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peron
2010-Jun-20, 01:39 PM
My question pertains mostly to General relativity. I know GR answer the question of what space is by calling it the geometric interval between two objects. But that doesn't satisfy me, I want to know what space is. Is space something physical? Is it made out of something? Or is space just like length and width, but then that doesn't really answer the question, if space is nothing more than a dimension what is that dimension made out of?

Can anyone answer my question?

kevin1981
2010-Jun-20, 11:35 PM
I am writing in this thread as i would like to keep an eye on the answers. Though to my knowledge, i don't think anybody can provide a solid answer because we don't have a quantum understanding of gravity yet. Also if it is made from something physical it will be at such small distance scales we will probably never be able to make observations. I think this is where people start talking about the quantum foam at the deepest and tiniest scales.

Hungry4info
2010-Jun-21, 12:08 AM
If I'm not mistaken, no one really knows.

The analogies of a fabric and what-not are little more than anaologies.

WayneFrancis
2010-Jun-21, 12:55 AM
There are probably a few people here that can give really good answers. I can tell you what space isn't. It isn't an absence of stuff. It isn't just a place holder for measurement. I would guess that in some way it could be described as a field. In the the end it is what it is...space. We might find metaphors, analogies and models to describe its behaviour and characteristics in certain situations but just like how matter and energy can't be described as just a particle or wave I imagine space can only really be completely defined as itself. I'm not sure how its definition would fit into a grand unified theory either but I imagine it will be fundamental :).

Cougar
2010-Jun-21, 01:21 AM
I want to know what space is. Is space something physical? Is it made out of something?

Indications are that it has some sort of "physicality," but it's not of the sort we're familiar with.

EDG
2010-Jun-21, 01:33 AM
It's a way for things happening at the same time to not happen in the same place? ;)

Jens
2010-Jun-21, 03:32 AM
I think part of what makes it a very difficult question is that in general, you need to step outside of something to be able to observe it. And with time and space, everything we do is so intimately related that there's no way that we know of of taking a step outside of space or time to be able to view it "from above," if you want.

Len Moran
2010-Jun-21, 07:05 AM
My question pertains mostly to General relativity. I know GR answer the question of what space is by calling it the geometric interval between two objects. But that doesn't satisfy me, I want to know what space is. Is space something physical? Is it made out of something? Or is space just like length and width, but then that doesn't really answer the question, if space is nothing more than a dimension what is that dimension made out of?

Can anyone answer my question?

Objects that are part of our macroscopic reality are localised, they exist in space and time. It’s not that space is “something physical” or “time is “something physical”, it is the localisation of objects that is physical.

Whether one wishes to say that space is filled with “fields” or “virtual particles”, or whatever, that “fill” does not define space as a physical entity, we envisage that “fill” as occupying “nothing”. “Nothing” is not and can never be something physical, but the localisation of objects requires that philosophical concept of “nothing”.

When you get to the quantum level, to the best of my understanding, localisation breaks down, we can no longer think of “space” between particles. For example, between a source and sink in vacuum, particles are not assumed to be localised. They only manifest themselves as "particles" with a "trajectory" through space when we make the measurement at the detector. Of course there is space between the macroscopic objects of source and detector, but in terms of space as we macroscopically think of the concept, that concept does not exist between "particles" that we imagine to exist in some form between a source and detector.

Scientists who hold the stance of physical or objectivist realism consider space and time to be real, real in the sense that these concepts exist (as we perceive them) outside of that very act of perceiving which brings forth very difficult questions of infinite space existing between objects. There are strong arguments for considering physical realism to be a philosophical stance given the thorny issues of observer dependence, thus rendering the scientific concepts of space and time as actually being philosophical concepts.

Those (like myself) who hold the philosophical stance of open realism consider that space and time are constructs of the observer and that outside of that observer those familiar concepts do not exist in that form. What may exist outside of our perception, in this sense, is beyond the scientific method that relies on being able to detach the observer from the observed. I believe Jens is saying something along these lines, if not to the extent that I consider to be the case.

So before you start trying to think about concepts of space and time and what they actually are in terms of familiar scientific concepts, you perhaps may think it worth while to examine the applicability of science to be able to answer such questions in terms of the strict scientific method and thus establish whether your desired answer is going to be a scientific one or a philosophical one.

Ken G
2010-Jun-21, 08:03 AM
I think the first thing to establish is that questions like "what is X", put to science, can either be answered by an experiment ("X is what we measure when we do such-and-such), or by a theory. In neither case is the answer "what X actually is" because science doesn't answer questions like that. Hoperfully the OPer will not be disappointed by that fact, but it is true. So we have a certain freedom in how we answer the question. If we adopt the experimental approach, we can say that space is whatever physical entity is spanned by a measurable distance, and distance measurements are done using objects we rely on to rigidly occupy a set distance (i.e., rulers). As with all experimental definitions, it suffers the limitations of experimental error, and breakdowns in the apparatus (say, if the ruler is under high strain, for example). But such it is with scientific answers, we accept limitations.

Note also that using rulers to measure distance limits the distance to being rather small. For larger distances, we can imagine doing ruler measurements hypothetically (like the distance a rocket travels on its way to the Moon), or we could use light travel times as a proxy, as we must with even larger distances. Here we enter the hybrid realm of mixing operational definitions of distance with theoretical support, like the theory that the speed of light is constant. We begin to see the mixing of the concepts of space and time that give birth to spacetime in relativity.

Since the OP cited general relativity, it is likely that what is desired is not so much an operational or measurable version of space, but rather a theoretical one. When using a theory to answer a question like "what is X", the answer is always "X is however it is used in the theory." In relativity, space is a component of spacetime, quantified by distances along the three spatial dimensions of the four-vector displacement that also includes time. So space becomes a kind of three-dimensional "shadow" of displacement in four dimensions. What makes this usage of "space" so strange is that it is observer dependent-- different observers will reckon different components of space, and different components of time, for the same displacement between any two events. But still, the crucial concepts are "displacement" or "separation" between events, but the spatial separation is not independent from the temporal separation.

One can go a step farther and use the language of invariants (let's stick to special relativity here), and say that the invariant separation between two causally connected events is a proper time (no space at all there), and the invariant separation between two causally unconnected events (neither could affect the other even in principle) is a proper distance (no time there at all, it's all spatial separation). So in this latter view, one might say that space is what separates events that can have nothing to do with each other, whereas time is what separates events that can. I suspect this continues to hold in general relativity, but I cannot state that this is categorically true in all situations.

So what about the space between two events that are causally connected, like the beginning and ending of a distance measurement? This is an observer-dependent version of space, not an invariant version, so it is kind of like a space that does not exist independently of the observer, but is reckoned to exist by the observer to make sense of what is observed in terms of some reference frame. It is a version of space that has more to do with our choices of how to coordinatize the events, than it has to do with any "real" version of space that separates the events independently of how we choose to think about them. If someone shoots a target with a rifle, it seems odd to say that the distance the bullet traveled is just a coordinate choice, and that all that "really" separated the gun and the target was time, but that is the language of recognizing what is invariant (true for all observers) in special relativity. In particular, the bullet perceives the gun and the target as being at the same place when the bullet left the (moving) gun and when it entered the (moving) target. So the normal usage of the concept of space is a usage of convenience, more than it is a statement of physical fact. Thus to get a fuller answer, even if you specify you want a relativistic answer, the question must be put to the OPer, "do you mean space as a physically real invariant that does not depend on the observer, or do you mean the convenience of space as adopted by a certain observer"?

Infinitenight2093
2010-Jun-21, 08:13 AM
ha! we can't even figure out what's in space, much less what space is. However, there can be no "in between" particles (or what was once called the "void"). I believe that space has to be filled with matter and energy like the ocean is filled with water.
Although, for the time being, it may be easier just to think of space-time as a fabric (general relativity), or even more modern, a membrane (M-Theory).

Strange
2010-Jun-21, 09:10 AM
Space is not "nothing" because it has measurable attributes such as permeability and permittivity.

That got me thinking: are these fundamental, measured attributes of empty space? Or do they fall out of something more fundamental in relativity or quantum theory? E.g. are they just macroscopic effects of quantum interactions, or are they fundamental constants that affect quantum interactions?

kevin1981
2010-Jun-21, 11:50 AM
When you get to the quantum level, to the best of my understanding, localisation breaks down, we can no longer think of “space” between particles. For example, between a source and sink in vacuum, particles are not assumed to be localised. They only manifest themselves as "particles" with a "trajectory" through space when we make the measurement at the detector. Of course there is space between the macroscopic objects of source and detector, but in terms of space as we macroscopically think of the concept, that concept does not exist between "particles" that we imagine to exist in some form between a source and detector.


Those (like myself) who hold the philosophical stance of open realism consider that space and time are constructs of the observer and that outside of that observer those familiar concepts do not exist in that form. What may exist outside of our perception, in this sense, is beyond the scientific method that relies on being able to detach the observer from the observed. I believe Jens is saying something along these lines, if not to the extent that I consider to be the case.


Len are you saying that in your opinion, at the most fundamental level, space and time do not exist. That everything is made from the quantum world upwards and what we see and feel as space and time are mearly constructs of what we perceive the world looks like as humans?

peron
2010-Jun-21, 01:35 PM
Thank you for the informative response. To answer your question you asked at the end, In general relativity space can be molded, ripped, and deformed this means that space has a underlying structure, space must be made out of something for it to allow to do these things. We can deformed and bend metals because they are made out of interacting particles. I become extremely confused when scientists talk about space as a physical object but they don't treat it like one.

Thanks.

Nereid
2010-Jun-21, 02:49 PM
Thank you for the informative response. To answer your question you asked at the end, In general relativity space can be molded, ripped, and deformed this means that space has a underlying structure, space must be made out of something for it to allow to do these things. We can deformed and bend metals because they are made out of interacting particles. I become extremely confused when scientists talk about space as a physical object but they don't treat it like one.

Thanks.
What follows has already been said (I think), by several BAUTians, in several different ways.

However, it seems that you may not have understood it, so I'll try explaining it in a slightly different way.

"Space", today, in physics has two different meanings.

Each meaning is associated with one theory, or class of theories, in physics. The two theories are the most spectacularly successful theories in physics, to date. However, the two theories are mutually incompatible, at a deep, fundamental, level. One aspect of that incompatibility relates to "space".

The two theories are the theory of general relativity (GR), and quantum mechanics (QM).

In GR, "space" is intimately related to geometry, and is part of something bigger, called space-time. The geometry of space-time is determined, in GR, by the amount and distribution of mass-energy. In other words, it is 'background dependent'.

In QM, well, no one has yet (I think) tried to explain what "space" is in QM; however, the key thing about 'space' in QM is that it is independent of anything in it. IOW, it exists in some absolute sense; or, it is "background independent".

This dependence on the 'background' is what makes GR and QM mutually incompatible.

So, the question "what is space?" has an answer that depends on which theory of physics you choose to frame the answer in.

One more thing: "space" can mean something like "the thing we are investigating in this experiment". If so, then "space" has whatever meaning the experimenters give to it, for the purposes of their experiment. That meaning may have nothing whatsoever to do with the meaning of "space" in GR or QM!

Len Moran
2010-Jun-21, 03:40 PM
Len are you saying that in your opinion, at the most fundamental level, space and time do not exist. That everything is made from the quantum world upwards and what we see and feel as space and time are mearly constructs of what we perceive the world looks like as humans?

Kevin,

Yes, that’s basically the philosophical stance that I hold, though the thinking behind that stance extends far beyond the example I gave of non locality of particles between a source and sink. My reasons for holding that stance are primarily derived through Ken G on this forum and the writings of Bernard d’Espagnat who as a physicist has thought about and written extensively on the conceptual foundations of quantum mechanics. As a philosopher he has used his knowledge of quantum mechanics to suggest that the weak objectivity at the quantum level can be shown to also exist at the macroscopic level if one considers quantum mechanics to be universal. The arguments he uses for the extension of quantum mechanics to macroscopic reality (and hence concepts of space and time) involve dechoerence theory.

What this means is that we can never escape from observer dependence, thus the scientific method which is based upon separating the observer from the observed is valid only within the remit of intersubjective agreement between sentient beings. That intersubjective agreement provides us with empirical reality, it is a scientific reality that cannot be separated from the observer, thus cannot be claimed to be the same as nature that exists outside of the combination of observer and the observed.

On this basis, nature as it exists outside of sentient beings cannot be addressed through the scientific method, what does exist may be of a form that we have no experience of – we just don’t know. So my philosophical stance of open realism is simply that – the “something” that exists independently of the observer (and importantly, I do consider there is something, albeit of a form that is unfamiliar to us, I don't consider that we entirely construct our reality in our heads in the manner of radical idealism) that is open, not reachable through science.

Now D’Espagnat considers nonseparability to be of fundamental importance within quantum mechanics. The correlations of nonseparability are shown through Bells theorem to be non local. Bells theorem is not something that can be replaced with Bell’s theorem Mk2 in the manner of a new or modified theory, the non local aspect is with us for ever. That it sits side by side with our local macroscopic reality gives rise for d‘Espagnat to (philosophically) consider that nature as it exists outside of the bond of observer and observed to be non local, in other words devoid of space and time. I agree with this, and whilst it may feel uncomfortable, I feel far more uncomfortable with notions of infinite distance, of the physical universe never ending. That to me seems bizarre, but within my philosophical framework, those notions of infinite distance show up as the breakdown of our macroscopic reality. By considering that space and time are constructs of our brains, questions of macroscopic notions of infinite distance are simply extrapolations we make from familiar measurements of distance and do not figure as such within nature as it exists outside of sentient beings.

The issue of observer dependence is the crux of this, and it is an aspect that Ken G has developed through his philosophical investigations of physics. He and d’Espagnat come to pretty much the same conclusions by slightly different routes, d’Espagnat starts from quantum mechanics, whereas Ken stars from basic philosophical problems that show up within macroscopic reality, but quantum mechanics forms an important part of his analysis.

It must be properly understood, that this position is entirely philosophical, it is not a scientific position. But likewise I consider that physical realism (that assumes space and time to be real, existing in the same familiar form outside of the observer) is also a philosophical position. This is simply because the primary bed rock of science – namely strong objectivity, may in fact be only of a weak variety. Scientifically we cannot mitigate for the brain because whatever model we build to represent the effect of the brain is, in itself a product of that brain. We cannot stand apart from our place within macroscopic reality and produce a mitigating model of sentient beings that could be used to establish the difference between nature within and outside of our involvement. That particular view – that physical (or objectivist) realism is a philosophical stance is very controversial and gives rise to many, often heated, arguments on this forum. But just keep in mind my basic premise – can we scientifically determine the level (if any) of observer dependence, given that philosophical investigations and lessons from quantum mechanics suggest that observer dependence is a real issue to be considered within physics? To my mind we can’t just sweep this issue under the carpet, we have to acknowledge it and move on from that point.

There is a lot to this, and this post perhaps is a long winded reply to your basic question, but I think it important for you to understand why I hold this position. It is not based on some philisophical ad hoc whim, it is based on the writings and research of practicing physicists - in d'Espagnat's case he worked at Cern for many years and was a collegue of John Bell, he oversaw the correlation experiments by the Alain Aspect group and has written extensively on this subject area including the considered classic "conceptual foundations of quantum mechanics". There is much that I don’t understand properly yet, but it makes one question the assumption that we are here, looking at the world out there. I don’t think we are, we are part and parcel of everything that we experience. What I find inspiring is that we see scientists like Ken G and d’Espagnat putting these ideas forward as opposed to pure philosophers who have tended (according to d’Espagnat) to ignore the contribution quantum mechanics can make to their philosophical views on the nature of reality.

Ken G
2010-Jun-21, 03:52 PM
And I would add to that nice summary that there is nothing mystical or anti-realist about asserting that the observer is part of the reality that science studies, because everywhere you find science, you find an observer participating in the reality. This is simply the fact-- it was mere assumption, hope, or wishful thinking, that science could ignore the role of the observer. Like everything else in science, ignoring the role of the observer (and their intelligence) is merely an idealization of the actual reality. We make idealizations to simplify the situation, and often we get away with them-- but we never take them seriously or literally. Except, for some odd reason, in this particular case many do seem to take our idealizations quite seriously, despite the proven limitations of that idealization. Quantum mechanics was the "wakeup call" for those limitations, but we should have always expected them anyway.

forrest noble
2010-Jun-22, 02:34 AM
peron,


what is Space?
My question pertains mostly to General relativity. I know GR answers the question of what space is by calling it the geometric interval between two objects. But that doesn't satisfy me, I want to know what space is. Is space something physical? Is it made out of something? Or is space just like length and width, but then that doesn't really answer the question, if space is nothing more than a dimension what is that dimension made out of?



Can anyone answer my question?

General Relativity does more than just call space a geometric entity between two objects, that idea is closer to classical physics. GR describes space as a physical entity that has its own existence which can warp beyond the confines of Cartesian co-ordinates as well as warping into a forth physical dimension that closes the boundaries of the universe in the presence of a universe of matter. The warping of space in GR is described mathematically by one of ten partial differential equations of tensor calculus called the Ricci tensor. Of course this still may not answer your question directly. If not you might have to look to other theories for answers. In QM space is mass independent for instance.

René Descartes called space an extension of matter and classical physics has called it the volume which matter occupies. Space in some modern hypotheses has sometimes been equated with the Zero Point Field (zero point field) rather than the ZPF being just a field that occupies space. The idea then would be that all of reality accordingly could have been created from the ZPF a.k.a space, such as in a number of multi-verse ideas. Many different theories have different explanations concerning the character and substance of space as you probably realize. Matter in its atomic form contains space within it and so could its particle forms including protons, electrons, etc. Space must exist outside of matter for motion and time to have a medium for their expression. Following this line of thought it would seem that René Descartes' idea that space is simply a dimension and extension of matter which allows for its relative motion which is an expression/ definition of time, hence space-time.

mc^2
2010-Jul-24, 05:56 AM
If I may sum up many of the informative posts above...

The simplest, most elegant and beautiful answer to the OP's question is actually implicit within General Relativity itself:

space-time is the gravitational field

;)

Cougar
2010-Jul-24, 03:56 PM
space-time is the gravitational field

That doesn't seem right. I would grant that space is "full" of such fields, but that doesn't make one equal to the other.







"These days we think of space not as some fixed and absolute state through which matter moves, but as a dynamical and lively entity in its own right..." - Sean Carroll, From Eternity to Here

cosmocrazy
2010-Jul-25, 09:18 AM
peron,





General Relativity does more than just call space a geometric entity between two objects, that idea is closer to classical physics. GR describes space as a physical entity that has its own existence which can warp beyond the confines of Cartesian co-ordinates as well as warping into a forth physical dimension that closes the boundaries of the universe in the presence of a universe of matter. The warping of space in GR is described mathematically by one of ten partial differential equations of tensor calculus called the Ricci tensor. Of course this still may not answer your question directly. If not you might have to look to other theories for answers. In QM space is mass independent for instance.

René Descartes called space an extension of matter and classical physics has called it the volume which matter occupies. Space in some modern hypotheses has sometimes been equated with the Zero Point Field rather than the ZPF being just a field that occupies space. The idea then would be that all of reality accordingly could have been created from the ZPF a.k.a space, such as a number of multi-verse ideas. Many different theories have different explanations concerning the character and substance of space as you probably realize. Matter in its atomic form contains space within it and so could its particle forms including protons, electrons, etc. It would seem that space must exist outside of matter for motion and time to have a means for its expression. Following this line of thought it would seem that René Descartes' idea that space is simply a necessary dimensional extension of matter which allows for relative motion which is an expression of time, hence space-time.

Which by conclusion of KenG and Len is observer dependent. The warping of space-time depends on an observers point of view, so it doesn't necessarily mean that "space" has to have some form of physical attribute to warp. Like time, space can be measured differently relative to one's frame of reference.

mugaliens
2010-Jul-28, 03:30 AM
If I had to gander an answer, it would be that space is a relativistic interactive construct (if not artifact) of matter.

Ken G
2010-Jul-28, 04:31 AM
And I would say it is a product of the effort by intelligence to understand and predict motion. Same with time. What is really amazing is that these two originally completely different constructs ended up getting married into spacetime. That either means that we were onto something when we invented these concepts, and reality "blessed" them by uniting them, or it means we were always just looking in the mirror at our own intelligence, and that's why they both ended up being aspects of the same basic thing (the concept of "invariant separation"). If the former, reality must be impressed by us. If the latter, reality is still having a chuckle at our hubris.

Spoons
2010-Jul-28, 06:25 AM
You could say that space is the theatre in which the actor yells his bad analogies at the audience, but you might come off sounding foolish.

Honestly, I don't think the OP is going to get a particularly satisfying answer to this one, as there aren't any really suitable analogies using everyday items which can very well describe it as a whole. You can use analogies to describe certain attributes of it (space is the paper on which the the writing of matter is scribed, the universe is fairy bread with space at the bread and matter as hundreds and thousands, yada yada) but even if you pick good ones they don't really bind together to make anything other than a hideous monster.

I think we probably need to delve further into the fundamentals of physics to really get a firm grasp on it all, though the posts in this thread give a pretty good "feel" to what space is. For the meantime you could probably consider it to be the fabric on which things are placed, and the fabric is made out of a liberal pasting of the quantum foam.

gzhpcu
2010-Jul-29, 07:06 AM
Einstein once said:

"Space-time does not claim existence in its own right, but only as a structural quality of the [gravitational] field".

and "Space and time are modes in which we think, not conditions in which we exist".

Spoons
2010-Jul-29, 07:26 AM
Einstein eh? He was quite an intelligent chap, wasn't he?

He must be - they named a beer after him at a nearby German brewery.

forrest noble
2010-Jul-29, 08:26 PM
cosmocrazy,


Which by conclusion of KenG and Len is observer dependent. The warping of space-time depends on an observers point of view, so it doesn't necessarily mean that "space" has to have some form of physical attribute to warp. Like time, space can be measured differently relative to one's frame of reference.

Don't recall the attributes of space-time being put forward quite like that before, but it sounds right to me -- something I seldom say concerning perspectives of obfuscatory theory like general relativity.

Ken G
2010-Jul-29, 08:43 PM
One clarification though-- we have to watch out for two very different possible meanings of "observer dependent." One such meaning is "varies from observer to observer." In GR, the "warping" of space is that type of observer-dependent, but the point of marrying space and time into spacetime is expressly such that the resulting warping, or curvature, should not be different for different observers. So in that meaning, the warping of spacetime is not observer dependent, and we can equate "observer dependent" with "not invariant."

But I think cosmocrazy was taking a different meaning, where "observer dependent" means "you need to pass the claim being made through the perceptions and inferences of some kind of observer", i.e., it means "not definable without reference to any observer or observation." Perhaps I can suggest the term "observation dependent" for this latter type-- we need to have an observation, but if we don't care what observer does it, then it is invariant, a situation that might be called "observation dependent but observer independent".

Also, to avoid "trees falling in the woods" kinds of issues, note that the observer is allowed to be hypothetical, but the observation is not allowed to be counterfactual. By that I mean, we can imagine the same reality contains an observer even when it doesn't, but we cannot imagine the same reality contains an observation when it in fact doesn't. Here an "observation" is defined as a "physical arrangement that would in principle allow an observer to know something if an observer had been privy to the details of that arrangement."

forrest noble
2010-Jul-29, 09:51 PM
Ken G,

snip from cosmocrazy quote

it doesn't necessarily mean that "space" has to have some form of physical attribute to warp.
This was the part of cosmocrazy's quote where I said "sounds right to me." --- basically is space really anything other than the volume which matter occupies? not considering the zpf or anything else that might be contained within space. --- or does space really warp? These questions concerning the true nature of space, is where I believe there is a wide divergence of opinion in theoretical physics.

slang
2010-Jul-30, 12:26 AM
[...] obfuscatory theory like general relativity.

What is obfuscatory about GR? Why is it more obfuscatory than any other scientific theory?

Ken G
2010-Jul-30, 02:52 AM
This was the part of cosmocrazy's quote where I said "sounds right to me." --- basically is space really anything other than the volume which matter occupies? not considering the zpf or anything else that might be contained within space. --- or does space really warp? These questions concerning the true nature of space, is where I believe there is a wide divergence of opinion in theoretical physics.I think GR is pretty clear on the point that space by itself is warped by however you choose to look at it (read, how you coordinatize it in ways that involve time), you have to internalize the externalities of how you are treating time, creating a single spacetime manifold, to achieve invariant geometric properties that could be termed an objective degree of warping. But GR may not be the last word on space, that much is certainly fodder for a wide array of opinions even among experts.

forrest noble
2010-Jul-30, 02:57 AM
What is obfuscatory about GR? Why is it more obfuscatory than any other scientific theory?

IMHO space is a simple thing, for it to warp it would seemingly need to be something much more complicated which does not appeal to me. Since GR does not propose what this something might be it is an unclear concept. The same thing applies to the expansion of space, which is a very well accepted concept. What is it that is actually expanding. In this case I'm using the word "obfuscatory" meaning a statement concerning something that is supposed to be happening that is not clearly defined or understood, such as the warping or expansion of space.

As you know I'm not fond of many theories that cannot follow in explanation according to my signature, Rutherford's statement. As many have said, the nature of what space really is, is no more than a matter of conjecture since theory varies widely concerning nearly all conceivable possibilities and then some. Theories that do not even follow common logic are far worse IMHO.

This does not mean that I think that we should throw out the baby with possibly dirty bath water concerning GR or the expansion of space hypothesis for possible comprehensive failings.

Ken G
2010-Jul-30, 04:41 AM
A term you may wish to consider, to replace "obfuscatory", is "pedagogical." It is perhaps both more flattering, and more accurate. What's more, it is important not to mistake the "baby" of GR with the "bath water" of popularized accounts of GR. One does not judge a theory by the way it is explained to barmaids, one judges the explanatory skill of the theorist that way. In other words, someone who cannot explain a theory clearly may not understand it themselves as well as could be hoped, but if the theory succeeds in its predictive power, we must separate the theory from our understanding of it. In partcular, our lack of understanding presents us with the mission not to discard the theory, but to understand it better.

gzhpcu
2010-Jul-30, 06:59 AM
What if space is just the "container" for matter and energy? Permeated, perhaps, by the Higgs boson, quantum foam, etc, but still, of itself, only spatial dimensions.

Couldn't our claims that it expands and warps just be attaching non-existent attributes to the container just because we are unable to explain the related phenomena by other means in our current models of physics?

Spoons
2010-Jul-30, 07:04 AM
What if space is just the "container" for matter and energy? Permeated, perhaps, by the Higgs boson, quantum foam, etc, but still, of itself, only spatial dimensions.

Couldn't our claims that it expands and warps just be attaching non-existent attributes to the container just because we are unable to explain the related phenomena by other means in our current models of physics?

That doesn't seem the least bit unreasonable. I would think it has to be a possibility. The matter of what space is seems like one of the deepest questions we could face, as it seems quite foundational to the rest of physics - I wonder whether there is any deeper perspective from which to break it down for an in depth analysis.

Ken G
2010-Jul-30, 11:34 AM
I would say the big breakthrough of relativity was to understand that space is not separable or distinct from what moves through it. This seems quite natural in hindsight, surely that distinction was always a bit overinterpreted. Sort of like how ancient cultures overinterpreted the distinction between day and night-- the Sun "disappearing to the underworld" or who knows what. Now we just say, day and night are not really any different, except for that big spherical rock in the way of the Sun. Same with space and time-- we used to think those were as different as, well, night and day, but now we see they share enough attributes to be joinable into a single spacetime manifold. Time to get a new expression-- "as different as night and day" just doesn't carry the meaning it used to.

Spoons
2010-Jul-30, 11:37 AM
Squid and donkeys?

Ken G
2010-Jul-30, 12:02 PM
Now there's a difference!

forrest noble
2010-Jul-30, 05:42 PM
A term you may wish to consider, to replace "obfuscatory", is "pedagogical." It is perhaps both more flattering, and more accurate. What's more, it is important not to mistake the "baby" of GR with the "bath water" of popularized accounts of GR. One does not judge a theory by the way it is explained to barmaids, one judges the explanatory skill of the theorist that way. In other words, someone who cannot explain a theory clearly may not understand it themselves as well as could be hoped, but if the theory succeeds in its predictive power, we must separate the theory from our understanding of it. In particular, our lack of understanding presents us with the mission not to discard the theory, but to understand it better.

sounds good to me.

chappell
2010-Aug-12, 06:24 AM
OK so space-time is nothing more math coordinates that describes everything but itself is nothing. And it can be nothing because we just made it up to make math work with the experimental data. I don't know I still think space-time could be something. We are still missing some pieces of the big pictures. Are you saying that it can't have any mass or force, it is just matter 1% nothing 99%. Well until they find a graviton I will be in the corner with my jell-o

Spoons
2010-Aug-12, 02:16 PM
I think you're right, but I don't think anyone can make a firm definition of what it is and isn't. Well, we can be pretty sure it isn't a giant carrot with wheels and a pumping stereo system. Pretty sure.

But exactly what it is, while quite an interesting question, isn't quite as important as what impact it has on us. And I'm not convinced that we can necessarily ever be completely sure of what it is. We can't get outside of it to observe what it is and isn't. That may not completely stop us from assessing it, but I think it's going to certainly make it tough, and I think it most likely will stop us from being 100% certain of all it's nature.

uncommonsense
2010-Aug-12, 08:08 PM
IMHO - Space is "light". To know what is light, may be to know what is space.

cosmocrazy
2010-Aug-13, 10:12 AM
IMHO - Space is "light". To know what is light, may be to know what is space.

You've lost me with this one? can you elaborate a bit more on how you came to this conclusion?

thanks

uncommonsense
2010-Aug-13, 02:52 PM
You've lost me with this one? can you elaborate a bit more on how you came to this conclusion?

thanks

As far as I can imagine, every bit of space is occupied by some frequency of light - therefor, I conclude that since light is "something", then space can not be nothing.

It is mainstream that a photon (from it's own perspective) arrives at its destination the instant it departs. Therefore, I imagine the entire "space" along its rout is occupied by the photon - and since space throughout the universe is filled with light, then all spaces are occupied by photons (or by whatever light is).

cosmocrazy
2010-Aug-13, 03:04 PM
Ok I see now what you are getting at. But does light not travel through space relative to everything else rather than create space?

uncommonsense
2010-Aug-13, 03:14 PM
Ok I see now what you are getting at. But does light not travel through space relative to everything else rather than create space?

Good question.

My understanding of mainstream is that as to a photon (and from its relative perspective) there is no "space" along its axis of travel - put onother way, it "fills" the space along its axis of travel. And since light is moving in all direction throughout the universe, then all space is light.

chappell
2010-Aug-13, 03:15 PM
I think he is saying space is a bunch if photons

cosmocrazy
2010-Aug-13, 03:22 PM
And your understanding is as mine in that respect, but does the light actually fill the space or create the space? From this you would conclude that space only exists for everything sub light speed, basically everything we observe other than EMR?

uncommonsense
2010-Aug-13, 03:29 PM
And your understanding is as mine in that respect, but does the light actually fill the space or create the space?

IMHO, the light defines the space. And so, to know what is light, may be to know what is space.

cosmocrazy
2010-Aug-13, 03:35 PM
Can we measure space without light?

uncommonsense
2010-Aug-13, 03:40 PM
Can we measure space without light?

I don't understand the question. Do you mean:

"can we measure space that does not have light"? or

"can we measure space without useing light as a measuring tool"?

cosmocrazy
2010-Aug-13, 03:54 PM
Your understanding is sound, both questions in one.

uncommonsense
2010-Aug-13, 04:02 PM
Your understanding is sound, both questions in one.

Tell me about "both".:)

cosmocrazy
2010-Aug-13, 04:33 PM
I don't understand the question. Do you mean:

"can we measure space that does not have light"? or

"can we measure space without using light as a measuring tool"?

Ok, can we measure space without light, is it possible? Can we measure space other than using light as one of the tools to measure with?

uncommonsense
2010-Aug-13, 05:00 PM
1. Some frequency of EMR exists in all spaces, and therfore there exists no space that is without light. (can you suggest any spaces that are without any EMR?)

2. If you consider a ruler is defined as a solid object that is without light, then yes - space can be measured without useing light as a measuring tool. But if you define a ruler as an object that has space between its smallest known particles, then no.

To know light may be to know space.

George
2010-Aug-13, 05:08 PM
It must be properly understood, that this position is entirely philosophical, it is not a scientific position. But likewise I consider that physical realism (that assumes space and time to be real, existing in the same familiar form outside of the observer) is also a philosophical position. This is simply because the primary bed rock of science – namely strong objectivity, may in fact be only of a weak variety. Scientifically we cannot mitigate for the brain because whatever model we build to represent the effect of the brain is, in itself a product of that brain.
[The entire post was nice, Len. Thanks.]

Also, weak strong objectivity is both logical and a Friday oxymoron. Thanks again. :)


If you can't explain anything to a barmaid then you probably don't have very good game – forrest. Cool. For those to whom this applies, I suggest they start their upward climb by learning barmaid jokes since they are often easily explained. :)


Squid and donkeys? :) Yet who would have guessed we’re 80% the genetic same as pumpkins and, perhaps, corn, though some more than others.


I hardly know what questions to ask regarding space.

1) Is there a maximum distance between any two specific points - say between two hydrogen atoms in a water molecule [a multi-viewpont question]? If not, can I put a kitchen sink between any two atoms that drain through it?
2) What uniqueness exists with co-moving space?
3) What ain’t space? It isn’t separate from time - that was an impressive discovery - but what else is it not that happens to be informative of what it might be?
4) Barmaid that I almost am, how does a planet know to follow the less dense side of space when it is warped by a massive white object? [The bowling ball on the trampoline helps very little since I am comfortable with Newtonian “forces” acting upon a marble as it moves within a gravitational field along a slope near the bowling ball.]

Len Moran
2010-Aug-13, 11:06 PM
[The entire post was nice, Len. Thanks.]

Thank you George. That's cheered me up, in another thread Strange commented that he found my post's "incredibly difficult to read" :((to be fair he said that was his fault not mine - but still, makes you wonder!)

astromark
2010-Aug-14, 01:42 AM
Can I say space is something... Oh, I just did.

It would seem that in order to explain the working of gravity were space is said to be distorted

By the mass of objects. That light and some other things have no trouble transversing it at c.

Particles sub atomic or not would be sparse. parts per million maybe. Empty, NO. What is space.. ? I do not know.

So what do we know of space ?

1/ its not empty.
2/ It can be bent.
3/ Its not nothing.
4/ Its easily penetrated.
5/ Light moves through it freely....

Is it part of some other thing. Dark energy ?
The more I try to simplify what space is... the more complex seems the question...
I am stuffed. stumped, and becoming confused... What is space... I have no idea.

I do not much like the words ' the either ' but can see the need for it.
Space would seem to be something more than nothing.

So it can not be substantially dense... Hmmm...? Can I call it a structure, a web. No, but I should call it something.
I will cal it 'Space.'

George
2010-Aug-14, 02:57 PM
Thank you George. That's cheered me up, in another thread Strange commented that he found my post's "incredibly difficult to read" :((to be fair he said that was his fault not mine - but still, makes you wonder!) Recognizing philosophical perspectives will help us get around corners, which seem to be getting harder to find and turn.

Strange
2010-Aug-14, 04:57 PM
Thank you George. That's cheered me up, in another thread Strange commented that he found my post's "incredibly difficult to read" :((to be fair he said that was his fault not mine - but still, makes you wonder!)

Ooops. Sorry.

I will keep trying. But they are dense (in a good way: packed full of meaning) and make me feel dense (in not such a good way!)

forrest noble
2010-Aug-14, 06:56 PM
Len Moran,


.........So before you start trying to think about concepts of space and time and what they actually are in terms of familiar scientific concepts, you perhaps may think it worth while to examine the applicability of science to be able to answer such questions in terms of the strict scientific method and thus establish whether your desired answer is going to be a scientific one or a philosophical one.
Re: what is space.
I think you are missing another choice concerning intellectual decisions concerning reality. For a better understanding of reality if one does not believe current ideas and theory are adequate, one can also examine alternative theory or formulate ones own hypothetical or theoretical ideas, rather than just philosophical musings, to explain such quandaries. You can always be wrong no matter what intellectual choices you choose to prefer concerning making sense out of reality, but I think the additional considerations may be worth the extra trouble for those inclined to want and need "understanding."

Len Moran
2010-Aug-14, 11:07 PM
Len Moran,


Re: what is space.
I think you are missing another choice concerning intellectual decisions concerning reality. For a better understanding of reality if one does not believe current ideas and theory are adequate, one can also examine alternative theory or formulate ones own hypothetical or theoretical ideas, rather than just philosophical musings, to explain such quandaries. You can always be wrong no matter what intellectual choices you choose to prefer concerning making sense out of reality, but I think the additional considerations may be worth the extra trouble for those inclined to want and need "understanding."


I would never advocate philosophical musings as an alternative to scientific models, the two modes of enquiry are quite separate. My philosophical stance of realism pointed to by the scientific model is open rather than objectivist. Objectivist realism takes the philosophical stance that says space (and time) exists in that form outside of empirical reality whereas open realism makes no claim that any familiar notions exist outside of empirical reality. All versions of realism are philosophical because the scientific method cannot mitigate for observer dependence. Within macroscopic reality, separation of the observer and observed allows the scientific method to work, but that separation is a philosophical assumption, hence scientific ontological extrapolation of models is untenable, any such extrapolation that takes place is philosophical.

There are a number of models that make use of the concept of space, but the relevance of those models to human independent reality depends on your particular stance of realism, but in any event, the relevance is philosophical, not scientific. For the relevance to be scientific, there has to be a known, quantifiable measure of observer dependence, and then we could mitigate for it. No such method that I know of or can conceive of, can provide that measure.

I don’t disbelieve any verifiable scientific model, its domain of applicability is determined through observational verification. The relevance of that model to mind independent reality is not a scientific question, it is a philosophical question. That’s what I meant by deciding from which angle to approach this question - from a scientific perspective or from a philosophical perspective. The former is a mathematical predictive model with domains of applicability, the latter concerns philosophical ontological extrapolations from the model.

astromark
2010-Aug-15, 02:24 AM
Mine is not the last word in this subject... or any subject. but... The use of scientific modeling is just a methodology of testing and challenging.

Its the true scientific way... To test and challenge is good. In a related thread over in ATM a fellow is asking of what is the Universe

and seems to be off on a tangent regarding Higgs boson particle physics... I can not comment on that subject having no knowledge of it... at all.

'What is space ?' Does seem to be a, easy answer... At first look, its all that is above of Earths atmosphere...

wow that was easy... but no, more seems to be wanted. Can or should this become a philosophical point... No. Its real. I can touch it.

Ken G
2010-Aug-15, 03:30 PM
Ok, can we measure space without light, is it possible? Can we measure space other than using light as one of the tools to measure with?Sure. Light is a convenient tool, nothing more. Intelligence species that have no eyes might still have a lot of useful physics, and they might never have discovered a way to detect light.

forrest noble
2010-Aug-15, 07:16 PM
Len Moran,


I would never advocate philosophical musings as an alternative to scientific models, the two modes of inquiry are quite separate. My point was that many people consider questions concerning the underlying nature of space and time as philosophical in nature. My opinion is that although such perspectives of what these things are in regard to the human psyche could be considered philosophical, they may also be explainable properly by science theory, and eventually I think, that the "correct," unambiguous, uncomplicated science explanations will eventually be explainable to most young teenagers with a normal education.


I don’t disbelieve any verifiable scientific model, its domain of applicability is determined through observational verification.

Realize that there are differences of opinions concerning what is a verifiable scientific model, two models with entirely different explanations of reality, can rely on exactly the same observation data, each stating that the other is totally misinterpreting related observations. One may be the mainstream understanding and the other may be the next theory that will totally replace it.

caveman1917
2010-Aug-15, 08:15 PM
My understanding of mainstream is that as to a photon (and from its relative perspective) there is no "space" along its axis of travel - put onother way, it "fills" the space along its axis of travel.

Technically it says that the relative perspective of a photon is invalid - it can't be a valid FoR. One can imagine the limit of a universe passing by faster and faster, and such we say that space in the direction of travel gets smaller and smaller until it reaches zero. But (according to SR) we can't deduce anything from the perspective of a photon.

astromark
2010-Aug-15, 09:23 PM
That is true... but whats it got to do with ' What is space.'

Its pleasing to see so many with a good understanding of relativity and the mechanics of the photons point of view...

That it is not what space is I am sure. Define space as a concept.

What is meant as space ?

WayneFrancis
2010-Aug-16, 12:14 AM
IMHO - Space is "light". To know what is light, may be to know what is space.

so if I create a box that is shielded from all EM Waves then there is no "space" inside the box...some type of negative Tardis.

Ken G
2010-Aug-16, 03:10 AM
My opinion is that although such perspectives of what these things are in regard to the human psyche could be considered philosophical, they may also be explainable properly by science theory, and eventually I think, that the "correct," unambiguous, uncomplicated science explanations will eventually be explainable to most young teenagers with a normal education. Then you believe something about science that has never been true about it. I see it more reasonable to imagine that science will, in the future, continue to be what it has always been.


Realize that there are differences of opinions concerning what is a verifiable scientific model, two models with entirely different explanations of reality, can rely on exactly the same observation data, each stating that the other is totally misinterpreting related observations.I believe, by "verifiable", Len Moran meant simply "succeeds in predicting the observations to satisfactory accuracy." His statements sounded highly empirical in nature to me. What constitutes a correct explanation is a much different kettle of fish, and I suspect Len is in more my own camp on that one-- the explanations will always be a function of their goals and target level of sophistication.

George
2010-Aug-16, 03:20 AM
Realize that there are differences of opinions concerning what is a verifiable scientific model, two models with entirely different explanations of reality, can rely on exactly the same observation data, each stating that the other is totally misinterpreting related observations. One may be the mainstream understanding and the other may be the next theory that will totally replace it.
A few minutes ago I was just reading of Kepler and Tycho, which serves as a related example of this. Tycho, at 57, was having little or no luck with anyone helping him with the orbital mechanics he needed done with his planetary data. Along came Kepler who had the superior math skills and needed Tycho's superior data to test and improve the geometrical harmonies he presented in his Mysterium Cosmographicum. Tycho wanted his tables calculated and made presentable and saleable, I think.

cosmocrazy
2010-Aug-16, 08:37 AM
Sure. Light is a convenient tool, nothing more. Intelligence species that have no eyes might still have a lot of useful physics, and they might never have discovered a way to detect light.

Yes my thoughts also, I was hoping uncommonsense could elaborate on how "space" is light. :)

Len Moran
2010-Aug-16, 09:00 AM
Realize that there are differences of opinions concerning what is a verifiable scientific model, two models with entirely different explanations of reality, can rely on exactly the same observation data, each stating that the other is totally misinterpreting related observations. One may be the mainstream understanding and the other may be the next theory that will totally replace it.
(my bold)

Ken G has pretty much answered for me, so this is just an addition to his post and in particular referenced to the words in your extract I have bolded, namely "explanations of reality". You do not specify whether you are talking about empirical reality or independent reality, and I'm not even sure that you acknowledge the difference. It is that difference that is crucial to your understanding of my posts.

If the mathematical predictive elements of a model are validated in terms of empirical observations, then that model is correct within the domain of those observations. That’s all there is to it. Now if you want to extrapolate those models to give an "explanation" of mind independent reality, then that is an entirely different question which involves the taking up of a philosophical stance.

You I suspect adopt the stance of objectivist realism, but do you accept that such a position makes a philosophical assumption that mind independent reality is of the same form as empirical reality? It has to be a philosophical assumption because we have no means in which to scientifically mitigate for the observer. So it very simply follows that any verified model, no matter whether you think it the “correct” or “final” one, cannot ever be considered to be a scientifically definitive (or even approximate) rendering of mind independent reality. That it represents , in a philosophical manner, mind independent reality is not to be denied, (that is the philosophical stance of realism) – but it can be taken no further than that. If you consider that it can, then you need to be able to scientifically mitigate for the observer (remembering that just because we establish strong objectivity within our macroscopic reality, that is not in itself a proof that the separation between observer and the observed is intrinsic to nature), but I have no idea how that could ever be carried out, even in principle.

So when the mathematical predictions of a model are verified through observation, that model becomes a valid one within its scope. Another model may come along and extend its scope making use of entirely differing descriptive language, (the classic example being Newton and Einstein), but the predictive element of the model is always (and always will be) valid within it’s domain of applicability within empirical reality (which always, by definition involves the observer). The problem arises when these elements of a model (especially the descriptive notions) are taken as being scientifically directly applicable to mind independent reality, as if there is a direct link, expressed in familiar empirical terms, between mind independent reality and empirical reality, with no conception of the brain, mind, and consciousness as existing in between.

uncommonsense
2010-Aug-16, 04:55 PM
so if I create a box that is shielded from all EM Waves then there is no "space" inside the box...some type of negative Tardis.

How would you know that there is no EMR inside the box? What would you use to test for EMR? Would you have to use EMR to test for EMR? Can such a box be built? I would like to hear more.

Nereid
2010-Aug-16, 06:30 PM
How would you know that there is no EMR inside the box? What would you use to test for EMR? Would you have to use EMR to test for EMR? Can such a box be built? I would like to hear more.
Have you heard of a Faraday cage?

uncommonsense
2010-Aug-16, 06:41 PM
Have you heard of a Faraday cage?

Not untill you mentioned it. But my sources say a Faraday cage does not block all EMR.

Nereid
2010-Aug-16, 06:54 PM
Not untill you mentioned it. But my sources say a Faraday cage does not block all EMR.
No, but it blocks some.

Now put your Faraday cage inside a deep mine, into a salt body (so you've blocked all EMR from the surface).

Further, put it inside a refrigerator, and bring its temperature down to, say, a microK.

Put all that inside yet another Faraday cage, itself inside a thick box made of pure 56Fe.

Am I getting closer?

uncommonsense
2010-Aug-16, 07:04 PM
No, but it blocks some.

Now put your Faraday cage inside a deep mine, into a salt body (so you've blocked all EMR from the surface).

Further, put it inside a refrigerator, and bring its temperature down to, say, a microK.

Put all that inside yet another Faraday cage, itself inside a thick box made of pure 56Fe.

Am I getting closer?

Closer -- yes.

What is the mainstream view of whether space can be completely void of all EMR? I don't know the answer but am anxious to find out. Do you know of any references that answer this?

Thank you.

Ken G
2010-Aug-16, 07:50 PM
I would certainly say that it is easier to rid space of EMR than of neutrinos, but that would still not lead me to say that "space is neutrinos."

astromark
2010-Aug-16, 08:17 PM
I would certainly say that it is easier to rid space of EMR than of neutrinos, but that would still not lead me to say that "space is neutrinos."

Yes... :)

My knowledge of a facility in Antarctica... a cavern as the result of a explosion some 60 meters down...

filled with water and equipment to measure neutrino's zipping through the Earth...

as far from other EMR's as it can be... No, I do not know how to define space in a absolute manor...but I know its not empty.

A point which must be made is that... we know of no more empty place than space.. Its almost empty. Its almost a perfect vacuum.

yet in it is all of that which we know...

In some way we have imagined a place outside of this Universe... where there is Nothing. Not space. Not time. Now thats empty. :eh:?

uncommonsense
2010-Aug-16, 09:48 PM
I would certainly say that it is easier to rid space of EMR than of neutrinos, but that would still not lead me to say that "space is neutrinos."

Ether, too, is easier to be rid of - but still would not lead me to say space is ether.

forrest noble
2010-Aug-16, 10:55 PM
Len Moran,


If the mathematical predictive elements of a model are validated in terms of empirical observations, then that model is correct within the domain of those observations. That’s all there is to it.

In the long run mathematical predictions of theory are rarely, if ever, validated by observations in all expected domains. The boundaries of such unpredictability can change over time until the theory is replaced by a new one.

A case in point is the BB model. What are the mathematical predictions of the model? The model over time has predicted/estimated many different ages of the universe based upon an expanding universe model.

Today the age of the universe is estimated to be 13.7 billion years old based upon that model. This age is accordingly based upon a cosmological constant rate of expansion or at least an average rate of expansion. If new observations contradict this, for instance, by continuously finding the same kind of galaxies no matter how far back in time we look, what mathematics are being violated? Although the equations reformulated from GR are the basis for the BB model, it is not GR that is being tested, it is the reformulation and perspectives concerning its application to the universe as a whole. Such reformulation includes possible "speculative elements" such as its application to galaxy interactions and a forth physical dimension of space which closes its bounds, hence accordingly no center to the universe and no periphery concerning finite bounds would accordingly exist.

GR also has shown to be very accurate at "close distances" (with few challenges) but it cannot predict the motion of stars within a galaxy or the rotation rates of galaxies within a cluster. To explain this the dark matter idea was proposed. Now there seems to be no theory that can make such predictions concerning galaxy interactions since it is said that all galaxies vary as to the extent of their dark matter. It is still debatable whether GR is the valid mathematics in these domains, or in the universe as a whole, or that it is sacrosanct in any domain. There are not any theories that I can think of which are immune from future observational contradiction. The mathematics of each theory has a domain of application presently, but the usefulness of the theory/ formulation in that domain could always change based upon observations.

Another example is The Hubble law, A.K.A the Hubble formula. It is still a theoretical formula with relatively simple mathematics. It predicts distances based upon galaxy redshifts yet when plotted out concerning type 1a supernova observations, observed redshifts based upon their brightness varies from what distances are predicted to be concerning a standard candle application to type 1a supernova. Since the average observation at any particular redshift seems quite consistent it would seem the standard candle expectation of these supernova seems to be valid. The question which then becomes apparent would be: does this formula need to be tweaked (which could solve the observational problems) or is there something else out there that we don't understand that keeps changing the expansion rates of the universe, proposed to be dark energy, and what is the more likely possibility of these two choices, for instance?

What is the essence of space concerning theory? The mathematical predictive elements of GR do not explain the query. Theories and their mathematics can and will change over time. All of them? who knows which will be the next "big theory" to fall or be drastically changed?

Len Moran
2010-Aug-17, 10:50 AM
In the long run mathematical predictions of theory are rarely, if ever, validated by observations in all expected domains. The boundaries of such unpredictability can change over time until the theory is replaced by a new one.


I am not disputing that at all – in any form or fashion. All I am saying is that the observationally verified predictions of a model are of eternal validity within its domain of applicability. We can certainly expect the model to be extended in scope by improved models, or radically different models. But each new model is empirically only valid in terms of confirmed predictions, and those verifications define it’s domain of applicability at any particular point in its history. From that point on, the model, along with it’s domain of applicability is forever correct – in ten thousand years, it will still be entirely valid as a predictive model within its scope. Now I can understand you saying that such a way of thinking dilutes the descriptive “explanatory” power the models are intended by many to invoke. I wouldn’t disagree with such a statement for it illustrates the important difference between us in that I don’t consider models to be especially robust in terms of descriptive notions, (as opposed to their predictive mathematical element, within their domain of applicability) but much, much more than that – the models do not have a proven scientific link to mind independent reality, so “explanatory” in this sense is associated only with empirical reality, and by default, that involves observation, and that observation involves mind independent reality, the mind, intelligence, and consiousness and it is within that grand mix that our objectivity, and hence the scientific method, operates and gives us the appearance of counterfactuality operating at the macroscopic level, but that objectivity cannot be scientifically shown to be intrinsic to nature, it is a philosophical assumption. We cannot scientifically claim that the most perfect model we can envisage takes us any closer to mind independent reality, that is a philosophical assumption based on the notion that mind is entirely separated from the physical world.

In any event, descriptive notions are often just convenient pictures, utilised by our intelligence to invoke some kind of familiarity. A travelling EM wave in the absence of a medium is just a picture and can’t possibly be taken seriously, but the predictive elements are used by countless engineers outside of the untenable notion of waves travelling in vacuum. A single photon “travelling” between a source and sink in vacuum is pictured by many as a little object with no mass that somehow “moves” from the source to sink, despite that particle never being localised prior to measurement. I don’t take that picture of a “moving” particle very seriously at all, but I take the predictions of quantum mechanics and an observer very seriously - and those predictions are eternally valid within their domain of applicability, where as the description of a photon as being a little travelling object I expect to be smiled at in a few hundred years. But those smiles will not be directed at all to the power of the predictions of QM; they will probably still be using them.



The mathematics of each theory has a domain of application presently, but the usefulness of the theory/ formulation in that domain could always change based upon observations.


And again, I am not disputing that. But it remains the case, that if I make an observation now that confirms a prediction, then that part of the model is for ever valid. If that procedure is of some use now within the context in which I use it, then it will have the same usefulness in the same context a thousand years from now. I don’t see models as being anything other than empirical bodies of knowledge (defined in terms of their verified applicability) that allow us to rationalise our macroscopic reality. Existing models will have shortcomings, but those shortcomings do not make them invalid, it just restricts their domain of applicability. A new model will perhaps deal with those shortcomings, but that doesn’t make it a more “correct” model, it just extends the domain of applicability. Maybe one day, an all embracing model will unite GR and QM, but that doesn’t render the old models invalid, it just means that the new model has a domain of applicability that was previously unavailable through one model. It doesn’t mean that the unification has got us a step closer to mind independent reality, it just means that we have rationalised empirical reality to a much greater degree in that we can account for many more observations through just one model. To see models in terms of “correct” or “incorrect” gives an impression that we are heading in a direction that will lead to a scientific model that eventually “explains” nature. But in the absence of properly defining what we mean by nature, it is false, what models account for is empirical reality, but the connection between empirical reality and mind independent reality is scientifically unknown, and I cannot conceive of any scientific procedure that will ever, even in principle, unravel that connection such that we will be able to mitigate for it. The scientific method allows us to account for nature in terms of predictive mathematical models, but it is a procedure that is embedded within empirical reality. We cannot scientifically escape from empirical reality and observe what is outside of that box. Our only means of escape is through making a philosophical connection between empirical reality and mind independent reality. And that philosophy is nothing new, it involves realism - philosophers have been debating it for goodness knows how long, but the number of physicists who properly consider the implications seem few and far between. Ken G is one of them on this forum, another, who I refer to very much is Bernard d’Espagnat who has written extensively on this whole area of realism.

So to get back to the original question, what is space?

Do we want to answer this question in terms of empirical reality or in terms of mind independent reality? In the former case, science is the master and can produce many useful models. In the latter case, only philosophy can address the question and it does so through the philosophical stance of realism. We each choose our realist stance individually, depending on what degree we consider that we can say “something” pertaining to the “truth” of independent reality. At the one end, physical realism pretty much asserts that we can, in principle, determine the whole “truth”. At the other, open realism asserts that mind independent reality is just that, it does not hinge on thought. Many take up the stance of physical realism, without at all realising that it is a philosophical stance just as much as my stance of open realism. If you disagree with this statement then you have to show how you can make a scientific connection between mind independent reality and empirical reality and thus render the age old question of realism as being solved. To make such a scientific connection, you would have to define mind, intelligence, consciousness in a manner that would allow you to understand the “effect” that the above terms have on the connection between mind independent reality and empirical reality. And don’t forget, that the very instrument you would be using to carry out that analysis would be the mind, intelligence and, consciousness.

For what it is worth, I prefer to address the question of what space is in terms of mind independent reality. From my stance of open realism, the term mind independent reality transcends description, so I choose not to say anything about it at all, other than to say there is no justification to assume that it consists of familiar notions as space and time, it may do, but equally it might not. Correlation experiments suggest that space (and hence time) are not universal in appearance within empirical reality, so that very contrast between the macroscopic experiment, embedded in familiar space time and the correlation that stands apart from familiar notions of space are indicative of something, and I think it is perfectly legitimate, from a philosophical perspective to question the existence of space and time within independent reality based upon those correlation experiments.

uncommonsense
2010-Aug-17, 04:55 PM
Some good stuff in posts. Liked it all. To say alittle more, as asked, about my "space is light" post:

When something is so difficult to define, such as "space", it is often necesary to simply encompass the definition by a symbiotic reference. I was simply thinking that a defining portiion of GR deals with black holes and event horizon issues Specifically: properties of space-like and time-like intervals are reversed when you hypothetically cross R=Rs. In other words, when R < Rs, because (1 - R/Rs) < 0 then (dR) becomes negative and (dT) becomes positive ......(where (dR) is time-like interval and (dT) is space-like interval). Put another way, there is a sign change in the metric upon crossing R=Rs.

So we are told that space-like and time-like intervals can be reversed and --------and this all hinges upon c.

So my simple mind was merely suggesting to know light may be to know space.:)

Nereid
2010-Aug-17, 05:15 PM
As this thread is in the Q&A section, and as there are some good guidelines on what should (and should not) be posted here, I think it is important to enter a number of caveats ...

Len Moran,



In the long run mathematical predictions of theory are rarely, if ever, validated by observations in all expected domains. The boundaries of such unpredictability can change over time until the theory is replaced by a new one.

A case in point is the BB model.

In the interests of getting more precision in language, there is no such thing as "the BB model", except, perhaps, in a company which manufactures ammunition for BB guns.

There is what is popularly referred to as the Big Bang Theory (and no, I'm not talking about the TV series).

Then there are LCDM (lambda cold dark matter) models, of which there are many, even many classes of such models. These are all based on the Big Bang theory. But, and this is very important, a model is not a theory, and a theory is not a model; the two are very different beasts.


What are the mathematical predictions of the model? The model over time has predicted/estimated many different ages of the universe based upon an expanding universe model.

Not so.

The *class* of theories popularly called the Big Bang theory (BBT) has been examined, and from this many different models built.

In the BBT, and the models built using it, the age of the universe is an output, critically dependent on H0, the Hubble constant. Change estimates of that constant, and the estimated age of the universe - from BBT-based models - changes too. A huge amount of effort has gone into refining estimates of the Hubble constant, and for several decades there were two 'camps', one pointing to a great deal of evidence that it is ~50 km/s/Mpc, the other ~100 km/s/Mpc. Only with the results of one of the Key Hubble Projects in hand has the question been settled, more or less (the value is ~70 km/s/Mpc (+/-~10%).


Today the age of the universe is estimated to be 13.7 billion years old based upon that model. This age is accordingly based upon a cosmological constant rate of expansion or at least an average rate of expansion.

Again, this is not accurate; however, it would take a very long post indeed to set the record straight.


If new observations contradict this, for instance, by continuously finding the same kind of galaxies no matter how far back in time we look, what mathematics are being violated?
That is a terrible example to use!

What galaxies 'look like' is something quite difficult to determine. However, as participants in the Hubble Zoo Citizen Science project (http://www.galaxyzoo.org/) will all readily attest, high-z galaxies, in general, look nothing like ones in the local universe.

And the question of how galaxies form and evolve has no direct bearing on the age of the universe.


Although the equations reformulated from GR are the basis for the BB model, it is not GR that is being tested, it is the reformulation and perspectives concerning its application to the universe as a whole. Such reformulation includes possible "speculative elements" such as its application to galaxy interactions and a forth physical dimension of space which closes its bounds, hence accordingly no center to the universe and no periphery concerning finite bounds would accordingly exist.

I really don't know what this means, but it is, in any case, a horrible misunderstanding of LCDM models!

GR, the theory, is a basic element of all these models; however, the GR equations are no more 'reformulated' than the equations of thermodynamics are 'reformulated' to apply to biological processes, say.

All tests of models are also tests of the theories on which they are built; usually such tests are indirect, but they are tests nonetheless.

The "speculative elements" listed either have nothing to do with GR ("its application to galaxy interactions"), or are simple consequences of the EFE ("a forth physical dimension of space which closes its bounds, hence accordingly no center to the universe and no periphery concerning finite bounds would accordingly exist").


GR also has shown to be very accurate at "close distances" (with few challenges) but it cannot predict the motion of stars within a galaxy

Not true - where did you get this idea from?

In any case, GR is rarely, if ever, used to model the motions of stars in a galaxy (Newtonian dynamics does just fine).


or the rotation rates of galaxies within a cluster.

No one knows what the rotation rates of galaxies within a cluster are; in fact, I don't think this expression is even meaningful.

Perhaps your are referring the measured velocity dispersion of galaxies in a cluster? And, maybe, indirectly to the virial theorem?

In any case, as with galaxy rotation, GR is rarely, if ever, used to model the motions of stars in a galaxy (Newtonian dynamics does just fine).


To explain this the dark matter idea was proposed.

The actual history is much more subtle, and complicated, than this!

Zwicky's papers refer to "Dunkle Materie", but mostly he was concerned with mass that wasn't showing up as light; back then no one could put robust bounds on the amount of mass in faint stars, gas which did not emit lines in the optical (nor absorb it), etc. Same with Rubin and Ford, several decades later, wrt spiral galaxy rotations curves. It was not until quite recently that all plausible forms of baryonic matter (which, paradoxically, includes electrons) have been ruled out as anything but minor contributors to the observed amounts of "missing mass".

Also, CDM explains far, far more than just the apparent line-of-sight velocity dispersions of rich clusters of galaxies and the rotation curves of spiral galaxies. Perhaps most wonderous is that it explains the angular power spectrum of the CMB, and BAO observations (galaxy-galaxy correlations); who'd have thought that such a simple concept would be so powerful, so extensive in its explanatory power?


Now there seems to be no theory that can make such predictions concerning galaxy interactions since it is said that all galaxies vary as to the extent of their dark matter. It is still debatable whether GR is the valid mathematics in these domains, or in the universe as a whole, or that it is sacrosanct in any domain.

Debatable by whom?

And concerning "galaxy interactions" (whatever this means): one astonishing result from studying galaxies which produce strong gravitational lenses is that the amount of CDM in them, estimated from the lensing, seems to match that estimated from rotation curve studies! If it's not CDM at work, then there is a most astonishing cosmic conspiracy at work.


There are not any theories that I can think of which are immune from future observational contradiction.

If there were, they wouldn't be scientific theories, by definition!


The mathematics of each theory has a domain of application presently, but the usefulness of the theory/ formulation in that domain could always change based upon observations.

Another example is The Hubble law, A.K.A the Hubble formula. It is still a theoretical formula with relatively simple mathematics.

I'm trying to hold my frustration in check; the Hubble law is entirely empirical!

It is the trend line through datapoints which are estimates of the redshift and distance of various objects (in the plot); it doesn't get any more empirical than that!


It predicts distances based upon galaxy redshifts yet when plotted out concerning type 1a supernova observations, observed redshifts based upon their brightness varies from what distances are predicted to be concerning a standard candle application to type 1a supernova.

Totally backward; the Hubble law (or Hubble's law) predicts nothing; it is just a trendline derived from data (a plot of observed redshifts vs estimated distances).


Since the average observation at any particular redshift seems quite consistent it would seem the standard candle expectation of these supernova seems to be valid.

Again, almost entirely backward.

The reasons why Ia SNe are 'standard candles' has to do with consistency in their light curves and spectra, simple models of the proximate causes of the variability in both, and consistency with other distance estimates in objects where both 1a SNe and other measures can be used (such as nearby galaxies with 1a SNe).


The question which then becomes apparent would be: does this formula need to be tweaked (which could solve the observational problems) or is there something else out there that we don't understand that keeps changing the expansion rates of the universe, proposed to be dark energy, and what is the more likely possibility of these two choices, for instance?

As should be apparent by now, that question is pretty much meaningless, as it is based on a misunderstanding of what Hubble's law actually is.


What is the essence of space concerning theory? The mathematical predictive elements of GR do not explain the query. Theories and their mathematics can and will change over time. All of them? who knows which will be the next "big theory" to fall or be drastically changed?
Sure.

However, this completely overlooks the fact that "space" itself has no meaningful definition outside a theory of physics!

forrest noble
2010-Aug-17, 05:18 PM
uncommonsense,


So my simple mind was merely suggesting to know light may be to know space.

This I think is valid, and the opposite may very well be true: To know the nature of the ZPF (which is contained by space) and its interactive constituents (known or otherwise), might explain the mechanics concerning EM radiation moving at light speed through space.

forrest noble
2010-Aug-17, 06:04 PM
Nereid,


In the BBT, and the models built using it, the age of the universe is an output, critically dependent on H0, the Hubble constant. Change estimates of that constant, and the estimated age of the universe - from BBT-based models - changes too. A huge amount of effort has gone into refining estimates of the Hubble constant, and for several decades there were two 'camps', one pointing to a great deal of evidence that it is ~50 km/s/Mpc, the other ~100 km/s/Mpc. Only with the results of one of the Key Hubble Projects in hand has the question been settled, more or less (the value is ~70 km/s/Mpc (+/-~10%).



I really don't know what this means, but it is, in any case, a horrible misunderstanding of LCDM models!
This response has nothing to do with a paricular BB model, it relates to the underlying equations.

Nereid, I'm sure you realize that if the dark energy idea is valid then there is no Hubble Constant concerning a constant expansion rate of the universe. Instead this expansion rate(s), according to the Dark Energy model, is believed to have varied/ changed over time, which might better be expressed as a "Hubble Variable."


Totally backward; the Hubble law (or Hubble's law) predicts nothing; it is just a trendline derived from data (a plot of observed redshifts vs estimated distances).

The Hubble Law, A.K.A Hubble formula, is the primary means that astronomers use to calculate galactic distances based upon observed redshifts, when no other information is available.

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html


The reasons why Ia SNe are 'standard candles' has to do with consistency in their light curves and spectra, simple models of the proximate causes of the variability in both, and consistency with other distance estimates in objects where both 1a SNe and other measures can be used (such as nearby galaxies with 1a SNe).

Of course. But my statement does not contradict this.

my quote

Since the average observation at any particular redshift seems quite consistent it would seem the standard candle expectation of these supernova seems to be valid.

your quote

The "speculative elements" listed either have nothing to do with GR ("its application to galaxy interactions"), or are simple consequences of the EFE ("a forth physical dimension of space which closes its bounds, hence accordingly no center to the universe and no periphery concerning finite bounds would accordingly exist").


This was the point, The BB is not backed mathematically by GR, instead it is backed by a reformulation of GR put together by Einstein to explain the gravity mechanics of the universe as a whole based upon General Relativity. These are called Einstein's Cosmological Equations based upon his paper in 1917 "Cosmological Considerations in the General Theory of Relativity." It was these field equations that De Sitter found an expanding universe solution, and it was here that Einstein proposed a cosmological contract .

http://www.scholarpedia.org/article/Cosmological_constant

your quote


What galaxies 'look like' is something quite difficult to determine. However, as participants in the Hubble Zoo Citizen Science project will all readily attest, high-z galaxies, in general, look nothing like ones in the local universe.

There has been contradicting evidence concerning how old the most distant galaxies appear to be. If the most distant galaxies all appear to be young concerning all observations and observers, and if the dark ages of the BB are discovered some day, then I think the BB will be on very high grounds indeed.
my quote

GR also has shown to be very accurate at "close distances" (with few challenges) but it cannot predict the motion of stars within a galaxy

The current dark matter idea is needed concerning the rotation rates of disk stars in a spiral galaxy. Since galaxies of all types are believed to have differing quantities of dark matter, then formulations alone, without observation, cannot make predictions of motions. Instead the quantity of dark matter is estimated based upon these stellar motions to predict the same motions. Maybe not a very good system.

Ken G
2010-Aug-17, 06:23 PM
Nereid, I'm sure you realize that if the dark energy idea is valid then there is no Hubble constant concerning expansion rates of the universe. Instead this expansion ratea, according to this model, is believed to have varied over time.
It is well known that the Hubble "constant" should vary with time, even without dark energy, that comes from general relativity.
The Hubble Law, A.K.A Hubble formula, is the primary means that astronomers use to calculate galactic distances based upon observed redshifts, when no other information is available.But only by interpolating within the "trend line" that Nereid is talking about. Without observations to determine that trend line, we'd have no idea what the "Hubble law" should be, since we don't know the energy density of the universe any other way.


This was the point, The BB is not backed mathematically by GR, instead it is backed by a reformulation of GR put together by Einstein to explain the gravity mechanics of the universe as a whole based upon General Relativity.It is true that GR by itself does not completely constrain the BB model, but that is generally true of theories when applied to specific models. For example, a model of the Sun needs to be told how much mass it has, and what its composition is. The same is true of cosmological models involving GR, if one considers dark matter and dark energy to be issues of "composition." If at some point the theory needs a new tweak for every new observation, it suggests the theory is not very good, but that is certainly not the case at the moment.

If the most distant galaxies all appear to be young concerning all observations and observers, and if the dark ages of the BB are discovered some day, then I think the BB will be on very high grounds indeed.Then your debate appears to center on whether or not that "day" is in fact today. That is a difficult issue-- it depends on how strongly you emphasize the outliers and surprises in any effort to organize and make sense of observations. Often, one should expect a few exceptional cases to "break the mold" of any attempt to categorize them, without invalidating that categorization, but sometimes, it is true that a few outliers are the "tip of the iceberg" of more common phenomena that have not yet been completely appreciated. That the "jury is out" is a standard element of science.



The current dark matter idea is needed concerning the rotation rates of disk stars in a spiral galaxy. Since galaxies of all types are believed to have differing quantities of dark matter, then formulations alone, without observation, cannot make predictions of motions. Instead the quantity of dark matter is estimated based upon these motions to predict the same motions. Maybe not a very good system.Note that none of that has anything do to with the theory of GR, because purely Newtonian gravitational physics encounters all the same problems-- and can be used to determine the orbits of stars in galaxies. What's more, when the orbit of Uranus was seen to not be predictable using Newton's laws and what was known at the time about the solar system, people did not say "Newton must not have a good system there", they said, "look for Neptune." Granted, it was ultimately the finding of Neptune that justified that approach, but it takes time to "find Neptune." That is no reason to abandon the theory, because one of the most important things that theories do is guide new observations. Does the search for dark matter guide new observations? It sure does. Does that make dark matter real? No, it will take more time to establish that. But it does make it a highly productive course of research to follow-- there is nothing that requires "fixing" there, although it is hoped that people will continue to look for alternative explanations in case they might find one.

Nereid
2010-Aug-17, 08:01 PM
fn, the main point I was trying to make in my post is that in the Q&A section we need to stick to the generally accepted mainstream astrophysics and cosmology, and that the post of yours I quoted was full of misconceptions, poorly-worded explanations, and generally not easily recognisable as being consistent with mainstream explanations.

I see that Ken G has further clarified some additional confusions etc; some more:

There has been contradicting evidence concerning how old the most distant galaxies appear to be. If the most distant galaxies all appear to be young concerning all observations and observers, and if the dark ages of the BB are discovered some day, then I think the BB will be on very high grounds indeed.
How "old" a high-z galaxy "appears to be" is highly dependent on ideas (and models) of galaxy evolution. This is a very active area of research, and there is a wide range of models (and ideas); at present it is nigh on impossible to be able to say how old a particular galaxy appears to be.

There are, of course, objective measures such as the estimated average metallicity, or the apparent fraction of post-main sequence stars; however, even allowing for the huge uncertainties in these measures, without a robust theory of (early) galaxy evolution, it is impossible to convert these to estimates of the galaxy's age. In fact, some recent observations suggest that a mere few hundred million years are more than enough for what looks - from our vantage point so far away - like an 'old' elliptical galaxy to form; further, some of the high-z galaxies show evidence of quite astonishing rates of star formation (tens, or even hundreds, of thousands, of sols per year!).

If by "the dark ages of the BB" you mean the era of re-ionisation (EoR) and/or the Gunn-Peterson troughWP (http://en.wikipedia.org/wiki/Gunn-Peterson_trough), then you'll be pleased to learn that both have been "discovered" (observed would be a better word). Indeed, one of LOFAR's (and the SKA's, and ...) key objectives is to explore the EoR in detail, now that it's been detected.

George
2010-Aug-18, 01:53 AM
.If by "the dark ages of the BB" you mean the era of re-ionisation (EoR) and/or the Gunn-Peterson troughWP (http://en.wikipedia.org/wiki/Gunn-Peterson_trough), then you'll be pleased to learn that both have been "discovered" (observed would be a better word). Indeed, one of LOFAR's (and the SKA's, and ...) key objectives is to explore the EoR in detail, now that it's been detected.
[The Wiki article is a bit misleading since Gunn and Peterson made their claim after noticing the trough in a presentation by Maarten Schmidt of quasars, specifically 3C9. The prediction followed the observation (limited), which was later verfied by much more significant observations. Why do I have the impression you are reading Ann Finkbeiner's enjoyable book A Grand and Bold Thing? :)]

forrest noble
2010-Aug-18, 02:05 AM
Nereid,


If by "the dark ages of the BB" you mean the era of re-ionisation (EoR) and/or the Gunn-Peterson troughWP, then you'll be pleased to learn that both have been "discovered" (observed would be a better word). Indeed, one of LOFAR's (and the SKA's, and ...) key objectives is to explore the EoR in detail, now that it's been detected.

I'm glad that you put quotes around the statement that the dark ages have been "discovered." It would require a search in all directions beyond the furthest observable galaxies, and it would take many years of consistent observations with no observable galaxies existing beyond a certain redshift limit to realistically believe that the dark ages have been observed. So far, as far back as we are able to look, galaxies can be seen. There are always those prematurely claiming to see what theory predicts, later to find that their interpretations were incorrect.

RE: dark ages

http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang

Nereid
2010-Aug-18, 02:28 AM
Hubble Space Telescope Advanced Camera for Surveys Observations of the z = 6.42 Quasar SDSS J1148+5251: A Leak in the Gunn-Peterson Trough (http://arxiv.org/abs/astro-ph/0411195)

The apparent shape of the "Strömgren sphere'' around the highest-redshift QSOs with Gunn-Peterson troughs (http://arxiv.org/abs/astro-ph/0411097)

Evidence for Reionization at z~6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar (http://arxiv.org/abs/astro-ph/0108097) - this 2001 AJ paper has been cited 533 times.

Seeing Through the Trough: Outflows and the Detectability of Lyman Alpha Emission from the First Galaxies (http://arxiv.org/abs/1004.2490)

Detection of Extended He II Reionization in the Temperature Evolution of the Intergalactic Medium (http://arxiv.org/abs/1008.2622)

(there are hundreds more papers I could cite).

The footprints of the EoR (Dark Ages) have been observed, fn. What remains to be done is understand it, in detail. The tools we have, today, are not up to that task; however, development of tools which are - such as LOFAR, JWST, SKA, and so on - is well advanced, and some just-prior-to-first-science-results engineering work is finished or almost done, at least for LOFAR and SKA test beds.

forrest noble
2010-Aug-18, 02:32 AM
Ken G,

regarding predictive falure of theory concerning orbital velocities of disk stars


Note that none of that has anything do to with the theory of GR, because purely Newtonian gravitational physics encounters all the same problems-

Point noted. I think my quote (below) referred to presently used gravitational theory in general, not just GR.

my quote:

Since galaxies of all types are believed to have differing quantities of dark matter, then formulations alone, without observation, cannot make predictions of motions concerning spiral galaxy disk stars, orbital velocities of galaxies in a cluster, and to some extent galaxy interactions in general.

Swift
2010-Aug-18, 02:39 AM
I am closing this thread, at least for the moment.

The OP seems to have dropped out of the discussion two months and four pages ago, the list of Reported Posts just keeps growing, some of the posts are getting very close to ATM, and Q&A long ago stopped being the proper home for this thread.

The moderators are going to think about this for a bit and see if, and where, we allow this discussion to continue.