Relativity Explained Via Movement, Not Time

[Dale]

The same stuff when you try to ask questions like which clock is "really" go slower.

Do you have a good definiton of the word "real"? I certainly don't. Without one you will always run into trouble whenever you ask any questions about the reality of anything. That is hardly any kind of argument against that thing.

Gr effects makes invariants verses constants issue even more relevant, since it distorts SR in ways that makes the constants more like a choice. Take the apparent mass of an object as its depth in a gravitational field varies. Einstein chose perfectly sensibly to define it as 'apparent' mass. But if you get exactly the same effect if the 'apparent' gravitational constant was what varied, or even the 'apparent' speed of light. In Einstein' words:



In context this does not invalidate the constancy of the speed of light. This general feature extends to all invariants, not constants. Hence the QG community has their controversy over how much this applies to Planck's constants. This is also the basic theme behind "doubly special relativity". Note why GR gets in trouble with Planck's 'constant' when in terms of Planck length and time:
c = \ell_p/t_p
Planck mass:
m_P=\sqrt{\frac{\hbar c}{G}}
So you can take any first order quantity and express it in terms of pure constants, called the indefinables of physics (space, time, and mass/energy), where all must 'locally' be invariant or more generally some multiple thereof. Yet globally they vary, in the same way light speed does in GR, where the manner in which they vary is both frame dependent and definition dependent, like the apparent mass verses apparent value of G. That is where the so called varying speed of light (VSL) theories get their 'theoretical' legitimacy from. Not from any claim that the speed of light 'actually' changed, as Einstein articulated following the quote I give above.

None of this seems to indicate why using the metric is a bad idea.

As you and I have already agreed, you cannot simply count events to get time, you must add some additinal constraints. In particular you mentioned causality and scaling, both of which are provided by the metric. So I don't see any difference between defining time in terms of counting events with scaling and causality constraints and defining time in terms of the metric.

 

[Islam Hassan]

In your estimation, that "something else" should be physical and not a man made notion. For otherwise, you'd simply be replacing what you believe to be one man made notion for another ... and then the big question is, would anything be gained or lost?

GrayGhost,

Yes I believe something would be gained, at least for laymen like myself. The phenomenon which led me to consider movement instead of time as the focus of an explanation for relativity is that of 'time' stopping at the speed of light (or at anything approaching the speed of light for a massive object). I found this very difficult to understand intuitively. Then I tried to reason from a movement perspective and found that an intuitive explanation suddenly snapped into place. The following is how it happened:

- A fan say, or any mechanical object traveling at 0.99999... the speed of light would gain mass according to special relativity. The closer it gets to c, the more massive it becomes and as it tends more to c its mass tends to infinity;
- It takes infinite energy to move a mass tending to infinity; and
- Therefore with the limited electrical energy feeding its motor, the fan's movement will tend to absolute immobility.

Explained this way, the layman that I am understands the phenomenon easily and intuitively. Explained in terms of the semantically funky 'time dilation', such is not the case at all.

I can quite understand that seasoned physicists are quite used to the present terminology and don't really need any other 'interpretation' to make sense of SR; my focus, as I said is on the layman for whom relativity can be quite a daunting proposition...

This is one example but I am sure there are others. My basic thesis therefore is that explaining relativity at the most basic, phenomenological level makes it more easily comprehensible. Just a lay opinion of course, but there you go...

I'm still working on your challenge re a simple example of how the extent of relative motion would be quantified w/o using time; get back to you soon.

IH

 

[dm4b]

All the spacetime metrics that I know of are relativistic.

Euclidean Metric

 

[my_wan]

Do you have a good definiton of the word "real"? I certainly don't. Without one you will always run into trouble whenever you ask any questions about the reality of anything. That is hardly any kind of argument against that thing.

As far as the word real, if someone is asking which clock is really going slower they are almost certainly assuming a Euclidean metric, such as in Newtonian physics. We know the absolutes this entails to be wrong. Hence specifically what is 'meant' by the the word 'real' is moot when the question itself entails demonstrably invalid assumptions.

None of this seems to indicate why using the metric is a bad idea.

Which metric? A Euclidean metric is demonstrably wrong in the general case. In terms of scale any coordinate choice is a nonphysical choice even if you apply the transforms needed to give a Euclidean metric some level of observer dependent validity. By assuming time is an independent variable from the events it 'smells' of Newtonian time with an added feature of malleability. This is not so.

Suppose you go 86% the speed of light getting a dilation factor of 1/2. To you time did not dilate, the distance to your destination was cut in half. Now suppose you decrease gravitational depth to the field around the ship to erase the relative time dilation factor between you and back home. Only now, without changing your proper motion from Earths perspective, you see as measured by you that you have twice as far to travel to get to your destination, hence will take you twice as long. The same amount of time it appears to take you from Earths perspective.

You cannot separate time from the events you observe under any circumstances, at least not without playing 'what if' games with energy conditions outside observable reach.

As you and I have already agreed, you cannot simply count events to get time, you must add some additinal constraints.

I agreed that saying time is a "bit oversimplified", not invalid. I would have left the debate there except that you quoted that naked sentence while the qualifiers that followed was ignored. In fact you can (and it is in fact what we do) to not only define time but to derive all the relativistic Lorentz transforms when event counts do not match.

When we measure something we record a series of events. Then we curve fit these events as if they occur on a continuum. Whether they actually do exist on a continuum or not is immaterial, as what we empirically record is not the continuum but a discrete series of events. So in fact everything we empirically know about time was derived from a discrete series of events, i.e., "what we measure".

In particular you mentioned causality and scaling, both of which are provided by the metric.

So you are using metric in the very narrow sense of a particular type of metric. Euclidean metrics explicitly require transforms for the very fact that they are not valid in the more general case. You say they are "provided by the metric", implicitly meaning Lorentz metric rather than metric. Even so you have a major reversal of logic here. The event count is not "provided by the (Lorentz) metric", the Lorentz metric is provided by the event count. Such as flashes of light on a train in Einstein's SR derivation. This reversal of logic is confusing to a lot of people. The empirical events justify the theory, the theory does not justify the empirical data.

So I don't see any difference between defining time in terms of counting events with scaling and causality constraints and defining time in terms of the metric.

Again, you implicitly referred to the Lorentz metric 'only' as if it was "the" metric. Yet the Lorentz metric was explicitly derived from discontinuities in counting the same discrete events from alternate perspectives and noting that they did not match the local discrete event counts in each of those perspectives. If no events occur there is nothing to count or do the counting hence the notion of time is moot. It is in fact discrete event from which the Lorentz metric was derived, however much we theoretically idealize it after the fact.

 

[atyy]

It is in fact discrete event from which the Lorentz metric was derived, however much we theoretically idealize it after the fact.

But if you want to have "theory-free" definitions, how can you even define an event?

Also, if you didn't need the theory to define time, how do you explain that we have theories with a preferred time, as well as theories with many times?

 

[Dale]

Which metric? ...
So you are using metric in the very narrow sense of a particular type of metric.

This is a relativity forum, so I am using "the metric" in the usual sense in relativity. I.e. the unique metric for a given spacetime manifold. There is only one for any given spacetime, so it is not just narrow, it is unique. It is never Euclidean so the bulk of your post is rather irrelevant.

I thought that this standard meaning of the phrase "the metric" would be well-understood by anyone posting here; I apologize for my poor communication.

The event count is not "provided by the (Lorentz) metric"

I never said it was. The scaling and causality constraints are provided by the metric. When you take a set of events, add a causality constraint, and scale it appropriately, and call the result "time", then you have done nothing more nor less than evaluate the metric between the events.

 

[my_wan]

But if you want to have "theory-free" definitions, how can you even define an event?

Also, if you didn't need the theory to define time, how do you explain that we have theories with a preferred time, as well as theories with many times?

I am not talking about "theory-free" definitions. I am talking about the fact that theory is empirically driven, not the other way around.

With respect to "preferred time" do you mean direction? I do not want to answer that presumptuously as I can relate it to too many concepts. However, I do not know in what way I said you do not need "theory to define time". I said that the legitimacy of theory is predicated on and justified by the empirical data, not the other way around. Without which it is nothing more that philosophy. And that this empirical data, as it relates to time, was in fact the result of counting discrete events. The fact that we need a theory for operational consistency does not raise theory above the empirical constraints it is predicated on.

My initial statement, which has been taken issue with, is that time can consistently be viewed in terms of event counts. A bit simple, but fully defensible empirically. When Einstein said "time is what we measure" it was simplistic also. My statement merely boils down to defining "what we measure", and that is discrete series of events. Theoretically it works whether it comes in discrete steps or not, but the fact remain: We measure discrete series of events.

 

[Dale]

My initial statement, which has been taken issue with, is that time can consistently be viewed in terms of event counts. A bit simple, but fully defensible empirically.

The complexities glossed over by the "bit simple" are important, as we have discussed. An arbitrary event count is NOT a measure of time without the causality and scaling constraints.

 

[my_wan]

This is a relativity forum, so I am using "the metric" in the usual sense in relativity. I.e. the unique metric for a given spacetime manifold. There is only one for any given spacetime, so it is not just narrow, it is unique. It is never Euclidean so the bulk of your post is rather irrelevant.

I thought that this standard meaning of the phrase "the metric" would be well-understood by anyone posting here; I apologize for my poor communication.

Are you saying that because I am on a Relativity forum I cannot use "metric" in the general sense, which includes any choice of coordinate system? It is GR that prides itself the most on treating all coordinate systems equally.

Perhaps some of these points are a bit on the pedantic side, but no more or less so than taking issue with defining time in terms of event sequences.

I never said it was. The scaling and causality constraints are provided by the metric. When you take a set of events, add a causality constraint, and scale it appropriately, and call the result "time", then you have done nothing more nor less than evaluate the metric between the events.

Funny, I can turn this around again and say "causality constraints" is not "provided by the metric", the "metric" is provided by the "causality constraints".

I wonder, how much of this inversion of logic is behind many of the established controversies in science?

 

[my_wan]

The complexities glossed over by the "bit simple" are important, as we have discussed. An arbitrary event count is NOT a measure of time without the causality and scaling constraints.

The same constraints I qualified with both before you responded and in my first response to you. The "bit simple" was no more or less "bit simple" than "time is what we measure". That was the point of the post where I said that. Only you chose to chop out the "bit simple" part for your quote of me.

 

[atyy]

With respect to "preferred time" do you mean direction? I do not want to answer that presumptuously as I can relate it to too many concepts. However, I do not know in what way I said you do not need "theory to define time". I said that the legitimacy of theory is predicated on and justified by the empirical data, not the other way around. Without which it is nothing more that philosophy. And that this empirical data, as it relates to time, was in fact the result of counting discrete events. The fact that we need a theory for operational consistency does not raise theory above the empirical constraints it is predicated on.

I just meant that each frame has its own coordinate time, and each worldline has its own proper time. So in relativity, we have many different things called "time". It seems to me that the theory is needed for that, not the "data" alone, whatever that may be. I guess time is a concept, or many different concepts, so it must be determined by the theory.

My initial statement, which has been taken issue with, is that time can consistently be viewed in terms of event counts. A bit simple, but fully defensible empirically. When Einstein said "time is what we measure" it was simplistic also. My statement merely boils down to defining "what we measure", and that is discrete series of events. Theoretically it works whether it comes in discrete steps or not, but the fact remain: We measure discrete series of events.

If all you have are events, how do you order them? Isn't it conceivable that events may not be ordered at all? Do you allow that time could be like space, whose points can't be ordered on a line (http://arxiv.org/abs/hep-th/0008164" )? Or is every possible order a possible time (which is what proper time is, with the restriction to timelike orderings)? Also, if spacetime is continuous, and all we have are continuous fields on the manifold, how do you "count" events?

I came across an interesting "[url[/URL]: "The question of the validity of the presuppositions of geometry in the infinitely small hangs together with the question of the inner ground of the metric relationships of space. In connection with the latter question... the above remark applies, that for a discrete manifold, the principle of its metric relationships is already contained in the concept of the manifold itself, whereas for a continuous manifold, it must come from somewhere else. Therefore, either the reality which underlies physical space must form a discrete manifold or else the basis of its metric relationships should be sought for outside it[...].

 

[harrylin]

There is no clock that will measure time independently of movement. And conversely, nothing ever happens that does not move.

Why then do physicists persist in using the notion of "time" in explaining relativity? It would be so much easier, more intuitive and correct to talk of (relative) movement and not time. Things like "time" stopping when we perceive a massive projectile traveling at the speed of light: "time" is a purely anthropic notion that neither begins nor stops since it has no physical existence in itself. What will stop is *movement* this is intuitively easy to understand since mass tends to infinity at the speed of light and you require infinite energy to make it *move*.

Why are physicists so hooked on "time" when only movement exits. I believe that explanations of physical phenomenon -including relativity- would be so much easier using *movement* instead...

IH

For centuries people have the habit to describe mechanics with "length" and "time"; therefore relativity is also expressed in those terms. That has nothing to do with "explanations".

What you write reminds me a bit the understanding of Poincare and Einstein at the start of relativity theory: "time" is after all a count of the repetitive motions of clocks.

Harald

 

[Dale]

Are you saying that because I am on a Relativity forum I cannot use "metric" in the general sense, which includes any choice of coordinate system? It is GR that prides itself the most on treating all coordinate systems equally.

The metric doesn't place any constraints on the coordinate system. It is a feature of the spacetime manifold, not the coordinate system. There is no coordinate system where the metric is Euclidean.

Funny, I can turn this around again and say "causality constraints" is not "provided by the metric", the "metric" is provided by the "causality constraints".

I am fine with that, but either way the metric is equivalent to a set of events with scaling and causality constraints. Without those constraints your count of events is not time and with those constraints they are equivalent to the metric.

 

[energydady]

REFERENCE FRAME is made of time and space in this theory. Space don't move, all movement you get coz of time. Even you measurement stick (speed of light) include time but beyond time (as theory say, hey my limitation is light speed, means i can't show you near light speed or on light speed, or i m not valid at light speed, under this you can trust me). Using this theory, Estein put time under pocket of speed of light and declare it a constant or limitation.
it convert: E= MGH+1/2MV2 IN TO E=MC2, no gravity, no interaction (H), no speed/time stuff. Only mass based thing.

 

[time_nerd]

At the fundamental level the universe is changing and in that sense there is a tension between the demands of the unfolding complexity and the altered entropic state of the universe. We can understand the change of the universe as 'temporal sequences' or phases but again all this refers to are different levels and layers of organisation we can see in the physical world. This however, is not time, although there is tempo and rhythm.

Even when the physical world settles down and the natural world emerges from this process there is still not 'time' but there is without question temporal sequence and different tempos depending on what system(s) grab your attention. This changes profoundly, dimensionally when humans emerge from the natural world and we have the beginning of the social sciences, arts and humanities.

The informational range that human engage in/through is meaning and all informational changes (informing motion) are interwoven with time, because they are time. They are the way we socially and meaningfully understand the changes all around us, as content and in connection with other changes. This is tricky to get across in a few lines but the present is a tension between/as time and meaning, and we call it 'meantime'. The effects of meantime are stored in placetime which acts as a memory providing a regulating rhythm to meantime(s).

Going geekier, time in this understanding is 'spin up' at the quantum level and meaning is 'spin down'. So it's no coincidence that social change is referred to as 'changing times', indeed the term zeitgeist is 'spirit of the age'. Term is the single word that pulls these two ideas together best:
1. the naming of something, and
2. a period of time

This shakes up our present way of understanding causality as cause and effect because time is meaning, and meaning is time, causes are effects and effects are causes. So if you live in an indigenous tribal community and the terms and conditions of human life are relatively unchanging then there is no time, and this is born out through anthropological evidence of tribes often having no word for time.

Summarising these points, meaning is the metric of human experience, and time is the metric between experiences. If you do something that is meaningful (a blend of cognitive and emotional experience) then time has to fly, it can't be different. However, 'informing motion' remains non-corporeal although the effect is very real, although relative.

We can see the trouble 'time' as a metric between experiences has when it comes to measuring the length of the universe. 'Time' as a social organised, human metric always has to have some kind of oscillation providing a regularity of measurement. Over the history of clocks and calendars we can see this with current move away from cesium atomic clocks to even more sophisticated ways of measuring time. However, there remains a profound misnomer when we use 'light years' as a metric for age of the universe and this does physics no favours at all.

Light years are a unit and measurement of distance and to say that the Universe is 13.7 billion light years away is to make a statement of distance, not duration. However, often high-profile communicators of science make this error. That is not to say that the Universe isn't really, really old, of course it is. As I have said every 'time' has to have an oscillating base from which to measure. I've worked this out in the past and traveling in a car at 60mph and heading off towards the big bang it would take me 1.123 billion billion billion years. Big difference between that and saying 13.7 billion years.

I'll leave 'time' as the tension between complexity and entropic capacity for another moment, but 'time' (as capacity) is certainly something we can run out of, so it's real although non-coporeal, like so much 'informing motion' around all of us.