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

[Michael Mozina]

No it couldn't. Most forms interact electromagnetically and therefore are not dark.

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.

 

[Michael Mozina]

I read about Kaluza–Klein cosmologies. But you really need to tell us which Kaluza–Klein model you are thinking of.

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.

 

[Perpetual Student]

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?

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.

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?

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?

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

 

[Reality Check]

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.

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 !

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.

 

[Michael Mozina]

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.

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.

 

[Reality Check]

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.

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.

 

[Michael Mozina]

Yes.

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?

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?),

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?

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

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.

 

[Reality Check]

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.

Wrong. If galaxies are really twice as bright as believe then there is about 20% more mass in galaxies.

Likewise we can fill in some of that missing mass with black holes (it's a small amount, but hey it all counts).

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%.

We evidently have been grossly underestimating the number of small stars compared to bigger (more visible) stars in a given galaxy.

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.

All these things add up and our technologies are improving.

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.

 

[Pythonic]

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.

 

[Reality Check]

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.

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.

 

[Tubbythin]

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.

Huh!!?!
Dark matter detection experiments are some of the most finely controlled experiments man has ever done.

 

[Tubbythin]

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.

We don't need to look at galaxies billions of light years away. We can look at our own.

 

[DazzaD]

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.

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.

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.

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.

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.

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?

 

[Dancing David]

Wow, even with MM on IGNORE these are massive threads, maybe the dark posts effect the mass of them.

 

[DazzaD]

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.

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?

 

[DazzaD]

I would be interested to hear what everyone's thoughts are on:

http://www.physics.upenn.edu/~lverde/darkgal.html

 

[Reality Check]

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.

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.

 

[Michael Mozina]

We don't need to look at galaxies billions of light years away. We can look at our own.

How many Earth sized planets have we observed in our own galaxy outside of this solar system?

 

[Michael Mozina]

Huh!!?!
Dark matter detection experiments are some of the most finely controlled experiments man has ever done.

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.

 

[Tubbythin]

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.

• 
  
  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 r^1/2.
  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!