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


Tim88
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The ad-hoc qualification is surely right when speaking of the theories around 1900. At that time, matter was considered to be (ideally) totally rigid, so there was no possible explanation for the length-contraction.

But is that still true, regarding the modern view on particles, atoms and molecules?

No today we know there are no rigid bodies. All bodies being comprised of particles. Which at the time of Lorentz. They only had the electron and proton.

So there was a natural effort to model gravity by electromagnetic charge dynamics. The neutron was discovered in 1932. So the view of the atom was just Proton-electron. (forgot photon though they were having problems with light. The quantization ie Planck-Einstein)

As these were the only two known particles at the time. It made sense to model spacetime with the electromagnetic.

On the mathematics side use of symmetry and fields were also developed later.

Edited by Mordred
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Okay, there are no rigid bodies, only particles that are (simply speaking) "held together" by EM forces?
But when the body is moving, those forces don't participate on the movement. So the body will physically contract. Or am I wrong?

 

(I know I'm over-simplifying, I'm just indicating a basic principle.)

Edited by bvr
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[...] Come on, people, with an elaboration of the car example I made a practical comparison between what "Space" and "Spacetime" supposedly can do on page 4, but likely I didn't do full justice to "Absolute Spacetime"; at least, I found my attempt less than satisfying and therefore probably unfair. Can't Block universe do more for understanding relativistic effects than giving a literal "perspective" and providing an "odometer" for clocks? When starting this thread, I supposed that that would have been dealt with upon reaching p.3...

[..]

But meanwhile we're already near the bottom of page 6 of this discussion with a lot of philosophical argumentation, but no improvement on my rather weak attempt on p.4.

[..] In this discussion I'm mostly interested in "causal power" (however, self contradicting causal power is quite useless of course).

 

So, is there nobody following this discussion who can improve on my Absolute Spacetime interpretation of events with the traveling car, clarifying by means of that case example (and you may of course add accessories as needed) such things as light propagation, cause and effect, real and apparent, if there is "real one-way light speed", or other? With Frozen or Evolving Absolute Spacetime, as you wish. [..]

 

Thanks for the added comments. Regretfully nobody accepted the challenge...

As already mentioned, it's high time to get back to business and see if we managed to improve the causal explanations by means of the two competing views. On hindsight, maybe I should have immediately started this topic with the car example according to both views, to avoid any possible ambiguity of what I expect from this discussion.

 

Some of the comments are certainly useful for improving the competing explications. I'll try to include as much as possible of the constructive contributions in the following further elaborated car example (I hope I don't overlook much). Slowly we can make the explanations clearer by working on this together. :)

 

For example, while the mathematical explanation equally applies to both views, I will elaborate a little more on the physical explanation of length contraction offered by the "Space" view, and make explicit mention of the apparent lack of any physical explanation for it by the Spacetime view. And as Celeritas thinks that the term "presentism" is reserved for Newton's Absolute time", I'll hereby introduce the term "relativistic presentism" to better convey the meaning. My opening sentence is somewhat inspired by a sentence from Celeritas.

 

-------------------------------------------------------------------------------------------

 

Physical effects such as inertia and time dilation can be modeled as caused by an underlying ether ("Absolute Space"), but a more widespread view is that they are caused by a block universe (2Absolute Spacetime"). One might ask, what is the practical difference? Here's a comparison of how the two models in "action" pretend to create special relativistic effects.

 

For a start, both models see themselves as causing the space-time metric:

 

Absolute Space:

Time is a measure for the progress of physical processes (relativistic presentism), therefore it plays a role that is different from our measurements of distances. Inertial frames can be set up just as in Newton's mechanics. Similarly as in the old theory, the state of motion (speed) cannot be detected although a change of motion with respect to Space can be detected, since Space literally induces an inertial effect at a change of motion. For the electron this can even be understood in a straightforward manner as self induction (QM improves on this quantitatively); this suggests that one day a unified theory may be found that explains all inertia as due to change of field energies. Other improvements to Newton's Space following from Maxwell and Lorentz are that radiation does not propagate like particles but as waves (or, since QM, like wavelets), so that its speed is determined by the Space that it propagates through; and that matter is affected by motion just the same as Heaviside's moving EM fields.The inertial frames of SR are the reference systems of Newton's mechanics.

 

Absolute Spacetime:

Time and Space form a single entity as proposed by Minkowski (leading to one form or another of eternalism). This model explains nothing about the passage of time. Inertial reference systems ("frames") can be set up just as in Newton's mechanics, similarly as in the old theory. However the state of motion (speed) is here interpreted as a trajectory of which the direction cannot be detected, implying that Spacetime must be homogeneous(?) although a change of angle (a change of motion) with respect to Spacetime can be detected.

[please someone else complete this, how does Spacetime explain inertia?? How does it explain the observation of time as being separate of space, and the one-way direction of time?].

 

Now we are going to make use of inertial reference systems related to a fast car that is driving over the ground, and we let either Space or Spacetime act on them to create the required effects.

 

Similar to classical mechanics, we are free to choose the landscape as pretended "rest frame" (neglecting rotation), in which case the car is "moving" (even if we are inside). But 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 caused[1] by 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). Thus the car's synchronization is chosen such that it seems as if the one-way speed of light (also called "closing speed") is the same in both directions.

According to the ground (here by chance the true "view"), it is obvious that the car's synchronization is wrong.

 

1c. As per the relativity principle these effects combine in such a way, that the car conductor measures that the ground is length contracted (he may of course choose to regard himself in motion, in which case he will measure that the ground is not length contracted but he is!). 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 Lorentz transformations follow from the conservation laws.

 

1d. Moreover, in this special case the clocks of the car truly tick slower; this is physically understandable by means of the "light clock" illustration (e.g. Simple_inference_of_time_dilation ). Due to the car's (mis)synchronization of clocks (together with its length contraction), it seems from the car's perspective as if instead the ground clocks run slow. In general no reference system corresponds to Newton's "Absolute Time"; all show Lorentz's "local time".

 

We now turn it into a "twin paradox" scenario. Let's just take a nearly infinitely sharp turn (ignoring the impossibly strong acceleration effects) and drive back without changing speed.

 

1e. The car is just as much length contracted as before. However, this time the car driver notices that his reference system has been messed up: the speed of light doesn't seem the same anymore in both directions. This follows directly if one considers that the true speed of light is the same as before, while the absolute effect of speed on the car's clocks is approximately the same (in this case the true clock rates can in theory be kept identical). Consequently the observational symmetry has been broken, and the absolute effects resulting from speed relative to the ether can thus be detected.

 

1f. If the car now passes clocks on the ground that it passed earlier in the other direction, the driver will notice that his clocks are behind on the ground clocks. That is as expected, since his clocks (in this simplified case) truly ticked slower all the time.

 

As the Lorentz transformations form a group similar to the Galilean transformations, the exact same phenomena are observed between a car in motion relative to a ground that itself is also in motion. While this point may be less intuitive due to our limited mental capability to conceive such complexity of different relative motions and effects, it is not too difficult to verify this fact mathematically.

 

 

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. Regretfully, no physical explanation is available why an object in a different state of motion is obliged by Spacetime to trace a different trajectory through Spacetime, and why we are fooled into perceiving this single "block of ice" as divided in entities called "length" and "time".

 

2a. The car appears Lorentz contracted to half its length from the perspective of the ground frame due to the car's trajectory through Spacetime which is at a different spacetime angle than the ground trajectory. The physical explication as to why this is the case is that "time" is an unexplained illusion from our senses. Everything is just trajectories through Spacetime that we can "slice" in different ways. No other explanation is given than that the physical source of length contraction and time dilation is in the geometry of space-time.

 

2b. The car uses the standard synchronization convention, such that the spacetime trajectory of light relative to the car appears to be symmetric in both directions. Also here one is free to choose the "angle", that is, the apparent one-way speed of light (also called "closing speed") relative to the car, depending on the choice of reference system. Unclear is how the isotropy of one-way light speed and its independence to the car's motion is understood [someone please clarify; without that it's insufficient!]

 

2c. The relativity principle is automatically built into this model. Here the relativistic effects are due to the different trajectories, affecting the recorded amount of "space" and "time" as if an odometer is tracing Spacetime.

 

2d. While the clocks in the car in reality don't tick at all, the perceived tick rate is just as truly the normal rate as those of that of clocks on the ground. Time dilation is again a matter of perspective, due to the different trajectories. A peculiarity is that a longer Spacetime trajectory between two points corresponds to less proper time increase.

 

We now turn it into a "twin paradox" scenario. Let's just take a nearly infinitely sharp turn (ignoring the impossibly strong acceleration effects) and drive back without changing speed.

 

2e. From the grounds perspective, the car is just as much length contracted as before because its trajectory has changed but the relative space-time angle is the same. However, this time the car driver notices that his reference system has been messed up: the speed of light doesn't seem the same anymore in both directions. This is because the car has made a turn in Spacetime, changing its trajectory through it. That is an absolute effect; the clocks were synchronized in relation with a different trajectory.

 

2f. If the car now passes clocks on the ground that it passed earlier in the other direction, the driver will notice that his clocks are behind on the ground clocks. That is as expected, since the Spacetime trajectory is longer between the same events (a curved line compared with a straight line).

 

-------------------------------------------------------------------------

 

Important philosophical consequences of the "Absolute Space" view of reality are that time and distance have not been totally robbed from their classical, intuitive aspects; however, physical length in the direction of motion and time rate are affected by motion through Space. In other words, only Space is causal in that view.

 

Important philosophical consequences of the "Absolute Spacetime" view of reality are that time and distance have been totally robbed from their classical, intuitive aspects: space and time form a single physical entity (studiot's book reference: "like a giant block of ice"), in which at least all events in the past and present (and commonly also the future) "coexist and are frozen in their locations in space and time". In the Spacetime view, Space and Time are coexisting causal physical entities, or even different aspects of a single causal physical entity. [The "Evolving Block Universe" variant doesn't have the coexisting future problem but it has the strange property of "double time", how to explain that?].

 

Once more, corrections of errors are welcome. :)

 

We should still give examples of interpretations of basic GR effects.

 

[1] Elaboration: what follows is from memory, in order to provide more context in view of comments by Celeritas and bvr as well as Mordred; it's slightly simplified and there may be a few inaccuracies but the gist of it is certainly correct (suggestions for improvement welcome of course; however I want to keep it compact!).

The discoveries related to Maxwell's theory and the electron (a moving electron's energy and mass roughly correspond to its electromagnetic field energies) gave way to the hope that all matter may be shown to be entirely electromagnetic. It was also realised that atoms are bonded by electromagnetic bonds.

At about the same time that observations forced the length contraction hypothesis on theory as the only reasonable solution to the puzzle, Heaviside calculated that electromagnetic fields should contract by the gamma factor when in motion (we now know that atoms must contract the same: details can be found in Bell's "How to teach special relativity").

Newton's assumption according to which matter is not affected by motion had already become implausible. The independent proposals by Fitzgerald and Lorentz that length contraction by the gamma factor must take place as the result of motion was, in the end, the only solution, imposed by both theory and experiment.

Soon after, it was found independently by Larmor and Lorentz, that motion similarly must slow down natural processes by the same factor (Bell also elaborated on this aspect in detail).

Edited by Tim88
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With the approach your taking, albiet your requests for improvement. By including the different views involved. I see no problem using this technique to help understand relativity.

 

I'll study it in more detail later on

it's high time to get back to business and see if we managed to improve the causal explanations by means of the two competing views. On hindsight, maybe I should have immediately started this topic with the car example according to both views, to avoid any possible ambiguity of what I expect from this discussion.

lol

 

I noted a request on time reversal symmetry. There is two (at least) valuable lessons in examining your cars.

Classical velocity is time reversal. The acceleration is not. This relates to twin paradox.

I'll work up a detailed explanation later on.

 

Isotropy of time means time symmetry which equates to reversible processes being modelled.

 

Edited by Mordred
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Thanks Mordred, it will be great if you can make the block universe look more capable than serving as little more than a necessary but mysterious background for the "odometer".

Meanwhile this thread is already getting impractically long, and there is more to discuss. It's high time to generate a few spin-off topics (with mention of it here) for discussing so far unanswered questions and loose ends. Summary results for this topic can then be injected back into this thread with links to those discussions in part.

Edited by Tim88
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For example this topic by Mordred is a candidate for such a spin-off thread:

I do not vote for the presentism argument. Nor the Lorentz ether absolute frame being a privileged observer. Relativity of simultaneity has specific requirements that are not merely "convention" The presentism argument (if I understand it correctly) is a 3d ontology as opposed to a 4d ontology.

[..]

(yes I spent some time studying the logic arguments) >:D

I could not follow the logical arguments that I didn't cite here, maybe I'm missing some information. If you still think that your reasoning applies (if it's a classical concept then it may not apply!), we could give that spin-off thread a title like "3D Space, relativity and presentism".

[edit:] I now see that it received a +1 vote, which suggests to me that we should elaborate on it. So I will start that topic here.

Edited by Tim88
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no prob already replied there. Anyways time isotropy is essentailly no preferred direction. The laws of physics in each IF is unchanged due to direction of time. It ties into time symmetry.

 

" We may note that temporal homogeneity implies (at least in special relativity) that all methods of time keeping based on repetitive processes are equivalent"

 

Direct quote from the textbook mentioned below.

 

Thanks for the added comments. Regretfully nobody accepted the challenge...

As already mentioned, it's high time to get back to business and see if we managed to improve the causal explanations by means of the two competing views. On hindsight, maybe I should have immediately started this topic with the car example according to both views, to avoid any possible ambiguity of what I expect from this discussion.

 

Some of the comments are certainly useful for improving the competing explications. I'll try to include as much as possible of the constructive contributions in the following further elaborated car example (I hope I don't overlook much). Slowly we can make the explanations clearer by working on this together. :)

 

For example, while the mathematical explanation equally applies to both views, I will elaborate a little more on the physical explanation of length contraction offered by the "Space" view, and make explicit mention of the apparent lack of any physical explanation for it by the Spacetime view. And as Celeritas thinks that the term "presentism" is reserved for Newton's Absolute time", I'll hereby introduce the term "relativistic presentism" to better convey the meaning. My opening sentence is somewhat inspired by a sentence from Celeritas.

 

-------------------------------------------------------------------------------------------

 

Physical effects such as inertia and time dilation can be modeled as caused by an underlying ether ("Absolute Space"), but a more widespread view is that they are caused by a block universe (2Absolute Spacetime"). One might ask, what is the practical difference? Here's a comparison of how the two models in "action" pretend to create special relativistic effects.

the absolute ether Lorentz ether is a 4d model.

For a start, both models see themselves as causing the space-time metric:

 

Absolute Space:

Time is a measure for the progress of physical processes (relativistic presentism), therefore it plays a role that is different from our measurements of distances. Inertial frames can be set up just as in Newton's mechanics. Similarly as in the old theory, the state of motion (speed) cannot be detected although a change of motion with respect to Space can be detected, since Space literally induces an inertial effect at a change of motion. For the electron this can even be understood in a straightforward manner as self induction (QM improves on this quantitatively); this suggests that one day a unified theory may be found that explains all inertia as due to change of field energies. Other improvements to Newton's Space following from Maxwell and Lorentz are that radiation does not propagate like particles but as waves (or, since QM, like wavelets), so that its speed is determined by the Space that it propagates through; and that matter is affected by motion just the same as Heaviside's moving EM fields.The inertial frames of SR are the reference systems of Newton's mechanics.

 

the inertial frames are designed to follow Newtonian physics. Ie the classical kinematics. The Lorentz transformations preserve each IF

 

Absolute Spacetime:

Time and Space form a single entity as proposed by Minkowski (leading to one form or another of eternalism). This model explains nothing about the passage of time. Inertial reference systems ("frames") can be set up just as in Newton's mechanics, similarly as in the old theory. However the state of motion (speed) is here interpreted as a trajectory of which the direction cannot be detected, implying that Spacetime must be homogeneous(?) although a change of angle (a change of motion) with respect to Spacetime can be detected.

[please someone else complete this, how does Spacetime explain inertia?? How does it explain the observation of time as being separate of space, and the one-way direction of time?]. I recomnend looking at the details under principle of relativity. Everyday kinematic motion within frames are still the same. However freefall motion itself is defined as due due to spacetime "not a force". The details require understanding how geodesics work

 

Now we are going to make use of inertial reference systems related to a fast car that is driving over the ground, and we let either Space or Spacetime act on them to create the required effects. this analysis is Galilean relativity vs SR. The Galilean transforms between frames leads to the Lorentz transform. In particular velocity addition is a good arena to show the difference

 

Similar to classical mechanics, we are free to choose the landscape as pretended "rest frame" (neglecting rotation), in which case the car is "moving" (even if we are inside). But 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". again were comparing Galilean relativity to SR. Absolute frame is still a 4d frame under Lorentz

 

1a. The car is then Lorentz contracted caused[1] by 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). Thus the car's synchronization is chosen such that it seems as if the one-way speed of light (also called "closing speed") is the same in both directions.

According to the ground (here by chance the true "view"), it is obvious that the car's synchronization is wrong.

 

1c. As per the relativity principle these effects combine in such a way, that the car conductor measures that the ground is length contracted (he may of course choose to regard himself in motion, in which case he will measure that the ground is not length contracted but he is!). 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 Lorentz transformations follow from the conservation laws.

 

1d. Moreover, in this special case the clocks of the car truly tick slower; this is physically understandable by means of the "light clock" illustration (e.g. Simple_inference_of_time_dilation ). Due to the car's (mis)synchronization of clocks (together with its length contraction), it seems from the car's perspective as if instead the ground clocks run slow. In general no reference system corresponds to Newton's "Absolute Time"; all show Lorentz's "local time".

 

We now turn it into a "twin paradox" scenario. Let's just take a nearly infinitely sharp turn (ignoring the impossibly strong acceleration effects) and drive back without changing speed.

acceleration is both magnitude and direction. A change in direction results in loss of synchronization (turnaround)

1e. The car is just as much length contracted as before. However, this time the car driver notices that his reference system has been messed up: the speed of light doesn't seem the same anymore in both directions. incorrect the speed of light stays constant the interval changes This follows directly if one considers that the true speed of light is the same as before, while the absolute effect of speed on the car's clocks is approximately the same (in this case the true clock rates can in theory be kept identical). Consequently the observational symmetry has been broken, and the absolute effects resulting from speed relative to the ether can thus be detected.

 

 

 

1f. If the car now passes clocks on the ground that it passed earlier in the other direction, the driver will notice that his clocks are behind on the ground clocks. That is as expected, since his clocks (in this simplified case) truly ticked slower all the time.

 

As the Lorentz transformations form a group similar to the Galilean transformations, the exact same phenomena are observed between a car in motion relative to a ground that itself is also in motion. While this point may be less intuitive due to our limited mental capability to conceive such complexity of different relative motions and effects, it is not too difficult to verify this fact mathematically.

 

 

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. Regretfully, no physical explanation is available why an object in a different state of motion is obliged by Spacetime to trace a different trajectory through Spacetime, and why we are fooled into perceiving this single "block of ice" as divided in entities called "length" and "time". the different paths follow the principle of least action. This action applies in both 3d and 4d

 

2a. The car appears Lorentz contracted to half its length from the perspective of the ground frame due to the car's trajectory through Spacetime which is at a different spacetime angle than the ground trajectory. The physical explication as to why this is the case is that "time" is an unexplained illusion from our senses. Everything is just trajectories through Spacetime that we can "slice" in different ways. No other explanation is given than that the physical source of length contraction and time dilation is in the geometry of space-time.this isn't true and highly misleading. Our signals while we strive to measure the object is influenced by individual worldline paths from each point of measurement. Just like refraction can alter our perceptions

 

2b. The car uses the standard synchronization convention, such that the spacetime trajectory of light relative to the car appears to be symmetric in both directions. Also here one is free to choose the "angle", that is, the apparent one-way speed of light (also called "closing speed") relative to the car, depending on the choice of reference system. Unclear is how the isotropy of one-way light speed and its independence to the car's motion is understood [someone please clarify; without that it's insufficient!] one way speed of light is specifically dealing with Ether drag. A classical example is a laser in moving water. The movement of the water causes different refraction indexes. If light being constant due to an ether. This drag should be identifiable. Lorentz tried length contraction to explain the null result

 

2c. The relativity principle is automatically built into this model. Here the relativistic effects are due to the different trajectories, affecting the recorded amount of "space" and "time" as if an odometer is tracing Spacetime.

 

2d. While the clocks in the car in reality don't tick at all, the perceived tick rate is just as truly the normal rate as those of that of clocks on the ground. Time dilation is again a matter of perspective, due to the different trajectories. A peculiarity is that a longer Spacetime trajectory between two points corresponds to less proper time increase.

 

We now turn it into a "twin paradox" scenario. Let's just take a nearly infinitely sharp turn (ignoring the impossibly strong acceleration effects) and drive back without changing speed.

 

2e. From the grounds perspective, the car is just as much length contracted as before because its trajectory has changed but the relative space-time angle is the same. However, this time the car driver notices that his reference system has been messed up: the speed of light doesn't seem the same anymore in both directions. This is because the car has made a turn in Spacetime, changing its trajectory through it. That is an absolute effect; the clocks were synchronized in relation with a different trajectory.

 

2f. If the car now passes clocks on the ground that it passed earlier in the other direction, the driver will notice that his clocks are behind on the ground clocks. That is as expected, since the Spacetime trajectory is longer between the same events (a curved line compared with a straight line).

 

-------------------------------------------------------------------------

 

Important philosophical consequences of the "Absolute Space" view of reality are that time and distance have not been totally robbed from their classical, intuitive aspects; however, physical length in the direction of motion and time rate are affected by motion through Space. In other words, only Space is causal in that view.

 

Important philosophical consequences of the "Absolute Spacetime" view of reality are that time and distance have been totally robbed from their classical, intuitive aspects: space and time form a single physical entity (studiot's book reference: "like a giant block of ice"), in which at least all events in the past and present (and commonly also the future) "coexist and are frozen in their locations in space and time". In the Spacetime view, Space and Time are coexisting causal physical entities, or even different aspects of a single causal physical entity. [The "Evolving Block Universe" variant doesn't have the coexisting future problem but it has the strange property of "double time", how to explain that?].

 

Once more, corrections of errors are welcome. :)

 

We should still give examples of interpretations of basic GR effects.

 

[1] Elaboration: what follows is from memory, in order to provide more context in view of comments by Celeritas and bvr as well as Mordred; it's slightly simplified and there may be a few inaccuracies but the gist of it is certainly correct (suggestions for improvement welcome of course; however I want to keep it compact!).

The discoveries related to Maxwell's theory and the electron (a moving electron's energy and mass roughly correspond to its electromagnetic field energies) gave way to the hope that all matter may be shown to be entirely electromagnetic. It was also realised that atoms are bonded by electromagnetic bonds.

At about the same time that observations forced the length contraction hypothesis on theory as the only reasonable solution to the puzzle, Heaviside calculated that electromagnetic fields should contract by the gamma factor when in motion (we now know that atoms must contract the same: details can be found in Bell's "How to teach special relativity").

Newton's assumption according to which matter is not affected by motion had already become implausible. The independent proposals by Fitzgerald and Lorentz that length contraction by the gamma factor must take place as the result of motion was, in the end, the only solution, imposed by both theory and experiment.

Soon after, it was found independently by Larmor and Lorentz, that motion similarly must slow down natural processes by the same factor (Bell also elaborated on this aspect in detail).

I may have missed a few bold comments are mine.

 

I highly recommend studying the Galilean relativity (strictly 3d ) to 4d. Lorentz ether isn't Galilean relativity. However in each frame it is galilean. The transformations between frames is not.

 

The transformations of Lorentz uses Galilean to define each frame.

 

One of the better coverages is Rindlers "Relativity" in the first 10 pages of his second edition. He keeps the math clasical to a high school student level.

Edited by Mordred
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Thanks Mordred!

 

Coincidentally, in the new thread I clarified that "space" of space-time is 3D, and that the physical entity called Lorentz ether is 3D; therefore, I find your clarification that "the absolute ether Lorentz ether is a 4d model" confusing at best; I perceive there another mix-up between mathematics and physics. It's better to phrase it like Einstein and Langevin did, and their formulations can be used to emphasize the philosophical differences between Lorentz's and Minkowski's models of reality.

 

Then, your statement:

"the inertial frames are designed to follow Newtonian physics. Ie the classical kinematics. The Lorentz transformations preserve each IF"

is not understandable to me. Newtonian physics is based on so-called Galilean frames, and so is SR. Although SR is based on the same inertial reference systems as Newtonian physics, SR does not follow Newtonian physics.

However, my sentence "The inertial frames of SR are the reference systems of Newton's mechanics" is a bit ambiguous. "SR uses the same inertial reference systems as Newtonian physics" may be clearer.

 

Regretfully we could not clarify if or how a block universe explains such facts as the observation of time as being separate of space, and the one-way direction of time. If those are not current discussion threads, I'll start a discussion on it. [edit:] and including two other remaining questions mentioned here below.

 

Further, the equivalence between inertial and gravitational effects is already understood in Newtonian mechanics. Here the question is if block universe explains the existence of inertia the same as Lorentz ether does, or if it explains it differently, or if it simply can't explain what causes the inertial reaction force of a body when you try to change its state of motion.

 

 

this analysis is Galilean relativity vs SR. The Galilean transforms between frames leads to the Lorentz transform. In particular velocity addition is a good arena to show the difference

 

Sorry, I don't see how that statement as well as the later comment "Lorentz ether isn't Galilean relativity" could be interpreted so that they may correct or useful. There is even no need to introduce the jargon "Galilean relativity". According to Wikipedia, "Galilean relativity states that the laws of motion are the same in all inertial frames".

- https://en.wikipedia.org/wiki/Galilean_invariance

 

The following clarification "again were comparing Galilean relativity to SR. Absolute frame is still a 4d frame under Lorentz " is similarly wrong, a bit like stating "a pipe is still a 2D object". A "reference frame" in SR is 3D, see http://plato.stanford.edu/entries/spacetime-iframes/

If there is ambiguity about the meaning of "reference frame", it's better to avoid it in the discussion; we don't need the jargon "frame"!

 

 

acceleration is both magnitude and direction. A change in direction results in loss of synchronization (turnaround)

 

Yes indeed. Consequently: "the speed of light doesn't seem the same anymore in both directions." However you commented:

 

 

incorrect the speed of light stays constant the interval changes

 

No, you can't eat the cake and keep it. ;)

Only after he resynchronizes his clocks so that the speed of light again appears to be isotropic with respect to the car, will he next measure a speed of light c in both directions.

[edit:] note that in this example the car driver does not touch his clocks before comparing them side by side with other clocks.

 

More useful are the following clarifications:

 

 

the different paths follow the principle of least action. This action applies in both 3d and 4d

Yes indeed. However, as that additional explanation is equally helpful for both views of reality, it does not help to answer the questions about the distinctive features of block universe: why an object in a different state of motion is obliged by Spacetime to trace a different trajectory through Spacetime, and why we are fooled into perceiving this single "block of ice" as divided in entities called "length" and "time". A principle is not a cause-and-effect explanation.

 

About how the block universe causes length contraction and time dilation effects:

 

Our signals while we strive to measure the object is influenced by individual worldline paths from each point of measurement. Just like refraction can alter our perceptions

That is constructive, thanks! Maybe it will lead to follow up questions.

 

About how Minkowski block universe understands the isotropy of one-way light speed and its independence to the car's motion:

 

one way speed of light is specifically dealing with Ether drag. A classical example is a laser in moving water. The movement of the water causes different refraction indexes. If light being constant due to an ether. This drag should be identifiable. Lorentz tried length contraction to explain the null result

Surely there is no "ether drag" in Minkowski block universe?! There even is no "ether drag" in Lorentz ether. It's unclear in what way Fizeau "drag" contributes to clarifying how block interprets and explains the isotropy of one-way light speed and its independence to the car's motion. During the discussion it was shown to be a point that requires clarification. I managed to do that for Lorentz ether, but not for block universe.

Edited by Tim88
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First off no matter what frame your in. When you measure c it is always invariant. No matter who measures it at whatever speed. It will always measure c. This alone conflicts with Galilean relativity under velocity addition.

 

Under Lorentz velocity addition if Im on a rocket and fire a laser. The laser will still move at c from the perspective of an observer Earth and the rocket. Even if the rocket is moving at 0.9999999999999999999 c. Direct conflict with Galilean relativity which would add the velocity of the rocket and the speed of the laser. for net result 1.99999999999... c

 

Isotropy of light follows from this invarience. Isotropy means no special direction. This means the one way speed in both directions is identical. Otherwise it would not be invariant to all observers.

 

An ether drag is a fluid dynamic with light to try to detect an ether. This is the null result in that led Lorentz to develop the Length contraction. The principle itself follows Snells law of refraction. A static ether with the Earth movement should have caused different refraction indexes. It didn't detect this dynamic. Hence Lorentz offered the length contraction to explain the null result.

 

The statement on action is a correction to the statement

 

"No other explanation is given than that the physical source of length contraction and time dilation is in the geometry of space-time."

 

The formula on potential and kinetic energy relations to action. Is an explanation. which conflicts with the quoted statement. The statement you posted failed to mention "action" which is another explanation other than spacetime geometry.

 

An IF frame in SR is one where our everyday formulas work. In this case geometry... Pythagoras theory is a main one. a^2+b^2=c^2. Within every IF frame this geometry is preserved. This is a rigid frame. All observers in the same frame will observe this geometry within his own frame.

 

When an observer examines another frame this isn't the case. He must use the Lorentz transforms in such a manner to recover Pythagoras. This is your transformation equations. Thats the very basis behind them.

 

I always hate resorting to merely words. Particularly in this case.

When I get a chance I will post the kinematics between Galilean relativity (each IF frame, internally follows these relations) to Lorentz. The transformations themself.

 

this is essentially how Lorentz derived the equations in the first place....I believe this will help understand the above comments.

 

I will also include the test for one way vs two way speed of light with regards to Ether.

 

(going to be busy today)

Edited by Mordred
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Tim Have you stopped talking to me?

 

I wondered at your reaction to this quote from another perceptive man, particularly the bit starred in the margin of the second page about the 'orientation'.

 

attachicon.gifintro1.jpg

 

attachicon.gifintro2.jpg

 

attachicon.gifintro3.jpg

 

 

Sorry I cannot spend more than a few hours per week on such discussions. Which question or comment of you that is pertinent for the discussion did I overlook? If you think that a question about the Absolute Spacetime explanation can be helped by the phrase near the star, please go ahead.

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First off no matter what frame your in. When you measure c it is always invariant. No matter who measures it at whatever speed. It will always measure c.

 

Isotropy of light follows from this invarience. Isotropy means no special direction. This means the one way speed in both directions is identical.

 

An ether drag is a fluid dynamic with light to try to detect an ether. This is the null result in that led Lorentz to develop the Length contraction.

 

The statement on action is a correction to the statement

 

"No other explanation is given than that the physical source of length contraction and time dilation is in the geometry of space-time."

 

The formula on potential and kinetic energy relations to action. Is an explanation. which conflicts with the quoted statement.

 

An IF frame in SR is one where our everyday formulas work. In this case geometry... Pythagoras theory is a main one. a^2+b^2=c^2. Within every IF frame this geometry is preserved. This is a rigid frame. All observers in the same frame will observe this geometry within his own frame.

 

When an observer examines another frame this isn't the case. He must use the Lorentz transforms in such a manner to recover Pythagoras. This is your transformation equations. Thats the very basis behind them.

 

I always hate resorting to merely words. Particularly in this case.

When I get a chance I will post the kinematics between Galilean relativity (each IF frame, internally follows these relations) to Lorentz. The transformations themself.

 

this is essentially how Lorentz derived the equations in the first place....I believe this will help understand the above comments.

 

I will also include the test for one way vs two way speed of light with regards to Ether.

 

(going to be busy today)

A correct understanding of synchronization is key. The one-way speed of light is determined by dividing the observed distance by the observed time interval.

And I already cited how the Lorentz transformations follow from the conservation laws; please don't waste time. What is still lacking is some better demonstration of what the Absolute Spacetime can do, and maybe studiot will help.

So your reaction is one of indifference.

 

Thank you for making that plain.

My reaction is: please be to the point; here you even did not bother to tell what your point is.

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You figure the laws of physics between Galilean to Lorentz under velocity addition and refraction a "waste of time" in describing the two models?

These are the key aspects behind the two models. It is velocity addition that alone could have been used to develop the Lorentz formulas.

Every decent SR textbook covers these details in the beginning lessons. Usually the first few chapters.

These same rules determine the required synchronization procedure in the first place....How did you think the synchronization procedure was determined?

 

Philosophical random chance?

 

(What I'm describing is incredibly important, to understanding the Lorentz transformations) It teaches how the Lorentz transformations was developed in the FIRST place. It is far more important than describing the paradoxes.

High speed velocity addition ALONE is enough to prove a 4d universe. Without the use of light or any other signal/medium.

 

Its amazing how such a key detail is often overlooked in Block papers lol. Considering if I wanted to I could write a block paper proof of eternalism just using velocity addition. Without using light or an ether. I can just assign any random invariant measuring stick over time. Just replace c in ct. Massless neutrinos would work they don't interact with the electromagnetic field. So the Lorentz ether does not apply to them. Yet the transforms are identical....(assuming of course I have a reliable neutrino detector.)

That's the problem I have with block papers. They pick and choose the dynamics that suit their personal view point. Often ignoring cases that contradict their personal philosophical leanings. Peer review doesn't necessarily correct this.

Edited by Mordred
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Please don't forget that the main purpose of this discussing is to present the two explanations in their own right, demonstrating their particular strengths. It appears that many books and papers are available where each tries to "prove" that the one is right and the other wrong; if that were allowed to happen to this discussion, that purpose would not be attainable. We should also add the causal views on gravitational time dilation and length contraction.

 

It will certainly be useful to compare philosophical arguments for or against each, which thanks to our demonstrations may show to be pertinent or not; but that's for a spin-off topic - if there isn't already a thread about it!

 

Meanwhile Mordred's comments convinced me that it's not only useful but quite important to elaborate on the synchronization - as that's crystal clear for me now, I had simply forgotten how it puzzled me many years ago. I'll work out an elaboration of the initial car's clock synchronization with the "Absolute Space" interpretation (point 1b), but please be patient - my purpose in life is not to spend all my days in front of a computer screen. Maybe someone else here volunteers to do the same for the "Absolute Spacetime" interpretation (point 2b)?

 

PS Mordred I know indeed how and why the synchronization method as we know was used by Poincare, and why Einstein agreed. Moreover, your historical claims about "ether drag fluid dynamics" and Lorentz are mistaken. But again, that's not the aim of the discussion here.

Edited by Tim88
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The aim is to compare Galilean relativity (3d) to Lorentz (4d). Velocity addition is an excellent tool to do so. Showing how the Lorentz transformation was derived by kinematics would show that our universe is 4D by itself.

 

It will also explain why we use velocity and not acceleration in the equations.

historical claims about "ether drag fluid dynamics" and Lorentz are mistaken.

Care to make a bet on that? How precisely did Lorentz determine only the x axis was affected. His original transforms all axis was affected. x,y,z and t. Edited by Mordred
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Tim88

My reaction is: please be to the point; here you even did not bother to tell what your point is.

 

Since you so peremptorily dismiss the words of the first man to experimentally prove Einstinian relativity in favour of your own offerings, there is nothing more to be said.

Edited by studiot
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Since you so peremptorily dismiss the words of the first man to experimentally prove Einstinian relativity in favour of your own offerings, there is nothing more to be said.

 

:blink: We are here comparing the offerings of two strongly disagreeing interpretations; I don't know how you could have read my invitation as "peremptorily dismiss".

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OOPS - I found an unspotted error in my example, due to the fact that this scenario is subtly different from others that I discussed in the past - sorry for that. :-(

It doesn't matter for the essence, but it's of course not acceptable to have an error in the SR description when trying to explain the causes!

 

Bold face by Mordred:

 

We now turn it into a "twin paradox" scenario. Let's just take a nearly infinitely sharp turn (ignoring the impossibly strong acceleration effects) and drive back without changing speed.
acceleration is both magnitude and direction. A change in direction results in loss of synchronization (turnaround)
1e. The car is just as much length contracted as before. However, this time the car driver notices that his reference system has been messed up: the speed of light doesn't seem the same anymore in both directions. incorrect the speed of light stays constant the interval changes

 

In fact I decided on that scenario in a second, but there is no need for an extremely sharp turn; it was only because I had in mind to let the car immediately retrace its original trajectory. Further, the first bold face is wrong in this ideal case. In general with acceleration, synchronization is required in order to reestablish an inertial reference system. But in this special case, there is only a change in direction; on purpose I kept the speed of the car and both clocks constant for ease of analysis (neglecting a very small error due to the asymmetry of the car). That is realizable if I'm not mistaken. By presenting a smoothly turning car at constant speed instead of a train that reverses direction, the result is totally different, for the front clock remains in front and the speed remains the same as well.

 

Following similar physical reasoning as Einstein in 1905 with his single clock that moves in a circle, a mere change in direction (circular turnaround) will not result in "loss of synchronization". This discussion turns out to be useful for me, as I had not carefully analyzed this particular case before (or in a way I had, but it looked differently: on a rotating disc). :)

 

Thus the corrected 1e becomes:

 

We now turn it into a "twin paradox" scenario. Let's just take a sharp turn (ignoring the strong acceleration effects) and drive back without changing speed.

1e. The car is just as much length contracted as before the turnaround. In this special case, the car and both clocks kept on moving at the same speed, with the front clock in front, and the rear clock at the back, even during the turnaround (we'll ignore a minor error due to the asymmetry of the car). The clocks have advanced equally and the physical state of the car is the same as before. Consequently, the car driver should still measure the one way speed of light as c in both directions, without touching the clocks; no resynchronization is required in this case.

Edited by Tim88
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No prob I posted the turnaround resynchronization corrections. Or rather the hyperbola curve correlation earlier on the turnaround previously.

 

Granted the metrics can be simplified somewhat.

 

Oops that was in relativity forum under one of the links you posted. let me dig it up

Edited by Mordred
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No prob I posted the turnaround resynchronization corrections. Or rather the hyperbola curve correlation earlier on the turnaround previously.

 

Granted the metrics can be simplified somewhat.

 

Oops that was in relativity forum under one of the links you posted. let me dig it up

 

A link to your calculation could be useful, thanks. [edit:] However, I don't know about this particular case in the relativity forums.

And just as Einstein replaced calculation by physical reasoning when feasible, here that is also preferred.

Further, what is again lacking, is 2e: to understand the physical motivation for the same from the viewpoint of the Block universe philosophy.

Edited by Tim88
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You were in that thread but probably focussed on helping others.

 

http://www.scienceforums.net/topic/97871-five-questions-re-sr/?p=939987

 

The last equation shows the x coordinate change ratio.

 

I would just use the caveat "constant velocity is lost due to direction change which is an acceleration. Re-synchronization is required. As your trying to keep your article short.

 

"2e. From the grounds perspective, the car is just as much length contracted as before because its trajectory has changed but the relative space-time angle is the same. However, this time the car driver notices that his reference system has been messed up: the speed of light doesn't seem the same anymore in both directions. This is because the car has made a turn in Spacetime, changing its trajectory through it. That is an absolute effect; the clocks were synchronized in relation with a different trajectory."

 

Yeah this definetely needs improving...

 

How about the Einstein synchronization is under constant velocity. A change in direction causes rapidity and hyperbolic motion. This causes an assymmetry in the time interval calculations during turnaround unless one includes a hyperbolic synchronization procedure

 

If you include the last equation for x^2 for the hyperbola. That should be enough with the added statement.

 

As we can now tell which twin was the inertial twin. We can now realize that we should have never expected the two twins to be the same age when they meet again. This becomes clear under proper examination

Edited by Mordred
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Bold face mine:

You were in that thread but probably focussed on helping others.

http://www.scienceforums.net/topic/97871-five-questions-re-sr/?p=939987

The last equation shows the x coordinate change ratio.

I would just use the caveat "constant velocity is lost due to direction change which is an acceleration. Re-synchronization is required. As your trying to keep your article short.
[..]

 

I'm not writing an article, just trying to have a discussion with valuable output: the aim is to end with posts that will be useful for referencing in other discussions.

 

Indeed, I had not seen that post by you; but even if I had, I don't see the relevance for the question of a need to resynchronize for this special case.

 

As already explained, I consider my original statement about resynchronization erroneous due to a subtlety of the scenario that I had overlooked, even though you next gave support to it with a statement that according to me is explicitly erroneous. Now, to my surprise you still don't notice the issue but continue to support my original statement. This has nothing to do with philosophy and it is both pertinent and useful for SR, so I'll spin it off: http://www.scienceforums.net/topic/99360-does-a-change-in-direction-turnaround-result-in-loss-of-synchronization/

Edited by Tim88
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Spinning off threads everytime you have difficulty with my statements isn't going to help. Fact is these details ARE INPORTANT. and should never be ignored when examining between models

 

Whether or not its a Philosophical argument or under math treatment. The philosophy should reflect the math and vice versa...

Edited by Mordred
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