My wife picked up, just for fun, some strong rare-earth magnets.
I’m baffled by how magnetism works. I can sort of wrap my head around gravity, but what is magnetism? Yes, yes, I know, it’s all about the electrons.
But when I push two of these magnets together, they start to influence each other six inches apart. The electrons aren’t touching THAT far out. How do the magnets, or their component particles, affect each other without touching? Sure, sure, there’s a magnetic field. But what IS it?
What is it that allows you to understand gravity but not magnetism? The Earth and the Sun are not touching, but they influence each other.
IANA physicist, but as I understand it, an electromagnetic field is a cloud of virtual photons around a charge.
If you can explain how gravity works at a distance, you’ll win the Nobel Prize.
I have a problem with this expression: “…electrons touching…”
I think we all narrow our ability grasp certain atomic-level concepts when we use such descriptions. It just doesn’t work that way.
Someone help me out here!
We picture a physical model of atoms, etc and then lock in on electrons in orbits, etc. It just ain’t that plain and dandy.
Nobody really understands it. Don’t feel bad.
ETA: I just remembered that I read an article in Discover magazine about this a while ago.
Here is the article: http://discovermagazine.com/2008/may/02-three-words-that-could-overthrow-physics/?searchterm=magnetism
I work with induction motors and solenoids a lot, thoughts about what magnetism really is are what keep me awake some nights. No one really knows how it works; we can measure it, we can harness it, we can’t explain how it ultimately works at a distance. It’s easier to explain how electricity works (and that’s saying a lot) so most sources I’ve come across focus more on the electro- part of electromagnetism.
Matter pushing against matter is doing a similar sort of thing. Matter isn’t made of little hard balls of stuff - it’s made from ‘particles’ that are probably more aptly described as fields - so when you poke your finger in your eye, the atoms on the end of your finger didn’t touch your cornea, the two things repelled each other’s presence - not unlike what happens with a couple of magnets, only at a smaller scale.
So magnets aren’t doing anything unusual at all.
All forces work by particle exchange. Imagine you and a friend, spaced apart, and you throw a medicine ball at your friend. Your friend catches the medicine ball and experiences a force from that medicine ball, caused by you, but without your touching the friend.
(That describes a repulsive force. Imagine throwing your friend a boomerang to get an attractive force.)
In electic and magnetic fields, the “medicine ball” that is exchanged is a photon. For gravity, it is a graviton. For weak forces, it is a W or Z particle, and for strong forces it is a gluon.
Feynman diagrams are used to illustrate the forces and also to itemize the mathematics involved (physics happens at the vertexes.)
Electromagnetic waves have two components, a wiggling electric field and a wiggling magnetic field, at right angles to one another. The force is transmitted by the electromagnetic force particle, the photon.
Most people think of photons as particles of light (which they are) but forget that light is just electromagnetism.
So the magnets interact by throwing photons at one another. They’re low energy photons, compared to light, so you can’t see them (much like you can’t see radio).
Editing to add: I read through the thread and was amazed I’d get the chance to be the first to tell you about the photons. Then a dang-ol’ PhD SDSAB lady gets in ahead of me!
Good to see you, Karen the Penquinist. You should write some more staff reports.
I like it! I’ve “always” had a hard time conceiving of the transfer of a virtual particle as being attractive in result. It was always easier to picture the sender recoiling and the receiver being shoved backward.
While it’s not a formal explanation of a Physics situation, it’s certainly as good an image as any. Frisbees would work for me as well.
It seems odd to me that no one has brought up quantum entanglement. There once was a baffling mystery of “action at a distance” that so perplexed researchers going back to Newton, IIRC. It has been settled by the introduction of virtual particle exchange, as has been covered.
However, once two particles become entangled, they really seem to interact without regard to distance. This seems to me (and apparently, others) to be a “resurrection” of the mystery, although in different terms.
Action at a distance had better be easier to understand than action by things that touch. As others are noting, NOTHING actually touches, if you dig deep enough. All action is action at a distance.
It may help to say that magnetism is just an Einsteinian relativistic effect, arising from moving electrons and the length contraction. That’s why they refer to the electromagnetic force. There is electrostatic force, like between balloons and hair, and nothing else. Magnetism is another view of that force, courtesy of Einstein’s special relativity.
I’m currently studying Einstein’s 1905 “On the Electrodynamics of Moving Bodies”, and it’s led me to dozens of moments like this: “Oh, right, nothing actually touches, because everything is essentially composed out of very tiny electromagnetic fields, not actual stuff. That makes perfect sense - how did I not realize that before?”
pause
“Wait, that makes no damn sense at all, because of course I can touch things…”
In reality, part of why we don’t understand these things is that it’s a relatively young field. Atomic theory really began to come into something like it’s modern form starting in the 1800’s, and we’ve only been aware of sub-atomic particles since 1897. And the discovery of these things was not a direct linear progression: different people did different things that maybe implied some things independently, but only really moved research forward when combined with a whole bunch of other experiments.
Which reminds me of one of my favorite threads: [thread=299054]Why can’t my hand go through my desk?[/thread]
Ultimately, the entire business with the exchange of gauge bosons (force carriers described by Karen Lingel) is something of a formalism; we can’t actually see these exchanges directly, all we can do is infer from the result. However, the math works out very well (at least in the case of the electromagnetic force, and strong and weak nuclear interactions) and allows us to predict the result of an interaction to a high degree of statistical certainty. Gravity is still a bit of a problem, but most physicists expect some kind of unifying field ultimately gives rise to the individual forces we observe.
Stranger
Whether it’s possible to truly “understand” anything in physics is a question for philosophers, not for physicists. We can describe things and predict how they’ll behave under various experiments, and if that’s not “understanding”, then I don’t know what is. But to the extent that it is possible to understand electromagnetism, you can’t really understand electrostatic forces and magnetism separately: They’re two aspects of what’s inherently the same thing. You might as well say that you understand a face viewed from the front, but have no idea what a profile is.
As usual, IMO the best answer to the OP. We have math models that seem to explain what we see or measure and have great predictive value, but no one knows **exactly **how things really really work.
I am not a physicist, but think of it like a portable source of gravity. It creates a hole like Wile E. Coyote uses on things that it magnetically attracts: The Road Runner is non-magnetic and pretends like the hole doesn’t exist and doesn’t fall into it; the Coyote falls right into the hole. (Do not confuse this with the Coyote’s painting a tunnel on the side of a hill, that is a different concept.)
A magnetic source does not need to be as big as the earth because electro-magnetism is 39 orders of magnitude stronger than gravity. http://www.lewrockwell.com/orig9/hogan1.html100,000,000,000,000,000,000,000,000,000,000,000,000 times stronger. So a tiny magnet can steal a paperclip from earth’s gravity well with ease. Gravity is called the “weak” force for good reason. It takes a huge amount of mass to have an amount of gravity that people can experience.
Why, then, do you ask, can magnetism not suck the moon down? Well, gravity doesn’t cancel out over distance and works at a distance. Magnetism drops off in power exponentially over distances. http://www.magnetsales.com/Design/FAQs_frames/FAQs_2.htm Gravity drops off in inverse proportion only and extends to infinity. http://www.physicsforums.com/archive/index.php/t-176879.html Household magnets have virtually no effect mere inches away. The earth is a giant magnet, and when a charged needle is well balanced on the end of a pin, that needle will align itself with earth’s magnetic field. A compass is what I call such a device. The entire earth’s magnetic field is not enough to rip the compass needle from your hand, but it is enough to tip a well balanced needle.
On edit: Lastly, I want to point out that scientists think they have a pretty good handle on what electricity and magnetism are. And compared to gravity, they are right. We really don’t know the sub-atomic particles that cause gravity, assuming that’s what causes gravity. We do know for electro magnetism. The LHC in Cern that is not going to destroy the world may show us particles that cause gravity. That is one of the experiments that it is designed to perform.
Its my understanding that if you could view your magnets at a super magnified scale you’ll see mostly space with particles spread out perhaps similar to the planets in the solar system. At this point you could ask yourself “What’s holding these particles together?”
These particles within each magnet interact through some very strong forces that hold them together while still able to share two of their weaker forces, gravity and magnetism with other objects to a degree inversely proportional to the square of the distance. (of their centre of mass I think)
Now that’s interesting. Could some kind of specialty camera directly take pictures or video of magnetic fields? I know you can approximate this with iron filings, but more direct visualization would be really cool.
>Now that’s interesting. Could some kind of specialty camera directly take pictures or video of magnetic fields?
Ordinary, camera-type cameras take pictures or videos of magnetic fields, at least those fluctuating at the right frequency.
You can build an electromagnet by winding wire around a nail, and if you connect it to a DC source it makes an unchanging field. If you connect it to an AC source it makes a changing field. The relationship between the power source and the field seems pretty straightforward. If you build a circuit that alternates its output millions of times per second, not difficult at all, then you get a field that alternates likewise.
In radio astronomy, with the big dishes, you can create pictures like a camera does, of fields that alternate like the nail field driven by an AC circuit. So, that’s a camera for frequencies we can count and time and so forth.