“It is possible to commit no mistakes and still lose. That is not a weakness. That is life.” -Jean-Luc Picard
We like to think of nature as beautiful, elegant and infallible. Yet our notions of what's beautiful and elegant don't always line up with what reality gives us. Take the notion of symmetry, for example: the gravitational force is symmetric, always exerting equal magnitude forces on whatever two masses it occurs between.
But as similar as they are, electricity and magnetism are not symmetric at all. There are no such things as magnetic charges or currents, and this has huge ramifications for physics. But it didn't need to be this way at all; the Universe could have been symmetric in this fashion. The fact that it isn't teaches us all sorts of things, including why the idea of a Grand Unified Theory (GUT) may not be in the cards for our Universe at all.
The May 1983 issue of Smithsonian had a huge, lavishly illustrated article about particle physics and the origins of the universe, which made mention of this experiment. I freaking loved it. ... Even though I subsequently had an occasional recurring nightmare about magnetic monopoles drifting in through my bedroom window and accreting on metal surfaces in the room, eventually growing into a large enough mass that I'd have to flee the room or even the house. Fortunately, it seemed to sharpen, rather than dull, my interest in the science, as it enhanced that sense of wonder about what's out there that drives a scientific mind. So I still love reading anything about magnetic monopoles.
The real punch line here, as Ethan (who knows me well) is aware, is that I was 4 going on 5 when that issue came out. :P
This article leads me to ask, - But what actually IS magnetism? On a fundamental level, how does it fit into physics? What particles or forces are interacting to cause magnetic effects?
Going off on a tangent, this is what a fresh planetary system looks like in the infra-red once gravity has been working on it for just a million years:
"Birth of planets revealed in astonishing detail in ALMA's 'best image ever' http://phys.org/news/2014-11-birth-planets-revealed-astonishing-alma.ht…
Special relativity and magnets
"What particles or forces are interacting to cause magnetic effects?"
mostly charged particles (i.e. electron) and their angular momentum. You can think of rotating electron as a rotating electric charge that will create a magnetic dipole moment.
A moving charge is not where it "really" is, and the difference of where it really is and where it appears give rise to the electromagnetic effect,BillK.
The first Feynman Lectures goes into this a bit.
Allowing for the Parker Limit, the magical 5 sigma level of proof is impossible to achieve.
Had Blas Cabrera made an eighteen loop coil and recorded a reading of eighteen magnetons, would such a finding also have been dismissed as an impossibility?
Thanks for this nice summary. You might want to highlight the fact that a time varying electric field produces a magnetic field. Also, I have heard that the electromagnetic force and the nuclear weak force have been harmonized in an electro-weak theory attributed to Feynman, meaning we could say there are only three fundamental forces. Is this true? Finally, it is also said that the electromagnetic force is mediated by an exchange of photons and that the electric and magnetic forces are just two aspects of the same thing. This I admit is beyond my grasp. Perhaps you could enlighten in a future post. Thanks again.
Do magnetic dipoles/monopoles pop in and out of existence like other virtual particles?
This is a question for your Answers column. Not sure how to find the proper way to submit my question.
Q. When planets are forming around a star, the material from which the planets will be constructed appears to be distributed in rings around the star such that the rings are all in a plane. Why isn't the material distributed in a more spherical shape rather than being confined to a plane?
@Delmas #10: A rotating sphere of gas or dust will necessarily flatten into a disk over time, because of the combination of gravitational attraction and conservation of angular momentum.
Parallel to the axis of rotation, gravity can pull the stuff together; it'll eventually (just from symmetry considerations) end up clumped around the original equatorial plane.
But within that plane (and in the absence of significant friction), stuff can't collapse inward, because doing so would require losing angular momentum.
You can ask, of course, why we assume the sphere is rotating in the first place. That is an issue which Ethan addressed quite well almost exactly a year ago: http://scienceblogs.com/startswithabang/2013/11/01/ask-ethan-9-why-ever…
Julian Schwinger proposed dyons, which have both electric and magnetic charge. He, as well as others before him, showed that a duality exists between magnetic and electric monopoles, where we can adjust our units of measure, to give the appearance of strictly electric charge.
#10 & #11
Ask Ethan #9: Why everything rotates was a great read.
The progression of matter and forces, once entangled as a tidal torque, then evolving into a triaxial ellipsoid, was very informative.
A moving electric charge produces a circular magnetic field, but it is a closed circle, so no magnetic charge. A rotating charge (or solenoid) produces a magnetic dipole along the axis of rotation, but the axis has two directions, so north and south magnetic poles. Period.
A "magnetic field" is only one interpretation of the relativistic effect of a moving charge. Einstein showed in his 1905 paper "On the Electrodynamics of Moving Bodies" that magnetic forces between two differently moving charges would disappear if the frame of reference was moving along with either of the charges. At the end of Section 6, Einstein offered the two choices of interpretation, one being the (old) view of magnetic forces.
Michael, mostly correct, but there's an additional point, that planetesimals that are not in the general plane of orbit of the majority CAN form, but they will more likely collide with planets and be disturbed out of that atypical orbit than planetesimals that are in the "consensus of planets" plane of orbit.
@Wow #5: You're quite right, of course, but that wasn't where I was going with my comment. I was responding to the broader question of "why a disk instead of a sphere," and essentially recounting Oppenheimer's analysis for why an initial spherical distribution will collapse to a disk. What happens with all of the dust after that is quite complicated, as you properly point out.
Fair enough, Michael. Cheers.
@Gary S #14:
I agree with you: magnetic fields only exist as an easier mathematical interpretation of what's going on with relatively moving charges...
Thus there can't exist magnetic monopoles. I wonder that there actually is serious research on them...