Scientists say dark matter doesn't exist

[tsg]

So, let me get this straight...

1) There is an undetectable 'something' exerting force on all matter in the universe.

No.

2) The force it exerts is used to explain certain phenomena that had puzzled scientists before its 'discovery.'

Yes.

3) Only a select few understand the real nature of this 'something' and the force it exerts.

No. The people trained in this area understand it best. But anyone, with enough motivation and a will to learn, can understand it at least on a cursory level.

4) Anyone who might have any real understanding of this 'something' is loath to share it, except with other members of the select few.

No.

5) Anyone who exercises a healthy measure of skepticism and asks for material - not theoretical - proof of this 'something,' is ignorant and unqualified to evaluate the proof in the first place.

No. Electrical engineers with no training in theoretical physics are unqualified to say the evidence is not sufficient.

6) Proof of the existance of this 'something' rests solely upon accepting the validity of the authorities who formed the hypothesis in the first place.

No.

Now, you all have to admit that from a certain point of view, it all seems to imply something supernatural.

No I don't.

I'm not saying that the Dark Matter hypothesis is invalid, but so far, the only 'proofs' have been less than convincing.

You are comparing it to pseudoscience and absolutely refusing to see the difference.

I am saying from an engineering standpoint that without a practical application, the Dark Matter hypothesis is irrelevant, no matter how truthful and valid it may be.

No, you compared it to pseudoscience and supernatural beliefs. No one claimed it had a practical application in engineering.

 

[Schneibster]

Our best current guess is that dark matter is an exotic particle LIKE neutrinos, in that it does not interact with light or normal matter, except through the weak interaction.

Well, and gravity.

 

[TV's Frank]

Well, and gravity.

Yeah, well since when does gravity matter?


Oh.

 

[sol invictus]

There is now very direct and compelling evidence for dark matter. Search "bullet cluster".

Briefly, two galaxy clusters collided "recently". Stars more or less continue in straight lines in such an event, but luminous gas (which constitutes most of the visible matter in these clusters) collides inelastically, meaning it gets left behind at the point of the collision while the stars fly right past each other.

So the stars are now where the clusters would have been had there been no collision, but the gas from both has "stuck" and remains at the point where the collision happened. That gas constitutes most of the visible matter, so if visible matter were all there was the gravitational field would be strongest at the collision point (where the gas is).

Instead, the gravitational field (measured via gravitational lensing) is peaked around the two collections of stars. Therefore there must be a third gravitating component, which must be considerably more massive than stars and gas put together, which did not interact in the collision and therefore followed the stars.

This is a very direct piece of evidence for dark matter halos, quite independent of other evidence (rotation curves, structure formation simulations, etc.). It is also very hard to see how any modified theory of gravity can accommodate this (although crackpots like Moffat are sure to claim otherwise).

 

[robinson]

So most of the Universe is composed of some kind of particle that nobody has ever seen? That is really, um... I don't know what that is. It sounds very very woo.

 

[robinson]

I love it when one scientist calls another one a crackpot. Especially when the "crackpot" is the one pointing out "the invisible mythical particle that makes up most of the Universe" might not be real.

High drama amongst the Ivory Towers...

 

[Lonewulf]

If anyone sounds like 9/11 twoofers, it's Robinson and Fnord.

Like discarding the NIST reports without even reading them, and saying that it doesn't make sense to them how an aluminum airplane could possibly have taken down a metal tower.

Then add in the EVIL SCIENTIST CONSPIRACY, and their desire to keep everyone ignorant as to the TWOOF!

Next up, they'll probably claim that the EVIL SCIENTIST CONSPIRATISTS went and killed NASA pilots to keep people from FINDING OUT THE TWOOF that the gravity effects was really caused by space aliens.

 

[Schneibster]

Yeah, well since when does gravity matter?

Oh.

I sentence you to five lashes with a wet noodle for today's worst pun.

 

[Fnord]

Yeah, well since when does gravity matter?


Oh.

Well, gravity is not to be taken lightly.

 

[Ziggurat]

So most of the Universe is composed of some kind of particle that nobody has ever seen? That is really, um... I don't know what that is. It sounds very very woo.

It can sound that way all you like, but there's eviddence for it, and the alternatives aren't really any simpler.

I haven't kept up with the issue, but last time I paid attention, there was still some debate about whether or not dark matter was exotic particles. The competing possibility was basically lots of brown dwarfs (proto-stars which are too small to ignite). The dueling theories were called MaCHOs and WIMPs (for Massive Compact Halo Objects and Weakly Interacting Massive Particles, respectively). Maybe someone else can tell me if MaCHO's have been ruled out yet.

Oh, and it took us a long time to find experimental evidence for neutrinos, but we knew they had to be there. So this is hardly without precedence.

 

[Lonewulf]

Oh, and it took us a long time to find experimental evidence for neutrinos, but we knew they had to be there. So this is hardly without precedence.

Neutrinos were invented by evil scientists in on the conspiracy. I mean, I can't go to a store and buy a neutrino. It's not relevant to me. That's how science works!

 

[robinson]

I noted it sounds woo. Lots of scientific things sound woo at first. Some still sound woo, even with practical evidence that they are indeed, measurable and real, in the sense experiments back up the theory.

Observation can seem woo at times. The proof is in the application. Does it work? Can it be observed? Does it fit the current data? While dark matter, or worse, dark energy sounds woo, we just don't know.


Yet.

If there is some unknown "stuff", and it behaves in a way that doesn't match any known element or particle, that just makes the Universe even stranger than we once thought it was. Massive black holes at the center of Galaxies was once considered just theory, shucks, black holes seemed woo. Now we think there are super massive black holes almost everywhere.

We can't bring a sample to class, but according to the evidence, there they are.

 

[FireGarden]

I haven't kept up with the issue, but last time I paid attention, there was still some debate about whether or not dark matter was exotic particles. The competing possibility was basically lots of brown dwarfs (proto-stars which are too small to ignite).

I was under the impression that brown dwarves would shine -- after all, they are made of matter and have a temperature. They just can't support nuclear fusion of hydrogen, so they sit there and cool down.

http://en.wikipedia.org/wiki/Brown_dwarf#Observations
Observational techniques involve detected faint but visible objects. So there may be more brown dwarves than we know about.

I thought black holes would be a candidate for dark matter. If matter isn't accreting into a disk as it falls in, black holes would be very difficult to detect -- except by gravity.

According to wiki http://en.wikipedia.org/wiki/Dark_matter
Galaxy sized black holes are ruled out by the gravitational lensing data. And Big Bang nuclear-synthesis models rule out an explanation based on large amounts of baryonic matter. ie: not brown dwarves either. (Except for small amounts)

 

[Cuddles]

Now, how do scientists make the leap from "we can't see it" and "we don't know what its properties are" to "It must be invisible!" Why posit a "special" state of matter beyond what current evidence allows? Why not just posit something like a normal hyperdense element (atomic #114+) that is simply ground down too fine, and dispersed too widely to see with current technology? I could buy into that, as well.

Because obviously the people who actually understand what they are talking about would never have thought of something like that by themselves.

 

[Wolverine]

There is now very direct and compelling evidence for dark matter. Search "bullet cluster".

Sean Carroll penned an excellent piece on the subject.

 

[sol invictus]

If there is some unknown "stuff", and it behaves in a way that doesn't match any known element or particle, that just makes the Universe even stranger than we once thought it was.

I don't find the existence of DM any stranger than any other fact about the universe. There are many possibilities for what it might be composed of, some of which are relatively prosaic, and some of which require the existence of a new particle. Every time a new particle accelerator has been constructed, new particles have been discovered, and there's just no reason at all why there shouldn't be a stable massive particle which constitutes DM. A priori there's no reason there should, either, except that we now have very strong observational evidence that there is.

The fact that we can't "see" it is overblown - we can't see it with our eyes, big deal. We can't see it with other frequencies of EM radiation, big deal again. We can "see" it by the gravitational effects it has - which really isn't so different from "seeing" something with an electron microscope, for example.

As for crackpots, the best definition is someone who thinks everything that came before them is wrong (as opposed to a curmudgeon, who thinks everything that came after them is wrong). All scientists fall somewhere on that scale, but Moffat is very far towards the crackpot end. It's not necessarily a bad thing.

 

[Paulhoff]

I can't see air, must not be there.

Paul

 

[nw843x]

GM2, nice. The Wikipedia article on galaxy rotation curves^WP is also pretty informative; MOND is discussed as well as TeVeS and MOG. Of particular note is the fact that not only does dark matter well explain galaxy groups, clusters, and superclusters, it also does a good job when it's added to simulations of the evolution of the universe. You get distributions that look like what we see, and you don't get that from any of the modified gravity theories; we'll see if Brownstein and Moffat manage to get that.

The "Pioneer Anomaly" has been thoroughly debunked, last I checked. However, it looks like there is still some legitimate question on the subject. The Planetary Society, which is generally fairly hard-headed, is funding a project to recover and analyze the data from the Pioneer probes; this is difficult because since the launches of Pioneer 10 and 11, we have gone from punch-card and punched-tape readers to USB thumb drives. Latest update was from August of this year.

Personally, I got to go with the majority on this one; dark matter is too good an explanation. But I'm not set on it. However, it's worth contemplating the fact that there are pictures of it.

Thanks for the link to the pictures. Truly amazing stuff.....now to spend the afternoon reading.

 

[Fnord]

Does the difficulty in relating neutrinos to "Dark Matter" have to do with (1) the difficulty in detecting neutrinos, (2) their infinitesimally small rest mass, and/or (3) the possibility of a so-called "Sterile" neutrino?

 

[The Bad Astronomer]

Okay, so which is it? Is Dark Matter transparent, translucent, or opaque? Can it be seen or not? Why does there seem to be equivocation or conflict, even from scientists, about the properties of Dark Matter?

It can be detected by its gravitic effects on light and matter. So why not just call it 'matter'? Is it necessary to posit the property of invisibility? Why not just say "We can't see it, but we know it's there by using the same principle we use to find extrasolar planets"?

I'm curious (seriously), are you asking these questions without having read about the topic? I have written quite a bit on this.

Dark matter was first posited when galaxy clusters didn't appear to have enough mass to hold them together. It was then found that galaxy rotation curves indicated a lot of extra mass that was also not seen. Both observations indicate that 90% or so of the mass needed was not detected. Hence, the logical and parsimonious explanation is that there is a type of matter out there we don't see.

Scientists made a list of potential candidates. Rogue planets, white dwarfs, black holes, cold gas, neutrinos ... all of these have been crossed off the list for various reasons. What's left now are weird things like WIMPs and axions. We are very close to being able to detect WIMPs, BTW.

Then the Bullet Cluster observation made things pretty clear, and a further series of observations made it even clearer.

MOND is interesting, but I don't see how it explains the shear effect seen in the gravitational lensing surveys (see the link above for more on that). Until they can explain that, I don't give them much credence. My opinion.

So dark matter is not supernatural, paranormal, conspiracy driven, or any of that. It was first proposed due to observations, predictions were made, observations were made to confirm predictions, and plenty of papers (both scientific and popular) have been written.

Scientists still argue, but that will always be true. But the press loves a controversy, so remember that the vast majority of astronomers think that dark matter is real and its effect observable. The few who disagree will get a disproportionate amount of press.