Space & Science

[MinaHarker]

*Rolls up sleeves and puts on "teacher" hat*

The existence of dark matter is inferred from the rotational speeds of individual stars in distant galaxies. If only the luminous matter had a gravitational effect, the linear speed of stars far from the central hub of their parent galaxy would drop off to lower values. HOWEVER, measurement has shown that the linear speed of stars reaches a constant value, once beyond the immediate central hub area, an stays there no matter how far out the star is. This can only be the case if there is some extra mass we cannot see. Since this mass is invisible (it is non-luminous) we call it "dark matter". All we know about it is that it is non-baryonic (not protons and neutrons), very massive and detectable only due to its gravitational effects. Not a fudge, very real.

[MinaHarker]

Precisely. The last thing a pilot wants to see at 40,000ft is 'this jet has performed an illegal operation and must be shut down. Would you like to send an error report?'

Given how many times we've seen planes go out of control and explode due to computer problems on "Destroyed In Seconds" (gotta love the Discovery Channel), I am amazed that computers are relied upon so much in advanced jets.

[Jason Thompson]

The problem with computer control in jet planes is not the control itself but the ability of the pilot to take control away from the computer. Some advanced military jets are actually incapable of flying without rapid computer-controlled adjustment of their aerodynamic surfaces. The problems arise when the computer system fails but doesn't let the pilot take control, or when the computer system is too easily turned off without making a big song and dance so the pilot knows its been turned off, or some other such errors in which, had the pilots known what was happening and been able to intercede, might not have ended so badly.

[Jason Thompson]

Question for Mrs Teacher Emma, which I've been meaning to ask for ages, but here and now seems a good place to do it:

How do we know that dark matter is non-baryonic? Wouldn't non-luminous baryonic matter also be invisible?

[MinaHarker]

Question for Mrs Teacher Emma, which I've been meaning to ask for ages, but here and now seems a good place to do it:

How do we know that dark matter is non-baryonic? Wouldn't non-luminous baryonic matter also be invisible?

It doesn't interact with electromagnetic waves at any wavelength, whereas baryonic matter (by its very nature) does.

[Jason Thompson]

Oh, right. Falling into the non-physicist error of assuming 'invisible' to refer only to the visible spectrum.

[Si Hunt]

Do you think it would be theoretically possible for science to invent a coat or bodypaint that makes you invisible when you wear it?

Si.

[Zbigniev Hamson]

There's plenty of baryonic dark matter too though, stuff that's just too cold or diffuse to detect any radiation from, but there doesn't seem possible to infer enough of that to account for the discrepancy.

Having said that... I'm not happy with dark matter. The evidence for it is incredibly circumstantial. There is a real problem there that can't be explained, but saying "oh well, there must just be something there that has mass but which we don't know anything about or understand in any way" is a rather poor attempt at an explanation. It solves a problem, but then, as it was conjured up specifically to solve that problem, it would wouldn't it. And there is as little known about dark matter as there was understanding about the original problem. So it is essentially a fudge. But a fudge that works for now, and might turn out to be right.

It could be just as possible that we don't actually understand how gravitation works on a large scale or in flat regions of space. It's certainly not the only explanation around Dark matter works quite well as a first stab at a sort of working hypothesis, but really it could turn out to be another "ether", steady state theory, or any other of the blind alleys of the past. Not that that's a bad thing of course, but it's good to be skeptical in science, especially over something as tenuous as dark matter.

The only real thing it has in its favour are the independent predictions from particle physics that there may actually be particles that would fit the bill as dark matter. But they are just hypothetical too.

Keep an open mind

[MinaHarker]

There's plenty of baryonic dark matter too though, stuff that's just too cold or diffuse to detect any radiation from, but there doesn't seem possible to infer enough of that to account for the discrepancy.

Having said that... I'm not happy with dark matter. The evidence for it is incredibly circumstantial. There is a real problem there that can't be explained, but saying "oh well, there must just be something there that has mass but which we don't know anything about or understand in any way" is a rather poor attempt at an explanation. It solves a problem, but then, as it was conjured up specifically to solve that problem, it would wouldn't it. And there is as little known about dark matter as there was understanding about the original problem. So it is essentially a fudge. But a fudge that works for now, and might turn out to be right.

It could be just as possible that we don't actually understand how gravitation works on a large scale or in flat regions of space. It's certainly not the only explanation around Dark matter works quite well as a first stab at a sort of working hypothesis, but really it could turn out to be another "ether", steady state theory, or any other of the blind alleys of the past. Not that that's a bad thing of course, but it's good to be skeptical in science, especially over something as tenuous as dark matter.

The only real thing it has in its favour are the independent predictions from particle physics that there may actually be particles that would fit the bill as dark matter. But they are just hypothetical too.

Keep an open mind

Some good points, although I disagree with the usage of "fudge". By that logic you could describe Newtonian mechanics as a "fudge" because they are non-relativistic like Einstein!

[Zbigniev Hamson]

Well yeah... it's not really a fudge, but that sounds better I have no idea what the truth is behind dark matter, but it's such a (relatively) new concept, and with so many unknowns surrounding it, that I can't help but think our ideas about it will change a lot over the next 50 years or so.

[Zbigniev Hamson]

Do you think it would be theoretically possible for science to invent a coat or bodypaint that makes you invisible when you wear it?

Si.

I think I actually saw an early version of something like this a few months ago, but it was just a quick thing on TV and I don't really remember it that well. I seem to remember it being a suit, probably made of a flexible LCD type thing, and probably Japanese too... perhaps. It certainly didn't make the wearer invisible, but it did make him blend in with the background a BIT. Basically the front of the suit showed an image of the wall behind him and as he moved it moved too. Maybe I dreamed it but I'm sure I really saw it

[Si Hunt]

I think I saw it too! I just thought it would be brilliant to be able to walk around invisible. And fly. Those are the two things I hope they crack before I croak.

Si.

[Andrew Curnow]

Since 'matter' has come up, can anybody tell me what strange matter is?

[Zbigniev Hamson]

Time and the Rani has all you need to know

[Fate]

Do you think it would be theoretically possible for science to invent a coat or bodypaint that makes you invisible when you wear it?

weara white coat in the artic and you find its quite possible

[Paul Monk]

I just thought it would be brilliant to be able to walk around invisible

There is an old magician's trick to enables you to be invisible on stage. Its quite cool and will give you that feeling of being somewhere and no-one being able to see you.
Find me a stage and some big mirrors and we'll recreate it!
And it is scientific!

[Jason Thompson]

Since 'matter' has come up, can anybody tell me what strange matter is?

According to Wikipedia it is a form of quark matter containing up, down and strange quarks. Clearer now?

[Fate]

http://news.bbc.co.uk/1/hi/sci/tech/8050157.stm

i think there are about 3 satellite telescopes being sent up to replace hubble. but they all use infrared instead of visual lite like the hubble does. which is rubbish really

[Jason Thompson]

Why is it rubbish? They are scientific instruments, not toys to gather pictures. The visible spectrum may look nice to us, but images taken in other parts of the specturm can be a lot more informative. It also allows us to see through the gas and dust clouds that obscure visible light, thus opening up whole new areas of study.

[Dirk Gently]

Jason, I think the point of the post was that 3 infrared telescopres are going up, not one of which is in the visible spectrum. Surely one of them could have been?

[Fate]

The visible spectrum may look nice to us, but images taken in other parts of the specturm can be a lot more informative.

i like the visual spectrum though and use it daily. pictures from hubble have really filtered down to the everyman to show the galaxy. hubble has been a great coup for people to see the universe as never before.

at the end of the day its the public who pays for these things. hubble will only last a few more years and the next visual telescope wont go up till 2020

take a look at these pictures - one in ir on in visual. which inspires most?





i think sometimes nasa just doesnt get it and has forgotten how to inspire and educate ppl. reminds me of the simpsons episode where they dont understand why people are unexcited about the latest launch which incldes a crew "There's a mathematician, a different _kind_ of mathematician, and a statistician"

[Jon Masters]

These new ones are not to replace Hubble, but to do a different job (and Hubble itself has instruments which look at infra-red and UV).

Since Hubble was launched, the development of Adaptive Optics has massively improved the clarity of ground based light telescope systems. However, to look for data based on IR or UV, or fine detail in the Microwave Background radiation (such as polarisation due to gravitational waves ) you have to be outside the Earth's atmosphere.

There are new telescopes planned which will collect visible light data, as well as other wavelengths; they're just not ready yet. Better to get them as future proof as possible first.

ETA Oh, and many of the images you see are computer enhanced for colour etc. anyway - and much closer in the first place.

[Fate]

thanks that explanes it nicely

[Zbigniev Hamson]

at the end of the day its the public who pays for these things. hubble will only last a few more years and the next visual telescope wont go up till 2020

Your point seems to be that the public are only interested in pretty pictures and interesting "characters" going on shuttle launches, rather than being happy for scientists to get on with actually learning things about the universe. That's a bit of a depressing outlook (though it might well be true).

[Jason Thompson]

Jason, I think the point of the post was that 3 infrared telescopres are going up, not one of which is in the visible spectrum. Surely one of them could have been?

Could have been, if you can find a suitable scientific justification for doing so. Funding, despite the popular misconception, is not thrown at space science willy-nilly. People in the field have to really fight their corner to secure the money, and that money is secured based on potential returns. Unfortunately, 'because the images look cool' is not in itself a justification for spending the millions on these things. It's a point I often have to bring up on other forums for people who think NASA should send something to the Moon just to take really high res images of the old Apollo hardware.