A question about light speed.

[Mismaah]

I think light slows down after passing through transparent surfaces but you can't notice the difference

But in all the books i read, the speed of light is stated as the same speed. Maybe it does have a constant speed.

[Demonhero]

I think light slows down after passing through transparent surfaces but you can't notice the difference

But in all the books i read, the speed of light is stated as the same speed. Maybe it does have a constant speed.

Light speed is believed to be constant. What happens when light passes through a transparent surface is called refraction, where light splits and deviates paths.

[gottibabe1]

Exactly what kind of light are you talking about Rota?

[imnothere]

you know we dont really know a whole lot about what we know. i mean does anyone know what electrons are really made of? we have theorized about their composition but its just that a theory.
what if the electrons are lying to us about who they are? what if they are made up of more then just the photons and neutrons we surmise they have?
all throughout human history we have ascribed traits and names to things that we surmise are but cant really know.
we do this especially with each other. and i've seen over and again that the way we treat each other is no different then the way we treat the knowable and the unknowable. we ascribe attributes to animals we dont know they have just as we ascribe attributes to our friends and family we dont know they have. we ascribe meaning to the stars and the motions of heavenly bodies just as we ascribe meaning and motive to the people we admire and what they do.

how do you really know you know anything you think you know? is anything a constant? if anything were constant would that be a good thing?


to answer the question of the op, yes i believe light can be slowed. other wise it would reach the darkest depths of the ocean unchanged. i also believe that it could be sped up, because anything you do to one side of an equation you can/ should/ must do to the other. by those two thoughts, governed by laymen observation and a minute knowledge of maths i have come to the conclusion that light is not constant.
i ascribe it the same inconstancy i look for in my own life and experience. for i am human and that is what we do.

[scythe]

Hmm, now this is an interesting thread.
Light is a form of energy (everything is), and that core nature of light has a constant speed. But if you ALTER the nature of light (so its not quite classed as light anymore) you can slow it down but not speed it up. Friction would affect the nature of light, as does other forces like gravity (although not sure why), but as we have not taken into account that time itself is not constant we do not know if gravity slowed light or if time was altered that made it APPEAR that way.
I would have thought that friction would DELAY the atoms, disrupting their path and causing microscopic reflections that would appear to slow down the progress but the wavelength itself would still be constant just happening in a localised area more intensely.
The nature of time, and gravity are still aspects not fully understood, and both have affected the rules that we thought were implacable.

To speed up light however is harder than slowing it down. It could be only achieved if wrapped in a conducting energy matrix that took out ALL friction (even in space there is friction as it is filled with particles and conflicting energy). A null void that could act as pocket tunnel for light waves. These ideas of changing the nature of space to travel faster is the core behind warp theory and teleportation. Light may not be the fastest energy form we have to work with either. As we discover more complex astrological features we may discover an energy form that is indeed faster. Since our limited vision is based on photoelectric stimulus we may require more techological breakthroughs to even identify these energy waves.

[Hired_Goon]

Can light move slower than the speed of light?

The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is very close to c.

The refractive index of air is approximately 1.0003. Denser media, such as water, glass, and diamond, have refractive indexes of around 1.3, 1.5 and 2.4 respectively for visible light.

So, the simple answer is Yes.

[Rota]

But, the example I gave earlier about the route between two cities... Does refraction truly slow down the light? or just detour it? Is light still moving at the same speed, but taking a longer route to get to it's destination (thus it only "appears" to go slower)?

[Bree Fletcher]

But, the example I gave earlier about the route between two cities... Does refraction truly slow down the light? or just detour it? Is light still moving at the same speed, but taking a longer route to get to it's destination (thus it only "appears" to go slower)?

I'm tempted to say that yes, this is correct. You aren't reducing the actual speed, but only average velocity of the light. Same with deflecting light by gravity.

[lkmus]

ok.. lightspeed (c) is a constant, 186,000 miles per second. and yes that is in a vacuum. it slows in atmosphere. even more so in water. however lightspeed (photons) and electromagnetism are different entities. as a constant they move at the same rate.

as for blackholes, yes that oter dude was right. its relative.. if im 1mile from a black hole and youre half a mile from a blackhole and you start flailin your arms goin "oh no bro!!" (well i wont hear what you say in a vacuum) but the arm flailin will look like a baywatch tribute (slow-mo).
you see we atribute time and light to be 1 and the same. as light needs to bounce off something then hit our eyes for us to see it. thats not the case though as the poor dude about to be sucked into the black hole is experiencing everything in frighteningly real time. so it is relative.

[Hired_Goon]

But, the example I gave earlier about the route between two cities... Does refraction truly slow down the light? or just detour it? Is light still moving at the same speed, but taking a longer route to get to it's destination (thus it only "appears" to go slower)?

Irrelevant. It has taken longer to get there, therefore, it has been slowed.

It is of course slowed by something, but the definition of a detour is then up for debate.

A perfect pane of glass will slow light down in a direct line, Therefore not a detour. A detour would be through a series of prism's or mirrors.

It's the same as the term Vacuum loosely used in previous posts. A vacuum doesn't really exist in reality. The term vacuum is used to define a lower pressure area that is created by the higher pressure of matter outside it. The terms of definition can always be argued, as can the interpretation.

But in reality, your simple question of "Can light move slower than the speed of light?" is Yes. It can. But not by itself.