Why does light travel at 299,792,458 meters per second

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Just note I couldn't find this on Google.

So why?

Why not slower, or faster?

This is a confusing question that I hope someone could answer.

And another question along these lines,

if a photon has no mass, how does it "fall" into a black hole.

Gravity is the force of attraction between two objects, right?

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The numerical figure is rather a historical fact based on how we chose to define our units. Today the speed of light is defined as exactly 299,792,458 m/s as we use light to define the metre.

If your question is why the speed of light is constant as measured by any inertial observer, no-one can really answer that, other than that is how the world is. Mathematically you can see this drop out of Maxwell's equations and this is what lead to the special theory of relativity.

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Thanks, I really appreciate the time you have put into answering my questions.

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Gravity bends space and defines the geometry of the path objects follow. Light simply follows the path defined by that space. A black hole has a curvature such that anything inside a certain distance doesn't have a path out.

The Newtonian view of gravity is that it's between masses, but it turns out that is only approximately true. Anything with energy is affected.

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Just to add a point to the excellent posts by AJB and Swansont:

The speed of light is a constant 299,792,458 mps in a vacuum.

But when light passes through matter, such as air, or glass, or water, its speed can vary.

This accounts for how glass lenses work. They slow light at a variable rate, according to the type of glass and how much it's curved.

The slowed-down light is bent and converged to a focus, where an image is formed.

This same principle applies to human eyes of course.

Otherwise you wouldn't be looking at this!

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The numerical figure is rather a historical fact based on how we chose to define our units. Today the speed of light is defined as exactly 299,792,458 m/s as we use light to define the metre.

If your question is why the speed of light is constant as measured by any inertial observer, no-one can really answer that, other than that is how the world is. Mathematically you can see this drop out of Maxwell's equations and this is what lead to the special theory of relativity.

I hope someone will in the future, before I die.

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As I already pointed out, light goes at different speeds, depending on the local medium it's travelling through.

For example, Its speeds through air,water and glass are quite different.

Isn't that hard to reconcile with the idea that light-speed is a Universal constant?

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As I already pointed out, light goes at different speeds, depending on the local medium it's travelling through.

For example, Its speeds through air,water and glass are quite different.

Isn't that hard to reconcile with the idea that light-speed is a Universal constant?

It is, as you yourself said, the speed in a vacuum that is a constant and maximum speed.

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Well it's not a Universal constant then. It only applies to a vacuum.

If it was truly a constant, it would apply everywhere.

I mean suppose someone said -

The diameter/circumference ratio of a circle is Pi. This is a constant - provided it's measured in a vacuum.

But if it's measured in air or underwater, it may vary a bit.

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Same applies: the ratio is only Pi for a circle in Euclidean geometry.

Also, the reason that light slows down when passing through a material is because the photons are continuously absorbed and re-emitted. In between, they travel at c. Universality restored!

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Well it's not a Universal constant then. It only applies to a vacuum.

If it was truly a constant, it would apply everywhere.

I mean suppose someone said -

The diameter/circumference ratio of a circle is Pi. This is a constant - provided it's measured in a vacuum.

But if it's measured in air or underwater, it may vary a bit.

It is universal.

Nothing in the Universe travels faster than C.

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It is universal.

Nothing in the Universe travels faster than C.

Except Space.

That is a major exception.

------------------

In order to be constructive:

C(in vacuum) is a constant. C is also a ratio, expressed in units Meters/sec.

So, if you put on the X axis roughly 300000 km and on the Y axis 1 second, the tiny-tiny angle represents C.

The OP question can be resumed as "why is the value of the angle this exactly value" and the answer as AJB said is "no one knows".

It seems that the Universe is governed by that ratio. It is geometric feature of the Universe. That's all.

Edited by michel123456
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--A similar way to see the situation is the following:

One could ask what is the geometric relation between the 3 space dimensions.

in fact there is no difference between the 3 spatial dimensions, one can rotate arbitrarily the system of axis without changing anything: it means that the geometric relation between the 3 axis is equal to one (the unity, 1). it means that space is isotropic.

Now, if one asks about the geometric relation between the spatial dimension and the temporal dimension, the scientist replies that geometric relation is C.

Even a very simple minded person would ask, how is that, why is it not one (the unity, 1)? And then scientists will reply that indeed, the relation is 1, simply the value C is the result of more common units.

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Just note I couldn't find this on Google.

So why?

Why not slower, or faster?

This is a confusing question that I hope someone could answer.

And another question along these lines,

if a photon has no mass, how does it "fall" into a black hole.

Gravity is the force of attraction between two objects, right?

Photons have energy, energy and mass are different forms of the same fundamental thing. E=MC2 Energy (Light)) is a form of electromagnetism, and effected by other force fields such as gravity, or a magnetic field itself and thus can be drawn into it.

The speed of light differs between different mediums, thus it goes slower in water than in the vacuum of space. As for why it goes at the speed it goes in the vacuum of space, 1) This is just a fact of our reality that we must accept, or 2) Maybe a cosmic traffic authority set the limit or god if you like?

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Light only travels at different speeds through a medium because if we think of light as a particle. It is bouncing off all these different molecules, but it still travels at the speed of light while doing so. The only reason for this change in speed is that as it is bouncing around, it takes longer to get from one end to the other as a result of that. The speed in the direction of motion will always be c. As for why c will always be the same, it is because it is the maximum speed. Because the speed of light is the maximum speed, you can't go faster then c, or else it would not be the fastest speed.

Edited by Endercreeper01
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Light only travels at different speeds through a medium because if we think of light as a particle. It is bouncing off all these different molecules, but it still travels at the speed of light while doing so. The only reason for this change in speed is that as it is bouncing around, it takes longer to get from one end to the other as a result of that. The speed in the direction of motion will always be c.

It's a little more subtle than that. The propagation speed of photons is always c, but it takes time to interact (absorption/emission in virtual states). The result is not because of a zig-zag path.

The slower propagation is also perfectly consistent with the classical wave nature of light. The wavelength decreases by a factor of 1/n, and propagation speed depends on the wavelength.

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It's a little more subtle than that. The propagation speed of photons is always c, but it takes time to interact (absorption/emission in virtual states). The result is not because of a zig-zag path.

The slower propagation is also perfectly consistent with the classical wave nature of light. The wavelength decreases by a factor of 1/n, and propagation speed depends on the wavelength.

Even though the light interacts with molecules, it doesn't mean the actual speed changes, and that was my point. The speed must be constant at all times, so the reason for the delay is because of the light interacting. The speed of light is c = λf, and the wavelength gets smaller because the frequency gets higher. Wavelength is c/f, so the frequency must increase to make up for this shortened wavelength.
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Even though the light interacts with molecules, it doesn't mean the actual speed changes, and that was my point. The speed must be constant at all times, so the reason for the delay is because of the light interacting. The speed of light is c = λf, and the wavelength gets smaller because the frequency gets higher. Wavelength is c/f, so the frequency must increase to make up for this shortened wavelength.

The frequency does not change. Classically, the wave slows down by a factor n when in a medium of index n.

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Light only travels at different speeds through a medium because if we think of light as a particle. It is bouncing off all these different molecules, but it still travels at the speed of light while doing so. The only reason for this change in speed is that as it is bouncing around, it takes longer to get from one end to the other as a result of that. The speed in the direction of motion will always be c. As for why c will always be the same, it is because it is the maximum speed. Because the speed of light is the maximum speed, you can't go faster then c, or else it would not be the fastest speed.

Light is both a particle or a wave it depends on how it is observed.

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Light is both a particle or a wave it depends on how it is observed.

And how, shall I ask, is that so. Does that mean sound is a particle too. That fact just totally screwed up my perception of reality. More research for me...

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Except Space.

That is a major exception.

Space isn't a thing though, is it?

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I hope someone will in the future, before I die.

What?

And how, shall I ask, is that so. Does that mean sound is a particle too. That fact just totally screwed up my perception of reality. More research for me...

Sound is energy of molecules vibrating, many molecules. Though individual molecules vibrate, they are not individual particle-waves of sound as photons are of light. The vibrating molecules pass their energy by transferring it to other molecules; photons do not pass their energy to other photons.

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Space isn't a thing though, is it?

What are you expecting me to say: yes or no?

Nothing in the Universe travels faster than C

-----------------------------------------------------

The numerical figure is rather a historical fact based on how we chose to define our units. Today the speed of light is defined as exactly 299,792,458 m/s as we use light to define the metre.

If your question is why the speed of light is constant as measured by any inertial observer, no-one can really answer that, other than that is how the world is. Mathematically you can see this drop out of Maxwell's equations and this is what lead to the special theory of relativity.

I hope someone will in the future, before I die.

What?

I said I hope that someone will explain why the speed of light is constant as measured by any inertial observer before I die.

In the meanwhile I have made my own idea on this. I prefer being wrong than to have no answer at all.

Edited by michel123456
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Is space a material object- can you , for example, pick it up and throw it?

" I hope that someone will explain why the speed of light is constant as measured by any inertial observer before I die."

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And how, shall I ask, is that so. Does that mean sound is a particle too. That fact just totally screwed up my perception of reality. More research for me...

You cant equate sound waves to the quantum world, sound waves are just that waves, in the macro- world In the micro- world, light just like other fundamental particles, can exist both as a wave and as a particle. Google the "Double Spit Experiment"

Space isn't a thing though, is it?

Yes "space is a thing", or something, it is a 3 dimensional reality, which contains the stuff of our universe.

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