## Fun with spacetime diagrams

This is not an everything goes forum, but rather a place to ask questions and request help for developing your ideas.

### Re: Fun with spacetime diagrams

Bangstrom,
I'm interested in what you're saying but don't quite grasp the context of c being a dimensional constant. I get that length is a dimension and time is a dimension but you're somehow saying c is something more than just length over time? Wouldn't that make it a dimensionless constant if it's not dependent on dimension?

I know something's not quite right where in the M-std light is always 1 light distance over 1 light time but in the E-std the speed of light varies with the relative velocity between 2 spacetimes plus it's infinite in its own spacetime. It has no units in either but in the M-std I've seen it necessary to consider 1 ly/yr as units for c. Of course musings like this just provoke Jorrie to close down threads without providing any relativistic explanations, if they even exist, for these questions. The forum administrators are content to remain silent.

P.S. If I ever feel like getting back into understanding relativity, I'm going to start a thread in the PHYSICS forum about relative velocity. If Alice leaves earth at .8c, she goes 4 ly in 5 yrs earth time but if Bob and Alice both leave earth in opposite directions at .5c, their relative velocity is still .8c but they separate 4ly in 4 yrs earth time. The relative velocity's the same but the dimensional velocity is not? Is this what you're talking about?
ralfcis
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### Re: Fun with spacetime diagrams

Oh no, I've moved back into Dave Oblad's absolute relative velocity universe. I've been thinking about pure relative velocity and there's no need for it. There's no need for a universally synchronized Earth time clock network so there's no need to express velocity relative to it. Proper time is universal within each frame and the accuracy of atomic clocks being a physical invariant allows us to trust atomic clock readings without needing to compare them to a master clock. Proper distance can be established when frames are stationary relative to each other. That's not even a requirement as stationary distance info can be messaged to a moving frame, it does not have to physically experience it.

So if a ship from earth takes only 3 yrs of its own proper time to travel to a planet 4 ly away, it can be calculated, using relativity, that its Minkowski-std relative velocity to Earth is .8c and its Epstein-std relative velocity is 1.25c since velocity in an E-std is not limited to c. But this brings back the huge problem of the age difference between a flyby of the distant planet and a stop there. There can be no aging difference between 2 inertial frames in a flyby even though the ship has flown by the 4ly miarker in 3 of its years.

I can't get past this paradox using relativity: the ship's clock clearly reads it has aged 2 yrs less than it should have at the 4 ly marker but it doesn't count unless the ship stops there? I can only understand it using ralfativity: age difference can only occur, between the participants, when there is a relative velocity mismatch that is unknown to one of them because of the speed of light delay. This means the propagation delay of any change causes age difference, not just a stop. The rate of age difference also occurs smoothly during the info delay interval. If relativity can show me the same behavior, I'd be more inclined to accept it.
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### Re: Fun with spacetime diagrams

Hmmm I got some glimmer of insight from a new physics post about c. In the E-std, the faster your gamma velocity Yv, the longer it takes for your light message signal to reach the other participant. So as your velocity approaches infinity using your proper time and the other's proper stationary space, the time for information transfer back to the other participant also approaches infinity. So the E-std is offering an alternative explanation of the trade off between c and relative velocity as an information transfer trade off rather than a spacetime contraction to maintain constant c for any relative velocity as is shown in the M-std. Just spitballin', this has not been explored yet.
ralfcis
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### Re: Fun with spacetime diagrams

ralfcis » 29 Aug 2017, 16:01 wrote:There can be no aging difference between 2 inertial frames in a flyby even though the ship has flown by the 4ly miarker in 3 of its years.

And the other party of the "2 inertial frames in a flyby" has flown by the ship's 4 lyr marker in 3 of its years. Completely reciprocal, as it should be for any two fully inertial frames.

Your problem still seems to be not defining the scenario properly and then tackling it with assumptions that do not hold for the scenario. Or it is so ill defined that answers are impossible. I said before: define the scenario and the question properly, then think through relativistically, then calculate (or draw a STD) and finally make a conclusion...

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### Re: Fun with spacetime diagrams

And the other party of the "2 inertial frames in a flyby" has flown by the ship's 4 lyr marker in 3 of its years. Completely reciprocal, as it should be for any two fully inertial frames.

You say this every time like it's my first time seeing it. The reciprocal time is not using the same clocks. There are 2 different clock networks and 2 different pocket watches. If Alice is not being followed through space by her proprietary clock network, then there is no reciprocal time measurement data. Even if there were, it does not cancel out the fact that Alice will see her pocket watch at 3 yrs and the external earth network clock she passes at the 4 ly mark at 5 yrs. Yes I get the fact that the invariance of the light-like spacetime interval will yield the result that Alice has actually aged 5 yrs unless she comes to a stop. I'm just paraphasing what you told me in the thread you didn't shut down. Maybe you could just show me the math proof which should be easy and would make me more sure of what I am saying. s2= (ct)2-x2.

I already went through an extensive STD analysis in another thread. Whatever Bob or Alice do does not affect the result that at the flyby, a clock comparison yields Alice = 3 and Bob =5. Bob can make a move that will allow him to overcome this disadvantage and eventually end up younger at the end of the spacetime interval but it still does not effect the result at the 4 ly mark. You don't even need to do the analysis with 4 clocks. you could arrive at the same result using light signal messaging or seeing how the tv image is reciprocally slowed at each ship.
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### Re: Fun with spacetime diagrams

ralfcis;
spacetime graphics are fun and instructive. They depict multple relations better than text.
Keeping them simple and uncluttered is key.

Showing clock synchronization via Minkowski.

Calibration curves (as labeled by Max born in his book on Relativity) are used to show clock synchronization. A and B agree to synch clocks at separation, and send signals (blue) at (.68) local time. The return signals include the remote clock reading (1.00) and return at local time of (1.47). We can conclude the A and B clocks will remain synched while maintaining their constant speeds.
Per the SR synch convention) (red) A and B assign the remote reading of (1.00) to a local time of half the round trip time. For both observers, the assigned local time is later than (1.00). Each concludes the other clock is running slower than their own clock, i.e. perceived doppler effects
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phyti
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### Re: Fun with spacetime diagrams

This appears to be so broad a definition of the word ‘speed’ as to include even jargon uses of the word that differ from ‘velocity’ such as the ‘speed’ of a trip to the store or the operating ‘speed’ of a computer.

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In the 1600's Ole Romer discovered light required a finite time to move a finite distance, while making astronomical observations of Jupiter and its satellites, thus eliminating the idea of instantaneous propagation.
A sequential definition of speed.
Position is the measured distance of an object relative to a reference object.
Motion is the changing position of an object relative to a reference object for a time interval.
Speed is the rate (ratio) of motion to time, distance interval/time interval. v=(x/(t.
For multiple applications of a word, the context should determine the correct usage.

For a speed to be a speed it has to be the speed of something that is physically observable and all speeds correctly identified obey the rule of the composition of velocities where velocities can be added or subtracted from other velocities relative to differently moving observers but light does not qualify by this definition.
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That is a definition in terms of moving material objects. Light has no inertial/rest mass, and only a constant propagation speed, that is independent of the source. The 2nd and 3rd properties prevent it from following the original vector addition of velocities, resulting in time dilation. The effects of motion on the measurements of time and space, both involving em processes, i.e. light speed, provides a self preservation of c.
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### Re: Fun with spacetime diagrams

phyti » October 22nd, 2017, 1:23 pm wrote:
In the 1600's Ole Romer discovered light required a finite time to move a finite distance, while making astronomical observations of Jupiter and its satellites, thus eliminating the idea of instantaneous propagation.

Roemer did not eliminate the idea of instantaneous propagation. Roemer discovered that units of distance and time are constantly related in a ratio of one second for every 300,000 km of space so objects separated by distance are also separated by time.
This observation does not rule out the possibility instantaneous propagation but it does imply that events on Jupiter should appear to quicken as the planet approaches because our distance from Jupiter measured in units of time decreases as our distance decreases at the constant ratio of ‘c’.

phyti » October 22nd, 2017, 1:23 pm wrote:
Light has no inertial/rest mass, and only a constant propagation speed, that is independent of the source. The 2nd and 3rd properties prevent it from following the original vector addition of velocities, resulting in time dilation. The effects of motion on the measurements of time and space, both involving em processes, i.e. light speed, provides a self preservation of c.

The value of ‘c’ has all the properties of a dimensional constant which should be our first clue that it is not a speed. Speeds are variable. Speeds also have the properties of addition but ratios do not. Nothing can go faster than the space/time ratio of ‘c’ just as nothing can travel faster than 1.6 km per mile. Speeds do not add to ratios.

To say that light has “a constant propagation speed, that is independent of the source” violates the Galilean principle of relativity. How can anything have the same speed relative to all possible sources independent of their varying individual velocities?
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### Re: Fun with spacetime diagrams

Bangstrom;
To say that light has “a constant propagation speed, that is independent of the source” violates the Galilean principle of relativity. How can anything have the same speed relative to all possible sources independent of their varying individual velocities?

Galileo was wrong.
The measured speed of light is constant because perception is altered resulting in that conclusion.
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### Re: Fun with spacetime diagrams

bangstrom » 23 Oct 2017, 02:25 wrote:To say that light has “a constant propagation speed, that is independent of the source” violates the Galilean principle of relativity.

I think it's the other way round. If the observed propagation speed of light was not the same in every inertial frame and/or dependent on the source speed, it would have violated the Galilean principle of relativity. The principle states that there is no physical way to differentiate between a body moving at a constant speed and an 'immobile' body. A difference in the observed propagation speed of light would have made it possible to make that differentiation.

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### Re: Fun with spacetime diagrams

phyti » October 24th, 2017, 1:19 pm wrote:
Galileo was wrong.
The measured speed of light is constant because perception is altered resulting in that conclusion.

The speed of light is not so much an altering of perception as it is a universal observation that every measured interval of space includes an interval of time proportional to one second for every 300,000 km of space. This makes c a spacetime dimensional constant rather than a speed.

BurtJordaan » October 24th, 2017, 3:41 pm wrote:
bangstrom » 23 Oct 2017, 02:25 wrote:To say that light has “a constant propagation speed, that is independent of the source” violates the Galilean principle of relativity.

I think it's the other way round. If the observed propagation speed of light was not the same in every inertial frame and/or dependent on the source speed, it would have violated the Galilean principle of relativity. The principle states that there is no physical way to differentiate between a body moving at a constant speed and an 'immobile' body. A difference in the observed propagation speed of light would have made it possible to make that differentiation.

How would an observed difference in the propagation speed of light make it possible to distinguish between a moving body and an ‘immobile’ body in violation of the Galilean principle? Consider some other fast moving particle such as an electron or muon, or better yet, a neutrino if you could easily detect them.

Neutrinos may travel at different speeds but how could you distinguish between a moving body and an ‘immobile’ body relative to the speed of neutrinos? And, if all observers measure the speed of neutrinos as the same, that would mean that neutrinos must be altering their speeds making them faster or slower depending on the relative speeds of their observers.
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### Re: Fun with spacetime diagrams

bangstrom » 25 Oct 2017, 07:30 wrote:How would an observed difference in the propagation speed of light make it possible to distinguish between a moving body and an ‘immobile’ body in violation of the Galilean principle?

If a proper one-way measurement of the propagation speed of light comes out differently in relatively moving frames of reference, the laws of physics must be different in those two frames, in violation of Galilean relativity. The secondary consequence would have been that we could have detected the "absolute frame", which we know we cannot (by experiment).

Consider some other fast moving particle such as an electron or muon, or better yet, a neutrino if you could easily detect them.

The principle only works for light and other massless particles. The neutrino is though to probably have a very tiny mass, so it might be approximately the same for neutrinos as for light (i.e. we could find them to move at roughly the same speed in every reference frame, irrespective of relative motion).

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### Re: Fun with spacetime diagrams

BurtJordaan » October 25th, 2017, 1:58 am wrote:
bangstrom » 25 Oct 2017, 07:30 wrote:How would an observed difference in the propagation speed of light make it possible to distinguish between a moving body and an ‘immobile’ body in violation of the Galilean principle?

If a proper one-way measurement of the propagation speed of light comes out differently in relatively moving frames of reference, the laws of physics must be different in those two frames, in violation of Galilean relativity. The secondary consequence would have been that we could have detected the "absolute frame", which we know we cannot (by experiment).

Your answers miss the point of my question so I will try to explain the problem.

BurtJordaan » October 24th, 2017, 3:41 pm wrote:
bangstrom » 23 Oct 2017, 02:25 wrote:To say that light has “a constant propagation speed, that is independent of the source” violates the Galilean principle of relativity.

I think it's the other way round. If the observed propagation speed of light was not the same in every inertial frame and/or dependent on the source speed, it would have violated the Galilean principle of relativity. The principle states that there is no physical way to differentiate between a body moving at a constant speed and an 'immobile' body. A difference in the observed propagation speed of light would have made it possible to make that differentiation.

Your statement above explains that light does not violate the Galilean principle because, if it had a variable speed, we could differentiate between a moving body and an ‘immobile’ body. You also explain how light is emitted at the same speed in all directions because light does not respond to an “absolute frame.”

The problem is that no moving objects respond to an “absolute frame” and even high speed particles with variable speeds through space (electrons, muons, and possibly neutrons) can not be used to distinguish between a moving body and an “immobile” body because none of these respond to an absolute frame.

The Galilean principle of relativity also explains that all observed speeds are relative because the speed of the observer adds to the speed of the object observed so all speeds are observer dependant. This is the part of the Galilean principle that is violated by light because its speed does not add and it is one of the ways the “speed” of light works as a dimensional constant rather than a speed.

If fast moving particles in space, such as electrons, were to change their speed when they entered an inertial reference frame so that they all had the same speed in all reference frames, it would be hard to say that they had a speed of their own.

Also, I don’t agree with your statement , “If the observed propagation speed of light was not the same in every inertial frame and/or dependent on the source speed, it would have violated the Galilean principle of relativity.” We have a world of objects with speeds that vary in every inertial frame and depend on the source speed but none of these violate the principle of relativity because they can not be used to differentiate between a body moving at constant speed and an immobile body and neither would light.
bangstrom
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### Re: Fun with spacetime diagrams

bangstrom » 25 Oct 2017, 22:08 wrote:The problem is that no moving objects respond to an “absolute frame” and even high speed particles with variable speeds through space (electrons, muons, and possibly neutrons) can not be used to distinguish between a moving body and an “immobile” body because none of these respond to an absolute frame.

Light is not a 'body' and I think that I have clearly stated that the constancy of speed in every inertial frame only applies to light, not particles with rest mass.

The relative speed of the source does add to the observed speed of the particle when it has mass - we just add it relativistically and not in the Galilean way.

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### Re: Fun with spacetime diagrams

Bangstrom;
How can anything have the same speed relative to all possible sources independent of their varying individual velocities?

The moving observer is the only one who perceives a contracted universe in the direction of motion, just as the user of hallucinogens is the only one who perceives images that no one else sees. His perception is altered by motion, just as the light clock, or any em process. For the anaut and the addict, the effects are real, as mental images, but without physical counterparts.
I refer to this as 'reality confined to the mind'.

The anaut has two choices.
If he chooses the anaut role, he knows from studying SR, all components of his frame experience td, and he will be unaware of the changing clock rate. His perception is an early arrival.
If he chooses to assume a pseudo rest frame, and the destination arrives early, with no error in his clock, nor his speed, he concludes the distance has changed.
It's one or the other.

A recent example on another forum. The poster argues that when A and B observe a moving clock running at two different rates, he argues the clock can't be in two different states simultaneously. I agree with him, since it's not about the clock, it's about different perceptions.

The value of ‘c’ has all the properties of a dimensional constant

'dimensionless' constant, a scalar by definition. So is g, 1 sec to 10 m, and there are many others.
For a speed to be a speed it has to be the speed of something that is physically observable

Light is modeled as a photon, a packet of energy, and can be manipulated many various ways. We are aware of it indirectly.

Lrt’s assume light motion is instantaneous and use the earlier time vs space graph.
An em signal that reflects from the moon’s surface, would be shown as a horizontal line at t=0 and a second horizontal line at t= 2.5. Now we have to explain the gap. Is it the time to turn the light around ?
Experimenting with more distant objects, planets, etc, someone might detect a pattern, that the time gap increases with the distance, and theorize that it’s nothing but transit time!

Galileo was correct for moving matter, since each component of a composite object had the same velocity. If you subtracted that velocity from each component, you are left with a static object. Galileo was not aware of the behvior of light, so didn’t know its speed was independent of its source, and did not add as velocities of material objects. He also therefore would not know what compensates for this difference, such that all inertial frames behave as rest frames.
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### Re: Fun with spacetime diagrams

phyti » October 26th, 2017, 12:15 pm wrote:
A recent example on another forum. The poster argues that when A and B observe a moving clock running at two different rates, he argues the clock can't be in two different states simultaneously. I agree with him, since it's not about the clock, it's about different perceptions.

Relativity is a physical effect. It affects clocks and meter sticks and all forms of inanimate objects such as satellites and stars. An observer moving towards a clock sees the clock moving faster because the amount of space and time between him and the clock is decreasing. The opposite is true for an observer moving away from the same clock. This is an objective physical effect and not a matter of cognition.

phyti » October 26th, 2017, 12:15 pm wrote:
“Bangstrom:The value of ‘c’ has all the properties of a dimensional constant.”
'dimensionless' constant, a scalar by definition. So is g, 1 sec to 10 m, and there are many others.

I said ‘c’ has all the properties of a dimensional constant… not a dimensionless constant. One second for 300,000 km is a dimensional constant.

phyti » October 26th, 2017, 12:15 pm wrote:
Light is modeled as a photon, a packet of energy, and can be manipulated many various ways. We are aware of it indirectly.

The photon is a model for light. It is an imaginary particle. A. F. Kracklauer calls the photon a paradigm and a folklore. The photon represents a quantum of energy in an EM event but its presence between signal and sink is purely conjecture.

phyti » October 26th, 2017, 12:15 pm wrote:
Lrt’s assume light motion is instantaneous and use the earlier time vs space graph.
An em signal that reflects from the moon’s surface, would be shown as a horizontal line at t=0 and a second horizontal line at t= 2.5. Now we have to explain the gap. Is it the time to turn the light around ?
Experimenting with more distant objects, planets, etc, someone might detect a pattern, that the time gap increases with the distance, and theorize that it’s nothing but transit time!

The gap is the distance to the moon measured in seconds rather than units of length. Units of space and time are interchangeable and this is the meaning of the constant c. C tells us that there is one second of time in every 300,000 km of space so the distance to the moon is 1.25 secx300,000 km or 375,000 km. The implication of this requires a non-Newtonian understanding of time much like in the Limerick about the young fellow named “Sprite” who could travel much faster than light.

Anything remote from your location is separated from you by spacetime. Space and time are essential aspects of the same thing “spacetime” and we can’t separate one from the other. This view places the surface of the moon I.25 seconds in our past.

An instant signal from the Earth to the moon arrives on the moon 1.25 seconds into the moon’s future. All EM signals are moving forward in time. A bounce-back signal from the moon to the Earth arrives an additional 1.25 seconds into our future so we need to wait a total of 2.5 seconds to receive the return signal.

This is quite counter intuitive but it is consistent with experiments in QM such as entanglement and quantum teleportation and, when applied to SR, it eliminates the familiar paradoxes and the only violation is of Einstein’s second postulate where c is defined as the speed of light. It makes no difference to the math because c has the same numerical value whether you call it a speed or a dimensional constant.

phyti » October 26th, 2017, 12:15 pm wrote:
Galileo was correct for moving matter, since each component of a composite object had the same velocity. If you subtracted that velocity from each component, you are left with a static object. Galileo was not aware of the behvior of light, so didn’t know its speed was independent of its source, and did not add as velocities of material objects. He also therefore would not know what compensates for this difference, such that all inertial frames behave as rest frames.

If light carries energy, why does it have no mass and why doesn’t the speed of its source add to the speed of light?
I would answer that c is a ratio and a spacetime dimensional constant and you can’t add a speed to a ratio just as you can’t go faster than I.6 kilometer per mile so speeds don’t add to c.
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### Re: Fun with spacetime diagrams

Bangstrom;

A lot to cover:

ReRelativity is a physical effect. It affects clocks and meter sticks and all forms of inanimate objects such as satellites and stars. An observer moving towards a clock sees the clock moving faster because the amount of space and time between him and the clock is decreasing. The opposite is true for an observer moving away from the same clock. This is an objective physical effect and not a matter of cognition.

The clock frequency is determined by the clock, and is not changed by the motion of objects, as verified be an historical record made at the clock. The images of the clock are intercepted at increasing or decreasing time intervals depending on diverging or converging velocity. Prior to SR, doppler shift calculation was a function of velocity only. After SR, it was modified to include time dilation, a motion induced phenomenon. In a scenario with A and B static, and the clock between them moving toward A, A perceives a blue shift while B perceives a red shift. How can the clock have three different frequencies simultaneously? The answer is the same for all the supposed contradictions. It's not about the clock, it's the perceptions. Physical laws prevent such states for objects, but do not prevent multiple perceptions.
Why didn't you include observers in your list of affected things?

I said ‘c’ has all the properties of a dimensional constant… not a dimensionless constant. One second for 300,000 km is a dimensional constant.

In the language of math, a constant is defined as a scalar, having only a magnitude, vs a vector, which has a magnitude and a direction. Proportionality constants convert one unit to another. The constant c in units is meters/second (speed by definition), and one instance of that class. Thus ct would result in meters. Planks constant h, converts frequency to energy, and there are many more. The second and the meter were arbitrarily defined for convenience, and finally redefined in terms of each other in terms of light speed. These constants are determined by experimental work with no explanation for the specific values discovered.

The photon is a model for light. It is an imaginary particle. A. F. Kracklauer calls the photon a paradigm and a folklore. The photon represents a quantum of energy in an EM event but its presence between signal and sink is purely conjecture.

Signals can be encoded for communication, therefore the return signal verified as the response to the one sent. This is part of the protocol for electronic communications and encryption. When the lunar module was behind the moon, there was no communication since the signals were blocked! Kracklauer should do more research.

The gap is the distance to the moon measured in seconds rather than units of length. Units of space and time are interchangeable and this is the meaning of the constant c. C tells us that there is one second of time in every 300,000 km of space so the distance to the moon is 1.25 secx300,000 km or 375,000 km. The implication of this requires a non-Newtonian understanding of time much like in the Limerick about the young fellow named “Sprite” who could travel much faster than light.

Expressions like 'a days ride', 'a 2 day march', 'a 40 min trip', are common expressions used in the past and today, with time and distance used interchangeably. Nothing new here.

Anything remote from your location is separated from you by spacetime. Space and time are essential aspects of the same thing “spacetime” and we can’t separate one from the other. This view places the surface of the moon I.25 seconds in our past.

An instant signal from the Earth to the moon arrives on the moon 1.25 seconds into the moon’s future. All EM signals are moving forward in time. A bounce-back signal from the moon to the Earth arrives an additional 1.25 seconds into our future so we need to wait a total of 2.5 seconds to receive the return signal.

Nothing moves in time! That's the lines on paper version of SR.

This is quite counter intuitive but it is consistent with experiments in QM such as entanglement and quantum teleportation and, when applied to SR, it eliminates the familiar paradoxes and the only violation is of Einstein’s second postulate where c is
defined as the speed of light. It makes no difference to the math because c has the same numerical value whether you call it a speed or a dimensional constant.

If the second postulate is violated, so is the first.

If light carries energy, why does it have no mass and why doesn’t the speed of its source add to the speed of light?

No one knows why, but it is verified by observation and experiment. The nature of light is different than that of matter. Matter is like a construction material, light is like a messenger that delivers energy. They serve different purposes.
One could speculate that space has a structure which determines the behavior of light, and possibly gravity.
phyti
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### Re: Fun with spacetime diagrams

phyti » October 30th, 2017, 12:57 pm wrote: How can the clock have three different frequencies simultaneously? The answer is the same for all the supposed contradictions. It's not about the clock, it's the perceptions. Physical laws prevent such states for objects, but do not prevent multiple perceptions.
Why didn't you include observers in your list of affected things?

The clock keeps time in its own reference frame. Outside observers may have delayed views of the clock’s time but their observations have no effect on the clock. The outside observers just don’t all see the clock in its real time ‘proper time’ reference frame.
SR works for both observed and observers alike. The effects are reciprocal.
phyti » October 30th, 2017, 12:57 pm wrote:
The photon is a model for light. It is an imaginary particle. A. F. Kracklauer calls the photon a paradigm and a folklore. The photon represents a quantum of energy in an EM event but its presence between signal and sink is purely conjecture.

Signals can be encoded for communication, therefore the return signal verified as the response to the one sent. This is part of the protocol for electronic communications and encryption. When the lunar module was behind the moon, there was no communication since the signals were blocked! Kracklauer should do more research.

How does a blocked signal make photons real?
phyti » October 30th, 2017, 12:57 pm wrote: Expressions like 'a days ride', 'a 2 day march', 'a 40 min trip', are common expressions used in the past and today, with time and distance used interchangeably. Nothing new here.

There is nothing new about c is being a conversion factor for converting between units of space and time. Herman Bondi interpreted the meaning of c as a constant ratio of length-units to time-units in our observational projections of optical phenomena, analogous to the constant 39.37 inches to the meter in the measuring of length, and 2.2046226 pounds to the kilogram in the measuring of weight.

The conversion factor for converting inches to meters is not a length and the conversion factor for converting pounds to kilograms is not a weight so why insist on calling the conversion factor for converting units of time to units of distance a “speed”?

Also, the constant , c^2 relating units of mass and energy which, like c, and other constants in general, is obviously the same for all observers in all states of motion or rest.
Also, what meaning can be found when you square a speed?
phyti » October 30th, 2017, 12:57 pm wrote: Nothing moves in time! That's the lines on paper version of SR.

Everything moves in time.
The lines on spacetime diagrams of SR are highly artificial but, like good maps, they describe an observed reality and the uniformity of the diagrams describes the scalar nature of c.
phyti » October 30th, 2017, 12:57 pm wrote:
If the second postulate is violated, so is the first.

Einstein’s first and second postulates are unrelated so how can violating the second violate the first.
Changing the definition of c from a speed to a dimensional constant does not change the numerical value so the math remains the same.
phyti » October 30th, 2017, 12:57 pm wrote:
One could speculate that space has a structure which determines the behavior of light, and possibly gravity.

The structure of space is such that every interval of space includes an interval of time. Any two otherwise simultaneous events separated by space are also separated by an interval of time equal to one second for every 300,000 km of space. That determines the behavior of both light and gravity.
bangstrom
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### Re: Fun with spacetime diagrams

Bangstrom;

How does a blocked signal make photons real?

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It shows something moves between emitter and receiver, and it can be blocked. An experiment involving photons can easily show they exist in intermediate locations other than emitter and detector. Photons are as real as any particle.

There is nothing new about c is being a conversion factor for converting between units of space and time. Herman Bondi interpreted the meaning of c as a constant ratio of length-units to time-units in our observational projections of optical phenomena, analogous to the constant 39.37 inches to the meter in the measuring of length, and 2.2046226 pounds to the kilogram in the measuring of weight.
The conversion factor for converting inches to meters is not a length and the conversion factor for converting pounds to kilograms is not a weight so why insist on calling the conversion factor for converting units of time to units of distance a “speed”?
Also, the constant , c^2 relating units of mass and energy which, like c, and other constants in general, is obviously the same for all observers in all states of motion or rest.

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A scalar is the ratio of two numbers, regardless of the units. The examples you list are for spatial measurements, and units of mass. Some common ratios of different units are standardized such as distance/time as speed, volume/time as flow/convection, mass/volume as density, etc. Different relations for different purposes.
Why is c a speed? Speed = distance/time=vt/t=v!

Also, what meaning can be found when you square a speed?

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v=a*a*t/2, it indicates an exponential increase of speed v in time vs a constant acceleration a. V is accumulating a and increasing with time. This example is not a simple conversion, but a more complex function.

Everything moves in time.
The lines on spacetime diagrams of SR are highly artificial but, like good maps, they describe an observed reality and the uniformity of the diagrams describes the scalar nature of c.

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Although Minkowski generalized time as a mathematical dimension, removing any independent identity, there were two beneficial effects for graphics. The nature of time vs space is eliminated thru the use of complex notation (ict), time is restored to a measurement of distance (which it was throughout history, and the scaling by c results in meaningful graphs for extreme speeds. The graphics now plot vt vs ct or v/c, a history of speed. In this setting 'c' becomes a conversion constant. It also simplifies calculation when assigned a value of 1 as a standard.

Einstein’s first and second postulates are unrelated so how can violating the second violate the first.
Changing the definition of c from a speed to a dimensional constant does not change the numerical value so the math remains the same.

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1. Light propagation in space can be considered as a physical process regulated by the laws of physics, thus constant in all frames, and included in the 1st postulate.
2. You can derive the 1st postulate using the 2nd, showing x'/t =x/t,

The structure of space is such that every interval of space includes an interval of time. Any two otherwise simultaneous events separated by space are also separated by an interval of time equal to one second for every 300,000 km of space. That determines the behavior of both light and gravity.

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If using SR graphics, 1 time unit ct = 1 space unit x. Measuring the speed of light does not explain how or why it has that specific value. If you introduce permittivity and permeability, then you need an explanation for those constants.
phyti
Member

Posts: 54
Joined: 04 Jul 2006

### Re: Fun with spacetime diagrams

phyti » November 2nd, 2017, 11:04 am wrote:Bangstrom;

How does a blocked signal make photons real?

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It shows something moves between emitter and receiver, and it can be blocked. An experiment involving photons can easily show they exist in intermediate locations other than emitter and detector. Photons are as real as any particle.

Photon particles (if they exist) can only be detected as electrons gaining and losing energy and blocking the signal only indicates that something in or about the space between can block a transfer of energy.
To say that “photons” are what is being blocked is an assumption rather than an observation.

phyti » November 2nd, 2017, 11:04 am wrote:Although Minkowski generalized time as a mathematical dimension, removing any independent identity, there were two beneficial effects for graphics. The nature of time vs space is eliminated thru the use of complex notation (ict), time is restored to a measurement of distance (which it was throughout history, and the scaling by c results in meaningful graphs for extreme speeds. The graphics now plot vt vs ct or v/c, a history of speed. In this setting 'c' becomes a conversion constant. It also
simplifies calculation when assigned a value of 1 as a standard.

In Minkowski diagrams, “c” is used as a dimensional constant rather than a speed where every square in the diagram represents a “time zone” that includes a unit of time with every unit of space and the proportion of time to space is a constant “c”. Every displacement in space includes an equivalent displacement in time independent of the speed of the object.

phyti » November 2nd, 2017, 11:04 am wrote:---------
1. Light propagation in space can be considered as a physical process regulated by the laws of physics, thus constant in all frames, and included in the 1st postulate.
2. You can derive the 1st postulate using the 2nd, showing x'/t =x/t,

There is nothing in Einsteins 1st Postulate that implies a speed and, in special relativity, “c” is used as a dimensional constant rather than a speed so, if we define “c” in Einstein’s second postulate as a dimensional constant rather than a speed, it simplifies SR and eliminates the frequent confusion that comes from trying to understand “c” as a speed. The uniformity of the diagrams should tell us that “c” is a dimensional constant and not a speed.

phyti » November 2nd, 2017, 11:04 am wrote:---------
If using SR graphics, 1 time unit ct = 1 space unit x. Measuring the speed of light does not explain how or why it has that specific value.

The structure and uniformity of spacetime diagrams where every square of space includes an interval of time proportional to “c” should tell us that “c” functions as a dimensional constant rather than as a speed. Trying to understand “c” as a speed only adds an element of confusion when trying to understand relativity and spacetime diagrams so it is an understanding best eliminated and forgotten.
bangstrom
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### Re: Fun with spacetime diagrams

Bangstrom,
I'm liking your stuff. If I'm interpreting it correctly it's fitting right in with my stuff if I ever get the chance to start writing again.
ralfcis
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