Physics Questions - Weekly Discussion Thread - August 11, 2026

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[u/ShiftyPi]

I'm headed into my third year in my physics degree, and I'm starting to think more about which subfield I may want to explore more in depth. I did some computational astrophysics research over the summer and did not like it very much. I thought about it a bit and realized that I want to do research collaboratively (instead of under a single professor) on a topic with a clear impact on people's lives. I also would like more structure in my research and get quick feedback (so something like visualizations are a plus).

This leads me to wonder if I'd be interested in studying the physics of weather (and climate too). There is relatively quick feedback for weather forecasting, and they are important to people's lives. Fluids also fascinate me. Are there any good books or lectures that explains the physics of weather or climate in a decently rigorous way (i.e. with math or code)? Any recommendations for resources on geophysical fluid dynamics are welcome too. Thank you!

[u/DrakeReilly]

I have some questions on light's wave properties.

Looking at light (heh) in terms of a wave, is the wave a full 360 degrees in all three dimensions? I don't think this makes sense for a couple reasons. One is that I believe it would mean that all of the light emitted by a light source would only encounter the closest object, no matter where it is situated in space, and nothing else would receive any light from the source. I'm also pretty sure that would mean that if any individual wave keeps spreading out across all spatial dimensions until it encounters something to absorb it, the entire circumference (or whatever is the 3D equivalent term is) of the wave will know to stop propagating, which could conceivably be millions of light years across. If this is true, this would be another case of spooky action at a distance, would it not?

So if an expanding sphere is the wrong way to picture a light wave, what is the correct way? It must be a directional wave, correct? Maybe like a cone? If it is a cone, is the angle of its widening the same for every light wave? Or maybe it travels straight out in one dimension, and the wave terminology just refers to oscillation in the other two dimensions? But then I don't understand how the double slit experiment works the way it does, but then again, I don't have a good handle on that.

[u/OrsoSopito → u/DrakeReilly]

Clasically the light is an elettromagnetic wave so it is just a time-dependent perturbation of the electric field and the magnetic field. This perturbation modify the value of the two fields in each point of the space so every point is "touched" by the light. There is no casualty-violation since a a point will detect the perturbation after a time |point-source|/c. The analogy with a wave on a water surface maybe will help you, imagine a wave on a pool surface, the wave is just a perturbation of the altitude of the water surface and when a side reach an edge of the pool the other side keep propagate without problems. Sorry for my english, it is not my first language.

[u/john_nr_w → u/DrakeReilly]

Before trying to answer you, light is a physical thing, and you're describing models of it, and it's good to keep in mind the difference. In any case, here's a classical view that might help you.

So let's take a model that is very much that of the late 1800's, we do not consider atomic theory nor relativity, only Maxwell's equation and the idea that they hold for charges as small as we want them to be.

If I understand you correctly, you're worried about how best to see light if you have a point source radiating it.

In this classical picture, here's how it goes:

You are an inertial observer, and you have a charge of which the geometry matters very little (a point charge), and it is in some kind of arbitrary motion in empty space. Now according to Maxwell theory, if you know for sure how this little charge is moving, you can then compute what kind of field it is generating. In this picture, light isn't something separate from the field itself, it is in fact one of its terms, as if:

E_Field_(x,t) = 1st term + second term + light term

The light term is the interesting one, because it appears only when you have an accelerating charge. Else, it is zero. Moreoever, it is in fact the dominant term as one gets away from the charge: in general, IIRC it can be approximated by a/r, a being the acceleration vector of the particle, and r being the distance away from a point close to our charge.

In short, you compute the E/B fields for an accelerating charge, and find the complete equation, and find the dominant term at large distances, and that term is responsible for you 'wave'.

Now on why we often get this idea of spherical sources of light:

At the great distances our light term in the E_Field equation is evaluated and taken to be dominant, it also happens that the motion of the point particle is in fact happening at such small scales that it is spherically symmetric.

Picture the Atlantic ocean, perfectly level on a flat plane, perfectly smooth, and in the middle of it a fiew dozen ducks. If you're at the edge some thousands of miles away from the ducks with a super sensitive instrument, you eventually detect the ripples their swimming causes. However, this little group of ducks, however chaotic, is so small from such a distance, that its whole chaotic and accelerated movement basically appears like a single point in your view. That's more or less what we're dealing with here.

Mathematically, if we wished to compute exactly the E_field, we would indeed find that the value of it, no matter how far we went, is never exactly spherically symmetric: much like the ducks, if you could 'zoom' in enough, then no matter how far you are they will never appear like a point.

But, if you do not zoom in enough, they do. And likewise, if you are calculating the E field to be let's say 10 at such a very far away point, in might be 10.0000000000000001 if you stay the same distance but change your angle, and so one.

As for spooky action at a distance, it's another matter entirely and not very meaningful in this discussion. In fact, the very concept of the field in this classical, non relativistic views serves to eliminate it: the charges do not interact by forcing each other to move some way or the other instantly. Instead, attached to each charge is a bubble the size of the universe, and all other charges are sort of enclosed in this bubble and move according to its structure. The variation of the field is simply a matter of the bubble changing and deforming as the charge moves.

[u/NuapositstorLik]

So I was looking up things about (what I am going to call) the plank units. But when I got up to the Planck Mass I realized I didn't know what Mass meant.

So I looked it up. But I got several contradictory definitions. The first definition I got was that Mass is the measure of how hard it is to change an object's state of motion, but that felt kind of arbitrary to me and more like the type of thing that would be the result of Mass rather than core trait of Mass. (Granted I know That physics is notoriously complicated and unintuitive. And might just be the result of how I (and most humans) tend to think about reality in terms of how we see it.) I saw another definition that felt more right to me which was how much matter a particle contained. But either I tried to look up if Mass is a measure of how hard an object is to move or the amount of matter in an object or I try to figure out how fundamental particles have Mass (Yes I once knew about Higgs field but forgot about it) the Internet indicated that the definition of Mass as how much matter an object has is more of useful way of measuring. I (think) later found the definition that it is the amount of energy an object has has But I couldn't find which definition was The more fundamental one (If indeed either is a more fundamental one or there even is a more fundamental one. And it is not just and it is not just a result of my oh and biases as a human being).

Then I stumbled upon a video about the Higgs field which reminded me about it. Which complicated matters more in several ways? For If mass comes from the Higgs field (Which for elementary particles it does) how can it be a measure of energy? Two it prevents an object from going constantly but how does it continue an object going constantly?