Speed of light for different observers

[sisoev]

If the graphics represent the contractel length, the just multiply most numbers by 5/4 (e.g. you don't multipl .6c by 5/4).

Aren't you sure that we will not enter in an endless need for contraction, PAllen

 

[PAllen]

Aren't you sure that we will not enter in an endless need for contraction, PAllen

Nope. Actually, don't change any numbers. You gave no dimensions in the OP. I supplied some. If you want to 'start' from the ground observer, use my ground observer numbers. If you want to start from the truck observer, use my truck observer numbers.

In short, the content of your comment is exactly empty.

 

[sisoev]

Nope. Actually, don't change any numbers. You gave no dimensions in the OP. I supplied some. If you want to 'start' from the ground observer, use my ground observer numbers. If you want to start from the truck observer, use my truck observer numbers.

In short, the content of your comment is exactly empty.

In your previous comment you said:

The flash being on the truck makes no difference whatsoever. (What matters is the 'event' of light emission. The motion of the source only matters for doppler effects, which were not part of the original scenario, and completely irrelevant to it).

It makes a BIG difference indeed.
It is in direct connection with your measuring tape.
See my comment to DaleSpam (few comments up)
Hope that it will add some volume to my comment

 

[PAllen]

In your previous comment you said:It makes a BIG difference indeed.
It is in direct connection with your measuring tape.
See my comment to DaleSpam (few comments up)
Hope that it will add some volume to my comment

Not at all. The motion of the source has nothing to do with the speed of light from the source for any observer. It only affects color of light.

In fact we can have two sources, one on the ground, one on the truck, that both go off the moment the truck passes ground signal. Nothing about my analysis would change. The light from both sources would travel identically for both observers. The only difference between the signals would be color.

Think about this. It is an experimental fact. Until you can accept facts, you must live in fantasyland.

 

[sisoev]

Not at all. The motion of the source has nothing to do with the speed of light from the source for any observer. It only affects color of light.

In fact we can have two sources, one on the ground, one on the truck, that both go off the moment the truck passes ground signal. Nothing about my analysis would change. The light from both sources would travel identically for both observers. The only difference between the signals would be color.

Think about this. It is an experimental fact. Until you can accept facts, you must live in fantasyland.

You didn't read my comment to DaleSpam, did you?
Why do you use measuring tape? - to measure the truck, right.
But if the light is shifted it won't represent the length of the truck.
As I said, it is "old" light.
To make you picture it out, imagine that you see light from a moving away source - you'll see it red and closer to you than it really is.
But I'm sure you know that. You just cannot connect it with my experiment.

 

[Dale]

So, why do we get this result?
Don't you think that it has something to do with not placing the emission point where it belongs, at the source point?

The emission point is at the source point, at the time of emission. It just does not follow where the source point moves to later.

With "old" light we cannot measure distance to the source unless we use its frequency in our calculation. Correct?

The frequency is unrelated to the distance.

Not putting the emission at the place of the source is not in any favour for the length contraction, because I could easily set the experiment with the contracted length of the truck and we would still have different length of the light for A and B.

In my equations L is the length of the truck in the frame where it is moving with speed v. It is not the rest length.

 

[PAllen]

You didn't read my comment to DaleSpam, did you?
Why do you use measuring tape? - to measure the truck, right.
But if the light is shifted it won't represent the length of the truck.
As I said, it is "old" light.
To make you picture it out, imagine that you see light from a moving away source - you'll see it red and closer to you than it really is.
But I'm sure you know that. You just cannot connect it with my experiment.

Sorry, you cannot accept reality.

I used measuring tape for an obvious reason. If we are going measure the speed of light, we cannot define distance using light, or light speed will be c by definition. So you need to measure distance some other way.

By virtue of using an independent measure of distance, all of your statements above are simply false.

 

[sisoev]

The emission point is at the source point, at the time of emission. It just does not follow where the source point moves to later.

It depends on the setting.
A wrong word order can change the meaning.
The right way to say it for a stationary observer is: The source point is the emission point.
Then if we have to measure the path of the light for the stationary observer, we measure it from the source.

The frequency is unrelated to the distance.

You are the expert here, but if frequency changes because of the changed distance, I thing that it is tightly connected with the distance.

In my equations L is the length of the truck in the frame where it is moving with speed v. It is not the rest length.

...

 

[sisoev]

Sorry, you cannot accept reality.

I used measuring tape for an obvious reason. If we are going measure the speed of light, we cannot define distance using light, or light speed will be c by definition. So you need to measure distance some other way.

By virtue of using an independent measure of distance, all of your statements above are simply false.

Lets cool of a little, PAllen :)
It will help both of us to see the other point more clearly.

 

[PAllen]

e.You are the expert here, but if frequency changes because of the changed distance, I thing that it is tightly connected with the distance....

Frequency doesn't change because of changed distance (1 mile, a billion miles, in either special relativity or pre-relativity physics). Doppler shift, both in pre-relativity physics and special relativity is determined only by relative velocity and angle of source and target (not distance). The only difference is the exact formula used. For 'ordinary' relative speeds they agree.

 

[sisoev]

Frequency doesn't change because of changed distance (1 mile, a billion miles, in either special relativity or pre-relativity physics). Doppler shift, both in pre-relativity physics and special relativity is determined only by relative velocity and angle of source and target (not distance). The only difference is the exact formula used. For 'ordinary' relative speeds they agree.

By now you should know that I understand the Doppler shift, DaleSpam.
OK, the next wave arrives later or sooner because of the velocity, not because of the changed by the velocity distance

 

[Dale]

It depends on the setting.
A wrong word order can change the meaning.
The right way to say it for a stationary observer is: The source point is the emission point.
Then if we have to measure the path of the light for the stationary observer, we measure it from the source.

I don't see the distinction you are trying to make here. But I think you mean "stationary source".

You are the expert here, but if frequency changes because of the changed distance, I thing that it is tightly connected with the distance.

Change in distance is speed. The frequency depends on speed, not distance. They are orthogonal.

 

[Denius1704]

DaleSpam didn't you write in one of your previous posts that from the truck Frame of Reference the light traveled the whole length of the truck and from the ground Frame of Reference it only traveled from initial emission? I believe that is what sisoev is also trying to say and you guys are just going back and forth talking about the same thing. It doesn't matter if the light does 2 or 200 cycles inside the truck, at the end of the day it's still going to traverse the whole length of the truck ACCORDING to the detector inside that FoR.

And yes you can't measure the speed of light with light itself, but what you can measure, and again that is what sisoev has been trying to say the whole time is that there is a difference in the length traversed.

The only thing which has a chance of explaining this "problem" is of course the time dilation as ghwellsjr suggested (or Pallen, too lazy to scroll back) and of course how can sisoev argue against something that explains a problem with itself? That's why in Psychology for instance no one is able to disprove Froyd's theory, because it explains everything, and it has an answer for everything by using itself as that answer.

P.S. By the way, i asked how is time dilation proven? Is it only with the whole clocks running slowly? And in "proven" i mean hard data. Could someone answer that question please?

 

[sisoev]

I don't see the distinction you are trying to make here. But I think you mean "stationary source".

Right, stationary source.
And I'm tired of this loop
We set an experiment to compare the paths of the light for A and B.
Then you say that according to C the path is the same, creating the paradox where the light travels distance shorter than the truck.
So, for A the source is the place of the emission and from there we measure the path of the light.

Change in distance is speed. The frequency depends on speed, not distance. They are orthogonal.

OK, but I'm sure that in the context it was quite clear what I mean.

 

[PAllen]

DaleSpam didn't you write in one of your previous posts that from the truck Frame of Reference the light traveled the whole length of the truck and from the ground Frame of Reference it only traveled from initial emission? I believe that is what sisoev is also trying to say and you guys are just going back and forth talking about the same thing. It doesn't matter if the light does 2 or 200 cycles inside the truck, at the end of the day it's still going to traverse the whole length of the truck ACCORDING to the detector inside that FoR.

And yes you can't measure the speed of light with light itself, but what you can measure, and again that is what sisoev has been trying to say the whole time is that there is a difference in the length traversed.

The only thing which has a chance of explaining this "problem" is of course the time dilation as ghwellsjr suggested (or Pallen, too lazy to scroll back) and of course how can sisoev argue against something that explains a problem with itself? That's why in Psychology for instance no one is able to disprove Froyd's theory, because it explains everything, and it has an answer for everything by using itself as that answer.

P.S. By the way, i asked how is time dilation proven? Is it only with the whole clocks running slowly? And in "proven" i mean hard data. Could someone answer that question please?

Muons wouldn't reach the ground from the upper atmosphere without time dilation. Muon accelerators wouldn't work based on slow muon half life without time dilation. Flying accurate clocks in airplanes shows time dilation.

 

[PAllen]

Right, stationary source.
And I'm tired of this loop
We set an experiment to compare the paths of the light for A and B.
Then you say that according to C the path is the same, creating the paradox where the light travels distance shorter than the truck.
So, for A the source is the place of the emission and from there we measure the path of the light.


OK, but I'm sure that in the context it was quite clear what I mean.

To my mind, you have not grappled in any serious way with your own experimental setup. I took it, made it precise (explaining also that whether the source is moving or not is of no matter; only *where* it is when it emits). I took great care to specify what is really needed to measure the speed of light: a distance between source and target measured without using light, a time of emission and time of reception. I filled in real numbers for all measurements (carefully chosen to come out nice, but they are all real numbers from applying special relativity).

 

[sisoev]

Muons wouldn't reach the ground from the upper atmosphere without time dilation. Muon accelerators wouldn't work based on slow muon half life without time dilation. Flying accurate clocks in airplanes shows time dilation.

This is a question, not an argument:
Is it possible the muon decay to be affected by a high speed in a gravitational field?
(Similar question I asked in the TIME DILATION topic)

 

[PAllen]

This is a question, not an argument:
Is it possible the muon decay to be affected by a high speed in a gravitational field?
(Similar question I asked in the TIME DILATION topic)

See my answer there.

 

[sisoev]

To my mind, you have not grappled in any serious way with your own experimental setup. I took it, made it precise (explaining also that whether the source is moving or not is of no matter; only *where* it is when it emits). I took great care to specify what is really needed to measure the speed of light: a distance between source and target measured without using light, a time of emission and time of reception. I filled in real numbers for all measurements (carefully chosen to come out nice, but they are all real numbers from applying special relativity).

OK, PAllen. I'll take a look again at your explanation.
I suppose I missed something.

 

[sisoev]

See my answer there.

Thanks for the answer :)
But seriously...
Doesn't it make more sense to say that in a low gravitation the clocks are moving differently, and in same gravitational field the speed affects the clocks.
May be the speed in gravitational field increases the gravitation.
Did they measure for gravitation difference in the two airplanes in Hafele–Keating experiment?

 

[PAllen]

Thanks for the answer :)
But seriously...
Doesn't it make more sense to say that in a low gravitation the clocks are moving differently, and in same gravitational field the speed affects the clocks.
May be the speed in gravitational field increases the gravitation.
Did they measure for gravitation difference in the two airplanes in Hafele–Keating experiment?

Well, you need a theory of combined effects of speed and gravity. That theory is general relativity which includes special relativity. That accounts quantitatively for all observed effects, include very high accumulated precision in the case of GPS (both speed and gravity effects are significant and need to be accurately accounted for).

Saying "maybe there's another theory that explains it because I don't like the one that works and don't want to learn it", but you can't display another one (that makes quantitative predictions) is an anti-scientific attitude.

They accounted for gravity in Hafele-Keating, at least to bound its impact; they couldn't just ignore it.

 

[sisoev]

Well, you need a theory of combined effects of speed and gravity. That theory is general relativity which includes special relativity. That accounts quantitatively for all observed effects, include very high accumulated precision in the case of GPS (both speed and gravity effects are significant and need to be accurately accounted for).

Saying "maybe there's another theory that explains it because I don't like the one that works and don't want to learn it", but you can't display another one (that makes quantitative predictions) is an anti-scientific attitude.

They accounted for gravity in Hafele-Keating, at least to bound its impact; they couldn't just ignore it.

I think you understand wrongly my question :)
My question was:
we can weigh the clocks on the ground and they should show equal weight.
Then put them on the airplanes and weigh them during the experiment, and see whether their weight stays equal in order to treat them as identical clocks.

 

[Dale]

DaleSpam didn't you write in one of your previous posts that from the truck Frame of Reference the light traveled the whole length of the truck and from the ground Frame of Reference it only traveled from initial emission? I believe that is what sisoev is also trying to say and you guys are just going back and forth talking about the same thing.

Well, maybe you have some special mind-reading power, but I can only go by what he writes and the figures he draws, both of which indicate that he does not believe that. His second figure is incorrect as I have shown, and he has not made any indication that he agrees that it is incorrect.

The only thing which has a chance of explaining this "problem" is of course the time dilation as ghwellsjr suggested (or Pallen, too lazy to scroll back) and of course how can sisoev argue against something that explains a problem with itself? That's why in Psychology for instance no one is able to disprove Froyd's theory, because it explains everything, and it has an answer for everything by using itself as that answer.

This is a completely baseless criticism of SR. SR is falsifiable and could certainly be disproven experimentally.

P.S. By the way, i asked how is time dilation proven? Is it only with the whole clocks running slowly? And in "proven" i mean hard data. Could someone answer that question please?

Here you go, more than a century worth of the most rigorous and precise hard data ever:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

 

[Dale]

Right, stationary source.
And I'm tired of this loop

Me too, but as long as you persist in posting incorrect physics I will continue to try to explain in the hopes of eventually helping you understand.

We set an experiment to compare the paths of the light for A and B.
Then you say that according to C the path is the same, creating the paradox where the light travels distance shorter than the truck.

From all frames the paths are the same length. There is certainly no genuine paradox in the fact that the distance the light travels is shorter than the truck, just a little bit of misunderstanding of non-relativistic physics.

So, for A the source is the place of the emission and from there we measure the path of the light.

Yes, in A's frame v=0, so the formulas posted above give L. I have always been clear that the distance is only different from L in frames where the truck is moving (non-zero v).

OK, but I'm sure that in the context it was quite clear what I mean.

The context was your statement: "With 'old' light we cannot measure distance to the source unless we use its frequency in our calculation." Which is wrong, we can measure the distance without using the frequency in our calculation because the frequency is unrelated to the distance as I explained.

Distance is measured using a radar-type ranging experiment, which only measures the round-trip travel time of light, not the frequency. If you additionally measure the frequency, then you are doing Doppler radar, which allows you to measure velocity in addition to distance.

 

[Dale]

sisoev, Denius1704 believes that you actually do understand now that your second figure is incorrect. Do you, in fact, now understand that?

Do you understand that the distance traveled is not equal to the length of the truck in any frame where the truck is moving? I.e. do you acknowledge the correctness of my brief derivation?

If not, then do you have a derivation that agrees with your assertion?

 

[PAllen]

I think you understand wrongly my question :)
My question was:
we can weigh the clocks on the ground and they should show equal weight.
Then put them on the airplanes and weigh them during the experiment, and see whether their weight stays equal in order to treat them as identical clocks.

Well, both Newtonian and GR make the same prediction for weight: they will weigh infinitesimally less in the airplane (and the amount agrees between the theories to way beyond experimental precision). Newtonian theory says this has no effect on clock rate. GR says it does, and can be computed. For Haefele-Keating, both speed and gravity effects had to be independently accounted for. The results matched prediction within experimental error.

You are saying something completely anti-scientific and nonsensical here: serious consideration should be given to some theory that explains the observation on some other basis, but we can't specify what that theory is or make any predictions using it. We should consider it because Sisoev doesn't like Special Relativity.

 

[Denius1704]

This is a completely baseless criticism of SR. SR is falsifiable and could certainly be disproven experimentally.

You seem to be under the impression that i am trying to say that the experimental data is wrong. The criticism i gave wasn't about the experiments done, but the way the data is interpreted. Time dilation is not a scientific factor, it is not something you can actually see, measure, touch etc. I am still struggling to understand how Einstein and the scientists that followed him actually came up with this kind of explanation for a change that happens at different speeds. And because of the nature of time dilation, every other experiment done can be explained with it without looking further into the mechanics of what is actually happening and why it is happening.

The twin paradox is is a purely theoretical example of how SR works. I do understand it now much better thanks to you guys, but that doesn't mean i started to believe that even if there is actual biological changes occurring in the bodies of the traveling objects they would be because time is "slowing down". The only way time dilation is proven is through decay of elementary particles and even though the experiments have been done with dozens of different particles, variation that is not. Those experiments just show that there might be a 3rd factor at play which is not accounted for. We can say that there is very strong correlation between decay of particles and increase in speed, and although i don't know the exact correlation i am 100% certain, it is not -1.

Here for instance is an article where a team of scientists in an american university noticed that the sun might also be causing changes in the decay times of particles.
http://www.dinosaurc14ages.com/changedecay.htm

 

[PAllen]

You seem to be under the impression that i am trying to say that the experimental data is wrong. The criticism i gave wasn't about the experiments done, but the way the data is interpreted. Time dilation is not a scientific factor, it is not something you can actually see, measure, touch etc. I am still struggling to understand how Einstein and the scientists that followed him actually came up with this kind of explanation for a change that happens at different speeds. And because of the nature of time dilation, every other experiment done can be explained with it without looking further into the mechanics of what is actually happening and why it is happening.

The twin paradox is is a purely theoretical example of how SR works. I do understand it now much better thanks to you guys, but that doesn't mean i started to believe that even if there is actual biological changes occurring in the bodies of the traveling objects they would be because time is "slowing down". The only way time dilation is proven is through decay of elementary particles and even though the experiments have been done with dozens of different particles, variation that is not. Those experiments just show that there might be a 3rd factor at play which is not accounted for. We can say that there is very strong correlation between decay of particles and increase in speed, and although i don't know the exact correlation i am 100% certain, it is not -1.

Here for instance is an article where a team of scientists in an american university noticed that the sun might also be causing changes in the decay times of particles.
http://www.dinosaurc14ages.com/changedecay.htm

That cited article is considered crank science, in the sense that numerous refutations and better experiments rejecting these observations have been ignored by these authors.

Scientists came to accept relativity because it accounted for a wide range observations with a minimum number hypotheses. There is at least one other philosophically (but not mathematically) distinguishable model that accounts for all special relativity phenomena (modern Lorentz Ether Theory). The choice between these is philosophical. If someone came up with a well defined theory that explained existing measurements, but made some predictions different from relativity, that would be considered an exciting test opportunity. For a hundred years or more, some people have tried to do what you suggest, without success. This, not some perverse pleasure with counter-intuitive theories, is what has led to universal acceptance of SR (or, in a few cases, the mathematically indistinguishable LET).

Let me repeat: for much of the 20th century, there were (a few) scientists working very hard to explain known observations with something they might like better than Special Relativity. No one succeeded. [EDIT: actually, this effort continues, in some sense. Quantum gravity research programs have come out with various predictions in disagreement with special relativity, while agreeing (or claiming to) with previously known measurements. So far, as people have figured out ways to test these differences, special relativity has continued to 'win'.]

 

[sisoev]

sisoev, Denius1704 believes that you actually do understand now that your second figure is incorrect. Do you, in fact, now understand that?

Do you understand that the distance traveled is not equal to the length of the truck in any frame where the truck is moving? I.e. do you acknowledge the correctness of my brief derivation?

If not, then do you have a derivation that agrees with your assertion?

You guys are seeing the graphics as third observers.
NO, forget about observing it from aside.
The graphics are to show the path of the light in every single frame.
"Single" frame means that it is treated the same way as the other; either both in motion or both in rest when examined for light path.
You should agree that in "A frame" this path is from the source to A, and in "B frame" it is from the place of emission to B.
Anything else will create paradox, which will show inconsistent logic in determining the facts.

 

[ghwellsjr]

You seem to be under the impression that i am trying to say that the experimental data is wrong. The criticism i gave wasn't about the experiments done, but the way the data is interpreted. Time dilation is not a scientific factor, it is not something you can actually see, measure, touch etc. I am still struggling to understand how Einstein and the scientists that followed him actually came up with this kind of explanation for a change that happens at different speeds. And because of the nature of time dilation, every other experiment done can be explained with it without looking further into the mechanics of what is actually happening and why it is happening.

Einstein didn't come up with time dilation, it was already an explanation used in the Lorentz Ether Theory.

How can you say that time dilation is not a scientific factor? Would you also say that time is not a scientific factor because you cannot actually see, measure, touch, etc, it?

I also don't understand your last sentence in the preceeding quote. Can you elaborate on what you mean?

The twin paradox is is a purely theoretical example of how SR works. I do understand it now much better thanks to you guys, but that doesn't mean i started to believe that even if there is actual biological changes occurring in the bodies of the traveling objects they would be because time is "slowing down". The only way time dilation is proven is through decay of elementary particles and even though the experiments have been done with dozens of different particles, variation that is not. Those experiments just show that there might be a 3rd factor at play which is not accounted for. We can say that there is very strong correlation between decay of particles and increase in speed, and although i don't know the exact correlation i am 100% certain, it is not -1.

The twin paradox is not a purely theoretical example of how SR works. It's the other way around. SR is an example of a theory that explains the facts of the twin paradox.

Are you objecting to the experiments proving the twin paradox because they were done with mechanical clocks rather than with living biological beings?

What correlation are you concerned with and what does -1 mean?