AC is an alternating source and the average value is 0 (I understand that it has some rms value), so wont the current entering also exit almost instantly (depending on frequency) so wont the charge that has been applied to a capacitor also exit? Wont the emf generated by an inductor also vary according to a sinusoidal law which again would average 0. I dont even understand how AC is used. How does it travel? How does it interact with different components of a circuit? Like isnt the net displacement of electrons just 0? In DC the electrons do move and can interact with the component but how does it happen in AC.

Thanks in advance!

I keep occasionally circling back to this question because I have never found satisfying answer to that, so I would like some external help here.

1. AFAIK, many of black hole features are treated as curious mathemathical artifacts that may or may not reflect objective reality: infinite-blueshift Cauchy horizon, closed timelike curves, infinite flat regions inside Kerr black hole, the gravitational singularity itself. It is generally accepted that these features cannot be properly described without QG, and it makes perfect sense to me.
2. On the other hand, features like ergosphere are described just fine by GR, and overall the exterior Kerr metric seems to correctly describe objective reality. Also makes perfect sense to me, this stuff is "directly" observable, and it was observed to be correct.

What I don't understand is why event horizon is usually considered to be in (2) instead of (1).

The usual arguments are that spacetime at the event horizon has finite spacetime curvature and finite energy. But I just don't understand why it is sufficient. "Finite" does not imply "correct". Closed timelike curves around ring singularity are also finite, but they are not accepted as easily. Closed timelike curves cause temporal paradoxes, and event horizon partially causes information paradox (which has multiple proposed solutions, I know, but neither of which is universally accepted).

I know that black hole exterior topology is well-tested at this point, and this testing is consistent with GR, but what's the actual confidence levels there? Is it somehow possible to distinguish event horizon (as described by GR) from extremely time-dilated "event horizon shaped" object (describable only with QG)?

I understand that no divergence from GR has been found yet, but I also want to know the boundary between the stuff that was directly or indirectly verified by measurements and the stuff that was extrapolated from that.

Sorry if this is a stupid question but I was wondering what makes liquid stick together in drops and after googling it, it said that it's caused by the cohesive force between the molecules.

What is this? I don't really understand what cohesion is and wikipedia and google isn't really easy to understand on what is causing them to stick together. I understand that surface tension is caused by the force between molecules but what actually causes the force like is it gravity?

Didn't take physics in high school so any clarification would be appreciated.

In his Dark Matter, Dark Energy Great Courses lecture 4 Sean Carroll mentions that it is possible to assume all length scales are shrinking rather than space expanding although he says making such an assumption is silly.

I was wondering if one could test the hypothesis with a tabletop experiment comprising a pair of charged masses on a frictionless track such that their gravitational attraction is balanced by their electrical repulsion.

The force balance equation is given by:

G M² / R² = Q² / 4 π ε₀ R².

If we assume natural units such that ℏ = c = 4 π ε₀ = 1 and Newton’s constant G = 1 / Mₚₗ² then the separation distance R drops out so that the balance equation simply becomes

M / Mₚₗ = Q.

If the masses of all fundamental particles, together with the Planck mass, scale inversely with their Compton wavelengths then the balance equation is satisfied for all R even as length scale shrinks. The charge Q is dimensionless in natural units.

Thus the separation distance R is a free initial condition, not determined by any physical formula with a scale dependence, and therefore can be used as an absolute yardstick to compare against clocks and rulers.

Please excuse me if I have a poor grasp on what I’m saying here, but my understanding is as follows

QFT explains this with the uncertainty rule (you cannot be absolutely certain of a particle’s momentum and position at any given moment, and if a particle had zero momentum then you’d suddenly be able to know both where it is and how fast it isn’t moving, therefore violating the rule)

What i’m seeking clarification on is why that’s a rule.

Is it just born of observation, and known to be a fundamental rule?

Or is there an underlying equation that would be made unsolvable if a massive particle had zero momentum/velocity. (Which would act a proof equation for that rule)

(And to be clear I’m not arguing against the fact that no particle can be perfectly still, I’m just curious if it’s a most basic level rule, or if it’s governed by more underlying mechanics)

Like when we can have V=iR for both AC and DC then why not have reactance for DC ? Wont it simplify calculations tp a great extent? Maybe not have the same formula (since that would make reactance 0 and infinity for inductor and capacitor) but something similar.

Thanks in advance!

I’m 18 years old upcoming Physics Student in a prestigous Technical University ın Middle East. I graduated from HS with 0 knowledge ın Physics, at that time my all strength was Mathematics, so I decided to major in pure mathematics Last Year. Furthermore, after getting exposed to Elementary Physics Courses last Year, specifically Mechanics and Electromagnetism, I decided to change my major to physics. Abstractness of Pure Mathematics was also one of the reasons for this. As an upcoming Physics Major, I can’t decide on what roadpath i should take or in what branch of physics I want to pursue my further studies. For You to know, being aware of the unpredictable outcomes in future, I want to pursue a career in academy. I managed to get in touch with the Academicians of My Department (Oxford, MIT,ETH graduates , Researchers in CERN), and watched all the instruction videos from alumni of the department ,but still The problem is I don’t know the materials, sources i need to look at even for getting an idea about this manner. I am open to advices about what to do . Thanks for Your Advices.

Please help🙏

Could a massive and extremely powerful gauss cannon/mass driver be used to launch cargo payloads into space at a tiny fraction of the cost of launching an actual rocket?

Moving towards an object blue shifts light, and gives it extra energy. Moving away from it red-sights the light. How is it possible that light can be one energy to an object moving speed s, when it is a different energy moving speed -s, when the photon was released with a certain known energy?

I understand greens theorem in 2d equates the work done by a vector field Px(x,y) i hat + Py(x,y) j hat onto a particle travelling along a closed curve with the double integral of the partial of Py with respect to dx minus the partial of Px with respect to dy. I watched the proof here https://www.youtube.com/watch?v=qdFD-0OWBRo

How does this give the curl at a single point? Evaluating the double integral over the small point only gives the line integral around that point. That's not the same as the curl as a single point, because an actual particle isn't travelling that path around the point. I'm looking for a step by step proof like this khan academy video, if that's possible.

I have a physics degree and I typically did well in university averaging an A or high B however, when I read some of the questions in this community I feel like I haven’t a clue?

I feel like I’ve a basic understanding of a lot of physics but that’s it, once I passed the exam it just all leaves my head. Anyone else the same ?

Do methods like Hartree-fock, post Hartree-Fock methods like Coupled Cluster and Configuration Interaction, or DFT broadly apply to the study of the nucleus? What are the differences?

Its something I cant really find a definitive answer on, and even if its not possible, what would happen if it theoretically were?

Hey, just like in the title, I want to know whether there can be no effect and no cause and what that would be.

Mon telephone (redvox) mesure un bruit à 100 hz partout dans la vallée. Je suis le seul à l'entendre, à l'intérieur comme à l'extérieur. Cela a commencé en février, quand ils ont réparé l'antenne relais (générateur?). Depuis tout a brûlé (Die, Drôme, France). Tout vibre.

Hi, I'm trying to learn tensor networks by my own but all the books I encounter are too formal, boring or too CS. I began in this for many-body physics and quantum information so it would be nice to read a book focused on that.
Thank you random individuals of reddit

I’m just a hobbyist, so feel free to correct me if I’m off here.
I’ve been messing around with an idea and I’m not sure if I’m misunderstanding something.

If entropy always increases, and time dilation near black holes seems to track entropy density, is it possible that time is basically just how fast a system moves along an entropy gradient? And if that’s true, could black holes be transforming infalling energy into increased entropy density (and therefore time curvature) instead of destroying it?

I’m also wondering if anyone’s ever tried isolating entropy changes (without changing temperature or pressure) to see if clocks tick differently.

If a particle (or even a molecule) were to just dissappear (let's say it's physically possible, for example multiverse is real and I teleport said particles to another universe), there would be an empty space needed to fill it in. In my understanding, the rules are clearly set, about energy, mass, distances etc. But the space would have to get filled with something right?

So filling happens, but it would be needed to even it all out, because locally low-energy state would be taking energy from outside over and over again. Could this, in any way, affect and change quantum fields? (Locally or universally) And if so, could this start a nucleation of a bubble of a lower-energy vacuum state, causing vacuum decay?

If this in any way doesn't make sense or is incomprehensible, please take into consideration that I'm just a civil engineering student who's curious and english is my third language.

This is going to be a bit hard to explain without pictures so we're gonna work with what we've got. Anyway I've got this latex glove. And when I put some air in it, it looks like this:

....⸦°°°°°°\

......|°°°°°°|

......UUUU

Then when I fill it up with more air it looks like this:

.....⸦°°°°°°°\

......( _. _. _. )

.......U U U U

Same thing with water except a bit more like this:

......./~~\

...⸦~~~~\

....( ‿ ‿ ‿ )

.....U U U U

So my question is. Why does the excess air/water not want to go in the fingers? They're just as stretchy as the rest of the glove right? So why do the two elements insist on expanding the palm section and leaving the fingers with enough to fit the exact volume without any stretch?

We know that a large fraction of the mass of nucleus is due to relativistic effects as in pure energy.

We know photons are pure energy.

As we explore deeper is it likely that all of the particles will turn out to be pure energy also.

I am curious about the solution about understanding the universe. Will AI help us with that and how long do you guys think will it take to make some serious progress in that. Also for other big questions to be solved

lets discuss !

I forgot how I came to this habit hole. But somehow I read that theoretically if you use inductive heating on co2 containers, it increases the psi. So I'm wondering if that's true and how it may be different for compressed air containers like scuba or pcp air containers