"Overwhelming" Evidence For Magnetic Monopoles 256
Thorfinn.au sends along big physics news: magnetic monopoles have been detected at low temperatures in "Dirac strings" within a single crystal of Dysprosium Titanate. Two papers are being published today in the journal Science and two more on arXiv.org, as yet unpublished, provide further evidence. "Theoretical work had shown that monopoles probably exist, and they have been measured indirectly. But the Science papers are the first direct experiments to record the monopole's effects on the spin-ice material. The papers use neutrons to detect atoms in the crystal aligned into long daisy chains. These daisy chains tie each north and south monopole together. Known as 'Dirac strings,' the chains, as well as the existence of monopoles, were predicted in the 1930s by the British theoretical physicist Paul Dirac. Heat measurements in one paper also support the monopole argument. The two, as yet unpublished, papers on arXiv add to the evidence. The first provides additional observations, and the second uses a new technique to determine the magnetic charge of each monopole to be 4.6x10-13 joules per tesla metre. All together, the evidence for magnetic monopoles 'is now overwhelming,' says Steve Bramwell, a materials scientist at University College London and author on one of the Science papers and one of the arXiv papers."
Not really useful (Score:1, Interesting)
They come in "pairs" huh. Sounds like the N S of a regular old fashioned magnet to me. If they could be separated ever then they really would be monopoles but otherwise how can you be sure its not just a regular magnet thats too small a scale to detect the flux coming from every angle around it?
not a "real" monopole (Score:5, Interesting)
I think what the summary is refering too is similar to the creation of a electron and hole pair in a semiconductor rather than a fundamental monopole particle. So they are in fact creating both poles but that inside the spin glass they are not confined with respect to each other so each one appears as a monopole in the material.
Comment removed (Score:3, Interesting)
Re:Analogy (Score:5, Interesting)
Are there any applications for it within our understanding of physics?
The existence of monopoles is a possible "explanation" for the quantization of electric charge. Maxwell's Equations are only self-consistent if:
1. magnetic monopoles don't exist, and charge is not quantized;
OR
2. magnetic monopoles do exist (at least one, somewhere), and charge is quantized.
As charge is quantized, it has always been a strong argument for monopoles' existence. Of course, perhaps Maxwell's Equations aren't applicable at the quantum level, but so far they've done a damned good job of being consistent and predicting and explaining things.
Re:lo, you have defeated me (Score:3, Interesting)
You should do some more research, anarchyboy is right, there is no theoretical reason (aside from never having observed them) why magnetic monopoles cannot exist.
What this work shows is that they can exist, although it is not in the 'real world', but as effective particles in a solid state system. The mechanism will be similar to spin-charge separation [wikipedia.org] that occurs in 1D systems, whereby the degrees of freedom of a particle separate into independently moving constituents. In this case, it will be the north and south poles of a dipole that become effectively independent and behave as distinct particles.
This doesn't mean that monopoles must be able to exist in a vacuum, possibly (probably?) they cannot, but the reason why will be due to the properties of the vacuum, not any fundamental restriction on monopoles.
Re:a magnetic monopole is like a one-sided coin: (Score:2, Interesting)
Wrong analogy. An electric charge exists statically, whereas a magnetic field only exists by virtue of a nearby moving electric charge. Whenever something is moving, the first derivative of its position can be described with a vector, which, unless the vector has no magnitude, indicates that it must be moving away one position while simultaneously moving towards another. This duality is, roughly speaking, where it comes from that you cannot have a magnetic field with only one pole... it is approximately mathematically equivalent to the notion of a non-zero vector having no additive inverse.
Re:Interesting, but... (Score:3, Interesting)
I don't see why monopoles should imply perpetual motion.
But the machine in the link you give doesn't make any sense at all. We could build it today, using electric charge instead of magnetic charge but it still won't work. Monopoles aren't some magic that mean the other laws of physics don't apply any more.
At the very least to be plausible, any perpetual motion machine that depended on magnetic monopoles would also have to depend on electric monopoles otherwise you can build an equivalent machine using electric monopoles instead of magnetic monopoles.
The universe is uncharged. Therefore every electric charge forms part of a dipole therefore electric charges aren't monopoles?
Tim.
Or neither of the above (Score:4, Interesting)
so i must be insane, or the whole lot of you are ignorant of what a magnetic field is
I'd like you to consider the possibility that it's neither of the above. I recognize your signature and remember you making many good posts in the past. I don't think you're crazy. I just think you don't understand the theory of electricity and magnetism very well.
Electric fields also begin and end at particles. And there are electric dipoles, just like there are magnetic dipoles. Why should magnetism only have dipoles and not monopoles like electricity?
Just as electric dipoles are made from positive and negative electric monopoles (charges), there is no reason magnetic dipoles can't be made from opposing magnetic monopoles. Electric monopoles are definitely MUCH easier to observe in nature, but that doesn't mean there are no magnetic dipoles.
Did you know that observers in different reference frames will disagree about the strength of electric and magnetic fields? Electric and magnetic fields vary (in a coordinated way) under Lorentz transforms. That is, what looks like a pure electric field to one observer might look like a combination of electric and magnetic fields to an observer in a different reference frame. Putting it differently, eletricity and magnetism are two aspects of a single force called, creatively enough, the electromagnetic force. That's a reason to believe that magnetic monopoles might exist.
Additionally, electric charge is observed to be quantized in nature. All free particles observed so far have charges that are integer multiples of the electron charge. Quarks are believed to have charges that are +/- 1/3 or 2/3 of the electron charge, but free quarks have not been directly observed, and in any case, even if the basic unit of charge quantization is 1/3 of the electron charge, charge is still quantized. And in the theory, the existence of magnetic monopoles automatically leads to charge quantization. That's a big reason many very smart folks with Ph.D.s in physics have been looking for magnetic monopoles for some time.
I remember a magnetic monopole detector that was sitting in a garage-like bay at HEP, the High Energy Physics group's building, at the University of Chicago in the late 1980s. I believe it was something Henry Frisch [uchicago.edu] had set up really cheaply, so the risk was low, and the potential return enormous. Think of it as a low-budget HEP nerd experiment in Chicago. If you look at Professor Frisch's CV, you'll see that he's written a bunch of papers about magnetic mnopoles and their detection.
Only tangentially related: it has been 20 years, so I shouldn't have been surprised, but seeing Frisch's hair that white was a bit of a shock. Probably because of what it implies about my own age.
Re:why a monopole implies perpetual motion (Score:5, Interesting)
Unending magnetic field lines and a particle with a net magnetic charge does not result in "perpetual motion", where that term always means "perpetual motion in the face of friction or other counteracting forces", because minus that "perpetual motion" is just Newton's 1st Law and completely uninteresting.
In the case of a magnetic monopole, it's actually little different than electricity (I know you think otherwise but you're wrong, look at the force equation), and in the case of electric fields, a charged particle in that field has a certain amount of potential energy, and that potential energy may be converted into kinetic, and that kinetic energy may be enough to reach escape velocity for the universe, but it isn't perpetual motion.
I know it's pointless explaining this to the deliberately dumb troll, since even if you wanted to understand it'd require you knowing some of the actual theory and math behind the physics you only understand through inaccurate analogy, but it's entertaining anyway.
P.S. Yes you're insane and yes you're stupid.