Dark matter highlights extra dimensions

[SimonA]

http://www.nature.com/news/2005/050829/full/050829-18.html

http://xxx.arxiv.org/PS_cache/astro-ph/pdf/0508/0508572.pdf[/URL]

 

[Garth]

From that Nature article

One explanation, they say, is that three extra dimensions, in addition to the three spatial ones to which we are accustomed, are altering the effects of gravity over very short distances of about a nanometre1.

The team argues that such astronomical observations of dark matter provide the first potential evidence for extra dimensions. Others are supportive, but unconvinced. Lisa Randall, a Harvard physicist who has explored the possibility of extra spatial dimensions, says "Even if their idea works, which it probably does, it may be an overstatement to use these observations as evidence of extra dimensions."

Silk himself acknowledges that the proposal is "extremely speculative".

Garth

 

[SimonA]

From that Nature article

Garth

Any more speculative than WIMPS etc. ? And why the missing dense dark matter halos at galaxy cores ? You can invent 'crumbly' forms of dark matter that could explain it but then you are inventing something purely to fit the data, with no fundamental basis for doing so. On the other hand there are plenty of fundamental mathematical reasons for considering extra dimensions.

Of course its not by itself "evidence for" extra dimensions. But the current trend of the multiplication of entities approach to physics will keep having to plaster up all the different invented entities to get them to fit the data - which gives you a "standard model" that's less 'speculative' - but is it more realistic ? 'Where' does gravity 'leak' to (heirarchy problem) ? How can a superposition of states collapse instantly across 3D space ? And what about quantum gravity ? ( http://www.calphysics.org/articles/gravity_arxiv.pdf )

There's no point simplifying what can't be simplified any further. But if there is a chance that a more fundamental look at the basics across all these 'anomalies' can resolve them all at a fundamental level, what a grand prize that would be :)

Simon

 

[ohwilleke]

You can invent 'crumbly' forms of dark matter that could explain it but then you are inventing something purely to fit the data, with no fundamental basis for doing so.

God forbid that theory could ever follow empirical evidence instead of the other way around!

 

[Garth]

Any more speculative than WIMPS etc. ?

My point exactly

And why the missing dense dark matter halos at galaxy cores ? You can invent 'crumbly' forms of dark matter that could explain it but then you are inventing something purely to fit the data, with no fundamental basis for doing so.

Until it is discovered in a laboratory exotic non-interacting DM is just "pixie dust" invented purely to fit the data

On the other hand there are plenty of fundamental mathematical reasons for considering extra dimensions.

Of course its not by itself "evidence for" extra dimensions. But the current trend of the multiplication of entities approach to physics will keep having to plaster up all the different invented entities to get them to fit the data - which gives you a "standard model" that's less 'speculative' - but is it more realistic ? 'Where' does gravity 'leak' to (heirarchy problem) ? How can a superposition of states collapse instantly across 3D space ? And what about quantum gravity ? ( http://www.calphysics.org/articles/gravity_arxiv.pdf )

There's no point simplifying what can't be simplified any further. But if there is a chance that a more fundamental look at the basics across all these 'anomalies' can resolve them all at a fundamental level, what a grand prize that would be :)

Simon

Check out Self Creation Cosmology - An Alternative Gravitational Theory .

Garth

 

[SimonA]

God forbid that theory could ever follow empirical evidence instead of the other way around!

Okay so you notice that the motion of galaxies do not fit Newtonian predictions, because there is not enough mass to hold it all together at that velocity in Newtonian terms. So, following what was missing from Newtons predictions - namely mass - invent a kind of mass that interacts 'weakly' with baryonic (normal) matter. Then you look a little closer and all kinds of things do not match predictions. Then you spend millions to try to detect this invented concept and fail to do so. So in effect the theory of non baryonic matter contained within 3D space has so far failed to find empirical support.

Science is not always about "follow[ing] empirical evidence". Ideally its about understanding empirical evidence. Einstein opened up a new level of understanding by considering time as a dimension. Surely there is room in your empirical world to consider there may be even more to it all ? According to E=mc^2 mass traveling at c becomes "energy". What does that mean ? If you where 'watching' an electron, specifically in the orbital shell of an atom, and that electron received enough energy to jump to another shell, what would you say had happened to that electron ?

 

[SpaceTiger]

I would say that it's considerably less ad hoc to postulate a weakly-interacting particle than it is to postulate an alternative theory of gravity and/or extra dimensions. I said it before and I'll say it again. If you're whining about why we haven't detected a particle that could be the dark matter, you need to stop and think about why it is that the particle would be dark and what implications that has for its detectability.

 

[turbo]

If you're whining about why we haven't detected a particle that could be the dark matter, you need to stop and think about why it is that the particle would be dark and what implications that has for its detectability.

Why does it need to be a particle? Could it not be a field of particle/antiparticle pairs that is difficult to detect except locally (quantum vacuum field)? This would entail a new model of gravitational interaction (a polarized self attractive vacuuum field), but is this a bad thing? The Newtonian inverse-square relationship works well for simple systems, and Einstein's improvement works well in some domains. Is it not appropriate to explore the question of whether we need an even better theory of gravitation, to explain the flat rotation curves of galaxies, the excess lensing of clusters, and the excess binding energy of clusters?

 

[SpaceTiger]

Why does it need to be a particle?

It doesn't, I was responding to the lack of verification of the leading theory.

Could it not be a field of particle/antiparticle pairs that is difficult to detect except locally (quantum vacuum field)?

No.

Is it not appropriate to explore the question of whether we need an even better theory of gravitation, to explain the flat rotation curves of galaxies, the excess lensing of clusters, and the excess binding energy of clusters?

It's perfectly appropriate, but it makes no sense to attack the conventionial theories for "making things up to fit the data" when the alternative gravity models do so in an even more egregious fashion.

 

[SimonA]

I would say that it's considerably less ad hoc to postulate a weakly-interacting particle than it is to postulate an alternative theory of gravity and/or extra dimensions.

Amusing.

From Websters;

ad hoc
For the special purpose or end at hand; also, by extension, improvised or impromptu. The term, Latin for "to this," is most often used for committees established for a specific purpose, as in The committee was formed ad hoc to address health insurance problems. The term is also used as an adjective (An ad hoc committee was formed), and has given rise to the noun adhocism for the tendency to use temporary, provisional, or improvised methods to deal with a particular problem.

I said it before and I'll say it again. If you're whining about why we haven't detected a particle that could be the dark matter, you need to stop and think about why it is that the particle would be dark and what implications that has for its detectability.

Errr ... whining ? Why do I need to stop and think about something so inately and implicitly obvious ?

 

[SpaceTiger]

ad hoc
For the special purpose or end at hand; also, by extension, improvised or impromptu. The term, Latin for "to this," is most often used for committees established for a specific purpose, as in The committee was formed ad hoc to address health insurance problems. The term is also used as an adjective (An ad hoc committee was formed), and has given rise to the noun adhocism for the tendency to use temporary, provisional, or improvised methods to deal with a particular problem.

Good, now explain to me which part of the definition you don't understand.

Errr ... whining ? Why do I need to stop and think about something so inately and implicitly obvious ?

I dunno, you tell me.

 

[SimonA]

It's perfectly appropriate, but it makes no sense to attack the conventional theories for "making things up to fit the data" when the alternative gravity models do so in an even more egregious fashion.

An "even more egregious fashion" ? Strange - I have no idea where you are coming from. Which gravity model are you talking about exactly ? Einsteins stretched-by-mass concept of spacetime ? I think we all can agree to accept that. So is M Theory the "alternative gravity model" you have a problem with ? It does have all those 'messy' extra dimensions that no one claims to understand properly. So I guess you consider the likes of Ed Witten and Lisa Randal to be the kind of people who willingly spend their time on "egregious" theories ?

What is this "attack the conventional theories" comment referring to ? The idea of science is to question. In fact its the heart of the scientific process.

So tell me how making things up purely to fit the data in cosmology, things that have no direct evidence whatsoever, let alone any kind of fundamental significant basis for their derivation, compare with a concept based on the broad horizon of cutting edge theoretical physics, derived from well established maths ? How do you weigh such things ?

Your comments are as dubious as Garth's paper. You say "It makes no sense to attack the conventional theories" ? Where would science be if we all followed your lead ? Of course you did qualify that, but in terms that where such nonsense my cat could do a better job of defending whatever was in your head when you thought of "standard gravity models".

If you're such a SpaceTiger then I assume that along with you guttural roar that shakes the ground - as all good tigers do, you will provide us all with a relativisticaly invariant description of youngs slit experiment that accounts for Bell's inequalities within Aspects experiment ?

And if relativistic principles are important to you, and you feel confident enough to mock theories of gravity when you yourself have not proposed anything significant in what everyone considers a troublesome question, then what are your comments about ? Why this talk of "alternative gravity models" that are "egregious" ? Tell me of this non-alternative gravity model you have confidence in and tell me why you feel confident about it. If you can't - then why on Earth did you reply on this thread as you did ?

Simon

 

[SpaceTiger]

An "even more egregious fashion" ? Strange - I have no idea where you are coming from. Which gravity model are you talking about exactly ? Einsteins stretched-by-mass concept of spacetime ? I think we all can agree to accept that. So is M Theory the "alternative gravity model" you have a problem with ? It does have all those 'messy' extra dimensions that no one claims to understand properly. So I guess you consider the likes of Ed Witten and Lisa Randal to be the kind of people who willingly spend their time on "egregious" theories ?

I don't "have a problem" with any of the above theories, I just think they're more ad hoc than the dark matter theory, seeing that there's no observational support for them. Perhaps you've forgotten that this was what we were discussing...

What is this "attack the conventionial theories" comment referring to ? The idea of science is to question. In fact its the heart of the scientific process.

When did I say one shouldn't question? That's rather nasty of you to put words in my mouth.

So tell me how making things up purely to fit the data in cosmology, things that have no direct evidence whatsoever...

So yeah, that's where I'll stop you. You see, the alternative gravity theory you're referring to in the post up top is not only lacking direct evidence, it's lacking any evidence at all other than that for which it was created to explain. Dark matter has made many successful predictions, including the CMB power spectrum, large scale structure, and lensing results. Meanwhile, alternative theories (like MOND), have done no such thing. I'll grant that we're not yet at the stage where we can rule them out, but it seems to me to be considerably more ad hoc to "invent" a theory that has no basis other than...

let alone any kind of fundamental significant basis for their derivation, compare with a concept based on the broad horizon of cutting edge theoretical physics, derived from well established maths ? How do you weigh such things ?

As a scientist (that is, not a philosopher), I would give those things little or no weight. Math and the physical world are two different things and, as much as we'd like to evaluate our theories based on their "beauty", I'm strongly inclined to say that observational support should always be the trump card.

Your comments are as dubious as Garth's paper.

Now that was just mean. :tongue2:

You say "It makes no sense to attack the conventionial theories" ? Where would science be if we all followed your lead ?

Wow, that's one of the most egregious (in italics so that you can plug it into Webster's) examples of taking a quote out of context that I've ever seen. The quote was:

"...it makes no sense to attack the conventionial theories for "making things up to fit the data" when the alternative gravity models do so in an even more egregious fashion."

Of course you did qualify that..."

Oh, this is fun. Let me try. You said:

"Of course...conventionial theories...are as dubious as Garth's paper."

Mr. SimonA, it's so foolish of you to say that. You must not be very smart. Of course, you did qualify those things...

If you're such a SpaceTiger then I assume that along with you gutteral roar that shakes the ground - as all good tigers do, you will provide us all with a relatavisticaly invariant description of youngs slit experiment ?

I think I pushed a button...

 

[SimonA]

I don't "have a problem" with any of the above theories, I just think they're more ad hoc than the dark matter theory, seeing that there's no observational support for them. Perhaps you've forgotten that this was what we were discussing...

Not at all. Your original quote was "I would say that it's considerably less ad hoc to postulate a weakly-interacting particle than it is to postulate an alternative theory of gravity and/or extra dimensions". Why are extra dimensions "more ad hoc than the dark matter theory, seeing that there's no observational support for them" ? What is the "observational support" to suggest that the motion of galaxies can be explained by a four dimensional universe ?

When did I say one shouldn't question? That's rather nasty of you to put words in my mouth.

Well I was questioning and you replied;

I said it before and I'll say it again. If you're whining about why we haven't detected a particle that could be the dark matter, you need to stop and think about why it is that the particle would be dark and what implications that has for its detectability.

So yeah, that's where I'll stop you. You see, the alternative gravity theory you're referring to in the post up top is not only lacking direct evidence, it's lacking any evidence at all other than that for which it was created to explain. Dark matter has made many successful predictions, including the CMB power spectrum, large scale structure, and lensing results. Meanwhile, alternative theories (like MOND), have done no such thing.

Hey I'm no fan of MOND

I'll grant that we're not yet at the stage where we can rule them out, but it seems to me to be considerably more ad hoc to "invent" a theory that has no basis other than...

?

Que ? You tell me - what is the basis for extra dimensions ? Is it all a new concept lacking any kind of scientific rigour ? Did Einstein have the final world by considering a 4D reality ?

As a scientist (that is, not a philosopher), I would give those things little or no weight. Math and the physical world are two different things and, as much as we'd like to evaluate our theories based on their "beauty", I'm strongly inclined to say that observational support should always be the trump card.

Yes and it rained yesterday and I need rain to survive and so it must be me that causes it to rain... "Observational support" relies on correct interpretation.

Now that was just mean. :tongue2:

:uhh:

Wow, that's one of the most egregious (in italics so that you can plug it into Webster's) examples of taking a quote out of context that I've ever seen. The quote was:

"...it makes no sense to attack the conventionial theories for "making things up to fit the data" when the alternative gravity models do so in an even more egregious fashion."

Yes and that's the one I was replying to. I did say that you qualified it and dealt with that as well...

Oh, this is fun. Let me try. You said:

"Of course...conventionial theories...are as dubious as Garth's paper."

Mr. SimonA, it's so foolish of you to say that. You must not be very smart. Of course, you did qualify those things...

Mmm ... it must be that I'm not very smart. But even in my half-witted and troubled with the whole concept of reality state, I can still see that this is fun :)

I think I pushed a button...

Do you have a button that answers the question ? :tongue2:

 

[SpaceTiger]

Why are extra dimensions "more ad hoc than the dark matter theory, seeing that there's no observational support for them" ? What is the "observational support" to suggest that the motion of galaxies can be explained by a four dimensional universe ?

I'm not sure what you're asking for here. Einstein's theory (specifically, GR) is well supported by observation, but I'm sure you know that. If you're asking how we can be sure that there aren't extra dimensions outside of the limits of our experiments, then we can't be...but the burden of proof is not on the negative...

Well I was questioning and you replied;

None of which said or even implied that one shouldn't question convention.

Que ? You tell me - what is the basis for extra dimensions ? Is it all a new concept lacking any kind of scientific rigour ? Did Einstein have the final world by considering a 4D reality ?

It is lacking observational/experimental support, which relegates it to the status of an untested possibility. Mathematically, I don't doubt its rigor -- what I doubt is its correspondence to reality. But that's fine, prove me wrong. I have no objection to extra dimensions as a concept and if the observations turn out to support it, then I will as well. Until then, however, I will not lend it support simply based on a philosophical prejudice.

Yes and it rained yesterday and I need rain to survive and so it must be me that causes it to rain... "Observational support" relies on correct interpretation.

Absolutely right, but I hope that you can see how the two are intertwined. The beauty of, say, relativity is certainly amazing in of itself, but it was not that alone that made it one of the foundations of modern physics. The important thing was that it survived rigorous experimental testing. If, as in your example, I postulated that you caused it to rain yesterday, what testable predictions could I draw from that? How does that contribute to the general acceptance or rejection of the theory?

Yes and that's the one I was replying to. I did say that you qualified it and dealt with that as well...

The point is that it makes no sense to argue based on something that was taken out of context. No rational person would conclude that this quote:

"...it makes no sense to attack the conventionial theories for "making things up to fit the data" when the alternative gravity models do so in an even more egregious fashion."

means that I think science should be done without challenges to tradition.

Mmm ... it must be that I'm not very smart. But even in my half-witted and troubled with the whole concept of reality state, I can still see that this is fun :)

Yeah, I've been copying and pasting this into some of my AIM conversations. I love your bit about the "guttural roar". :rofl:

 

[SimonA]

I'm not sure what you're asking for here. Einstein's theory (specifically, GR) is well supported by observation, but I'm sure you know that. If you're asking how we can be sure that there aren't extra dimensions outside of the limits of our experiments, then we can't be...but the burden of proof is not on the negative...

Sure - of course the "burden of proof" in science must admit at least the same space to less fundamental issues that don't even provide any hope of providing answers across the broad reach of enquiry - such as "how can we be sure there are weakly interacting particles that exist within 3D space" ?

It is lacking observational/experimental support, which relegates it to the status of an untested possibility.

Now wait just one second (or more) there. How can you say that the heirarchy issue, the motion of galaxies, the accelerating expansion of the universe, quantum entanglement and inertia are "lacking observational/experimental support" ? I've deliberately turned what you said upside down. Its a question of epistemology in many ways.

Mathematically, I don't doubt its rigor -- what I doubt is its correspondence to reality. But that's fine, prove me wrong. I have no objection to extra dimensions as a concept and if the observations turn out to support it, then I will as well. Until then, however, I will not lend it support simply based on a philosophical prejudice.

Where is the "philosophical prejudice" ? The observations support extra dimensions far better than the standard 4D cosmology - unless you wish to invent particles like the Higgs Bosun that have never been seen and are unlikely to ever be seen. What gives mass to the Higgs Bosun itself ? Its all nonsense speculation "based on a philosophical prejudice".

Absolutely right, but I hope that you can see how the two are intertwined. The beauty of, say, relativity is certainly amazing in of itself, but it was not that alone that made it one of the foundations of modern physics. The important thing was that it survived rigorous experimental testing. If, as in your example, I postulated that you caused it to rain yesterday, what testable predictions could I draw from that? How does that contribute to the general acceptance or rejection of the theory?

Well it doesn't contribute anything because its nonsense - that was my point.

The point is that it makes no sense to argue based on something that was taken out of context. No rational person would conclude that this quote:

"...it makes no sense to attack the conventionial theories for "making things up to fit the data" when the alternative gravity models do so in an even more egregious fashion."

means that I think science should be done without challenges to tradition.

So what exactly is the non-alternative gravity model you are implicitly referring to ? Stretched spacetime

Yeah, I've been copying and pasting this into some of my AIM conversations. I love your bit about the "guttural roar". :rofl:

LOL

Its well past my bedtime ... :zzz:

 

[Chronos]

SpaceTigers reasoning is quite sound, IMO. I have some doubts about this

Okay so you notice that the motion of galaxies do not fit Newtonian predictions, because there is not enough mass to hold it all together at that velocity in Newtonian terms. So, following what was missing from Newtons predictions - namely mass - invent a kind of mass that interacts 'weakly' with baryonic (normal) matter. Then you look a little closer and all kinds of things do not match predictions. Then you spend millions to try to detect this invented concept and fail to do so. So in effect the theory of non baryonic matter contained within 3D space has so far failed to find empirical support.

There are more than a few reasons to suspect the existence of dark matter. While direct detection is still lacking, there is plenty of 'empirical' evidence favoring DM:

The Dark Side of the Universe
http://arxiv.org/abs/astro-ph/0508279

Cosmological Parameters and the case for Cold Dark Matter
http://arxiv.org/abs/astro-ph/9906277

More Evidence that Dark Matter Rules the Universe
http://www.space.com/scienceastronomy/dark_matter_021023.html

Science is not always about "follow[ing] empirical evidence". Ideally its about understanding empirical evidence.

I disagree. Science is all about following empirical evidence to its logical conclusion.

Einstein opened up a new level of understanding by considering time as a dimension.

That is a gross oversimplification, at best.

Surely there is room in your empirical world to consider there may be even more to it all ? According to E=mc^2 mass traveling at c becomes "energy". What does that mean ?

It means you do not understand basic relativity.

If you where 'watching' an electron, specifically in the orbital shell of an atom, and that electron received enough energy to jump to another shell, what would you say had happened to that electron ?

It obeyed the rules of quantum physics.

 

[SpaceTiger]

Sure - of course the "burden of proof" in science must admit at least the same space to less fundamental issues that don't even provide any hope of providing answers across the broad reach of enquiry - such as "how can we be sure there are weakly interacting particles that exist within 3D space" ?

You either ignored the part of my post where I gave you examples of evidence for the dark matter theory or hold much higher standards for those theories that don't align with your beliefs.

Now wait just one second (or more) there. How can you say that the heirarchy issue, the motion of galaxies, the accelerating expansion of the universe, quantum entanglement and inertia are "lacking observational/experimental support" ?

Those things were not predicted by your "extra dimensions" theory. In fact, extra dimensions are instead being used to try to explain those phenomena. You know, that ad hoc thing we were talking about...

Where is the "philosophical prejudice" ? The observations support extra dimensions far better than the standard 4D cosmology

Oh really? Please, link away.

Well it doesn't contribute anything because its nonsense - that was my point.

Apparently, you missed mine. Theories need to make predictions to be useful. The theory that you caused it to rain yesterday might lead to some predictions -- for example, a correlation between rain and your presence -- but they would be very quickly refuted by experiment. If theories are going to be of any scientific value, they must make predictions as well. It's not enough to go back to your unsolved problems and say, "Hey, if we introduce this length scale into the theory, we can explain this old observation!" Theories invoking extra dimensions are notoriously bad in this regard. Oh, and please don't quote me in your next post as having said, "Theories invoking extra dimensions are notoriously bad."

So what exactly is the non-alternative gravity model you are implicitly referring to ? Stretched spacetime

It's called general relativity.

 

[SimonA]

SpaceTigers reasoning is quite sound, IMO. I have some doubts about this There are more than a few reasons to suspect the existence of dark matter. While direct detection is still lacking, there is plenty of 'empirical' evidence favoring DM:

The Dark Side of the Universe
http://arxiv.org/abs/astro-ph/0508279

Mmmm - "empirical evidence" ? The three forms of 'evidence' quoted for the existence of dark matter are "(i) rotation curves, (ii) gravitational lensing, and (iii) hot gas in clusters". Where have I said anything that contradicts these anomalies ? This paper is pretty much just a rehash or summary of current standard theories and DOES NOT provide any substantial empirical evidence for WIMPs or MACHOs whatsoever.

Cosmological Parameters and the case for Cold Dark Matter
http://arxiv.org/abs/astro-ph/9906277

This one is great! Starts of with the assumption;

Most dark matter searches rely on a substantial fraction of the dark halo of our Galaxy being made up of cold dark matter, and that this cold dark matter consists of the neutralino.

Then discusses the possibility that the effects could be caused by baryonic matter, then openly admits the paper is based on the assumption of cold dark matter as a first starting point;

In this paper I review the current evidence on cosmological parameters and assess their relevance to cold dark matter searches.

And surprise surprise the final conclusion is;

it is likely that most of the dark matter in the halo of our Galaxy is in the form of cold dark matter.

More Evidence that Dark Matter Rules the Universe
http://www.space.com/scienceastronomy/dark_matter_021023.html

Yes this one has a good start;

Most astronomers already view dark matter as the only logical way to explain the orbits of stars and shapes of galaxies. Nobody has ever seen dark matter, and scientists don't know exactly what it is, but without it galaxies would fly apart.

Then goes on to discuss evidence of why MOND is not suitable to explain dark matter. Where on Earth do you see me supporting MOND ?

I disagree. Science is all about following empirical evidence to its logical conclusion.

You mean like the logical conclusion that if you chased a beam of light fast enough you would eventualy catch it up ?

That is a gross oversimplification, at best.

LOL

I wasn't trying to prove relativity from first principles! What is the "over.." part of your "..simplification" for ? Was it not one of the many fundamental changes Einstein made to scientific thought ? One of the most significant ?

It means you do not understand basic relativity.

Okay so in those particle accelerators you have particles that get heavier and heavier as they get closer to the speed of light. If you could (and we can't get anywhere near the amount of energy needed at present) get that particle to the actual speed of light (in a vacuum), what would happen to it according to "basic relativity" ?

It obeyed the rules of quantum physics.

http://phorum.internalspace.co.uk/smileys/wallbash.gif

 

[SimonA]

You either ignored the part of my post where I gave you examples of evidence for the dark matter theory or hold much higher standards for those theories that don't align with your beliefs.

There is no "evidence for the dark matter theory". The "dark matter theory" as you call it is a theory invented to explain anomalies that do not fit established and proven laws governing gravity related dynamics.

Those things were not predicted by your "extra dimensions" theory.

Hey ? What exactly is my "extra dimensions theory" ? I was stating a couple of anomalies that could potentially be explained by extra dimensions. Are you suggesting that WIMPs and MACHOs where derived from first principles rather than being a proposed plaster (come educated guess) for gaping holes that are the anomalies themselves.

In fact, extra dimensions are instead being used to try to explain those phenomena.

Yes exactly and they make a far better job of doing so than inventing imaginary particles like WIMPs or MACHOs.

Oh really? Please, link away.

Errr ... http://xxx.arxiv.org/PS_cache/astro-ph/pdf/0508/0508572.pdf ?

Apparently, you missed mine. Theories need to make predictions to be useful. The theory that you caused it to rain yesterday might lead to some predictions -- for example, a correlation between rain and your presence -- but they would be very quickly refuted by experiment. If theories are going to be of any scientific value, they must make predictions as well. It's not enough to go back to your unsolved problems and say, "Hey, if we introduce this length scale into the theory, we can explain this old observation!" Theories invoking extra dimensions are notoriously bad in this regard. Oh, and please don't quote me in your next post as having said, "Theories invoking extra dimensions are notoriously bad."

It quite an uphill strugle teaching myself all the different areas that are necessary to build a theory that has direct predictions. However I'm working from the ground upwards and the likes of string theory are as good as useless because of all their confusion related to the 'shape' of extra dimensions - something rediculous in itself. Lisa Randall, Nima Arkani-Hamed and now this new paper from Oxford are heading in a far more promising direction.

But a significant point is that current dark matter theories don't really make any specific predictions other than the anomalies they where designed to explain. I say 'really' because of course there is 'clumpiness' in the universe and galaxies are 'seeded' in some way etc. But those are models retro-fitted onto dark matter because its the current theory and so many smart people are using it as a basis for their models. That doesn't mean its the accurate description of what causes these anomalies or that extra dimensions could not describe those phenomena just as well. Certainly they are not of the calibre that relativity is when it makes predictions.

It's called general relativity.

Hey ? When have I disputed GR ?

Simon

 

[turbo]

Could it not be a field of particle/antiparticle pairs that is difficult to detect except locally (quantum vacuum field)?

No.

Wow! All of space is suffused with a vacuum field that is projected variously to hold 120 OOM expansive energy AND 120 OOM more gravitational equivalence than observed (that's some fine balance!), and somehow you know that this field cannot be gravitationally dynamic. Apparently, you are aware of some research that I have not been able to dig up. The authors must have avoided the use of words like "vacuum", "energy", "gravity", etc, or published in a language other than English.

When we need additional entities to keep GR predictive on galactic and larger scales, why not explore the entities that we know exist instead of chasing "pixie dust"? (Thanks, Garth!) We know that the quantum vacuum exists, although since it is the ground state of our universe, it is difficult to detect. If GR is going to be united with quantum theory, it will have to take this ground state into account.

 

[SpaceTiger]

There is no "evidence for the dark matter theory". The "dark matter theory" as you call it is a theory invented to explain anomalies that do not fit established and proven laws governing gravity related dynamics.

What you fail to understand is that those problems are solved consistently -- that is, all of the alternative gravity models have so far failed to explain all of these things at once without invoking a significant amount of dark matter. The initial introduction of dark matter was completely ad hoc, I agree, but from the "invented" solution to the rotation curve problem, we can construct models to predict other phenomena, such as the CMB power spectrum, and the distribution of large scale structure. There are still some kinks (such as the halo cusps mentioned in the "extra dimensions" paper), but they're in regimes that are hard to model, so they're not particularly surprising.

Hey ? What exactly is my "extra dimensions theory" ? I was stating a couple of anomalies that could potentially be explained by extra dimensions. Are you suggesting that WIMPs and MACHOs where derived from first principles rather than being a proposed plaster (come educated guess) for gaping holes that are the anomalies themselves.

Read above, cold dark matter was invented initially (of course) and succeeded in predicting other phenomena.

Yes exactly and they make a far better job of doing so than inventing imaginary particles like WIMPs or MACHOs.

...

http://xxx.arxiv.org/PS_cache/astro-ph/pdf/0508/0508572.pdf

The only thing the "extra dimensions" add, according to the paper you link, is a possible solution to the halo cuspiness problem. In every other respect, it is a dark matter theory.

But a significant point is that current dark matter theories don't really make any specific predictions other than the anomalies they where designed to explain. I say 'really' because of course there is 'clumpiness' in the universe and galaxies are 'seeded' in some way etc. But those are models retro-fitted onto dark matter because its the current theory and so many smart people are using it as a basis for their models. That doesn't mean its the accurate description of what causes these anomalies or that extra dimensions could not describe those phenomena just as well. Certainly they are not of the calibre that relativity is when it makes predictions.

You're right that the evidence is much more sketchy than for general relativity, I would not deny that -- and perhaps there exist reasonable alternative theories to explain the observations. All I'm saying is that none have yet come up.

Hey ? When have I disputed GR ?

Unless we're defining the bounds of Einstein's theory differently, adding extra dimensions (beyond 4-D spacetime) would be "disputing" GR.

 

[SimonA]

What you fail to understand is that those problems are solved consistently -- that is, all of the alternative gravity models have so far failed to explain all of these things at once without invoking a significant amount of dark matter. The initial introduction of dark matter was completely ad hoc, I agree, but from the "invented" solution to the rotation curve problem, we can construct models to predict other phenomena, such as the CMB power spectrum, and the distribution of large scale structure. There are still some kinks (such as the halo cusps mentioned in the "extra dimensions" paper), but they're in regimes that are hard to model, so they're not particularly surprising.

I do understand this but I think you're missing my argument. "Dark matter" used as a kind of like a place holder for 'something' that affects large scale gravitational dynamics in a way that has a weaker effect than baryonic matter is something I accept. What I'm contesting is this is non-baryonic matter that exists within 3D space. The same predictions, such as large scale structure, could equally be obtained from considerng that "dark matter" is in fact an 'equivalent' of matter in extra dimensions. Its just that non-baryonic dark matter within 3D space ('above' the 'zero point') is the asociation being made with this unknown element and so gets the credit for what is in effect a place holder for something that in not understood.

The only thing the "extra dimensions" add, according to the paper you link, is a possible solution to the halo cuspiness problem. In every other respect, it is a dark matter theory.

Et voila!

Unless we're defining the bounds of Einstein's theory differently, adding extra dimensions (beyond 4-D spacetime) would be "disputing" GR.

Well I'd prefer to suggest GR is relevant to a subsection of reality. Its kind of like considering the solar system as an isolated unit in terms of thermodynamics/entropy. It works most of the time but if you want to understand the full picture you really need to consider the input of gamma rays, the ouput of radiation from the sun etc...

 

[SpaceTiger]

I do understand this but I think you're missing my argument. "Dark matter" used as a kind of like a place holder for 'something' that affects large scale gravitational dynamics in a way that has a weaker effect than baryonic matter is something I accept. What I'm contesting is this is non-baryonic matter that exists within 3D space. The same predictions, such as large scale structure, could equally be obtained from considerng that "dark matter" is in fact an 'equivalent' of matter in extra dimensions. Its just that non-baryonic dark matter within 3D space ('above' the 'zero point') is the asociation being made with this unknown element and so gets the credit for what is in effect a place holder for something that in not understood.

Well, if you're not disputing dark matter, then your argument makes even less sense. The paper you link supports one of the popular non-baryonic particle dark matter candidates -- which was no less a "place-holder" than the others -- and then simply adds another detail, extra dimensions, to the dark matter theory. In fact, this particle is even weakly interacting. The only reason it's not called a WIMP is that it's not massive.

Well I'd prefer to suggest GR is relevant to a subsection of reality. Its kind of like considering the solar system as an isolated unit in terms of thermodynamics/entropy. It works most of the time but if you want to understand the full picture you really need to consider the input of gamma rays, the ouput of radiation from the sun etc...

I understand how those things work. I think very few physicists believe that GR is valid in all regimes.

 

[SimonA]

Well, if you're not disputing dark matter, then your argument makes even less sense. The paper you link supports one of the popular non-baryonic particle dark matter candidates -- which was no less a "place-holder" than the others -- and then simply adds another detail, extra dimensions, to the dark matter theory. In fact, this particle is even weakly interacting. The only reason it's not called a WIMP is that it's not massive.

Of course its "weakly interacting" - whatever dark matter is it interacts with normal matter gravitationally in a far 'weaker' way than normal matter does with itself.

The reason I quoted that study was that it involves extra dimensions and can explain the data better than the basic 4D theories (in terms of galactic core density) - in response to your request to "link away" when I suggested as much. There are of course many different theories on extra dimensions and the ideas are changing fairly rapidly.

My own theory would be more that 3D space is a surface phenomena, with time continuing to be an axis through it all. Perhaps the closest to this is Lisa Randalls 'sinkhole' space;

More recently, with Karch, I studied a
theory that is in some ways even more surprising
(13). In that theory, space looks four
dimensional on the brane and at some distance
away from the brane. This is because
there is again a mode that looks like a fourdimensional
graviton. However, the majority
of the space is not sensitive to the force
mediated by this four-dimensional graviton,
because it only couples in a small portion of
the space. The part of the space where the
trapped mode does not couple sees itself as
five dimensional. This leads one to consider
the possibility of gravitational “islands”; the
dimensionality of space you think you see
depends on where you are in the bulk. The
brane can be considered to be a four-dimensional
sinkhole. This is truly a possibility of
nature; we only ever see a finite region of
space, even with cosmological observations.

http://www.physics.harvard.edu/Sciencearticle.pdf

But like I said I'm not claiming that any of the extra dimension theories are correct at present. I'd be more confident in predicting that the Higgs Bosun will never be found no matter what its ever changing predicted mass is. But I do rekon that dark energy will not be properly understood without considering more than three spatial dimensions.

Simon

 

[Garth]

But like I said I'm not claiming that any of the extra dimension theories are correct at present. I'd be more confident in predicting that the Higgs Bosun will never be found no matter what its ever changing predicted mass is. But I do rekon that dark energy will not be properly understood without considering more than three spatial dimensions.

Simon

As an old navy man the idea of hunting for a Bosun called Higgs sounds familiar! However the fact that the search for a Higgs boson has drawn a blank so far begins to stretch the credibility of the standard cosmological model. With any of these hypotheses the need to be able to verify and falsify in a local laboratory with known experimental constraints is paramount.
How do you falsify either Inflation or higher dimension theories with 'sinkhole space' with clapping branes?

At least SCC, which as you know does not need to invoke inflation, non-baryonic DM or DE will be falsified, or otherwise , in the next few months.

Garth

 

[SpaceTiger]

Of course its "weakly interacting" - whatever dark matter is it interacts with normal matter gravitationally in a far 'weaker' way than normal matter does with itself.

The reason I quoted that study was that it involves extra dimensions and can explain the data better than the basic 4D theories (in terms of galactic core density) - in response to your request to "link away" when I suggested as much.

I understand why you posted the article, but what completely befuddles me is your apparent criticism of the standard dark matter theory. At the beginning, I was under the impression that you didn't believe dark matter at all and, reading back over the posts, I still think that was a reasonable interpretation of what you wrote, but I'll admit you didn't say it outright. I assume Chronos interpreted you this way as well, since he linked a bunch of papers supporting the dark matter theory (and you argued against them, for some reason). However, you did say several things about how cold dark matter hadn't been directly detected and how WIMPs had been "invented" to fit the data. This is just as true for axions, the particles supported by the paper you linked, as for neutralinos or for any of the other dark matter candidates. In fact, a lot of those dark matter detection experiments you were criticizing are looking specifically for axions, one example of cold dark matter.

Perhaps the source of the misunderstanding can be elucidated with this quote from one of your old posts:

Are you suggesting that WIMPs and MACHOs where derived from first principles rather than being a proposed plaster (come educated guess) for gaping holes that are the anomalies themselves?

The term "WIMP" means simply "weakly interacting massive particle" and does not refer to a specific particle, but is rather a generic term for something that might fit observations of dark matter. It is completely standard within dark matter theory to assume that the dark matter particles are a product of unknown or unconfirmed physics. As for "MACHO", that's simply a MAssive Compact Halo Object and has nothing to do with particle physics.

 

[SimonA]

As an old navy man the idea of hunting for a Bosun called Higgs sounds familiar!

I'm off next week to captain my first boat so I need to brush up on these nautical terms! Although its only a 30 footer and as the only remaining member of the crew I guess my girlfriend will be the bosun - more of a bosun bird than a higgs bosun :)

However the fact that the search for a Higgs boson has drawn a blank so far begins to stretch the credibility of the standard cosmological model.

Yes I'm no fan of the whole concept of the Higgs field. I have to admit I haven't really got my head around what you are proposing - it really takes a lot of effort to fully consider a theory. I'm currently working with the Haish model of mass/inertia - which is consistent with GR - but considering that the Zero Point is like an edge of 3D space.

With any of these hypotheses the need to be able to verify and falsify in a local laboratory with known experimental constraints is paramount.
How do you falsify either Inflation or higher dimension theories with 'sinkhole space' with clapping branes?

What is the sound of one brane clapping ?

Simon

 

[SimonA]

I understand why you posted the article, but what completely befuddles me is your apparent criticism of the standard dark matter theory. At the beginning, I was under the impression that you didn't believe dark matter at all and, reading back over the posts, I still think that was a reasonable interpretation of what you wrote, but I'll admit you didn't say it outright. I assume Chronos interpreted you this way as well, since he linked a bunch of papers supporting the dark matter theory (and you argued against them, for some reason). However, you did say several things about how cold dark matter hadn't been directly detected and how WIMPs had been "invented" to fit the data. This is just as true for axions, the particles supported by the paper you linked, as for neutralinos or for any of the other dark matter candidates. In fact, a lot of those dark matter detection experiments you were criticizing are looking specifically for axions, one example of cold dark matter.

Okay maybe I wasn't clear - most of my early posts where late last night - well early in the morning. Is it clearer if I say that its all the current dark matter candidates I'm critical of - not the fact that there is an issue with the motion of galaxies in Newtonian terms that points to something that plays an important role in other aspects of the universe such as large scale structure/clumpiness, seeding of galaxies etc. The paper I linked to could have been based on bananas as the dark matter candidate - its the fact that adding extra dimensions to the standard dark matter theories produces more accurate predictive power.

I was trying not to get too far into this because its obviously wildly speculative but it may help you understand where I'm coming from (or not :tongue2: ) What I'm thinking about is considering 3D space as one 'super-dimension', with there being several of these (currently I'm assuming 4) that sit consecutively, each having mirror symmetry to its neighbour. Each of these have a substance to them (as 3D space does) and an axis of time, and each has its own equivalence to energy/matter. In the first superdimension (3D space), the Zero Point is one 'edge' if you like, the other is defined by c. For me it is these dimensions that 'weakly interact' in gravitational terms. So the motion of galaxies is a bit like looking at a whirlpool on the surface of the water (in 2D) and being confused that its edges are moving so fast. A full understanding in 3D of course explains this motion in a natural way. The maths has for a long time pointed towards a multi-dimensional universe. The theories with regards to this have been mostly speculation, but the maths itself seems fairly clear from several areas - be it M Theory, quasi-crystals, the hierarchy problem etc etc. So which is the more reasonable solution to all these missing parts of the universe according to CMB ? To continue on assuming a 4D universe with plenty of anomalies that require the 'invention' new particles that just happen to behave differently from all the matter we can detect with our instruments based in space-time - or to look again at the fundamental basis of our theories in terms suggested by the maths in many areas ?

I suspect I know what your answer will be - and you may decide I'm crazy if you hadn't already - but hopefully you're less "befuddled" about where I'm coming from now anyway :)

Simon

 

[SpaceTiger]

Okay maybe I wasn't clear - most of my early posts where late last night - well early in the morning. Is it clearer if I say that its all the current dark matter candidates I'm critical of - not the fact that there is an issue with the motion of galaxies in Newtonian terms that points to something that plays an important role in other aspects of the universe such as large scale structure/clumpiness, seeding of galaxies etc. The paper I linked to could have been based on bananas as the dark matter candidate - its the fact that adding extra dimensions to the standard dark matter theories produces more accurate predictive power.

Then we may have no disagreement. Although I'm far from simply accepting the paper as truth, I certainly view it as an intriguing possibility. As for your theory, it's hard to judge based only on what you've described, but nothing immediately jumps out at me as being inconsistent with observations. I wouldn't, however, consider it very surprising that adding extra dimensions (or any other extra free parameters) makes a theory more consistent with data.

I may also have given a false impression of my views of alternative gravity. In fact, I don't think GR is the whole picture and I do think we'll have to alter gravity eventually. However, I get a bit irked with people who simply assume the truth of theories that have a lot of mathematical elegance. There are so many cases in the history of science where we've gone horribly wrong by trying to force our philosophical prejudices on nature. Geocentric models of the solar system, creationism, "ether", steady-state universes...the list goes on and on. I'm not saying this to accuse you of anything, just to explain why I'm so dubious about things like "extra dimensions". However, I would be committing the same sin to reject these theories outright, so let's just agree to withhold judgement for the time being.

 

[SimonA]

I may also have given a false impression of my views of alternative gravity. In fact, I don't think GR is the whole picture and I do think we'll have to alter gravity eventually. However, I get a bit irked with people who simply assume the truth of theories that have a lot of mathematical elegance. There are so many cases in the history of science where we've gone horribly wrong by trying to force our philosophical prejudices on nature. Geocentric models of the solar system, creationism, "ether", steady-state universes...the list goes on and on.

Yes I agree completely - that's what the scientific process is all about

Although of course some argue that the "ether" isn't completely dead - like Maurizio Consoli

However, I would be committing the same sin to reject these theories outright, so let's just agree to withhold judgement for the time being.

Yes I don't think we have any fundamental disagreement - I just have some further maths to learn in areas from cosmology to QM before I can put anything forward for serious consideration.

Simon

 

[Garth]

There are many cases of the present LCDM model being verified or confirmed by observations, but the trick is to find ways that this model and any others might be falsified.

You can always add another 'epicycle' to keep a theory on track, then mathematical and conceptual elegance and beauty may play an important part in identifying the way to go.

Garth

 

[setAI]

poor little Earth monkeys-

dark matter= computronium (^___^)

 

[SimonA]

There are many cases of the present LCDM model being verified or confirmed by observations, but the trick is to find ways that this model and any others might be falsified.

Yes and that's the scientific process. I'd prefer to employ whatever common sense I have left at my disposal to understand the reality - and then subject it to any kind of falsification that relies on truth and reality and the likes. If its wrong I'm the first person to want to know !

You can always add another 'epicycle' to keep a theory on track, then mathematical and conceptual elegance and beauty may play an important part in identifying the way to go.

Poor old Ptolemy. At least he knew the world was round and not flat. Some people still find the idea that he was mainstream educated thought in the time of Columbus controversial...

 

[setAI]

um simon- it was just a little illuminating and interesting [to me] joke [ a natural idea based on the ideas in my sticky thread ]- and you are clearly an obsessive- there is no excuse for your offensive personal attacks-

if you actually did read the essays on my website and my post history here you will see that I do contribute mature and insightful ideas to this forum and that my contributions are generally well reguarded by the members and mods even when I go a little off the deep end [because I do it honestly and never allow myself to get fully suckered by crack-pottery- I'm sure that Warren would have disapproved of my comment- but ultimately it WAS just a joke]- you need to step back and put away the straw-man

and I expect an APOLOGY