Speed of light

[aristarchusinexile]

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.

I think we should remember that many new major discoveries seem to throw doubt on what we thought we knew beforehand .. so I absolutely cannot rule out areas of space empty of fields .. and we will never be able to rule it out because space is so huge.

[aristarchusinexile]

Why should gravity be forbiden to expand in a void. Void mean almost nothig in it but it is a place where there are few matter. A star all alone there will not be visible.
A void is space time without a lot of matter. It does'nt mean "without the gravity field" of all the galaxies that surround it or all galaxies clusters that surround it. Gravity deform space time. It even close spacetime on itself (Black hole). So i dont see any reason why gravity should be forbiden in a zone of spacetime that is almost empty.

Doum - I can't see why voids free of gravity should be forbidden. Nor do I see any reason why a void should not be completely free of matter. Perhaps the supposed 'voids' in which some matter is said to exist are in reality two seperate voids, the matter existing between those voids.

[aristarchusinexile]

I believe that the 'sum of all integers' is one of those undefined values, since it doesn't converge to any particular value. You have something like this:

0 + 1 + (-1) + 2 + (-2) + 3 + (-3) +...

The sum of the first two terms is 1, the sum of the first three terms is 0, the sum of the first four terms is 2... basically, as you continue the summation the result diverges, and as such, has no sum.

Qev - thou art prophetic. I placed tie for 3rd at the Slam last night - your +3 -3 was certainly timely. Perhaps your name, Qev, qualifies you best to tell us how the little tail got on the 'Q'.

[Chris Peterson]

I can't see why voids free of gravity should be forbidden.

I don't know how to interpret "forbidden". I'd take that to mean a violation of natural law, and if so, you're correct that nothing prevents a region from being free of gravitational fields. However, we have certainly never seen any region of our Universe that is free of gravitational fields, because we have never seen any region that is causally disconnected from us, the viewers. If we can see it, it can feel us. That is essentially a proof that it is impossible to observe a region free of gravitational forces. (And of course, in practice, we've never seen any region of the Universe that wasn't causally connected to many other observable areas, and therefore containing gravitational, electrical, and magnetic fields from those areas.)

[bystander]

I can't see why voids free of gravity should be forbidden. Nor do I see any reason why a void should not be completely free of matter. Perhaps the supposed 'voids' in which some matter is said to exist are in reality two seperate voids, the matter existing between those voids.

Perfect vacuums do not exist within the observable universe, and anywhere matter exists, gravity exists. But even if the void was without matter of any kind, it would still be surrounded by matter, and gravity doesn't observe borders.

[aristarchusinexile]

Perfect vacuums do not exist within the observable universe, and anywhere matter exists, gravity exists. But even if the void was without matter of any kind, it would still be surrounded by matter, and gravity doesn't observe borders.

So far I know two things about the borders of some observed voids: some of them are roughly spherical and in one illustration the Bootes was illustrated as a sphere; and galaxies align themselves parallel to some of their borders. To me, that alignment might indicate something acting in opposition to the gravity of the galaxies, forbidding the galaxies from approaching any closer.

[Chris Peterson]

So far I know two things about the borders of some observed voids: some of them are roughly spherical and in one illustration the Bootes was illustrated as a sphere; and galaxies align themselves parallel to some of their borders. To me, that alignment might indicate something acting in opposition to the gravity of the galaxies, forbidding the galaxies from approaching any closer.

Gravity draws matter together, which leaves relatively empty areas behind. This is a positive feedback system: dense areas get denser, sparse areas get sparser. Since we already have a well understood attractive force, which in simulations produces very similar structure to what we actually observe in the Universe, there's no need for a repulsive force to explain voids. You are proposing a solution that is in search of a problem.

[aristarchusinexile]

I can't see why voids free of gravity should be forbidden.

I don't know how to interpret "forbidden". I'd take that to mean a violation of natural law, and if so, you're correct that nothing prevents a region from being free of gravitational fields. However, we have certainly never seen any region of our Universe that is free of gravitational fields, because we have never seen any region that is causally disconnected from us, the viewers. If we can see it, it can feel us. That is essentially a proof that it is impossible to observe a region free of gravitational forces. (And of course, in practice, we've never seen any region of the Universe that wasn't causally connected to many other observable areas, and therefore containing gravitational, electrical, and magnetic fields from those areas.)

I can't see why your "if we can see it, it can feels us" should be taken as unquestionable fact. Something seems to be preventing galaxies from entering voids .. at least the parallel alignment of galaxies along voids' borders suggests that to me. If gravity were at work from within the voids, the galaxies should continue on through the borders unhindered. I suggest that we often do not recognize what we see because we have never seen it before, or because of what our normal associations are, or because of what we want to see. An example: someone sent me an email one time .. an illustration of dolphins .. but all I could see was a naked woman. But for sure, after questioning the person who sent me the email, asking if they had made an error, and being told to look harder, yes, several very clear dolphins made up the dark areas of the woman. Perhaps if I had associated with dolphins more I would have seen them right away .. but children don't often associate with dolphins, and children instantly recognize dolphins instead of the naked woman. The naked woman was also there .. the artist deliberately causing the optical effect.

[aristarchusinexile]

So far I know two things about the borders of some observed voids: some of them are roughly spherical and in one illustration the Bootes was illustrated as a sphere; and galaxies align themselves parallel to some of their borders. To me, that alignment might indicate something acting in opposition to the gravity of the galaxies, forbidding the galaxies from approaching any closer.

Gravity draws matter together, which leaves relatively empty areas behind. This is a positive feedback system: dense areas get denser, sparse areas get sparser. Since we already have a well understood attractive force, which in simulations produces very similar structure to what we actually observe in the Universe, there's no need for a repulsive force to explain voids. You are proposing a solution that is in search of a problem.

Please explain the parallel alignment of galaxies at void borders .. as if the galaxies are clustering along the borders instead of among themselves .. which gravity would suggest they should be doing.

[Chris Peterson]

I can't see why your "if we can see it, it can feels us" should be taken as unquestionable fact.

Don't take it as fact. But it's a very simple argument. In what way do you think it fails? Every theory we have, and every experiment we've performed, tells us that if an object's light is reaching some point, its gravitational field is as well.

Something seems to be preventing galaxies from entering voids .. at least the parallel alignment of galaxies along voids' borders suggests that to me.

The idea that gravity is holding the wall structure intact makes much more sense to me than the idea that some completely unknown force inside voids is preventing galaxies from entering. Think about soap bubbles. The walls are held together (in an oriented way) by the attractive forces between soap molecules. There's nothing special about the interior (including air pressure) that is preventing the soap molecules from moving into the interior "void". In fact, a small number do so.

If gravity were at work from within the voids, the galaxies should continue on through the borders unhindered.

What does that mean, "gravity at work from within the voids"? The voids can be full of gravitational fields, and that doesn't mean that there is any net attraction. What force would you propose to cause galaxies to "continue on through"? It is the absence of any such forces, or the absence of any that approach the attractive forces present in the filaments and walls, that keeps the galaxies where they are.

[aristarchusinexile]

Every theory we have, and every experiment we've performed, tells us that if an object's light is reaching some point, its gravitational field is as well.

Void's light does not reach us as they have no light .. it is the redshift measurements of galaxies outside the void which reveal the void.

What force would you propose to cause galaxies to "continue on through"? It is the absence of any such forces, or the absence of any that approach the attractive forces present in the filaments and walls, that keeps the galaxies where they are.

I propose that it is the energy within the void, energy unknown to us, which prevents the galaxies penetration.

Pleas explain why the voids are aligned parallel with the void's border instead of grouping among themselves.

[Chris Peterson]

Please explain the parallel alignment of galaxies at void borders .. as if the galaxies are clustering along the borders instead of among themselves .. which gravity would suggest they should be doing.

I can't. In fact, I don't even understand structure you are describing.

[Chris Peterson]

Void's light does not reach us as they have no light .. it is the redshift measurements of galaxies outside the void which reveal the void.

Clearly, the void itself doesn't produce any light. But what about all the galaxies inside the voids? We get plenty of light from them, and that light doesn't show any unusual characteristics- it is no different than the light from galaxies on the edges of voids.

What force would you propose to cause galaxies to "continue on through"? It is the absence of any such forces, or the absence of any that approach the attractive forces present in the filaments and walls, that keeps the galaxies where they are.

I propose that it is the energy within the void, energy unknown to us, which prevents the galaxies penetration.

You missed the point of my question. What force would cause the galaxies to fall in towards the voids in the first place? That is, what force is it that this proposed force of yours is opposing? You don't doubt Newton's First Law, do you?

[astrolabe]

Hello aristarchusinexile,

I suggest that we often do not recognize what we see because we have never seen it before, or because of what our normal associations are, or because of what we want to see.

And this would apply to.................whom?

[astrolabe]

Hello aricharchusinexile,

An example: someone sent me an email one time .. an illustration of dolphins .. but all I could see was a naked woman. But for sure, after questioning the person who sent me the email, asking if they had made an error, and being told to look harder, yes, several very clear dolphins made up the dark areas of the woman. Perhaps if I had associated with dolphins more I would have seen them right away .. but children don't often associate with dolphins, and children instantly recognize dolphins instead of the naked woman. The naked woman was also there

AH! Nevermind.

[Doum]

Hi Aricharchusinexile,

Just dont forget that void is so big that a few billion stars being inside it, it will still not be visible to us because we can't detect or see a single star in there from here. So what i am telling you is that the void is fill with matter but it is very disperse compare to the galaxies abondances we live in. Gravity create the void naturaly and it is also logical for it to exist. The void have nothing magic in it. It's a natural phenomenon. No mystery there. There are still matter in there but we dont see it with the today's tool. It is my opinion.

[Chris Peterson]

Just dont forget that void is so big that a few billion stas being inside it, it will still not be visible to us because we can't detect or see a single star in there for now. So what i am telling you is that the void is fill with matter but it is very disperse compare to the galaxies abondances we live in.

Inside the Boötes Void which is under discussion, there are at least 60 galaxies alone. So while the average density is very low compared with other parts of the Universe, it is far from empty.

[harry]

G'day from the land of ozzzzz

Chris said

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.

That hits the nail on the head.

I came across this paper, I may have posted it before. Interesting reading
http://arxiv.org/abs/astro-ph/0305457
New varying speed of light theories

Authors: Joao Magueijo
(Submitted on 23 May 2003 (v1), last revised 15 Oct 2003 (this version, v3))

Abstract: We review recent work on the possibility of a varying speed of light (VSL). We start by discussing the physical meaning of a varying $c$, dispelling the myth that the constancy of $c$ is a matter of logical consistency. We then summarize the main VSL mechanisms proposed so far: hard breaking of Lorentz invariance; bimetric theories (where the speeds of gravity and light are not the same); locally Lorentz invariant VSL theories; theories exhibiting a color dependent speed of light; varying $c$ induced by extra dimensions (e.g. in the brane-world scenario); and field theories where VSL results from vacuum polarization or CPT violation. We show how VSL scenarios may solve the cosmological problems usually tackled by inflation, and also how they may produce a scale-invariant spectrum of Gaussian fluctuations, capable of explaining the WMAP data. We then review the connection between VSL and theories of quantum gravity, showing how ``doubly special'' relativity has emerged as a VSL effective model of quantum space-time, with observational implications for ultra high energy cosmic rays and gamma ray bursts. Some recent work on the physics of ``black'' holes and other compact objects in VSL theories is also described, highlighting phenomena associated with spatial (as opposed to temporal) variations in $c$. Finally we describe the observational status of the theory. The evidence is currently slim -- redshift dependence in the atomic fine structure, anomalies with ultra high energy cosmic rays, and (to a much lesser extent) the acceleration of the universe and the WMAP data. The constraints (e.g. those arising from nucleosynthesis or geological bounds) are tight, but not insurmountable. We conclude with the observational predictions of the theory, and the prospects for its refutation or vindication.

[apodman]

Intensity of cafe discussions has been directly linked to intensity of postings by certain accounts.

This is blatantly true. Legitimate contributors are not picky enough. They will get on the same broken bus to nowhere every time. Show some patience. Let the broken bus leave without you. A worthy catalyst for discussion will appear.

existing theory was that this forum can generate enough purely scientific discussion, which it failed to do.

Give it time. There's no quota or hurry. I would rather see one real question and one real answer than 100 responses to nothing.

with all the accounts in question ... banned, this place would go back to complete silence.

On our last break from the malignant trolls, real discussion actually started moving in. But the trolls jumped on it, people who should know better responded to the trolls, and the real discussions were successfully hijacked. So it's no wonder new discussion is scarce. But go ahead and create the vacuum. Ban the trolls or don't ban them, but in either case don't fill the forum responding to them.

[astrolabe]

Hello All,

Found this: http://www.fonts.com/aboutfonts/article ... etterq.htm

"For as long as there have been Qs, designers have been having fun with the letter’s tail. This opportunity for typographic playfulness may even date back to the Phoenicians: the original ancestor of our Q was called “ooph,” the Phoenician word for monkey. The ooph represented an emphatic guttural sound not found in English, or in any Indo-European language.

Most historians believe that the ooph, which also went by the name “gogh,” originated in the Phoenician language, with no lineage to previous written forms. Historians also believe that the character’s shape depicted the back view of a person’s head, with the tail representing the neck or throat. It’s possible, but if you consider that the letter’s name meant monkey, then perhaps the round part of the symbol represents another kind of backside, and the tail of what became our Q may have started out as, well, a tail.

The Greeks adopted the ooph, but found it difficult to pronounce, and changed it slightly to “koppa.” The Greeks also modified the design by stopping the vertical stroke, or tail, at the outside of the circle. The koppa, however, represented virtually the same sound as “kappa,” another Greek letter. One of them had to go, and koppa was ultimately the loser, perhaps because it had begun to look much like another Greek letter, the P.

Unlike the Greeks, the Etruscans could live with the somewhat redundant nature of the koppa, and continued to use the letter. In fact, they had two other k-sound letters to contend with. The Romans elected to use all three signs when they adopted much of the Etruscan alphabet.

The first Roman Q had the Etruscan vertical tail, but over time it evolved into the graceful curved shape that cradles the U which usually follows it."

[bystander]

It seems even you have a hard time resisting temptation.

http://asterisk.apod.com/vie ... 44#p100554

[apodman]

It seems even you have a hard time resisting temptation.

You caught me. Not so hard to do. But consider the game theorist who also participates in the game. Success requires mixed strategy. Any statement indicating strict adherence to a pure strategy is a ruse, and unpredictability is part of the game. Don't tell anyone.

[aristarchusinexile]

Trolls? Or lunatics like Michael Faraday? Imagine, 'electromagnetic waves' - such a density of ultimate rubbish was never dreamed of in scientific speculation. Even the once spurned but now enobled Aristarchus might laugh himself soundly to sleep.

[aristarchusinexile]

Why should nature abhor a vacuum? A vacuum could signify rest, tranquility, an absence of turmoil. A vacuum could be protected by its own powerlessness .. unable to draw into itself the turmoil around it .. its powerlessness not attractive to the turmoil around it, and therefore ignored in its tranquility by those powers of turmoil which cannot recognize or respond to tranquility.

'Intensity'
1. the quality or condition of being intense.
2. great energy, strength, concentration, vehemence, etc., as of activity, thought, or feeling: He went at the job with great intensity.
3. a high or extreme degree, as of cold or heat.
4. the degree or extent to which something is intense.
5. a high degree of emotional excitement; depth of feeling: The poem lacked intensity and left me unmoved.
6. the strength or sharpness of a color due esp. to its degree of freedom from admixture with its complementary color.
7. Physics. magnitude, as of energy or a force per unit of area, volume, time, etc.
8. Speech. a. the correlate of physical energy and the degree of loudness of a speech sound.
b. the relative carrying power of vocal utterance.

[aristarchusinexile]

Hello All,

Found this: http://www.fonts.com/aboutfonts/article ... etterq.htm

"For as long as there have been Qs, designers have been having fun with the letter’s tail. This opportunity for typographic playfulness may even date back to the Phoenicians: the original ancestor of our Q was called “ooph,” the Phoenician word for monkey. The ooph represented an emphatic guttural sound not found in English, or in any Indo-European language.

Most historians believe that the ooph, which also went by the name “gogh,” originated in the Phoenician language, with no lineage to previous written forms. Historians also believe that the character’s shape depicted the back view of a person’s head, with the tail representing the neck or throat. It’s possible, but if you consider that the letter’s name meant monkey, then perhaps the round part of the symbol represents another kind of backside, and the tail of what became our Q may have started out as, well, a tail.

The Greeks adopted the ooph, but found it difficult to pronounce, and changed it slightly to “koppa.” The Greeks also modified the design by stopping the vertical stroke, or tail, at the outside of the circle. The koppa, however, represented virtually the same sound as “kappa,” another Greek letter. One of them had to go, and koppa was ultimately the loser, perhaps because it had begun to look much like another Greek letter, the P.

Unlike the Greeks, the Etruscans could live with the somewhat redundant nature of the koppa, and continued to use the letter. In fact, they had two other k-sound letters to contend with. The Romans elected to use all three signs when they adopted much of the Etruscan alphabet.

The first Roman Q had the Etruscan vertical tail, but over time it evolved into the graceful curved shape that cradles the U which usually follows it."

Astro, I thought we wuz buddies - but here you are making a monkey out of my nothingness. I thankest thee tho for thy informative and interesting post.