Magnets one of the most fascinating objects we encounter daily, they also inspired Albert Einstein when he was five years old, he received a compass. Young Albert was fascinated by the fact that no matter which way he turned the compass, the needle always pointed the same direction. This was his introduction to scientific inquiry. "That experience made a deep and lasting impression on me," he wrote years later.
So, in this blog we will take dive into currently a theoretical concept called magnetic mono-poles. A slightly fancier name to magnet is magnetic dipole. You must have seen this as a child that even if we break down a magnet it still has two poles left, why is that case? And why can’t we isolate the two poles.
To understand all these lets take a detour on what does modern theory of electromagnetism has to offer.
a) magnetic domains
In a ferromagnet, the field is the sum of the countless tiny aligned dipole fields of electrons in the magnet’s atoms.The other popular way to make a dipole magnetic field is the electromagnet - where were push electrons around in a circle In both cases - electron spin or or a circular electric current there’s a sense of electric charge in motion. And according to classical electrodynamics, moving electric charge is the source of the magnetic field. If that’s true then, why should we even expect there to be isolated magnetic charges - magnetic monopoles?Well, according the classical theory we shouldn’t.The non-existence of magnetic monopoles is codified in the mathematics of electrodynamics. In particular, Gauss’s law for magnetism,one of the four Maxwell’s equations.
b) Maxwell's Equations
It states that the divergence of a magnetic field is zero.The divergence is just this mathy term for
the amount that a field points inward toward a sink or outward toward a source. Zero divergence means no source and no sink.Magnetic field lines can form loops or head out toward infinity, but they never end.According to this law there are no magnetic monopoles. On the other hand, Gauss’ law for electric fields tells us that the divergence of the electric field is not zero - it’s equal
to the electric charge density. That charge density is where the electric field lines can end - it forms their source or their sink.So there are such things as isolated electric charges. Let’s take a quick gander at Maxwell’s equations.This is them without any charges - electric or magnetic.E is the electric field and B is the magnetic field.
c) Maxwell's Equations when electric charge is zero
There’s a near perfect symmetry between electricity and magnetism which only gets screwed up when you put in the electric charge - here in the form of charge density and current density.You could also have symmetry between these equations if there was such a thing as magnetic charge.
If you add magnetic charges to these equations then you get a magnetic force that looks exactly like the electrostatic force. The physicist Murray Gell-Mann said that "Everything not forbidden is compulsory."meaning that if the math of our physical theory allows it, then it exists in nature.
There’s nothing in Maxwell’s equations that really says magnetic monopoles can’t exist except for the fact that James Clark Maxwell set the magnetic charge to zero because he didn’t believe it existed.But in principle it could exist, and so could magnetic monopoles. At least according to classical theory.But what about quantum mechanics?When quantum theory first appeared it quickly revolutionized our understanding of electromagnetism by explaining it in terms of quantum fields
rather than charges and forces. We know that how electromagnetism arose automatically from the equations of quantum mechanics had a particular symmetry - the measurements they predict are unaltered by changes in one simple property - the phase of the wavefunction. Electromagnetism pops into the equations as soon as we require this - but in that version of electromagnetism, the electric and magnetic fields are VERY different from each other,and not at all interchangeable as they are in Maxwell’s equations. In particular, the magnetic field emerging from the quantum theory must have zero divergence - its field lines can never end - so it can’t have its own charge, unlike the electric field. So perhaps here we have our reason for theapparent non-existence of magnetic monopoles. Quantum mechanics, as the saying goes, forbids it. Well, not so fast. Don’t underestimate the power of the obsessed physicist. The great Paul Dirac had a habit of discovering particles just by staring at the math. In 1928 he predicted the existence of antimatter this way, But then in 1931, just before his antimatter thing was verified, Dirac made another prediction of the existence of magnetic monopoles.
His argument goes something like this. If you start with a dipole magnetic field, you can approximate a monopole by moving the ends far enough apart and somehow vanishing the connecting field lines. And there is a way to do that. If you build a solenoid - just a coil carrying
an electric current - you get a dipole field whose connecting field lines are constrained within the coil. So make the width of the coil much smaller than the length, and it looks like two isolated
magnetic charges.This construction is called the “Dirac string”, and Dirac’s argument is that if the string part of the Dirac string is fundamentally undetectable, then magnetic monopoles can
exist. The second part of the argument is under what conditions that string is undetectable.
d) Illustration of dirac string
So magnetic fields affect charged particles.In quantum mechanics, this works by shifting the phase of the particle’s wavefunction. Imagine a charged particle - say an electron- passing by a Dirac string.To plot that trajectory you add up all possible paths of the electron, including paths to
the left and to the right at the string. The presence of the string, with its magnetic fields, should introduce different phase shifts depending on which side of the string the electron passes - and that would actually have a noticeable effect on the path of the electron. In other words, the string would be detectable. But there’s one scenario where the string can never be detected.The amount of the phase shift is proportional to the electric charge. For the right value of that charge, the phase shift induced between the different sides of the string is exactly one wave cycle - which means no observable difference.
So for the Dirac string to be undetectable then electric charge can only exist in integer
multiples of that basic charge This is a very loose form of the argument - and you can get to it in different ways.But the upshot is that the string connecting monopoles is fundamentally unobservable, and Dirac argued that this makes it a mathematical figment, kind of like virtual particles. Reality should only be assigned to the monopoles themselves. On the one hand this was taken as a prediction of the quantization of electric charge - electric charge has to be discrete if there’s even
a single magnetic mono-pole in the entire universe. And of course we know that electric charge really is quantized - it can only be integer multiples of the charge of the electron. Or maybe of quarks - a third the electron charge. But instead of taking this as a prediction of charge quantization, you can also flip it: magnetic monopoles are possible if electric charge is quantized.
Charge turns out to be quantized, so quantum mechanics doesn’t actually forbid monopoles.
Well all that being said if we ever discovered this particles what are its uses
1)Magnetic monopoles can contain or isolate fields of ether.
The reason is, by polarizing a spherical metallic chamber with an outward field (or by building dividers made of connected loops), the chamber gets loaded up with an etheric vacuum. This has demonstrated to be an exceptionally solid obstruction against outside attacks, particularly electromagnetic and etheric ones.
2)Charged magnetic monopoles repulse each other actually like magnets.
This could likely be utilized to construct a genuine magnetic levitation rail route, by setting sheets of comparative monopoles under the train and on the tracks. Propulsion would be possible by calculating the sheets, which would speed up or decelerate the train (however, making a monopole out of a sheet of metal has proven difficult, and impractical work).
Comments