what's Dark Matter to you?

[Crispy]

I think dark matter is just a massive miscalculation.

Astronomers are still finding objects floating around in our own solar system so still don't know what the mass of our solar system is let alone the mass of galaxies or the universe.

Yeah but still, the total mass of all the planets and rocks in the solar system is still a fraction of the mass of the sun (we can tell, because if there was much more mass hanging around, we'd be able to see its effect on orbits etc). The trouble comes when you start looking at galaxies, where you can see the amount of regular matter in them (we know how dense galaxies are from looking at our own), but that amount is far too small to keep the galaxy together the way it does, or to interact with other galxies the way they do. They act as if they were about 15 times more massive than they appear. Therfore, there must be matter we can't see. So it's called dark matter.

However, al these things are based on measurements at very large distances indeed, where it is very difficult to be sure about anything. Moreso than in any other field of science, cosmology is a delicate tower of assumptions and theories. I personally suspect that 'dark matter' is a particularly flimsy strut in that tower.

 

[girasol]

Astronomers have for the first time put some real numbers on the physical characteristics of dark matter.

Those astronomers, they are oh so crazy, aren't they?

weakly interacting massive particle, or Wimp.

one of my friends is an astronomer turned computer programmer, I know what they're like!

 

[WouldBe]

Yeah but still, the total mass of all the planets and rocks in the solar system is still a fraction of the mass of the sun (we can tell, because if there was much more mass hanging around, we'd be able to see its effect on orbits etc).

What happens to the mass of stars when they go supernova?
Is this spread out in interstella space which means we wouldn't be able to see it as it's not illuminated well enough but it's mass is still there. And what about the planets that surrounded that star?

How do we know what the exact composition is of distant stars?
The only place that fusion is known to take place is in stars and heavy elements found on earth are supposed to come from exploded / collapsed stars, so there must be stars out there with large amounts of heavy elements in them making their mass greater than expected. Due to the distance to these stars any spectral lines from these elements may be too feint to be detected here on earth plus the fact that heavier elements would most likely sink towards the center of any star with the resulting spectral lines being masked by the all the other material.

How much interplanetary dust / gas is there?
Although 1cc of this wouldn't weigh much there are billions and billions of cc's to take into consideration. I don't suspect this will be a significant amount but still accounts for some 'missing' mass.

What about stars that have simply burnt out without exploding. How would we be able to see these?

 

[Crispy]

What happens to the mass of stars when they go supernova?
Is this spread out in interstella space which means we wouldn't be able to see it as it's not illuminated well enough but it's mass is still there. And what about the planets that surrounded that star?

How do we know what the exact composition is of distant stars?
The only place that fusion is known to take place is in stars and heavy elements found on earth are supposed to come from exploded / collapsed stars, so there must be stars out there with large amounts of heavy elements in them making their mass greater than expected. Due to the distance to these stars any spectral lines from these elements may be too feint to be detected here on earth plus the fact that heavier elements would most likely sink towards the center of any star with the resulting spectral lines being masked by the all the other material.

How much interplanetary dust / gas is there?
Although 1cc of this wouldn't weigh much there are billions and billions of cc's to take into consideration. I don't suspect this will be a significant amount but still accounts for some 'missing' mass.

What about stars that have simply burnt out without exploding. How would we be able to see these?

My my, we are full of questions today

 

[WouldBe]

I just don't see the point in inventing 'sky pixies' when there are lots of other possible explanations.

 

[Groucho]

What happens to the mass of stars when they go supernova?
Is this spread out in interstella space which means we wouldn't be able to see it as it's not illuminated well enough but it's mass is still there. And what about the planets that surrounded that star?

How do we know what the exact composition is of distant stars?
The only place that fusion is known to take place is in stars and heavy elements found on earth are supposed to come from exploded / collapsed stars, so there must be stars out there with large amounts of heavy elements in them making their mass greater than expected. Due to the distance to these stars any spectral lines from these elements may be too feint to be detected here on earth plus the fact that heavier elements would most likely sink towards the center of any star with the resulting spectral lines being masked by the all the other material.

How much interplanetary dust / gas is there?
Although 1cc of this wouldn't weigh much there are billions and billions of cc's to take into consideration. I don't suspect this will be a significant amount but still accounts for some 'missing' mass.

What about stars that have simply burnt out without exploding. How would we be able to see these?

I need to just format something at work but will answer all your Qs in due course.

 

[spiralx]

I think dark matter is just a massive miscalculation.

Astronomers are still finding objects floating around in our own solar system so still don't know what the mass of our solar system is let alone the mass of galaxies or the universe.

You do realise that one possibility for what dark matter is is nothing more than large, dark objects e.g. black holes or brown dwarf stars? They're called MACHOs , which stands for massive compact halo objects. Another is massive neutrinoes. Dark matter isn't just random new particles, there are plenty of candidates for what it could be. Whichever it is though, it still seems more likely than the alternatives.

Dark energy (different from dark matter) is a much newer idea, and there are plenty of explainations floating around at the moment. It's definitely a much more speculative idea than dark matter, give it a few years for the situation to calm down.

 

[WouldBe]

Dark energy (different from dark matter) is a much newer idea, and there are plenty of explainations floating around at the moment. It's definitely a much more speculative idea than dark matter, give it a few years for the situation to calm down.

I think dark energy is more daft than dark matter. Since when did energy have a mass? How much does an x-ray weigh?

I prefer the dark particle theory. Get the dp right and the calculations add up.

 

[Crispy]

I think dark energy is more daft than dark matter. Since when did energy have a mass? How much does an x-ray weigh?

The effective mass of an xray is it's energy divided by the speed of light squared.

 

[WouldBe]

How much interplanetary gas is there?
Although 1cc of this wouldn't weigh much there are billions and billions of cc's to take into consideration. I don't suspect this will be a significant amount but still accounts for some 'missing' mass.

Done a quick calculation.
I remember seeing on a NASA webpage (IIRC) a figure of 1 atom of hydrogen per cc of space so just in our solar system (upto the orbit of pluto) that works out as

1.5^15 tonnes of hydrogen.

Edit: that should be 1.5 x 10^15 tonnes of hydrogen.

 

[laptop]

And in other news, dark matter, dark energy, the big bang, the arrow of time, expansion of the universe, redshift-magnitude-distance equivalence and singularities do not exist!

http://www.stanford.edu/~afmayer/

Access forbidden!

You don't have permission to access the requested directory. There is either no index document or the directory is read-protected.

Do you think his calculations have found an error in him?

 

[WouldBe]

From the amount of space dust falling to earth each year you can calculate there is

4.349 x 10^17 tonnes of space dust in our solar system.

From the site I found the space dust figure interstellar space contains a higher quantity which is stopped from entering our solar system due to the magnetic field of the sun.

 

[Crispy]

Do you think his calculations have found an error in him?

You're looking in the wrong time direction.

 

[merlin wood]

"This strange material that dominates the Universe but which is invisible to current telescope technology is one of the great enigmas of modern science."

phlogiston indeed. So this website still only reports on inferred properties of dark matter. And not only is (non-baryonic) dark matter invisible to telescopes but it can't be detected by its collision with ordinary matter in experiments carried out for more than ten years. http://cdms.berkeley.edu/.

Yet neutinos have been detected that are a lot less massive than dark matter particles need to be and so have tau particles even though there are a lot fewer of them than the estimsted quantity of dark matter particles.

The behaviour of quatum objects can't be explained by action of any force so why not conclude that this is so of galaxies. So what causes quantum wave behaviour could be the same as what causes galaxies to be the way that they are.

So that what a physics of the forces alone can't explain is the natural organisation of matter either on the smallest or cosmic scale.

 

[spiralx]

So your answer to the problem of galactic rotation is to say "there is no explaination" i.e. it might as well be magic?

 

[J77]

the claimed 'standard' structure of the universe is now 4% atoms, 21% dark matter and 75% dark energy.

Yeah - it's all about dark energy now

 

[DarthSydodyas]

The dark side rules!

 

[kyser_soze]

Dark matter and energy, while providing some fun and amusing stuff in sci-fi and potty jokes for me is the glaring hole in the side of any argument with Dwyer-likes and their co-religionists/sky pixie fans. It's difficult to convincingly argue against the existance of God when they can turn round and say 'Well look at Dark Matter! Sounds about as credible as my sky pixie!'

Of course, then it becomes a nuanced and subtle argument concerning 'belief' in dark matter isn't some fixed thing like belief in sky pixies and that it's a provisional theory. I think it's a collosal balls up in the math somewhere - either there's tons of matter that simply has been missed/unaccounted for or cosmology is basically a discipline of sky pixies with calculus.

So, anyway...

 

[Crispy]

sky pixies with calculus

Tagline!

 

[DarthSydodyas]

I find your lack of faith.... disturbing...

 

[kyser_soze]

I find your lack of faith.... disturbing...

And that's the problem right there - faith. We're expected to have faith that 'One day we'll detect Dark Matter, you wait and see'

 

[merlin wood]

So your answer to the problem of galactic rotation is to say "there is no explaination" i.e. it might as well be magic?

Not at all, although you could say this depends on what you mean by 'magic'.

So, as I say, there's no explanation of galaxy rotation by decribing any known details of a force just as there is no explanation of the electron's orbital around the nucleus by describing details of any force, and so both the lage and small scale oganisation of matter is inexplicable by the physics of the the push or pull forces.

So what is needed is a general theory that provides a sufficiently detailed justification and description of an organising cause acting in addition to the forces. Such being a cause that, on the smallest scale, produces quantum wave, spin and ebtanglement. While physicists of the forces might well think to the effect that the postulation of the existence of such a cause is tantamount to proposing a kind of magic.

 

[Crispy]

Any sufficiently advanced technology is indistinguishable from magic

Obvious quote for the circumstances prize goes to Crispy.

 

[laptop]

So, as I say, there's no explanation of galaxy rotation by decribing any known details of a force just as there is no explanation of the electron's orbital around the nucleus by describing details of any force, and so both the lage and small scale oganisation of matter is inexplicable by the physics of the the push or pull forces.

You've decided in advance that "as above, so below", yes?

But it ain't so.

Yes, there's a big hole in theory when it comes to explaining galactic rotation.

It's interesting.

No, there isn't such a hole on the very small scale. Quantum theory is amazingly successful. It doen't describe electrons having "orbits" in the sense of going round and round the nucleus - that's just a lie-to-children to ease into describing the components. Quantum theory does predict what electrons do do. (The computer I'm typing this on is testing quantum theory all the time, and it's passing.)

The fact that we haven't managed to produce a useful "commonsense" metaphor for quantum mechanics isn't it's problem.

It's not even clear what a "commonsense" metaphor for quantum mechanics would be about. Would it be a description of what the quantum world would look like if we could see it from the inside? We can't. Would it be a description of what our world would be like if quantum effects were significant at our scale? They aren't.

So what is needed is a general theory that provides a sufficiently detailed justification and description of an organising cause acting in addition to the forces. Such being a cause that, on the smallest scale, produces quantum wave, spin and ebtanglement. While physicists of the forces might well think to the effect that the postulation of the existence of such a cause is tantamount to proposing a kind of magic.

Now you're just wanting to believe in a Mystery for its own sake, aren't you?

 

[kyser_soze]

The fact that we haven't managed to produce a useful "commonsense" metaphor for quantum mechanics isn't it's problem.

In the truly great 'Bluffers guide to the quantum universe' the author (a Cambridge Physicist) makes the point that a 'commonsense' metaphor for QP isn't possible since by it's very nature it defys 'commonsense' in every way - to even approach QP you have to ditch pretty much every assumption you make about the macroverse.

 

[merlin wood]

You've decided in advance that "as above, so below", yes?

But it ain't so.

Yes, there's a big hole in theory when it comes to explaining galactic rotation.

It's interesting.

No, there isn't such a hole on the very small scale. Quantum theory is amazingly successful. It doen't describe electrons having "orbits" in the sense of going round and round the nucleus - that's just a lie-to-children to ease into describing the components. Quantum theory does predict what electrons do do. (The computer I'm typing this on is testing quantum theory all the time, and it's passing.)

The fact that we haven't managed to produce a useful "commonsense" metaphor for quantum mechanics isn't it's problem.

It's not even clear what a "commonsense" metaphor for quantum mechanics would be about. Would it be a description of what the quantum world would look like if we could see it from the inside? We can't. Would it be a description of what our world would be like if quantum effects were significant at our scale? They aren't. Now you're just wanting to believe in a Mystery for its own sake, aren't you?

Kepler's principles of orbital motion were very successful in predicting the orbits of moons and planets but the mystery of a cause of orbital motion took another 80 odd years or so to unravel.

Scientific discoveries have only been made, in the the first place, by pointing out and admitting to natural mysteries.

Of cousre quantum effects are significant on our scale we are made of subatomic particles, atoms and molecules aren't we?

And why should it be assumed that push or pull causes should have acted alone to evolve all life on Earth and galaxies of stars and planets from a Cosmic Big Bang?

 

[laptop]

Of course quantum effects are significant on our scale we are made of subatomic particles, atoms and molecules aren't we?

That's the mistake people make when they try to call quantum mechanics in aid of some other idea.

Just because we're made of subatomic particles doesn't mean that the way they behave in vast numbers (us) in any way rembles the way they behave individually. If this wasn't so, then at this moment I'd be 47% at this desk and 53% out on the porch having a ciggy... without having passed through the door.

 

[J77]

And that's the problem right there - faith. We're expected to have faith that 'One day we'll detect Dark Matter, you wait and see'

There were quite a few scientists on the Horizon programme who thought that the detection of dark matter was a waste of time, money and resources.

Am certinly no expert. However, I think they try to measure collisions of dark matter at the very ends of pressure and temperature scales (high or low...???). Anyway, trouble is that dark matter has by definition no mass, so this makes it very difficult... but still the research money flows in.

I wonder if anyone's tried to detect the stuff in Bose-Einstein type experiments...???

 

[Crispy]

That's the mistake people make when they try to call quantum mechanics in aid of some other idea.

Just because we're made of subatomic particles doesn't mean that the way they behave in vast numbers (us) in any way rembles the way they behave individually. If this wasn't so, then at this moment I'd be 47% at this desk and 53% out on the porch having a ciggy... without having passed through the door.

Actually, the figures are more like 98% and 2%, which is why the cat is hissing at an empty space on the porch.

 

[merlin wood]

J77: Anyway, trouble is that dark matter has by definition no mass, so this makes it very difficult...

Not true, dark matter has to have mass for it to have gravitatioal effects.

And this is the problem: why should stuff consisting of particles of a significant mass that's supposed to comprise at least 90% of all matter not have been detected in years? of painstaking experimentsl research, and when tiny things like neutrinos were detected decades ago and as soon as an appropriate experiment was set up?