# What sets the speed of light?

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#### SJQ

##### Guest
Why is c equal to (roughly) 3^10E8 m/s? Why not 3^10E108 m/s? Or 3^10E1 m/s? Is c some arbitrary value that just "falls out of the math", or is there actually a physical characteristic that sets it?

'S been a looong time since I got out of school, and the electron-pushing business is much more interested in what happens than why. A similar (related?) question applies to Zo, the characteristic impedance of free space.

SJQ

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The Universe.

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#### SJQ

##### Guest
Well, I guess that is a physical characteristic.... :lol:

Congratulations on achieving the Micro Soft Standard for Documentation Utility: technically accurate AND totally useless. For this accomplishment, you are hereby awarded the Double Uber-Geek: :ugeek: :ugeek:

Seriously, I'm interpreting your answer to mean "we don't know"; fair enough. It just seemed to me that since c is so independent of the frame of reference it is measured in, there has to be some underlying reason for that particular magic value, vice any other, therefore there is some mechanism that sets and controls c. Should I assume that anyone with an explanation for c's specific velocity but without a Nobel prize to go with it is in the "woo" category, or are there physicists actually asking questions like this?

SJQ

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#### Gravity_Ray

##### Guest
Well I am not a psycist, but I'll take a crack at this

Two things; One is dimensionful numbers and one is dimensionless numbers.

Dimensionful constants depend on the units used. Speed of light (c) is one. This value is expressed in meters per second and is not a value that a theory of physics can predict. It is observed.
Dimensionless constants can be at some point or are right now predicted by physics. These things are fundamental physical constants like the gravitational constant (G).
Many people (mostly physicists) think that at some point we can explain values of dimensionless constants with a theory.

Obviously the universe would be very different if one of these constants took a different value. If the ‘fine structure constant’ was just slightly different (very slightly) then our sun for example would not exist.

Now some people will try an anthropic explanation for these physical constants. I would say that Jesus Christ my lord and savior made the universe in just such a way as to make my existence possible so that I can experience his glory and the glory of God. But others would just mock me. :lol:

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#### MeteorWayne

##### Guest
SJQ":2elinlk8 said:
Well, I guess that is a physical characteristic.... :lol:

Congratulations on achieving the Micro Soft Standard for Documentation Utility: technically accurate AND totally useless. For this accomplishment, you are hereby awarded the Double Uber-Geek: :ugeek: :ugeek:

Seriously, I'm interpreting your answer to mean "we don't know"; fair enough. It just seemed to me that since c is so independent of the frame of reference it is measured in, there has to be some underlying reason for that particular magic value, vice any other, therefore there is some mechanism that sets and controls c. Should I assume that anyone with an explanation for c's specific velocity but without a Nobel prize to go with it is in the "woo" category, or are there physicists actually asking questions like this?

SJQ
Look, you want another answer, fine. But the fact is, that in our Universe, that's what c is. Why? It really doesn't make much difference. It is what it is. Maybe when we have a GUT, there will be a reason that comes out of the equations...but for now, all we know it is the most immutable constant in our reality.

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#### SJQ

##### Guest
Gravity_Ray, I understand dimensioned/dimensionless. The speed of light doesn't change whether you measure in meters per second, or furlongs per micro-fortnight. These are ratios, distance per unit time, but they are equivalent because c is a constant. The photon doesn't care which ratio you use, it's going places fast either way. All I was wondering is if there were any particular reasons we knew of in the construction of the universe as to why any ratio you care to choose resolves to a specific value we call c.

From your answer and from MeteorWayne's, we do not know why c is c, and I'm fine with that. I'm not advancing any theory of my own - my maths aren't up to it - and I wasn't trying to irritate MW, it just seems to me that something as fundamental as c would be something we would be curious about. If we do not (yet) have the analytical tools, then as MW says, c "is what it is" (something we can know only by measurement), and my question is answered.

Thank you, gentlemen,

SJQ

Micro Soft documentation: the words are English, but the language isn't.

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#### captdude

##### Guest
SJQ, Welcome to the community. (You didn't irritate MW thats just how he is) I think that you are asking an interesting question. I would think there IS a reason the speed of light has the value it does. I actually have not read anything along those lines. Todays physics are probably not up to the task of solving that one but askiing questions like that helps others take their minds down new paths....................

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#### KhashayarShatti

##### Guest
SJQ":13d38e2b said:
Why is c equal to (roughly) 3^10E8 m/s? Why not 3^10E108 m/s? Or 3^10E1 m/s? Is c some arbitrary value that just "falls out of the math", or is there actually a physical characteristic that sets it?

'S been a looong time since I got out of school, and the electron-pushing business is much more interested in what happens than why. A similar (related?) question applies to Zo, the characteristic impedance of free space.

SJQ
The way electron interacts with vacuum. One way,if you make an excited electron vibrate you will get something different.
Analogy: Air can not travel faster than air in air with the same property. So change property you get something else.

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##### Guest
KhashayaShatti - this is the science forum area. Stick to Unexplained with the junk science you're pedaling.

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#### centsworth_II

##### Guest
The speed of light is determined by the electromagnetic force, so maybe the question should be, 'why is the electromagnetic force what it is?' The answer is the same though, no one knows.

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#### Jerromy

##### Guest
The most logical reason I can contemplate :twisted: is like centsworth_II mentioned... the electromagnetic force dictates how EMR propogates. Since it all travels in the same bandwidth that must say something for the "width" of the equation equalling a constant. Since the length varies with the amount of energy each photon carries then the ratio of velocity to width must be a significant value. Perhaps the range of electromagnetic influence is related to c? It could be in my GUT anyway...

Does anyone have any input to offer on magnetars? From what I've read recently they are very rare... perhaps gravity and the speed of light could also have some common characteristics worth evaluating. Man, science is fun if you don't care what people think about what you are thinking about. :lol:

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#### ArcCentral

##### Guest
I suspect the speed of light is arbitrary, such that if it was half the speed it is now, the universe would still run like a swiss watch.

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#### SJQ

##### Guest
ArcCentral":1qftv8c5 said:
I suspect the speed of light is arbitrary, such that if it was half the speed it is now, the universe would still run like a swiss watch.
Given c's fundamental nature, you could be right - I don't know. But if you are, would MeteorWayne have to deal with twice as many woo FTL threads as a result? That would make his day!

However, I suspect Newton's clockwork universe would have used a British Admiralty chronometer....

SJQ

(edited for spelling)

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#### undidly

##### Guest
Maxwell calculated the speed of the then only theoretical electromagnetic waves using the magnetic and electrical
characteristics of space.

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#### KhashayarShatti

##### Guest
Dear friend SJQ
Let's come back to pure physics. Wave-particle duality. We may say for as long as energy is concerned light is a wave, but for as long as movement is concerned light is particle. Similar to sound. Sound energy is a wave but sound movement concerns particles. it may be possible to imagine that photon energy is wave and photon momentum is particle. Speed of light in glass and fiber optics reduces by almost 35 to 40% for some wavelengths. Reduction and increase of light as it gets in and out of glass is a real phenomina interpretd by some people as being due to photon interaction with glass particles. This is also true for air as n for air is 1.0003. We can think of vacuum as a medium which sets the speed of light.(we can think). Now let's see what happens when speed of sound in air is changed. Due to extra energy of hot air sound can travel faster. If T=288*4 deg. then a=2*a0 (pure physics). Hot air at this temp. has twice speed of sound in air at T=288 deg. Detonated gas can have 8 times the speed of sound in air at STP.
For us to move energy we must change special property otherwise infinite pressure can not move air faster than a0 at similar properties. In fact pressure itself is another property but it doesn't have the same effect. We have a formula for sound concerning properties but when we think of permittivity and permeability of free space some people think of vacuum as nothing. Comments may help to get to a better understanding of the subject as in general it is a good question that needs extra thinking. There has been 300 years that when we ask what is the property of light we get the answer, reflection, refraction, and photon. Lets see if light has other properties related to your question. Any bright idea please.

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#### origin

##### Guest
KhashayarShatti":2qs2bd87 said:
Dear friend SJQ
Let's come back to pure physics. Wave-particle duality. We may say for as long as energy is concerned light is a wave, but for as long as movement is concerned light is particle. Similar to sound. Sound energy is a wave but sound movement concerns particles. it may be possible to imagine that photon energy is wave and photon momentum is particle. Speed of light in glass and fiber optics reduces by almost 35 to 40% for some wavelengths. Reduction and increase of light as it gets in and out of glass is a real phenomina interpretd by some people as being due to photon interaction with glass particles. This is also true for air as n for air is 1.0003. We can think of vacuum as a medium which sets the speed of light.(we can think). Now let's see what happens when speed of sound in air is changed. Due to extra energy of hot air sound can travel faster. If T=288*4 deg. then a=2*a0 (pure physics). Hot air at this temp. has twice speed of sound in air at T=288 deg. Detonated gas can have 8 times the speed of sound in air at STP.
For us to move energy we must change special property otherwise infinite pressure can not move air faster than a0 at similar properties. In fact pressure itself is another property but it doesn't have the same effect. We have a formula for sound concerning properties but when we think of permittivity and permeability of free space some people think of vacuum as nothing. Comments may help to get to a better understanding of the subject as in general it is a good question that needs extra thinking. There has been 300 years that when we ask what is the property of light we get the answer, reflection, refraction, and photon. Lets see if light has other properties related to your question. Any bright idea please.
Trying to use sound waves to describe the quantum nature of light is a really bad idea that can do nothing but confuse the issue.

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