Today, 04:09 AM
(Today, 12:41 AM)Astyanax Wrote: The bell-jar story is a very good illustrative example. By the way, it’s called a bell jar because of its shape. Robert Boyle (1627–1691, who discovered the law which relates gas pressure to volume), famously conducted a series of experiments with such a jar, putting various objects inside, pumping out the air and seeing how the objects were affected. One of the objects introduced was a bird, which promptly suffocated. There’s a famous painting by Joseph Wright ‘of Derby’ that depicts that experiment being performed, though Boyle is not shown in it.
I don’t want to be difficult (not that I need to try, I suppose), but this is not correct, and since we’re upholding the scientific side of the conversation in this thread, I think we should get our science as right as we can.
There are not one but three critical errors in the above sentence.
Charge is an electrostatic, not an electromagnetic phenomenon. Objects are electrically charged when the number of protons in them is unequal to the number of electrons. Charged objects attract or repel one another, like opposing magnetic poles. So charge is a form of energy, ie the capacity to move masses through space.
- there is no such thing as an electromagnetic charge
- a photon has zero electrical charge
- uncharged photons are the only force carriers of electromagnetism
When charged objects move through space, what we call an electromagnetic field is produced. What this means is that there is a sphere of potential energy surrounding the moving object, and any other charged or magnetized object within this sphere will tend to move towards the first object or away from it. The force tending to cause this motion varies in an inverse-square relationship with the distance from the first object.
Something has to carry this energy through space from one object to another. We know from a long history of experiment that it is carried by waves of light, which can helpfully be treated mathematically by thinking of them as packets of fixed amounts of energy, called photons.
We think of photons as having kinetic energy (even though they are massless). This is converted into electrical potential energy (charge) when a photon strikes an atom. Electrons, a kind of charged subatomic particle, are usually found tightly bound to atomic nuclei. The kinetic impact of a photon can increase their energy, making the bond unstable or even breaking it altogether. To return to stability, the atom needs to emit photons of energy equal to the one that struck it.
To produce those photons, positive and negative charges are annihilated by the conversion of their energy into light. This is what happens when, for instance, an electric spark is produced. It is also what happens when you a heat an object; the heat (kinetic energy) is dissipated partly through radiation, which is the emission of photons. Even if we don’t see the object glow red hot, it’s still emitting photons in the infrared spectrum, which are invisible to us though we can sometimes feel them as heat on our skins.
* * *
To be honest, I’m not sure an explanation of the kind I have given here really helps any lay person understand these phenomena. It seems full of illogicality and paradox. This, I think, is why people like MonkMode prefer to explain them through made-up stories; the objective explanations we favour are conceptually difficult, often very complicated, and don’t seem to add up. How can a massless particle have momentum? How can this massless (and chargeless) object produce, by spontaneous division, two massive objects, one positively and one negatively charged? Why do electricity and magnetism sometimes seem related and at other times completely different? The more one thinks about such things, the less sense they seem to make.
But though words fail us, the paradoxes that appear when we use them to describe these things are resolved when we treat them mathematically. We find that the maths not only accurately describes the phenomena we observe but that the accounting all adds up along the bottom line. But mathematics is hard, and the mathematics which describes the motion of charges in an electromagnetic field is some of the hardest I have ever been invited to wrap my head around: Maxwell’s Equations. If I ever understood them fully, that day is long gone.
I sometimes envy our fantastical friends, who feel no need to have their explanations all add up and cancel out neatly, but can let their minds roam free and devise whatever narrative they can dream up (the sillier the better) without anxiety or embarrassment.
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PS: could some kind soul please explain how to add a static image to a post? I would have loved to feature the painting mentioned above. Can I upload an image here, as we did on ATS, and what should I do after that?
You are quite right. Apologies.
I have edited my previous post to fix it.
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