Why is the speed of light 186,000 miles per second?

[thejun]

Why is the speed of light 186,000 miles per second? Is that how fast the ether will allow it to travel? and if that is the case, if the edge of the universe; the edge to which the universe is speeding up, would the ether out there let light travel at higher or lower speeds? Which to me means that light is 186,000 miles per second in our are of the universe?

 

[rootone]

What ether?

 

[thejun]

the ether that all particles travel through, what gets there momentum, and probably their spin

 

[rootone]

'Ether' is a very wrong term to use to describe space in modern physics.
It is a term used for a long discarded idea, in which space is a substance through which light propagates in a way similar way to sound propagating through air.
Transmission of light (or any electromagnetism) in a vacuum is very different, but it does have a fixed speed 'c', and this has been verified repeatedly in different ways.

Why 'c' has that particular value is unknown, it just does.
According to special relativity 'c' is constant for all points in space, if it wasn't then SR wouldn't work, but clearly it does work.

 

[thejun]

let me start with a simpler question.
Why does light go at 186,000 miles per second. Why not 196,000, or 296,000.
What makes it travel at 186,000 miles per second?

 

[rootone]

We don't know why it has that particular value any more than we know why Pi has a particular value.
It just does, it has been experimentally confirmed repeatedly, c is not a theory.

 

[thejun]

Hence, the ether, and you don't know if Pi has a particular value... the answer "it just does", sounds religious to me... Physics is theory, just wondering what people are theorizing...

 

[rootone]

The existence of Ether has been proven wrong experimentally.
http://en.wikipedia.org/wiki/Michelson–Morley_experiment
and also other experiments.
Aether theories are not consistent with what is actually observed.
Special relativity IS consistent with what is actually observed (repeatedly)

Observations, measurements, are facts, not a religion.

 

[phinds]

Why is the speed of light 186,000 miles per second? Is that how fast the ether will allow it to travel? and if that is the case, if the edge of the universe; the edge to which the universe is speeding up, would the ether out there let light travel at higher or lower speeds? Which to me means that light is 186,000 miles per second in our are of the universe?

In addition to no ether that light travels in, there is no edge to the universe. You would do well to study some very basic cosmology.

 

[thejun]

im not talking about measurements. how do you smash to protons together to get the higgs? the higgs is way more massive than the the 2 protons, no matter how much energy you throw at it... if you can't answer why the speed of light is c, and you don't have any theories, than just say I don't know, and let somebody else theorize the question..
thanks for talking with me though!

 

[rootone]

Protons colliding at near light speed apparently IS able to produce a particle with a rest mass in the range where the Higgs particle was predicted to be.
That's what the LHC run1 set out to look for, that predicted particle (amongst other things), and they found it.

 

[bahamagreen]

I believe current thinking is that the ether theory and relativity theory make identical predictions so they appear experimentally indistinguishable, the only difference being that the ether theory assumes of all possible inertial frame of reference there is one unique frame at absolute rest (which can never be experimentally identified from the others) and relativity theory assumes there is no such unique absolute frame of rest.

thejun, I think the best explanation about c comes from Minkowski's famous "valiant piece of chalk" address, but it is not easy going; here is a step by step walk through that paper... Minkowski.

 

[Drakkith]

let me start with a simpler question.
Why does light go at 186,000 miles per second. Why not 196,000, or 296,000.
What makes it travel at 186,000 miles per second?

It travels that fast because free space has very specific values for the electric and magnetic constants: http://en.wikipedia.org/wiki/Speed_of_light#Propagation_of_light

In classical physics, light is described as a type of electromagnetic wave. The classical behaviour of the electromagnetic field is described by Maxwell's equations, which predict that the speed c with which electromagnetic waves (such as light) propagate through the vacuum is related to the electric constantε0 and the magnetic constantμ0 by the equation c = 1/√ε0μ0.[47]

Now, if you were to ask why those values are what they are, then the only answer we can give is that "we don't know".

the answer "it just does", sounds religious to me...

Take it as "we don't know" instead. There are plenty of fundamental constants and rules which have no underlying explanation. That's the nature of science. You always have something which isn't currently explained.

 

[quincy harman]

We don't know why it has that particular value any more than we know why Pi has a particular value.
It just does, it has been experimentally confirmed repeatedly, c is not a theory.

Pi is the ratio of a circles diameter by the circumference. In other words it's how many times you can fit the diameter in the circumference of any given circle.

 

[Greg Bernhardt]

Here are few discussions worth checking out
https://www.physicsforums.com/threads/why-does-light-travel-at-light-speed.36548/
https://www.physicsforums.com/threads/speed-of-light.424622/
https://www.physicsforums.com/threads/why-is-the-speed-of-light-the-same-in-all-frames-of-reference.534862/

 

[rootone]

Pi is the ratio of a circles diameter by the circumference. In other words it's how many times you can fit the diameter in the circumference of any given circle.

Yes that's right, and that ratio is a universal constant, having the same value for all circles.
The same can be said of 'c', it is similarly a universal constant
We know what the value of PI is and we know what the value of C is, to a very high degree of precision.

The OP asked why 'c' has the value it does, and the fact is that we don't know, just as we don't know why Pi has the value it has.
All we do know in both cases is that they are universal constants, and knowing their value is extremely useful.

The situation with Pi is exactly analogous to that of 'c', and there are several other such universal constants.
We know what the value of the constant is, but we don't know why they have the values they do.
Universal constants such as these are observed facts, not a consequence of any theory.
As such they simply are what they are and we can make use of them without the neccessity of an underlying explanation for them.

 

[phinds]

Pi is the ratio of a circles diameter by the circumference. In other words it's how many times you can fit the diameter in the circumference of any given circle.

Were you making a point with that statement or did you think we didn't know that?

 

[quincy harman]

Were you making a point with that statement or did you think we didn't know that?

well he said we don't know why the value of pi is pi. so I didn't know if he knew. lol

 

[rootone]

well he said we don't know why the value of pi is pi

That's right, we don't know why Pi has the value it has.
We can measure it, and we calculate it to many decimal places,
but that doesn't explain why the value Pi is what it is.

 

[wabbit]

But is the question about c ? In natural units c=1, there's no mystery in that. The number we get is an effect of our choice of units it seems to me, is there more to it than that?

 

[quincy harman]

That's right, we don't know why Pi has the value it has.
We can measure it, and we calculate it to many decimal places,
but that doesn't explain why the value Pi is what it is.

so what you're saying is we don't know why that's how many times the diameter fits into a circle?

 

[wabbit]

I can't even think of what would count as an explanation for pi having the value it has. Other than $\pi=\pi$?

 

[rootone]

But is the question about c ? In natural units c=1, there's no mystery in that. The number we get is an effect of our choice of units it seems to me, is there more to it than that?

Well the OP was asking why it is that C has a particular value and not some other value.
He used miles per second as the measurement unit, which although is not a unit used in modern science , is as good as any for the purpose of the question.

 

[rootone]

so what you're saying is we don't know why that's how many times the diameter fits into a circle?

That's right, we do know the value of Pi, and very accurately so, but we don't know why it has that particular value.

 

[wabbit]

@rootone, OK then, but it is a matter of units, and in fact that value seems arbitrary only because of our using peculiar units : if we used seconds and light-seconds as a standard unit, would OP be asking the question "why is c equal to one"?

On the other hand, if the question is "why is the ratio of c to some other speed such and such"? then it is no more about units - and there is probably, implicit in OP's question, such a formulation, quite possibly about the value of one of the dimensionless constant of nature - but I am not sure which one.

 

[rootone]

OK then, but it is a matter of units, and in fact that value seems arbitrary only because of our using peculiar units : if we used seconds and light-seconds as a standard unit, would OP be asking the question "why is c equal to one"?.

Sure the numerical value depends on the units used and he could indeed ask why c = 1 if the units of measure was light seconds per second instead of miles per second.

 

[wabbit]

Then the answer would be the same as "why is 1km going up the same as 1km going horizontally", we just use the same unit for two dimensions of spacetime. c=1 isn't arbitrary.

But I must admit this is not quite true, for I think I might just have understood OP 's question, or a possible version of it :

Why is the speed of light in a vacuum equal to the maximum speed of signals?

This is an interesting question, an answer might be "because photons are massless".

 

[rootone]

Or it's like asking why is a kilometer a kilometer, why can't it be 1.5 kilometers.

 

[Drakkith]

The most basic explanation is that our universe simply has a maximum speed limit and that anything without mass must travel at this speed. Why this speed limit exists, and why its value (in whichever units you choose) is what it is, is not known.

 

[prairiemain]

There are a number of universal constants for which there is no explanation ... yet. Some think all of these universal constants -- like the gravitational constant G -- are connected at some fundamental level but for now there is no way to show this. Human science has come a long way but it did not happen overnight -- give it time. Just to get some verification of the Higgs required CERN, a massive project using inconceivable energies (but not nearly enough to study more fundamental issues).

The OP wondered how two protons with a mass much less than the Higgs boson could generate that boson. Simple. The rest mass energy is only a part of the total energy in a collision between these two protons. Each proton is traveling in opposite directions with high kinetic energy when they collide, enough to generate thousands of particles. The Higgs boson is actually rare in such collisions but enough are expected to be detectable. They are and they were.

In science, statements of fact are supposed to be verifiable. It is not a "religion" to state that water freezes at 32 degrees (sea level pressure etc) because an experiment can be set up to test this declaration by anyone.

However, any system of knowledge that is logically consistent will have "defined" elements as part of it that are not strictly verifiable by experiment, nor are they intended to be verifiable. Take mass or distance or units of time -- mass represents a resistance to change in motion but exactly what "mass" is measuring is largely speculation. Protons and electrons have a specific mass, and the ration of their masses is of great importance in science. But "why" of that can't be answered yet. Science does not need a complete explanation of the nature of things in order to advance and for that reason scientific discovery has exploded in the past two centuries.

So, keep in mind that some a prioris must exist in science which are axiomatic to the logical system -- these are somewhat like articles of "faith" in that they can be defined but not derived from experiment. You're welcome to formulate a logically consistent and useful system that does not depend on a prioris but it is a fool's quest.

 

[|Glitch|]

Why is the speed of light 186,000 miles per second? Is that how fast the ether will allow it to travel?

First and foremost, the speed of light has been converted into a completely arbitrary unit of measure that we can comprehend. About 339 years ago Danish Astronomer Ole Rømer determined that light had a finite speed. Since then we have been able to observe and measure the speed of light in a vacuum with great precision (299,792,458 m/s with a measurement of uncertainty of 4 parts per billion). Furthermore, we have since changed the unit of measure, making one meter equal to the distance light travels in a vacuum at 1/299,792,458 of a second. Therefore, the unit of measure "meter" is now fixed to the value of c in meters per second.

The short answer is that the speed of light has the specific velocity it does because we have observed and accurately measured it. We do not know why light moves at that specific velocity, just like we do not know what gives mass gravity. But we can measure the speed of light and understand its effects, just like we can with gravity.

and if that is the case, if the edge of the universe; the edge to which the universe is speeding up, would the ether out there let light travel at higher or lower speeds? Which to me means that light is 186,000 miles per second in our are of the universe?

The speed of light can be slowed down, but not sped up. Although, there have been theories that suggest certain hypothetical particles can travel faster than the speed of light, just as tachyons, but they have never been observed. When visible light hits our atmosphere all kinds of things start happening, from scattering, absorption, emission, and reflection. As a result, the speed of light is slowed down by ~90 m/s as it passes through our atmosphere.

 

[thejun]

Yes, remember, my question is not how you measure things directly (a kilometer), or indirectly (slamming protons together and performing a rule out process to get the measurement you want). measurements are just a way to quantify something. A lot of you say light can slow down in air, or in water. so the water is determining the fastest speed it can travel. well in space i think its the same thing, that I'm calling the ether. maybe its why dark matter clumps, who knows.. I'm just thinking out loud. now if this ether exists, the edge of the expansion, it may be stretched, therefore light may go faster there by default, maybe that explains why it looks like its increasing faster when its really not. I have a dozen more questions, but verrrry curious what you guys think about this!

 

[Nugatory]

Yes, remember, my question is not how you measure things directly (a kilometer), or indirectly (slamming protons together and performing a rule out process to get the measurement you want). measurements are just a way to quantify something. A lot of you say light can slow down in air, or in water. so the water is determining the fastest speed it can travel.

You can calculate the speed of light in vacuum from the observed behavior of electrical and magnetic fields in a vacuum, and you can calculate the speed of light in air and water by allowing for the observed differences in the behavior of electrical and magnetic fields in those mediums.

well in space i think its the same thing, that I'm calling the ether. maybe its why dark matter clumps, who knows.. I'm just thinking out loud. now if this ether exists, the edge of the expansion, it may be stretched, therefore light may go faster there by default, maybe that explains why it looks like its increasing faster when its really not. I have a dozen more questions, but verrrry curious what you guys think about this!

Please remember that any posts that argues for something on the basis of "I think" is likely a violation of the Physics Forums rules prohibiting personal theories and speculation; this part of your post certainly is.

As a matter of history, there was once a hypothesis that something in empty space called "ether" was the medium through which light propagated in a vacuum. This hypothesis died in 1905 when it became clear that it wasn't needed - the straightforward ether theories don't match experimental results and the complicated ones answer only a subset of the questions that special and general relativity answer.

 

[mfb]

maybe its why dark matter clumps, who knows

Speculations without any model backing that up are pointless.

There is no indication of any "edge of expansion". The universe looks the same in all directions, and no model predicts anything in space that could be called "edge".

 

[Niflheim]

Yes, remember, my question is not how you measure things directly (a kilometer), or indirectly (slamming protons together and performing a rule out process to get the measurement you want). measurements are just a way to quantify something. A lot of you say light can slow down in air, or in water. so the water is determining the fastest speed it can travel. well in space i think its the same thing, that I'm calling the ether. maybe its why dark matter clumps, who knows.. I'm just thinking out loud. now if this ether exists, the edge of the expansion, it may be stretched, therefore light may go faster there by default, maybe that explains why it looks like its increasing faster when its really not. I have a dozen more questions, but verrrry curious what you guys think about this!

You can think it's the "same thing" all you want, it isn't. As multiple people have repeatedly told you, the ether does not exist. A vacuum is truly empty, there is nothing there. And why would c be constant here and everywhere else in the universe that we can observe but not at the "edge" of the universe, which has also been proven not to exist? It sounds like you really don't have all the facts here, I would consider doing some more research on the topic. I would recommend Stephen Hawking's a Brief (or Briefer) History of Time to give you the basic facts.

 

[thejun]

the universe cannot look the same in all directions, that doesn't make sense at all. Everything you guys say is speculation, and you are criticizing my question. I don't want you to answer it with facts. i know that is impossible. But I am a person that tries to think outside the box. you say that space is a vacuum, there is nothing there, then all of a sudden there is dark matter and dark energy, which no one can see, yet you are ok with believing that. And your right nugatory, I apologize for asking this here.

 

[Nugatory]

the universe cannot look the same in all directions, that doesn't make sense at all.

Have you looked? It is an observational fact that, to the limits of accuracy of our devices, the universe is indeed isotropic on a large scale (which is what people mean when they use the less precise "looks the same in all directions"). One of the harder lessons for humans to absorb is that the universe really doesn't care what we think makes sense - it is the way it is.

... you say that space is a vacuum, there is nothing there, then all of a sudden there is dark matter and dark energy, which no one can see, yet you are ok with believing that.

The dark energy and dark matter hypotheses do not disagree in any way with the experimentally confirmed theories of how a vacuum behaves, and "space is a vacuum" is a misstatement of what scientists say about what's in space. Yes, you will hear even professional scientists say "space is a vacuum" when they're speaking to a non-technical audience... but that's a simplification for a non-technical audience. A strictly correct description would be something along the lines of "a perfect vacuum is a very good approximation for outer space; there's a little bit of stuff, maybe a few atoms or so, in every cubic meter of space, but so little that its effects are locally negligible".

 

[Nugatory]

We can close this thread at this point. The original question has been answered, and the subsequent discussion into other topics that should be discussed in their own threads or not at all.