Speed of light discussion

[Guest MacPhee]

I welcome all participants. I love logic, but not tendentious interpretation of the results of experiments in physics, and I want to find objective answers.

In mathematics, this time I was interested about prime numbers.

 

Do you think there's a connection between prime numbers and the velocity of light "c".

 

That's an interesting thought. Suppose we try to measure "c". Our measurements are always approximations, such as 186,200 miles per second.

 

Are there any units in which "c" can be written exactly. Or is "c" a prime number?

[CraigD]

Suppose we try to measure "c". Our measurements are always approximations, such as 186,200 miles per second.

 

Are there any units in which "c" can be written exactly[?] ...

The speed of light - c - is exactly 299,792,458 meters per second.

 

One would be expected to wonder how any natural phenomenon can be exactly measured, and the answer in this case is a bit of trickiness involving the definition of the meter and the second: the meter is defined as the distance light in a vacuum travels in 1/299792458th of a second, while the second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom, another natural phenomenon believed to be unvarying, and one we're good at measuring.

 

... Or is "c" a prime number?

No speed is a "pure" (also called unitless or dimensionless) number. The integers, of which the primes are a subset, are. So it's not sensible to say c is or isn't a prime number.

[Dane]

I am sorry to be misunderstood...

I said what I was interested in mathematics on the one hand and what I was interested in physics on the other (excuse me but my English is not very good)

We do not measure the speed of light, but we make conclusions about it based on the results of the experiments.

Which experiments show that the speed of light always eqauls c?

[Rade]

Which experiments show that the speed of light always equals c?

Putting aside the word 'always' in your question, here is a published experiment for a high school physics class:

 

http://eprints.usq.edu.au/1198/1/Parisi_Mottram_Kimlin_Wilson_Wollstein_699.pdf

Edited April 10, 2013 by Rade

[Dane]

Putting aside the word 'always' in your question,...

I did not ask for an experiment to determine the value of the speed of light.

The word “always” refers to the independence of the speed of light on the relative

motion between the light source and the observer (detector)

[JMJones0424]

We do not measure the speed of light, but we make conclusions about it based on the results of the experiments.

Which experiments show that the speed of light always eqauls c?

I'm not sure I understand your assertion that we don't measure the speed of light. However, perhaps the wikipedia article on refutations of emission theory will give examples of how we measure the invariant speed of light regardless of the emitter's velocity relative to the measuring device.

 

EDIT: The wikipedia article on measurement of the speed of light may be useful to you as well.

Edited April 10, 2013 by JMJones0424

[Dane]

I have not found on Wikipedia the information I was looking for. Light from a star was used in

Michelson's experiment. One final question - Could you, please, confirm what was the speed of

the star, as the light source, in relation to Michelson device i.e. in relation to Earth?

[JMJones0424]

I have not found on Wikipedia the information I was looking for.

Then I don't understand what you're looking for. You've made a number of assertions that have been shown to be false. We DO measure the speed of light. It has been shown that the relative velocity of the emitter is irrelevant to the measured velocity of light. And finally:

 

Light from a star was used in Michelson's experiment.

This too is false, unless I misunderstand which experiment you are referring to. Again, wikipedia has an article on the experiments.

[Dane]

That does not answer my question. See drawing

[JMJones0424]

I've taken the liberty of posting your document as an image so that others can view it without having to download a file.

 

I'm operating at the edge of my very limited knowledge, so perhaps someone more knowledgable will step in and rescue me. However, I think I can answer your questions. First, the light source is indeed terrestrial. The light source, mirrors, and detector are all in the same device and therefore have zero velocity relative to each other. The velocity is the movement of the device through the proposed aether.

 

Essentially, what this device was intended to test is the idea that since light is wave-like, and since waves generally need a medium to travel through, then space must be filled with a medium called aether that light travels through. This concept has been discredited, in part due to the null result of this test. There was no statistically measurable difference in travel time from light sent along the axis of movement versus light sent perpendicular to the axis of movement. The axis of movement in this case is the movement of the Earth as it traveled through the aether.

 

This test alone is, I think, insufficient to show the invariant speed of light, as all components are traveling at zero velocity relative to themselves.

[Dane]

Let's try it another way!

What does "redshift" in the visible region of the electromagnetic spectrum from a star means?

Or even better:

what does some particular value (size) of the redshift mean?

[JMJones0424]

When a particular star's (or galaxy's) emitted light is observed through a spectrometer, a baseline fingerprint is observed which can be used to compare the spectrum of that source to other known sources. Because the spectral line frequencies of common elements are known, we can compare the frequency of these lines to determine the relative velocity of the emitter to us. The greater the redshift, then the greater the relative velocity away from us. The greater the blueshift, then the greater the relative velocity towards us. Redshift = longer wavelengths, blue = shorter wavelengths. The same phenomenon can be observed more easily with sound. An approaching source of sound will emit what appears to be a higher pitch while a receding source of sound will emit a what appears to be a lower pitch.

[Aethelwulf]

The speed of light - c - is exactly 299,792,458 meters per second.

 

One would be expected to wonder how any natural phenomenon can be exactly measured, and the answer in this case is a bit of trickiness involving the definition of the meter and the second: the meter is defined as the distance light in a vacuum travels in 1/299792458th of a second, while the second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom, another natural phenomenon believed to be unvarying, and one we're good at measuring.

 

 

No speed is a "pure" (also called unitless or dimensionless) number. The integers, of which the primes are a subset, are. So it's not sensible to say c is or isn't a prime number.

 

Hi Craig. I have to disagree, the speed of light is not a dimensionless number. If it was, then mass would be equal to energy directly, but it isn't. In conventional units, the energy is defined as

 

[math]E = Mc^2[/math]

 

Even when setting c=1, this is dimensional analysis, energy still doesn't directly equal mass per se. Light speed has units of velocity.

[Dane]

Spectral_line frequencies of common elements are known, we can compare the frequency of these lines to determine the relative velocity of the emitter to us.

Thank you for your response.

I suppose you think that a particular spectralshift corresponds to a uniform motion of the star at some specific speed.

But the star is not a light source, just like as a swarm of bees is not a signle bee.

Star has a huge set of light sources that have very large and different relative velocities in different directions. (like our Sun)

There is no one light source on the Sune moving uniformly.

This is the same with elementary light sources (on atomic level) which oscillate and have an infinite number of different speeds during a single oscillation.

It follows from this conclusion:

 

1 Uniform motion between the light source and the detector does not exist.

 

The modern scientific interpretation of the Doppler effect is not right because a set of source of a star can not give a single spectralshift ever.

Question for Science:

 

How light sources that have different speeds can only give a single spectralshift?

Edited April 13, 2013 by galet

[JMJones0424]

How light sources that have different speeds can only give a single spectralshift?

They don't. This was covered in the wikipedia article I linked on spectral lines.

[Dane]

But then the star has what speed?

[JMJones0424]

But then the star has what speed?

You tell me. You're the one that dreamed up the ludicrous notion that spectral lines have no width. Had you read the article I linked, you'd have realized that your unfounded preconceptions are wrong.