I can say that GPS works on the assumption that light travels at a finite speed of a precisely known value.
The speed of light is no longer a matter of experimentation, but is fixed by an international standard.
In the revised SI unit system, the speed of light in a vacuum is precisely equal to 299,792,458 m/s, and it helps to define the metre, kilogram and kelvin.
The GPS system uses this standard value of the speed of light in order to locate you.
If the speed of light were not finite, then GPS would not work.
Or to state it another way, the fact that GPS does work demonstrates that the speed of light can not be infinite.
The speed of light is no longer a matter of experimentation, but is fixed by an international standard.
In the revised SI unit system, the speed of light in a vacuum is precisely equal to 299,792,458 m/s, and it helps to define the metre, kilogram and kelvin.
The GPS system uses this standard value of the speed of light in order to locate you.
If the speed of light were not finite, then GPS would not work.
Or to state it another way, the fact that GPS does work demonstrates that the speed of light can not be infinite.
Right, I've now found this extensive article: https://www.intechopen.com/chapters...asuring,atomic clocks in its operation [ 16 ].
Notice the "appears to" that I've highlighted.
It's all about synchronised clocks again, the physics of which (Einstein and inertial frames) is given in the above article.
Doubts are cast on the methodology, as in "Since light was used to synchronise the clocks the objection to light speed measurement using these same clocks might be raised."
I'm not convinced, benb. 😒
Notice the "appears to" that I've highlighted.
It's all about synchronised clocks again, the physics of which (Einstein and inertial frames) is given in the above article.
Doubts are cast on the methodology, as in "Since light was used to synchronise the clocks the objection to light speed measurement using these same clocks might be raised."
I'm not convinced, benb. 😒
I finally reached the "Conclusion" section of that long "GPS and the one-way speed of light" article.
It included this statement:
That is a bold statement indeed! 😱
It included this statement:
That is a bold statement indeed! 😱
The "one-way" speed of light, from a source to a detector, cannot be measured independently of a convention as to how to synchronise the clocks at the source and the detector.
Telegraphers in the mid 19th century used a synchronisation method that was later applied to light signals by Einstein, who recognised its fundamental role in the special theory of relativity.
Einstein's clock synchronisation method was an attempt to set up an identical display on two remote clocks in a single inertial frame at the same time.
There is a method to synchronise two moving clocks with a third clock. However, if clock 1 and clock 2 are not synchronised directly, but by using an intermediate clock, the synchronisation depends on the path chosen.
This is the case with synchronisation around the circumference of the rotating Earth and results in a time difference that depends on the direction used.
Apparently, the Global Positioning System takes this time difference into account.
NOTE: I did a a HEAVY EDIT to tie in the third clock to the discussion! 😎
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... it's constant in any given environment. Usually specified as in a vacuum. But it varies in different media.
However, refraction (the change in speed when light crosses the boundary between two media of different optical densities) is not the factor in question in the GPS discussion.
There's a time difference that depends on the direction of travel around the rotating Earth.
At issue as is in the link I posted... the 'Einstein syncronization convention'. Simply that the two way speed of light is open to anyone's definition in terms of whether and how much of a difference there may be in the speed of light 'there' vs 'back'. No laws of physics are broken as long as they add up to C. So in fact, all the travelling time light uses could be on the way there but infinitely fast/instantaneous on the way back. Einstein himself conceded this.
Interesting and can lead to a discussion about the double slit experiment. Feynman is said to have remarked that all of physics secrets are bound up in understanding the double slit experiment. This was a tongue in cheek comment because no one has been able to successfully explain how light can have both a particle function and a wave function. It remains an enigma.
It is possible to generate single photon emissions and detect them as individual photons with a suitable detector. However, if you place another detector between the emitter and the original detector and turn it on so that both detectors are active, the original detector will not detect any photons - only the first one will. Assuming the photon radiation pattern is omni-directional, you can then move the second detector behind the emitter, but closer than the original, and the original detector will again not detect any photons. Turn the second detector off, and the original detector again picks up the photon emissions.
It is possible to generate single photon emissions and detect them as individual photons with a suitable detector. However, if you place another detector between the emitter and the original detector and turn it on so that both detectors are active, the original detector will not detect any photons - only the first one will. Assuming the photon radiation pattern is omni-directional, you can then move the second detector behind the emitter, but closer than the original, and the original detector will again not detect any photons. Turn the second detector off, and the original detector again picks up the photon emissions.
There has to be a 'conscious law' yet to be discovered intertwined in there because there has to be an observer. Has anyone tried using an animal as the observer? It could be as simple as having a cat notice the dot. Like when playing with a laser pointer.
A photon cannot simply be an expanding spherical wave because several light detectors placed equidistant from the source will not fire simultaneously.
Regarding the double slit experiment, interference requires a superposition of waves from two different points that are in phase with one another. This leads to the conclusion that a photon, whatever we conceive it to be, has to pass through both slits on its journey from the source to the screen or detectors. This means that, in it's extent from side to side, the photon it has to be at least as large as the slit separation!
QED theory mysteriously says that a photon has a number of possible paths it can take in order to get from A to B. This allows interference to take place between the wave amplitudes for the different paths. If we try to determine which path an individual photon took, by placing detectors behind the slits, we lose the interference pattern.
All very weird! 😵
No wonder we have given up trying to understand the inner workings of light!
Attachments
‘A photon cannot simply be an expanding spherical wave because several light detectors placed equidistant from the source will not fire simultaneously.’
And therein lies the mystery! One and only one detector will fire.
Schrodinger’s wave function shows that the wave collapses as soon as it interacts with an electron and the wave ceases to exist instantly for all potential observers.
And therein lies the mystery! One and only one detector will fire.
Schrodinger’s wave function shows that the wave collapses as soon as it interacts with an electron and the wave ceases to exist instantly for all potential observers.
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I originally started off my post with "All very weird!" then moved it further down.
I didn't intend to contradict you. Therein lies the mystery indeed!
Strange statement indeed given that we know it’s exactly 299,792,458 m/s. If it wasn’t fixed, Einstein would be in a whole lot of trouble.
Thought clarification experiment:-
A photon leaves a star some 5 billion LY distant. The ‘wave front’ of the photon is say 500 million LY across. When that photon interacts with an electron on the mirror coating of the telescope observing the distant star, it ceases to exist across the entire wave front of the photon. So the photon travelled across the cosmos as a wave, but the instant it interacted with an electron, it behaved like a particle.
A photon leaves a star some 5 billion LY distant. The ‘wave front’ of the photon is say 500 million LY across. When that photon interacts with an electron on the mirror coating of the telescope observing the distant star, it ceases to exist across the entire wave front of the photon. So the photon travelled across the cosmos as a wave, but the instant it interacted with an electron, it behaved like a particle.
Vabratasium got well deserved hate for his vedio tho . He is a fraud . Watch action lab he is genuine
It still has wave/particle duality afaik.
The trick is to look at things from the photon’s perspective. Time does not exist for a photon travelling at c. That being the case, how does a photon ‘experience’ distance?
You also have to consider the difference - especially wrt the double slit case - between a single photon and a light beam of many photons.
interesting article: https://physicsworld.com/a/double-slits-with-single-atoms/
interesting article: https://physicsworld.com/a/double-slits-with-single-atoms/
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