r/AskPhysics

Because if time is running differently in different parts of the universe and the universe as a whole has undergone shifts in time dilation then what exactly is the absolute referent?

Consider a capacitor that is comprised of two long, thin conductors of significant length

As we know, electrons flowing through a conductor of any length produces a slight inductance which increases with length

My theory is having a capacitor, with its capacitance determined by the proximity and size of the conductors, will also have an inductive effect by the increased length the electrons must flow from the ‘furthest’ part of the electrical field

Compare this with a circular plated capacitor with the same field area, but with of course a vastly reduced diameter and therefore much negligible conductor length

Ergo, if you fine tuned the design of this long, thin theoretical capacitor you would have a resonant circuit that doesn’t technically contain a inductive device, just resonant from the capacitance plus the aforementioned increased conductor length giving the inductive element of the resonance

I am a PhD Chemist currently self-studying some nuclear physics, but am finding myself a bit confused on some notation in the nuclear shell model. Particularly the spectroscopic notation for the subshells.

I understand arriving at the combinations of quantum numbers as follows:

>1st shell: 2 states (n = 0, j = ⁠1/2⁠).

>2nd shell: 6 states (n = 1, j = ⁠1/2⁠ or ⁠3/2⁠).

>3rd shell: 12 states (n = 2, j = ⁠1/2⁠, ⁠3/2⁠ or ⁠5/2⁠).

>4th shell: 8 states (n = 3, j = ⁠7/2⁠).

>5th shell: 22 states (n = 3, j = ⁠1/2⁠, ⁠3/2⁠ or ⁠5/2⁠; n = 4, j = ⁠9/2⁠).

>6th shell: 32 states (n = 4, j = ⁠1/2⁠, ⁠3/2⁠, ⁠5/2⁠ or ⁠7/2⁠; n = 5, j = ⁠11/2⁠).

>7th shell: 44 states (n = 5, j = ⁠1/2⁠, ⁠3/2⁠, ⁠5/2⁠, ⁠7/2⁠ or ⁠9/2⁠; n = 6, j = ⁠13/2⁠).

>8th shell: 58 states (n = 6, j = ⁠1/2⁠, ⁠3/2⁠, ⁠5/2⁠, ⁠7/2⁠, ⁠9/2⁠ or ⁠11/2⁠; n = 7, j = ⁠15/2⁠).

I also understand the relationship between j and l.

But when it comes to the spectroscopic notation, I am finding that the notation is nlj.

That value n definitely doesn't correspond to the quantum number n above and I am not finding anything on how to arrive at this different value of n.

I have figured out a pattern that seems to work as far as I can tell where this value for this spectroscopic notation value is that it seems to = 1+(n-l)/2.

I found something that indicated it could be related to radial nodes, which seems to go along with the whole n-l situation. But, I am not quite able to explain to myself why that pattern is working.

1st question, is it not simply that a star has a maximum size before gravity will overpower the other interactions? There’s star size comparison videos on YouTube, but they don’t mention some theoretical maximum, they just keep zooming out to show the next bigger star. I get that some stars are giving off less repulsive force to counter, so it’s not like all black holes form at the same mass cutoff.

2nd, when a black hole evaporates enough mass from hawking radiation, does it stay super super dense, or do the repulsive forces then spread it back out, like does it rein flat to a star or some other stellar body?

I'm trying to understand how people develop a deep conceptual understanding of physics, where they can recognize which principle to use just by looking at the question, even when the textbook doesn't explicitly tell you to use that logic in a specific topic.

I want to know how some people can look at a numerical and immediately recognize a hidden concept or subtle twist that isn't obvious at first glance. How they seem to pick up on patterns and connections that can be overlooked commonly. I know every problem seems to teach something slightly different, I've been told that this kind of intuition comes mainly from practice and practice has definitely helped me recognize and solve different types of numericals. But whenever I face an unfamiliar question, I still struggle to figure out what approach to take or what hidden idea I'm supposed to notice. That's what I'm trying to understand.

Are there specific problem-solving strategies or ways of practicing that help develop this intuition?

Basically, how do you go from knowing the laws to developing the "common sense" to know when, why and how to apply them? (Sorry for the stupid question and the rant)

Explanations for why FTL travel/communication violate causality or introduce paradoxes generally rely on at least one party going relativistic speeds. Imagine instead that there are two planets in star systems 10 light years apart, communicating instantaneously using a sci-fi standard, the ansible. It seems like this should cause problems, because the messages are traveling faster than the speed of light. How does it cause these problems? If FTL in this situation is not problematic, why not?

Does the density of mass/energy not affect the way it curves space time? With the various analogies for visualizing space time curvature, it seems like a denser object would curve more sharply

I know electrons and protons have negative and positive charges but what exactly gives them charges and what exactly is a charge? As far as i know in electromagnetism when the electron moves in an atom it gives it charge(i know that an electron doesn't move in an individual atom), but is it an actual force or perhaps a work of gravity?

Trying to understand some concepts about dark energy in layman's terms.

From what I've read and seen, dark energy is responsible for the expansion of the universe and cosmic inflation. From what's been asked before, far away objects (that are not graviationally bound) expand faster than objects closer to us. The space between these objects may expand faster than light, as opposed to the objects themselves moving away from each other faster than light.

So my questions are:

1. Is dark energy really strong, or really weak? Or neither? Because I still have a hard time conceptualizing the force to move galaxies and clusters away from each other. On one hand, simply making more empty space doesn't seem like it takes much energy because space is pretty empty. But on the other hand, these forces are acting on massive objects?
2. Is dark energy supposed to be equal everywhere? Going back to expansion, far away objects are moving away faster. Doesn't that imply more dark energy in those regions? But if I were in the faraway region and observing Earth, wouldn't the expansion where I am seem slower such that there's less dark energy locally?

Thanks!

Edit: Thanks for the responses. So informative and I'm learning a lot.

Imagine a charged capacitor with two plates, each connected to a wire. The wires aren't connected yet:

+----|  |----+
|            |
+-----  -----+   <- not connected yet

As far as I know, this is an equilibrium state, no charges will move, and the capacitor will stay charged.

But then you connect the wires, and everything changes. This is no longer a state of equilibrium, a current is created and the capacitor discharges.

Now here's the part that I don't understand: In the illustration, the geometry of the wires require the charges to move away from the other plate in order to reach it, and yet the charges do that. Which should be impossible for the same reason water in a glass doesn't jump out to fall on the floor.

If the wires were connected between the plates, then that's understandable. But in this case the wires are connected around the plates.

I want to understand from a field theory level (not circuit theory) how the charges seem to understand that gaining some potential energy to reach the other end is a small sacrifice towards a greater goal. But charges don't think! And if you calculate the electric field at a plate, it should always point towards the other, regardless whether the wires are connected or not. So the charges should stay there.

For context, I just finished Physics 2 in my first year in electrical engineering college, it only covers electrostatics, capacitors, and foundational magnetism like Faraday's law. I haven't taken the more advanced courses about circuits yet. This question has been lingering in my mind for quite some time, what am I missing here?

And please don't give me explanations with circuit theory elements, like "the wires have low resistance so current flows, but air has high resistance so current can't flow," that's not what I'm asking about. How did the fathers of electricity answer questions like these in order to reach conclusions and develop abstract frameworks like circuit theory in the first place?

Is there any evidence that nature is fundamentally continuous, or could reality be fundamentally discrete? And if it is discrete at the most basic level, would that suggest that nature could behave like a computational system?

I understand that magnetic and electric fields are closely related. But I am confused on how one propogating makes the other.

Lets say in scenario 1 the scale is on the ground on earth at sea level but in a vacuum in a box and in scenario 2 its free floating in a vacuum like space, would that make any difference?

Let's say I discover a magic wand that can invert the mass of an object--all other properties remain the same, but the sign is reversed so that F= -G(m1*m2/r^r). What kind of technologies would become possible?

Entropy is defined as the number of substates in a state, and QFT says the state of a quanta contains a superposition of every possible states, or infinite substates. Is superposition a property of entropy?

If you can use a double slit in time to set certain bands of frequencies contained in the light, is it possible to do calculations on the full spectrum, then use a prism or scattering to separate the frequencies so the information is not lost when it is observed?

Is it possible to model a photon as a point the propagates an EM wave that travels behind the photon like a wake, but make the photon highly subjective to its own field, making the interference with itself that feels so confusing?

※ this sentence was translated from Japanese to English by Chat GPT. Feel free to answer in English. However, I only understand Japanese, so I would really appreciate clear and simple English that is less likely to be mistranslated.

If proton decay occurs, the predicted half-life of the proton is somewhere between 10^34 and 10^36 years. This made me wonder: what will actually happen to the things that exist in the universe between now and that unimaginably distant era?
I often see timelines describing the future evolution of stars, but I’d like to know what will happen, scientifically, to the following six things by around 10^36 years from now.

1: 1 kg iron sphere
(I’ve heard that iron is one of the most stable elements.)
2: stone monument
(Would inscriptions remain readable for an extremely long time, or would the writing eventually disappear?)
3: can of food
(What would happen to food sealed inside a can over such an enormous span of time?)
4: manufactured industrial product
(Any particular example of an interesting industrial product would be fine.)
5: planet
(What would happen to a planet if it somehow avoided being swallowed by its star?)
6: intelligent civilization
(Could an intelligent civilization that made extensive use of reversible computing potentially survive for an extremely long time in a simulated or virtual environment?)

For #1–4, please assume that the objects are floating in a vacuum. If they would eventually be destroyed or worn away by interactions with the interstellar medium, I’d also be interested to know what would happen if we ignore the interstellar medium.
I’d also love to hear about anything else you think would be particularly noteworthy or interesting. Thank you!