Relativity Explained Via Movement, Not Time

  • #51
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Events.
Well, it can't just be any events since some events are space-like separated, and even for timelike separated events I can think of examples where you wouldn't call the resulting count time.
 
  • #52
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It is events. When I say "Time is a count", it's really saying that since the first caveman looked at the moon and grunted out something like, "moon above again," and then made a mark on the wall, and then another the next time the moon was above, is counting up some events and calling that Time. It's the counting that comes first and the definition of Time that comes after. You can count moons moving around the earth or suns appearing to move around the earth or the ticks of a grandfather clock or water clock or atomic clock. But for comparing our lives against, and meeting someone down at the dock, it's good to have some sort of counter that's pretty regular. Doesn't matter what it is though.
 
  • #53
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It is events. ... Doesn't matter what it is though.
So counting ticks on my Geiger counter is time. If I put my Geiger counter in a lead box time stops. Is that really what you meant, because that is what you said.

Here is another set of events, the tick marks on my ruler when illuminated by a specific of light. The count is 12. So time is 12. Doesn't sound like your definition is related to the usual idea of time.
 
  • #54
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Well, it can't just be any events since some events are space-like separated, and even for timelike separated events I can think of examples where you wouldn't call the resulting count time.
True, which is exactly what gets us into trouble with simultaneity, which I even recently embarrassed myself with. Yet even then the one constraint that allows us to define the relativity of simultaneity is the constraint that a 'local' event set sequence, E_i --> E_j --> E_k, cannot place any event in the set both before and after some other event in that set. That would amount to time travel.

Even if we assumed some 'toy' model of purely mechanistic events such as molecular collisions, if the background is undefined then local event sets must disagree on clock rates in many different circumstances.
 
  • #55
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True, which is exactly what gets us into trouble with simultaneity, which I even recently embarrassed myself with. Yet even then the one constraint that allows us to define the relativity of simultaneity is the constraint that a 'local' event set sequence, E_i --> E_j --> E_k, cannot place any event in the set both before and after some other event in that set. That would amount to time travel.

Even if we assumed some 'toy' model of purely mechanistic events such as molecular collisions, if the background is undefined then local event sets must disagree on clock rates in many different circumstances.
So then what sets of events can you count and call the resulting count "time"?
 
  • #56
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So counting ticks on my Geiger counter is time. If I put my Geiger counter in a lead box time stops. Is that really what you meant, because that is what you said.

Here is another set of events, the tick marks on my ruler when illuminated by a specific of light. The count is 12. So time is 12. Doesn't sound like your definition is related to the usual idea of time.
If you insure that those ticks are scaled properly yes, which is why we can do carbon dating. Yet like the linear discontinuities you can get from any given pair of individual clicks we have the uncertainty principle telling us we are getting these small scale discontinuities at a fundamental level also. But averaged over they go away.
 
  • #57
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If you insure that those ticks are scaled properly yes
OK, so now we are no longer counting, but counting and scaling our count. That is fine, how do we determine the correct scaling factor for the count?
 
  • #58
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OK, so now we are no longer counting, but counting and scaling our count. That is fine, how do we determine the correct scaling factor for the count?
Relative to any other local event set with has a reasonably stable linearity. The most fundamental of which is apparently a Planck unit of time, which is subject to the Uncertainty Principle. If you arbitrarily presume some mechanistic basis then what makes it linear does not mean linear in any absolute sense, it just means linear with respect to the mean local fundamental event sets defining the system. After all, relative to a clock under an acceleration of proper motion, linearity in terms of time alone loses relevance.
 
  • #59
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The scaling is required simply so that our choice of event sets to count time is independent of the particular set of events used to do the counting.
 
  • #60
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Relative to any other local event set with has a reasonably stable linearity.
So the tick marks on a ruler is a good example since it is stable and very linear.
 
  • #61
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The scaling is required simply so that our choice of event sets to count time is independent of the particular set of events used to do the counting.
That doesn't make any sense at all if time IS the count. How can time be the count of events and yet be independent of the events counted?
 
  • #62
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That doesn't make any sense at all if time IS the count. How can time be the count of events and yet be independent of the events counted?
It is not independent of the count, which is the point. But if you have an event set, and many different ways of combining those set and subsets, then to get any meaningful count they all must be given a consistent scale, even though nature is scale independent in general. The reason they can be scaled together would be because they are are mere regrouping of the same sets.
 
  • #63
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It is not independent of the count
You just said that you needed to scale it so that it was independent.

to get any meaningful count they all must be given a consistent scale
And exactly what is it that must be consistent about the scale? In other words, you have two valid sets of events to count and you scale one by a factor of two in order to achieve consistency, what is it about the events that required a factor of two scaling to achieve consistency, and how can you know that you need a factor of two and not three?
 
  • #64
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You just said that you needed to scale it so that it was independent.
I said independent of our "choice" of event sets, not independent of the events themselves.

And exactly what is it that must be consistent about the scale? In other words, you have two valid sets of events to count and you scale one by a factor of two in order to achieve consistency, what is it about the events that required a factor of two scaling to achieve consistency, and how can you know that you need a factor of two and not three?
Two parts:
1: "events that required a factor of two"
If you have a single finite superset of events and you have a measuring device that measures ticks for ever pair of events, then that MUST relativistically scale as 2 times every event. How much linearity there is between the individual events is immaterial, like claiming you can stop time for some specified period of time. Even if it we overlook the silliness and presumed it did occur it has NO empirical meaning.

2: "how can you know that you need a factor of two and not three"
Because the clock that counted one event for every two events would not be linear by any measure other than a 2 to 1 ratio. This ratio is what defines what we can measure, not the naked quantity in itself. That would require absolutes like in Newtonian physics.
 
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  • #65
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Unfortunately, I will not be able to continue the conversation tonight. I thought it would take fewer iterations than it did.

The point is that this definition of "time is counting events" is not sufficient. There are some events which counting them doesn't measure time because the events are separated by space, not time. There are other events which counting them does not measure time because they are at random intervals. For still other sets of events you have a good feeling that they are measuring time, but you have to scale your counts in order to say that they are all measuring time. So for all of these reasons there is more to measuring time than simply counting events.

All of these objections can be addressed, but to do so requires that you identify something about the various counts beyond the mere counting itself. The very fact that you can use counts of a variety of sets of events (properly scaled) to measure time indicates that there is something else besides simply the counting.

Unless you already have some concept of time already then there is no way to distinguish between spacelike sets of events and timelike sets of events. Unless you already have some concept of time then there is no way to determine if the scaling is correct.

What the counts and their scaling do is to define a unit of time, not to define time.
 
  • #66
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I don't know how this post 'relativity explained by movement, not time' got so far off track.
You got movement, you got:

(amount of) space/time.

Time will always be around in the physics-conversation.
 
  • #67
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Unfortunately, I will not be able to continue the conversation tonight. I thought it would take fewer iterations than it did.
I am accustomed to certain people, including physicist, who seem to grasp it straight away as though it was too obvious to mention, and others who find it very difficult.

The point is that this definition of "time is counting events" is not sufficient.
Is actually is sufficient. In fact from a purely empirical perspective some form of event counting is ALL we have. The derivation of the relativity of simultaneity is possible exactly because we can count event rates of external observers as measured by our own evet rate counters and compare the compare the incongruities. If time existed independently of these event counts why would the difference in events counts result in an actual difference in time rates per Lorentz? The one issue that imposes any other constraints that might qualify as indicating "count" is not "sufficient" is the extra constraint imposed by causality itself, i.e., the same event cannot occur both before and after a reference event at a point in space.

There are some events which counting them doesn't measure time because the events are separated by space, not time.
In those situations where the event count does not match your own local event count then you are measuring is not your own event count but somebody else's. Which we know to be real differences in real time else you could not come back younger than your own kids. The separation by space rather than time is moot by the inverse relation between space and time such that empirically they are not separate quantities.

There are other events which counting them does not measure time because they are at random intervals.
The randomness of an interval does not invalidate the linearity of those intervals on average. The rate of molecular collisions also have highly random intervals. Yet in order for Gibbs ensembles to have any empirical meaning they must average to a constant if equilibrium is maintained. This is the physical basis of emergent gravity theories based on relations defined by Brustein and Hadad and others where equilibrium is not maintained.
http://arxiv.org/abs/0903.0823

Randomness of intervals do not have any relevance to the constancy of average intervals one way or the other, but it would have relevance to the certainty with which we could, even in principle, determine a precise location in space or time relative to any observer.

For still other sets of events you have a good feeling that they are measuring time, but you have to scale your counts in order to say that they are all measuring time.
If I locally measure an inertial string and say it has a lengths of X and you measure it locally and say it has has a length of Y, why must we scale X and Y so to be equivalent? Because we are measuring the "same" string. Same thing if we are both measuring the "same" general set of local events. How do you treat background independence by any other means?

So for all of these reasons there is more to measuring time than simply counting events.
For all those same reasons, plus background independence causality, "counting events" is completely "sufficient".

All of these objections can be addressed, but to do so requires that you identify something about the various counts beyond the mere counting itself.
Yes, they can be enumerated as such:
1: Causality - The same event A cannot occur 'both' before and after event B at any given point in space-time.
2: Background Independence - The rate of a non-observable is empirically moot irrespective of what role it plays in the theoretical framework.
3: Relational, i.e., Relativity - The only value we can measure are not naked values, rather ratios which we assign a specific value to as though our local base event sets defined absolutes.

The very fact that you can use counts of a variety of sets of events (properly scaled) to measure time indicates that there is something else besides simply the counting.
Yes causality constraints. Yet the fact that locally the event sets being measured in for all practical purposes the same set of events requires that both measures scale together. Hence the scaling requirement is a physical requirement of consistency. Not some magical entity that exist in a matter free background.

Unless you already have some concept of time already then there is no way to distinguish between spacelike sets of events and timelike sets of events.
Absolutely true and well established physics, which is precisely why we get the so called clock paradox in SR. We can only make such distinction locally, due to the fact that we are essentially measuring the same space-like and time-like sets. Once you consider other points in space-time what you say here about the event count ideology is exactly true and well defined by Relativity. You can only pretend that space and time-like intervals are unique in pair of reference frames by assuming that one of those frames has a special status in its capacity to define those distinctions.

Unless you already have some concept of time then there is no way to determine if the scaling is correct.
If a ruler and a string were all that existed in the Universe how do you know the scaling of the ruler is correct. With background independence (also called coordinate independence) 'correctness' of a scale makes no difference whatsoever. We know that the ruler can linearly scale to itself and we know the ratio between the ruler and the string, what else empirically matters? How big the ruler and the string both are is a physically absurd empirically moot question.

What the counts and their scaling do is to define a unit of time, not to define time.
So if a Hilbert space is a mathematical tool with no 'real' physical significance, what makes the mathematics of defining time so special that somehow it is not only more real but 'real' independently of the intervals we measure? (That is not saying it is dependent on our choice of interval sets.)
 
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  • #68
atyy
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@DaleSpam: @my wan: Is the difference between your points of view that physics is always the study of change dy/dx, but if there is only one "dimension" DaleSpam would call that "space" and my wan would call it "time"?
 
  • #69
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In those situations where the event count does not match your own local event count then you are measuring is not your own event count but somebody else's.
No, the count of a set of spacelike separated events is not measuring anyone's time.

For all those same reasons, plus background independence causality, "counting events" is completely "sufficient".
Yes, they can be enumerated as such:
1: Causality - The same event A cannot occur 'both' before and after event B at any given point in space-time.
2: Background Independence - The rate of a non-observable is empirically moot irrespective of what role it plays in the theoretical framework.
3: Relational, i.e., Relativity - The only value we can measure are not naked values, rather ratios which we assign a specific value to as though our local base event sets defined absolutes.
Yes causality constraints.
You are contradicting yourself saying that "counting events" is completely sufficient and then adding constraints. The "time is counting events" definition is clearly insufficient as you have de facto conceded. You must add such enumerated constraints or clarifications as above.

The causality constraints are particularly problematic for a definition of time. Causality requires a notion of time, so putting a causality constraint into your definition of time makes the definition circular. In particular, without a definition of time how do you determine "before" and "after"?

Btw, I am not opposed to a background independent relational definition of time. I just think that "time is counting events" is way oversimplified. Something this important needs quite a bit more effort and care than that. Many things which qualify as counting events do not qualify as measuring time.
 
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  • #70
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@DaleSpam: @my wan: Is the difference between your points of view that physics is always the study of change dy/dx, but if there is only one "dimension" DaleSpam would call that "space" and my wan would call it "time"?
I have not asserted a point of view here, I am only pointing out that "time is counting events" does not work. I believe that I understand my_wan's motivation, I think he wants to avoid the Newtonian idea of time as some undetectable thing which flows and instead focus only on the physical observables. I agree with that goal; I just think that his approach is not right.
 
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  • #71
atyy
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I have not asserted a point of view here, I am only pointing out that "time is counting events" does not work. I believe that I understand my_wan's motivation, I think he wants to avoid the Newtonian idea of time as some undetectable thing which flows and instead focus only on the physical observables. I agree with that goal; I just think that his approach is not right.
That's sounds interesting. Is the undetectable point of view to define time as the proper time along a time-like curve even though no physical clock exists on the curve? Is the detectable point of view to define time via a clock such as the number of vibrations of an atom/light?
 
  • #72
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The undetectable view would be something along the lines of Newton's definition of "absolute" time or Lorentz's definition as "real" time in the aether frame. I wouldn't be bothered with something that is detectable in principle (like the proper time along a curve) even if you don't detect it, but I don't know my_wan's opinion on something like that.
 
  • #73
atyy
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The undetectable view would be something along the lines of Newton's definition of "absolute" time or Lorentz's definition as "real" time in the aether frame. I wouldn't be bothered with something that is detectable in principle (like the proper time along a curve) even if you don't detect it, but I don't know my_wan's opinion on something like that.
Why is Newtonian time undetectable in a way that the proper time along a time-like curve isn't?
 
  • #74
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Why is Newtonian time undetectable in a way that the proper time along a time-like curve isn't?
Because Newton defined it that way:

"Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time"

So here he expressly differentiates between "apparent" time and "true" time based on the idea that "true" time cannot be detected even in principle.
 
  • #75
atyy
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Because Newton defined it that way:

"Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time"

So here he expressly differentiates between "apparent" time and "true" time based on the idea that "true" time cannot be detected even in principle.
Oh, I was just thinking that Newtonian time is the t when the equations are expressed in an inertial frame. Would that definition be detectable (in principle)?
 

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