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# why is C the speed that it is?

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Why is the speed of light the speed that it is? What is the limiting factor involved?

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This is from wikipedia and I think this may best answer that question:

"its square is the constant of proportionality between mass and energy (E = mc2)"

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It has that value because of our past choices of the length of the meter and duration of the second.

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All the above is absolutely correct.

I have a better answer: I don't know.

But:

_a good answer would be that C should be a geometric coefficient, like Pi. But the first problem is that C has units meters/sec, that is not a good beginning for a coefficient. If the units came to disappear, that would be great.

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But then it is not a velocity anymore, which kinda beats the definition of C being the velocity of light in a vacuum.

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Thankyou all for your responses to my question. I'm still a little confused as to what the cause of the velocity of light is. Would it be fair to say that the speed of light is actually the "speed" of the expansion of space?

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interesting notion but since the universe may actually be expanding faster than the speed of light I'd have to say that it would not be a fair assumption. As to why C is constant you might have to ask God that question. Good luck getting an answer.

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The first mention of it was a calculation of the speed of an electromagnetic wave, a solution to Maxwell's equations, $c = \frac{1}{\sqrt{\mu_0\epsilon_0}}$. When it was found to be the same speed as light, it got called the shorter "speed of light". Later we defined the meter in terms of the speed of light, making it now a defined constant rather than a measured constant.

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This is from wikipedia and I think this may best answer that question:

"its square is the constant of proportionality between mass and energy (E = mc2)"

...which is weird, IMO.

We already dicussed that, and I still find it weird.

In e=mc^2, the constant is Csquared=8.98755179 × 10^16 m2 / s2.

IMO very weird units. A speed multiplied by a speed, what is that?

So we have

e=energy, lets say we know what it is.

m=mass, lets say we know what it is.

C^2=????

If you make a search about C, you will find thousands of interesting articles, and about Csquared so few.

IMO Csquared is the thing.

IMO the fact that we are measuring C and not Csquared is another trick of Mother Nature.

.........

A lot of IMO's here. Sorry.

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The first mention of it was a calculation of the speed of an electromagnetic wave, a solution to Maxwell's equations, $c = \frac{1}{\sqrt{\mu_0\epsilon_0}}$. When it was found to be the same speed as light, it got called the shorter "speed of light". Later we defined the meter in terms of the speed of light, making it now a defined constant rather than a measured constant.

yep that's correct ,the actual speed of light that is 299792458m/s was give by maxwell and his equation give above .he found that this speed is same for all wave which are electomagantic wave ,that is speed of light, radio wave, x ray, gamma ray etc. all in the electomagnetic wave band have that same velocity...........

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...which is weird, IMO.

We already dicussed that, and I still find it weird.

In e=mc^2, the constant is Csquared=8.98755179 × 10^16 m2 / s2.

IMO very weird units. A speed multiplied by a speed, what is that?

So we have

e=energy, lets say we know what it is.

m=mass, lets say we know what it is.

C^2=????

If you make a search about C, you will find thousands of interesting articles, and about Csquared so few.

IMO Csquared is the thing.

IMO the fact that we are measuring C and not Csquared is another trick of Mother Nature.

.........

A lot of IMO's here. Sorry.

C is the derivative of C^2 - it's a transform of ""coordinates" between the energy framework and the mass framework.

^^^^^^This may be Bogus^^^^^^^

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If an object is travelling at almost the speed of light and it emits an electromagnetic wave in the same direction it is travelling, this electromagnetic wave will still only travel at C. To me this implies that there is some sort of underlying (moving) medium that is carrying electromagnetic waves at the constant speed. I assumed it would be the expansion of space itself.

As for the universe expanding faster than the speed of light, over vast distances there is a much greater amount of expanding space which is compounding the effect perhaps giving the impression of the universe expanding faster.

Just ideas...

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...which is weird, IMO.

We already dicussed that, and I still find it weird.

In e=mc^2, the constant is Csquared=8.98755179 × 10^16 m2 / s2.

IMO very weird units. A speed multiplied by a speed, what is that?

So we have

e=energy, lets say we know what it is.

m=mass, lets say we know what it is.

C^2=????

If you make a search about C, you will find thousands of interesting articles, and about Csquared so few.

IMO Csquared is the thing.

IMO the fact that we are measuring C and not Csquared is another trick of Mother Nature.

.........

A lot of IMO's here. Sorry.

They are not really very weird units, they are just units that are man made and the equations bring them out that way. Instead of using m2/s2, which is complicated and doesn't make sense, we use a new unit like joules per kilogram. If you met an alien race, they may know the speed of light as we know the speed of light, but their equations could be much different depending on the units of measurements they have created, the values could be different.

It is also good to note, the metric system has values designed to work together easily mathematically.

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They are not really very weird units, they are just units that are man made and the equations bring them out that way. Instead of using m2/s2, which is complicated and doesn't make sense, we use a new unit like joules per kilogram. (...)

Toasty thank you. It is really amazing when someone tells you what was so obvious.

Joules is the unit for energy.

If a layman had to answer, what is that for a thing: energy/kilogram? he would answer , I guess: the amount of energy/kg is still energy.

........

It is the fundamental amount of energy.

You multiply this fundamental amount by the amount of mass, and you get the total energy.

Correct?

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If an object is travelling at almost the speed of light and it emits an electromagnetic wave in the same direction it is travelling, this electromagnetic wave will still only travel at C. To me this implies that there is some sort of underlying (moving) medium that is carrying electromagnetic waves at the constant speed. I assumed it would be the expansion of space itself.

As for the universe expanding faster than the speed of light, over vast distances there is a much greater amount of expanding space which is compounding the effect perhaps giving the impression of the universe expanding faster.

Just ideas...

One of the limiting factors that a lot of people put forth, in this case, is the speed at which the stuff of space (which some call Higgs Bosons) can 'get out of the way' of a moving object. It's a little like the speed of sound, which until you exceed it, works quite similarly. Of course, the difference is that the speed of sound has been exceeded by human technology since the first bull whip (maybe 10,000 years ago). The 'sound barrier' can be broken (it really can't, but that's a different discussion), the 'light barrier', cannot. They just aren't the same thing.

Something to remember is that this mythical object is emitting electromagnetic radiation in ALL directions.

. . .including 'behind' it as it travels through space.

And that EMR is at the same speed as the emanations in front. It's still the speed of light. It's not like a doppler effect (where you would subtract the 'almost C' from the speed.) but the frequency would be affected, by quite a lot. It would be way down, to an observer who was watching from the rear.

Don't forget that radiation can be at just about any frequency, but it's still traveling through space at the same speed. Some folks confuse this, but it's important.

Bill Wolfe

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It's not like a doppler effect (where you would subtract the 'almost C' from the speed.) but the frequency would be affected, by quite a lot. It would be way down, to an observer who was watching from the rear.

Don't forget that radiation can be at just about any frequency, but it's still traveling through space at the same speed. Some folks confuse this, but it's important.

Bill Wolfe

Thanks Bill. You are perfectly right. Mention of the doppler effect for light is misleading.

But I am surprised that nobody commented my last post.

So I repeat myself:

what is that for a thing: energy/kilogram? he would answer , I guess: the amount of energy/kg is still energy.

To make it clear like water:

For any system under observation we have

e=mc^2

Where

e=total energy of the system in Joules =kg*(m/s^2)*m or kg*m^2/s^2

m=total mass of the system in kilograms =kg

and

C^2= elementary unit of energy= m^2/s^2 or (m/s^2)*m, and it is a constant.

Is that correct?

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Thanks Bill. You are perfectly right. Mention of the doppler effect for light is misleading.

But I am surprised that nobody commented my last post.

So I repeat myself:

To make it clear like water:

For any system under observation we have

e=mc^2

Where . . .

C^2= elementary unit of energy= m^2/s^2 or (m/s^2)*m, and it is a constant.

Is that correct?

Not for any system, really. It doesn't work terribly well for a system of photons (no mass), Magnetic fields (similar problem) or singularities (too much mass), a flock of angels (nonexistent), or a few other 'exotic' things.

You know what E=mC2 means, don't you? It's a relatively simple and easy to use, matter-to-energy conversion formula. It only works for rest mass, until things get relativistic.

For rest mass, when you run a nuclear reactor or blow up an atomic bomb, you actually convert a little bit of matter into energy. And I mean a little bit. I think it was Nagasaki where about one gram of matter was converted, which by my handy dandy little E=mC2 converter program would have equaled 21.481 kilotons of TNT, which is pretty close.

One gram is the approximate mass of a regular-sized paperclip.

It's basically how much energy--in some unit--that a certain mass (in some other unit) of matter, contains. Calling all Purists, yeah, I know it's more complicated, but I'm trying to make it plain.

To say it describes any system under observation is a bit of a stretch. It describes a few things about some aspects of some systems, but has no bearing at all on some others.

When you accelerate a bit of mass to the speed of light (impossible), you are basically converting that mass into a photon equivalent, which is pretty close to pure energy. And that's why E=mC2 has some relevance, there, as well.

(If I missed something on this last one, Purists, please feel free. Too much simplification can be a problem when we deal with these topics, but I think that's accurate.)

So while there is some relativistic use for E=mC2, it's mostly a matter-to-energy conversion formula. Try not to use it to explain just everything.

C^2= elementary unit of energy= m^2/s^2 or (m/s^2)*m, and it is a constant.

Is that correct?

Well, the speed the light is a constant, but in many ways, its a simple velocity, with a real number. So no, that is not correct. Velocity effects some kinds of energy (kinetic energy, impulse, etc.,) but it isn't any kind of unit of energy.

Is the water more clear?

Bill Wolfe

Edited by StrontiDog
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Why is the speed of light the speed that it is? What is the limiting factor involved?

it is 1/sqrt(Mu*Epsilon) Where Mu and Epsilon are the permittivity and permeablity of free space. This is derived from maxwell's equations by taking a couple of the equations and developing the wave equation from them.

the detail can be found here:

http://en.wikipedia.org/wiki/Electromagnetic_wave_equation

but that is the basic answer.

Merged post follows:

Consecutive posts merged
Thanks Bill. You are perfectly right. Mention of the doppler effect for light is misleading.

But I am surprised that nobody commented my last post.

So I repeat myself:

To make it clear like water:

For any system under observation we have

e=mc^2

Where

e=total energy of the system in Joules =kg*(m/s^2)*m or kg*m^2/s^2

m=total mass of the system in kilograms =kg

and

C^2= elementary unit of energy= m^2/s^2 or (m/s^2)*m, and it is a constant.

Is that correct?

e=mc2 is for rest mass. You'll notice immediately that momentum is missing from that equation, so it can't be right.

The full equation for energy wrt mass and momentum is

E2=p2c2+m2c4

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Just a few things which may help: 1)There is the 'natural' system of units in which c=1, and is dimensionless. A device to simplify calculations in which c crops up like measles! The trade-off, however, is that there is no 'table' to easily return to mks, etc. It's a bit sticky. 2)The question of its absolute value is certainly valid, but far more intriguing is how does it come to be that two observers, one at rest and the other spinning, zooming, and twirling in any which way, measure the speed and always get the same, exact result? 3)Finally, an anectdote(true story). A prominent physicist once toured the 'Clock' of all clocks deep within a mountain in Colorado. He remarked, "So this is where the 'gold standard' of time is set, eh?". His guide matter-of-factly replied, "No. This is where we measure a thing which you, in turn, call 'Time'. "What's in a number? That which we call Time, by any other value would 'smell as sweet'. Exactly!"

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Finally, an anectdote(true story). A prominent physicist once toured the 'Clock' of all clocks deep within a mountain in Colorado. He remarked, "So this is where the 'gold standard' of time is set, eh?". His guide matter-of-factly replied, "No. This is where we measure a thing which you, in turn, call 'Time'. "What's in a number? That which we call Time, by any other value would 'smell as sweet'. Exactly!"

Doubtful. The clock ensembles which are the time standards in the US are not located deep within a mountain in Colorado.

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1)There is the 'natural' system of units in which c=1, and is dimensionless.

Equal to one, yes. Dimensionless, no.

A dimensionless quantity is the same in any system of units.

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Equal to one, yes. Dimensionless, no.

A dimensionless quantity is the same in any system of units.

Thanks. I was going to say that....

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Yeah, and you can use c=1 and dimensionless in any system of units. It will make no difference, since there are no units.

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Yeah, and you can use c=1 and dimensionless in any system of units.

Maybe I don't follow your meaning, but using SI, for example, won't let you set c=1. One unit distance per one unit time in SI is 1 m/s.

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In "natural" units c=1 and has no dimensions (along with hbar and G). Generally loved by theorists and reviled by experimentalists.

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