Why does the light travel at precisely the speed...

[mreddie1611]

The topic description pretty well spells it out. Light travels at 186282 miles per second, a velocity at which time and space fully dilate, and where an infinite amount of energy would be required to for matter to travel at the same speed. OK, fine. So why light speed, in particular?

 

And please don't answer "because if it traveled any faster it would go back in time", or "because that is as fast as it could go in normal space". I want to know why the two are dependent upon each other. A better way of putting it might be "What physical rule in our universe makes it impossible for light speed to be some lesser velocity, and if it was would that necessarily change the space-time dilation threshold to match the new velocity, and why?"

[IM Egdall]

I think it has to do with the fact that light has zero mass. Any particle with zero mass (e.g. gluons, gravitons, photons) travels at the speed of light; and always at that speed. So complete time and space dilation occur at the speed which massless particles travel.

 

Also time and space are connected by the spacetime interval (the square root of the difference between the square of the space interval and the square of the time interval). The spacetime interval is absolute. Unlike the space and time interval, the spacetime interval is unaffected by uniform motion. And for particles traveling at the speed of light through space; the spacetime interval is zero.

 

Also the velocity of any object traveling through space and time (spacetime) is the speed of light. So all particles travel through spacetime at the speed of light.

 

The particular value for the speed of light depends on the units used, so it is an arbitrary number. But the "speed of light" is intimately connected with mass and spacetime. Hope this helps.

Edited February 8, 2011 by I ME

[alpha2cen]

Has the light speed no distribution?

Are all the photon speed same?

Edited February 9, 2011 by alpha2cen

[swansont]

Has the light speed no distribution?

Are all the photon speed same?

 

No.

 

Yes.

[ajb]

"What physical rule in our universe makes it impossible for light speed to be some lesser velocity, and if it was would that necessarily change the space-time dilation threshold to match the new velocity, and why?"

 

As I ME says, it is rooted in special relativity.

 

Light is understood to be an electromagnetic wave. The equations that govern this are Maxwell's equations. You can show that wave solutions to these equation (in vacuum ) must travel at the speed c. This is independent of the observer and it is this that is really written into nature.

[davey2222]

Has the light speed no distribution?

Are all the photon speed same?

 

Yes, but only if light travels in a medium.

 

Yes, only in vacuum. No if you consider a medium.

[alpha2cen]

No.

 

Yes.

 

At the light speed measuring experiment, which digit we can find the number vary?

I think the measured values have a mean value and a stand deviation.

Is really the standard deviation zero? Is the standard deviation is only measuring error?

[steevey]

I don't really think we can answer this question right now. Why doesn't light travel at 196,000 miles per second or at 200,000,000,000 miles per second?

[lemur]

I don't really think we can answer this question right now. Why doesn't light travel at 196,000 miles per second or at 200,000,000,000 miles per second?

I have heard this answered in terms of experimental/observational results confirming the exact number, but I still don't understand how it was measured. Logically, it makes sense to me that if light has mass, nothing with mass could travel as fast because mass requires energy to change speed. Also it is logical that, without mass, light would not change speed because it doesn't have any mass/inertia to cause it to resist changes in speed. Then, if light has a fixed speed limit, it makes logical sense that more distant objects take longer to reach than closer ones. I would think you would have to measure the actual speed by triangulating light-events in some way, but I don't know how that would be possible from just Earth if you were trying to measure the speed of light across interplanetary or larger distances. Maybe someone else can explain exactly how light speed is empirically measured over interplanetary distances, if at all (or why it's unnecessary).

[alpha2cen]

I don't really think we can answer this question right now. Why doesn't light travel at 196,000 miles per second or at 200,000,000,000 miles per second?

 

I mean this kind of measured data.

299700000

299800000

299100000

299600000

This data mean significant figure 4 digit number is varied.

How about really measured light speed data?

Edited February 10, 2011 by alpha2cen

[swansont]

At the light speed measuring experiment, which digit we can find the number vary?

I think the measured values have a mean value and a stand deviation.

Is really the standard deviation zero? Is the standard deviation is only measuring error?

 

The speed of light is currently a defined value, i.e. it is exact. If you want measurement error, you can look at measurement errors of quantities that depend on the constancy of c. The second, for example, is realized to about a part in 10^15. The meter is determined to better than a part in 10^11.

[IM Egdall]

I have heard this answered in terms of experimental/observational results confirming the exact number, but I still don't understand how it was measured. Logically, it makes sense to me that if light has mass, nothing with mass could travel as fast because mass requires energy to change speed. Also it is logical that, without mass, light would not change speed because it doesn't have any mass/inertia to cause it to resist changes in speed. Then, if light has a fixed speed limit, it makes logical sense that more distant objects take longer to reach than closer ones. I would think you would have to measure the actual speed by triangulating light-events in some way, but I don't know how that would be possible from just Earth if you were trying to measure the speed of light across interplanetary or larger distances. Maybe someone else can explain exactly how light speed is empirically measured over interplanetary distances, if at all (or why it's unnecessary).

 

Light (like all energy) has inertia. Per E= mc^2, properties of mass (like inertia) are also properties of energy. And vice versa. Another example. Mass and energy are both sources of gravity.

[alpha2cen]

The speed of light is currently a defined value, i.e. it is exact. If you want measurement error, you can look at measurement errors of quantities that depend on the constancy of c. The second, for example, is realized to about a part in 10^15. The meter is determined to better than a part in 10^11.

 

If light speed has very significant figure digit (above 15 digit) and all photons have the same speed (measured SD = 1.000... above 15digit), we have to rewrite all the physics book.

Except classical physics chapter, we have to place the light speed theory at the first line. Every things comes from this.

[michel123456]

If you look at the question, it does not really matter why SOL has this or that value. In any chosen unit system, the value will be different. The real weird thing is that SOL is not a dimensionless physical constant, like the fine structure constant, or number[math] pi [/math].

 

When someone translates the [math] e=mc^2 [/math] equation into the statement that "mass is energy", he omits to realize that [math] c^2 [/math] has units, and that the real constant is not what we measure ([math] {c} [/math]), but [math] c^2 [/math] with bizarre units of square meters by square seconds (what is that?).

 

If "mass is energy" were correct, the multiplying factor should be dimensionless. But it is not. The multiplying factor has units that transform something called "mass" into something else called "energy". The correct statement is that "mass is proportional to energy".

 

And the most weird thing is that nobody seems interested in the question of "what are these strange units representing"?

The common answer is "square speed" (the speed of a speed??) which is not an acceptable answer IMHO.

Edited February 12, 2011 by michel123456

[swansont]

If you look at the question, it does not really matter why SOL has this or that value. In any chosen unit system, the value will be different. The real weird thing is that SOL is not a dimensionless physical constant, like the fine structure constant, or number[math] pi [/math].

 

When someone translates the [math] e=mc^2 [/math] equation into the statement that "mass is energy", he omits to realize that [math] c^2 [/math] has units, and that the real constant is not what we measure ([math] {c} [/math]), but [math] c^2 [/math] with bizarre units of square meters by square seconds (what is that?).

 

If "mass is energy" were correct, the multiplying factor should be dimensionless. But it is not. The multiplying factor has units that transform something called "mass" into something else called "energy". The correct statement is that "mass is proportional to energy".

 

And the most weird thing is that nobody seems interested in the question of "what are these strange units representing"?

The common answer is "square speed" (the speed of a speed??) which is not an acceptable answer IMHO.

 

What about the gravitation constant G, m^3/(kg s) or the electrostatic constant k, kg m^3/(Coul^2 s^2)?

 

Count me among the ones who are not at all fascinated by the units.

[alpha2cen]

If you look at the question, it does not really matter why SOL has this or that value. In any chosen unit system, the value will be different. The real weird thing is that SOL is not a dimensionless physical constant, like the fine structure constant, or number[math] pi [/math].

 

When someone translates the [math] e=mc^2 [/math] equation into the statement that "mass is energy", he omits to realize that [math] c^2 [/math] has units, and that the real constant is not what we measure ([math] {c} [/math]), but [math] c^2 [/math] with bizarre units of square meters by square seconds (what is that?).

 

If "mass is energy" were correct, the multiplying factor should be dimensionless. But it is not. The multiplying factor has units that transform something called "mass" into something else called "energy". The correct statement is that "mass is proportional to energy".

 

And the most weird thing is that nobody seems interested in the question of "what are these strange units representing"?

The common answer is "square speed" (the speed of a speed??) which is not an acceptable answer IMHO.

 

If the measured value is very accurate, I think, the light velocity or light phenomena is at the core of all physical phenomena.

Any theory should be tested by this constant.

[John Cuthber]

 

 

When someone translates the [math] e=mc^2 [/math] equation into the statement that "mass is energy", he omits to realize that [math] c^2 [/math] has units, and that the real constant is not what we measure ([math] {c} [/math]), but [math] c^2 [/math] with bizarre units of square meters by square seconds (what is that?).

 

 

And the most weird thing is that nobody seems interested in the question of "what are these strange units representing"?

The common answer is "square speed" (the speed of a speed??) which is not an acceptable answer IMHO.

 

The units are Joules per kilogram.

Why is that a problem?

[IM Egdall]

If you look at the question, it does not really matter why SOL has this or that value. In any chosen unit system, the value will be different. The real weird thing is that SOL is not a dimensionless physical constant, like the fine structure constant, or number[math] pi [/math].

 

When someone translates the [math] e=mc^2 [/math] equation into the statement that "mass is energy", he omits to realize that [math] c^2 [/math] has units, and that the real constant is not what we measure ([math] {c} [/math]), but [math] c^2 [/math] with bizarre units of square meters by square seconds (what is that?).

 

If "mass is energy" were correct, the multiplying factor should be dimensionless. But it is not. The multiplying factor has units that transform something called "mass" into something else called "energy". The correct statement is that "mass is proportional to energy".

 

And the most weird thing is that nobody seems interested in the question of "what are these strange units representing"?

The common answer is "square speed" (the speed of a speed??) which is not an acceptable answer IMHO.

 

Mass and energy are two aspects of the same thing. The fact that they have different conventional units is just because these units were assigned before we realized that they are linked.

 

The same is true of space and time. The spacetime interval tells us that there is a basic link between space and time. So let's use units which more properly represent this link:

 

A light year is a unit of distance. Speed is in units of distance per time. So we can give speed in units of light-years per year. Using these units, the speed of light is 1 light-year per year.

 

So in these units, the famous equation E = mc^2 becomes: E = m

 

Thus the correct statement is that mass equals energy!

Edited February 12, 2011 by I ME

[D H]

If you look at the question, it does not really matter why SOL has this or that value. In any chosen unit system, the value will be different. The real weird thing is that SOL is not a dimensionless physical constant, like the fine structure constant, or number [math] \pi [/math].

Why is that wierd? The speed of light has different values when expressed in meters per second, miles per hour, or furlongs per fortnight.

 

If "mass is energy" were correct, the multiplying factor should be dimensionless. But it is not. The multiplying factor has units that transform something called "mass" into something else called "energy". The correct statement is that "mass is proportional to energy".

There are several ways to look at mass-energy equivalence.

 

By way of analogy, look at Newton's second law as expressed by Newton: Force is proportional to the product of mass and acceleration: F=kma. The constant of proportionality has a numeric value of 1 when working in metric units, yielding F=ma. The constant of proportionality is 32.1740486 lbf/(ft/sec^2)/pound when working in English units. So is F=ma as expressed in metric units a convenience or is it a reflection of something deeper? In other words, does force represent a dimension separate from the dimensions of mass, length, and time, or is it a derived unit? The consensus is that force is not fundamental, that F=ma is the correct way of looking at things. That we need to use F=kma in English units is an artifice of the English system rather than something deep and fundamental.

 

So, one way to look at E=mc^2 is that this is an artifice of the metric system (and the English system of units, and even the furlongs-firkins-fortnights system). In this viewpoint, length and time are not independent fundamental units. Length and time are instead the same thing. That means that length/time is a unitless quantity. The c^2 in E=mc^2 is an artifice of our view that length and time are fundamentally different. In this view, the natural choice is to choose units such that c=1, yielding E=m.

 

This is a widespread but not a universally accepted view. Others do view length and time as being different but related things, related by the metric tensor, but different as well. That the signature of the metric tensor is +++- (or -+++, etc) indicates to some that time and length are fundamentally distinct concepts. In this point of view, that [math]E^2-p^2c^2=(m_0c^2)^2[/math] indicates that mass can be converted to energy (and vice versa) rather than being one and the same.

Edited February 12, 2011 by D H

[michel123456]

What about the gravitation constant G, m^3/(kg s) or the electrostatic constant k, kg m^3/(Coul^2 s^2)?

 

Count me among the ones who are not at all fascinated by the units.

 

I am.

The gravitation constant is another puzzling question like C.

 

The units are Joules per kilogram.

Why is that a problem?

 

So you say that Energy = kilograms by Joules divided by kilograms, after simplification Energy = Joules. Does that help?

 

Personally, I prefer say that Csquared is acceleration by distance (m/s^2 by m). But that doesn't help either.

 

(...)

There are several ways to look at mass-energy equivalence. (...)

 

IMHO one of the best posts. I just became a DH fan.

Edited February 12, 2011 by michel123456

[lemur]

The speed of light is currently a defined value, i.e. it is exact. If you want measurement error, you can look at measurement errors of quantities that depend on the constancy of c. The second, for example, is realized to about a part in 10^15. The meter is determined to better than a part in 10^11.

Are there ways of measuring the speed of light in radically different situations, such as between planets and/or stars as well as in laboratory settings on Earth?

[alpha2cen]

Are there ways of measuring the speed of light in radically different situations, such as between planets and/or stars as well as in laboratory settings on Earth?

 

Important thing is degree of precision.

If any data is very precise, the data comes from the original factor.

We obtain many kinds of data from experiment.

For example

1st step data------->2nd step data--------->3nd step data

length..........................velocity.......................reaction rate

Form this, length data have very little variation, the error is only rely on measuring error.

Velocity data is rely on length measuring and time measuring, so probability of making error is increased.

Reaction rate data is rely on temperature, pressure, concentration, etc., so how many times we tried, we could not obtain SD(standard deviation )zero data, i.e., the data have basic SD error.

So, if the measured light velocity data have no SD and are very accurate, light phenomena is the core of all physical phenomena in our Universe.

[swansont]

Are there ways of measuring the speed of light in radically different situations, such as between planets and/or stars as well as in laboratory settings on Earth?

 

Someone usually links to a list of measurements in virtually every speed of light thread. It's easily Googled otherwise.

[lemur]

Someone usually links to a list of measurements in virtually every speed of light thread. It's easily Googled otherwise.

I've googled it and I've only read about laboratory measurements that have been conducted on Earth. I've heard that time dilation is accurately compensated for by GPS. What I haven't ever heard of is a way of measuring the speed of light over long distances. I have read that long ago measurements were made astronomically but I don't understand the methodology, which is why I raised the question in this thread, since I would assume that once one understands the methodologies of measuring the speed of light, one would also understand why the experimental/observation parameters work and thus more accurately consider the question of why those parameters are related in the way they are.

[Sisyphus]

I've googled it and I've only read about laboratory measurements that have been conducted on Earth. I've heard that time dilation is accurately compensated for by GPS. What I haven't ever heard of is a way of measuring the speed of light over long distances. I have read that long ago measurements were made astronomically but I don't understand the methodology, which is why I raised the question in this thread, since I would assume that once one understands the methodologies of measuring the speed of light, one would also understand why the experimental/observation parameters work and thus more accurately consider the question of why those parameters are related in the way they are.

 

http://en.wikipedia.org/wiki/Speed_of_light#Measurement

 

That includes three different astronomical methods. The simplest, now that we have space probes all over the solar system, is to simply time a signal between them.

 

There is also a separate article on Ole Romer's initial calculations based on the relative velocity of light, Earth, and Jupiter, as evident by anomalies in the observed transit times of Jupiter's moons:

 

http://en.wikipedia.org/wiki/R%C3%B8mer%27s_determination_of_the_speed_of_light