiences' a differing 'now' foliation, and a differing past light cone, of the block.

From the video, if you agree with it, you may observe the slot that moves upward. It represents the simultaneity between events. In cosmology, the slot is not horizontal, it is inclined (at 45 degrees) in such a way to show that the observer gets information from the past. But fundamentally that changes nothing, the only events that currently happen belong to the slot.

 If we send a spaceship to Alpha Centauri (that we observe as it was some time ago) we will see it all along its path during the travel & we will eventually see it land (or orbit) Alpha Centauri, constantly inside the slot. At no time the traveler will escape the slot. The entire observable universe is upon this slot. The rest is supposedly full if you believe in the Block Universe, or empty following the "vanishing past" concept.

23 hours ago, MigL said:

I don't follow ( and don't agree ) with your conclusions.
Please elaborate.

I will not elaborate but ask : If the imprint vanishes what would be your conclusion?