Sometimes when reading about physics, I will come across a sentence like, "So-and-so is proposing ____ as a new solution to the _____ equation."

Apologies right now for not being able to give a concrete example—because I don't get it, I don't remember it—but it's things like "this proposal is to build a Higgs boson out of fermions instead of bosons".

Upon writing this, I am beginning to see that it may be that the equations are somehow unsolved at this point, but given how accurately physics models experiments, I don't understand that either.

Thanks for helping me muddle through this.

hello! i'm a first year undergrad student. at my uni, first year for science is undeclared to encourage students to explore choices and classes before making a decision.

up until recently, my decision was going to be something like chemistry. but, i took a physics class and i really enjoyed it. i'm even considering majoring in it.

the problem is, i do very average in physics. i finished the course with a 76 (B or B+ in canada but i am not too sure), which is alright but i really wish i had done better over the term. i did very well in chemistry, and i did very well in biology too, but my interests lie in physics.

just seeing if anyone had any tips to "get better" for lack of better wording? i have no problem understanding the math for the most part, it's mostly the theory that gets me.

any help is appreciated, thanks. :)

So, hypothetically there were people observing a system at the same time and they dont know about each others existance at the start. One observing position and the other observing velocity momentum. If they find results outside of what their expectations, then can they infer that there is another person looking at that system too? Is there some other wierd behavior that would prevent that? Or am I just misunderstanding what the uncertenty principle means?

What are some of the latest theories to try and explain wavefunction collapse? Are there any names of main researchers I should be aware of who are studying this problem and potential answers? Links to specific papers/articles are more than welcome.

Personally, I think this is the most interesting problem in all of physics right now and as someone studying physics I would love to know what the field is currently thinking about it, as there's potential I would want to do research related to the topic in the future, so I'd love to read their papers (as much as I can understand right now) and potentially get into contact with some of these people, but I'm not sure how else to go about finding them with just google

In this screenshot of my textbook discussing the WKB approximation, you can see in the middle of the page they state i(-i)^1/3 = -1

https://i.imgur.com/YhVxJWG.jpeg

This implies that they define -i = exp(i3π/2), which is not the principal root. This choice plays a meaningful/non-negotiable role in the ensuing argument.

Then at the bottom of the screenshot, you can see they recite (without proof anywhere in the book) the large argument limiting form of the Bessel functions of the first kind.

To properly understand this limiting form, I used pg 10-12 of these notes: https://young.physics.ucsc.edu/250/bessel.pdf

But this Bessel proof uses -i = exp(-iπ/2) and eventually this ends up getting raised to the power of -(v+1) where v is an arbitrary real number. So the choice of arg(-i) does matter here. Using -i = exp(i3π/2) in this derivation would not work because adding the results of the steepest descent approximations to the two contours in figure 4 will no longer satisfy Euler's formula.

What should I make of this incompatibility? Strictly speaking, to accept this WKB argument, do I need to somehow find a different derivation of the Bessel limiting form that uses the non-principal root or doesn't involve any nth roots of -i?

The only escape hatch I can see is that in the WKB notes, the -i = exp(3π/2) appears for the variable of J_v(z), whereas in the Bessel notes, the -i = exp(-π/2) appears as a specification of the dummy variable t in the contour integral. So maybe it's okay to say that in the complex "t" plane vs the complex "z" plane, we can make different choices for which arg(-i) appears in an nth root?

I'd appreciate any thoughts on the correct way to handle this issue, or generally the issue of there being different choices for the nth root of -i across various proofs/results that we might end up simultaneously incorporating into the same problem/scenario.

I’m educated as a historian, and I have actively detested things like mathematics my entire life. Numbers have been the bane of my existence for as long as I can remember. Now, however, I have become intensely interested in physics - specifically quantum mechanics - through communicators like Sean M. Carroll (whose podcast is great).

Generally speaking, where should I go to learn more about physics and cosmology? I’ve been trying to read various publications and needless to say they’ve gone way over my head. Perhaps I should try reading a more “pop physics” type book? Thanks in advance for you recommendations.

TL;DR: Historian needs physics book(s) recommendations.

Hello! First time poster here.

I was recently watching some videos on the uncertainty principle and particle physics. I was curious about what would happen if we knew both the exact position and velocity of particles. (I'm not a physicist so I hope I'm getting that right)

One thing I thought about was teleportation/cloning. If for example, we knew the position and velocity of every particle in a person and were somehow able to replicate all of the particles (their velocity and position), would we exactly clone that person? Would that person have all of the same memories? If we replicated them in a different location, would it seem as though they teleported? Would their consciousness continue as if nothing happened?

Some of these questions might be outside the realm of what physics can explain, but I thought I would ask nonetheless. I'm mostly just curious if something could be duplicated by recreating the same particles with their exact velocity and position.

Thank you!

Every once in a while you will see a bead of water that seems to be sitting on top of the surface of some kind of body of water after you were pouring water or something like that. It will float around for a few seconds and then pop back in with the rest of the water below it. How is that happening?

If angular acceleration = r×a, wouldn't the units for angular acceleration be m^2/s^2? Also, doesn't the formula net torque/moment of inertia give the units /s^2? This is my first time looking at rotational dynamics and I am so confused

I’m looking for a very basic, 10,000ft view on why electromagnetic absorption in mediums such as human tissue/blood are non-linear across the electromagnetic spectrum.

My company works with a few different types of medical lasers operating in the visible and infrared light spectrum (445nm-10,600nm). I’m trying to help some of our people understand why in some instances, such as water, the absorption coefficient is generally linear over that range (shorter wavelengths have low absorption, longer wavelengths have high absorption) where as in hemoglobin, for example, those same wavelengths can have peaks of 10x/100x absorption only at specific wavelengths.

Edit: I should note we are doing this to help people understand why a specific wavelength or laser type is better in different treatment applications.

The way I understood it, the Planck length (about 10^(-35) m) is the scale below which physics as we know it stops making sense. We simply can't describe what happens at that scale with our current tools and knowledge.

Meanwhile, for a photon, the higher the energy, the shorter the wavelength. As far as I know, there is no known limit to photon energy, you could always, at least theoretically, imagine emitting a higher energy photon provided you have enough energy to do so.

Which leads me to that question: what would happen if you tried to emit a photon that is so energetic that its wavelength is shorter than Planck length ? Let's assume this is happening in a sufficiently big and stable referential that you can't dodge the question with Dopler effect, like the entire known universe referential.

How far would we need to put our own sun if we made one from nukes, so that even at night time we can harvest solar energy?

Pretty much the title. I understand it's heavily dependent on the shape and material of the object and wall in question, but I'm generally looking for a starting point calculation that I can build on for more specific scenarios. I'd love some help!

Working on this problem. I want to calculate the potential at the center of the sphere based on the constitutive relation. Since I know that the potential depends on the electric field, my idea was to derive the electric field by solving for E by the constitutive relation. So I did and calculated the electric displacement field D for R>=a and R<a.

I then tried calculating the electric potential by using the definition (the very last line in my notes), but I get a term that evaluates to infinity which is not ok. I'm assuming that there isnt an error in my calculation of the electric field, perhaps there is.

Can I solve for the potential by using the definition or should I go about it another way?

This is referring to the techno toy we find in malls, with the tesla coil immersed in an inert gas enclosed in a glass ball.

The electrical discharges extend from the coil through the gas to the inner surface of the glass sphere. Brand new, the discharges are thin, sharply-focused tendrils. According to the literature, the discharges act as plasma antennae, creating RF at about 35hz.

As the device is used, over time, the discharges degrade, and the tendrils become thicker and less sharply-defined.

My question is: What exactly is happening? I presume, although perhaps incorrectly, that particles from the sphere or the coil begin to pollute the gas? And that the coil itself begins to break down due to metal fatigue? Am I wrong? Is there more to it?

And, as the degradation proceeds, what is happening with the discharge? Does the frequency emitted change?

I would love some help with this, please. I am taking daily readings of the electric and magnetic field strengths, and the milliwattage, at a distance of 3 ft. I have ordered an antenna to the RF spectrum analyzer I have, but it hasn't arrived yet. And because the RF is coming, not from a single antenna but from thousands of plasma antennae, the readings (on a trifield meter) bounce all over the place, and I have to guess at an average.

The tendrils are beginning to degrade, become fuzzier and less sharply-defined, but so far the V/m, the mG, and the mW/m2, are not in general changing.

What am I missing?

Is this a real concern scientists have? I'm not asking if it's likely, but is it a possibility at all? (In the spirit of trying to anticipate all outcomes)

Let's say we create a system inside a electric car so that the car runs on induced current,now my question is If the induced current depends upon the no. of turns in coil , and what if we keep rotating a highly strong magnetic at high speed with a battery of a very low power around the coil which has a extremely high no. of turns ,so won't the current produced in that coil be more than the current produced by a normal battery in the electric car,(which has higher power than the battery used to rotate the magnetic), Why can't this logic be used to produce large amount of electricity in electric vehicles ,

Hello,

If a rocket ship was travelling from Earth to Mars and could accelerate indefinitely, how much acceleration would be needed to maintain an Earth like Gravity/thrust inside the ship?

It's been a while since I took thermodynamics and this seemingly simple question has me nerdsniped.

What is the total internal energy of a block of ice under some well specified set of conditions, say 1kg at 270K, standard atmospheric pressure.

Keyword: total.

I know about flow of heat, the dU = m×c×dT thing, latent heat of melting, etc. Pretty much everything I recall is about changes in internal energy, the exception being in kinetic gas theory. This question is specifically about the total internal energy.

I suppose I could say U(T) - U(0K) = U(T) = integral_0^T m×c(T)×dT, but this moves the problem to finding a good expression for c(T) down to 0K.

Any ideas on how to tackle this?

Context: Someone is arguing that thermal energy equilibrates between systems. This should of course be temperature, but they are convinced these are the same.

I was trying to show that by this argument heat should flow from an iceberg to a cup of tea. Due to the latter being signicifantly smaller and having a lower internal energy, otherwise, take an even bigger iceberg.

Conceptually: a lot of water × some energy per kg > a small amount of water × a bit more energy per kg.

But just how much energy per kg?

Finding the numbers turns out to be surprisingly challenging. Any ideas?

Reading some posts on free will where posters said that free will is as essential assumption in quantum experiments and even Bell acknowledged this.

Is this correct?

What are the implications of free will of the experimenters in this debate?

In the double slit experiment shooting 1 particle at a time, if you see the signal photo land on the detection screen in an area that would be a destructive band (were there an interference pattern imagined on the screen), can you assume it took one path because it could not land in a destructive band area of the screen had it taken both paths (been coherent)?

I’m kind of thinking about this in terms of the delayed choice quantum eraser. But I guess it applies to the normal double slit experiment too if say the person running the experiment didn’t know if a which path detector was on or not.

Just a lay person so apologies if I am framing this wrong.

I apologize if this question seems trivial, but I have been troubled by this issue for quite some time. The redshift observed in the wavelengths of the light from distant galaxies is a significant piece of evidence regarding the expansion of the universe. The reason behind this observed redshift is the relative motion of light, the fact that space itself is expanding, right? Isn't this circular reasoning? Evidence for expansion? Redshift. Reason behind the redshift? Expansion.

I would greatly appreciate it if someone could elucidate the relationship between these two concepts.

Or is there a reason this isn't possible?

I am currently studying ferromagnetic materials and am measuring their magnetic flux density. The measurement is in nanowebers and I am converting it to teslas by dividing by the area. My question is, if thin films have less magnetic material than regular films (volume/height comparison) how does this not impact their magnetic flux density? If i put a thick film and a thin film with the same area should i expect the same or different flux densities?

In the show Genius, Stephen Hawking (Ep 3 second half if someone wants to check it out) sets up a random experiment where a Geiger counter waits for a sub-atomic particle and fires a gun at random.

He say 'the participants have been told' that this is the setup.

1. Was this really done in the TV show?

2. Is this possible to do in the real world?

I’ve been trying to wrap my head around the concept of quantum entanglement and black holes. If two entangled particles exist, and one particle falls into a black hole while the other stays outside, what happens to the entanglement? Does the particle outside “lose” its connection to the one that fell in? Or does the black hole somehow preserve it? 

I'm not a physicist, so please excuse me for perhaps not being very eloquent. According to my understanding things are random on a quantum level. What I don't understand is that it's possible to predict the probability of a particle's position or spin with high precision. If these processes were truly random, would not the probability for any position or spin movement always be equal. To me the fact that it is not seems to suggest an underlying mechanism. For example. I can predict that the probability of getting a six when I throw a die is 1/6. If I could predict the result with greater precision, then the die has to be loaded.

Since FTL will likely never be possible, it got me wondering how far we could get if our max speed was around 90-95% the speed of light. I know there’s stuff we can see that we will never reach due to the expansion of spacetime faster than light. So, assuming we manage to have some significant propulsion breakthroughs in the next 1000 or so years like an antimatter or black hole drive of some sort, how far can we get? To my knowledge, the Milky Way will never reach the great attractor despite how fast it’s moving towards it. But the Milky Way’s speed is only around .2% of c. If we were to achieve at least 90% of c, how far could we get? Could we make it to the furthest galaxy of the Laniakea supercluster?

I won't like... go into a lot of the first half of the dream as it involved details that my mind has already forgotten, but it involved talking to a professor about a quote from Death in one of Terry Pratchetts books, but I'm pretty sure I've never read any of those books and my dream was just trying to sound magnanimous I guess.

However what did stick with me was the below (and I may not explain it well but I basically summarise it at the bottom) as the principle I wondered if had been researched/discussed/whatever.

Say you had like a chain that was infinitely long and you were standing on the edge of (idk) a ledge of a cliff, and you jumped off into a void and fell with someone else holding on to the chain waiting for a signal to pull you up again ( or even maybe a bell? For those wondering how you pull on a chain if you're falling).

Eventually there would be a point where you could no longer perceive the ledge and all you had left was the void and the chain.

But if you tried to send a signal by pulling on the chain, then how would you know if the signal was received as your perception of the finite universe would have ceased, as all you can now perceive is infinite void and chain, and the signal of you pulling on the chain would just infinitely ripple through the (now) perceived infinite void & chain.

So tldr - the infinite can only be perceived through the lens of the finite universe and if we fall beyond that lens then arguably the finite universe ends, and you start a new universe?

This is a concept that I didn't expect to be sharing at 04:33am on a Tuesday morning, but i just had to write it down 😂 I fully expect this is likely something already discussed or maybe there's loads of holes in the argument, but i just wanted to add it to the wide world as you never know. Maybe it's an original thought for once.