# Thread: Has the One-Way Speed of Light Really Been Tested?

1. Have any experiments really tested the one-way speed of light?

Many experiments claiming to be one-way tests have either been shown to be really two way tests or to be compatible with theories postulating that all matter undergoes length compression and time dilation, according to the Wikipedia article “One-way speed of light.”

Tom Roberts list of tests still contains many one-way tests. I have found some of them compatible with Lorentz-Poincare universal-reference-frame theory. Mossbauer type anisotrophic tests miss time dilation affecting emitter and receiver. Cole Very Long Baseline Interferometry misses contraction in the baseline and the angle of the celestial body.

Is anyone familiar with Zhang's work reviewing the “one way” tests or with the four test theories of Special Relativity?

2.

3. The one paragraph in the Wikipedia article that stands out for me is this one :

In Einstein's special theory of relativity, all inertial frames of reference are equivalent and there is no preferred frame. There are theories, such as Lorentz ether theory that are experimentally and mathematically equivalent to special relativity but have a preferred reference frame. In order for these theories to be compatible with experimental results the preferred frame must be undetectable. In other words it is a preferred frame in principle only, in practice all inertial frames must be equivalent, as in special relativity.
Thus, it is possible to formulate a theory that incorporates a preferred frame, but such a theory would be indistinguishable in experiment from SRT.

4. Between one way direction and two way it,s not said two way direction is symmetrical for both directions.
In the theory for graviton exchange for instance there is an assumed symmetry because gravity is assumed symmetric. Gravitons go from A to B as well as vice versa (kinda pointless idea ; exchanging same thing).

It,s not impossible to have a symmetric exchange with particles. For instance economic interactions are mostly two way (at least not one way) but not symmetric.

Reference frames in fysics are not just tied to (human or technical) observers also to emitters (at least one) and even energysources, for instance a battery or generator is an emittor in a system of wires to the connected lamps.

For such a system the lamps are not emitters but receivers/observers before they can be emitter in visual spectrum.

This means with any particular choice of spectrum there is specific distinction of emitter(s) and receivers.
Assumed one emitter in light spectrum (a lamp or laser for instance) it needs at least one receiver to speak of light.

It doesn,t need a preferred frame of reference then not two identical frames of reference.

Only when the frames of references are personalized ; using a person that uses a lamp for instance. But this person is just as well an observer to his own lamp. Only at very short distance.

5. The main problem for you to measure 1 way speed of light is, how does the person detecting it determine when the light was emitted? Knowing how far it has traveled isn't all that hard, but knowing how long it took is a bit of a problem if you don't know when it left.

6. The detection is an experience. Experiences don,t travel. Same as with sound ; Someone can shout but there is no sound without hearing because sound is an experience.
So how can sound travel if there is no ear travelling from the mouth that shouts ?
Or an eye from the laser a radio from the radiotransmitter ?

I prefer a more geometrical view for this lightspeed. The energy of a radio creates it,s own timespace using vacuum (enough of that). A first timecoordinate t=0 and any following coordinate regarded as part of information itself. hence t=0 travels at lightspeed just as well. According to laws of nature.

All radios at all distances will detect t=0 at t=0 for this particular timespace. The local clock at the radio-emitter is like the bug in the fur of the hare (the signal) or the turtle on it,s back.

Local clocks will meassure timedistance just the same when they where set to each other at close distance. But not when they used the radio to set the clock.

If every radio has an inbuild clock functioning on the emitter the local clock (not inbuild) will still show 1 sec difference to the inbuild clock when the distance is 1 Ls.

This says something about the distance but not about travelling signals in timespace when timespace is created by the radio-emitter (energy) and the radio,s (at least one) tuned to it,s frequency at particular distance. Every radiofrequency is a timespace of emitters and receivers then. The emitter will always need energy to be active for this but not the receiver (except for amplifying).

Timespace can be the specific frame for the emission then. Unicquely different to the referenceframe of a radio but not one way system. There is no emitted signal from a radiotransmitter without at least one radio. No timespace for it or from it nothing.

The radiotransmitter with the radioreceiver together is radio. A radiotransmitter that emits at a frequency that is not detected anywhere or somewhere doesn,t have a signal or frequency or timespace or anything. It,s not a radiotransmitter then. To proof that wrong needs a radio and that immediately disprooves this disproval.

7. What are you talking about? Complete gibberish.

The detection is an experience. Experiences don,t travel. Same as with sound ; Someone can shout but there is no sound without a hearing because sound is an experience.
So how can sound travel then if there is no ear travelling from the mouth that shouts ?
Or an eye from the laser or radio from the radiotransmitter ?
Sound and light are phenomena. They happen, even if nothing is there to "experience" it.

8. Completely incomprehensible word salad.

9. Incomprehensible is open for different interpretations.

"They happen, even if nothing is there to "experience" it".

Experimental verification is the technical analogue to human experience or observation. Basically it can be considered an experience by the detectingdevice included a distance to the source. The data outcome, a photonegative, soundrecording is the registration.
As long as light would be travelling it can,t have reached a detection device. So no experimental verification or showing is possible.
This makes the quote religion or methaphysics. Incomprehensible wordsalad if you want.

How to show "light happens" experimental before it reaches a photocamera or some other detectiondevice ?

Be brave and try find an experiment and suggest it here or admit it is impossible ?
Maybe bring a camera closer to what it photographs ? Keep an ear to a speakerbox or someones mouth ? It still has a distance then or it hears or sees nothing.

Other question ? What does a photography negative show when a lightsource is photographed ? Black.
The negative is the interesting part of photography for fysics more then the photo from the negative....

10. Originally Posted by Ghrasp
Incomprehensible is open for different interpretations.
This may well be. However, it appears I am not alone in my opinion.

"They happen, even if nothing is there to "experience" it".
This really belongs in the realm of Philosophy, for which there is a separate sub-forum.

11. "Not alone in you,re opinion" ......congratulated, does it feel comfortable ?

Some problems thrown up by philosophers are inescapable. Filosophy is not the study of filosophy it,s the filophying. Can you philosophy in the realm of fysics or does this conflikt with feeling comfortable

12. Originally Posted by Ghrasp
Can you philosophy in the realm of fysics or does this conflikt with feeling comfortable
The problem is that physics is science and philosophy, well, isn't.

Philosophy isn't particularly useful in the real world.

Whereas science and applied science (aka engineering) are. You do know that the computer you are using was designed using scientific and engineering principles. Not philosophy.

13. "Philosophy isn't particularly useful in the real world".

Wow, you never philosophy on anything ?

Such a distinction (or trying to make it) is totally artificial. It,s the distinction universities use for there studies to follow. In our culture such a distinction never was obvious and isn,t obvious.
One example of a philosophic work in modern culture making a vivid connection to fysics is Wittgensteins "on colors". An underestimated part of his work by philophers maybe for similar reason ; philosophers feel uncomfortable with it, not knowing what to do with it as they think it belongs to fysics more. Just as fysicists may think it belongs to philosophy.
Then it belongs to nothing. But truly it belongs to our culture, to us.

"You do know that the computer you are using was designed using scientific and engineering principles. Not philosophy".

I know and it bugs me. You think I should not use it ? I often do (think so). Sure will do after this post .... goodbye then.

14. Originally Posted by Ghrasp
"Philosophy isn't particularly useful in the real world".

Wow, you never philosophy on anything ?
So what practical results has it produced? Is there a branch of applied philosophy that produces improvements in people's lives?

One example of a philosophic work in modern culture making a vivid connection to fysics is Wittgensteins "on colors".
How many people other than philosophers have heard of it (never mind read it)? What practical difference has it made to anything?

15. Would science methods of today have existed without philosophers as David Hume ?
Theory,s in science have to show themself experimental or in practical use. Show me (practice or experimental) sound to exist before detection.
That would show it before scientific verification then also.

A- "sound travels from my mouth to you,re ear (or any membrane)".
B, (Testing) : -"can this sound be a specific word for this ?"
A- "Why not ?"
B- "Then this word travels from you,re mouth to my ear ?"
A - "
It should yes."
B - "What if this specific word is the word "sound" ?
Does "sound" travel at speed of sound then" ?

16. Originally Posted by Ghrasp
Would science methods of today have existed without philosophers as David Hume ?
Well, Roger Bacon is perhaps more important. But, yes, I will grant you that the philosophy of science has, perhaps, been useful in refining the scientific method. But it is science that has done all the real work since.

Theory,s in science have to show themself experimental or in practical use. Show me (practice or experimental) sound to exist before detection.
That would show it before scientific verification then also.
Any practical or experimental detection of sound would be science not philosophy. Science tells us what sound is, how fast it travels and everything about it. What does philosophy tell us? Meaningless speculation about whether a sound exists if there is no one there to hear it is (perhaps) philosophy. And useless.

A- "sound travels from my mouth to you,re ear (or any membrane)".
B, (Testing) : -"can this sound be a specific word for this ?"
A- "Why not ?"
B- "Then this word travels from you,re mouth to my ear ?"
A - "
It should yes."
B - "What if this specific word is the word "sound" ?
Does "sound" travel at speed of sound then" ?
I have no idea what that is supposed to mean. Maybe it is a language problem. But if that is philosophy, I think you have proved my point.

17. A and B are in a dialogue that needs some sense for absurdity to make sense.

18. Originally Posted by Ghrasp
A and B are in a dialogue that needs some sense for absurdity to make sense.
Sorry, it just looks like a bad joke to me. "Sound" travels at the speed of sound. Hilarious.

Meanwhile, science continues to produce useful results.

19. Better to look for original questions for "light travels with one way speed of light" or phrases as
"sound travels at soundspeed" what meaningfull questions can be found where this could be a meaningfull answer ?

Then concentrate on provabillity for these questions.

"what speed does sound travel" ?
this allready assumes "sound has speed" ; soundspeed as a meaningfull phrase.
A fitting question for that : "does sound have speed" ?

Proof the provabillity makes it a meaningfull science question. Disproof provabillity makes it meaningless question for science.
I disprooved the provabillity.

If these questions are without provabillity then how can an answer on these questions be different then meaningless just the same ?

Even speculating on an answer is meaningless then. Trying to disproof a meaningless answer to a meaningless questions is meaningless also. Light has no speed is just as meaningless for instance. But my posts are on provabillity not on a proof or disproof discussion.
Just as the topic starters first post was asking for provabillity with an existing experiment or thinkable experiment with abillity to show. It,s legitimate and necessary part of every realm of science to discuss provabillity first. I know that and I haven,t even studied at university level.

Or someone must come up here with a meaningfull question for : "sound travels one way" or "Light has one-way speed".

Without any meaningfull question to begin with there is no way to have an idea on provabillity. Without that it,s not science.

20. Sound has many different speeds depending on the medium through which it is transmitted. So as such, that is completely different than the speed of light in a vacuum in our Universe, which is a fundamental property of the Universe.

21. The speed of light in a vacuum seems well established. The two way speed of light in any inertial frame seems well established by experiment. That a one-way speed of light would be identical in all inertial frames seems to be the first and most important step on the road to abandoning all causality and the first and most important step to becoming a physicist in the early twenty first century. It seems to be a major source of philosophical writing and confusion, too. Hence the original question.

Yet frame independence should be testable.

Is it becoming possible to test length compression? (Not yet, it seems)
Is it becoming possible to run tests from frames moving fast, at least with respect to the Earth?
What do the GPS satellites see of the clocks on Earth? Corrections for the differing gravity potential seem to work well for Earth views of the satellite clocks. Has viewing Earth clocks from the satellites been predicted or measured?

Do pictures taken from satellites, preferably minimizing lenses, show a narrower earth or shorter distance between cities as suggested by Special Relativity with corrections for General Relativity effects? Speeds may be too slow, ...
Can sensors on a rotating platform be moving fast enough to measure distances in the Earth frame?

22. Originally Posted by mnpguy
Is it becoming possible to test length compression? (Not yet, it seems)
Actually it is possible, because length contraction is intimately connected to time dilation. The classic observation here is atmospheric muon decay; those muons can only reach Earth's surface if the atmosphere is length contracted from the point of view of the muon itself.

Is it becoming possible to run tests from frames moving fast, at least with respect to the Earth?
Can you specify what you mean by this. If you are referring to labs onboard spacecraft which move at a substantial fraction of the speed of light, then the answer is no. If you mean in general, then the answer is yes - any particle accelerator experiment qualifies. The above mentioned muon decay observations are also a good example.

What do the GPS satellites see of the clocks on Earth? Corrections for the differing gravity potential seem to work well for Earth views of the satellite clocks. Has viewing Earth clocks from the satellites been predicted or measured?
Any GPS device adjusts for the difference between the two clocks; we know the results are very accurate, so I don't really get what your question is hinting at.

Do pictures taken from satellites, preferably minimizing lenses, show a narrower earth or shorter distance between cities as suggested by Special Relativity with corrections for General Relativity effects
No, because the effect is far too small to be detected/observed in this way.

Can sensors on a rotating platform be moving fast enough to measure distances in the Earth frame?
Not sure what you mean by this.

23. Originally Posted by mnpguy
Is it becoming possible to test length compression? (Not yet, it seems)
In addition to the muons, there are other indirect verifications of length compression.

Length contraction - Wikipedia, the free encyclopedia

Heavy ions that are spherical when at rest should assume the form of "pancakes" or flat disks when traveling nearly at the speed of light. And in fact, the results obtained from particle collisions can only be explained, when the increased nucleon density due to Lorentz contraction is considered. Another confirmation is the increased ionization ability of electrically charged particles in motion. According to pre-relativistic physics the ability should decrease at high speed, however, the Lorentz contraction of the Coulomb field leads to an increase of the electrical field strength normal to the line of motion, which leads to the actually observed increase of the ionization ability

24. Regarding tests of length compression,

Originally Posted by Markus Hanke
Actually it is possible, because length contraction is intimately connected to time dilation. The classic observation here is atmospheric muon decay; those muons can only reach Earth's surface if the atmosphere is length contracted from the point of view of the muon itself.
Or the muon would reach Earth's surface if its "clock" is actually slowed by its movement through a universal or local frame. That view is admittedly out of favor.

Regarding "Is it becoming possible to run tests from frames moving fast, at least with respect to the Earth?

Can you specify what you mean by this. If you are referring to labs onboard spacecraft which move at a substantial fraction of the speed of light, then the answer is no.
Yes, the hope is to actually know what the frame moving fast (with respect to the Earth) sees rather than surmising as in

If you mean in general, then the answer is yes - any particle accelerator experiment qualifies. The above mentioned muon decay observations are also a good example.
Any GPS device adjusts for the difference between the two clocks; we know the results are very accurate, so I don't really get what your question is hinting at.
If the GPS satellites were looking at clocks broadcasting from Earth, what corrections would they need? Corrections on Earth allow for Special Relativistic effects (due to movement and signal travel) as well as General Relativistic effects (gravitational potential), and are considered strong proof of Relativity. If corrections on a satellite require seeing the Earth as moving (for the movement part of the corrections for Special Relativistic effects), I'd consider that strong proof of inertial frame independence.

Regarding relativistic effects on pictures taken from satellites

No, because the effect is far too small to be detected/observed in this way.
Regarding sensors on a rotating platform be moving fast enough to measure distances in the Earth frame?

Not sure what you mean by this.
Can a rotating platform with separated sensors record when it simultaneously sees separated emitters in the Earth frame, with the emitters' position adjusted until simultaneity occurs?

Originally Posted by AlexG
In addition to the muons, there are other indirect verifications of length compression.

Length contraction - Wikipedia, the free encyclopedia
Good reference, the article offers detail and insight into current and historical thinking. Comments on Penrose-Terrell Rotation regarding taking pictures are interesting, though spaceships are currently not fast enough to take pictures that would show relativistic effects. (Reference article by Baez notes that the idea of taking snapshots arose in the late 1950's).

Thanks too for noting that the verification is indirect.

25. Originally Posted by mnpguy
Or the muon would reach Earth's surface if its "clock" is actually slowed by its movement through a universal or local frame.
Yes, that's the viewpoint of a stationary outside observer. Like I said, time dilation and length contraction are two facets of the same relativistic effect.

If the GPS satellites were looking at clocks broadcasting from Earth, what corrections would they need?
The same ones, just with an opposite sign.

Thanks too for noting that the verification is indirect.
It is indeed. The only verification which I would consider more or less direct is the aforementioned atmospheric muon.

26. If an experiment has a distance of a meter with corresponding time.

Calculating to meters to seconds is an upscale factor of 299,792,458 to the real experiment.

going from one meter to two, to three, following this upscaling it seems like a speed.
What it really is is a corresponding ratio between two ways to meassure distance.

Same as with a universe of thousand trains all driving 100 mph. An hour drive or a 100 miles drive. It becomes the same (better equivalants) because the trains all have this speed in this "universe of trains".

A universe of one single train driving this ratio (the train we are in with a traindrive) can travel 100 mp/h , fifty /half an hour or threehundred/three hour. But not three hundred M /three H ánd hundred mile/ one hour. That would become a mess of trains.

As long as it hasn,t travelled a distance (and time) yet it has no ratio for distance to hours either.

How far is it ? : "one hour walking" ...this uses a mediated walking speed instead of constant speed and also becomes as a constant then ; time is distance as in corresponds to meter-meassured-distance in a constant ratio and both can be used as equivalents then.

The idea of lightsspeed is from this scale difference between single units (imaginary scaled down or up experiment) and real distance and time for experiments.

The steps can be seconds or meters. If seconds then some come from these steps to a travel idea just as walking with steps of one second each. This type of stepwise logic (computers are very good at it ) is sometimes referred to as "straightlined logic".

27. Originally Posted by KALSTER
What are you talking about? Complete gibberish.

The detection is an experience. Experiences don,t travel. Same as with sound ; Someone can shout but there is no sound without a hearing because sound is an experience.
So how can sound travel then if there is no ear travelling from the mouth that shouts ?
Or an eye from the laser or radio from the radiotransmitter ?
Sound and light are phenomena. They happen, even if nothing is there to "experience" it.
I believe that sound and light happen with or without a human present to listen to observe them. An event related to light or sound is not observer dependent.

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