Dark Matter a Conspiracy?

[matthew809]

No, what he's actually saying is that he looks for scientific explanations instead of speculating wildly on zero evidence.

With that kind of attitude, if the milky way's unaccounted gravity really is due solely to the black hole at the center, then scientists will unfortunately never figure it out.

But for the sake of elimination, how would you go about disproving my idea?

Or better yet, if your life depended on it, how would you go about proving that my theory might be true. Think of yourself as a lawyer defending a person you know to be guilty.

There's nothing wrong with "speculating wildly", especially in the pseudoscience section.

[Dywyddyr]

With that kind of attitude, if the milky way's unaccounted gravity really is due solely to the black hole at the center, then scientists will unfortunately never figure it out.

Science seems to have done pretty well so far with "that attitude". And what makes you think they'll never figure it out?

But for the sake of elimination, how would you go about disproving my idea?

What, that black holes generate "extra gravity"? What would be the mechanism?

Or better yet, if your life depended on it, how would you go about proving that my theory might be true. Think of yourself as a lawyer defending a person you know to be guilty.

Sure. Gonna pay me at lawyers' rates to defend an idea I don't give any credence to?

There's nothing wrong with "speculating wildly", especially in the pseudoscience section.

If all you want to do is speculate wildly I suggest you read the forum rules.
There's a great deal wrong with doing so: you need some supporting data and a structure. Otherwise why don't you claim it's teddy bears pulling at things?

[Shogun]

There is evidence for Dark Matter. It is not just "extra" gravity, it is gravitational forces existing where there seems to be nothing there. It is undetectable by electromagnetic radiation. There is a gravitational signature and it causes gravitational lensing.

[Janus58]

So there is no dark matter in our solar system? Is there dark matter within our galaxy, or is it only outside of our galaxy?

Some estimates put the total amount of DM in the solar system as being 1e20 kg or about 1/9 the mass of the asteroid Ceres. This DM would be spread out spherically around the Solar system. to get an idea of how thinly spread out this is, if we assume that this means a volume encompassed by a radius equal to that of the Oort cloud, it works out to a density of 1e-19 kg per square km. At this density, the entire volume of the Earth would contain only 1/10,000 of a gram of DM.

[Shogun]

Some estimates put the total amount of DM in the solar system as being 1e20 kg or about 1/9 the mass of the asteroid Ceres. This DM would be spread out spherically around the Solar system. to get an idea of how thinly spread out this is, if we assume that this means a volume encompassed by a radius equal to that of the Oort cloud, it works out to a density of 1e-19 kg per square km. At this density, the entire volume of the Earth would contain only 1/10,000 of a gram of DM.

Also, there are dark matter passing through the Earth. Since it is one of its properties, going through matter.

[AlphaNumeric]

So you are saying that you lack enough imagination to contemplate the idea that black holes, or at least our galaxy's black hole, might be responsible for the apparent extra gravity of the galaxy rotation problem?

No, I'm saying that within GR it is proven that there's only 4 kinds of black hole in 3+1 dimensions and none of them can create the gravitational profile needed. Despite what you might think if you watch TV documentaries the long distance properties of black holes are well understood, they are completely categorised. Schwarzchild, Reissner-Nordstrom, Kerr, Kerr-Newman. That's it. In 4+1 dimensions there's a lot more interesting ones, like black rings, but that's beside the point.

This isn't a matter of imagination, black holes aren't some kind of magical "You can do what you want", they follow basic rules, like any other object in the universe. Just because black holes seem mysterious to you doesn't mean you can just say "Oh its a black hole" and be done with it. The devil is in the details, if you can't come up with a quantitative model then all the qualitative arm waving in the universe isn't going to help.

But for the sake of elimination, how would you go about disproving my idea?

Not that is bad science. You're proposing something, its on you to justify it. If you think a black hole can explain things demonstrate it. Going around saying "I'll believe [X] without evidence until people prove me wrong" is flawed reasoning. And if you bothered to learn any black hole mechanics (I can provide some lecture notes if you wish, though you'll need a lot of prerequisite courses) you'd know you can't just use black holes to do what you want.

Or better yet, if your life depended on it, how would you go about proving that my theory might be true. Think of yourself as a lawyer defending a person you know to be guilty.

You're shifting the burden of proof. Physicists have demonstrated dark matter can explain observations, with quantitative work. You've simply made claims about black holes, which you obviously know nothing about.

[matthew809]

How does dark matter explain the distinct spiral arms?

Also, I was wondering about the fact that a star traveling around the inner track of the galactic core travels the same speed as a star traveling along the outer track. According to dark matter theory, is this just pure coincidence that the surrounding dark matter is in the exact right configuration to make this happen, or is there a larger mechanism at work here?

[spidergoat]

...the angular speed of rotation of the galactic disk varies with distance from the centre of the galaxy...{wiki}

[AlphaNumeric]

How does dark matter explain the distinct spiral arms?

The same way any other gravitational model does, angular momentum. Not all galaxies have spiral arms, so it obviously depends also on the initial configuration of the cloud which eventually forms a given galaxy (and whether any other galaxies go past at any point).

Dark matter isn't about explaining spiral arms existence but the rate at which they orbit the galactic core.

Also, I was wondering about the fact that a star traveling around the inner track of the galactic core travels the same speed as a star traveling along the outer track. According to dark matter theory, is this just pure coincidence that the surrounding dark matter is in the exact right configuration to make this happen, or is there a larger mechanism at work here?

It's not exact, so there's no issue about somehow a too convenient result. An example of such things being not uncommon is the Moon-Sun-Earth system and eclipses. The ratio of Moon radius to Sun radius is about that of the ratio of the distance from the Earth to the Moon as the Earth to the Sun. As first glance it might seem a a perfect result, when in fact the ratio varies with orbital position of the Moon and almost no eclipse is 'perfect', in that the Moon covers all of the Sun and then some or the Moon doesn't cover all of the Sun, even if their centres are aligned.

Besides, you're not really arguing from anything viable. Your point is that it seems a little too perfect but whether or not the result is dubious depends on how dark matter behaves. For instance, if a generic galaxy sized diffuse cloud of dark matter and normal matter collapses under gravitational processes and leads to such galaxy dynamics then dark matter is more viable because it means you don't have to worry about having to come up with more convoluted models or less generic cases.

I can't think of a better analogy right now but I'll say it anyway, black holes. As I mentioned in a previous post there's very very few different kinds of black holes which you can get in 3+1 dimensional GR, all that you need to uniquely define a black hole is its mass, M, its charge, Q, and its angular momentum, J. This might seem odd, given that two black holes with say Q=J=0 and equal masses could have come from wildly different stars. What happens? Well when you do the GR calculations you find that gravitational collapse 'strips' a star of its unique defining features. All the anistropy or clumping within the star is thrown off via gravitational radiation. This would be expected, as if you could work out what the original matter which made up the black hole was then you're effectively 'looking' into the black hole somehow. Thus GR provides a simple physical explanation for something which might otherwise be very difficult to motivate.

If you had a computer program which models galaxy formation with both light and dark matter, you generated a million different starting examples, modelled each one as it collapsed and found that 99.99% of the time they end up with rotations as we observe then it would be fair to conclude that the properties of dark matter lend themselves to the kind of orbital mechanics we see and want in a model. If you only see it 1% of the time then you'd need to develop the model further, as you're trying to imply might be the case.

I'm not an astronomer so I don't keep up to day with the latest work but certainly dark matter interactions are regularly done by particle physicists and galaxy formation by clouds of material containing billions of components are done by cosmologists on supercomputers (or at least they'd already done it about a decade ago). I know it might seem like physicists just ignore 'intuitively obvious' approaches but almost without exception its the case that they've already tried it and it can't come up with the goods. Believe me, there's tons of physicists who'd love to be doing some wacko black hole stuff in astronomy, of the kind you mentioned, but they can't ignore the reality of GR, it doesn't allow for such things. After all a black hole has no hair.