# Is the Future Mapped Out ?

1. Feb 16, 2012

### paulselhi

I have a basic grasp of special relativity and understand why different observers will have different perspectives on the timing of events. My question is this, if Observer 1 sees two events occuring which change in time i.e of 2 lights opposite each other with the same color which change simultaneously, so red-red blue-blue green- green, and an observer moving at speed relative to Observer 1 may see red-blue blue-green green-red due to the change in angle of his time slice

Both obervers are justified in saying that their observations are correct ( equivalence principle ?)

Does this mean that for a moving observer 2 the observations of observer 1 are his past, and for observer 1 they are his present and the observations of observer 2 are observer 1's future

So in effect Observer 1's future as "already occured" as observer 2 is experencing it.

Am i living in someone elses past and someone elses future ? If so when does the future stop being mapped out ? Is/Was the whole of all time ( past future and present) concieved at once ?

Clearly i am blaberring now and there is a good reason why the future is not already mapped out !! Please enlighten me !!

2. Feb 16, 2012

### bobc2

Good job, paulselhi! Not everyone notices that implication of special relativity. You have nailed it pretty well. And yes, it is all of time as described by Hermann Weyl (Einstein's close friend and colleague at The Princeton Institute for Advanced Studies).

You are not blabbering at all, paulselhi. However, that kind of discussion is sometimes not regarded as appropriate for this forum.

3. Feb 17, 2012

### e^(i Pi)+1=0

Note that the farther away the observers are, the greater their discrepancy, even if they are moving very slowly relative to one another.

4. Feb 17, 2012

### paulselhi

Does the speed of light limit mean that the possible future-past range may be limited?
So if observer 1 sees an event happening there would be a limit as to how much into the past or future another observer can reside since these differences in observations will be based on the other observers speed relative to observer 1

And as .. err.. the last poster mentioned that distance is relevant, would the size on the universe put a cap on this as well

Thanks BobC for turning me on to Herman Weyl

"The objective world simply is, it does not happen. Only to the gaze of my consciousness, crawling upward along the life line of my body, does a section of this world come to life as a fleeting image in space which continuously changes in time." Hermann Weyl, Philosophy of Mathematics and Natural Science (Princeton University Press, Princeton, 1949)

"What has been will be again, what has been done will be done again; there is nothing
new under the sun. Is there anything of which one can say, "Look! This is something
new?" It was here already, long ago; it was here before our time."

King Solomon

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5. Feb 17, 2012

### bobc2

Those are pretty heavy quotes there, paulselhi. I was familiar with the Weyl quote but did not realize King Solomon was so knowlegable about special relativity. How did you ever come up with that one? Anyway, nice work.

6. Feb 17, 2012

### nitsuj

In my opinion this is no different then saying my future experience of the sun / moon / anything not in the same location as me has happened prior to my experience of it. whoopty doo
(yes this is Galilean transformation, but what do I care of the measure of someone elses proper time/length?)

The next step in the concept is to realize that past, present and future are relative terms, all from the perspective of assigning an arbitrary "now".

The only part of the future that's "mapped out" is it will become your "now" & then your "past".

When thinking of SR you should ditch the common conceptions of past / future and now. And think more in terms of cause & effect. From there (cause & effect) consider the constancy of the laws of physics and relativity of simultinaity.

Cause (present) and effect (future) all according to the laws of physics (mapped out). Relativity of simultinaity; "now" is a relative term, and inturn "future" & "past".

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7. Feb 17, 2012

### paulselhi

I assume that is KS from Israel and not some enlightened Rasta who has been " 'erbing it out"

8. Feb 17, 2012

### bobc2

I think he hit on something far more profound than that.

His insight is directly related to Lorentz transformations, not Galilean. And of course no one has to care about implications of special relativity. Some are passionately curious about them and others shrug their shoulders. And no value judgement is involved.

But, cause & effect just becomes a definition with Weyl's model. One event does not cause another event in the sense that you imply, because it is all there at once. As Weyl said, "The objective world simply is, it does not happen..."
But, it was the relativity of simultaneity with the different angles of the slices of the 3-D cross-sections across the 4-D universe that let to his recognition of the implications of special relativity.

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9. Feb 17, 2012

### nitsuj

It is not more profound, that is the problem. Thinking it is profound. The profoundness is a consiquence of having a brain, in that we can consider other FoR and think but they have a "now" momnet too and that persons "now" moment is in my past, wow cool!"

That is my point of who cares if another observers proper time length is of different measurements then mine, what is the implication in the context of past & future? The words their "now" is my "past"? It is of no consiquence to cause/effect.

So no his insights are not strickly lorentz, it is strickly about overextending a "now" momment to beyond local, where it starts to loose meaning in the more common sense of "now".

These are measurements we are talking about. You're stretching this to the universe is static via words such as "now" past future.

A quote such as "The objective world simply is, it does not happen..." without strickly defining the words I think is nonsense.

The universe IS 4D, there are no "now" "slices", so anything you derive from these "slices" is not speaking of the "nature" of a 4D continuum.

The direction of this discussion is transparent bobc2,

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10. Feb 17, 2012

### nitsuj

He/she needs to recognize the implication of SR in this context is redefining the concepts of past, present & future. Specificaly "now" / relativity of simultinaity.

11. Feb 17, 2012

### bobc2

From "The Fabric Of The Cosmos" - Brian Greene (pg 141 hard copy):

"A particular moment can no more change in time than a particular location can move in space: if the location were to move, it would be a different location in space; if a moment in time were to change, it would be a different moment in time."

"Under close scrutiny, the flowing river of time more closely resembles a giant block of ice with every moment forever frozen into place."

12. Feb 17, 2012

### bobc2

Special relativity gives us many "now slices." But the "now slices" for different observers moving at different velocities cut the 4-D universe at different angles--that was the clue that led to the understanding of a 4-dimensional continuum.

That's why Brian Greene, in his book "The Fabric Of The Cosmos" spent so much time developing the loaf of bread analogy with the slices of bread sliced at different angles. He associated physical reality (the entire 4-dimensional universe) with the whole loaf of bread and associated the different slices with the different 3-D universes that different observers live in at any given instant of time (different "now slices").

And that's why so many physicists have been captivated by the concept of the block universe. Paulselhi, I think you would be interested to google "block universe."

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13. Feb 17, 2012

### bobc2

That's a really good point, e^(iPi)+1=0 (how did you come up with that interesting handle?). This was dramatized in Roger Penrose's famous Andromeda Paradox shown below (my graphics version).

Bill and Ruth walk past each other. Since they are in relative relative motion, they are living in different instantaneous 3-D worlds. In Bill's world the Andromeda leaders are meeting to discuss whether to attack earth. In Ruth's world they have already made their decision and the attack is under way.

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14. Feb 17, 2012

### e^(i Pi)+1=0

15. Feb 17, 2012

### nitsuj

As if the analogy you quote is the one that got me to stop "learning" SR from Brian Greene's poetic physics books.

I'm pretty sure he "spent so much time developing the loaf of bread analogy" because it sells books. It only confuses the reality that physics "describes".

Lastly, if this is how you believe it is (block universe) then this perspective of a block universe has to also be true for every single bit of anything there is in the universe (that's subject to SR type physics) does it not? Given the relativity of simultaneity this can't be true.
How could anything move? (note spacetime is isotropic)

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16. Feb 17, 2012

### Staff: Mentor

Actually, no, this is just the principle of relativity.

No. For the time ordering of events to be observer-dependent, the events must be spacelike separated; each must be outside the other's light cone. That means there can be no causal connection between the two events. So what observer 2 is experiencing can't directly be observer 1's "future", because observer 1 can causally affect his future.

As nitsuj has commented, Brian Greene's talk about the "block universe" obfuscates this crucial point.

17. Feb 17, 2012

### Staff: Mentor

But this is only true if the distinction between Bill's world and Ruth's world has no causal consequences; in other words, Bill can't causally affect the Andromeda leaders' decision any more than Ruth can, even though in Bill's world the decision hasn't happened "yet" but in Ruth's world it has "already happened". So this presumed distinction actually has no physical content.

18. Feb 17, 2012

### bobc2

Actually, Brian Greene does one of the better jobs of describing what's going on with special relativity for the layman--and also for some physicists who have not thought too much about some of its implications.

Yes. And of course it is.

That's the whole point. Nothing does move in the block universe model. And it's the relativity of simultaneity that implies the block universe.

19. Feb 17, 2012

### bobc2

This is a popular objection to the block universe model. However, it is totally irrelavent. Theoretical physicists are interested in a model that represents the entire universe. The range of modeling would certainly not be limited to one's personal light cone.

And when paulselhi was talking about observer1's "future" I think he was referring to the future 3-D cross-section cut across the 4-D universe (not the directly experienced future that he actually experiences with light transmittal information). Just as when talking about an observer's "Now", a convention is typically adapted that assumes we've accounted for all of the distracting details such as speed of light time delays before actually "seeing", etc. Brian Greene makes all of that very clear in his book. So, we know what he is talking about when he talks about the "future" and the instantaneous 3-D cross-section (or slice of the loaf) that an observer "sees" in language that is understood in the context of Greene's discussion. And we know what Roger Penrose is talking about when he compares the events in the andromeda galaxy for Bill and for Ruth in our sketch--the inability of Bill or Ruth to influence events is irrelavent to the fundamental issues related to 4-dimensional existence. These issues are very profound for many physicists.

We easily have a concept of the sun existing "right now", regardless of not receiving light for another few minutes. We have a concept of stars existing "out there" even though it may be years before their existence is confirmed with the arrival of the light.

We don't ignore knowledge about the content of the distant reaches of the universe because it is not in our light cone. We don't ignore the theory of quarks because they are not directly observable. We pursue string theory even though it may never be possible to confirm the theory by experiment.

The block universe is implied by special relativity. It is a logical model. That does not make it a fact of external objective reality. It's not a concept embraced by every physicist. Some physicists don't even embrace any kind of external objective physical reality.

No. The block universe concept is the crucial point. The outside-of-light-cone issue is a red herring.

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20. Feb 17, 2012

### bobc2

The physical content is manifest directly and is profound. Whether Bill or Ruth can influence the Andromeda decisions has nothing to do with whether events really exist in Andromeda. Physicists are interested in external physical reality that is independent of observers. What exists "out there" does not depend on observers. The existence of the early universe did not and does not depend on observers. The existence of objects on the other side of the moon does not depend on observers. Just because the event of a rock rolling down the side of a mountain on mars "right now" cannot be affected by us does not have anything to do with the reality of the existence of the rock or the event.

The no-physical-content presumption just because there is no possibility of intervention from outside the light cone is a red herring argument.

21. Feb 17, 2012

### nitsuj

With all due respect, outside the light cone is your "red herring". What shape is the light cone in three spacial dimensions?

removing any of the dimensions from the 4D continuum is an "abstract". With in this context of reducing dimensions of spacetime, the whole is more then the sum of it's parts.

Outside the light cone in 3D is ">c interval" away from me, continuum.

Here is some poetic physics bobc2, EM propagates towards the observer at c, the length measurement is the past tense of the time measurement*. Measuring the two dimensions, length & time simultaneously is a coordinating event, that is assuming "perpendicular" (?) measurements of time & length. Speed is the assumed "now" along some arbitrary spatial axis, one of an infinite number of possibilities (just ask pi) in isotropic space; motion is relative.

Outada park, block universe is debunked, as this* can only work via continuum.

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22. Feb 18, 2012

### nitsuj

Thinking of block universe some more, I agree the concept is "valid" from the perspective of EM.

If EM takes the shortest path, it's existence then is literally a slice in the three spacial dimensions. Said differently photon does not "experience" time, it never has more then one absolute set of spacial coordinates (that I can think of) but that of it's geodesic path; axis x. (there is no time to "effect" this cause [wave], hello uncertainty, lol sorry pf.)

This is just the perspective of EM, For each existence of a wave, maybe the universe is as if it is like the block universe concept, so each wave's existence is only of length. An "I'm here, then I'm there" type existence. Then upon the wave's next event in the continuum passes the "baton" onto the next bit of whatever, cause effect it sounds like. A block universe continuum from EM's perspective.

Going into the deep, it seems like being human is what adds to this confusion of time & length in relativity. It is where, very literally the two concepts/perspectives "blend", absolute length & time, arbitrary "now" of EM visually.

Last edited: Feb 18, 2012
23. Feb 18, 2012

### bobc2

You're O.K., nitsuj. And you have carried this deeper than my limited intellect is capable of keeping up. Thanks for your ideas.

24. Feb 18, 2012

### Staff: Mentor

I'm not sure I understand what you mean by this. A photon's worldline is a null line; I don't see how a null line can be described as "a slice in the three spatial dimensions". Can you elaborate?

25. Feb 18, 2012

### Staff: Mentor

I don't disagree with this, but I don't think it means what you think it means. I probably haven't been clear enough about what *I* think it means; see below.

To be more precise, I believe he was referring to the fact that, for example, the event "Andromeda leaders send the fleet to attack Earth" is to the future of Bill's simultaneous space but to the past of Ruth's simultaneous space. I don't disagree with this.

But paulsehi claimed that this implies that the event "Andromeda leaders send the fleet to attack Earth" has "already occurred" for Ruth but not for Bill. I do disagree with that. The event is spacelike separated from both Ruth and Bill, so neither of them can causally influence it. Therefore, I would say the event has "already occurred" for *both* of them; neither of them can change it, so as far as they are concerned, it's fixed.

However, there is also a different question, about what Bill or Ruth can *know* about what's happening in the Andromeda galaxy "right now". See below.

But we don't know the Sun's state "right now"; we only know it up to eight minutes ago (the light travel time). If the Sun was exploding "right now", we would have no way of knowing about it for eight minutes; so for those eight minutes, our model of the Sun, which does not include it exploding, would be wrong.

You're conflating different issues. The theory of quarks has many observable consequences, which have been confirmed. Even string theory will hopefully have some observable consequences eventually (if it never does, it won't be a proper scientific theory IMO). But the question of whether these general theories have observable consequences is a different question than the question of what knowledge we have of the specific states of individual objects far distant from us. We do not know their states "right now"; we only know their states as they were at the boundary of our past light cone. If those states change outside our past light cone, we have no way of knowing about it until we see light or some other signal (moving at the speed of light) that conveys the information to us. So we cannot claim "knowledge" about what is happening at events spacelike separated from us; we can model what "might" be happening there, based on what we know from our past light cone, but we can't be certain that those models are right, not because of any theoretical issues but simply because the information hasn't reached us yet.

But I'm not objecting to the claim that the events in Andromeda "really exist" even though they are spacelike separated from us. I agree that they do; I agree that there is an objective reality out there that is independent of observers.

I am objecting to the claim that we somehow can know for sure *what those events are*, what the objective reality actually is, when the events are still spacelike separated from us. We can't. We ignore this when we are setting up thought experiments because in thought experiments we simply *dictate*, by fiat, what the events are; we dictate, by fiat, that the Andromeda leaders sent the fleet at some particular event, which happens to be to the future of Bill's simultaneous space but to the past of Ruth's. But in the real world we can't dictate that; in the real world, neither Bill nor Ruth would know whether or not the Andromeda fleet was coming for two million years after the leaders decided to send it. So in the real world, any portion of a "block universe" model that is not in our past light cone is tentative. That doesn't mean those portions of spacetime aren't real; but it does mean that we don't know for sure what that portion of reality looks like until we see it.