That’s giving QCD a bit too much credit, I think. QED we understand damned near perfectly, and its predictions are more detailed, and confirmed to more detail, than any other theory in all of science. QCD, by contrast, shows good agreement between experiment and theory… everywhere we can pull off the experiments, and where we can figure out the math underlying the theory. But the experiments for QCD are much more difficult to perform than for QED, and our usual mathematical techniques which work so beautifully for QED usually don’t work at all for most practical situations in QCD. Occasionally someone manages to figure out some new mathematical trick for solving the problems of QCD, but only in a handful of very restricted situations. There’s a lot of work yet to be done.
Probably. I’m sort of biased, I spent a lot of time in a previous life working next to some seriously smart guys working in Lattice Gauge QCD, and perhaps their hubris rubbed off a little.
We are very different people.
- In plain classical electrostatics, iyou cannot make two point charges collide – they have zero width. If you fire a positive point charge as close as you can to a negative point charge (and you can get arbitrarily close), the projective accelerates on the way in, whips around the target in a high-speed turn, then recedes to infinity, decelerating as it goes. It’s very much like what happens when a long-period comet whips around the Sun. The orbit has the general shape of a hyperbola, although sometimes it can be a parabola.
If we add in electrodynamics (meaning we’re turning on relativity), then the situation is much more complex, because the acceleration experienced by the charges will produce electromagnetic radiation, which will cause the projective to lose energy. If it doesn’t come too close to the target, it could still escape to infinity. But otherwise it will enter an orbit which then proceeds to decay (since the centripetal acceleration required to keep it in an orbit will cause it to radiate energy away). If the charges have finite size, they just eventually collide – classical physics has no problem with this, you then simply have a rotating composite object with a positive charge on one end and a negative charge on the other. Lots of stuff looks like that, including most molecules. If you still want to imagine the charge are point, you get an unreal situation, because they can just spiral in closer and closer forever, radiating away an infinite amount of energy (which is the potential energy they had at infinity, relative to zero separation). It’s a good question what the rate of power emission would be – whether it increases, stays constant, or declines. This strange behaviour was one of the motivations for quantum mechanics.
If you now add quantum mechanics, the situation is saved, even for point particles. The uncertainty principle forces the kinetic energy of the projective to rise faster than what’s required to keep it in orbit as the size of the orbit shrinks. That forces it back out again. What you find is that there turns out to be a smallest possible orbit, and energy cannot be radiated to make the orbit smaller. This is now a stable situation – and indeed describes the ground state of an atom.
So what happens for point charges, with the correct physics, is that the projectile approaches the target, accelerating and radiating, and if it is aimed close enough, the target captures it and, possibly after one final burst of radiation, the two form a stable nonradiating bound state that looks neutral from the outside. An approximation would be the capture of an electron by a free proton, to form a stable H atom.
If one of the charges is not point, then it’s possible for it to collide with the other. Nothing may happen – they may bounce off each other – or it may be that some nuclear physics takes place and you get a new particle that combines the charge of the two. For example, a proton and an electron can collide to form a neutron. Then more things may happen. For example, a free neutron is not stable, and will decay again to a proton and electron. On the other hand, if this happens within an atomic nucleus, the neutron may be stable, and what has happened is electron-capture or inverse beta decay. Many unstable nuclei do this.
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Electrons in an atom stay away from each other, in part because they repel each other, and even more so because the Pauli exclusion principle. But even if they did not, as long as the probability density of their being right on top of each other is finite, the electrostatic energy will be finite. You have to remember the potential energy contribution goes like 1/r but the volume element of integration goes like r^2. As long as the probability P® of their being at a distance r remains finite as r->0, the value of the integrand as r->0 goes to zero. If you’re not familiar with calculus that may be an opaque statement, so I will crudely approximate by saying that, yes, the potential energy goes to infinity as r->0 like 1/r but the time the two electrons spend closer together than r goes to zero faster than r, so it turns out they spend zero time infinitely close, and too little time very close to influence the total energy of the system.
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You have a couple ways of looking at this. You can consider the field as a fiction that is used to more easily calculate the forces charges exert on each other. Trapping a charge magnetically does not block electrostatic forces, so of course they can reach through a magnetic trap, which means the electric field escapes the trap. Or you can regard the electric field as a set of virtual photons (particles of electromagnetic radiation) that are emitted and absorbed by charged particles, and which cause them to act as if they feel forces – sort of like a fan making a wind that then pushes a sail, the photons playing the part of the wind. But photons are not affected by magnetic fields (up to a point), because they have no charge, so of course they can escape, which again means the field escapes.
Sorry, forgot to answer the underlying question: what is charge? Charge is a property of matter that causes it to exert forces on other matter in a certain typical way (the rules of electrostatics). How do we know charge exists? Because electromagnetic forces exist. You can think of charge as in some sense the susceptibility of matter to electromagnetic forces, just as mass is the susceptibility of matter to gravitational forces. Anything without a charge does not respond to electromagnetic forces, nor generate them. To say charge does not exist is logically equivalent to saying electromagnetic forces do not exist.
Carl Pham, impressive explanation.
There is only one other force in nature that can attract and repel and that is magnetism.
So, in answer to your challenge, my proposal would be to replace the ‘electrostatic charge’ of particle theory with a ‘magnetostatic charge’. Hence particles would carry a magnetic charge with north or south polarity and their anti-particles would carry the opposite polarity. So, like particles still repel and unlike particles still attract.
The switch from electrics to magnetics should not affect the basic understanding that our physicists have of the interactions within particle physics, but may offer new insights into how they work. That would be my hope.
Is this a whoosh? Electricity and magnetism are united in electromagnetism and have been since Maxwell. This is classical physics.
Whoosh or not, could that work?
I mean, as electromagnetism unites electrodynamics and magnetism, could you invert the formulation like this and get sensible, self-consistent physics?
If so, would the resulting physics be less elegant, or just strange-looking?
If it doesn’t change our basic understanding all you’ve done is changed the names. You’re also going to have to change the names of the north and south pole of magnets though, since electric particles aren’t attracted to the poles of magnets. So now magnets have a negative and positive end, and electricity is defined as the flow of north through a wire, or south flowing in the opposite direction.
Or did you have something else in mind? Preferably something that’s compatible with electric current giving rise to magnetic fields, moving magnets inducing currents, moving electric particles experiencing forces perpendicular to the direction of travel and the magnetic field lines when moving through a magnetic field, and so on and so forth.
The formulation is already symmetric, mathematically. Electric charges provide electric fields; moving electric charges provide magnetic fields; magnetic charges provide magnetic fields; and moving magnetic charges provide electric fields. Empirically, however, there don’t seem to be any* magnetic charges in the universe, so we tend to ignore the terms in Maxwell’s equations that require them.
*nitpick bait here
The way my old advisor put it: “We know that magnetic monopoles exist. There might, however, be a very small number of them, such as zero.”
Francis, I liked your analogy. Even I acknowledge that a force can only be overcome by a bigger force. If we had a device that could harvest protons in the same way that we are able to harvest electrons onto a storage device and then bring it close to the Penning trap, then perhaps that will do the job and drag the electron through the magnetic barriers.
But there is another implication that I was driving at with the Penning Trap question. If it’s a fact and I have no reason to doubt it now, that the electrostatic field from an electron can penetrate a magnetic field and not combine to form an electromagnetic field, then how do electromagnetic fields ever form!
Harvesting protons is pretty easy - not much more difficult than electrons in principle. They are after all sitting around inside hydrogen atoms, and only need enough energy to separate them from their single electron.
The simplest thing to realise about electrostatic, magnetic and electromagnetic forces is that they are all the same thing. The clue about the way they all work is in the name - electrostatic - static - not moving. The moment your charge moves the game gets vastly more complex. A moving charge has a magnetic field. Whilst your notional proton is sitting still relative to the electrons and the Penning Trap there is no magnetic interaction (save, pedantically, the proton’s own magnetic moment). Once it starts to move, game changes, and the fields interact (or perhaps more properly the total field becomes more complex).
The manner in which this happens is, astoundingly, and rather satisfactorily, explained by the application of special relativity. It is one of the more astonishing aspects of relativity that, whilst we are used to explanations invoking velocities approaching some fraction of light to see the effects, charges moving at a snails pace are also covered, and the remarkable result is electrodynamics.
I suppose that I do have something else in mind, but be aware that eventually it will involve butting heads with Maxwell and to achieve this, I believe it needs a group of physicists with the knowledge and intellect to think the ramifications right through. But I’ll try to sow the seeds.
The proposal is to eliminate the concept of charge and replace it with a magnetic capability, which, from measurements of the magnetic moments of particles, is already known to exist. So nothing contentious there, I trust.
All particles with spin, have the capability of creating a magnetic field ring around themselves and this is generated when undergoing an accelerating force. The spin, by convention, is viewed as clockwise along a particle’s axis and this determines the direction of spin of its magnetic field ring. The magnetic field ring rotates in a plane that is perpendicular to the axis of electron’s spin. This direction of rotation of the magnetic ring determines whether its ‘north seeking’ or ‘south seeking’ to use current, but dated, terminology. So two electrons will repel each other by opposing polarity, not by opposite electric charges.
By flipping the electron’s axis by 180 degrees, the two particles now of opposite polarity will attract and form an electron pair. This flipping of the electron creates its anti-particle and this simple process should be true for all particles.
Turning to the more basic phenomena of physics, an electron accelerated in a wire absorbs this energy by generating its magnetic ring, which appears outside of the conducting wire, along with billions of other magnetic rings and this is termed a magnetic field. The rings spread out in greater and greater diameters all around the wire, obeying Pauli’s exclusion principle, namely, that two magnetic rings cannot reside in the same location in space.
It becomes interesting when the current in the wire is alternated. The established set of rings of one polarity are reversed, collapsing back into the wire and a new set of magnetic rings with opposite polarity are established. Iconic experiments with an alternating current found that at a certain frequency, radiant energy was produced and the frequency of the radiant energy was found to equal the alternating current frequency.
The explanation lies in the finite time it takes the outermost magnetic rings to collapse in sequence back into the wire, before the next set of magnetic rings of opposite polarity grow. The two sets of magnetic rings compete for the same space and as the new rings have an opposite polarity and are growing, the established outer set of magnetic rings are displaced and repelled from the circuit as pulses of radiant energy. This is contentious now, because I am not saying electromagnetic energy. But with no electric charge to play with, that is the outcome.
I think this is a good point to sign off and batter down the hatches! But if I find I can open the hatch again, there is probably more to come.
What problem are you trying to solve with this proposal? What is wrong with “charge” that isn’t wrong with “spin” or any other intrinsic property?
The charges of particles are also known from experiment.
No armchair physicist has ever sown seeds that overturned basic physics after real physicists thought through the ramifications. And that is despite many physicists being real patient in thinking the ramifications through and then explaining to armchair physicists what the evidence is for their seeds being grains of sand.
As Pasta just said, you’re trying to solve problems that don’t exist except to you. Your reasons for calling them problems are cherry picked to justify a personal hangup, not the results of an unbiased analysis. This is evidenced again in your approach to arguing for your idea, as Chronos just pointed out you are picking and choosing which experiments and observations to bring along into your new world, and the only criterion is whether or not you’ve managed to contrive an explanation for them in your new physics.
And that analogy would be incorrect. Electrons are not classical particles; their masses, charges, etc. are completely fixed. There’s no classical analogue for this; it’s a feature of quantum theory.
Understandable to whom? QED makes extraordinaily, unreasonably accurate predictions that have been confirmed by experiment. With all due respect, you’re rejecting a theory with a huge pile of theoretical and experimental proof behind it solely because you arbitrarily dislike it. To take one particular example:
These aren’t separate ‘positive’ and ‘negative’ forms of charge; they’re both electrical charge. I’m not sure what you mean by a ‘neutral charge’, but there are certainly other processes in particle physics besides electromagnetism. The decay of a neutron into a proton, for example, is a result of the weak interaction: the down quark in a neutron (udd) becomes an up quark in a proton (udu), emitting a W boson that decays into an electron and antineutrino. This is not an electromagnetic process. The weak interaction looks completely different: it changes quark flavor, behaves very differently over different distances (since it’s mediated by massive particles, rather than the photon), has a coupling constant that varies more strongly with energy, etc.
What naita said. Physics isn’t arbitrary. If you want to propose a new theory of electromagnetism, you’ll have to explain why the current theory doesn’t work (and QED is probably the most rigorously confirmed physical theory we have) and why yours does. Many people have mentioned QED or quantum field theory here. The right response is to go read books on the subject and learn more about it, rather than trying to come up with a thought-experiment to solve a problem that doesn’t exist. You talk about quarks, for example, like they “stretch incredulity,” despite being a well-established idea that’s been confirmed experimentally. Physics is awesome. There are answers to the questions you asked. There are also questions in physics that haven’t been answered yet, but this is not one of them.
It is clearly time to wind up this post following a damning indictment and unanimous support for the concept of an electric charge.
But perversely, I was encouraged by the posts, because as the debate moved on to magnetism, no one actually put a finger upon the concept of QMD (Quantum Magnetodynamics), with a ‘show stopping’ question. Truthfully, there was one which nearly made me throw in the towel, but obtusely, it led to a re-consideration of the theoretical concept of a ‘magnetic monopole’.
The thought it generated was that all electrons must carry an intrinsic ‘magnetic monopole’. Whether it replaces the electrostatic charge or compliments it, is a mute point. I would say it does replace it, simply because it strikes off the list of ‘perceived’ shortcomings of electrostatic charge theory, which I itemised to initiate the debate. But I could live with both, as taken together they could strengthen the concept of electromagnetism.
The replacing or addition of a ‘magnetic monopole’ characteristic, gives every electron the intrinsic ability to generate a magnetic ring, which starts from the electron and follows a finite loop before returning back to its home electron. Its edge over the electron charge concept, is that the energy is quantised, finite and never dissipated, except under electron acceleration, when it can radiate the excess energy away.
Magnetic rings obey Pauli’s exclusion principle, which means they can never occupy the same space, nor can they cross each other, which affects the behaviour of particles that carry the magnetic monopole. Finally, besides being able to attract and repel, the magnetic ring has one other useful characteristic in that its rings can be cut and reformed.
My thanks to all those who have commented on, taught or given advice upon this topic. Many I have not been able to reply to, but sensing their competence and courtesy, they were greatly appreciated.
Despite being roundly derided for my challenge to the concept of electric charge, the alternative idea of QMD is out there and if it has any merit, it will be picked up by someone. I also hope that the 1800+ people who have viewed this unfolding debate have enjoyed it, been entertained by it, but mostly have learnt from it, as have I.