Fermi and dark matter

[Michael Mozina]

I'm curious why astronomers as a group are allowed to simply point at the sky and make stuff up in an ad hoc manner? What empirical evidence demonstrates that "dark matter" releases gamma rays or positrons? Without such empirical validation, what it the world are they doing pointing at the sky with the Fermi telescope and claiming "dark matter did it" ?

 

[Ziggurat]

I'm curious why astronomers as a group are allowed to simply point at the sky and make stuff up in an ad hoc manner? What empirical evidence demonstrates that "dark matter" releases gamma rays or positrons? Without such empirical validation, what it the world are they doing pointing at the sky with the Fermi telescope and claiming "dark matter did it" ?

Oh, the irony of you accusing others of making stuff up.

And you clearly don't understand what the Fermi telescope is doing. Nobody is claiming that dark matter is emitting gamma rays or positrons.

 

[edd]

Dark matter is something currently unexplained. That does not mean there are no tentative explanations. Some of these tentative explanations expect dark matter to annihilate with itself, but for the chance of this to be very low. However, we expect dark matter densities to peak strongly at the centre of galaxies and so there is a prediction that dark matter will annihilate at an appreciable rate at galactic cores.

One of the things Fermi is doing is looking for this. Having predictions and testing them is a good thing.

A negative result does not rule out dark matter but it constrains what it might be.

The idea is to test hypotheses. Is this so unreasonable?

 

[Michael Mozina]

Oh, the irony of you accusing others of making stuff up.

http://www.newscientist.com/article/dn15126-where-will-new-fermi-telescope-find-dark-matter.html

What the hell are you talking about?

And you clearly don't understand what the Fermi telescope is doing. Nobody is claiming that dark matter is emitting gamma rays or positrons.

From the article:

No one knows what dark matter is, since its presence is inferred only by its gravitational pull on normal matter. But researchers believe it is made up of particles that annihilate when they collide with each other. This produces gamma-ray photons that could be detected by telescopes such as Fermi (formerly called GLAST), which launched in June.

What empirical evidence shows that dark matter annihilates or that this annihilation produces gamma rays?

 

[edd]

There is no empirical evidence as such - that's why it's being looked for. There are however well motivated theoretical reasons for thinking that it might.

 

[edd]

Note that 'believe it is' in that article is journalistic exaggeration perhaps.

 

[Ziggurat]

The idea is to test hypotheses. Is this so unreasonable?

edd, perhaps you have not met Michael Mozina before. I think you should know a few things about him before you delve in too deeply. He's the owner of this web page:
http://www.thesurfaceofthesun.com/
Among other unconventional beliefs, he believes that the sun has a solid shell surface, and this web page advocates for this idea. Aside from the obvious mechanical instability of such a system, it also contradicts thermodynamics. But Michael refuses to believe what is plain for everyone else to see.

Now my point here isn't actually to discuss the faults of Michael's ideas, because that's been done at length in other threads. We don't need to go over them here. But before you waste too much time trying to convince Michael about rather basic science issues, you should be aware of how futile the task is likely to be.

 

[edd]

Oh no, Michael and I have conversed here before

I am just an optimist.

 

[sol invictus]

I'm curious why astronomers as a group are allowed to simply point at the sky and make stuff up in an ad hoc manner?

What do you think science is, Michael?

Let me explain this at a grade school level so you might get it. Scientists make stuff up. Then they test it. If it fails the test, they make something else up. If it passes it, they test it more.

What empirical evidence demonstrates that "dark matter" releases gamma rays or positrons?

Fermi's results?

Without such empirical validation, what it the world are they doing pointing at the sky with the Fermi telescope and claiming "dark matter did it" ?

How the hell are they going to get empirical validation if they don't look for it? And by the way, no one is claiming "dark matter did it". They're claiming that dark matter might have done it, and that certain DM models are consistent with Fermi's results (and others are not and are ruled out by them).

You know what that's called? It's called "science".

 

[Michael Mozina]

There is no empirical evidence as such - that's why it's being looked for. There are however well motivated theoretical reasons for thinking that it might.

Those "theoretical reasons" have not been verified empirically in any lab on Earth, so what's the point of trying to claim it happens "out there somewhere"? It seems to me that this is a *horrible* way to use Fermi data.

 

[Michael Mozina]

What do you think science is, Michael?

That seems to depend on who's doing the "science" evidently. What empirical "science" supports the claim that DM annihilates and produces gamma rays?

Let me explain this at a grade school level so you might get it.

Ah, the ever (not so clever) useless personal insult. Yawn.

Scientists make stuff up. Then they test it. If it fails the test, they make something else up. If it passes it, they test it more.

How did they "test" this annihilation claim exactly?

Fermi's results?

What makes you believe that Fermi sees anything other than standard gamma rays from standard sources (like our own sun)?

How the hell are they going to get empirical validation if they don't look for it?

There is no empirical validation possible in a non controlled pure observation! There is no way to achieve "empirical validation" outside of a real "experiment" with actual control mechanisms. Pointing at the sky with Fermi and claiming "dark matter did it" is not a form of "empirical verification" of the claim of DM annihilation.

And by the way, no one is claiming "dark matter did it". They're claiming that dark matter might have done it, and that certain DM models are consistent with Fermi's results (and others are not and are ruled out by them).

Anything and everything "might" do it, but only things that are KNOWN to release gamma rays. Claiming that "invisible elves might have done it" isn't a form of "science" only because you then see gamma rays in space.

You know what that's called? It's called "science".

I'm beginning to think that astronomers simply do not comprehend the difference between "science" and "make believe". As long as the math works out, you guys will accept anything and everything as a form of "science", with or without empirical support.

 

[edd]

If everything Fermi did had to be confirmed in a laboratory, I would suggest we should have spent the money elsewhere.

Personally I do not hold that all empirical evidence comes from an Earth-based laboratory.

 

[Ziggurat]

Those "theoretical reasons" have not been verified empirically in any lab on Earth, so what's the point of trying to claim it happens "out there somewhere"?

Same with General Relativity. Einstein had no way of testing it in a lab. So what was the point in looking at the orbit of Mercury?

 

[Dancing David]

Dark matter is something currently unexplained. That does not mean there are no tentative explanations. Some of these tentative explanations expect dark matter to annihilate with itself, but for the chance of this to be very low. However, we expect dark matter densities to peak strongly at the centre of galaxies and so there is a prediction that dark matter will annihilate at an appreciable rate at galactic cores.

One of the things Fermi is doing is looking for this. Having predictions and testing them is a good thing.

A negative result does not rule out dark matter but it constrains what it might be.

The idea is to test hypotheses. Is this so unreasonable?

Thanks Edd!

 

[Michael Mozina]

If everything Fermi did had to be confirmed in a laboratory, I would suggest we should have spent the money elsewhere.

Personally I do not hold that all empirical evidence comes from an Earth-based laboratory.

Put yourself in my shoes for a second Ed. *If* DM had already been shown to exist (say via LHC or some other collider experiment), *and* it had also been shown to annihilate and emit gamma rays, *then* I really would have nothing to complain about. Since steps A) and B) were never demonstrated, C) looks like pure "made up" speculation from where I sit. What empirical evidence actually supports the claim that DM emits *ANYTHING* let alone gamma rays? The whole thing is one big fallacy of affirming the consequent.

http://www.fallacyfiles.org/afthecon.html

The example they use is:

If it's raining then the streets are wet.
The streets are wet.
Therefore, it's raining.

In this case the circular feedback loop goes:

If DM exists in nature and it annihilates, it will produce gamma rays.
There are gamma rays in space.
Therefore DM annihilates and emits gamma rays.

 

[Michael Mozina]

Same with General Relativity. Einstein had no way of testing it in a lab. So what was the point in looking at the orbit of Mercury?

The empirical difference is that gravity actually shows up in empirical experiments on Earth, whereas the annihilation claim is pure speculation.

 

[Michael Mozina]

Dark matter is something currently unexplained. That does not mean there are no tentative explanations. Some of these tentative explanations expect dark matter to annihilate with itself, but for the chance of this to be very low. However, we expect dark matter densities to peak strongly at the centre of galaxies and so there is a prediction that dark matter will annihilate at an appreciable rate at galactic cores.

One of the things Fermi is doing is looking for this. Having predictions and testing them is a good thing.

A negative result does not rule out dark matter but it constrains what it might be.

The idea is to test hypotheses. Is this so unreasonable?

The "test" of that "string of assumptions" that you are calling a hypothesis is not reasonable. There's no evidence that exotic forms of matter exist. There's no evidence that DM annihilates to produce gamma rays or that it "collects" anywhere. There's no control mechanism in your "test".

The whole thing is one giant logical fallacy. If you knew for a fact that DM actually exists and does annihilate, then it might be "ok" to look for such signatures at the core of galaxies and such. Since every single one of these string of claims lacks any empirical support, the whole thing is a house of cards. You can't 'test' that theory in an uncontrolled observation. There could be any number of logical reasons why the core of a galaxy emits gamma rays, and no form of DM is known to emit gamma rays. Therefore the presence of gamma rays near the core of a galaxy is not automatic validation of this idea.

 

[Ziggurat]

The empirical difference is that gravity actually shows up in empirical experiments on Earth, whereas the annihilation claim is pure speculation.

Particle annihilation shows up in laboratories. Curved space does not.

 

[Ziggurat]

There's no control mechanism in your "test".

Einstein had no control mechanism for his tests of GR either.

 

[Michael Mozina]

http://arxiv.org/PS_cache/arxiv/pdf/0910/0910.2998v1.pdf

Here's a great example of that same fallacy in a paper by the way....

Searches for dark matter annihilation products are among the most exciting missions of the Fermi Gamma Ray Space Telescope (FGST).

Why? There's no evidence Fermi sees anything other than standard gamma rays from standard sources and lots of things emit gamma rays.

In particular, the FGST collaboration hopes to observe and identify gamma rays from dark matter annihilations occuring cosmologically [1], as well as within the Galactic Halo [2], dwarf galaxies [3], microhalos [4], and the inner region of the Milky Way [5].

Due to the very high densities of dark matter predicted to be present in the central region of our galaxy, the inner Milky Way is expected to be the single brightest source of dark matter annihilation radiation in the sky.

Here the authors simply "assume" that DM exists, that DM annihilates and emits gamma rays, and that exotic forms of DM are present in the inner part of the Milky way. None of these assumptions has been demonstrated. Any observations of gamma ray emissions we might come across in space are not automatic evidence of DM, they are simply "pure observations" of gamma rays. Period. Any claim about that gamma ray being associated with DM annihilation from a pure observation is purely arbitrary. Any number of things could generate gamma rays in and around a galaxy. In fact our own sun releases them on a regular basis. Gamma ray "observations" are *not* evidence of DM. Fermi sees gamma rays alright, but there is no evidence that any gamma rays come from DM. There is no control mechanism in a pure observation that could isolate a 'cause' of such emissions and there is no evidence that DM emits these wavelengths to begin with. Whatever "excitement" they might feel is purely arbitrary and entirely subjective because none of these scientists can isolate a cause from a pure observation.