From the human perspective, there is a variable amount of time between any two moments in time depending on the frame of reference. — Metaphysician Undercover

But time isn't indeterminate in a particular frame of reference. It's just relative--due to factors such as velocity--when you compare different frames of reference. We can predictively calculate those differences to a high degree of precision, which wouldn't make much sense if it were indeterminate.

But time isn't indeterminate in a particular frame of reference. — Terrapin Station

I know, but the human perspective gives us the potential for infinite frames of reference. Therefore from the human perspective, time is indeterminate.

It's just relative--due to factors such as velocity--when you compare different frames of reference. We can predictively calculate those differences to a high degree of precision, which wouldn't make much sense if it were indeterminate. — Terrapin Station

I can't see the point here. The very fact that there are differences in the amount of time which passes between one moment and another moment according to human measurement, is clear proof that time, which is what passes between those moments, is indeterminate from the human perspective. Unless the means of quantifying the differences provides an absolute solution, then all it does is veil the indeterminacy, hiding it behind an illusion of determinacy. Perhaps you'll understand if you consider that there is a limit, the speed of light, and as the frame of reference approaches the speed of light there is an infinitely small quantity of time between two moments. Infinite is synonymous with indeterminate.

I know, but the human perspective gives us the potential for infinite frames of reference. Therefore from the human perspective, time is indeterminate. — Metaphysician Undercover

So "psychological time"? Yeah, that's highly variable.

I never said anything about "psychological time". I'm talking about time itself. From the human perspective, time is indeterminate.

If I assumed a "Master Time", then I couldn't conclude that time is indeterminate. — Metaphysician Undercover

It is called a preferred reference frame, or at least a preferred foliation (an objective ordering of events). Presentism must assume such a thing, but the existence of a preferred foliation does not necessarily imply the existence of a present (a preferred moment).

Anyway, under the preferred foliation, there is a fixed amount of time between any two moments in time, and frames which do not correspond to this preferred frame are simply not representative of the absolute ordering of events. Hence clocks are all wrong because they're all dilated, some more than others.

Can I make the further, more generalized conclusion, that the amount of time between any two points in time, is indeterminate? — Metaphysician Undercover

In the spacetime model, there is no concept of 'point in time'. Time is just one of 4 dimension, all of which need to be specified to identify a point, which is called an event. There is a fixed (frame independent) separation of any two events, but that separation is called the interval, not the duration between them. Both the time and the space between any two events is frame dependent (indeterminate), but the combination of the two (the interval) is always the same.

I never said anything about "psychological time". I'm talking about time itself. From the human perspective, time is indeterminate. — Metaphysician Undercover

But that's not true. Again, we can know that on the ground, clocks are going to read, say, 500 hours on the nose, while on the space station, clocks read, say, 499-point-whatever hours (I don't know what the exact difference is--I'd have to research it) relative to the 500 hours on the ground.

How is that indeterminate?

It is called a preferred reference frame, or at least a preferred foliation (an objective ordering of events). Presentism must assume such a thing, but the existence of a preferred foliation does not necessarily imply the existence of a present (a preferred moment). — noAxioms

I don't see why presentism requires a preferred reference frame. When we as human beings meet together, and communicate, we call this the present. We only need to produce a reference frame if we want to measure the passing of time. Presentism doesn't necessarily require this, so it doesn't require a preferred reference frame. But when we proceed toward measuring time, time is indeterminate due to the possibilities of reference frames.

Anyway, under the preferred foliation, there is a fixed amount of time between any two moments in time, and frames which do not correspond to this preferred frame are simply not representative of the absolute ordering of events. Hence clocks are all wrong because they're all dilated, some more than others. — noAxioms

A "preferred foliation" might validate determinacy in time, if the preferred foliation was justified, not arbitrary. But if the preferred foliation were justified, wouldn't special relativity be contradicted?

In the spacetime model, there is no concept of 'point in time'. — noAxioms

Removing the possibility of a point in time is another indication that any claimed amount of time is indeterminate.

Both the time and the space between any two events is frame dependent (indeterminate), but the combination of the two (the interval) is always the same. — noAxioms

Right, there is a combined value of time and space. However, since what is actually measured by us, according to our capacities, is time, and space independently, and these are indeterminate, then the combined value is fundamentally indeterminate.

But that's not true. Again, we can know that on the ground, clocks are going to read, say, 500 hours on the nose, while on the space station, clocks read, say, 499-point-whatever (I don't know what the exact difference is--I'd have to research it) hours relative to the 500 hours on the ground.

How is that indeterminate? — Terrapin Station

You seem to be forgetting that there are two definite points, between which the time is measured. One clock measures 499, the other measures 500. Therefore the amount of time between those two points is indefinite. You can say, as noAxioms does, that there is no such thing as a point in time, but that is just an admittance that any so-called amount of time is indeterminate.

One clock measures 499, the other measures 500. Therefore the amount of time between those two points is indefinite. — Metaphysician Undercover

?? This makes no sense to me. If the one reads 500 hours on the nose and the other reads 499 hours, 58 minutes and 30 seconds, then the amount of time between those two is not indefinite, it's a minute and 30 seconds. That's very definite.

I don't see why presentism requires a preferred reference frame. When we as human beings meet together, and communicate, we call this the present. We only need to produce a reference frame if we want to measure the passing of time. Presentism doesn't necessarily require this, so it doesn't require a preferred reference frame. — Metaphysician Undercover

I think you have a different concept of presentism than the one typically presented on philosophy sites, which might ask when the twins get back together and notice 10 or 20 years elapsed, isn't one of them more correct about how many years actually went by? Presentism would say yes to that, but you seem to say no, since a different amount time passed for each of them, so they're both right about it.

A "preferred foliation" might validate determinacy in time, if the preferred foliation was justified, not arbitrary. But if the preferred foliation were justified, wouldn't special relativity be contradicted? — Metaphysician Undercover

Determinacy is unaffected by any choice of foliation. Different frames of reference do not in any way alter the causal relationship between any two events.
SR just says no preferred folation is locally detectable. It doesn't forbid its existence.

Right, there is a combined value of time and space. However, since what is actually measured by us, according to our capacities, is time, and space independently, and these are indeterminate, then the combined value is fundamentally indeterminate. — Metaphysician Undercover

You seem to use 'indeterminate' as 'not absolute'. The word means 'uncalculable', or 'unpredictable', and as Terrapin has been trying to point out, it is quite calculable. These things are just frame dependent, but completely determined given a choice of frames.
That said, time and space between any two events is indeed frame dependent, but their combination always yields the same interval. That part is thus frame independent. The interval between any two events can be given by one fixed value, and different perspectives do not change that value.

A misconception in a post from another thread:

It is one of the most fundamental aspects of our experience, that past events are substantially different from future events. Past events cannot be changed, while we can influence the occurrence of future events. — Metaphysician Undercover

This is a feature of your future light cone. That cone, not the present, delimits events which can and cannot be changed.
Similarly, the past light cone, not the present, delimits that about which we can know (events which can have an effect on us, vs those which cannot).

Neither of these fundamental things changes at the boundary of the present, except where the two cones happen to intersect the present. So no fundamental change as described here occurs at the present.

Those light cones are not frame dependent. They are 'determinate' as you put it.

Literally everything in relative motion inhabits a different present. These presents become more strikingly in disagreement as relative speeds increase and with distance. A classic example of this is Penrose's Andromeda Paradox, inappropriately named, because it is not a paradox. — Inis

Yes, that's relativity of simultaneity. The events that are simultaneous for Alice need not be simultaneous for Bob. But, again, any apparent disagreement is resolved by factoring in their respective reference frames. If they shared the same reference frame then the same events would be simultaneous for both of them.

So I don't see a conflict between presentism and realism. A problem only occurs if one assumes an absolute reference frame for determining simultaneity. (Note: one could consider a reference frame for the whole universe, but then time drops out.)

So I may conclude that from the point in time when Bob left, to the point when Bob returned, the amount of time which passes is dependent on one's frame of reference. Can I make the further, more generalized conclusion, that the amount of time between any two points in time, is indeterminate? — Metaphysician Undercover

No, it is determinate. This is just arithmetic (the amount of time between t1 and t2 is t2 - t1). Note that to specify times at all is to assume a particular reference frame. Normally we don't have to think about this because we (and most matter in the universe) age at about the same rate (because we move at similarly slow speeds relative to the speed of light).

This makes no sense to me. If the one reads 500 hours on the nose and the other reads 499 hours, 58 minutes and 30 seconds, then the amount of time between those two is not indefinite, it's a minute and 30 seconds. That's very definite. — Terrapin Station

There is a beginning point, and an ending point to the time period being measured. One clock measures that time period as 500 hours. Another clock measure it as 400 hours. Another, 499 hours, 58 minutes and 30 seconds, and so on. Since there is an infinity of possibilities, to the amount of time between that beginning point and the ending point, that amount of time is indeterminate.

I think you have a different concept of presentism than the one typically presented on philosophy sites, which might ask when the twins get back together and notice 10 or 20 years elapsed, isn't one of them more correct about how many years actually went by? Presentism would say yes to that, but you seem to say no, since a different amount time passed for each of them, so they're both right about it. — noAxioms

Presentism assumes that only the present is real. If both the twins experienced only the present, for the entire time of separation, and continue to experience only the present, how could this be a problem to presentism? The fact that they have aged differently is irrelevant to presentism.

I don't think that presentism is capable of providing a premise for counting a quantity of time, because any past time would become unreal, therefore there can be nothing to count. So what is inconsistent to presentism, in this thought experiment, is that one twin measured 10 year and the other measured 20. Presentism really does not allow any reality to such measurements of past time.

SR just says no preferred folation is locally detectable. It doesn't forbid its existence. — noAxioms

I think you misunderstand SR. It strictly stipulates that no frame of reference could be preferred in the sense of being more real than another.

You seem to use 'indeterminate' as 'not absolute'. The word means 'uncalculable', or 'unpredictable', and as Terrapin has been trying to point out, it is quite calculable. These things are just frame dependent, but completely determined given a choice of frames. — noAxioms

Indeterminate means without a fixed value. If the quantity of time measured between when the twins separated, to when they reunited, varies from one frame of reference to another, it is without a fixed value, and is therefore indeterminate.

This is a feature of your future light cone. That cone, not the present, delimits events which can and cannot be changed.
Similarly, the past light cone, not the present, delimits that about which we can know (events which can have an effect on us, vs those which cannot).

Neither of these fundamental things changes at the boundary of the present, except where the two cones happen to intersect the present. So no fundamental change as described here occurs at the present.

Those light cones are not frame dependent. They are 'determinate' as you put it. — noAxioms

I think you are wrong to say that the light cones are not frame dependent. Any event has a light cone. According to SR, the present of an event, or time that an event occurs, is frame dependent. Therefore the light cone for any event is frame dependent.

No, it is determinate. This is just arithmetic (the amount of time between t1 and t2 is t2 - t1). Note that to specify times at all is to assume a particular reference frame. Normally we don't have to think about this because we (and most matter in the universe) age at about the same rate (because we move at similarly slow speeds relative to the speed of light). — Andrew M

Obviously not, because Bob measures the time between t1 and t2 as 6 years, and Alice measures the time between t1 and t2 as 10 years. Therefore the quantity of time between t1 and t2 is indeterminate. So I disagree\ with you again, and I really wonder where you are getting your information from. That your statement is wrong is evident from the fact that physicists employ a "proper time". The employment of "proper time" is to create a semblance of determinacy. It's a similar principle to your "preferred foliation", it provides an illusion of determinacy.

Since there is an infinity of possibilities, to the amount of time between that beginning point and the ending point, that amount of time is indeterminate. — Metaphysician Undercover

There's not an infinity of possibilities with respect to the frames of reference in question. There are different possibilities in different frames of reference, but none of them are indeterminate.

The point is that there is a multitude of possible amounts of time between the first point and the second. Therefore the amount of time between those two points is indeterminate.

Indeterminate means without a fixed value. If the quantity of time measured between when the twins separated, to when they reunited, varies from one frame of reference to another, it is without a fixed value, and is therefore indeterminate. — Metaphysician Undercover

I can measure the distance between myself and that tree over there, and get an indeterminate value because one of the measuring tapes takes a path around that other tree to the left over there, and thus measures a different distance. So all measurements are indeterminate in that sense. But I could have calculated how each of those measurements would come out ahead of time. Those measurements are fixed before they are done, as opposed say to quantum measurements which are not predictable in advance.

I think you are wrong to say that the light cones are not frame dependent. Any event has a light cone. According to SR, the present of an event, or time that an event occurs, is frame dependent. Therefore the light cone for any event is frame dependent. — Metaphysician Undercover

Events are fixed (by definition), not frame dependent at all. They're points in spacetime, and don't have frame dependent qualities such as velocity, duration, or length and so on. Their light cones are determined by light speed, not the frames, so those are also fixed.

Obviously not, because Bob measures the time between t1 and t2 as 6 years, and Alice measures the time between t1 and t2 as 10 years. Therefore the quantity of time between t1 and t2 is indeterminate. — Metaphysician Undercover

t1 and t2 are 20 years and 30 years if you're using Alice's clock. Alternatively, t1 and t2 are 20 years and 26 years if you're using Bob's clock. They travel different spacetime paths which is why their ages are different.

What you can say is that the time between two points in spacetime is indeterminate.

can measure the distance between myself and that tree over there, and get an indeterminate value because one of the measuring tapes takes a path around that other tree to the left over there, and thus measures a different distance. So all measurements are indeterminate in that sense. — noAxioms

It's not analogous unless you are claiming that the distance between yourself and the tree is indeterminate. And that's not what your claiming, because taking a side trip around another tree is not measuring the distance between yourself and the tree.


OK, I'll go with that then.

And that's not what your claiming, because taking a side trip around another tree is not measuring the distance between yourself and the tree. — Metaphysician Undercover

Exactly, just as the twin that takes a side trip to some other star and back is not measuring the duration between the two events of departure and return.

Exactly, just as the twin that takes a side trip to some other star and back is not measuring the duration between the two events of departure and return. — noAxioms

All things change place as time passes, it's a premise of relativity. If moving means that one cannot measure duration, then time is indefterminate.

time travel to the future is already possible and has been done in practice. The only problem is that there is no practical application that can bring you back in time. Also under the current circumstances, it takes alot of time to travel only a little in time. I don't feel like doing the exact calculations right now, but it is in order of a minute timetravel towards the future if you spend a year. In other words, with the current method, you can leave earth for a year to travel in time, and when you come back after a year for you has passed, on earth a year and one minute will have passed.
So yes it is possible, just not very practical yet.

All things change place as time passes, it's a premise of relativity. — Metaphysician Undercover

I know of two premises of SR (one of which predates the theory by several centuries), and a third for GR. None of them are "All things change place as time passes".

The point is that there is a multitude of possible amounts of time between the first point and the second. Therefore the amount of time between those two points is indeterminate. — Metaphysician Undercover

It's only indeterminate if you're looking for an overaching time perspective, which is why I brought that up first.

Since there is no overarching time perspective, then it's not indeterminate. You just have to specify the reference frames. There's no reference frame-free time. The idea of that doesn't make any sense.

It is called a preferred reference frame, or at least a preferred foliation (an objective ordering of events). Presentism must assume such a thing, but the existence of a preferred foliation does not necessarily imply the existence of a present (a preferred moment). — noAxioms

I think it's worse than that. Presentism cannot assume a preferred foliation of something it claims does not exist. Presentism cannot admit spacetime or foliations, and has to treat scientific theories such relativity as useful fictions.

Anyway, under the preferred foliation, there is a fixed amount of time between any two moments in time, and frames which do not correspond to this preferred frame are simply not representative of the absolute ordering of events. Hence clocks are all wrong because they're all dilated, some more than others. — noAxioms

Alternatively, presentism may dispense with an observer independent objective reality.

Newtonian relativity. Inertia is frame of reference dependent. There is no absolute rest.

It's only indeterminate if you're looking for an overaching time perspective, which is why I brought that up first. — Terrapin Station

It has nothing to do with an overarching time perspective, we went through that already. Why do you allow that idea to distract you? It's the human perspective. We designate points in time as the beginning and ending of a period of measurement. That's how we quantify time. Without such points we have no measurement of time, but the human capacity to designate such points is deficient. Therefore from the human perspective, time is indeterminate.

Indeterminate means having no fixed value. So consider this analogy. Some one asks you what time it is. By the time you say what time it is, it is no longer that time. So "what time it is" has no fixed value, and time is inherently indeterminate.

Indeterminate means having no fixed value. So consider this analogy. Some one asks you what time it is. By the time you say what time it is, it is no longer that time. So "what time it is" has no fixed value, and time is inherently indeterminate. — Metaphysician Undercover

So now it's a point about, what--the notion that we can subdivide time further, or the idea that we can subdivide it into units that are quicker than we can say something?

That was an analogy, not an attempt to change the subject.

In other words, with the current method, you can leave earth for a year to travel in time, and when you come back after a year for you has passed, on earth a year and one minute will have passed. — Tomseltje

Sounds to me like you traveled about a year into the future, just like we all do. Travel into the future seems effortless. It's not doing it that's the trick.

Anyway, the subject of the thread implies that one's interpretation of time has anything to do with the possibility of time travel. Assuming time travel is to the past, as is typically assumed, it is impossible, period. A-theory has nothing to do with that.
Such a concept would involve sending information to the past, and that has never been possible under any valid interpretation of physics.
Forward is easy, at least for things with reasonably limited information. Information travels that way no problem. High speed isn't required to do it.

Anyway, the subject of the thread implies that one's interpretation of time has anything to do with the possibility of time travel. Assuming time travel is to the past, as is typically assumed, it is impossible, period. A-theory has nothing to do with that. — noAxioms

The question of whether closed time-like curves exist in our universe is still open, Hawking's Chronology Protection Conjecture notwhithstanding.

https://www.nature.com/articles/s41467-018-08100-1

So, physicists are really studying time-travel into the past. A-theory says they are wasting their time. They aren't.

Such a concept would involve sending information to the past, and that has never been possible under any valid interpretation of physics. — noAxioms

You are mistaken, see the above link and references therein.

Alternatively, presentism may dispense with an observer independent objective reality. — Inis

Have you worked out yet how to account for eternalism's lack of motion, or are you still ignoring that eternalism has this problem?

Many physicists argue that Einstein’s position is implied by the two pillars of modern physics: Einstein’s masterpiece, the general theory of relativity, and the Standard Model of particle physics. The laws that underlie these theories are time-symmetric — that is, the physics they describe is the same, regardless of whether the variable called “time” increases or decreases. Moreover, they say nothing at all about the point we call “now” — a special moment (or so it appears) for us, but seemingly undefined when we talk about the universe at large. The resulting timeless cosmos is sometimes called a “block universe” — a static block of space-time in which any flow of time, or passage through it, must presumably be a mental construct or other illusion.

https://www.quantamagazine.org/a-debate-over-the-physics-of-time-20160719/