Why C?

[aguy2]

What constraints set C at 186,000 mps? Why not 196,000, or 176,000, or for that matter 1,860?

 

aguy2

[JaKiri]

Becuase that's the speed it goes.

[swansont]

The "fabric of space" has a specific magnetic permeability and electric permittivity. Light is an EM wave, and is limited in propagation speed by the values of those parameters.

[RawThinkTank]

The "fabric of space" has a specific magnetic permeability and electric permittivity. Light is an EM wave, and is limited in propagation speed by the values of those parameters.

 

If that is so then why is light not affected by magnets or electrical fields ?

[JaKiri]

If that is so then why is light not affected by magnets or electrical fields ?

 

Light is the exchange particle of magnets and electrical fields. Try and work out why it isn't affected by them.

[fermions]

I heard that light can be affected by magnetic fields... but I still don't quite understnad I think one of the effects has some problems with polarization

[aguy2]

The "fabric of space" has a specific magnetic permeability and electric permittivity. Light is an EM wave, and is limited in propagation speed by the values of those parameters.

 

Are you saying that the "fabric of space" is an active contraint?

 

aguy2

[bloodhound]

yes. i believe the speed of light can be theoritically worked out. i saw some formula for it, but i am not into physics anymore.

[Martin]

What constraints set C at 186' date='000 mph? Why not 196,000, or 176,000, or for that matter 1,860?

 

aguy2[/quote']

 

this could be the start of a good line of questioning

 

But it is only a start, because this question is not quite good enough.

 

the trouble is that the mile is defined based on the meter (by international convention an inch is 2.54 centimeters). the idea of "miles per hour" has no independent meaning except as a certain fraction of a meter per second.

U.S. units are based on the metric system, OK?

 

But in the metric system, it is not possible for C to be anything other than

299792458 meters per second. It is established by law and by international treaty. It is definitely a manmade thing. In 1983 a big convention of scientists and government people got together and said that from then on the meter would be defined as the distance light (in vacuum) travels in a certain definite fraction of a second and that this fraction would be officially set at 1/299792458.

 

the number was chosen to some extent arbitrarily. they could have specified 299792458.1

or they could have said 299792457.9

and it would have worked just as well to define the meter

but they arbitrarily chose to have it be exactly a whole number 299792458.

 

At the present time scientists cannot measure the speed of light because it is established by law (in the way the meter is defined, based on the atomic clock time standard)

 

If you want to really ask the question you have to think of some other benchmark for comparison besides "miles per hour"

because "miles per hour" is locked in by law to a certain relation with C.

 

Try asking something like "why does light travel faster than I can throw a ball? "

 

why cant light travel slower than I ride my bicycle?

could light travel slower than the earth goes in it's orbit around the sun?

What prevents light from traveling exactly a 100 times faster than a bird can fly?

 

If you dont like those questions (maybe they sound stupid to you) think of some other natural standard of speed and some other way to ask.

 

Like, think of a supernova. A star explodes and all sorts of crud comes flying out at various speeds. what is the upper limit of speed the crud can go? what is the relation of the speed of light to the limiting speed of crud blown out of an exploding star?

 

Now use your own words: "WHAT CONSTRAINTS" make light have to travel right around the limiting speed of the crud? Why couldnt light travel at exactly twice the crud's top speed? Or why couldnt light travel at exactly half the crud's top speed? what constrains light to go at right about the same speed as the fastest neutral particles whizzing out of a supernova?

[Martin]

Are you saying that the "fabric of space" is an active contraint?

 

aguy2

 

hello aguy2, I am not sure that there is a "fabric of space"

that sounds a bit like the "luminiferous aether" of 100 years ago.

so I would be inclined not to worry about it

 

but everybody should approach the problem as he thinks best

[aguy2]

this could be the start of a good line of questioning

 

But it is only a start' date=' because this question is not quite good enough.

[/quote']

 

My question is not about the speed of light. It is about the 'constraints'.

Would that be easier to see if I ask, "What constraints set C?"

 

aguy2

[mtong]

I believe that 'c' was derived from some of Maxwell’s formulas....which agreed with some previously taken measurements.

[Jacques]

I think that C was mesured

[Martin]

I think that C was mesured

I agree that it was measured

IIRC it was first measured (within some 10 percent accuracy) in 1675 or 1676 by Ole Roemer, at the paris observatory.

he was timing the orbit period of the jovian moon Io.

 

but there is always the question (never too clear, a little slippery)

of why it is what it is, and not some other speed

 

can one even ask this? any ideas jacques?

[Jacques]

I have no idea why it is that speed. I think the big question is why it is always that speed no matter the speed of the source or the observer. Einstein explain that in his theory of relativity by making time varied. It is a concept that we are not willing to accept. Our view of time is something absolute. Time flow always the same way...

But, as strange as it seem we can't just ignore the data from the GPS nad other experiments.

[Gilded]

"yes. i believe the speed of light can be theoritically worked out."

 

Bah! All you need is a chocolate bar, a ruler and a microwave oven. )

http://physics.about.com/cs/opticsexperiments/a/290903.htm (thanks to ed84c for originally posting the link)

 

Also, I recall swansont telling the formula for something involving photons, but I think it was for the kinetic energy (= Planck's constant * frequency ?).

[5614]

Also, I recall swansont telling the formula for something involving photons, but I think it was for the kinetic energy (= Planck's constant * frequency ?).

 

yup, that's the one, e=hf where e = energy, h = planck's constant and f = frequency

[aguy2]

I have no idea why it is that speed. I think the big question is why it is always that speed no matter the speed of the source or the observer. Einstein explain that in his theory of relativity by making time varied. It is a concept that we are not willing to accept. Our view of time is something absolute. Time flow always the same way...

But' date=' as strange as it seem we can't just ignore the data from the GPS nad other experiments.[/quote']

 

The data from GPS and numerous other experiments can't be ignored. Observational evidence tells us that time or 'temporal flow' is quite elastic. I think that a 'temporal' or some other type of 'flow' will prove to be the key to finally understanding the 'constraints' that determine that photons and other 'virtual particles' are propagated at C. It would seem to me that either 'virtual particles' hitch a ride on some sort of preexisting 'flow' and run into 'real particles' or 'real particles' are being carried along and run into relatively stationary 'virtual particles'. The temporal dimension (or dimensions) would seem to be a prime candidate for an ongoing, generalized 'flow'.

 

aguy2

[Martin]

"yes. i believe the speed of light can be theoritically worked out."

 

Bah! All you need is a chocolate bar' date=' a ruler and a microwave oven. )

http://physics.about.com/cs/opticsexperiments/a/290903.htm (thanks to ed84c for originally posting the link)

...[/quote']

 

obviously you are joking when you say Bah!....and so on.

But maybe not everyone gets the joke.

 

the point of having theory and experiment is that one can measure the speed of light-----and on the other hand maybe one can work it out from theory

 

the most interesting would be if one could do both: derive from theory, and then measure, and see if the observed value agrees with theory

 

also if you read page 2 of that chocolate bar link you will see that he actually did not measure the microwave frequency. He could not find the frequency of his oven, so he looked on the web and found a page that said that a common frequency for microwave ovens is 2.5 GHz

and he just used that figure for the frequency of his oven

 

If you are going to measure the speed of light that way you must measure both the wavelength and the frequency of the waves (in that particular device) and compare wavelength and frequency.

 

Incidentally a friend of mine from years back was one of the first people to apply this method to measure the speed of light accurately by the frequency/wavelength comparison, using microwaves, and published a paper about it (in the 1940s or 1950s long before I knew him). Older guy, dead many years now.

 

Anyway the essential of that method is to measure the frequency (the rate the humps are arriving) and the wavelength (the distance between humps) and compare.

 

there is nothing "quantum" about this. It is purely classical. the model is vintage 1870 or earlier. You can measure the speed of sound this way very nicely. If you know that a soundwave is A = 440 humps per second, and if you can measure that the distance between humps is 80 centimeters

(or distance between nodes is 40 centimeters same thing) then you can just mulitply 440 X 80

 

440 per second times 80 centimeters gives 35200 centimeters per second

or 352 meters per second (that would be at some fairly ordinary temperature I guess)

 

but the key is to be able to reliably measure both the wavelength and the frequency OF THE SAME WAVE, which is what has always made it a bit challenging.

[Mart]

Light travels slower in more dense media (used to explain refraction). A vaccuum is most often conceived as a totally empty medium. Could be that it isn't. Virtual particles .... ?

[Klaynos]

The "fabric of space" has a specific magnetic permeability and electric permittivity. Light is an EM wave, and is limited in propagation speed by the values of those parameters.

 

I happened to come accross this equation today.

 

It goes something like, I can't remember it exactly.

 

permittivity of a vacuum=permeability of a vacuum^-1 * c^-2

 

The permittivity of a vacuum relates to electronic perittivity, and permeability of a vacuum relates to magnetic. These values are differnt for different substances which makes c change. This is try due to the fact that photons are bootstrapping electromagnetic waves... or something like that.

 

It is possible to experimentally prove this using the michelson-morley experiment which proves that light doesn't travel through an ether, and does this my measuring the speed of light in multiple directions, which always results to the same showing that it isn't effected by the earths motion through the ether.