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Models for making sense of relativity - physical space vs physical spacetime


Tim88
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As I understand it, the mechanical aether was due to Fresnel.

 

A.J. Fresnel, Ann de chimie, at de physique. 9, 57 (1818)

 

That's probably right, in view of this paper by Stokes: https://en.wikisource.org/wiki/On_Fresnel%27s_Theory_of_the_Aberration_of_Light

Anyway, such a model is not compatible with SR.

I think that the reason why Relativity is more questioned than other physics subjects, is because it handles about things we can relate to our every-day life, and confronts us with the way we imagine the world.

 

For me, both models (3D space and spacetime) are complementary. I wonder why physicists so vehemently reject the first.

I understand that physicists feel more confortable with the 4D mathematical representation.

But as a layman, I don't have the impression that I live a 4D reality. Time, space and motion are physical notions for me. When I'm driving my car, I know I am in motion, not the landscape. And if I hit a tree, I don't think it's the kinetic energy of the tree that crashes my car.

Relativistic effects are much more understandable by thinking of a theoretical rest frame (maybe the frame wherein the vectorial sum of the velocity of all the particles of the universe is zero?). No ether is needed.

For me, nature is not weird at all (as far as relativity is concerned). c-invariance, time dilation, length contraction etc are all very understandable.

[..]

 

 

Your statement about physicists is not generally true. Historically ether theory was advanced by physicists, and block universe by a mathematician. I suspect that mathematicians and those with mostly mathematical skills prefer the block universe idea because "time", "speed of light" and "distance" are for them just symbols and variables. And for sure the mathematically difficult field of GR (at full precision) is practiced by mathematical physicists. Note that your "theoretical rest frame" is another word for "Lorentz ether".

 

And indeed, the main purpose of this thread is to make relativistic effects fully understandable for skilled laymen and practicing physicists.

For me also, ether theory makes more sense than block universe; but it is arguably uglier (at least, I disliked the idea) and for some people block universe is just what they need to make sense of relativity.

 

[edit:] just one little correction: no matter which of the two models for SR you use, "when I'm driving my car, I know I am in motion, not the landscape" is imprecise. Perhaps this is a good point to start explaining by means of the 3D and 4D views of reality.

 

Basic fact: similar to classical mechanics, you are free to choose the landscape as pretended "rest frame" (neglecting rotation).

1. Stationary ether (Absolute Space model): When you are driving your car, in general both your car and the landscape are in motion.

2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory.

 

I'm not sure if I introduced the block universe model altogether correctly as I don't find it intuitive; please correct if needed. Maybe my intuition for that model will be improved after the discussion here. :)

Edited by Tim88
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Tim88

And "rest frame" is another word for "Lorentz ether".

 

 

Are you referring to

 

H.A. Lorenz, The Theory of Electrons, Leipzig, 1916 ?

 

As I understand it this was introduced to modify earlier aether theories which foundered at the experimental fact that refractive index depends upon frequency.

 

The Lorenz rest frame was an inertial system in which the aether was at rest.

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But as a layman, I don't have the impression that I live a 4D reality. Time, space and motion are physical notions for me. When I'm driving my car, I know I am in motion, not the landscape. And if I hit a tree, I don't think it's the kinetic energy of the tree that crashes my car.

[...]

For me, nature is not weird at all (as far as relativity is concerned). [...]

But, of course, I also see that SR, with the 4D Minkowski spacetime, is a much more powerfull model and must be prefered for physics work.

Don't get confused with analogies for the block universe, or an earth-bound reality with our dense atmosphere keeping us dishonest. You do understand why astronauts float around in the ISS, no?

 

 

2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory.

 

I'm not sure if I introduced the block universe model altogether correctly as I don't find it intuitive; please correct if needed. Maybe my intuition for that model will be improved after the discussion here. :)

I am not sure if "selecting a slice" is the appropriate term, more like "experiencing a slice"..?

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The Lorenz rest frame was an inertial system in which the aether was at rest.

This is my understanding - so there is in Lorentz-Poincare models some aether, but the idea is that we can chose a frame for which this can be considered at rest. If this is possible, then there would be a preferred inertial frame. So, Lorentz's theory does not sit well with special relativity at all.

 

 

 

Tim88...

 

As for mathematical elegance, there can be no difference between the same mathematics - that is just nonsense!

I don't quite agree with this. The point is that when we pass to special relativity the mathematics is really based on the symmetries of Minkowski space-time. We have a clear geometric understanding of what is going on, and furthermore this leads to general relativity.

 

 

The Newtonian notion of space is not very different from the Lorentzian notion of "ether" (perhaps he should have used another word?); no additional "medium" is required.

There is no notion of absolute rest in Newtonian mechanics - but absolute time does make sense.

 

Minkowski's notion of space-time is 4 dimensional spacetime, as expressed by him in the reference I gave; it's nowadays called "block universe". What you call "the 3+1 dimensional notion of Minkowski space-time" is probably the 3+1 dimensional notion of Poincare space-time;

Of course I am think of Minkowski space-time... the total number of dimensions is 4, or as common we think of 3 space and one time dimension.

 

You probably did not know that in 1907 Einstein published a paper in which he presented the preceding work of Lorentz and his own as one and the same theory; and that was so because he considered the mathematical predictions, and not differences in philosophy. His own philosophy changed several times anyway.

Einstein and almost all of the other names at the time thought about how Maxwell's theory and related things could be understood in terms of some aether theory - whatever they meant by 'aether'. As the aether seems not to be required due to the work of Einstein and others, physics took another direction.

Edited by ajb
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[edit:] just one little correction: no matter which of the two models for SR you use, "when I'm driving my car, I know I am in motion, not the landscape" is imprecise.

 

You are right, that statement is quite imprecise. I meant that, at some time, the car accelerated wrt the landscape, and that in my opinion, that change in motion has a physical sense.

 

Don't get confused with analogies for the block universe, or an earth-bound reality with our dense atmosphere keeping us dishonest. You do understand why astronauts float around in the ISS, no?

 

Yes, I understand that, but the role of the atmosphere is unclear to me.

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ajb

This is my understanding - so there is in Lorentz-Poincare models some aether, but the idea is that we can chose a frame for which this can be considered at rest. If this is possible, then there would be a preferred inertial frame. So, Lorentz's theory does not sit well with special relativity at all.

 

This was your reply to my post#27, whilst I was pondering this additional comment.

 

Thank you.

 

Unfortunately the rest of your post#29 seems to have gone awry with some missing

tabs ?

 

It should be noted that Lorenz was a committed aether man.

 

Note the date of his 'electron theory', which was a long time after he proposed the contraction of length to explain the Michelson 1881 experiment.

 

H.A. Lorenz Amst Verk Akad v. Wet.1, 74 (1892)

 

The point is that up to the Michelson experiment all experiments yielded results accurate only to first order effects and consistent with an aether theory.

Michelson was the first to conduct experiments sensitive enough to detect the second order effects that would accompany any sort of aether.

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It should be noted that Lorenz was a committed aether man.

I have not read any of these old papers carefully - I have looked quickly at modern historical accounts - but my general impression is that people quickly became loose, and a careful description of the aether and its nature was missing. Maxwell passed to a more abstract notion and this I think that this heavily influenced Lorentz. One had to remember that this was all formulated before the modern formulation of fields.

Edited by ajb
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Are you referring to

 

H.A. Lorenz, The Theory of Electrons, Leipzig, 1916 ?

 

As I understand it this was introduced to modify earlier aether theories which foundered at the experimental fact that refractive index depends upon frequency.

The Lorenz rest frame was an inertial system in which the aether was at rest.

 

I was merely referring to bvr's "theoretical rest frame". Concerning Lorentz's ether concept, that's contained in many of his papers.

This is my understanding - so there is in Lorentz-Poincare models some aether, but the idea is that we can chose a frame for which this can be considered at rest. If this is possible, then there would be a preferred inertial frame. So, Lorentz's theory does not sit well with special relativity at all. [..]

 

Not so. :-( It will be better that I continue the elaboration of the example with both models, then it will become clear without wasting words.

I don't quite agree with this. The point is that when we pass to special relativity the mathematics is really based on the symmetries of Minkowski space-time.

[..]

There is no notion of absolute rest in Newtonian mechanics [..]

 

You did not agree because your history is incorrect on two accounts... History is not the topic here, but it can be the topic of a spin-off thread if you know which forum to put it on (just let me know and I'll join the conversation).

 

 

You are right, that statement is quite imprecise. I meant that, at some time, the car accelerated wrt the landscape, and that in my opinion, that change in motion has a physical sense.

 

Ah yes, very good! We must cover that aspect in the comparative description. In both models it has a physical sense. :)

 

[edit:] removed a remark about words

Here is a very cogent discussion, also relevant to the thread on whether spacetime is a real or just a mathematical construct, from

 

Modern Physics by Wilson published as part of the Blackie Student Physics series.

 

 

attachicon.gifaether1.jpg

 

Nice one! Indeed, the Lorentz "ether" may be a kind of misnomer from that philosophical perspective. But enough background information I think, it's essential to continue the competing explanations with the car example that bvr started, else this thread will not fulfill its goal. I'll do that tomorrow.

Edited by Tim88
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Tim88

However, I know of two physical models that can be used to explain the theoretical predictions, and possibly there is another model that I don't know of.

 

I'm still at a bit of a disadvantage or loss to know exactly what you are seeking in this thread.

 

You say you are aware of two physical models (whatever physical models means). Are you asking for more?

 

You have confined your remarks to a very small part of physics - that of the purely mechanical and only one corner of mechanics at that.

 

What about the relativity of charge or fields or continuous (elastic) media, Hamiltonian-Lagrangian mechanics or......?

 

The problems with transformations in Minkowski 4D is that whilst they work well in the corner of mechanics you have discussed (dynamics) different formulations have to be introduced to discuss very physical matters such as charge, momentum, energy, Lagrangians, and so forth.

 

Such matters are discussed in elementary form in famous texts such as

 

Goldstein - Classical Mechanics

 

Grant and Phillips - Electromagnetism

 

Eisberg - Fundamentals of Modern Physics

 

Newman and Searle - General Properties of Matter

 

and in greater detail

 

Moller - The Theory of Relativity

 

and no doubt in many more.

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I'm still at a bit of a disadvantage or loss to know exactly what you are seeking in this thread.

 

You say you are aware of two physical models (whatever physical models means). Are you asking for more?

[..]

What about the relativity of charge or fields or continuous (elastic) media, Hamiltonian-Lagrangian mechanics or......?

 

The problems with transformations in Minkowski 4D is that whilst they work well in the corner of mechanics you have discussed (dynamics) different formulations have to be introduced to discuss very physical matters such as charge, momentum, energy, Lagrangians, and so forth.

 

Such matters are discussed in elementary form in famous texts such as

 

Goldstein - Classical Mechanics

[..]

Moller - The Theory of Relativity

[..]

 

What really triggered this topic were endless discussions in the relativity forum with members who either want to know "what really is going on", or who question the physical self consistency of relativity theory because "apparent" or "relative" effects can have "absolute" consequences, and they want to know how that can work. Relativity theory doesn't fully answer such questions because it's solidly founded on laws about phenomena that are based on observation: it's "shut up and calculate" on purpose.

 

We know that we can do much better, and this thread is meant to satisfy their intellectual need to understand how it can be understood to work "in reality". And yes, for this thread to remain manageable I intend to limit it to basic stuff such as mutual length contraction, time dilation and kinetic energy. We may spin off threads on related topics.

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I don't understand why relativity theory doesn't explain what "really" happens (in as much as any theory can explain that). It is not a "shut up and calculate" theory; it is solidly based on the geometry of space and time. It has as much, if not more more, basis in reality than, say, the electromagnetic field.

 

Just because it doesn't coincide with our intuitive notions of time and space doesn't mean you need to invent something else. And that "something else" won't really explain anything because you can ask: "why does it do that" or "what is it made of" or whatever.

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I don't understand why relativity theory doesn't explain what "really" happens (in as much as any theory can explain that). It is not a "shut up and calculate" theory; it is solidly based on the geometry of space and time. It has as much, if not more more, basis in reality than, say, the electromagnetic field.

 

Just because it doesn't coincide with our intuitive notions of time and space doesn't mean you need to invent something else. And that "something else" won't really explain anything because you can ask: "why does it do that" or "what is it made of" or whatever.

 

It sounds as if you think that the block universe philosophy was the basis for relativity theory, or as if you think that relativity is not based on facts of observation; if so, please check out the first post (incl. the "mother" thread) and study the references. :)

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Relativity theory doesn't fully answer such questions because it's solidly founded on laws about phenomena that are based on observation: it's "shut up and calculate" on purpose.

I am not sure how this is really any different to other physical theories. The only thing to be careful with is that most of our intuition is based on Newtonian ideas - some of which do survive passing to special relativity.

 

Anyway, can you tell me what is understood by 'aether' in Lorentz-Poincare theory?

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That's probably right, in view of this paper by Stokes: https://en.wikisource.org/wiki/On_Fresnel%27s_Theory_of_the_Aberration_of_Light

Anyway, such a model is not compatible with SR.

 

Your statement about physicists is not generally true. Historically ether theory was advanced by physicists, and block universe by a mathematician. I suspect that mathematicians and those with mostly mathematical skills prefer the block universe idea because "time", "speed of light" and "distance" are for them just symbols and variables. And for sure the mathematically difficult field of GR (at full precision) is practiced by mathematical physicists. Note that your "theoretical rest frame" is another word for "Lorentz ether".

 

And indeed, the main purpose of this thread is to make relativistic effects fully understandable for skilled laymen and practicing physicists.

For me also, ether theory makes more sense than block universe; but it is arguably uglier (at least, I disliked the idea) and for some people block universe is just what they need to make sense of relativity.

 

[edit:] just one little correction: no matter which of the two models for SR you use, "when I'm driving my car, I know I am in motion, not the landscape" is imprecise. Perhaps this is a good point to start explaining by means of the 3D and 4D views of reality.

 

Basic fact: similar to classical mechanics, you are free to choose the landscape as pretended "rest frame" (neglecting rotation).

1. Stationary ether (Absolute Space model): When you are driving your car, in general both your car and the landscape are in motion.

2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory.

 

I'm not sure if I introduced the block universe model altogether correctly as I don't find it intuitive; please correct if needed. Maybe my intuition for that model will be improved after the discussion here. :)

 

So, picking up where the competitive explanation was left (still almost at the start!)

 

Basic fact: similar to classical mechanics, you are free to choose the landscape as pretended "rest frame" (neglecting rotation), in which case your car is "moving".

 

I will borrow from a recent thread a pictorial presentation of a fast car (original by bvr and improved by me):

 

Different from common practice, we assume here that the car conductor has set up an inertial reference system according to the assumption that the car is in rest and the ground is moving under it. Moreover the car happens to be driving at the crazy speed of 0.86c.

Let's say that there are clocks c1 and c2 above two openings in the car, and these clocks have been "Einstein synced".

Now the car driver drops two balls, presumably simultaneously, so that from his perspective :

_________________________

| |

| |_

| ___ c1 c2 ___|

/ \--- ----1m---- ---/ \

_______\___/___o__________o___\___/_________

<- v

 

According to the car the balls were dropped simultaneously at 1 m distance, so that they also hit the moving ground at 1 m distance.

 

According to the ground however the car is length contracted, and the balls are not dropped at the same time so that they hit the ground at different times:

_____________

| |

| |

| | v ---->

/ \- -----o-/ \

____________\_/___o_____\_/_____________________________________

 

 

______________

| |

| |

| | v ----->

/ \- ----- -/ \

__________________o________\_/2m_____o_\_/____________________________

Distance between the corresponding events as measured with a ruler on Earth in blue.

 

Now the differing worldviews:

 

1. Stationary ether (Absolute Space model): When you are driving your car, in general both your car and the landscape are in motion, resulting in what may be figuratively called different perspectives of the same reality. This is an essential point to keep in mind before reading on. Only for simplicity of explanation we'll first pretend in this introduction that the landscape is, by pure chance, in "absolute rest".

 

1a. The car is then Lorentz contracted due to the car's motion through space, as would be expected if fundamentally all matter consists of some kind of waves. In this example one could (in principle) measure that the car is half its proper length.

 

1b. The car's synchronization is in this case also messed up due to the car's motion, as can be easily understood by working out the timing errors from the light pulses as they propagate through space (we may ignore the air).

 

1c. As per the relativity principle these effects combine so that according to the car conductor it seems as if the ground is length contracted. Moreover, just as was the case in Newtonian mechanics, the same relationships occur between two reference systems in uniform translational motion. In other words, both inertial reference systems provide in general a somewhat "distorted" perspective on reality. Note that these combined effects are not a "conspiracy", as the PoR follows from the conservation laws.

 

2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting or experiencing a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory.

 

"Time-out" for me; maybe a block universe adept will be so kind to complete the explanation by means of Spacetime trajectories that traverse the block universe at different angles, resulting in different perspectives of the same reality, and so on. :)

I am not sure how this is really any different to other physical theories. The only thing to be careful with is that most of our intuition is based on Newtonian ideas - some of which do survive passing to special relativity.

 

Anyway, can you tell me what is understood by 'aether' in Lorentz-Poincare theory?

 

It's essentially what is understood by "space" in studiot's reference in post #34 - thanks again studiot, for finding such a neat one-page summary. :)

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It's essentially what is understood by "space" in studiot's reference in post #34 - thanks again studiot, for finding such a neat one-page summary. :)

Space, or space-time?

 

This is not what one would usually mean by aether, though space-time and fields would be the modern equivalent to what the 19th century physicists were looking for.

 

However, there are some subtle differences. The basic idea of a aether is some mechanical or quasi-mechanics material that is responsible for electromagnetic waves. This idea became more and more abstract and Maxwell, Poincare and Lorentz all worked with more and more looser concepts. The exact mechanical properties are not properly explained in these old works - if I am not mistaken just about the only thing that Lorentz needed was the immobility of this medium.

 

Lorentz used more ad hoc ideas such as length contraction to make his theory fit. The trouble is that the aether is now undetectable, and so the theory is not fully testable. The question for philosophers need to think about is in what sense does this medium exist if we cannot really see it?

 

Now, if you have some medium that fills all of space then you can think about a preferred rest frame - in this case the one in which the speed of light is always c. Your idea that 'Lorentz aether = choice of rest frame' is not really correct. The point is that there should be some canonical choice of rest frame. (There are such frames in cosmology, but these arise due to special solutions to general relativity rather than being written into general relativity from the start)

 

So, at some level the aether should be some 'material' in that it is a localised notion - think about waves in a pond, you have particles of water going up an down. Results like the MM-experiment and so on, together with Einstein's special relativity and field theory show that the 'aether' (space + time + metric + other fields) are not really 'rigid things' in the sense that we have a universally defined rest frame. Classically we should think of 'fields' as the 'aether' or quantum mechanically one may like to think about vacuum states (but forget the idea of a universal frame).

Edited by ajb
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2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting or experiencing a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory.

 

"Time-out" for me; maybe a block universe adept will be so kind to complete the explanation by means of Spacetime trajectories that traverse the block universe at different angles, resulting in different perspectives of the same reality, and so on. :)

I hope that I am allowed to, but I cannot explain it much better than this:

Space, Time and Einstein: An Introduction (Page 54)

By J.B. Kennedy

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the biggest problem with block universe is irreversible processes. Thermodynamics itself argues against block universe. Hence the development of the evolving block universe model. Which is a seperate model.

 

I'm not what the logic here is. Why would we try to teach relativity using models outside of what relativity describes.

 

If your going to teach a model. Stick to just that model. Adding other models just adds unnecessary complexity.

 

For example lack of drag (medium characteristics in eather )

 

For block universe the complexity of reversible vs irreversible processes in the numerous block universe models. (which hasn't been shown to work at all measurement scales. In particular QM.)

 

Stick to just GR. Use the energy density to pressure aspects of the stress tensor.

After all it is the stress tensor itself that tells space how to curve...

 

You don't require an absolute frame, this is one of the greatest contributions to science. Why throw it away?. How can you possibly teach relativity if you require an absolute frame to compare to? Quite frankly one should be able to transform between any frames.

 

Quite frankly relativity becomes easier to comprehend when you detail how thermodynamics work within GR. The medium can be accurately described as a field or just use the intergalactic medium of standard model particles.

 

Fundamentally the last approach will better equip the reader to handle GR and cosmology combined...

Edited by Mordred
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[...] The trouble is that the aether is now undetectable, and so the theory is not fully testable. The question for philosophers need to think about is in what sense does this medium exist if we cannot really see it?

 

Now, if you have some medium that fills all of space then you can think about a preferred rest frame - in this case the one in which the speed of light is always c. Your idea that 'Lorentz aether = choice of rest frame' is not really correct. The point is that there should be some canonical choice of rest frame. (There are such frames in cosmology, but these arise due to special solutions to general relativity rather than being written into general relativity from the start)

 

So, at some level the aether should be some 'material' in that it is a localised notion - think about waves in a pond, you have particles of water going up an down. Results like the MM-experiment and so on, together with Einstein's special relativity and field theory show that the 'aether' (space + time + metric + other fields) are not really 'rigid things' in the sense that we have a universally defined rest frame. Classically we should think of 'fields' as the 'aether' or quantum mechanically one may like to think about vacuum states (but forget the idea of a universal frame).

 

I could not follow your reasoning which seems to be based on a misunderstanding that I already clarified twice (and did you actually read studiots one page explanation?) but it's immaterial for this discussion. Either you know of a third "model of reality" for SR (and if so, please present it!), or you can watch the "fight" between two known models, and hopefully inject some more stimulating questions!

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What really triggered this topic were endless discussions in the relativity forum with members who either want to know "what really is going on", or who question the physical self consistency of relativity theory because "apparent" or "relative" effects can have "absolute" consequences, and they want to know how that can work. Relativity theory doesn't fully answer such questions because it's solidly founded on laws about phenomena that are based on observation: it's "shut up and calculate" on purpose.

 

We know that we can do much better, and this thread is meant to satisfy their intellectual need to understand how it can be understood to work "in reality". And yes, for this thread to remain manageable I intend to limit it to basic stuff such as mutual length contraction, time dilation and kinetic energy. We may spin off threads on related topics.

 

Emblazoned in the title of this thread is the word model.

 

We construct models to obtain desired information about the thing we are modelling.

 

You say that you want to keep it simple (basic stuff) and I come from a generation where this approach was a watchword.

To this end geometric models were once much in vogue.

 

 

 

A feature of a model is that we can "ask it a question" .

So for instance we can easily calculate the (invariant) interval given the time and distance between two events A and B in the same frame, using the standard formulae.

 

But we can also do this geometrically (and very simply) and assign meaning to the drawing.

 

1) With centre A draw a circle equal to the distance light travels in the elapsed time, to some suitable scale.

 

2) Draw line AB equal to the distance between the events, to the same scale.

 

3) Erect a perpendicular at B to cut the circle in C

 

4) Length BC is equal to the interval to the same scale

 

Would such a model be of interest?

Say for a more difficult problem, based on this method.

 

A station inspector, A stands on a station platform and is passed by a passenger B on a train at t=0

Some time later A see a flash of lightning strike the train at a point he knows to be be distance d ahead and he notes the time on his watch.

 

Thus knowing the time and distance he wishes to find the time the passenger thinks the flash occurred and how far away it was from him (the passenger)

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It sounds as if you think that the block universe philosophy was the basis for relativity theory

 

 

No, I don't think that. (The "block universe" model seems to me to be just a rather unhelpful philosophical idea.)

 

 

 

or as if you think that relativity is not based on facts of observation

 

It very obviously is. (As well as being readily derived purely theoretically; e.g. from Maxwell's equations.) Which is why I can't see it as a "shut up and calculate" model.

 

 

 

if so, please check out the first post (incl. the "mother" thread) and study the references. :)

 

Well, I have reread the first post and skimmed the references. I don't see much of interest there.

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[..] We construct models to obtain desired information about the thing we are modelling.

[..]

A feature of a model is that we can "ask it a question" .

So for instance we can easily calculate the (invariant) interval given the time and distance between two events A and B in the same frame, using the standard formulae.

 

But we can also do this geometrically (and very simply) and assign meaning to the drawing.

[..]

Would such a model be of interest?

Say for a more difficult problem, based on this method.

 

A station inspector, A stands on a station platform and is passed by a passenger B on a train at t=0

Some time later A see a flash of lightning strike the train at a point he knows to be be distance d ahead and he notes the time on his watch.

 

Thus knowing the time and distance he wishes to find the time the passenger thinks the flash occurred and how far away it was from him (the passenger)

 

A geometric method for solving such applied mathematical questions would likely be of interest in either the relativity forum or in the homework forum. It will be of no interest here, except if that method provides a different explanation for the car example than the two models of reality already under discussion.

the biggest problem with block universe is irreversible processes. Thermodynamics itself argues against block universe. Hence the development of the evolving block universe model. Which is a seperate model. [..]

 

Thanks, that's interesting input. I'm not sure if it is valid though... Maybe someone would like to come to the defense?

Apart of that, regretfully:

 

I'm not what the logic here is. Why would we try to teach relativity using models outside of what relativity describes.

 

If your going to teach a model. Stick to just that model. Adding other models just adds unnecessary complexity.

[..]

You don't require an absolute frame, this is one of the greatest contributions to science. [..]

 

Those comments are a bit off topic here but certainly belong in the thread from which this one is a fork, for further discussion there:

http://www.sciencefo...ematical-model/

Quite frankly relativity becomes easier to comprehend when you detail how thermodynamics work within GR. The medium can be accurately described as a field or just use the intergalactic medium of standard model particles.

 

Fundamentally the last approach will better equip the reader to handle GR and cosmology combined...

 

I find that rather puzzling; I have to assume that you propose "the intergalactic medium of standard model particles" as an alternative explanation to either Absolute Space or Absolute Spacetime. Certainly such particles can't do all the things that are required, as discussed in the "mother" thread linked here above!

 

Sorry but I can't access this link, it seems to want more money or something in the meter.

 

I could access it, and if no one else does, then tomorrow I'll play the devil's advocate and I'll do my best to apply that view of reality to the car example. :)

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