Extraordinary claims require extraordinary proof

[GreyICE]

But the cosmic background of neutrinos - which would be what the dark matter is made from, not the ones emitted from stars - is not necessarily relativistic today. Neutrinos decouple from other matter very early in the universe (at about 1 second after the big bang), and so they've been out of thermal equilibrium for a long time. As the universe expands they cool, and today they actually have a very low temperature. With even a small mass, they will be quite non-relativistic by now. So if they had turned out to be a bit more massive than they are, they could have been DM. As it turns out they are not, but it shows how non-exotic and rather unsurprising the existence of DM is.

So basically its not moving close to C? Or is it?

We know that it interacts only quite weakly (like neutrinos). There is no way for such stuff to cluster, because it cannot reduce its energy. Think about a massive neutrino, even a non-relativistic one, coming close to the sun. It can just pass right through the center and shoot out the other side, because its mean free path is much longer than the sun is big. So there is no way for it to get stuck or cluster - and that's for an incredibly unusual one which passes right through the middle of the sun. Almost all the rest never come anywhere near a dense region.

Earth and Jupiter need never touch the sun to go into orbit around it. Just because it never hits a star doesn't mean it won't form orbital paths around them. It doesn't have to strongly interact. All it has to do is have mass, and it will start to orbit (actually it doesn't need to have that. Light could theoretically orbit a black hole for quite some time).

 

[sol invictus]

So basically its not moving close to C? Or is it?

It depends on the mass. If cosmic neutrinos were massive enough to account for DM, they would be non-relativistic now.

Earth and Jupiter need never touch the sun to go into orbit around it. Just because it never hits a star doesn't mean it won't form orbital paths around them. It doesn't have to strongly interact. All it has to do is have mass, and it will start to orbit (actually it doesn't need to have that. Light could theoretically orbit a black hole for quite some time).

You're not getting the point. Planets already have a very low kinetic energy in the rest frame of the sun, so they can't escape from its pull. But a typical object in the galaxy has a velocity (relative to our sun) which is far beyond escape velocity. If such an object happened to pass near the sun, it would simply fly by it with a slight deflection of its trajectory. Unless it interacted and lost energy there's no way it could become bound or go into orbit.

Make sense?

 

[robinson]

The initial reason that dark matter was needed is because galaxies rotate slower than they should according to the visible matter that we see.

That is the exact opposite of why dark matter was first imagined to exist! People, please, check your facts.

Galaxy that shows "expected" rotation baffles observers.

What do you call an absence of darkness? Dark matter is supposed to be spread throughout the universe, but a new study reports a spiral galaxy that seems to be empty of the stuff, and astrophysicists cannot easily explain why.

In the outer regions of most galaxies, stars orbit around the centre so fast that they should fly away. The combined mass of all the observable inner stars and gas does not exert strong enough gravity to hold onto these speeding outliers, suggesting some mass is missing.

Most astronomers believe that the missing mass is made up of some exotic invisible substance, labelled dark matter, which forms vast spherical halos around each galaxy. Another possibility is that the force of gravity behaves in an unexpected way, a theory known as modified Newtonian dynamics, or MOND.

In the spiral galaxy NGC 4736, however, the rotation slows down as you move farther out from the crowded inner reaches of the galaxy. At first glance, that declining rotation curve is just what you would expect if there is no extended halo of dark matter, and no modification to gravity. As you move far away from the swarming stars of the inner galaxy, gravity becomes weaker, and so motions become more sedate.

http://space.newscientist.com/article/dn13280-galaxy-without-dark-matter-puzzles-astronomers.html

Note the skepticism that greets this discovery

"If this paper is correct, then this galaxy contains very little or no dark matter," says astrophysicist Jürg Diemand of the University of California, Santa Cruz, US, who is not a member of the team. "That is surprising."

Diemand says numerous other techniques – including studies of how galaxies move inside clusters and measurements of the big bang's afterglow – all show evidence for dark matter.

So could the new analysis be faulty? "One really needs excellent data to pull this off," says Stacy McGaugh of the University of Maryland in College Park, US, an expert in galaxy formation and evolution. "I'm afraid my grumpy first impression is that I just don't buy it."

I know what you mean man, I know what you mean.


More problems with dark matter theory.

Disturbing evidence has emerged from the wreckage of an intergalactic pile-up suggesting that the already mysterious substance known as dark matter may be even less well understood than astronomers thought.

The observations come from a massive galaxy cluster called Abell 520 that lies 3 billion light years away, the product of a high-speed collision between smaller galaxy clusters. Astronomers examined the wreckage using a technique called weak lensing, which relies on the fact that the gravity of any matter in the cluster bends the light of background galaxies. This distorts their images and so reveals where the cluster's matter lies.

Abell 520 turns out to hold a massive dark core, empty of bright galaxies. Some of the core is made up of hot gas, which the team detected from its emission of X-rays, but most of it has to be something else – presumably the same dark matter that astronomers detect elsewhere in the universe.

Except that dark matter and galaxies usually stick together. How have they become separated here? One possibility is that the galaxies were once in the core, along with the dark matter, but then close encounters between the galaxies threw them out to the cluster's fringes. Unfortunately, the team can't get that to happen in their computer simulations, even if they tailor the initial conditions to encourage these gravitational slingshots.

http://space.newscientist.com/article/dn12497

Dark Galaxy puzzles experts

The Hubble Space Telescope has failed to reveal the expected number of stars in the mysterious, galaxy-sized cloud of hydrogen known as VIRGOHI21. The research bolsters the idea that the gas cloud is the only known example of a 'dark galaxy' that never kick-started star birth.

Galaxies are thought to coalesce from normal, or baryonic, matter that has collected in clouds of hypothetical dark matter. But surveys have turned up fewer galaxies than expected, suggesting that – for unknown reasons – some galaxies are stillborn, and simply fail to form stars.

The discovery of VIRGOHI21 in 2005 seemed to provide the first evidence that dark galaxies existed. However, a number of researchers suggested that VIRGOHI21 was pulled out of the nearby galaxy NGC 4254 when another galaxy called NGC 4262 shot past it at 900 kilometres per second. Indeed, NGC 4254 has a single prominent arm of stars that curls round towards VIRGOHI21, suggesting some sort of link between the two.

But Robert Minchin of the Arecibo Observatory discounts such "hit-and-run" models. "If the hydrogen in VIRGOHI21 had been pulled out of a nearby galaxy, the same interaction should have pulled out stars as well," says Minchin.

http://space.newscientist.com/article/dn12100

And finally, some of those damn skeptics who just keep challenging that whole dark matter/energy thing.

General Relativity Resolves Galactic Rotation Without Exotic Dark Matter
Authors: F. I. Cooperstock, S. Tieu
(Submitted on 26 Jul 2005)

Abstract: A galaxy is modeled as a stationary axially symmetric pressure-free fluid in general relativity. For the weak gravitational fields under consideration, the field equations and the equations of motion ultimately lead to one linear and one nonlinear equation relating the angular velocity to the fluid density. It is shown that the rotation curves for the Milky Way, NGC 3031, NGC 3198 and NGC 7331 are consistent with the mass density distributions of the visible matter concentrated in flattened disks. Thus the need for a massive halo of exotic dark matter is removed. For these galaxies we determine the mass density for the luminous threshold as 10^{-21.75} kg.m$^{-3}.

http://arxiv.org/abs/astro-ph/0507619

Skeptics, who needs them? Why can't we all just accept everything, no matter how unbelievable it sounds?

 

[Reality Check]

WTF?

galaxies rotate slower than they should according to the visible matter that we see

You know, while I enjoy making fun of people when they say dumb stuff, lobbing a soft pitch like that over the plate kind of takes the challenge out of it.

It is also sad that nobody pointed out the glaring error in that statement, which is so wrong it makes me wonder. Is it that everybody else is dumb, or do people just not read your postings?

Maybe it was dark post, and nobody saw it.

You are right - got the curves on the diagram in Wikipedia mixed up.

 

[sol invictus]

http://arxiv.org/abs/astro-ph/0507619

Oh yeah, I remember this one - we found the problem with it in ten minutes at a chalkboard. It has a unphysical singularity somewhere, along a disk if I remember correctly. In other words: it's wrong.

I've already discussed several of the other observations you mention there, but of course you ignored what I said - I guess because it went against your faith.

Skeptics, who needs them? Why can't we all just accept everything, no matter how unbelievable it sounds?

Good point!

 

[Klimax]

What are you referring to and what do you mean by “expanded”?

Don't wory about spalin mustakes

ETA - Hope my sub-discussion isn't derailing your thread robinson. I can go away if it's annoying.

I am referring to your list of possibilities for one simple equation.And by expanded I meant -What does it mean???

I hope that it was joke.(Sometimes jokes are difficult to spot on forum...)

 

[ynot]

That is right - it is an analogy. If you want to, try visualising a 4D space-time instead! That is much harder. It is easier to forget about a space dimension and think about a 2D balloon that changes with time.
There is no "crust". The balloon has a volume (the area that it encloses) and a surface but the surface has no "depth".

The “crust” was referring to the raisin bread. In the balloon analogy there’s just the outer surface and no internal volume. If their was an internal volume, points on opposite sides of the balloon wouldn’t be uniformly expanding relative to each other. The analogy removes everything from the balloon except the very outer surface. In the real, actual universe however this is absolutely impossible, the skins of balloons have (and have to have) a skin with both and outer and inner surface with “depth” in between (and an internal volume). The 2D balloon analogy is very easy to understand, but it’s impossible for me to accept as it has no more chance of actual existence than a mythical god.

 

[ynot]

I am referring to your list of possibilities for one simple equation.And by expanded I meant -What does it mean???

I hope that it was joke.(Sometimes jokes are difficult to spot on forum...)

The E=mc² post was mainly a joke. But along with the joke there was a point. If you don’t get the joke you probably won’t get the point.

Expanded = Increase in area, bulk or volume. Enlarge, spread out or extended.

 

[Reality Check]

The “crust” was referring to the raisin bread. In the balloon analogy there’s just the outer surface and no internal volume. If their was an internal volume, points on opposite sides of the balloon wouldn’t be uniformly expanding relative to each other. The analogy removes everything from the balloon except the very outer surface. In the real, actual universe however this is absolutely impossible, the skins of balloons have (and have to have) a skin with both and outer and inner surface with “depth” in between (and an internal volume). The 2D balloon analogy is very easy to understand, but it’s impossible for me to accept as it has no more chance of actual existence than a mythical god.

You are right - the 2D balloon analogy does not exist - it is an analogy.

 

[ynot]

You are right - the 2D balloon analogy does not exist - it is an analogy.

Analogy = “A similarity between like features of two things, on which a comparison may be based’.

Can’t see any “like features” between a totally abstract and impossible 2D surface and an actual 3D universe. Where’s the analogy?

 

[Reality Check]

Analogy = “A similarity between like features of two things, on which a comparison may be based’.

Can’t see any “like features” between a totally abstract and impossible 2D surface and an actual 3D universe. Where’s the analogy?

Are you saying that balloons don't exist?
The anology is beteween a totally abstract and impossible 2D surface and a a totally abstract and impossible 4D object - the space-time model that we have for the universe.

 

[Reality Check]

Analogy = “A similarity between like features of two things, on which a comparison may be based’.

Can’t see any “like features” between a totally abstract and impossible 2D surface and an actual 3D universe. Where’s the analogy?

Actually lets make this more explicit for you:
Look around you. How many dimensions do you think that you exist in?
If it is 1 then don't try standing up.
If it is 2 then welcome to Flatland.
I hope that you come up with 3 because that is how many I deduce.
Congratulations, you have just constructed an abstract model of the universe! And using abstract math!

But you have just spent time deducing that there exists a 3D universe. So the actual universe includes time. If you want to keep track of change then you need to include time in your model of the universe. You now have an abstract space-time model of the universe using 4 dimensions.
Can you visualize 4 dimensions and see what happens when the space part of the universe expands with time? I cannot.

Scientists have a technique to deal with things that are hard to visualize - they simplify. To simplify a 4D model we just drop 1 dimension. Thus a 3D sphere that expands with time simplifies to a 2D sphere that expands with time. Scientists call that a balloon. You are right that it does not have a volume - the inside of the balloon is the time dimension.

 

[robinson]

Oh yeah, I remember this one - we found the problem with it in ten minutes at a chalkboard. It has a unphysical singularity somewhere, along a disk if I remember correctly. In other words: it's wrong.

Nope. But nice try.

 

[ben m]

Nope. But nice try.

Wow.

Robinson: suppose that we give you have 100 credibility points. You can win more points by being right about something, especially something interesting and non-obvious. You can lose points by making stupid statements which later turn out to be wrong. To make things fair, you have the option of betting credibility points depending on how confident you are. For example, you stand to lose or gain very little from a statement like, "Wasn't Judi Dench in one of the Indiana Jones movies? Maybe I'm misremembering." You'd be staking a lot of credibility on the statement, "Sorry, Zig, your sources must be wrong; I've test-driven every Corolla model from '96 to '08 and the gas cap is always always always on the left." Or whatever.

It looks like you just staked 110% of your credibility on the statement that Cooperstock and Tieu's 2005 paper does not contain an obvious GR mistake which was noticed by every grad student from Aachen to Zurich. Is this really what you want to do? Are you sure? Is your casual dismissal of Sol in the one-point "I think I heard something about that once, but I'll happily drop it after looking it up" category or the bet-the-farm "You're wrong and I'm right and I'll defend my view" category? Please let us know.

PS. I highly recommend paying some attention to the facts before placing your bets.

PPS. I have no desire to read the posts of either (a) someone who is very more often wrong than right, i.e. who has negative credibility, nor (b) someone who wagers nothing on each of a thousand posts which are half right and half wrong, effectively refusing responsibility for anything they say.

 

[BeAChooser]

That is so wrong. It is like this:

You: "My dog has invisible fleas."
Me: "Hang on,there is no such thing as invisible feas."
You: "I dunno, lots of dogs have fleas, I bet there are invisible fleas."
Me: "How can you say that?"
You: "Fleas are invisible anyway, you're probably missing them. You're going to have a hard time convincing me that my dog doesn't have a invisible fleas."
Me: "Um? Fleas are not invisible."
You: "Oh yeah? How do you know? Someone who doesn't know that fleas are invisible and can teleport has no business making wild claims about dogs with invisible fleas!."

Me: "What makes you think your dog has invisible fleas?"
Him: "I observe them."
Me: "How do you observe something that's invisible?"
Him: "My dog is scratching. I calculate that must be due to invisible fleas."
Me: "You are infering them from the scratching."
Him: "No I'm observing them."
Me: "But other things can make dogs scratch. Did you consider that?"
Him: "Why should I? I know fleas make dogs scratch. Ergo must be more invisible fleas."
Me: "But what about the dog's diet? Or allergies? There are papers on both as a cause."
Him: "Papers by Crackpots!"
Me: "No, papers by renowned veterinarians."
Him: "Crackpots, I say! Invisible fleas is the only answer."

 

[BeAChooser]

DM obeys all the laws of physics as we understand them.

Too bad you can't seem to figure out what it is. And you know more about it than you do DE.

 

[BeAChooser]

Galactic rotation curves show that there is about 400 times the observed mass in the galaxies.

I think you have the facts about your favorite theory wrong in light of this recent extraordinary claim by a mainstream astrophysicist:

http://www.space.com/scienceastronomy/050223_dark_galaxy.html "First Invisible Galaxy Discovered in Cosmology Breakthrough, 23 February 2005 ... snip ... The ratio of dark matter to regular matter is at least 500-to-1, which is higher than I would expect in an ordinary galaxy," Minchin said." Hard to believe an invisible dark galaxy would have a 500 to 1 ratio if an ordinary Milky Way like galaxy has a 400 to 1 ratio.

Plus, there are mainstream articles like these"

http://www.sciencemag.org/cgi/content/summary/302/5652/1902 "Most galaxies are enveloped in huge dark halos that contain 10 to 20 times as much mass as the luminous stars and cold gas in the galaxies."

http://www-thphys.physics.ox.ac.uk/users/Astrophysics/guides/galaxies/dkmatter.shtml " Within galaxies the amount of dark matter appears to exceed the amount of visible matter by a factor of 10 to 1 in some cases, and even more than this for a few galaxies."

And say, RC ... would an invisible galaxy consist of dark energy stars and dark matter black holes?

 

[BeAChooser]

So if there isn’t a lot of stuff out there that we can’t see, we have three possibilities:

1. The observations are wrong;
2. The laws of physics (which are themselves supported by a large body of observations) are wrong;
3. Both the observations and the laws of physics are wrong.

Actually, there's one more possibility:

4. The observations are right (within the uncertainties) and the laws of physics are right too, but BB supporting astrophysicists are ignoring some of the laws because they are too focused on gravity as an explanation for everything. Now what does Occam's Razor tell you?

 

[BeAChooser]

Brilliantly put. Wins this thread.

See post #138.

 

[BeAChooser]

The initial reason that dark matter was needed is because galaxies rotate slower than they should according to the visible matter that we see.

No, RC, wrong again.

The outer regions of galaxies rotate FASTER than can be accounted for by the gravity from visible matter alone. (Assuming MOG isn't correct.)