Absolute motion

Morbert

Masteroid wrote: »

And I think roosh would say that that is the shared present, shared with each other.

The problem is when we consider observers moving relative to us. They would not agree with us about the present moment.

roosh

Morbert wrote: »

You haven't challenged my previous post at all. If premise 3 is not assumed then they can either conclude their measurements of the speed of light are trustworthy, and that simultaneity is relative, or they can assume a set of hidden dynamics that conspire to make measurements of the speed of light the same for all observers.

The third premise isn't required, because in order to conclude the former they must assume co-existent past and future; in order to conclude the latter all they have to do is not make that assumption.

All they are required to do is acknowledge that events which are (non-)simultaneous for them are (non-)simultaneous for them; their relatively moving counterpart, who is in their present moment, makes a different set of measurements; they don't have to assume that the events are (non-)simultaneous for everyone, they just need to explain why there are different measurements. Only by assuming past and future do they arrive at the conclusion that simultaneity is relative; without those assumptions the different measurements are attributed to dynamics which they don't understand, without ever assuming absolute simultaneity.


That there is a single present moment shared by all observers is self-evidently true, if we simply don't assume that the past and future exist; because if we don't assume past and future, all that is left is the present. The existence of past and/or future isn't self-evidently true if we don't assume presentism, they must still be assumed by every single observer.

Another way of looking at it is, if presentism isn't true then we are left with the following possibilites:
- past and future exist
- past exists but future doesn't
- future exists but past doesn't

All of those require an assumption on behalf of every observer that either the past or the future, or both exist;so, neither the existence of the past or the future is self-evidently true if we don't assume presentism, whereas presentism is self-evidently true if we don't assume past and/or future.

Simply by not assuming an existential past and future we are left with presentism and dynamics that we do not understand.

citrus burst

roosh wrote: »

Another way of looking at it is, if presentism isn't true then we are left with the following possibilites:
- past and future exist
- past exists but future doesn't
- future exists but past doesn't

All of those require an assumption on behalf of every observer that either the past or the future, or both exist;so, neither the existence of the past or the future is self-evidently true if we don't assume presentism, whereas presentism is self-evidently true if we don't assume past and/or future.

Simply by not assuming an existential past and future we are left with presentism and dynamics that we do not understand.

The way I look at it, we have to pick one of the five assumptions (you only mentioned four).
- only the present exists
- past and future exist
- past exists but future doesn't
- future exists but past doesn't
- they all exist

Each has compelling pro's and con's. I don't really care which is true as long as they are consistent. Personally I'd pick 3 or 5.

roosh

citrus burst wrote: »

The way I look at it, we have to pick one of the five assumptions (you only mentioned four).
- only the present exists
- past and future exist
- past exists but future doesn't
- future exists but past doesn't
- they all exist

Each has compelling pro's and con's. I don't really care which is true as long as they are consistent. Personally I'd pick 3 or 5.

Presentism
You don't have to assume that only the present exists; you only need to acknowledge that you only ever experience the present moment; this is self evidently true. You don't need to assume that the present moment you occupy is the same for all observers, but that doesn't mean that you assume that it is different either; you don't assume either way.

In order to conclude that the present moment isn't the same for all observers you have to assume that past and/or future exist; in order to conclude that it is the same for all observers, all you need to do is not make that assumption. So, from your experience of your present moment, simply by not assuming past and/or future exist you are left with presentism. If you don't "assume" presentism, you are left with a possibility of alternatives, all of which require you to make an assumption about them.


Absolute Simultaneity
Similarly, we don't need to assume absolute simultaneity; if absolute simultaneity is a necessary condition of presentism, then simply not assuming past and future also gives us absolute simultaneity. Now, it might be tempting to think that, just like past and future we also have to assume absolute simultaneity, but that isn't true; it only seems true when we think RoS is an option, but by considering RoS as an option we necessarily have to assume that past and future exist.

Theoretically, what we would have, is a set of measurements which are at odds with each other. Without any assumptions of past, future, or absolute simultaneity, we are left needing an explanation for how observers measure the same speed of light regardless of their motion relative to the source. In order to conclude that RoS is the answer, we have to assume that past and future exist; if we don't assume that past and future exist we are left with presentism, and a set of dynamics which are not understood accounts for the discrepancy in the measurements and the issue of simultaneity was never really an issue in the first place.

Time
The issue of simultaneity is probably, in no small part, attributable to our assumptions about time, of which past and future are an integral part. When we say that events are simultaneous if they "happen at the same time", then how we view "time" affects our interpretation of simultaneity. How we view "time" also affects our interpretation of how clocks work; if we assume that clocks measure something physical called "time", then the discrepancy between the measurements, which requires the explanation, carries a different interpretation. If, however, we examine how a clock operates and discover that nowhere in the process is something physical called time actually measured, then we can start to question the nature and existence of time. If we have no evidence of the existence of time, or at least, no evidence that time is a physical property of the universe - that doesn't require us to assume it a priori - then our definition of simultaneity as being "events which happen at the same time" has a different interpretation.

If clocks don't measure time, then the disagreement over measurements isn't a disagreement over the simultaneity of events; it only becomes one with the additional assumption that time is physical and that a clock measures that physical property - which would represent and additional assumption which is required.

Morbert

roosh wrote: »

The third premise isn't required, because in order to conclude the former they must assume co-existent past and future; in order to conclude the latter all they have to do is not make that assumption.

All they are required to do is acknowledge that events which are (non-)simultaneous for them are (non-)simultaneous for them; their relatively moving counterpart, who is in their present moment, makes a different set of measurements; they don't have to assume that the events are (non-)simultaneous for everyone, they just need to explain why there are different measurements. Only by assuming past and future do they arrive at the conclusion that simultaneity is relative; without those assumptions the different measurements are attributed to dynamics which they don't understand, without ever assuming absolute simultaneity.


That there is a single present moment shared by all observers is self-evidently true, if we simply don't assume that the past and future exist; because if we don't assume past and future, all that is left is the present. The existence of past and/or future isn't self-evidently true if we don't assume presentism, they must still be assumed by every single observer.

Another way of looking at it is, if presentism isn't true then we are left with the following possibilites:
- past and future exist
- past exists but future doesn't
- future exists but past doesn't

All of those require an assumption on behalf of every observer that either the past or the future, or both exist;so, neither the existence of the past or the future is self-evidently true if we don't assume presentism, whereas presentism is self-evidently true if we don't assume past and/or future.

Simply by not assuming an existential past and future we are left with presentism and dynamics that we do not understand.

Not assuming X is not the same as assuming X is false. If you don't assume the existence of spacetime, you are left with observers experiencing their present moments, and observers measuring the speed of light to be c. People can then either a) Accept these measurements as real, and conclude relativity of simultaneity and the existence of spacetime, or b) Posit dynamics which conspire to make everyone measure the speed of light to be c, no matter how they do the measurement, and conclude the possibility of presentism.

Masteroid

Morbert wrote: »

The problem is when we consider observers moving relative to us. They would not agree with us about the present moment.

We don't disagree on this and we must surely agree that the fact that light has a finite speed predicts this. I cannot know about you now until I find out later.

This seems obvious now, the fact that information cannot be received and transmitted simultaneously suggests as much.

However, if one were to consider the time-slice where it is 12:04 for me, then that same time-slice would contain the events that are roosh at 12:08 and you observing roosh at 12:07.

And in the time-slice where you are observing roosh at 12:07, my clock would read 12:04 while roosh's clock reads 12:08.

In other words, if I were to map out a time-slice at my 12:04, and you were to map out a time-slice at your 12:07 and roosh was to map out a time-slice at his 12:08, then all three of us should create identical maps.

No? If not how not?

Masteroid

Morbert wrote: »

Premise 1) All experiences and empirical observations occur in the present moment, for every observer

Premise 2) The speed of light is the same for all observers.

Presentism does not follow from these premises. Instead, you need a third premise.

Premise 3) All observers agree with what events are occurring in the present.

Premise 3 is not self-evident.

Well no because if you have premise 1 then premise 2 need neither be present and nor even to be true. Causality emerges from premise 1 and all that needs to be realised is that light has a finite speed, that information cannot be simultaneously transmitted by one system and received by another and therefore, even if the speed of light is not the same for all observers, premise 1 predicts that not all observers will agree with what events are occurring in the present.

Premise 1 actually dismisses premise 3 which is self-evident.

In fact premise 1 predicts that it is impossible to accurately measure the speed of light since all photon absorbers are in motion relative to the path of any emitted photon, i.e., there will always be a small amoun't of spectral shift of a photon's energy regardless of who makes the measurement. Even the same apparatus in the same experiment will yield different results at different times.

The other thing that is self-evident from premise 1 is absolute motion. The process of change is the story of motion, photons being emitted and absorbed, collisions, the movement of energy is what gives rise to reality. If nothing moved then nothing would change.

If premise 1 can be boiled down to the assumption that there is one 'time-slice' and that that time-slice is experienced by all the observers on it then determinism emerges.

If we remove the concept of time from this altogether, we are left with a slice, a slice that represents the entire set of events that comprise the universe as they occur. The slice would be dynamic by nature since it would actually reflect the process of change and regardless of time.

And only systems that are comprised of events occurring now can experience the universe as it is.

If we start with premise 1 and thermodynamics, the only thing that is unexplained is 'motion' and how it came about.

Or, to put it another way, the only question left for the determinist is, 'Why did it move?'

roosh

Morbert wrote: »

Not assuming X is not the same as assuming X is false. If you don't assume the existence of spacetime, you are left with observers experiencing their present moments, and observers measuring the speed of light to be c. People can then either a) Accept these measurements as real, and conclude relativity of simultaneity and the existence of spacetime, or b) Posit dynamics which conspire to make everyone measure the speed of light to be c, no matter how they do the measurement, and conclude the possibility of presentism.

Observers don't need to assume that the present moment exists*, it is self-evident that it does; but to conclude that more than that exists requires the assumption that it does. To conclude that nothing more exists, simply requires observers not to make that assumption that more exists; because, either more exists, or it doesn't.

Either, or
Either the present moment is all that exists* or one of the following is true; simultaneity is relative and the present moment co-exists with:
- the past and future
- the past
- the future

or

simultaneity is absolute and the present co-exists with:
- the past and future
- the past
- the future


So, even if we assume that the present moment isn't all that exists*, or don't assume the positive form of that proposition, we still don't arrive at the conclusion of spacetime. We require further assumptions, not least assuming that either past and/or future exist.

I'm wondering is it entirely arbitrary which we assume exists, or does spacetime necessitate that both must exist, or that either the past or the future must exist; that is, that all observers must make those particular assumptions. The growing block theory would suggest that an observers past can exist without their future existing, but would it be possible to have a shrinking block, where only the future exists and the past decays as an observer progresses through it?

neither, nor
Now, given that either the present moment is all that exists* or past and/or future exist, and that the existence of past and/or future must be assumed, simply not making the assumption of past and/or future leaves the observer with the conclusion that the present moment is all that exists.

This is because neither past, nor future are necessary conclusions of assuming the present isn't all that exists; if we assume that more than the present exists, then we still have to make a positive assumption about the conclusion; we must positively assume that either the past, the future, or both exist.

So, not assuming past and future leaves you with presentism, but not assuming presentism doesn't specifically leave you with one of the following:
- past and future exist
- the past exists
- the future exists


By assuming past and future alone, you still don't necessarily arrive at the conclusion of spacetime, but simply not assuming past and future leaves you with presentism, because it's either or. Simply not assuming past and future leaves you with presentism, which means that the conclusion of hidden dynamics is reached.




* We are talking about from the perspective of any given observer.

Morbert

roosh wrote: »

Observers don't need to assume that the present moment exists*, it is self-evident that it does; but to conclude that more than that exists requires the assumption that it does. To conclude that nothing more exists, simply requires observers not to make that assumption that more exists; because, either more exists, or it doesn't.

Either, or
Either the present moment is all that exists* or one of the following is true; simultaneity is relative and the present moment co-exists with:
- the past and future
- the past
- the future

If simultaneity is relative, then the past and future must exist.

or

simultaneity is absolute and the present co-exists with:
- the past and future
- the past
- the future


So, even if we assume that the present moment isn't all that exists*, or don't assume the positive form of that proposition, we still don't arrive at the conclusion of spacetime. We require further assumptions, not least assuming that either past and/or future exist.

I'm wondering is it entirely arbitrary which we assume exists, or does spacetime necessitate that both must exist, or that either the past or the future must exist; that is, that all observers must make those particular assumptions. The growing block theory would suggest that an observers past can exist without their future existing, but would it be possible to have a shrinking block, where only the future exists and the past decays as an observer progresses through it?

neither, nor
Now, given that either the present moment is all that exists* or past and/or future exist, and that the existence of past and/or future must be assumed, simply not making the assumption of past and/or future leaves the observer with the conclusion that the present moment is all that exists.

This is because neither past, nor future are necessary conclusions of assuming the present isn't all that exists; if we assume that more than the present exists, then we still have to make a positive assumption about the conclusion; we must positively assume that either the past, the future, or both exist.

So, not assuming past and future leaves you with presentism, but not assuming presentism doesn't specifically leave you with one of the following:
- past and future exist
- the past exists
- the future exists


By assuming past and future alone, you still don't necessarily arrive at the conclusion of spacetime, but simply not assuming past and future leaves you with presentism, because it's either or. Simply not assuming past and future leaves you with presentism, which means that the conclusion of hidden dynamics is reached.




* We are talking about from the perspective of any given observer.

If we assume relativity of simultaneity is the correct interpretation of experimental observations and Lorentz transformations, then both the past and the future must exist. This is tedious to show mathematically, but not difficult if you would like to see it.

So my original description is still valid: Each observer experiences a present moment, and each observer measures the speed of light to be c. For these two experiences to be the same for all observers, there must be either new dynamics and absolute simultaneity, or spacetime and relativity of simultaneity. Neither is more empirical than the other.

roosh

Morbert wrote: »

If simultaneity is relative, then the past and future must exist.

If we assume relativity of simultaneity is the correct interpretation of experimental observations and Lorentz transformations, then both the past and the future must exist. This is tedious to show mathematically, but not difficult if you would like to see it.

The point was more taking a look at the "assumption" of presentism and the possibilities we are left with, if we don't assume the present moment is all that exists. Not assuming presentism, or even assuming that the present moment is not all that exists, doesn't necessarily give us spacetime, because past and future could both co-exist with a present moment which is shared by all observers.

I don't think there's need to go through the mathematics; I think we can work off that premise anyway.

On a related note though, is growing block theory not a viable possibility also?

Morbert wrote: »

So my original description is still valid: Each observer experiences a present moment, and each observer measures the speed of light to be c. For these two experiences to be the same for all observers, there must be either new dynamics and absolute simultaneity, or spacetime and relativity of simultaneity. Neither is more empirical than the other.

Each observer experiences their present moment and measures the speed of light to be c. Now, either:
a) their present moment is all that exists and new dynamics is responsible for the constancy of c;
or b) past and future co-exist with a shared present and the new dynamics are still responsible;
or c) RoS and spacetime are the conclusions.

In short, either their present moment is all that exists or their past and/or future also exist. To conclude that past and future exist, they must assume that they do. If they don't make those assumptions, then they are left with the conclusion that their present is all that exists and a) above.

Even assuming that past and future exist, they are still left with options b) and c), which means that there must be a further assumption required to distinguish between them. That assumption, I would think, is the assumption that a clock measures a physical property called time.

Morbert

roosh wrote: »

The point was more taking a look at the "assumption" of presentism and the possibilities we are left with, if we don't assume the present moment is all that exists. Not assuming presentism, or even assuming that the present moment is not all that exists, doesn't necessarily give us spacetime, because past and future could both co-exist with a present moment which is shared by all observers.

I don't think there's need to go through the mathematics; I think we can work off that premise anyway.

On a related note though, is growing block theory not a viable possibility also?

You have it slightly backwards. Assuming a common present moment does not necessarily rule out spacetime. Instead, spacetime merely becomes a superfluous assumption. If we do not share a common present moment, then spacetime must exist.

Growing block theory would not be compatible with RoS because the Lorentz transformation of simultaneity is somewhat analogous to a stick. If one end is pushed across someone's future, then the other end must be pushed across someone's past. E.g. The "now slices" (the lines labelled with x, x', and x'') in the picture below.

Each observer experiences their present moment and measures the speed of light to be c. Now, either:
a) their present moment is all that exists and new dynamics is responsible for the constancy of c;
or b) past and future co-exist with a shared present and the new dynamics are still responsible;
or c) RoS and spacetime are the conclusions.

In short, either their present moment is all that exists or their past and/or future also exist. To conclude that past and future exist, they must assume that they do. If they don't make those assumptions, then they are left with the conclusion that their present is all that exists and a) above.

Even assuming that past and future exist, they are still left with options b) and c), which means that there must be a further assumption required to distinguish between them. That assumption, I would think, is the assumption that a clock measures a physical property called time.

This is also reversed. b) Can be dismissed immediately. It is simply a) with an extra, unnecessary assumption about spacetime. Therefore the choices are a) or c). One says dynamics are responsible for everyone being able to measure the speed of light to be c. The other says spacetime is responsible.

roosh

Morbert wrote: »

You have it slightly backwards. Assuming a common present moment does not necessarily rule out spacetime. Instead, spacetime merely becomes a superfluous assumption. If we do not share a common present moment, then spacetime must exist.

Apologies, by spacetime I meant Minkowski spacetime; the idea that spacetime isn't ruled out if there is a common present moment is reflected in option b) above.

Morbert wrote: »

Growing block theory would not be compatible with RoS because the Lorentz transformation of simultaneity is somewhat analogous to a stick. If one end is pushed across someone's future, then the other end must be pushed across someone's past. E.g. The "now slices" (the lines labelled with x, x', and x'') in the picture below.

Do you know, are there still physicists who are attempting to develop a growing block theory; just out of interest?

Morbert wrote: »

This is also reversed. b) Can be dismissed immediately. It is simply a) with an extra, unnecessary assumption about spacetime. Therefore the choices are a) or c). One says dynamics are responsible for everyone being able to measure the speed of light to be c. The other says spacetime is responsible.

The point is that assuming more than the present moment exists doesn't necessarily give us Minkowski spacetimme; it is possible that past and/or future co-exist with a shared present. In order to arrive at the conclusions of either Minkowksi spacetime or a spacetime where the present moment is shared by all, requires, not only, the assumptions of past and future, but a further assumption on both counts. The latter is no more unnecessary than the former. In both cases the conclusions have to be assumed.

Option a) however, doesn't require such assumptions. Again, either presentism - the idea that only the present moment exists - is true, or else past and/or future exist. For an observer to arrive at the conclusion that more than their own present moment exists, they must assume the conclusions of past and/or future. Simply not assuming such conclusions leaves the observer with presentism, and dynamics that they don't understand. This is true even when the options are only a) and c).