Where Grey Matter meets Dark Matter
Episode 10 - 17 April 2009
When people think of magnets, the main thing that probably comes to mind is a lump of metal that will attach to certain other lumps of metal. And if you bring two magnets together in one way, they repel, otherwise they stick. Or you might think of a fridge magnet, which barely sticks to anything. These are known as permanent magnets, since they stay magnetic for a while.
Another magnetic image that might appear is that of a crane in a wrecking yard, lifting a car into a compacter for cubifying. These magnets are called electromagnets - they work as long as the electricity is on. And it's these electromagnets that are really at the heart of all magnets.
An electromagnet is just a loop of wire with electricity running through it. Thanks to some equations put together in the 19th Century by a guy called James Maxwell. We know that any piece of wire with a current in it will generate a magnetic field, but these fields don't have north and south poles, so they're not what you ordinarily think of as a magnet. But if the wire is looped into a circle, then geometry tells you that it forms exactly a magnet, with north and south poles and everything.
A funky-looking electromagnet. Note the many coils.
The amazing part of all this is not only that just a thin piece of wire, with only air in the middle, is a magnet, but that ALL magnets are basically these loops of wire.
Imagine an atom. Atoms are made up of a small nucleus with electrons buzzing around the outside. You can think of the electrons as 'orbiting' the nucleus (this is isn't exactly correct, but it gives the right answer in this case). So we have electrons going around in a circle; which is exactly what happens in a loop of wire when you put electricity in it. And so maybe they also make a magnet? The answer, you keen inquirer you, is yes. See the following handy diagram for clearness of extraordinary magnitude.
Diagram promising extraordinarily magnitudinous clarity: imagine the spinning electron is orbiting the nucleus, generating a magnetic field pointing from the 'S' side to the 'N' side.
It all comes down to 'angular momentum' which is just regular old momentum (the force you feel when something hits you) but for an object going in a circle. If electrons have angular momentum, then they have a 'magnetic moment'. They get this angular momentum from orbiting the nucleus like the earth orbits the sun (not really, but close enough) and because they are spinning on their own axis, like the earth's rotation (also not really, but close enough). These 'magnetic moments' turn each atom into little magnets, with north and south poles.
Stuff is made of atoms, so it's no surprise that stuff is magnetic. If enough of the atomic magnets could be convinced to point in the same way then, overall, the whole lump of stuff will be a magnet. And that's what happens if there's an external magnetic field affecting the lump - the external field can convince the atoms to line up. It's the effect of this external field that lets you divide stuff into three categories of magnetism: paramagnetism, ferromagnetism and diamagnetism.
Paramagnetism: The external magnetic field convinces enough of the little magnets to line up to make the lump magnetic. When the external field goes away, then the atoms rotate off into random directions again, and the effect is lost.
Ferromagnetism: Again the external field makes the magnets line up, but now they stay lined up after the external field turns off. This is how you get cheesy, overpriced touristic junk to stick on your fridge.
Diamagnetism: These are the too-cool-to-conform types of the magnetism world - if an external field is applied, then they line up in the opposite direction, and are slightly repelled. And just like the hipsters and emos of our world, diamagnets don't have any real conviction either - diamagnetism is a much, much weaker effect than para or ferromagnetism.
It's more complicated than that, involving electronic states of atoms and molecules, but that's enough for now.
If you want to know more about how people try to (mis)use magnets for health and wellbeing, just type 'magnets for health and wellbeen [sic]' into Google.
Some people claim to be magnetic, but this trick usually turns out to be sticky, greasy sweat.
- Here's the ad for the wine-ager (sent to us by Em) which started the whole discussion: http://www.skymall.com/shopping/detail.htm?pid=102726830&c=
- Real information can be found all over the place. Most first year university textbooks have a good qualitative description - you can usually skip over all the Biot-Savart and Maxwell maths.
- Here's some info about strengths of magnets: http://www.coolmagnetman.com/magflux.htm
On the scale of commonly used internet-related phrases 'Look it up on Wikipedia' must rank right up there with 'Google it' and 'It's down'. Wiki has become synonymous with accessible, immediate, if somewhat questionable, information. According to Wikipedia (co)founder Jimmy Wales: "Imagine a world in which every single person on the planet is given free access to the sum of all human knowledge. That's what we're doing."
Lofty goals. But what happens when people who don't agree on the facts all try and write the same article? - Wikipedia happens. As part of its own lexicon of new jargon, 'edit wars' has been coined to describe the arguments (often petty) of editors (often petty) with different agendas editing and counter-editing the words of other editors. Without any real screening process of the editors this sort of factual 'roshambo' is an unavoidable part of the system. But is that so bad? People have arguments. People have arguments on Wikipedia - the circle of life rolls on.
Another criticism of Wikipedia is that it's too full of nerd trivia, in other words it suffers from 'wikigroaning' (you can't criticise the thing without coining a phrase, it's probably a rule). A description of Grey's Anatomy is likely to be more lengthy than an article on Gray's Anatomy. You'll also find a lot more detail and coverage of topics in western Europe and North America than anywhere else on Earth. Again, is this so bad? People do this for free (unless they're up to nefarious acts) and so it makes sense that they will only write about things they know and care about. To say that Wikipedia is not good enough because it only has these things on it is tantamount to saying that books aren't good enough since there are some topics about which no books have been written.
Of course, since people edit this from the comfort (and anonymity) of their chosen computer, the door is wide open for naughty people to be up to no good. For example (from here):
- The National Rifle Association of America replaced a passage on increasing gun-fatalities in the USA with a reference to the association's conservation work in America.
- A bishop in the USA reportedly ordered his assistant to delete info on Wikipedia about a $11.6M cover-up attempt of child sexual-abuse case. (Barbara Alton, assistant to Episcopal Bishop Charles Bennison, in America, deleted information concerning a cover-up of child sexual abuse, allegations that the Bishop misappropriated $11.6 million in trust funds, and evidence of other scandals. When challenged about this, Alton claims she was ordered to delete the information by Presiding Bishop Katherine Jefferts Schori).
And from somebody who should know better (ref):
- Jimmy Wales' public edit logs reveal that he changed his own Wikipedia bio 18 times, deleting phrases describing former Wikipedia employee Larry Sanger as a co-founder of the site.
Many people will know that there were encyclopedias before Wiki, and the most well-known was the grand old lady, Encyclopaedia Britannica. The question naturally arises: how much more accurate is a professional encyclopedia, like Britannica, than Wikipedia? Well Jim Giles asked that exact question, and conducted a study, publishing the results in another venerable English institution, Nature. His results: about 3 errors per page for Brittannica and about 4 for Wikipedia. Given that Britannica stands for the highest quality information on offer, we can no doubt expect them to respond in a fashion that encourages criticism: "Almost everything about the journal's investigation, from the criteria for identifying inaccuracies to the discrepancy between the article text and its headline, was wrong and misleading." Well, maybe they're right.
In the end we do need to worry about 'Wikiisation' (has a new phrase just been coined?) of knowledge. Wiki relies on democratic concensus among the editors to get the facts right, but science (and history for that matter) isn't a democracy, and not everybody's say is equal. Only those people with the relevant knowledge are qualified to speak up. At this point people will often say, 'But the peer-review process is all about having another person's opinion' - this is where the definition of 'peer' becomes integral to the discussion. You don't ask a geologist to review a paper on the lymphatic system, nor do you care for the comments of a graphic designer on the status of the field of combinatorial group theory. A person becomes a 'peer' only when they have knowledge relevant to the discussion at hand. Once you open up comment to all and sundry, you are looking for a democratic concensus, which can be a problem. This type of concensus can easily be warped through a concerted campaign by the wackos (using arguments based on hunches and emotions), each of whom is just as much an editor as anybody else.
Or let's say that the knowledgeable people just get tired of arguing - nobody is getting paid, remember. But then there's one last line of defence: the administrators. Like something out of a Star Wars expanded universe novel, they strike fear and anger into the hearts of many. These 1500 special editors try to keep things friendly, consistent and referenced. But with at least 10 million pages, their task is none too easy. And of course there is always the conspiracy-minded question: who administrates the administrators?
- Here's an article from PC Authority, including an interesting test of how quickly errors are corrected.
- More about Wikigroaning here and here.
- The Nature article comparing Wikipedia and Britannica: Giles J . (2005), "Internet encyclopaedias go head to head", Nature, 438 , pp.900-901.
- Britannica's response.
- And back to Nature for a counter-counter-point.
- People can and do use WikiScanner to find who is making changes to Wikipedia pages.
Note the cosmic transition to the quiz this week. And for those who didn't recognise our satirised version of the commerical for Flea Market Montgomery, here's the original: ***.
Oops. Mistakes we shouldn't have made but did:
Anthony didn't make exactly clear the difference between magnet strengths. The reason is that defining magnet strengths isn't exactly clear. You can list the field stength in Tesla or Gauss, but that is also a function of distance from the source. A small magnet may have a huge field strength on the surface, but will drop off to nothing within a few tens of centimetres. Yet a huge MRI magnet may 'only' be a few Tesla but it might extend for 10 metres or more.
Nini mentioned flamewars without describing them - these are heated online arguments which usually have nothing to do with the topic and everything to do with making the other person angry.