Split Thread Michael Mozina's thread on Dark Matter, Inflation and Cosmology

Tubbythin said:
No it couldn't. Most forms interact electromagnetically and therefore are not dark.
Click to expand...

Before I tackle the rest of the post I wanted to point out something that seems to be different between us on this topic. When you say "dark", I automatically think "limits of our technology", as in "we can't see very far with our current technology". I'm not sure of your age, and this could be an age related bias because "dark matter" was pretty much equated with MACHO brands of "dark matter" when I was first introduced to the concept. It's since "morphed" into "exotic matter" with supernatural properties.

You seem to be suggesting that the just because we can't "see" it from here, it must not interact electromagnetically in it's local environment. I disagree with that concept entirely. A little dust and enough distance, and there's just no way our technology will pick up photons from here. I don't think you can just jump to the conclusion that if we can't see photons from it from million if not billions of light years away, it must not interact electromagnetically. That seems like an extreme claim considering the limits of our current technologies.
 
Reality Check said:
I read about Kaluza–Klein cosmologies. But you really need to tell us which Kaluza–Klein model you are thinking of.
Click to expand...

If you have read their work then you should realize by now that a homogeneous layout of matter is simply a given in their model. Inflation has no relevance in determining homogeneity in such a model. If we change the original parameters (in the beginning was.....), all of your so called evidence for inflation goes up in smoke.
 
Michael Mozina said:
Sure. Would you agree that a proponent of a new particle of mass has the burden of proof to physically demonstrate that it actually exists in nature and has all of the ascribed "properties" that it is claimed to have?
Click to expand...
Yes.

Well, if you read those links carefully, you'll notice that they found some of that missing mass. Evidently we underestimated the amount of mass in the black hole at the core of a galaxy by up to a factor of 4. We found there is substantially more 'dust" than we first believed and therefore the galaxies are twice as bright as we first thought. That is certain to affect the mass estimates. We also evidently underestimated the number of smaller stars in a galaxy by several multiples.
Click to expand...
I understand that the "missing mass" is still quite substantial. Would it matter much if the estimate of dark matter were reduced by, say, one half?

Now, what "proof' do you or I have that any of that "missing matter" comes from an exotic form of matter?
Click to expand...
I understand that the case for ordinary matter to account for the missing mass is a difficult case to make (can you show otherwise?), consequently, the theory involves the possible existence of some form of mass not yet understood. Why is that so far fetched?


I didn't say it "could not be" the cause, I said that there are more likely causes. Surely you can appreciate that position?
Click to expand...
I can, but the problem is that observations show that the causes you feel are more likely -- actually appear to be less likely
 
Michael Mozina said:
If you have read their work then you should realize by now that a homogeneous layout of matter is simply a given in their model. Inflation has no relevance in determining homogeneity in such a model. If we change the original parameters (in the beginning was.....), all of your so called evidence for inflation goes up in smoke.
Click to expand...
What work by Kaluza–Klein? I hope that you do not mean every paper that each author ever wrote and every paper and book that has ever been written on the topic :eye-poppi !

Which specific model are you tallking about?

How about a link to the source for this assertion?

Inflation is not only used to explain that the universe is homogeneous.
It also expalins that the universe is flat.
It also predicts that the large scale structure of the universe should have a certain distribution. This has been measured and agrees with the prediction.


ETA:
Much of brane cosmology theory (what you call the Klein model) does deal with homogeneous AdS spaces but these are quite a few papers dealing with anisotropic spaces.

ETA2:
I wonder what this paper is talking about (I do not have access to the paper itself).
D-term inflation in D-brane cosmology

ETA3:
Of the brane cosmologies, the ekpyrotic universe is the one that is most often cited as replacing the inflation part of the consensus cosmology. The standard big bang Lambda-CDM model of our universe remains as an appropriate description up to very early times in that model.
 
Last edited:
Tubbythin said:
Well I suppose they are made up in the sense that any theory is made up. But your Michaeltons were something you made up on the spot.
Click to expand...

FYI, that's my primary complaint with Guth's inflation. It has that "made up on the spot" feel to it, especially since he's intentionally curve fitting it's properties (and the properties of space) to match a homogeneous fit when he's done. The only difference is he didn't call it an an Alanton. :)

I do have some some sympathy for your argument about SUSY theory since it's roots go back to Dirac's equations and I do see a logical progression from concepts with historical roots. On the other hand, nature is not always kind to mathematical concepts.

It seems to me that our primary difference is that you seem to have much more confidence in our current mass estimation techniques and our current technologies than I do. I see these things as a bit like 'limited/primitive tools' that are 'improving with time'.

We are only now starting to identify smaller planets with our current technologies. Until a decade or so ago, we really couldn't even directly confirm their existence, and even today we do not directly observe them in most instances, just their effect on the light from the parent star.

I simply don't think we have the technology or correct enough models to leap to the conclusion that the 'dark matter' is necessarily related to "exotic matter'. That seems to be our fundamental difference as I see things.
 
Michael Mozina said:
FYI, that's my primary complaint with Guth's inflation. It has that "made up on the spot" feel to it, especially since he's intentionally curve fitting it's properties (and the properties of space) to match a homogeneous fit when he's done.
Click to expand...
Then your primary complaint is with the scientific method. Every scientific theory begins by matching the existing observatons. The universe is observed to be homogeneous. If inflation did not produce a homogeneous universe then it would be wrong.
 
Perpetual Student said:
Yes.
Click to expand...

Alright, then the best you might hope for at the moment with exotic matter is a "draw" with any other "dark matter" theory because it lacks empirical support. Even if LHC finds some type of unexpected form of matter, will it actually have the "properties" (like longevity) that astronomers expect? What are the odds?

I understand that the "missing mass" is still quite substantial. Would it matter much if the estimate of dark matter were reduced by, say, one half?
Click to expand...

It wouldn't matter much to me right now whether it is substantial or less substantial, I would still tend to favor any theory that did not evoke a new entity. Just out of curiosity, would it matter to you?

From my perspective that 'substantial' part is directly related to our own human ignorance. Yes, it could be related to an exotic particle, or it could just be there are currents in space, and rotational patterns are affected by them. It could be that here is more dust, more suns, more of everything than we imagine. I just don't have any physical evidence that exotic forms of matter or necessary or empirically justified.

I understand that the case for ordinary matter to account for the missing mass is a difficult case to make (can you show otherwise?),
Click to expand...

Well, ok, but those recent papers suggest that we are making steady progress in identifying that missing mass. If galaxies are really twice as bright as believed, then we can easily double the point sources and improve our mass estimates accordingly. Likewise we can fill in some of that missing mass with black holes (it's a small amount, but hey it all counts). We evidently have been grossly underestimating the number of small stars compared to bigger (more visible) stars in a given galaxy. All these things add up and our technologies are improving. I'm optimistic that our technologies will eventually help us to figure it out, and so far I see no reason to assume our missing mass comes in any exotic forms.

consequently, the theory involves the possible existence of some form of mass not yet understood. Why is that so far fetched?
Click to expand...

We'll have to discuss "probability" here sooner or later I suppose. I don't know. Define "far fetched". From my perspective it seems "far fetched" especially in light of all those recent "discoveries" I cited earlier. It seems like we still have a lot to learn about the layout of matter in a galaxy, and even our own solar system. It just seems premature from my perspective to "assume" that exotic forms of matter are necessary. Maybe we just need to launch the James Webb telescope and we may find a lot more mass.

I can, but the problem is that observations show that the causes you feel are more likely -- actually appear to be less likely
Click to expand...

Those "observations" seem pretty "primitive" to me considering we have a hard time directly observing an Earth sized planet in our own galaxy, let alone one that is millions or billions of light years away.

There does seem to be a "subjectivity factor" here between the concept of a "better" theory. I'm not quite sure how to bridge that gap given the limits of our current technologies.
 
Last edited:
Michael Mozina said:
Well, ok, but those recent papers suggest that we are making steady progress in identifying that missing mass. If galaxies are really twice as bright as believed, then we can easily double the point sources and improve our mass estimates accordingly.
Click to expand...
Wrong. If galaxies are really twice as bright as believe then there is about 20% more mass in galaxies.

Michael Mozina said:
Likewise we can fill in some of that missing mass with black holes (it's a small amount, but hey it all counts).
Click to expand...
It is a really really small amount - For example Sagittarius A* has a mass of ~4.1 x 106 solar masses. The Milky Way has a mass of 5.8 x 1011.
This is 0.001%.

Michael Mozina said:
We evidently have been grossly underestimating the number of small stars compared to bigger (more visible) stars in a given galaxy.
Click to expand...
No we have not.
We evidently have been grossly underestimating the number of small stars compared to bigger (more visible) stars in a given type of galaxy.

Michael Mozina said:
All these things add up and our technologies are improving.
Click to expand...
Not really.
Before:
  • 0.4% of the mass of the universe is measured to be in stars and galaxies.
  • 3.6% of the mass of the universe is measured to be in gas, mostly the intracluster medium.
  • 96% of the mass of the universe is unaccounted for.
Now:
  • 0.4801% of the mass of the universe is measured to be in stars and galaxies.
  • 3.6% of the mass of the universe is measured to be in gas, mostly the intracluster medium.
  • 95.9199% of the mass of the universe is unaccounted for.
 
I believe faith is different than trust. I don't have "faith" in science, I trust it because it has a proven track record and makes every reasonable attempt to verify itself. And if it's wrong, it usually will get around to correcting itself. Thus, it has earned my trust. Faith, on the other hand, is a leap of thought not based on anything other than belief.
 
Michael Mozina said:
Well, ok, but those recent papers suggest that we are making steady progress in identifying that missing mass. If galaxies are really twice as bright as believed, then we can easily double the point sources and improve our mass estimates accordingly. Likewise we can fill in some of that missing mass with black holes (it's a small amount, but hey it all counts). We evidently have been grossly underestimating the number of small stars compared to bigger (more visible) stars in a given galaxy. All these things add up and our technologies are improving. I'm optimistic that our technologies will eventually help us to figure it out, and so far I see no reason to assume our missing mass comes in any exotic forms.
Click to expand...
A little more on this.
I believe that you pointed out this preprint:
Dark Matter: The evidence from astronomy, astrophysics and cosmology
You may want to read sections 9 and 10. These give methods of determining the density of matter in the universe (no calculation of galactic mass need apply :)).
  • Analysis of the WMAP data tells us that
    • the total mass density parameter is ~0.26
    • baryonic density parameter is ~0.04. This agrees with the amount of visible matter that astronomers calculate in other techniques.
    • thus the density of dark matter in the universe is ~0.22.
  • Baryonic acoustic oscillations (BAO) tell us that
    • the total mass density parameter is ~0.26.
    • the ratio between the baryonic and total density parameters at very large scales is 0.18 +/- 0.04. So the baryonic density parameter is ~0.05 +/- 0.01.
The BAO results mean that astronomers have found about 80% of the baryonic matter in the universe (at least 66% if we use the pessimistic limit of the result).

However that is moot because the above results give a limit on the density of baryonic matter in the universe of < 6%. That means that ~94% of the universe is dark matter and dark energy.
 
Michael Mozina said:
That's hard to classify since there's evidently no "control mechanism" of any sort in some detection methods I've read. Personally I would think that the LHC is a 'better' type of 'experiment' IMO.
Click to expand...

Huh!!?!
Dark matter detection experiments are some of the most finely controlled experiments man has ever done.
 
Michael Mozina said:
Before I tackle the rest of the post I wanted to point out something that seems to be different between us on this topic. When you say "dark", I automatically think "limits of our technology", as in "we can't see very far with our current technology". I'm not sure of your age, and this could be an age related bias because "dark matter" was pretty much equated with MACHO brands of "dark matter" when I was first introduced to the concept. It's since "morphed" into "exotic matter" with supernatural properties.

You seem to be suggesting that the just because we can't "see" it from here, it must not interact electromagnetically in it's local environment. I disagree with that concept entirely. A little dust and enough distance, and there's just no way our technology will pick up photons from here. I don't think you can just jump to the conclusion that if we can't see photons from it from million if not billions of light years away, it must not interact electromagnetically. That seems like an extreme claim considering the limits of our current technologies.
Click to expand...

We don't need to look at galaxies billions of light years away. We can look at our own.
 
Michael Mozina said:
Before I tackle the rest of the post I wanted to point out something that seems to be different between us on this topic. When you say "dark", I automatically think "limits of our technology", as in "we can't see very far with our current technology". I'm not sure of your age, and this could be an age related bias because "dark matter" was pretty much equated with MACHO brands of "dark matter" when I was first introduced to the concept. It's since "morphed" into "exotic matter" with supernatural properties.
Click to expand...

Oh I dunno.

Dark matter really just refers to the fact that it is difficult or not possible to detect from emitted radiation (be that in the visible region or otherwise).

In that sense (as used by practically everyone) it is a collection of quite a wide variety of objects and things.

It has never really stood for any one thing in particular, it has always been a case of many scientists proposing many mechanisms, each of which could account for a certain percentage of the dark matter.

It is good that you bring this up though, I find when teaching that small matters like this can make an incredible difference when scientists attempt to communicate (often difficult) concepts to the general public.

Michael Mozina said:
You seem to be suggesting that the just because we can't "see" it from here, it must not interact electromagnetically in it's local environment. I disagree with that concept entirely. A little dust and enough distance, and there's just no way our technology will pick up photons from here. I don't think you can just jump to the conclusion that if we can't see photons from it from million if not billions of light years away, it must not interact electromagnetically. That seems like an extreme claim considering the limits of our current technologies.
Click to expand...

Undetectable doesnt have to mean the photons come from the object and stream direct into your eyes.

If a star blasts away vast chunks of surrounding material and we detect that "unusual change" in the surrounding material, without ever having directly observed photons coming straight from the star itself, does that count as a "detection".

Again, this seems to be an issue of the technical use of the word, perhaps we as scientists should stop and consider more carefully how our explanations can be misinterpreted.




Michael Mozina said:
If you have read their work then you should realize by now that a homogeneous layout of matter is simply a given in their model. Inflation has no relevance in determining homogeneity in such a model. If we change the original parameters (in the beginning was.....), all of your so called evidence for inflation goes up in smoke.
Click to expand...

When you say a given, do you mean it "pops out" as a direct result or do you mean it is a required assumption in order for the model to work?
 
Michael Mozina said:
From my perspective that 'substantial' part is directly related to our own human ignorance. Yes, it could be related to an exotic particle, or it could just be there are currents in space, and rotational patterns are affected by them. It could be that here is more dust, more suns, more of everything than we imagine. I just don't have any physical evidence that exotic forms of matter or necessary or empirically justified.



Well, ok, but those recent papers suggest that we are making steady progress in identifying that missing mass. If galaxies are really twice as bright as believed, then we can easily double the point sources and improve our mass estimates accordingly. Likewise we can fill in some of that missing mass with black holes (it's a small amount, but hey it all counts). We evidently have been grossly underestimating the number of small stars compared to bigger (more visible) stars in a given galaxy. All these things add up and our technologies are improving. I'm optimistic that our technologies will eventually help us to figure it out, and so far I see no reason to assume our missing mass comes in any exotic forms.



We'll have to discuss "probability" here sooner or later I suppose. I don't know. Define "far fetched". From my perspective it seems "far fetched" especially in light of all those recent "discoveries" I cited earlier. It seems like we still have a lot to learn about the layout of matter in a galaxy, and even our own solar system. It just seems premature from my perspective to "assume" that exotic forms of matter are necessary. Maybe we just need to launch the James Webb telescope and we may find a lot more mass.
Click to expand...

Can I ask what specifically is wrong then with over 40 years of detailed observations?

http://www.astr.ua.edu/keel/galaxies/darkmatter.html

and can I ask how 'long' anyone needs to wait before we give up searching for mass that isnt there?

I mean, when does this theory become accepted (or not)? How long do you look? When do you decide that the framework that couples such a bewildering array of scales and items across the whole of astrophysics is actually on very dodgy ground and at what point do you bring the whole thing crashing to the ground to start afresh with ... well... nothing?

I mean if we were discussing a very specific point in astrophysics or a very tenuous branch of physics then I would heartily agree.

But being as we talking about millions of man hours of observation, theory, prediction, experimentation, confirmation and development across hundreds of branches of physics then I am not so sure that we should give it all up on the say so of an idea that is so vague it would not even make it as a GCSE coursework.

Or am I being unfair?
 
Michael Mozina said:
Before I tackle the rest of the post I wanted to point out something that seems to be different between us on this topic. When you say "dark", I automatically think "limits of our technology", as in "we can't see very far with our current technology". I'm not sure of your age, and this could be an age related bias because "dark matter" was pretty much equated with MACHO brands of "dark matter" when I was first introduced to the concept. It's since "morphed" into "exotic matter" with supernatural properties.

You seem to be suggesting that the just because we can't "see" it from here, it must not interact electromagnetically in it's local environment. I disagree with that concept entirely. A little dust and enough distance, and there's just no way our technology will pick up photons from here. I don't think you can just jump to the conclusion that if we can't see photons from it from million if not billions of light years away, it must not interact electromagnetically. That seems like an extreme claim considering the limits of our current technologies.
Click to expand...
Adding onto Tubbythin reply:
To scientists the "dark" part of dark matter means that it cannot be detected electromagnetically. There is a technological limit to the detection in that
  • We cannot detect every part of the electromagnetic spectrum. For example radio waves with wavelengths longer than the width of the solar system. We can detect light expected from any "non-dark" matter interactions such as the X-rays that it would emit in colliding galaxay clusters.
  • Detectors need long exposures to deteect far objects, e.g. the Hubble telescope was points at one spot in the sky for days to get the deep field images.
But there is a lot of dark matter and it is everywhere, including the Milky Way and here in the Solar System. If it was not dark then it would be easier to detect than the interstellar medium.
If it was not dark then we would already be detecting it here on Earth in the existing dark matter detection experiments.
 
Tubbythin said:
Huh!!?!
Dark matter detection experiments are some of the most finely controlled experiments man has ever done.
Click to expand...

If you're referring to the LHC experiments I agree. If you're referring to other underground observations which seem to lack control mechanisms, I would tend to disagree. There is no control mechanism of any sort in such detection methods.
 
Reality Check said:
MM: You need to learn some astronomy:
  • The mass contained in supermassive black holes is a small proportion of the mass of their host galaxy.
    For example Sagittarius A* has a mass of ~4.1 x 106 solar masses. The Milky Way has a mass of 5.8 x 1011. You do the math.
Click to expand...


  • I think (though I haven't thought this through rigorously) its actually worse than that.

    For a circular orbit around a central, spherically symmetric mass we have:

    GMmr-2 = mv2r-1Hence we have:
    v = (GMr-1)1/2.

    That is the rotational velocity decreases as r1/2.
    Now your typical spiral galaxy is made up of different bits - typically a central black hole, a bulge around this and then the disk bit. But the rotation curves are seen to be flat - that is v is roughly independent of radial distance from the centre. So, as far as I can tell, increasing the mass of the black hole at the centre actually increases (by a miniscule amount) the discrepancy between theory and observation!
 
Last edited:
DazzaD said:
Can I ask what specifically is wrong then with over 40 years of detailed observations?
Click to expand...

Keep in mind that I have no doubt that there is "missing mass" in these galaxies that is not properly accounted for in our mass estimation techniques. In other words, those 40 years of observations should be telling us that our galaxy mass estimate models are almost if not completely useless.

There could be an age bias here to consider as I am over 50 years old now. When I was taught the concept of "dark matter" as it relates to 'missing mass" in astronomy, it was more or less equated with MACHO brands of 'dark matter'. We understood then that our technologies were still very limited (still are limited) and there was just no way to know what we could not yet "see" with our limited technology.

The concept however has "morphed", particularly over the past 10 years or so, from being "openly ignorant" about what that missing mass might be made of, toward insisting that the vast majority of that mass must be composed of some type of exotic matter, typically WIMPS or axions. That change toward exotic matter, and preference for exotic matter is A) premature IMO, and B) extreme in terms of the amount they discuss, particularly given the limits of our current technologies.

I mean, when does this theory become accepted (or not)? How long do you look? When do you decide that the framework that couples such a bewildering array of scales and items across the whole of astrophysics is actually on very dodgy ground and at what point do you bring the whole thing crashing to the ground to start afresh with ... well... nothing?
Click to expand...

In terms of astronomy, I would say that when more than 50% of a given theory is based upon mythical forms of matter and energy, it's probably time to scrap it and try again. :)

What do we really know about space in your opinion? Humans as a species haven't even traveled outside of our own solar system yet. We haven't even physically (as physical beings) stepped foot on another planet yet.

I mean if we were discussing a very specific point in astrophysics or a very tenuous branch of physics then I would heartily agree.

But being as we talking about millions of man hours of observation, theory, prediction, experimentation, confirmation and development across hundreds of branches of physics then I am not so sure that we should give it all up on the say so of an idea that is so vague it would not even make it as a GCSE coursework.

Or am I being unfair?
Click to expand...

I don't think you're being unfair, perhaps you just don't quite understand my position on this topic. I'm inclined to believe that those 40 years of observations demonstrate that our technologies are still limited but improving all the time, and our mass estimation techniques of galaxies needs a lot of work. :)
 
Michael Mozina said:
If you're referring to the LHC experiments I agree. If you're referring to other underground observations which seem to lack control mechanisms, I would tend to disagree. There is no control mechanism of any sort in such detection methods.
Click to expand...

WHAT??? Why do you think these experiments are hundreds of metres underground. For fun? Why do you think they use germanium detectors that are cooled to a fraction above absolute zero? Why do you think they only use lead shielding that has been salvaged from old, deep shipwrecks?
 
Michael Mozina said:
FYI, that's my primary complaint with Guth's inflation. It has that "made up on the spot" feel to it, especially since he's intentionally curve fitting it's properties (and the properties of space) to match a homogeneous fit when he's done. The only difference is he didn't call it an an Alanton. :)
Click to expand...
Well a theory that didn't match prior observations would be a bit useless wouldn't it?

I do have some some sympathy for your argument about SUSY theory since it's roots go back to Dirac's equations and I do see a logical progression from concepts with historical roots. On the other hand, nature is not always kind to mathematical concepts.
Click to expand...
Maths is "just" a logical formalism. Show me a single instsnce where the Universe has been shown to be logically nconsistent.

It seems to me that our primary difference is that you seem to have much more confidence in our current mass estimation techniques and our current technologies than I do. I see these things as a bit like 'limited/primitive tools' that are 'improving with time'.
Click to expand...
You have repeatedly ahown that you don't understand them.

We are only now starting to identify smaller planets with our current technologies. Until a decade or so ago, we really couldn't even directly confirm their existence, and even today we do not directly observe them in most instances, just their effect on the light from the parent star.
Click to expand...
So?

I simply don't think we have the technology or correct enough models to leap to the conclusion that the 'dark matter' is necessarily related to "exotic matter'. That seems to be our fundamental difference as I see things.
Click to expand...
But you don't understand the technology we do have. Or the results from them. Or quantitative physics.
 
Exactly what control mechanisms are missing from the DM detection experiments

Michael Mozina said:
If you're referring to the LHC experiments I agree. If you're referring to other underground observations which seem to lack control mechanisms, I would tend to disagree. There is no control mechanism of any sort in such detection methods.
Click to expand...
He is refering to the some of the most finely controlled experiments man has done - dark matter detection experiments.

Given your ignorance of what empirical means in science (it happens to include observations), I suspect that you have your own definition of "control mechanism". So:

First asked 7 January 2010

Michael Mozina
  1. Exactly what control mechanisms are missing from the dark matter detection experiments?
  2. What effect have these missing control mechanisms have on the validity of their results?
Note that if your control mechanisms are missing from these experiments then there lack in other experiments will have a similar effect. For example we may have to consider whether solar neutrinos exist since the experiments are comparable.
 
DazzaD said:
Oh I dunno.

Dark matter really just refers to the fact that it is difficult or not possible to detect from emitted radiation (be that in the visible region or otherwise).
Click to expand...

Ok, but is it "not possible" because of the limits of our technologies, or not possible because the the matter is "invisible"?
 
Tubbythin said:
WHAT??? Why do you think these experiments are hundreds of metres underground. For fun? Why do you think they use germanium detectors that are cooled to a fraction above absolute zero? Why do you think they only use lead shielding that has been salvaged from old, deep shipwrecks?
Click to expand...

How do they turn on and off the "dark matter"?
 
Michael Mozina said:
Since Klein's model produces the same homogeneous results without it, why do I need it again? When do we apply Occum's razor to various arguments?
Click to expand...

The Alfven-Klein model is inconsistent with observation. You really need to learn that Occam's razor is only relevant for discriminating between two models that account for the same set of facts.
 
Tubbythin said:
How do you turn off a neutron?
Click to expand...

It is possible to turn on and off a source of them.
http://neutrons.ornl.gov/

Your question makes no sense.
Click to expand...

Yes is does. That cave amounts to "shielding" for the experiment, it's not a "control mechanism" in terms of turning on and off a known source of something, like a reactor was used to turn "on and off" a known/suspected source of neutrinos. What's the known source of "dark matter", and how do I turn it on and off like neutrinos or electron, or protons, or neutrons or photons or anything else that is known to empirically exist in nature? How do I "control" dark matter?
 
Michael Mozina said:
Ok, but is it "not possible" because of the limits of our technologies, or not possible because the the matter is "invisible"?
Click to expand...

The relevant bit actually is "from emitted radiation".... in that the "dark matter", pretty much by definition, doesn't interact with "ordinary" matter in the same way that say hydrogen does.

When we say "dark" we may not mean dark in the sense you cannot see it with your own eyes, but in the sense that you cannot "see" it across the electromagnetic spectrum as you would say, a large planet or a cloud of gas.

It's presence is inferred from the effect it has on the surrounding matter, its gravitational influence for instance.

As has been pointed out many times, it is the type of effect it has which is rather unique and simply cannot be accounted for using any combination of "non-dark" matter, regardless of how much of that non-dark matter you have.

If you have a certain structure of ordinary matter that can explain the dynamics of the system, but you then fail to observe the "light" from that distribution (which you would expect to be able to given the experimental bias and constraints)....would you not conclude that something was amiss and that perhaps there was something you "couldnt see"?

An analogy here may be direct observational evidence for the existence of an atom.
 
Tubbythin said:
The Alfven-Klein model is inconsistent with observation.
Click to expand...

Which observation? Not the observation of homogeneity?

You really need to learn that Occam's razor is only relevant for discriminating between two models that account for the same set of facts.
Click to expand...

The point is that "inflation" came from a human imagination of a single human being, with no previous scientific history of any sort. It's non existent. It was "postdicted" to fit what it fits, and it still being postdicted to fit whatever someone wants it to fit like any handy-dandy metaphysical "Gumby" theory. How handy that it's dead now so we can never "test" any of the "properties" being assigned to Gumbyflation.
 
Michael Mozina said:
It is possible to turn on and off a source of them.
http://neutrons.ornl.gov/



Yes is does. That cave amounts to "shielding" for the experiment, it's not a "control mechanism" in terms of turning on and off a known source of something, like a reactor was used to turn "on and off" a known/suspected source of neutrinos. What's the known source of "dark matter", and how do I turn it on and off like neutrinos or electron, or protons, or neutrons or photons or anything else that is known to empirically exist in nature? How do I "control" dark matter?
Click to expand...

May I ask how you turn on or off the electromagnetic emissions from the Sun?

Or its gravitational field?
 
Michael Mozina said:
Before I tackle the rest of the post I wanted to point out something that seems to be different between us on this topic. When you say "dark", I automatically think "limits of our technology", as in "we can't see very far with our current technology". I'm not sure of your age, and this could be an age related bias because "dark matter" was pretty much equated with MACHO brands of "dark matter" when I was first introduced to the concept. It's since "morphed" into "exotic matter" with supernatural properties.

You seem to be suggesting that the just because we can't "see" it from here, it must not interact electromagnetically in it's local environment. I disagree with that concept entirely. A little dust and enough distance, and there's just no way our technology will pick up photons from here. I don't think you can just jump to the conclusion that if we can't see photons from it from million if not billions of light years away, it must not interact electromagnetically. That seems like an extreme claim considering the limits of our current technologies.
Click to expand...

The amount of dust (or any other baryonic matter) needed to account for observations of lensing and rotational curves would greatly dwarf the amount of normal matter found in stars. While you obviously can't see the individual particles millions of light years away, when they exist in the necessary quantity, you CAN see the infrared that they unavoidably create when they absorb light from there host galaxies. This is just one of the ways we know there can't be enough baryonic dark matter to account for the unseen mass. The amount that's missing can't be hidden if it's made of the stuff we're familiar with.
 
DazzaD said:
The relevant bit actually is "from emitted radiation".... in that the "dark matter", pretty much by definition, doesn't interact with "ordinary" matter in the same way that say hydrogen does.
Click to expand...

But you can't demonstrate such a form of matter even exists. It may not be "dark" at all, but instead those photons may simply be being absorbed or scattered another direction. How do you know that the missing mass doesn't interact with light of the EM field?

When we say "dark" we may not mean dark in the sense you cannot see it with your own eyes, but in the sense that you cannot "see" it across the electromagnetic spectrum as you would say, a large planet or a cloud of gas.
Click to expand...

Sound's pretty "invisible" to me. Next you'll want me to believe it walks through walls too. :) I sure hope you have a sense of humor. :)

It's presence is inferred from the effect it has on the surrounding matter, its gravitational influence for instance.
Click to expand...

Any form of matter would have a gravitational influence, so how did you rule out every other option under the sun? To claim that exotic matter is necessary is a pretty "extraordinary" claim don't you think?

As has been pointed out many times, it is the type of effect it has which is rather unique and simply cannot be accounted for using any combination of "non-dark" matter, regardless of how much of that non-dark matter you have.
Click to expand...

Well, I find that hard to believe frankly. We can double the amount of mass in galaxy just by doing so. We can probably triple it too and justify it via "dust"' or heavy ions. How much "dark matter" can you produce here on Earth for us to experiment with?

If you have a certain structure of ordinary matter that can explain the dynamics of the system, but you then fail to observe the "light" from that distribution (which you would expect to be able to given the experimental bias and constraints)....would you not conclude that something was amiss and that perhaps there was something you "couldnt see"?
Click to expand...

Ya, but then it could be due to almost anything including more "dust" that we "predicted". How do you know it's related to a special invisibility property of any sort?

An analogy here may be direct observational evidence for the existence of an atom.
Click to expand...

I don't see how that analogy applies, but I'm fighting a cold today so maybe I not following you very well. Atoms show up in real experiments and I can do things to them. I can even classify them based upon their various properties and weights and there is nothing "unusual" about them from the standpoint of empirical physics with the possible exception of the Higgs particle. Maybe that would be a more appropriate analogy?
 
phunk said:
The amount of dust (or any other baryonic matter) needed to account for observations of lensing and rotational curves would greatly dwarf the amount of normal matter found in stars.
Click to expand...

True, but Birkeland's very first rough calculation of the mass of the universe that was not found in stars was orders of magnitude "greater than" what we actually observe, even with all that "dark matter".
 
DazzaD said:
May I ask how you turn on or off the electromagnetic emissions from the Sun?
Click to expand...

You can't and I'm not asking you to do so. You can produce electromagnetic emissions on Earth. If you want to say that other objects emit light, you're not adding anything "new" that you can't demonstrate. If however you tell me it emits "magic energy", you've introduced a new variable that requires a physical demonstration of concept. Where does the magic/dark energy come from? Where do I get a gram of "dark matter" to play with in a lab? What's the source of "dark matter" that I might use as a control mechanism somehow in the experiment?

Or its gravitational field?
Click to expand...

Again, gravity shows up in real empirical experiments on Earth. The analogy is therefore inapplicable.
 
Michael Mozina said:
True, but Birkeland's very first rough calculation of the mass of the universe that was not found in stars was orders of magnitude "greater than" what we actually observe, even with all that "dark matter".
Click to expand...
Can you give a citation to "Birkeland's very first rough calculation of the mass of the universe that was not found in stars"?
When was this?

Modern calcuations put an upper limit on the mass of the universe that is found in stars (the baryonic density parameter):
Reality Check said:
A little more on this.
I believe that you pointed out this preprint:
Dark Matter: The evidence from astronomy, astrophysics and cosmology

You may want to read sections 9 and 10. These give methods of determining the density of matter in the universe (no calculation of galactic mass need apply :)).
  • Analysis of the WMAP data tells us that
    • the total mass density parameter is ~0.26
    • baryonic density parameter is ~0.04. This agrees with the amount of visible matter that astronomers calculate in other techniques.
    • thus the density of dark matter in the universe is ~0.22.
  • Baryonic acoustic oscillations (BAO) tell us that
    • the total mass density parameter is ~0.26.
    • the ratio between the baryonic and total density parameters at very large scales is 0.18 +/- 0.04. So the baryonic density parameter is ~0.05 +/- 0.01.
The BAO results mean that astronomers have found about 80% of the baryonic matter in the universe (at least 66% if we use the pessimistic limit of the result).


However that is moot because the above results give a limit on the density of baryonic matter in the universe of < 6%. That means that ~94% of the universe is dark matter and dark energy.
Click to expand...
 
You must log in or register to reply here.

Back
Top Bottom