Relativity Explained Via Movement, Not Time

  • #26
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This is all getting very confusing very quickly...regarding defining movement without an implicit involvement of time however, how about this: when my car has travelled X meters, i measure the distance travelled by a ray of light which was emitted as the car started to move. My car would then have travelled an equivalent Y meters of light. This is how I would think of doing it since light is my absolute displacement reference.

IH
I think this is going in the right direction. This scenario necessarily involves temporal markers 'when', 'has (travelled)', 'was', 'then' etc, and the notions of signals and 'simultaneity'. If you follow through long enough, you will have to deal with time. Einstein also had to wrestle with such things and the whole thing was inextricably entangled in time. At least that's an impression I recall when I went through his little book on SP years ago.
 
  • #27
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I actually have to support Hassan to a degree. I would qualify it more as an event sequence but to say it has some absolute reality outside of the event sequence used to measure it smacks of Newtonian physics to me. It is this artificialness as an independent variable that gets us in trouble with common notions of simultaneity.
Time is mysterious, but not artificial. It was Einstein's insight that length and time are bound inextricably in a cosmic ying-yang: specifically the L/t 'c', and that that value is a constant, either by measure, or by axiom.

length and time both are relative to this fixed value, still a very counterintuitive notion.
 
  • #28
atyy
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Agreed, and I would add that the operative word in your post is "derive". Our measure of time can only ever be indirect, via phenomena -like frequency- linked to movement. Nothing *in* the photon is moving but its frequency is linked to a dynamic phenomenon, that of its wave-like nature. So we are back to movement...

IH

[I am quite the layman, and may be making a right fool of myself here, but this time thing has been bugging me for a while now...]
This is possible in special relativity. The speed of light (movement) is defined to be fundamental and exact, while the second is defined as an integer number of periods of a certain vibration (movement). (I seem to have used "movement" in 2 different ways there!)

http://physics.nist.gov/cgi-bin/cuu/Value?c
http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html

You can also look at Woodhouse's notes http://people.maths.ox.ac.uk/nwoodh/sr/index.html [Broken], p12, where he says we don't know what a thing is unless we specify how we measure it. He proposes to accept vibrations (movement) of an atom as fundamental, and from there define a clock (time).

Another line of thinking that seems related to your intuition is given by Barbour in http://arxiv.org/abs/0903.3489 .

Generally, there are many notions of "time" in physics - coordinate time, proper time, cosmological time, second law time etc. So a proper discussion usually needs to specify which "time" one is talking about. Although I have agreed with you to some extent that time is most easily defined if we have vibrations, it is actually not necessary. In Newtonian physics, time is defined so as to make Newton's second law (movement!) true.
 
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  • #29
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This is possible in special relativity. The speed of light (movement) is defined to be fundamental and exact, while the second is defined as an integer number of periods of a certain vibration.

http://physics.nist.gov/cgi-bin/cuu/Value?c
http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html

Another line of thinking that seems related to your intuition is given by Barbour in http://arxiv.org/abs/0903.3489 .
The link is using time, in m s-1. That's an L/t relationship. Also 'period' entails time.
 
  • #30
pervect
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The quantum-mechanical transitions that occur in an atomic clock are only vaguely related to any physical "movement" or motion.

So, I don't think the case for making movement "more fundamental" than time is very good at all when analyzed properly.

Physics actually does a pretty good job of separating time into at least two very different but useful notions which are (IMO) commonly confused and conflated by the non-physicist.

Proper time is the time measured by a clock. In the language of physics, its an interval of time, similar to the way the meter is an interval of space. Proper time is what you measure with a clock. It is well defined, the SI unit of time is a specified transition of a certain quantum-mechanical transition of a particular isotope of cesium, and it doesn't "slow down" or "stop" in any meaningful sense.


Coordinate time is the assignment of a time coordinate to events for bookeeping purposes. Physics recognizes that this assignment is more or less arbitrary. It's the laypeople here who often get the most confused (in my opinion, anyway).

Coordinate time leads to the notion of comparing distant clocks, to create an "instant of time", a "now". This notion is more or less subjective as physics recognizes (though it seems to be a problem often to get the lay audience to come to the same realization.) It's a totally different notion of time than the notion of proper time.

Coordinate time, also leads to the concept of time "slowing down", when one measures the actual proper time that elapses with a clock given a particular choice of coordinate systems. In my opinion, the popularizations that think of time as slowing down miss the point. Time always passes at 1 second per second - it's the coordinate system that changes, not anything related to the rate at which time "happens".

Since the coordinates are a purely human invention, and furthermore a matter of convention -one is free to chose to use different coordinate systems - it's somewhat illogical to give them such priority. But many people do anyway.

So, in conclusion, I think time is here to stay, and is a much better basis that "movement" to describe physics. However, it is useful to break the notion of time down into separate issues, the notion of proper time, which one measures with a clock, and which is independent of the observer, and the notion of coordinate time, which is a convention that is observer-dependent.
 
  • #31
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Time is mysterious, but not artificial. It was Einstein's insight that length and time are bound inextricably in a cosmic ying-yang: specifically the L/t 'c', and that that value is a constant, either by measure, or by axiom.

length and time both are relative to this fixed value, still a very counterintuitive notion.
Time is only intrinsic to the degree that the sequence of events at a given point cannot involve the exact same event happening both before and after a reference event. Yet it becomes undefined relative to a separable point, hence both really simultaneous and really not simultaneous at the same time if time is given an independent status. Hence a violation of the principle of contradiction. Same thing happens when consider you how long now is relative to another observer. Two observers at 86% C are correct in saying that their now is twice as big as the others now.

If I claimed to have a light switch that stopped time in the Universe for a day, what would be the physical consequence if the claim was true? Zilch, nothing. It would have no empirical consequence whatsoever. Not even the day it was supposed to be turned off is real, since there is no events to define a day. How the information defined in a physical event set can vary in relation to one another to allow relativistic time dilation is trivial to outline. How such time dilation can somehow manipulate time defined as an independent variable seems to require a magic wand. Do you need an outline of a mechanistic analogy of the relation between space and time (not a claim of how it 'really' is)?
 
  • #32
ZapperZ
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This is all getting very confusing very quickly...regarding defining movement without an implicit involvement of time however, how about this: when my car has travelled X meters, i measure the distance travelled by a ray of light which was emitted as the car started to move. My car would then have travelled an equivalent Y meters of light. This is how I would think of doing it since light is my absolute displacement reference.

IH
That light would have traveled a distance in a particle time! It doesn't do that instantaneously! There is a time component here!

Zz.
 
  • #33
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Pervect pretty much nailed it. The second notion of time (not proper time) in my opinion is merely the consequence of requirement to impose causal constraints on the order of such events. Hence it is a bookkeeping or symmetry that appears sort of like a background time. But is is just a causal constraint, not some absolute that runs independently from the proper time.
 
  • #34
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Time is only intrinsic to the degree that the sequence of events at a given point cannot involve the exact same event happening both before and after a reference event. ....

If I claimed to have a light switch that stopped time in the Universe for a day, what would be the physical consequence if the claim was true? Zilch, nothing. It would have no empirical consequence whatsoever. ...Do you need an outline of a mechanistic analogy of the relation between space and time (not a claim of how it 'really' is)?
The way you use time-markers tells me that 'time' is a very real psychological/linguistic entity. The way physicists use 'time' likewise indicates they regard it as not only real, but in the formalism of 4-space description, entirely interchangeable with 'space'. And Einstein necessarily needed time in his analysis of simultaneity: things either happen at the same 'time', or they do not. 'Events' are informally time entities, not space or movement entities. One could almost consider an 'event' a motionless scalar thing.
 
  • #35
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Pervect pretty much nailed it. The second notion of time (not proper time) in my opinion is merely the consequence of requirement to impose causal constraints on the order of such events. Hence it is a bookkeeping or symmetry that appears sort of like a background time. But is is just a causal constraint, not some absolute that runs independently from the proper time.
The thing is the thesis of this post: Relativity explained via Movement, not "Time". In fact, we could re-write the title:

'Relativity Explained by L/t, not "t".'

Well enough. I don't think that's too far from what Einstein said, the L/t in question being c, which is a constant in all observers' frames of reference. Sorta QED, no?
 
  • #36
atyy
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OK, let's try to see if some version of Hassan's proposal can hold. How about "time requires movement, but movement does not require time"?

Let me define movement as change dy/dx. dy/dx does not require time, since x, especially if x is 3D Euclidean space in Newtonian physics, doesn't seem to be necessarily time.

However, time requires dy/dx to be operationally defined, in some special cases where x = "time".

In this sense movement is primary, but time is not.
 
  • #37
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I believe that explanations of physical phenomenon -including relativity- would be so much easier using *movement* instead...

IH
How would you explain relativity using movement instead of time? In particular, how would you make the quantitative experimental predictions of relativity without time?
 
  • #38
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The thing is the thesis of this post: Relativity explained via Movement, not "Time". In fact, we could re-write the title:

'Relativity Explained by L/t, not "t".'

Well enough. I don't think that's too far from what Einstein said, the L/t in question being c, which is a constant in all observers' frames of reference. Sorta QED, no?
:approve:

There it is. A lot of OPs are started with a sliver of recognition followed by alphabet soup.
 
  • #39
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4


Originally Posted by danR
The thing is the thesis of this post: Relativity explained via Movement, not "Time". In fact, we could re-write the title:

'Relativity Explained by L/t, not "t".'

Well enough. I don't think that's too far from what Einstein said, the L/t in question being c, which is a constant in all observers' frames of reference. Sorta QED, no?


:approve:

There it is. A lot of OPs are started with a sliver of recognition followed by alphabet soup.
Let me clean it up a bit then:

The OP could be titled:

'Relativity Explained by Length/time, not time.'

For Einstein the Length/time in question being distance travelled by light/time, which is a constant in all frames of reference. So we are right back stuck with time, and Einstein and everyone still using time are actually still right to do so, Which was the thing to be demonstrated (by way of rebuttal).
 
  • #40
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4


OK, let's try to see if some version of Hassan's proposal can hold. How about "time requires movement, but movement does not require time"?

Let me define movement as change dy/dx. dy/dx does not require time, since x, especially if x is 3D Euclidean space in Newtonian physics, doesn't seem to be necessarily time.

However, time requires dy/dx to be operationally defined, in some special cases where x = "time".

In this sense movement is primary, but time is not.
Only by treating time as a spacial axis. This seems akin to a Minkowski manifold.

But now there is no movement!
 
  • #41
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Let me formulate the subject a little differently then: does time exist in the sense of some immaterial yet physically effective 'ether' flowing through space? To my (rather confused) mind if it is immaterial in the sense that it is not observable *in itself*, it does not exist per se but is a practical concept we evolved in order to facilitate communication.

IH
 
  • #42
ZapperZ
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Let me formulate the subject a little differently then: does time exist in the sense of some immaterial yet physically effective 'ether' flowing through space? To my (rather confused) mind if it is immaterial in the sense that it is not observable *in itself*, it does not exist per se but is a practical concept we evolved in order to facilitate communication.

IH
This is a very tired topic because it has been discussed ad nauseum in this forum.

It is also quite confusing because you are asking for whether time, which can be measured quantitatively, can be defined using some esoteric, undefined quality ("immaterial yet phyically effective ether flowing through space"). That's like asking how physics can be defined using metaphysics! All of this is ignoring the fact that space itself can't be decoupled and separately measured without time!

Considering that there are numerous phenomena that are characterized by their broken time reversal symmetry, from that point of view, it is awfully silly to ask if time exists.

Zz.
 
  • #43
dx
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Independent 'existence' of space, time as well as matter is charactertic of Newtonian physics, i.e. we imagine a 'space' which is 'unaccelerated', and point particles (which in principle are imagined to constitute material objects) moving in this space. Thus we ascribe physical reality to space as well as to its state of motion. This is necessary because the idea of acceleration appears in Newton's law of motion. The same applies to time, which likewise enters into the concept of acceleration. So to summarize, in Newtonian physics 'physical reality' consists of space, time and material points moving with respect to space and time.

In the special theory of relativity, the four dimensional continuum of spacetime is no longer objectively resolvable into space and time, but this space (Minkowski space) occurs as an independent component in the representation of physical reality as carrier of matter and field.

In the general theory of relativity, the inertial frame loses its objective significance for the following reason. A frame accelerated with respect to an inertial frame can be thought of as an inertial frame together with a uniform gravitational field. Thus, space, as opposed to what fills space (represented by fields, and which depend on the coordinates) has no independent existence.
 
  • #44
atyy
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Let me formulate the subject a little differently then: does time exist in the sense of some immaterial yet physically effective 'ether' flowing through space? To my (rather confused) mind if it is immaterial in the sense that it is not observable *in itself*, it does not exist per se but is a practical concept we evolved in order to facilitate communication.
All quantities in physics are not observable "in themselves". For example, what is a charge? What is an electric field? There isn't a concept of charge independent of the field, and there isn't a concept of the field independent of the charge. Although there are formal solutions for fields without charges, we cannot observe these fields unless we have a charge.

All quantities in physics are concepts we evolved to consistently describe our observations, communicate with each other, and design devices that work the way we predict. But they are all (as far as we know) wrong at some level.

So a question about what "time" is, must take place within each of our limited but useful theories. Each theory will have its own definition of "time", which may overlap only partially with the notion of "time" in another one of our theories. Among these different notions of time are coordinate time and proper time of general relativity, cosmological time in the FRW solution of general relativity, thermodynamic time in the second law of thermodynamics, Newtonian coordinate time in Newtonian physics, psychological time in psychological experiments etc.
 
  • #45
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All quantities in physics are not observable "in themselves". For example, what is a charge? What is an electric field? There isn't a concept of charge independent of the field, and there isn't a concept of the field independent of the charge. Although there are formal solutions for fields without charges, we cannot observe these fields unless we have a charge.
Taken from wiki:
Electric charge is a physical property of matter which causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two negatively charged objects. the electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields.

Time is not matter, is a notion we use to determine movement of an object from A position to B , respective to another movement made from another object from C to D.
 
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  • #46
DaveC426913
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Electric charge is a physical property of matter which causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two negatively charged objects. the electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields.
Well there you go atyy; you have been educated on what electric charge is. :rofl:


Arens, seriously though. Quoting someone else's material - http://en.wikipedia.org/wiki/Electric_charge" [Broken] - without credit is forbidden, and will result in infractions.
 
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  • #47
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Ok thanks to everyone! Sorry I didn't realise that this topic had been discussed 'ad nauseam' before in PF: it was my very first post here. Will be more careful with my posts in the future.

At any rate, it seems that time is a considerably more intricate subject than I imagined; thank you again for your kind forebearance.

IH
 
  • #48
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I'm with you, Islam, except Time's not that complicated. Time's a count. Nothing more. I don't know why people make it so complicated. Aristotle started off okay, calling it a count, but he mucked it all up with the Now. And Einstein made it a fourth dimension and got everyone excited about space-time. But Time's a count. Even the NIST guys, who are supposedly measuring 'Proper Time' call Time a count right outside their clock. (Yep, I was there. It’s a big tube with mirrors all around. I even saw the new one, which wasn’t working. Really cool, the NIST guys and the clocks.) Here’s what the sign says:

“Time is defined as the accumulation of atomic seconds beginning 0000 Hours UT (Earth time) 1 January, 1958.”

That's why I can't go with ZapperZ:

"It is also quite confusing because you are asking for whether time, which can be measured quantitatively..."

Unless Time is defined as the changes in a cesium atom, or a count of changes, then Time can't be measured quantitatively. Every time you ask someone to measure Time, they find some counter that measures some change in something else. Clocks, sundials, whatever, they're all counters. And none of them works the same.

Even the NIST guys have to synchronize their clocks. They’ve got a few, and they only start the main one for a week every month so that they can set the others and then send out the official count all over the world. No clock counts the same all the time. It depends on where they are and the temperature and all sorts of things.

Atyy, though, got me thinking when he said that concepts in physics are wrong in some way. My problem is that whenever you look at a measure for just about anything, somewhere back there is little t. And little t is a count of some counter, which always changes, because how your counter works depends on where it is and what all the conditions are around it. Still, thinking’s good.
 
  • #50
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A count of what?
Events. Nobody can claim to absolutely know what a base event is or even if there is such a thing as a base event predicated on any particular ontology. Yet as long as there are events and systems are defined by sets of event, or sets of sets, and so on, then certain higher order events, linear relative to the base event sets of whatever ontology, can then be used as proxies to count said events. It works that way whether the system is purely mechanistic or it is merely relative to some abstraction of the laws of physics. Hence we have higher order measuring devices called clocks that count these linear events.
 

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