Speed of light

[tansy]

The other day my husband was trying to remember the formula for working out something like velocity or acceleration over a certain distance at so many miles per hour (or something like that) re a particular motor-bike.

Anyhow, it made me wonder about the speed of light. My question is, is the speed of light constant, or does it accelerate.
For example when light comes from the sun, as it is 'ejected' so to speak, does it gather speed until it reaches a constant?
Also when light hits something and maybe is absorbed or rebounds somewhat, does that slow it down?

Sorry, I'm sure this is a very simplistic question and absolutely shows my lack of knowledge of these things...I'm not even posing the question in the right terms, probably, but I hope you understand what I'm querying.

 

[joshua 1 9]

The other day my husband was trying to remember the formula for working out something like velocity or acceleration over a certain distance at so many miles per hour (or something like that) re a particular motor-bike.

Anyhow, it made me wonder about the speed of light. My question is, is the speed of light constant, or does it accelerate.
For example when light comes from the sun, as it is 'ejected' so to speak, does it gather speed until it reaches a constant?
Also when light hits something and maybe is absorbed or rebounds somewhat, does that slow it down?

Sorry, I'm sure this is a very simplistic question and absolutely shows my lack of knowledge of these things...I'm not even posing the question in the right terms, probably, but I hope you understand what I'm querying.

The speed of light is not believed to be as constant as what they use to believe. There is very much a limit to the speed of light. They do not talk about warp speed anymore. Now they talk about worm holes as the means of very fast transportation from one area of the universe to another area. A new theory is that the universe may appear to expand or inflate when actually the universe is unfolding. This theory seems to be more consistent with the data we have.

 

[WolfGate]

Light does not accelerate.

 

[John Hyperspace]

The other day my husband was trying to remember the formula for working out something like velocity or acceleration over a certain distance at so many miles per hour (or something like that) re a particular motor-bike.

Anyhow, it made me wonder about the speed of light. My question is, is the speed of light constant, or does it accelerate.
For example when light comes from the sun, as it is 'ejected' so to speak, does it gather speed until it reaches a constant?
Also when light hits something and maybe is absorbed or rebounds somewhat, does that slow it down?

Sorry, I'm sure this is a very simplistic question and absolutely shows my lack of knowledge of these things...I'm not even posing the question in the right terms, probably, but I hope you understand what I'm querying.

According to, some of the people other people think are smart, light is only constant in a vacuum. Moving through different mediums can slow it down. I remember a paper where the speed of light was slowed down to, like, 5 miles per hour? Which raises all kinds of questions because allegedly the speed of light was the result of Maxwell's Field Equations precluding a static light wave. So Einstein's relativity came into play making the speed of light uncatchable (due to time dilation) because if you could catch up to it, you could look over at it and that would constitute a relative static light wave, which can't exist. Presto chango, relativity. So my question was, when they slowed light to a walking speed, how did you not introduce a relatively static light wave?

But then, what is a vacuum? I read that a true vacuum doesn't exist (at least, not naturally) and so that should mean, what? Light isn't naturally constant? There's no such a thing in nature as a constant speed of light. To make matters worse, I remember a paper just a year or so ago in which even in a vacuum light doesn't appear to be constant. Something about twisting a planar wave into a wave front.

In the end, I'm confident nobody knows anything. It's just a bunch of imaginary conjecture.

 

[tansy]

Light does not accelerate.

Nor slow down? Even infinitesimally?

 

[joshua 1 9]

Light does not accelerate.

The point is when they go to measure the speed of light they do not get consistent measurements. Warp speed on star trek was not light traveling faster it was people traveling faster than the speed of light and this in now known not to be possible. Time stops at the speed of light.
If you go faster then light that will increase the decay rate accordingly so you have a very high price to pay for braking the speed limit of light.

 

[Archie the Preacher]

As with many things, it depends.

The speed of light - "c", as it is abbreviated - is normally cited for velocity as being in a vacuum as (according to Wiki) 299,792,458 meters per second; or about 186,282 miles per second. It does slow down in various 'mediums' like glass, atmosphere or water.

So yes, it does slow down at times in various materials allowing transmission. (Obviously, it slows down a lot on concrete or steel.)

However, it does not slow down by running out of energy. It is going just as fast coming from another galaxy as it does from the Sun.

Nor does the form of 'generation' make any difference. For instance, when a baseball is thrown by a person, it has a specific velocity. If the person throwing is standing (with suitable safety devices) in the bed of a moving pickup truck and throwing in the direction of travel, the ball will be moving (relative to the ground) at a combined velocity of the thrower and the truck.

That doesn't happen with light. If the person in the prior paragraph turns on a forward facing flashlight in the moving truck, the light coming from the flashlight is still moving at the speed of light, not the speed of light PLUS the speed of the truck.

The reason for that is the subject of PhD papers on "Relativity". In short, velocity alters time; the speed of light alters time a lot.

If you are really curious, learning more about it is a life long hobby.

 

[joshua 1 9]

In the end, I'm confident nobody knows anything. It's just a bunch of imaginary conjecture.

The additive and subtractive color theory maybe "JUST" a theory, but we use the theory every day when we mix paint or when we filter light.

 

[Presbyterian Continuist]

Question: If you were driving your motor vehicle at the speed of light and you turned your headlights on, would they work?

 

[tansy]

According to, some of the people other people think are smart, light is only constant in a vacuum. Moving through different mediums can slow it down. I remember a paper where the speed of light was slowed down to, like, 5 miles per hour? Which raises all kinds of questions because allegedly the speed of light was the result of Maxwell's Field Equations precluding a static light wave. So Einstein's relativity came into play making the speed of light uncatchable (due to time dilation) because if you could catch up to it, you could look over at it and that would constitute a relative static light wave, which can't exist. Presto chango, relativity. So my question was, when they slowed light to a walking speed, how did you not introduce a relatively static light wave?

But then, what is a vacuum? I read that a true vacuum doesn't exist (at least, not naturally) and so that should mean, what? Light isn't naturally constant? There's no such a thing in nature as a constant speed of light. To make matters worse, I remember a paper just a year or so ago in which even in a vacuum light doesn't appear to be constant. Something about twisting a planar wave into a wave front.

In the end, I'm confident nobody knows anything. It's just a bunch of imaginary conjecture.

That's very interesting..thanks

 

[joshua 1 9]

(Obviously, it slows down a lot on concrete or steel.)

Light is absorbed or reflected. There is also refraction. Underwater photography is very difficult because the water distorts the light. There is an eye doctor in NYC that does underwater photography and he is one of the few people that is able to understand how to get good photos underwater.

 

[lesliedellow]

Nor slow down? Even infinitesimally?

Light in a vacuum does not speed up or slow down, even slightly. The speed of light is the speed at which a wave can move through an electromagnetic field. It is not made up of massive particles which can be accelerated or decelerated.

 

[tansy]

Question: If you were driving your motor vehicle at the speed of light and you turned your headlights on, would they work?

What is this, a trick question? I should think that if I were driving my car at the speed of light, I and the car would be annihilated

 

[John Hyperspace]

The additive and subtractive color theory maybe "JUST" a theory, but we use the theory every day when we mix paint or when we filter light.

Okay call me when we travel the speed of light every day.

 

[tansy]

Light in a vacuum does not speed up or slow down, even slightly. The speed of light is the speed at which a wave can move through an electromagnetic field. It is not made up of massive particles which can be accelerated or decelerated.

Yes, but I thought photons were 'part' of light. So couldn't they move faster, and if not, why not?
And actually, I wonder what makes light move at a certain speed.

 

[joshua 1 9]

It is not made up of massive particles

e=mc2 means that there is a direct connection between energy and matter.[/QUOTE]The point is we work with light. People who design lighting work with light. People who do photography work with light. That is why we study the physics of lighting in college so we can do our job.

 

[lesliedellow]

Yes, but I thought photons were 'part' of light. So couldn't they move faster, and if not, why not?
And actually, I wonder what makes light move at a certain speed.

Photons are massless particles, unlike electrons, protons or neutrons. The speed of light is determined by a couple of physical constants called the permeability of free space and the permittivity of free space. There is no known reason why they have the values they do.

 

[lesliedellow]

e=mc2 means that there is a direct connection between energy and matter. The point is we work with light. People who design lighting work with light. People who do photography work with light. That is why we study the physics of lighting in college so we can do our job.

Photons have momentum, but not mass. If they did have mass, the Theory of Relativity would imply that light cannot travel at the speed of light.

 

[tansy]

Photons are massless particles, unlike electrons, protons or neutrons. The speed of light is determined by a couple of physical constants called the permeability of free space and the permittivity of free space. There is no known reason why they have the values they do.

Oh my goodness, I knew my questions were simplistic . Um, what is 'free space'? I've never heard of that.
This is the trouble when I ask questions, it always leads to a thousand more...I do wish I could have done more physics at school. And it never seemed that I had chance to ask thequestions I wanted to know

 

[lesliedellow]

Oh my goodness, I knew my questions were simplistic . Um, what is 'free space?

It is a fancy name for a vacuum, but somebody christened those two constants with the names they have.