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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: flummoxed on 06/05/2019 16:53:38

Title: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 06/05/2019 16:53:38
Can Special Relativity be derived from Newtonian mechanics?  :-\

https://futurism.com/newtonian-physics-vs-special-realtivity


Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Bored chemist on 06/05/2019 17:03:03
No.
because they contradict eachother
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 06/05/2019 17:20:59
Can Special Relativity be derived from Newtonian mechanics?  :-\
To add to what @Bored chemist said, Newtonian mechanics does not contain any theory of electromagnetism which is key to special relativity.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: yor_on on 06/05/2019 19:48:56
No Newtonian mechanics came from a belief, that the world could be counted at.
Hup does not give you that

It might give you 'statistics'
But that's the long run

It does not include yourself.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 06/05/2019 20:15:54
I was thinking in terms of light clocks in a moving reference frame. ie The photon moves further and so ticks slower for a stationary observer. This could be modelled using newtons equations of motion.

How would special relativity give a different answer in this case to a Newtonian explanation of the same thing. Both are modelling the exact same light clock. Both are limited by the speed of light, are they not?


Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 06/05/2019 20:18:05
No Newtonian mechanics came from a belief, that the world could be counted at.
Hup does not give you that

It might give you 'statistics'
But that's the long run

It does not include yourself.

Does the HUP limit the speed of light to c via quantum foam. ?

How is the HUP related to special relativity or Newton mechanics ?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Bored chemist on 06/05/2019 20:47:42
If I start with a 1 Kg rock and apply 1 newton to it then it will accelerate at 1m/s/s.
Per Newton it will accelerate forever.
Per Einstein it will accelerate less as time goes on, because there's a limit at C.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: yor_on on 06/05/2019 21:18:10
Beautiful BC :)

As for a quantum foam? Under Planck scale?
Your guess is as good as mine.

Scaling it up 'c' will be a limit though.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: yor_on on 06/05/2019 21:24:23
I don't expect Newton to have known about 'HUP', I read someone say that everything has its season. What it might me think is that even though you stand upon someones shoulders gaining new ideas, it also might be read as time have passed on.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: evan_au on 06/05/2019 23:04:16
Quote from: flummoxed
The photon moves further and so ticks slower for a stationary observer.
Perhaps you are thinking that Newton could have discovered the Doppler effect long before Doppler: the frequency of light shifts towards the red when you are moving away from an object.

But this depends on understanding light as a wave - and Newton came down on the side of the debate that said "light is a particle".

See: https://en.wikipedia.org/wiki/Corpuscular_theory_of_light#Isaac_Newton

Now we understand that light has characteristics of both a wave and a particle, so we can apply Doppler shift to light (such as in Police radar).

But this is a long way from understanding that:
- Light has a specific speed (in a vacuum): would not have been known until Maxwell's equations of electromagnetism
- Every observer sees light with this speed (in their own lab)
- This paradox is related to time dilation of observers moving relative to each other
- The existence of this paradox would not have been understood before the Michelson-Morley experiment
See: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Most_famous_%22failed%22_experiment
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 07/05/2019 00:00:11
If I start with a 1 Kg rock and apply 1 newton to it then it will accelerate at 1m/s/s.
Per Newton it will accelerate forever.
Per Einstein it will accelerate less as time goes on, because there's a limit at C.

Am I correct in thinking acceleration is to do with general relativity and not special relativity? Special relativity deals with none accelerating objects does it not.

Using simple algebra and tracing the path of a photon between two moving mirrors, will result in time dilation for an observer in a stationary reference frame. Assuming of course that light is fixed at c for the observer and someone moving with the mirrors.

Would Newton have assumed that light speeded up for the observer, so that the clocks would still tick at the same rate, for the observer and for someone moving with the mirrors?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 07/05/2019 00:21:13
Perhaps you are thinking that Newton could have discovered the Doppler effect long before Doppler: the frequency of light shifts towards the red when you are moving away from an object.But this depends on understanding light as a wave - and Newton came down on the side of the debate that said "light is a particle".

Both Newton and Einstein viewed photons as particles.

How does viewing light as a wave affect a photons movement between two moving none accelerated mirrors?

I understand special relativity has been inccorporated into quantum field theory and QED. But Special relativity does not need Quantum field theory. What am I missing in what way does special relativity include waves and quantum theory?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Halc on 07/05/2019 02:53:02
Am I correct in thinking acceleration is to do with general relativity and not special relativity? Special relativity deals with none accelerating objects does it not.
Special relativity deals with acceleration just fine.  General relativity introduce the equivalence principle with allowed the properties of gravitational fields to be (locally) described in terms of accelerating reference frames.
Newton's equations did not cap speed of mass at c.  F=ma.  If you continue to apply force to an object, the acceleration will continue up to any beyond c.  With SR, acceleration (not proper acceleration) drops off and that same force just drives up m after a while.  They do this in particle accelerators where getting a particle to near light speed is easy, but then they just add mass to the thing until up to the limits of the magnetic field to hold it in its path.

Quote
Using simple algebra and tracing the path of a photon between two moving mirrors, will result in time dilation for an observer in a stationary reference frame.
Reference frames are not stationary.  Things are stationary relative to them.
That said, I see what you are getting at.  Newton probably wouldn't consider the light device to be a clock since without knowing its speed, there is no way to tell how far the light needs to travel.  Not like there is any real light clock anyway.  How would you get it to work?  You can't measure a photon going between mirrors, counting cycles.  A photon can be measured but once.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 07/05/2019 10:36:47
They do this in particle accelerators where getting a particle to near light speed is easy, but then they just add mass to the thing until up to the limits of the magnetic field to hold it in its path.

How is this explained, is it that does the particle shrinks to the observers, and Its inertia and or wavefunction frequency, increases. 
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: geordief on 07/05/2019 11:51:48
They do this in particle accelerators where getting a particle to near light speed is easy, but then they just add mass to the thing until up to the limits of the magnetic field to hold it in its path.
Can it be argued that the force applied in a particle accelerator has its own speed of propagation and that it would for this reason be unreasonable for the particle to be accelerated to a speed higher than that of the speed of the force itself?

If true ,would that observation have any theoretical consequences?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Halc on 07/05/2019 12:20:49
How is this explained, is it that does the particle shrinks to the observers, and Its inertia and or wavefunction frequency, increases.
Newton has no explanaion.  He'd say that a continued force would give it more kinetic energy (correct) and so the v must be going up (it is accelerating indefinitely, wrong).  E = ĹMV≤, so V can get highter than c.  You could outrun light just like you could theoretically accelerate past sound.  Neither had been demonstrated in Newton's time.

Anyway, SR says a (acceleration in F=ma) approaches zero as v approaches c, so kinetic energy must be gained by an increase of mass.  You called it inertia.  Same thing.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Halc on 07/05/2019 12:33:36
Can it be argued that the force applied in a particle accelerator has its own speed of propagation and that it would for this reason be unreasonable for the particle to be accelerated to a speed higher than that of the speed of the force itself?

If true ,would that observation have any theoretical consequences?
That would imply that as a particle approached c, the force on it would decrease, which would be measurable in the drop in reaction magnitude.  The recoil of a railgun would approach zero if the projectile is already going fast.

The force is applied via a field set up along the entire length of the accelerator, so is is not an issue of trying to keep up. The particle isn't pushed from some endpoint like it is in a chemical gun or a light sail, both of which would nevertheless have recoil even without a projectile since it uses mass to convey force to the projectile whether it is there or not.  Fire a cannon without a ball and it still has some recoil due to the accelerating powder, but not nearly as much as with the ball.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: geordief on 07/05/2019 13:48:28
which would be measurable in the drop in reaction magnitude. 
How would that be measurable. Isn't the acceleration (change in speed) the only measurable effect?
The force is applied via a field set up along the entire length of the accelerator, so is is not an issue of trying to keep up. The particle isn't pushed from some endpoint like it is in a chemical gun or a light sail, both of which would nevertheless have recoil even without a projectile since it uses mass to convey force to the projectile whether it is there or not.  Fire a cannon without a ball and it still has some recoil due to the accelerating powder, but not nearly as much as with the ball. 

Yes ,I appreciate that the force is applied equally at every point along the trajectory (no one point of emanation) ,but does this force  still always have a (same) speed of propagation at every point regardless?

If this force propagates at c  how could it propel any object to a faster speed?

Am I right to imagine that the speed of propagation of force is actually a valid concept?( ordinary physical waves in a medium  do apply a force that applies an acceleration as a function of their speed of propagation;would  the same hold for em waves?)

I apologize if I am showing my ignorance ;-)
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Halc on 07/05/2019 15:19:30
Quote from: Halc
which would be measurable in the drop in reaction magnitude.
How would that be measurable. Isn't the acceleration (change in speed) the only measurable effect?
One can measure force, no?  Most of the force applied by a cyclotron (as opposed to a linear accelerator) is used to bend the fast moving particle into a circular path.  That goes up as the the particles gains mass even though the increase in speed (not the same as acceleration) drops to near zero.
Quote
Yes ,I appreciate that the force is applied equally at every point along the trajectory (no one point of emanation) ,but does this force  still always have a (same) speed of propagation at every point regardless?
A force is a field, not something that needs to propagate. Gravity has no propagation speed for instance.  A change in the field does need to propagate, so that is indeed confined to light speed, just like gravity waves.
I don't know enough about particle accelerators to say if the field needs to change and thus need an awareness of the particle location or an awareness of the focus of the beam. I suspect not on the former at least, even though a mag-lev train certainly involves such awareness of the projectile as it passes, possibly only for energy efficiency and levitation purposes.

Quote
If this force propagates at c  how could it propel any object to a faster speed?
Oh, you're asking about the Newton thing.
Did Newton have any idea that EM force was a field or that light speed was relevant at all here?  Why not use gravity?  Throw a rock at nearly light speed into a star and the gravity (which is a field, but Newton might not have known that) would boost it over c.  The gravity would hardly need to 'keep up' since the rock is not moving away from the star.
Newton did have a crude speed of light figure available to him.  It was first measured when Newton was about age 35.

Quote
Am I right to imagine that the speed of propagation of force is actually a valid concept?
A change in a field needs to propagate, but the field itself isn't something that has a velocity.  Again, Newton likely wouldn't have worded things that way.
Quote
( ordinary physical waves in a medium  do apply a force that applies an acceleration as a function of their speed of propagation;would  the same hold for em waves?)
I'm trying to figure out a case where waves do that.  In general, a bit of flotsam on the water tends to go nowhere as waves pass, but a surfer can ride a wave if he can stay consistently on one side of it, and propel himself to considerably higher speeds than the speed of the wave.  Similarly, a sailboat can move faster than the wind.
A field is more like a hill and less like a wave.  I can accelerate as I roll down a hill and don't need to worry about the speed of the medium as I do so.

Quote
I apologize if I am showing my ignorance ;-)
Don't think there is ignorance here.  We're trying to posit what Newton might have concluded for these question given the state of science at the time.  We know he suspected light speed to frame dependent, so the conclusions drawn from it being otherwise were unavailable to him.  The universe appeared more or less static.  There are other stars, and they have a bit of relative motion, but nothing anywhere appeared to be going particularly fast.  The idea of galaxies (or any large structure held together with mutual gravity) was unknown at the time, let alone the fact that they recede from each other, which wasn't even known to Einstein at first.  So the model of the universe was just sort of a soup of stars wandering here and there.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: geordief on 07/05/2019 18:40:46
I think I might have been a little off topic .I have just started a new thread on this subject.

Hope it goes well.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 08/05/2019 09:03:27

How is the HUP related to special relativity or Newton mechanics ?
Relativity makes accurate predictions for all sizes of objects from astronomical to atomic/quantum, but HUP is only relevant to atomic/quantum.

You might better turn your question around and ask whether Newtonian mechanics can be derived from special relativity: answer, it can as it is an approximation of relativistic mechanics at low speeds.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 08/05/2019 10:09:14

How is the HUP related to special relativity or Newton mechanics ?
Relativity makes accurate predictions for all sizes of objects from astronomical to atomic/quantum, but HUP is only relevant to atomic/quantum.

You might better turn your question around and ask whether Newtonian mechanics can be derived from special relativity: answer, it can as it is an approximation of relativistic mechanics at low speeds.

Yor_on raised the HUP in post 3, I guess ultimatly all field equations will be replaced, or modified to include a quantum mechanical explanation.

Ah Ah Bingo; Do you have a paper showing how the approximate derivation is done??   
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 08/05/2019 22:53:27
Ah Ah Bingo; Do you have a paper showing how the approximate derivation is done??   
No one would write a paper on something that is so obvious, just follow the Lorentz transforms at low speeds.

Note that Newtonian mechanics vs relativistic mecanics is not the end of the story, Einsteinís paper which introduced special relativity was on a problem in electrodynamics which he solved.

I guess ultimatly all field equations will be replaced, or modified to include a quantum mechanical explanation.
You guess wrong, qft is a development of qm to explain particle creation/destruction. In qft the photon description is based on Maxwellís equations.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 09/05/2019 09:59:41
Ah Ah Bingo; Do you have a paper showing how the approximate derivation is done??   
No one would write a paper on something that is so obvious, just follow the Lorentz transforms at low speeds.

Note that Newtonian mechanics vs relativistic mecanics is not the end of the story, Einsteinís paper which introduced special relativity was on a problem in electrodynamics which he solved.

I guess ultimatly all field equations will be replaced, or modified to include a quantum mechanical explanation.
You guess wrong, qft is a development of qm to explain particle creation/destruction. In qft the photon description is based on Maxwellís equations.

Some one has written a pdf involving NM and SR  http://www.trybasics.com/ewExternalFiles/Understanding%20SRT%202c%204-2-17.pdf 
I started reading it last night, I require a print out to follow it.

I think maybe it is time to buy another book, does anyone have a good recommendation for a book on QFT including a good section on QED. ??????????????

I had viewed radio waves as being electrical polarisations of the EM field prior to this thread. Now I know a radio wave is made up of photons which are NOT influenced by electrical or magnetic fields. These photons may be due to virtual particle pairs near the transmitter recombining to produce a wave of photons. 
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 09/05/2019 16:40:23
Some one has written a pdf involving NM and SR  http://www.trybasics.com/ewExternalFiles/Understanding%20SRT%202c%204-2-17.pdf 
I started reading it last night, I require a print out to follow it.
I had a quick look at the paper. Quite amusing, let me know when you spot the problems.

These photons may be due to virtual particle pairs near the transmitter recombining to produce a wave of photons.
Or not!  ;D
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 10/05/2019 10:47:09
Some one has written a pdf involving NM and SR  I started reading it last night, I require a print out to follow it.
I had a quick look at the paper. Quite amusing, let me know when you spot the problems.

These photons may be due to virtual particle pairs near the transmitter recombining to produce a wave of photons.
Or not!  ;D

A number of issues have already been pointed out on this thread, and yes I have spotted what I think are problems.

Or What :)

Edit I must admit I only glanced at the link before posting it, in response to your other none answer :)
 

Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 10/05/2019 14:42:50
I have spotted what I think are problems.
To giive him his due, it is a better attempt at a new theory/relativity denyer then most, but suffers from the problem most do, a lack of understanding of special relativity and in this case also of Galilean relativity
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: yor_on on 10/05/2019 19:23:19
As far as I get it you're correct. " Am I correct in thinking acceleration is to do with general relativity and not special relativity? Special relativity deals with none accelerating objects. "

It's actually very weird.
And you have one of two simple choices.

Either you believe it to be correct, or you don't.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 10/05/2019 23:20:01
As far as I get it you're correct. " Am I correct in thinking acceleration is to do with general relativity and not special relativity? Special relativity deals with none accelerating objects. "
No, heís incorrect.
Although SR is most often used for contant velocity, it can handle acceleration.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 11/05/2019 21:17:43
How did Newton think of light? From his perspective light was made of particles. Robert Hooke and others believed light was wavelike. Yes this debate went all that way back!

http://www.thestargarden.co.uk/Newtons-theory-of-light.html

Nothing about the speed of light though. Here is more on that journey of discovery.

http://www.thestargarden.co.uk/Speed-of-light.html
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 11/05/2019 21:30:48
BTW take note of Fitzeau and Foucault's use of the rotating mirror. Using reflection to destroy Newton's assumption. That was genius!
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 11/05/2019 22:51:34
Oh, and by the way where did Lorentz pick up the idea for his transformation?
https://en.m.wikipedia.org/wiki/Woldemar_Voigt
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 11/05/2019 22:56:18
Hint: It wasn't from Voigt.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: set fair on 12/05/2019 01:58:50
Special relativity was derived from Newtonian physics.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 12/05/2019 07:59:53
Special relativity was derived from Newtonian physics.
Please explain how.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 12/05/2019 12:13:23
Well consider something else unknown to Newton. The effect of media on the speed of light.

https://en.m.wikiversity.org/wiki/Light_in_moving_media

This includes media in motion. All of this has a part to play in special relativity. Newtonian mechanics cannot produce the equations of special relativity. If you believe it can you are misguided. If you are saying it can just to be contrary then you are being dishonest. Which is it?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 12/05/2019 14:33:53
One last thing. The movement of light through a moving medium guarantees an observer to measure the speed of light as constant irrespective of its direction of travel towards the observer. As long as the frame of reference is inertial and the observer is moving with the medium.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: set fair on 12/05/2019 14:53:22
Special relativity was derived from Newtonian physics.
Please explain how.

Einstein took Newtonian theory and the observation that the speed of light was the same whether the observer was at rest or moving relative to the light source and that led him to the special theory of relativity.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 12/05/2019 15:02:37
Einstein took Newtonian theory and the observation that the speed of light was the same whether the observer was at rest or moving relative to the light source and that led him to the special theory of relativity.
Wrong, thatís not what he did.
Guess again.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 13/05/2019 21:16:54
Here is another point to ponder. The speed of light through a medium is dependent upon the refractive index of the medium. What is the refractive index of the vacuum? The vacuum is an absence of anything. So why is the value of c the speed of light in the vacuum? Why not 10c or 1000c or 602.5c? What exactly is limiting the speed of light?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 13/05/2019 21:20:42
Hint: you cannot use the ratio itself to answer this question. That would be circular reasoning.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: geordief on 13/05/2019 22:17:42
Here is another point to ponder. The speed of light through a medium is dependent upon the refractive index of the medium. What is the refractive index of the vacuum? The vacuum is an absence of anything. So why is the value of c the speed of light in the vacuum? Why not 10c or 1000c or 602.5c? What exactly is limiting the speed of light?
Mass seems to make things move more slowly so massless objects should move fastest.

Since things must move at a finite speed (the alternative would be that everything would happen at the same time and causality would  collapse),massless objects must move at this maximum  but finite speed.

This speed is found experimentally to be c.

So nothing is limiting the speed of light  and it just moves at the maximum speed.

That is my take.I hope it is right ;-)
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 13/05/2019 23:15:49
Mass seems to make things move more slowly so massless objects should move fastest.
That logic doesnít work here. Mass makes things accelerate more slowly for a given force, but final speed is dependent on both force and time, both of which are variable.

Since things must move at a finite speed (the alternative would be that everything would happen at the same time and causality would  collapse)
Again this  isnít logical. Even if everything could move at infinite speed it doesnít mean everything would happen at once.

This speed is found experimentally to be c.
It hasnít been found experimentally, it is a consequence of SR. No experiments to date have taken objects with mass to c, but the experiments below c show that the speed/energy relationship follows the predictions of SR and therefore c appears to be the limiting speed for objects with mass.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Bogie_smiles on 13/05/2019 23:33:43
Here is another point to ponder. The speed of light through a medium is dependent upon the refractive index of the medium. What is the refractive index of the vacuum? The vacuum is an absence of anything. So why is the value of c the speed of light in the vacuum? Why not 10c or 1000c or 602.5c? What exactly is limiting the speed of light?
Mass seems to make things move more slowly so massless objects should move fastest.

Since things must move at a finite speed (the alternative would be that everything would happen at the same time and causality would  collapse), massless objects must move at this maximum  but finite speed.

This speed is found experimentally to be c.

So nothing is limiting the speed of light  and it just moves at the maximum speed.

That is my take. I hope it is right ;-)
There is no perfect vacuum, and in that context, there is never an ďabsence of anythingĒ. So can we say that the refractive index is variable, relative to the medium?

Refractive index
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium. It is defined as.

From Wikipedia, the free encyclopedia



A ray of light being refracted in a plastic block
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light propagates through the material. It is defined as
n=c/v

where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times as fast in vacuum as in water.

Edit: See Wiki on Refractive index
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 14/05/2019 09:14:08
There is no perfect vacuum, and in that context, there is never an ďabsence of anythingĒ. So can we say that the refractive index is variable, relative to the medium?
You have copied a large section of Wiki but donít seem to have answered the question or shown itís relevance to the topic.
Although there is rarely a perfect vacuum, space is extremely close (even the speed of light in air is not far off vacuum) and CERN is able to produce pressure of the order of 10-10 to 10-11 mbar - a vacuum almost as rarefied as that found on the surface of the Moon. At these pressures there is little practical difference between the theoretical speed of light in vacuum and that measured in the accelerator.

So, within the limits we can measure SR hangs together and tests in particle accelerators confirm this.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: geordief on 14/05/2019 13:06:59
Mass seems to make things move more slowly so massless objects should move fastest.
That logic doesnít work here. Mass makes things accelerate more slowly for a given force, but final speed is dependent on both force and time, both of which are variable.

Quote from: geordief on Yesterday at 22:17:42
Since things must move at a finite speed (the alternative would be that everything would happen at the same time and causality would  collapse)
Again this  isnít logical. Even if everything could move at infinite speed it doesnít mean everything would happen at once.

I accept that.

Is there any reason to suppose that the maximum speed limited is connected to the size of the observable plus unobservable universe?

Have I gone off topic now?
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 14/05/2019 14:52:31
Is there any reason to suppose that the maximum speed limited is connected to the size of the observable plus unobservable universe?
No, size never came into the equation.
It has to do with electrodynamics, specifically the physics of electric and magnetic fields as derived by Faraday, Amper, Coulomb and Gauss, and what happens when they move. Einstein just followed it through to its logical conclusion. I say Ďjustí, but in reality it was a big leap solving problems which had been puzzling scientists for quite a while.
This is also why you canít derive SR from Newtonian mechanics.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: jeffreyH on 15/05/2019 20:44:27
The question of why the speed limit of light in a vacuum is c is one of those unanswerable questions, as Feynman pointed out in interviews. The problem with posters who pose questions such as the one in this thread is that they do not appreciate these types of issues.

When you argue against established knowledge you need to be able to support your position. You cannot simply guess that you have found a 'loophole'. That benefits no one.

Newton was around at a time when Galilean relativity was still the norm. He was a very clever man but was limited in his knowledge nonetheless.
Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: flummoxed on 16/05/2019 09:49:13
Here is another point to ponder. The speed of light through a medium is dependent upon the refractive index of the medium. What is the refractive index of the vacuum? The vacuum is an absence of anything. So why is the value of c the speed of light in the vacuum? Why not 10c or 1000c or 602.5c? What exactly is limiting the speed of light?
Mass seems to make things move more slowly so massless objects should move fastest.

Since things must move at a finite speed (the alternative would be that everything would happen at the same time and causality would  collapse),massless objects must move at this maximum  but finite speed.

This speed is found experimentally to be c.

So nothing is limiting the speed of light  and it just moves at the maximum speed.

That is my take.I hope it is right ;-)

You can view c as being a fixed constant that goes in exactly straight lines.

But

It is reasonable to assume light is limited by the medium it travels through "in all cases". For space c=1/fcfe13476a678364404ce0a3c2fb5b6f.gif 

Light speed has been measured to be c, as it travels through space which is full of virtual particles, CBR, and various other little bits of matter :) which probably dont matter too much in the scheme of things. It will be absorbed and reemitted and interact with virtual particles it passes through. Similiar to the way it moves through other materials.

Space has no refractive index and is transparent to electromagnetic waves.

Generally the speed of light is thought to be c, but these guys think they might be able to go faster :)

https://www.livescience.com/29111-speed-of-light-not-constant.html  ;D


Title: Re: Can Special Relativity be derived from Newtonian Mechanics?
Post by: Colin2B on 17/05/2019 10:55:10

Light speed has been measured to be c, as it travels through space which is full of virtual particles, CBR, and various other little bits of matter :) which probably dont matter too much in the scheme of things. It will be absorbed and reemitted and interact with virtual particles it passes through. Similiar to the way it moves through other materials.
Please don't put speculation and New Theories into this section of the forum.
Thank you
We'll answer on this occasion but bear in mind that in future posts may be moved or you could be limited to 'The Lighter Side'  ;)

The amount of matter in space is very sparse and the main interactions are scattering and absorption. Even air, which is relatively dense makes only a small decrease in the speed compared to vacuum and to suggest light is slowed significantly by matter Ė virtual or otherwise Ė implies very dense matter.
One interesting aspect is dispersion, which occurs when light travels through a medium. This can be seen with pulsars where higher frequencies arrive earlier than lower frequencies which interact with free electrons. However, in the sort of vacuum we see in, say, CERN accelerators, the speed is as close to theoretical as is measurable.

References to virtual particles can be very misleading and are often taken out of context.
I know I keep banging on about people misinterpreting jargon and shorthand terms, but itís worth reading eg https://www.physicsforums.com/insights/misconceptions-virtual-particles and https://www.physicsforums.com/insights/physics-virtual-particles also https://www.physicsforums.com/insights/vacuum-fluctuation-myth
This is also why virtual photons donít become real photons in the near field, and why photons canít Ďbang intoí virtual particles. Itís also why pop science descriptions of the Casmir effect which quote virtual photons are misleading.


Generally the speed of light is thought to be c, but these guys think they might be able to go faster :)
https://www.livescience.com/29111-speed-of-light-not-constant.html ;D
Very new theory and 2 separate views. As quoted in the article ďSome scientists are a bit skeptical, though. Jay Wacker, a particle physicist at the SLAC National Accelerator Laboratory, said he wasn't confident about the mathematical techniques used, and that it seemed in both cases the scientists weren't applying the mathematical tools in the way that most would. "The proper way to do this is with the Feynman diagrams," Wacker said. "It's a very interesting question [the speed of light]," he added, but the methods used in these papers are probably not sufficient to investigate it.Ē