Speed of light

[aristarchusinexile]

If space and time were locked time would not alter so quickly and at such infinitesimal distances on the cosmological scale. Time and space are separate entities co-existing for mutual benefit at times in some spaces, but capable of existing separately from each other, and because they are capable of doing so, they do so, in some times and in some spaces.

From Wikipedia: Spacetime

• In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, however, time cannot be separated from the three dimensions of space, because the rate at which time passes depends on an object's velocity relative to the speed of light and also the strength of intense gravitational fields which can slow the passage of time.

Eactly! Except the Wiki writer needs to expand his knowledge a bit, for instance by exploring the existance of space without gravity, time as a separate entity, etc.

[bystander]

... gravity is so weak that 'it is said' that galaxies cannot be held together by it, so Dark Matter was theorized as accounting for the shape of spiral gravities. ...

Dark Matter was proposed as a solution to the "missing mass problem", gravitational effects were observed that couldn't be explained by the visible mass available.

Eactly! Except the Wiki writer needs to expand his knowledge a bit, for instance by exploring the existance of space without gravity, time as a separate entity, etc.

I think you misread the wiki, time cannot be separated from the three dimensions of space, except in classical mechanics where time is treated as universal and constant.

[stkegg]

Chris Peterson wrote:
"The speed of light doesn't change"

apodman wrote:
"short explanations mean loose descriptions"

The ONLY thing that does not change is the mathematical value of "c", that has been used as a LABEL to represent the 'speed of light', but the LIGHT, as an Universal fenomena, changes and adapts its speed according to the electromagnetic characteristics of the MEDIUM it is passing on.

c = 1 / ( (e0*e*u0*u)^1/2 )

(e0 = permittivity of the vacuum)
(e= permittivity of the medium where the light is passing)
(u0 = permeability of the of the vacuum)
(u = permeability of the medium where the light is passing)


The "speed of light" is NOT THE SAME inside a glass than in vacuum.
The "speed of light" is NOT THE SAME in water than in vacuum.
The "speed of light" is NOT THE SAME in water than in glass.


http://en.wikipedia.org/wiki/Prism_(optics)
"How prisms work
Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism)."

How it can be categorically said that "The speed of light doesn't change"?

[Chris Peterson]

How it can be categorically said that "The speed of light doesn't change"?

You can only read that in what I said if you take it out of context. The discussion (as such) was not about the speed of light in a medium, but about the speed of light in a vacuum, subject only to different strength gravitational fields. As you say, c is a constant (or so it appears). But the speed of light is equal to c in the absence of any medium, and does not vary in speed because of varying gravitational fields.

There is certainly no doubt that light travels slower than c in any medium.

[Wayne Watson]

The speed of light can be slowed dramatically--to almost walking speed in a laboratory. Google should help. Here's a very recent article, 38 mph*, <http://query.nytimes.com/gst/fullpage.h ... A96F958260>. From time to time, Nova shows a three part (2?) series on the lowest temperature. I think it's mentioned there for another source.

I'm not sure why they are writing about 38 mph, but a woman physicist, maybe at IBM, and her team slowed it down ever further if my memory serves me properly maybe 6-8 years ago.

[aristarchusinexile]

... gravity is so weak that 'it is said' that galaxies cannot be held together by it, so Dark Matter was theorized as accounting for the shape of spiral gravities. ...

Dark Matter was proposed as a solution to the "missing mass problem", gravitational effects were observed that couldn't be explained by the visible mass available.

Eactly! Except the Wiki writer needs to expand his knowledge a bit, for instance by exploring the existance of space without gravity, time as a separate entity, etc.

I think you misread the wiki, time cannot be separated from the three dimensions of space, except in classical mechanics where time is treated as universal and constant.

It's not a matter of misreading the Wiki, it's just a matter of preferring not to believe everything I see in print. And so far, no one has responded to the statement that Enstein raised the speed of light to constancy for work in inertial fields, never saying speed of light was constant; and as he raised it only to constancy in inertial fields, he left open the probability raised to a certainty by my investigation, that light travels instantaneously in the absence of gravity between gravity fields.

[aristarchusinexile]

The speed of light can be slowed dramatically--to almost walking speed in a laboratory. Google should help. Here's a very recent article, 38 mph*, <http://query.nytimes.com/gst/fullpage.h ... A96F958260>. From time to time, Nova shows a three part (2?) series on the lowest temperature. I think it's mentioned there for another source.

I'm not sure why they are writing about 38 mph, but a woman physicist, maybe at IBM, and her team slowed it down ever further if my memory serves me properly maybe 6-8 years ago.

Yes, and at the lowest point in a gravity field (the singularity principle perhaps?) where time stops, and thus, where speed stops, because speed is a measurement in relationship to time, light also will come to a stop. My curiosity wonders what light looks like when it is at a stop .. how it effects its environment ..etc. Does it 'compress' into such huge energies that they eject themselves out of dark holes as Jets?

[aristarchusinexile]

How it can be categorically said that "The speed of light doesn't change"?

You can only read that in what I said if you take it out of context. The discussion (as such) was not about the speed of light in a medium, but about the speed of light in a vacuum, subject only to different strength gravitational fields. As you say, c is a constant (or so it appears). But the speed of light is equal to c in the absence of any medium, and does not vary in speed because of varying gravitational fields.

There is certainly no doubt that light travels slower than c in any medium.

We must repeat that perhaps the speed of light in relationship to time does not change in a vacuum (although the measurement of the speed of light has been done only on a tiny blip of space in relationship to the breadth of the cosmos) but time itself changes in a gravity field, a 'second' in our normal consciousness for instance (a hypothetical example only) becoming 'two seconds' of time because of time's speedup in the lesser gravity, light therefore travelling twice as far in terms of the original second. Since time and space relate to each other but are not dependant on each other, they act separately from each other, allowing the instantaneous transmission of light through vacuum in regions of zero gravity. Spacetime is an error. There is space, and there is time. They weave together or not as needs arise, but are seperate strands.

[Chris Peterson]

The speed of light can be slowed dramatically--to almost walking speed in a laboratory. Google should help. Here's a very recent article, 38 mph*, <http://query.nytimes.com/gst/fullpage.h ... A96F958260>. From time to time, Nova shows a three part (2?) series on the lowest temperature. I think it's mentioned there for another source.

This is a misconception. The speed of light in the normal sense we think of it- the speed of a photon- can't be slowed much. This is called the phase velocity, and is always c in a vacuum, and a little less in media. What is being slowed (and in some cases raised above c) is the group velocity. These guys are playing games with waves and interference, but the speed of light in its most meaningful sense isn't being changed.

[aristarchusinexile]

The speed of light can be slowed dramatically--to almost walking speed in a laboratory. Google should help. Here's a very recent article, 38 mph*, <http://query.nytimes.com/gst/fullpage.h ... A96F958260>. From time to time, Nova shows a three part (2?) series on the lowest temperature. I think it's mentioned there for another source.

I'm not sure why they are writing about 38 mph, but a woman physicist, maybe at IBM, and her team slowed it down ever further if my memory serves me properly maybe 6-8 years ago.

You are sure to hear the argument that the speed can be slowed only a small amount, but those arguments will be made only because the complete picture has not yet been seen or considered. How can we consider what we haven't seen? And Hawking says 'either we have not yet seen 99 percent of the universe, or our idea about about how it started is wrong.'

[astrolabe]

Hello aristarchusinexile,

You said: "We must repeat that perhaps the speed of light in relationship to time does not change in a vacuum (although the measurement of the speed of light has been done only on a tiny blip of space in relationship to the breadth of the cosmos) but time itself changes in a gravity field, a 'second' in our normal consciousness for instance (a hypothetical example only) becoming 'two seconds' of time because of time's speedup in the lesser gravity, light therefore travelling twice as far in terms of the original second. Since time and space relate to each other but are not dependant on each other, they act separately from each other, allowing the instantaneous transmission of light through vacuum in regions of zero gravity. Spacetime is an error. There is space, and there is time. They weave together or not as needs arise, but are seperate strands."

Looks like basic general relativity to me when discussing light speed WRT gravity wells. I can assume it to mean to an observer in the "one second" location? Because in the location with the "two seconds" it would appear no different except for the fact that the original light at the "one second " location would now appear to be moving at one half second light seen from that vantage point. This is not a complete response to your more complete post. Now I don't know about light transmitting instantaneously in a zero vacuum, AFAIK that envoronment does/cannot exist so the argument could be hypothetical at best.

To be honest I don't even know why I responded to this. I've been a bit disillusioned about astronomy for a while now. Pretty pictures, lots of ideas, a big theory surrounded by lesser theories, heated discussions, formulas and equations by the tens of thousands, topics that have discussions way over my head, threads that go off topic (like I'm doing now) and sometimes generalities that make no sense. The point? No one seems, all in all, to know anything. And if everything WAS known? There would somehow still be no satisfaction in it- I just know it!

[aristarchusinexile]

You know Astro, I'm almost at the same state of mind. But perhaps my family difficulties are just weighing heavy .. a daughter in emotional trouble. Astronomy barely seems important right now, but maybe my curiousity will improve with time.
But at times like this, when we can easily see how little we know, how little anyone knows about our physical existance, we can assume a more humble mind.

[aristarchusinexile]

A movie of an ice cube melting will show time passing .. play the movie backwards and it is 'obvious' the movie is played in reverse. However, film the growth of certain crystals which form into cubes, cubes upon cubes, that someone not familiar with these cubes will think the film is being played backwards. Is time reversed in the creation of the cubes? No. But it seems like that to someone watching the film. These things tell me time must become far better understood in its relationship to our understanding of our universe. More on this later.

[Qev]

All this tells anyone is that they need to learn the differences between melting and crystallization.

[astrolabe]

Hello All,

Time is, of course a useless concept unless one actually uses it to measure an event of some kind.The melting of an icecube in an of itself is only an event and has little to do with time per se other than to demonstrate that the event proves that there is a "past". I hate to split hairs but in order to use an icecube melting to PROVE that "time is passing" I think one has to actually "clock" the event and be there to watch it then, for the fun part, calculate how much time passed from start to finish. The result will be valid and also, while duplicating the exact circumstances of the environment, the content and size of the cube etc., one should be able repeat the test and, with predictably, get the the same result every time. As far as runing the "movie" in reverse: the time will be exact but not........ itself............ reversed.......... Hmmmm............ Well, maybe if there was a clock on the wall that one saw in the movie?

[astrolabe]

Hello aristarchusinexile,

Thank you. Yes, you are right. Good wishes for your daughter's quick recovery.

[harry]

G'day from the land of ozzz

When the chinese whisper is applied to TIME, we end up with many fantasy models, of time machines, black hole dimensions and the actual ability to change time.

[harry]

G'day

Actual time cannot change.

Relative time can

[aristarchusinexile]

I've read both responses (oops, now there are three) and probably they might have been slightly different if I had had more time to explain my topic .. but I have no internet at home, and use public access computers with restricted time, and I was cut off by the public library's closure before I could finish my thoughts.

My point is that we operate, experiment, measure, calculate, make conclusions, make hypothesis, according to our perception of time. To a casual observer, a film of a cubic crystal forming, which is time running forward, might persuade him/her to think they are watching a film of an ice cube melting but run backwards .. time running backwards. Their perception would be wrong, but it would be their perception, the same as the well known example of two passenger trains sitting side by side at a station, and when one pulls out persons on the other train think they're train is moving .. but their perception is wrong. Stephen Hawking positions us all, and that is a wide sweeping "all", as casual observers of our universe by his statement, "either we have not seen 99 percent of the universe, or our idea of its beginning is wrong." I think our perception of time is at the same stage of development. We may (probably) have seen and understand only 1 percent of the realities of time. E=mc2 might be missing T, even though superficially T is thought to be recognized as a factor in c - speed being measured against a unit of time. I have said elsewhere here that I no longer believe in Spacetime .. but that space and time are two separate existences, woven together at some times in some spaces, but not being dependent on each other for existence. These are just my thoughts for whatever they are worth to anyone. I don't expect to be agreed with, I just wanted to express my ideas because this forum is about observations and ideas .. and I would like to thank everyone here for contributing their ideas which give me 'food for thought'.

[astrolabe]

Hello aristarchusinexile,

I see your point but if time exists as a separate entity we have at present no way to know. IMO if there is any movement of any kind then there has to be time. No time, no movement. And like you say it is all realitive to the observer- it is us who increment time and place values on it. Now things occur that we don't observe but time would be nonetheless a factor involving any changes whatsoever in positional variations. Harry said it correctly in a post where he stated that one cannot change time. That would be true. If time stopped nothing would be moving and an argument surrounding whether or not a an increment less than Plank time could be a segment that would demonstrate an example of time in a halted state seems interesting- infinity maybe?

[Qev]

G'day

Actual time cannot change.

Relative time can

Define "actual time".

[harry]

G'day from the land of ozzzzz

Here down under we have our time upside down and inside out.

OK

If time cannot change, what is all the who haa about time.

So far our method of time has been measured by several means.

If we use EMR to measure time than we have to understand what happens to the speed of EMR in various situations.

Under situations where C is contstant it becomes an easy calculation to calaculate the time from position A to position B moving or non moving.

If we have the extreme situation such as a so called black hole where the compact matter having extreme electromagnetic fields surrounding it effects the speed of light. Than the relative time can be calculated by the resultant speed of the EMR.

This becomes very difficult when the compact matter either forms a trapping Horizon or the theoretical Event Horizin where all EMR is trapped within the Trapping Zone of the compact matter (so called black hole)

Time is simple, we usully complicate it for better or worse.

Would it not be great to have a time machine? We can all dream.
What about santa?

[makc]

Define "actual time".

he probably mean "proper" time

[stkegg]

"Faster than light astronomical observation reports"...

http://xxx.soton.ac.uk/find/astro-ph/1/ ... +years/8/0

"Einstein Doesn't Work Here Anymore"
(By Maurice B. Cooke)

[Chris Peterson]

"Faster than light astronomical observation reports"...

Superluminal motion in jets, despite the name, doesn't require that anything is actually moving faster than c, and very few physicists consider that the effect is anything other than a pretty well understood illusion. That's the position, also, taken in the handful of papers I scanned in your link.