Speed of light

[Chris Peterson]

Now i am not sure i understand it. :shock: :? should it be said instead "it is the effects of this distort spacetime we call gravity" . ? Wich happen to affect the mass. Ohhh need to rethink it now. :shock:

I think you understand it just fine.

[aristarchusinexile]

Chris, your quote, "There is certainly no doubt that light travels slower than c in any medium."

From what is theorized about space, that it is not empty, but contains vast amounts of Dark Matter and Dark Energy, would you call it a medium? And can you see a possibility that if space is a medium, light will perhaps travel faster than c in voids, where DM and DE might not exist to make up the normal medium of space?

[BMAONE23]

I can not see it traveling faster than C but would in fact travel @ C (fastest possible) through the voids and some slight % slower (like .9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999...%)through the intergalactic meduim of space.

[Chris Peterson]

Chris, your quote, "There is certainly no doubt that light travels slower than c in any medium."

From what is theorized about space, that it is not empty, but contains vast amounts of Dark Matter and Dark Energy, would you call it a medium? And can you see a possibility that if space is a medium, light will perhaps travel faster than c in voids, where DM and DE might not exist to make up the normal medium of space?

Space is not a medium. Dark energy is not a medium. Dark matter is, but it doesn't interact with electromagnetic radiation, so it probably doesn't affect the speed of light- but since dark matter is not well understood, nobody knows for sure.

I don't believe there is anyplace in the Universe that is completely free of matter, just regions where it is quite sparse. I know of nothing to suggest that "voids" as you describe them even exist, and there is nothing to be found in any well supported theory to suggest that light can ever travel faster than c, and there is no good reason to think that c isn't a constant. As much as I'm sure of anything, I'm sure that light never travels faster than c, anywhere in the Universe.

[Doum]

I think what Doum is trying to say is mass distorts spacetime and the greater the mass, the greater the distortion.

I think so, too. I just think Qev expressed it in a better way.

From those quote i also say
I just think Chris expressed it in a better way then i do. And all that time he let me babling something. Thank for the right answer.

[Doum]

Uhhh wich happen to be :

Chris, your quote, "There is certainly no doubt that light travels slower than c in any medium."

From what is theorized about space, that it is not empty, but contains vast amounts of Dark Matter and Dark Energy, would you call it a medium? And can you see a possibility that if space is a medium, light will perhaps travel faster than c in voids, where DM and DE might not exist to make up the normal medium of space?

Space is not a medium. Dark energy is not a medium. Dark matter is, but it doesn't interact with electromagnetic radiation, so it probably doesn't affect the speed of light- but since dark matter is not well understood, nobody knows for sure.

I don't believe there is anyplace in the Universe that is completely free of matter, just regions where it is quite sparse. I know of nothing to suggest that "voids" as you describe them even exist, and there is nothing to be found in any well supported theory to suggest that light can ever travel faster than c, and there is no good reason to think that c isn't a constant. As much as I'm sure of anything, I'm sure that light never travels faster than c, anywhere in the Universe.

It seem so easy to write. But it is how i see it. I just cant find the right word. Well said.

[aristarchusinexile]

Voids .. From what I've read the universe is contains many voids, like Swiss Cheese according to one description. I will search for more .. but here is what I found quickly.

Title:
Voids and filaments
Authors:
Icke, V.
Affiliation:
AA(Minnesota, University, Minneapolis, MN)
Publication:
Royal Astronomical Society, Monthly Notices (ISSN 0035-8711), vol. 206, Jan. 1, 1984, p. 1P-3P. (MNRAS Homepage)
Publication Date:
01/1984
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
COSMOLOGY, GALACTIC EVOLUTION, GRAVITATIONAL COLLAPSE, ASTRONOMICAL MODELS, CLOUDS, FILAMENTS, VOIDS
Bibliographic Code:
1984MNRAS.206P...1I

Abstract
Results of numerical calculations of the gravitational collapse of pregalactic matter have been reported by various investigators. Centrella and Melott (1983) have shown that the typical result of such a collapse is a filamentary structure surrounding sphere-like voids. The present investigation is concerned with the reasons for the roughly spherical form of voids between condensations. It is reaffirmed that the condensations are more likely to be filaments than pancakes. Attention is given to the shape of high- and low-density regions, and hyperboloidal filaments.

Second find - (I have not read the book) Bubbles, Voids and Bumps in Time: The New Cosmology (Paperback) by James Cornell (Editor)

Third find .. The Bootes Void .. I hope this passes copyright guidelines.
The Bootes Void Saturday, Apr 22 2006 http://www.acceleratingfuture.com/micha ... otes-void/
space Michael Anissimov 3:37 pm

illustration missing

The Boötes void, named after the constellation where it can be found, is the largest known region of empty space in the observable universe. Because it is so large, it is sometimes referred to as a supervoid. The void is roughly spherical and has a diameter of approximately 75 megaparsecs, or 250 million light-years, which is about 2% the diameter of the entire observable universe(!)

For comparison, our Milky Way Galaxy has a diameter of about 100,000 light-years, and the largest known galaxy is about 250,000 light years across, a thousandth the width of the void. Within this vast emptiness, only about 53 luminous galaxies have been detected, which extend in a rough tube-shape through the middle of the void. Other galaxies surely exist within the void, including structures of dark matter, but these galaxies are smaller and less massive than the 53 primaries. These 53 galaxies have an average brightness about 25% more intense than the universal average, a phenomenon that needs explaining.

illustration missing

Greg Aldering, an astronomer who now works at Lawrence Berkeley Laboratory, once said, “If the Milky Way had been in the center of the Boötes void, we wouldn’t have known there were other galaxies until the 1960s.” Imagine that kind of a discovery!

The void was discovered in 1981 by Robert Kirshner, Augustus Oemler Jr, Paul Schechter and Stephen Shectman in a survey of galactic redshifts. Their results were published in the paper, “A million cubic megaparsec void in Bootes” in Astrophysics Journal 248. Further studies throughout the early 80s confirmed the existence of the void, which was one of the first large voids to be detected, and is hence the most famous.

Wow .. according to the article 98 % of the universe is composed of intergalactic voids.

[aristarchusinexile]

"Boötes void may one day be seen as the ultimate time capsule - fire off a pattern of photons, only for the pattern to be rediscovered hundreds of millions of years later when it reaches the other side."

So many edits trying to get the link to work

http://www.acceleratingfuture.com/micha ... otes-void/

If the pattern of photons doesn't change after hundreds of millions of years, has the pattern experienced 'Time'? Further - If there is no gravity in a void to slow time .. does time speed to infinite?

From the Bootes Void discussion:

"Great post on a fascinating topic, but I do have a minor correction. You say “Particles of matter, having much more mass than both photons and neutrinos, would of course get pulled towards the walls of the void.” In fact, a particle inside a hollow spherical shell, with all mass evenly distributed at the exterior of the shell, experiences no net gravitational force.

It’s non-intuitive at first, but have a seat inside the shell (away from the center) and let’s take a look around. If you consider a 1-degree arc in the direction of the closer wall of the shell, it will define a circle on that wall, with a radius related linearly to the distance to the wall. A 1-degree arc in the opposite direction defines a much larger circle, and the amount of gravity-inducing mass inside that circle grows with the square of the radius. So the mass increasing with the square of radius and the gravity decreasing with the square of distance cancel each other out, leaving zero net gravitational force."

[Chris Peterson]

Voids .. From what I've read the universe is contains many voids, like Swiss Cheese according to one description. I will search for more .. but here is what I found quickly...

No one doubts the Universe is filled with voids. But I don't think you understand what this means. Voids are regions that contain very little luminous matter (the jury is still out with respect to dark matter, but they may well be lacking much of that as well). Voids are not completely free of matter, nor are they free of gravitational fields, nor to they have any exotic properties. They (as well as regions that are matter rich) are simply the fossil pattern of processes that occurred early in the evolution of the Universe. There's no reason to think that physics isn't exactly the same whether you are in a void or in a filament.

[aristarchusinexile]

Voids .. From what I've read the universe is contains many voids, like Swiss Cheese according to one description. I will search for more .. but here is what I found quickly...

No one doubts the Universe is filled with voids. But I don't think you understand what this means. Voids are regions that contain very little luminous matter (the jury is still out with respect to dark matter, but they may well be lacking much of that as well). Voids are not completely free of matter, nor are they free of gravitational fields, nor to they have any exotic properties. They (as well as regions that are matter rich) are simply the fossil pattern of processes that occurred early in the evolution of the Universe. There's no reason to think that physics isn't exactly the same whether you are in a void or in a filament.

From the Bootes Void discussion:

"Great post on a fascinating topic, but I do have a minor correction. You say “Particles of matter, having much more mass than both photons and neutrinos, would of course get pulled towards the walls of the void.” In fact, a particle inside a hollow spherical shell, with all mass evenly distributed at the exterior of the shell, experiences no net gravitational force.

It’s non-intuitive at first, but have a seat inside the shell (away from the center) and let’s take a look around. If you consider a 1-degree arc in the direction of the closer wall of the shell, it will define a circle on that wall, with a radius related linearly to the distance to the wall. A 1-degree arc in the opposite direction defines a much larger circle, and the amount of gravity-inducing mass inside that circle grows with the square of the radius. So the mass increasing with the square of radius and the gravity decreasing with the square of distance cancel each other out, leaving zero net gravitational force."

[Chris Peterson]

From the Bootes Void discussion:

"Great post on a fascinating topic, but I do have a minor correction. You say “Particles of matter, having much more mass than both photons and neutrinos, would of course get pulled towards the walls of the void.” In fact, a particle inside a hollow spherical shell, with all mass evenly distributed at the exterior of the shell, experiences no net gravitational force.

I didn't say that, although your quoting makes it appear so. Of course, it's true, but I don't see the relevance. This only applies to the interior of a perfect spherical shell, where the shell walls are of uniform density, and- very important- there are no external gravity fields. That doesn't remotely describe any place in the Universe. Even if you found a single spherical void surrounded by a shell wall, the fields from the rest of the Universe wouldn't be magically canceled. It would only be the material in the wall itself that contributes no net gravitational force on an interior object.

[harry]

G'day from the land of ozz


A vacuum with or without magnetic fields?

[Chris Peterson]

A vacuum with or without magnetic fields?

Surely there is no place in the Universe without gravitational, magnetic, and electric fields. Equally sure, in most of the Universe all of those fields are very weak- especially electric and magnetic. But not zero.

[tballou]

I am glad to see these recent posts on my original question, which was "why is the speed of light 300K m/s" and not some higher or lower value, or put another way, does the fact that light travels at a certain speed reveal anything about the relationship between mass and energy?

So, given the recent posts, does anyone have anything else to add that relates directly to this original question?

[bystander]

I am glad to see these recent posts on my original question, which was "why is the speed of light 300K m/s" and not some higher or lower value, or put another way, does the fact that light travels at a certain speed reveal anything about the relationship between mass and energy?

So, given the recent posts, does anyone have anything else to add that relates directly to this original question?

c is a physical constant defined to be exactly 299,792,458 metres per second (m/s). In a vacuum, the speed of not just light, but any electromagnetic radiation or anything having a rest mass of zero, is said to be equal to c. In any other medium, the speed is measurably slower.

[Qev]

If the pattern of photons doesn't change after hundreds of millions of years, has the pattern experienced 'Time'? Further - If there is no gravity in a void to slow time .. does time speed to infinite?

I don't think photons, travelling at c, experience time at all, do they?

From the Bootes Void discussion:

"Great post on a fascinating topic, but I do have a minor correction. You say “Particles of matter, having much more mass than both photons and neutrinos, would of course get pulled towards the walls of the void.” In fact, a particle inside a hollow spherical shell, with all mass evenly distributed at the exterior of the shell, experiences no net gravitational force.

Bear in mind that this only applies in conditions of (near-)perfect symmetry. A void in intergalactic space is unlikely to have all matter in its visible universe in a spherically symmetric distribution surrounding it. (This peculiar effect also occurs between two parallel infinite planes of equal thickness, but that's even less likely than spherical distribution )

[Qev]

A vacuum with or without magnetic fields?

Surely there is no place in the Universe without gravitational, magnetic, and electric fields. Equally sure, in most of the Universe all of those fields are very weak- especially electric and magnetic. But not zero.

Our friend Heisenberg pretty much forbids 'perfect' vacuum, yeah.

[astrolabe]

Hello Qev,

I don't think photons, travelling at c, experience time at all, do they?

No,I don't think so. Nor do I think that c is a necessarily a criterium for the statement to be correct. I am under the understanding that this fact would hold true for any other massless particle as well.

[astrolabe]

Hello All,

If the pattern of photons doesn't change after hundreds of millions of years, has the pattern experienced 'Time'? Further - If there is no gravity in a void to slow time .. does time speed to infinite?

I believe that in order for time to speed to infinite everything including c must be in a state of suspension, in other words, stopped-including time itself- because, in this particular four dimensional reality, space and time are indivisibly linked. On that note, WRT light experiencing time- a person in motion sees objects close by moving past very quickly and more distant objects appearing to move slower. It would seem that light would "see" objects nearby move past at lightspeed and far distant objects moving slower in like fashion. However I still don't think light "experiences" time any more than we do. Only evidence of it.

[Qev]

Hello Qev,

I don't think photons, travelling at c, experience time at all, do they?

No,I don't think so. Nor do I think that c is a necessarily a criterium for the statement to be correct. I am under the understanding that this fact would hold true for any other massless particle as well.

I'm pretty certain that all zero rest mass particles are required to travel at c.

[makc]

I don't think photons, travelling at c, experience time at all, do they?

well, in theory, it takes photons exactly 0 seconds to cover any finite distance, and so, they dont have time to experience it between their emission and absorbtion. but, situation changes if photon is never absorbed - now the length of its path is infinite and so its "own" clock might have some time to tick. this would be interesting to see the world from such photon's perspective - everything we see now would be gone in under an instant, but next few nano/whatever seconds of its "life" would earn the most exciting (and useless at the same time) knowledge ever.

[astrolabe]

Hello Qev,

I reread my post and feel that I should clarify that a zero mass particle traveling through a medium is moving at less than c even though generally c is the accepted representative of particle speed. That's why I misstated that c wasn't a necessary gauge for light/time.

[Qev]

Hello Qev,

I reread my post and feel that I should clarify that a zero mass particle traveling through a medium is moving at less than c even though generally c is the accepted representative of particle speed. That's why I misstated that c wasn't a necessary gauge for light/time.

Gotcha, I see what you mean, now.

well, in theory, it takes photons exactly 0 seconds to cover any finite distance, and so, they dont have time to experience it between their emission and absorbtion. but, situation changes if photon is never absorbed - now the length of its path is infinite and so its "own" clock might have some time to tick. this would be interesting to see the world from such photon's perspective - everything we see now would be gone in under an instant, but next few nano/whatever seconds of its "life" would earn the most exciting (and useless at the same time) knowledge ever.

I've read it written (I guess that would be the proper text-medium analogue to "I've heard it said"? ) that light doesn't have a frame of reference, such that trying to imagine things from a photon's point of view is more-or-less meaningless. I mean... at c, time dilation becomes infinite, length contraction becomes infinite... you wouldn't have any time at all to see that everything has become nothing at all.

[makc]

I mean... at c, time dilation becomes infinite, length contraction becomes infinite.

leave these lame excuses for the weak inverse of these infinite quantities is 0 - pretty much finite number - so you can still operate with numbers to certain extent.

[Superdoc]

Hi All,

I came up with this thought or u can call it an idea, Its known that there is a satellite thats in space travelling into deep space displaying Human image and voice of the human species that we're peaceful.., it may take hundreds of years or more to reach any alien world but IF these aliens are far superior and have Sophisticated Technology for instance they might have developed Time Travelling machine like we think we will also be able to do that, and why wouldnt they use it to come back to this Time if they're well known that the people may not exist since it has been so long it had reached to them.

Regards,