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[Philosophy Explorer]

Note the parentheses. Currently the speed of light is said to be about 300,000 meters per second. I have no problem with the number. It's the vacuum part I have a problem with.

There is no such thing as a perfect vacuum. Never was and never will be. So the speed of light, at best, must be theoretical. How do we determine what the actual speed of light is to exact precision without a vacuum to work with?

PhilX

[DarwinX]

Note the parentheses. Currently the speed of light is said to be about 300,000 meters per second. I have no problem with the number. It's the vacuum part I have a problem with.

There is no such thing as a perfect vacuum. Never was and never will be. So the speed of light, at best, must be theoretical. How do we determine what the actual speed of light is to exact precision without a vacuum to work with?

PhilX

The only vacuum that exists is in the minds of scientists that think there is a vacuum.

[Logicus]

First, the speed of light is roughly 300,000 KILOmeters per second.

Secondly, the vacuum of space, however it is conceived of, is the environment in which this speed has been measured.

It doesn't matter what is contained within that space, the speed of light is at its greatest there.

Of course, this begs a question: Is there a truly empty space somewhere, and would light travel faster in that environment?

[Philosophy Explorer]

First, sorry about being off by a factor of 1,000 as my memory isn't 100%.

It's natural to ask what experiment established the speed of light to be about 300,000 km/s? So I did an internet check and turned up this article: http://math.ucr.edu/home/baez/physics/R ... light.html

As it turns out, that speed was agreed upon at a 1983 conference. The article talks about Dayton Miller and the ether/aether and many things in a nontechnical way that many can enjoy reading.

My opinion is that many things are going on at CERN and elsewhere so I would expect many forthcoming announcements. In the meantime, if you want to philosophize about a perfect vacuum's effect on the speed of light, feel free to do so.

PhilX

[Mechsmith]

Well PhilX, The important thing about the speed of light is that is the speed that nothing can go faster than. Consequently it is a constant called "c". It is "a" constant not constant but since we can call it a constant we can use it as a basis for time.

Since we know that light responds to a gravity well and that light cannot go any faster than "c" so therefore as light is "blue shifted" to an observer at the bottom of a gravity well then it is time that must change. The speed of time therefore is affected by gravity.

So it it a simple fact that light travels at about 300,000 KMsec or 186,000 miles per second that determines the length of our second. At some point the accelerations acting on this light will result it's being "blue shifted" somewhere towards the infinitely short wavelength. Then we have (to us) a "black hole" (red shifted towards infinite long wavelength),since no energy can escape that region of spacetime. In a massive black hole the temperatures and pressures will be so great that nothing can move. Since time is a measurement of rate of change this is the point where time stops. This also is probably where gravity stops also.

As to determining the speed of light itself this has been done both experimentally and theoretically with reasonable correlation betwixt the two methods.

The thing that has been hardest to wrap my head around is the (probably) fact that the speed of light doesn't change. It's actually the speed of time that changes. This change is caused by mass-gravity. But when you understand that then the universe itself becomes a bit more understandable. After all it's a rather simple mechanical device. Just BIG Relative to us, of course Life and women are less understandable. Best, M

[The Truth]

Note the parentheses. Currently the speed of light is said to be about 300,000 meters per second. I have no problem with the number. It's the vacuum part I have a problem with.

There is no such thing as a perfect vacuum. Never was and never will be. So the speed of light, at best, must be theoretical. How do we determine what the actual speed of light is to exact precision without a vacuum to work with?

PhilX

The speed of light is always C, and it doesn't matter whether it's traveling through a vacuum or through any other medium. Photons always travel at C.

What slows light down is the absorption and re-emission of the photons as they travel through a given medium. But wherever you have an actual photon, it will always be traveling at C. Although technically a perfect vacuum is space that's devoid of stuff, it's more aptly thought of, as the space in between the stuff.

[Philosophy Explorer]

From The Truth:

"What slows light down is the absorption and re-emission of the photons as they travel through a given medium."

This I knew already.

Let's say we have this situation:

We have a room with an aquarium with clear glass, air and water. Let's say the room is dark and there's light in the water with a white rock at the bottom. Some of the rays of the light travel through the water and get reflected off the rock back through the water, then goes through the glass, then goes through the air finally reaching our eyes/brain.

A few questions based on this scenario:

1) Do the photons lose strenghth as they go through each medium?

2) Why does the rock appear the same out of the water as it does inside? (assuming you don't see a refraction - this assumes you turn on a room light once the rock is out of the water)

PhilX

[Logicus]

What do you mean by "strength"?

The rock looks the same for two reasons:

It is viewed by reflected light, and your eye/brain makes automatic color corrections under different lighting.

[HZY]

Note the parentheses. Currently the speed of light is said to be about 300,000 meters per second. I have no problem with the number. It's the vacuum part I have a problem with.

There is no such thing as a perfect vacuum. Never was and never will be. So the speed of light, at best, must be theoretical. How do we determine what the actual speed of light is to exact precision without a vacuum to work with?

PhilX

Light is both particle and wave. Once in a perfect vacuum, it will de-vacuum the vacuum and you will have no vacuum again. So impossible.

[Forfriends]

And what if light is only what we perceive and the atmosphere works as a gigantic lens but the light itself doesn't travel at all? Could it be co relevant conditioning of senses and sensors? The signal is sent to our eyes and eyes reflect this signal back as a projection. Many of things we look at doesn't exist. Rainbow is just one of the examples.

[Mgrinder]

Note the parentheses. Currently the speed of light is said to be about 300,000 meters per second. I have no problem with the number. It's the vacuum part I have a problem with.

There is no such thing as a perfect vacuum. Never was and never will be. So the speed of light, at best, must be theoretical. How do we determine what the actual speed of light is to exact precision without a vacuum to work with?

PhilX

The speed of light in a vacuum is now defined to be exactly 299792458 m/s. A second is also defined to be exactly "the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."

This also defines the meter as the distance light travels in a vacuum in 1/299792458 of a second. With these defined exact values, the project is not to measure the speed of light anymore, it's to get a better measurement of a meter by better clocks and better vacuums. look it up.

-- Updated Fri Mar 27, 2015 10:08 pm to add the following --

Just to add a bit to my post after reading you OP more carefully, trying to see what you are getting at with your question. I think what happens is that as you evacuate a chamber and approach a vacuum, the speed of light gets constant beyond our ability to measure any difference. Once you get a decent vacuum, the speed of light you measure is the same as you get when you get a vacuum 100 times better. (I think, can't find a reference) Our instruments aren't good enough to detect a difference.

Hence the speed of light in a vacuum is an extrapolated one (or rather the meter is, since the speed of light is a defined value), kind of like absolute zero is an extrapolated value. As you cool a gas, you hit a practical limit where you can't cool it anymore. The volume of the gas reduces, and the temperature goes down. THe graph of Volume versus Temperature is a line with positive slope. It hits the teperature axis at -273.15 Celcius, as VOlume goes to zero.

So absolute zero is an extrapolated value, as is what happens to light speed as you approach a vacuum (sort of, sicne it's an exact, defined value). That answer your question?

[Cogito ergo sum]

Note the parentheses. Currently the speed of light is said to be about 300,000 meters per second. I have no problem with the number. It's the vacuum part I have a problem with.

There is no such thing as a perfect vacuum. Never was and never will be. So the speed of light, at best, must be theoretical. How do we determine what the actual speed of light is to exact precision without a vacuum to work with?

PhilX

You don't. It's all based of off a close approximation.

[Niebieskieucho]

Speed of light could not be greater if we assume the pure (perfect) vacuum might exist. The universal space contains apart of matter, the medium called ether. Motion, gravity and interactions between physical entities are feasible due to the ether. Space cannot be devoid of ether, because ether is a condition of existence of space. If space could be empty, it meant a perfect insulation, thus no interactions between physical entities could be possible.