Gisin's ideas on time vs. special relativity—how does one reconcile them?

[Freixas]

TL;DR Summary

Gisin suggests that the future is being created as we go. Special relativity says that the observers don't agree on what constitutes the future. Assuming Gisin isn't undermining relativity, how are the two reconciled?

I’ve tagged this question as “Basic”, although I’m not sure if it can be answered at that level.

A friend pointed me to this article: https://www.msn.com/en-ph/news/opinion/what-einstein-may-have-gotten-wrong/ar-BB12w95x

Here’s a quote:

In other words, the world is indeterministic; the future is open. Time, Gisin said, “is not unfolding like a movie in the cinema. It is really a creative unfolding. The new digits really get created as time passes.”

I read that as saying that the “present” has a special meaning and that the future doesn’t actually yet exist.

Nicolas Gisin appears to be a respected physicist working at a lab at the University of Geneva. He has published articles in Nature Physics, which appears to be a decent journal, as far as I can tell. The article quotes other physicists taking his ideas seriously. Anyway, he doesn't sound like a crackpot.

This seems counter to a relativistic view of the universe. Perhaps the “present” is a difficult term to define? I would choose as a definition all the points in spacetime which have the same time coordinate. Since spacetime coordinates are relative to an observer, it would seem that observers moving at different speeds would never be able to agree on which events are in the “present”, “past” or “future”.

Yet we share the same universe—even if we disagree on the coordinates for an event, the event is universal. It would seem that if my future has yet to be created, you might consider that a chunk of your past is missing.

Is there anyone familiar enough with Gisin’s work to provide some insight at a basic level, how Gisin manages to support the concept of a future that is being created without undermining relativity theory?

 

[PeterDonis]

Nicolas Gisin appears to be a respected physicist

Yes, but this article is not a peer-reviewed paper. "Respected physicists" will say a lot of things in pop science articles, or when talking to reporters that are writing pop science articles, that they know they would never get away with in a peer-reviewed paper. For a proper basis for discussion, you would really need to find one of Gisin's actual peer-reviewed papers (the article mentions that he has published four on this topic), read it, and then start a new thread if you have questions based on the paper.

observers moving at different speeds would never be able to agree on which events are in the “present”, “past” or “future”.

That's not the real issue. The real issue is that, if we look at what relativity is actually saying, it's telling us that the three categories you mention are not the right ones. The right categories are: "within the past light cone", "spacelike separated", and "within the future light cone". The first and last of these are the proper referents in relativity for what we intuitively understand to be "past" and "future". The third category, however, is significantly different from our intuitive understaning of "present", and that is the source of many misconceptions about relativity.

Also, the three categories are event-dependent; at each event, since the light cones are different from those of any other event, the division of the rest of the spacetime into the three categories is different. However, all observers at a given event agree on which category any event in the rest of the spacetime falls into, with respect to the event they are at, even if they are in relative motion.

I discuss this topic in the following Insights article:

https://www.physicsforums.com/insights/block-universe-refuting-common-argument/

 

[Freixas]

Thanks, Peter,

I'm not surprised to discover that there is a long history of discussion on some of the things I think about (even to the point of having dandy acronyms!). I had the sense that, in the end, it was more of a philosophical question than a physics one.

At my level, I depend on actual physicists to explain things to me (in simple terms). I now know that there are (at least) two philosophical models for spacetime: BU and LET. Gisin's ideas (as reflected through the pop article) sounds like it could be another acronym candidate—interesting, but perhaps equally untestable.

Searching for "Nicolas Gisin" on Nature Physics, I found just one article, and it was behind a paywall. I can't really ask a physicist to read it just to let me know whether it's just another version of BU/LET, but if anyone has actually read one of Gisin's articles and cares to address this point, feel free. Perhaps it addresses some problems in quantum physics that make it more interesting.

 

[PeterDonis]

Searching for "Nicolas Gisin" on Nature Physics,

Searching on arxiv turns up a number of papers, two of which look like they might be relevant to the particular topic of this thread:

https://arxiv.org/abs/1602.01497

https://arxiv.org/abs/1909.03697

The first is based on a talk (and seems more speculative); the second appears to have been published in Physical Review A.

 

[phyzguy]

This idea is not unique to Gisin. It has been proposed by others, and most recently is the basis of Steven Wolfram's work (see this thread on pf). Note that it is not possible for different observers to disagree on the causal relationship between two events. So if at each point in space-time, new events are created in the future light-cone based on information from the past light-cone, there can be no contradiction. At least, I believe this to be the case. @PeterDonis, do you agree with the underlined statement? I much enjoyed your Insights article on this by the way.

 

[PeterDonis]

do you agree with the underlined statement?

Not as it stands. If you just said that information at any given point in spacetime (i.e., not in the future light cone, just at that point itself) is created based on information in the past light cone of that event, then there would indeed be no possibility of contradiction. But events in the future light cone of a given event can be affected by information at other events that are spacelike separated from that event. So that event by itself does not provide enough information to construct new events in its future light cone without the possibility of contradiction.

 

[phyzguy]

OK, so it should read as below. Thank you.

So if at each point in space-time, a new event is created based on information from the past light-cone, there can be no contradiction.

 

[PeterDonis]

if at each point in space-time, new events are created

Each point in spacetime is one event, so it should be "a new event is created", singular.

 

[phyzguy]

So edited.

 

[Grinkle]

@PeterDonis I conclude from your Insights article that whether the universe is 'block' or not is untestable given the finite speed of light - is that a correct takeaway?

I was wondering why @phyzguy 's statement is phrased as a hypothesis so I re-read your article and want to confirm my thinking.

 

[PeterDonis]

I conclude from your Insights article that whether the universe is 'block' or not is untestable given the finite speed of light - is that a correct takeaway?

No. The article does not discuss whether the universe being "block" or not is testable. It simply shows why a common argument claiming to show that special relativity logically requires that the universe is "block" is not valid. The finite speed of light only plays a role in the argument because it means that the "present" is not directly observable; only the past light cone at a given event is directly observable. The "present" is a construction from the data in the past light cone.

If one wants to ask whether the universe being "block" or not is testable, it seems to me that the answer is obvious that it cannot be, because it would require one to get experimental data from the future. That has nothing to do with the finite speed of light; even in Newtonian physics, with no finite limiting speed, it is impossible to get experimental data from the future.

 

[atyy]

Haag seems to have written similarly things in "Local Quantum Physics" (1996), p314:

"Our question is rather: why should there be any difference between quantum physics and classical physics with respect to the status of irreversibility? ... The future is open, not precisely determined by the past. ...

Starting from this question we come almost unavoidably to an evolutionary picture of physics. There is an evolving pattern of events. At any stage the past consists of the part which has been realized, the future is open and allows possibilities for new events. Altogether we have a growing graph ..."

 

[Freixas]

The finite speed of light only plays a role in the argument because it means that the "present" is not directly observable; only the past light cone at a given event is directly observable. The "present" is a construction from the data in the past light cone.

I think one of the reasons some people get in heated discussions about this is because it is difficult to follow the logic. For example, the statement above seems weak. Don't a lot of physicists spend a lot of time studying things that are not directly observable? I'm thinking about all those atom smashers.

If one wants to ask whether the universe being "block" or not is testable, it seems to me that the answer is obvious that it cannot be, because it would require one to get experimental data from the future.

This follow up sentence is more interesting, but I dislike the use of the word "obvious". It is obvious to some people and obscure to others.

I suspect the missing piece is that constructing the "present" from the past light cone requires assuming your conclusion; a different construct might yield a different result.

I think that when you say "get experimental data from the future", you mean getting experimental data from the "present" for a location other than yours--the speed of light restriction meaning such data could only come from the future.

The important point with respect to Gisin is that he's welcome to come up with any other mathematical model he wants as long as it doesn't contradict observable evidence. Relativity does not prove that we have a block universe, so he is not obliged to respect that philosophical view.

If this statement is a valid summary of the answer to my question, perhaps we should close this thread, as I can see it getting dragged into the relativity implies BU question (I'm tempted, but even I should start a new thread).

A discussion of Gisin's work might be interesting, but might also be best in a new thread. My question was specifically on what I thought was a contradiction.

 

[PeterDonis]

Don't a lot of physicists spend a lot of time studying things that are not directly observable? I'm thinking about all those atom smashers.

You are using "directly observable" in a different sense from the one that is relevant to this discussion. Yes, quarks, for example, aren't "directly observable" in the way that rocks are; but all the quark events that appear in the data from a collider like the LHC occurred in the past light cone of the events that recorded the data. So quarks are "directly observable" in the sense that we're using the term here: all the evidence we have for the existence of quarks is in our past light cone. But the "present" in the sense that block universe proponents use the term (basically, some spacelike surface that includes the event of us "here and now") is not directly observable in this sense--it's outside our past light cone.

constructing the "present" from the past light cone requires assuming your conclusion; a different construct might yield a different result

This is true, but it's not the objection I was making. See below.

I think that when you say "get experimental data from the future", you mean getting experimental data from the "present" for a location other than yours

No, I mean literally getting data from the future. If the block universe is true, then events in our future light cone (meaning the future light cone of us "here and now") are just as "real" as the event of us "here and now". Obviously there is no way for us to test that by experiment, since we can't get experimental data "here and now" from our future light cone.

Note that, as I explicitly pointed out in my previous post, this is true even in Newtonian physics, where the "present" in the sense that block universe proponents use the term is directly observable (because information can travel instantaneously).

Relativity does not prove that we have a block universe, so he is not obliged to respect that philosophical view.

Yes, this is correct.

 

[Freixas]

No, I mean literally getting data from the future. If the block universe is true, then events in our future light cone (meaning the future light cone of us "here and now") are just as "real" as the event of us "here and now".

I went round and round on this. If you mean literally data from the future, then I have some questions. If you mean data from my future light cone (i.e. everything that is not my past light cone), which would include events that I might now consider part of my "present" or "past", then I agree.

I believe any data reaching me faster than light could be used to exclude at least some versions of a block universe. I say "some" mostly due to ignorance; for instance, I don't know enough about the LET model to know if it absolutely excludes a block universe or makes it irrelevant.

When I first looked into special relativity, people had clever spacetime diagrams showing how FTP communication could lead to time paradoxes. Now I think that these explanations all assumed a block universe. The assumption is never spelled out. If we don't have a block universe, then I don't see how we could have a time paradox.

 

[PeterDonis]

If you mean data from my future light cone (i.e. everything that is not my past light cone)

Your future light cone is not everything that is not in your past light cone. Your future light cone is only those events that can be reached by a timelike or null curve from the event of you here and now. It does not include events that are spacelike separated from the event of you here and now (which includes events that block universe proponents view as "present").

any data reaching me faster than light could be used to exclude at least some versions of a block universe

This looks like personal speculation, and is probably off topic (and your mention of LET makes that presumption stronger). If you can find a reference that discusses this, you can provide a link to me via PM and I will consider it.

If we don't have a block universe, then I don't see how we could have a time paradox.

Even without a block universe, all the events in your past light cone have to be fixed and certain for your model to be consistent. So any scenario which claims that you can go back to an event in your past light cone and change what happened at that event creates what you call a "time paradox", independent of what your view is on the status of events in your future light cone here and now (or, for that matter, of events spacelike separated from you here and now). And going back to events in your past light cone and changing what happens at them is the key factor that all of the FTL scenarios you mention have in common.

 

[FactChecker]

Summary:: Gisin suggests that the future is being created as we go. Special relativity says that the observers don't agree on what constitutes the future. Assuming Gisin isn't undermining relativity, how are the two reconciled?

This may be a significant point in this context:
Although SR asserts that there can be disagreement on the time interval between events, it never allows enough time disagreement to cause disagreement about cause and effect. Given two spatially separated events, there may be some disagreement about which occurred first, but only if they are so far separated spatially and so close time-wise that there can not be a cause-effect relationship between them. So for all observers, the past-future in terms of cause-effect is well defined in SR. That is, the "future" is well enough defined for any cause-effect discussion.

 

[PeroK]

This may be a significant point in this context:
Although SR asserts that there can be disagreement on the time interval between events, it never allows enough time disagreement to cause disagreement about cause and effect. Given two spatially separated events, there may be some disagreement about which occurred first, but only if they are so far separated spatially and so close time-wise that there can not be a cause-effect relationship between them. So for all observers, the past-future in terms of cause-effect is well defined in SR. That is, the "future" is well enough defined for any cause-effect discussion.

What does "disagree" actually mean? At the moment it's 9am in London and 4am in New York. Does that mean that people in London and New York "disagree" about what time it is?

The principle of relativity states that the laws of the physics are the same in all reference frames. In that sense, SR fundamentally says that all observers agree about everything that is physically meaningful.

It turns out that the simultaneity of physically separated events is not physically meaningful.

 

[jbriggs444]

Haag seems to have written similarly things in "Local Quantum Physics" (1996), p314:

Starting from this question we come almost unavoidably to an evolutionary picture of physics. There is an evolving pattern of events. At any stage the past consists of the part which has been realized, the future is open and allows possibilities for new events. Altogether we have a growing graph ..."

If one is trying to construct a logical argument, it seems short-sighted to assume that the past is precisely determined by the present.

 

[FactChecker]

What does "disagree" actually mean? At the moment it's 9am in London and 4am in New York. Does that mean that people in London and New York "disagree" about what time it is?

Every time in my post that I use the term "disagree", I tried to state specifically what the disagreement is about.

The point is that while SR states that observers may disagree to a limited extent about the time interval between events, they will not disagree to the extent that any cause-effect relationships are in question.

 

[Freixas]

If one wants to ask whether the universe being "block" or not is testable, it seems to me that the answer is obvious that it cannot be, because it would require one to get experimental data from the future.

If you mean data from my future light cone (i.e. everything that is not my past light cone), which would include events that I might now consider part of my "present" or "past", then I agree.

Your future light cone is not everything that is not in your past light cone. Your future light cone is only those events that can be reached by a timelike or null curve from the event of you here and now. It does not include events that are spacelike separated from the event of you here and now (which includes events that block universe proponents view as "present").

Sorry, I'm sure your point is subtle and precise and that what I heard is not what you said. What I heard you say was "To test for a block universe requires the ability to do something impossible, that is, get experimental data from the future". Following the "if wishes were fishes" philosophy, I then replied "I could also test for a block universe if given the impossible ability to access data from 'events that are spacelike separated from the event of you here and now.'"

I believe any data reaching me faster than light could be used to exclude at least some versions of a block universe.

This looks like personal speculation, and is probably off topic

I tried to "PM" you (is that the same as a "conversation"?). My message was rejected as being either spammy or inappropriate. I am totally baffled as to why and the filter cleverly doesn't spell it out. In my quote above, I included the "I believe..." which you left out, so yes, this is speculation.

Even without a block universe, all the events in your past light cone have to be fixed and certain for your model to be consistent.

I've been assuming that a block universe is like a spacetime diagram based on special relativity, with tilted time and space axes depending on relative velocity. If allowed FTL data, scenarios could be created where you receive information about your future. Then I assumed that the opposite of a block universe was something where there was a common present—no tilted time axes and no opportunity to use FTL data to send a message to the past.

I'm sure there are multiple errors in the paragraph above, probably starting with what exactly a block universe is and what it's opposite is. I'm not trying to make any point here; I'm just trying to spell out my thinking so maybe you can see why I said what I did.

While I didn't mean to dredge up all this talk about block universes, confusion about the topic is at the heart of my original OP. Your Insight article may not provide as much insight as you think. It's rather like coming in in the middle of a conversation. I'll see if I can find a primer on the topic.

 

[PeterDonis]

What I heard you say was "To test for a block universe requires the ability to do something impossible, that is, get experimental data from the future".

That is what I said, so you heard correctly.

Following the "if wishes were fishes" philosophy, I then replied "I could also test for a block universe if given the impossible ability to access data from 'events that are spacelike separated from the event of you here and now.'"

And I responded that that is not sufficient. The block universe does not just claim that events spacelike separated from you here and now are "real". It claims that all events in the entire 4-d spacetime are "real". That includes the events in the future light cone of you here and now. So to test whether the block universe is true, you have to be able to get experimental data from all of 4-d spacetime, including the future light cone of you here and now. And you can't.

I've been assuming that a block universe is like a spacetime diagram based on special relativity

I don't know why you would assume that. The block universe is the claim that all events in 4-d spacetime are "real". That has nothing whatever to do with how you choose to represent the events in a diagram or a mathematical equation or anything else.

Your Insight article may not provide as much insight as you think. It's rather like coming in in the middle of a conversation.

Of course it is. I didn't want to take the time in the article to explain in detail what the "block universe" hypothesis says, because that's already been done by people who actually believe the hypothesis, and they did a much better job than I could do since I don't believe it. That's why I gave a specific reference in the Insights article to use as a basis for the discussion there.

 

[PeterDonis]

I tried to "PM" you (is that the same as a "conversation"?).

Yes.

My message was rejected as being either spammy or inappropriate.

That's odd; I didn't think we filtered PM conversations. I'll try starting one with you so you can respond to it instead of having to start it yourself; maybe that will get around whatever weird thing the forum software is doing.

 

[vanhees71]

Every time in my post that I use the term "disagree", I tried to state specifically what the disagreement is about.

The point is that while SR states that observers may disagree to a limited extent about the time interval between events, they will not disagree to the extent that any cause-effect relationships are in question.

It depends on what you define as "time interval". If you mean the measurement of the time difference between events in terms of the times of observers in relative motion to each other, of course they get different results (time dilation). If each of them meausures an invariant property, they will get the same result (which is a tautology, because that's what "invariant property" means).

 

[FactChecker]

It depends on what you define as "time interval". If you mean the measurement of the time difference between events in terms of the times of observers in relative motion to each other, of course they get different results (time dilation). If each of them meausures an invariant property, they will get the same result (which is a tautology, because that's what "invariant property" means).

Yes. I guess that my post was not very clear. I was trying to put that in some terms that might apply more directly to the issue of "SR says that observers don't agree on what constitutes the future " in the OP. If in SR there can be no disagreement on any cause-effect relationship, I wonder if there can be any significant disagreement on "the future"? SR only allows small differences in timing that have no effect on the invariant properties. It seems to me that the invariant properties define what most people would mean by the "future".

 

[vanhees71]

It's clear that two events can only be related by cause and effect if the one event lies within the future light cone of the other and thus are time-like separated. Then there's no ambiguity which event is temporally before the other, i.e., all observers agree about what's past and what's future. Space-like separated events cannot be in a cause-effect relation and indeed here observers don't agree about which one was temporally before the other. Particularly in this case one can always find a frame of reference, where the events are simultaneous.

 

[bhobba]

I think one of the reasons some people get in heated discussions about this is because it is difficult to follow the logic.

I think the reason some people get confused is they do not realize its a theory about the geometry of space-time. During the 19th century geometry was greatly elucidated by the Erlangen Program:
https://en.wikipedia.org/wiki/Erlangen_program

We see the strong relationship between geometry and symmetry. Now when one looks at the symmetries of space-time to discover its geometry you discover the geometry depends on a parameter c:
http://physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

Many different experiments in many different areas show that c is the speed of light - in fact one can leave c undetermined and derive Maxwell's Equations, and hence c must be the speed of light:
http://www.cse.secs.oakland.edu/haskell/Special Relativity and Maxwells Equations.pdf

Once you realize it's just geometry seemingly difficult issues are much easier. For example length contraction is like getting a rod through a door. It will not fit so you simply rotate it a bit - length contraction is really the same - only instead of normal rotation is hyperbolic rotation - the hyperbolic being associated with the space-time geometry.

Thanks
Bill

 

[Freixas]

Once you realize it's just geometry seemingly difficult issues are much easier.

Actually, it's thinking about it as "just" geometry that got me into trouble. The geometric interpretation (or even the Lorentz transform) will happily generate coordinates for any event. The Minkowsky spacetime diagram and the block universe appear go together like jam on bread.

Peter's point (and it's always dangerous for me to try to paraphrase him) is that an event cannot be guaranteed to be "fixed and certain" to an observer until it is part of his past light cone. And because my past light cone is not the same as yours, we won't share a common view of what is "fixed and certain".

 

[PeroK]

And because my past light cone is not the same as yours, we won't share a common view of what is "fixed and certain".

This is, of course, not correct at all. And highlights the problem with the over-emphasis on observers "disagreeing" about things that are simply coordinate-dependent. Relativity is a self-consistent theory, which includes the requirement that there can be no disagreement about physical events, their cause and effect.

To take an example. It looks like the star Betelgeuse is about to go supernova . Given that it is 700 light years away it may very well have gone several hundred years ago, but we don't know about it yet. To an observer closer to Betelgeuse it is already an event long past and is in their past light cone. There is no physical significance in the fact that we don't know about it yet as the event is not in our past light cone.

Another example is that if you and I are together and you are cycling about on a bicycle backwards and forwards, then the time "now" at Beteleuse is different for you and me depending on the speed and direction you are cycling. If you look online you will find a number of sources, including pop science, who make a big deal out of this. But, clearly, getting on a bicycle is not altering what has happened, is happening or will happen 700 light years away in any physically meaningful sense. You must, therefore, adjust the significance you give to the "now" at Betelgeuse according to one system of coordinates or another. The physical reality of its supernova and the information of that event reaching Earth are not affected by whether or not you happen to be on a bicycle (*).

There's a strong analogy here with us looking at a house. As you cycle about your view of the house, its shape and apparent dimensions changes. But, this change of perspective is not physically meaningful. Anything you can say about a house that is dependent on a particular perspective is not physically significant. Relative motion of observers creates an analogous change of perspective, but no physically significant changes. But, the change of perspective regarding the time coordinates (rather than only the spatial perspective) associated with relative motion is harder to grasp and often causes misconceptions until the lack of its physical significance has been grasped by the student.

It's important to grasp the lack of physical significance of relative motion; not to fall into the trap of elevating it to a physical and philosophical conundrum, which it is not.

(*) To make the time difference significant we would have to go much further than Betelgeuse for a relative velocity of say $10m/s$ on a bicycle.

 

[Freixas]

This is, of course, not correct at all. And highlights the problem with the over-emphasis on observers "disagreeing" about things that are simply coordinate-dependent. Relativity is a self-consistent theory, which includes the requirement that there can be no disagreement about physical events, their cause and effect.

Did you read Peter Insight article linked to in the first response?

 

[PeroK]

Did you read Peter Insight article linked to in the first response?

Okay, everything I've said is already in there.

 

[Freixas]

Okay, everything I've said is already in there.

Ok, good. It wasn't sounding quite the same.

This is, of course, not correct at all. And highlights the problem with the over-emphasis on observers "disagreeing" about things that are simply coordinate-dependent.

The comment you were disagreeing with probably didn't mean what you thought it meant. I wasn't talking about disagreement, but about the fact that two observers at different locations cannot both verify all the same events. They don't disagree—they just don't have access to the same information.

My point about geometry and coordinate systems is that they assume a God-like view. You can seemingly confirm anything you want, totally ignoring light speed limits and thus are led down the primrose path to thinking that a block universe is the only workable model. Or at least, that was my experience.

 

[PeroK]

My point about geometry and coordinate systems is that they assume a God-like view. You can seemingly confirm anything you want, totally ignoring light speed limits and thus are led down the primrose path to thinking that a block universe is the only workable model. Or at least, that was my experience.

Does Peter's Insight not explode that myth?

 

[jbriggs444]

My point about geometry and coordinate systems is that they assume a God-like view. You can seemingly confirm anything you want, totally ignoring light speed limits

I do not see that point at all. A coordinate system is nothing more than a way of attaching numeric tuples to events. A happenstance at an event in one's causal future does not become somehow more real because there is a coordinate tuple associated with that event.

 

[PeterDonis]

My point about geometry and coordinate systems is that they assume a God-like view.

In a hypothetical scenario, yes, that's true. But that's precisely because the scenario is hypothetical. In a hypothetical scenario, the person making up the scenario can simply dictate by fiat what happens. That includes dictating by fiat what happens in the causal future of any event of interest. So the person making up the scenario does have a "God-like view" of what happens in the scenario.

In the real world, however, nobody has such a view; yet we routinely assign coordinates to hypothetical events in our causal future. For example, when the Apollo program sent astronauts to the Moon, the engineers calculated coordinates at which the spacecraft would be at future times. That doesn't mean they were assuming a "God-like view" where they knew for certain what would happen in the future--the most obvious counterexample to that claim is Apollo 13, in which the spacecraft ended up following a very different trajectory from the one that was calculated before launch. But the fact that calculations of what is expected to happen in the future are never certain does not make them useless; far from it. Apollo 13 would never have made it back to Earth if the engineers at NASA had not been able to quickly make new calculations once they knew there was a problem aboard the spacecraft .

In other words, calculations about hypothetical future events are predictions. They are constructions of a model that extends what is currently known based on the laws of physics and particular assumptions about the specific situation--for example, the assumption that the Apollo third stage is going to fire at a particular time at a particular point in low Earth orbit to boost the spacecraft towards an expected arrival at a particular point in the Moon's orbit at a particular time. And that constructed model gets built the same way all models in physics, or at least all models that are going to be used for numerical calculations, get built--using coordinates and spacetime geometry. (Strictly speaking, the Apollo calculations were non-relativistic, but that doesn't change the fundamental point.)

In short, building a model using coordinates and spacetime geometry that extends what is currently known based on certain assumptions is not the same as claiming that every single event in that model, including ones in the causal future of the event where the model is built, is fixed and certain.