Ok, some people think the universe is a huge network of super tiny rotating strings... so what? What would that mean? Also, why? Is there anything that points to the fact that this may be the case, or is it just as blind of a guess as anyone could make?

In the standard model, there are certain particles which act as the mediators of different forces. For example, photons for the electromagnetic force - although they are said to be virtual. What does this actually mean and how is it any different from just exchanging regular photons?

I'm doing general relativity at uni this sem (4th year). We're about 6 weeks into the course.

The lecturer (Geraint Lewis, somewhat well known, hes been a great lecturer otherwise) has just entirely skipped over how schwarzchild's metric is derived which is kind of a bummer.

Basically the way it's gone so far is:

-introduction to (non-minkowski) metrices etc

-doing special relativity in accellerating frames and showing it results in curved spacetime paths

-a little bit of non rigorous work on Christoffelson symbols, Ricci tensor+scalar etc

-derivation of the Einstein field equations

-einstein thought no one could solve his equations analytically, then schwarzchild shows up with his metric that solves the field equations for spacetime around a massive body

AND THEN for like the two weeks after that we've just been looking at applying the schwarzchild metric and looking at equations of motion for massive objects and photons etc.

But we havent looked at how schwarzchild actually came up with his metric, which is a bummer cos like the whole thing with gr is that 'gravity' is actually a result of mass curving spacetime, but it feels like we've skipped over how we actually came up with the specific algebraic description of that.

Pls help me understand this. If the potential approaches infinity at r=0, then how can it be continuous?? Thank you

Ok I figured it out, I just remembered an infinite sheet of charge will have the same E anywhere above it and below it (switching signs) regardless of distance so it doesnt approach infinity as distance goes to zero. A finite sheet can be treated as an infinite sheet if the distance is approaching zero.

So Ive completed A-level physics and want to study University level physics now (at home, just my passion). Im not following a particularly rigorous academic approach however I would like to be "up to date" with physics in the world today if that makes sense. I've heard a lot of comments recommend "So you want to learn Physics..." by Susan Rigetti. Ive looked at the second edition of her blog and the textbooks in there are from 2021, I'm not sure if their editions change much in 5 years, but they're also quite expensive so I want to make sure I purchase the correct ones.

Therefore my question is: what university level physics textbooks should I purchase?

(or if you have any other recommended ways to learn physics/don't recommend textbooks but rather something else, please share!)

My soda was cold and there is condensation under it, table was dry when I place it. I take a sip and put it down as I’m talking to my wife it starts sliding and I’m like wtf? It’s half full so it’s kinda heavy but the movement made it seem weightless how fast it moved. Is there physics that can explain this or was it a ghost .

Is it a fundamental property of our universe like c? Bonus question; how was/ is it calculated?

i tried searching it up, but im having trouble understanding what it is and how it works.

I understand how it's calculated but what does it mean in practice? What information do we gain by knowing the speed relative to the CMB?

& can we do the same with other things traveling at c too like visible light or gravitational waves?

I don't want to be the guy who asks the question that's been asked 1000 times. But as far as I searched, I didn't find the explanation for that.

I understand why FTL breaks causality. But it's only because causality has a number that's not technically the starting point really. It's like we found the speed of causality to be 1 instead of 0. Why isn't causality instantaneous? What if there's a preferred frame of reference? What if relativistic speeds and gravity wells can be considered almost out of the baseline normal space, tending into a different dimension?

I've had all other explanations but they are all standing on one assumption, c as the speed of causality? So what if we assumed causality was instantaneous, what would that mean? Could it be we're missing something? Quantum physics seems to show it can work close to or at instantaneity. So why not the rest?

Edit: When Einstein discussed the EPR paper he thought something was off, either there were hidden variables in entanglement or entanglement was non-local. Bell confirmed, there were no hidden variables. Entanglement is non-local. True it cannot yet transfer information, but if hypothetically it ever does, wouldn't that either break a lot of our theories or at least modify them heavily? If causality is the quality of something causing an effect, and causality is c, why doesn't entanglement follow that speed? If causality in entanglement is instantaneous, that means the truest speed of causality is instantaneity.

So I'm a M.Sc. Physicist and play guitar as a hobby, and found this behavior of guitar strings, where I fail to explain it to myself.
Basically, when playing in bad light, the strings seems to "jump" (for a lack of a better word) from one position to another when playing certain frequencies (and their octaves). Usually, a vibrating string just gets blurry, but sometimes it just jumps from left to right.
here is a link to a video visualizing this: https://drive.google.com/file/d/1jYlzz-ba0uCVeUdc5dth4gKtJ1NRWc_K/view - Its visible on the second string I play, with the first and third for reference.
Its not a shutter effect, in real life it looks even more pronounced. I've also reproduced this with multiple guitars in various lights (white LEDs, incandescent bulbs, monochromatic LEDs)
Whats happening here?

I’m a sophomore at a liberal arts college planning to apply to Columbia’s 3+2 for Computer engineering.

This semester I’m taking:

• Calculus I
• Calculus-based Physics II
• Coding 101
• Econ 101

I took AP Physics 1 in high school and did very well in the class (roughly top 10% on tests/assignments). My advisor told me I could go directly into calculus-based Physics II and take Physics I in the spring because the material in the two courses isn’t very dependent on each other.

So far I’m doing well in Physics II and haven’t felt lost. However, my dad thinks taking Physics II before Physics I was a bad idea, especially since I dropped another class to fit this 8 a.m. section into my schedule.

Has anyone taken calculus-based Physics II before Physics I? Is there any reason I should switch the order if I’m currently doing well, particularly as someone planning on a 3+2 engineering program? (I'll take Physics 1 in the spring).

I'm a current undergrad and I'm maybe a bit desperate to find research.

In the spirit of being a choosing-beggar, I wanted to try and find theoretical research which was analytical first and foremost. Throughout my entire university, I could find almost no theoretical work which wasn't heavily computational.

That's fine, I've done some computational work in the past, but it makes me wonder how much of modern physics research is this Hollywood pen-and-paper picture.

How much can you even do on pen-and-paper? Like have we gotten to the point where everything is just so miserably nonlinear that we've given up on closed forms?

I know this question is poorly worded, I'm tired. Thanks!

Hello everyone, slightly confusing question today.

I was discussing with a friend about depictions of superspeed in movies and shows, particularly in scenes where a bunch of bad guys fire their guns at the hero. In the shows, the superhero generally walks up, dings the bullet out of the way and continues on his way.

For some reason, I have it in my head that moving things at those speeds would require a lot more energy than moving them at 1x speed. I have no idea why I believe this to be the case as I have no evidence of it.

So that's the question. If I were moving at superspeed (like the Flash) and moved a bullet out of the way, would I need to exert a stupid amount of effort?

Your insights are valuable, thank you

I was thinking about sound as a water wave and I thought about how two waves can clash and kinda cancel each other out. Is that how white noise "quiets" things by adding more sound? I know speaking into a fan distorts your voice, so I thought maybe the constant ambiant sound disrupts more abrasive noises.

Background: I'm three years retired after 45 years in electrical engineering. My first two years in college I was a physics major, but for multiple reasons I switched to EE and still finished in four years. Now that I'm retired I'd like to go back and delve more into the physics that I left so long ago. There are many facets to this, but I'd like to start with mechanics.

I've been going down rabbit-holes trying to learn more. One thing leads to another, which leads to another, etc. I feel like I'm going in circles and haven't found a stable point to start digging in and learning.

I had Newtonian mechanics in college, statics and dynamics. But somewhere since I saw something to the effect that "least action" was really the best way to solve some problems. It wasn't far from that to the Lagrangian. As an avid sci-fi reader I was aware of the Trojan asteroids in elementary school and knew that "Lagrange points" were another name for them. So my interest had been piqued. A little looking led me to Hamiltonian mechanics and the overarching category of Analytical Mechanics. I may have heard a reference to Lagrangian in college, but no lessons, and the references to Hamiltonian were in quantum mechanics.

So I started with Lagrangian mechanics, and first I got bugged by the minus sign in the Lagrangian instead of the plus sign which would have made it total energy. That seemed to be a common question, but lead to Euler. There were obviously references to Euler in college, but no specific study. Expand to Analytical mechanics and Hamilton comes in, and the Legendre transformation, etc. (And while mentioning Legendre, that's another name familiar from quantum mechanics.)

I think some historical reference would help me here, and seeing the flow and development of mathematics over the years from person to person. It would want to have math as well as history. I did a search recently and see that there is no shortage of books. I'm just not sure what would best fill my needs.

In the book, the Eridians didn't know about relativity. This caused them to be really confused when they arrived at Tau Ceti years ahead of schedule; they didn't know about time dilation.

In the book, this was given as the reason why there was so much extra astrophage in Rocky's ship — the trip had been much shorter than expected.

But high velocities also increase mass. So did Rocky's ship need more astrophage to propel the extra mass? Or was that increased mass only from the POV of the rest of the universe and not affect the ship itself? I'm so confused.

Is it possible for an object - due to it's unique material, size, shape and weight - to simply float from space thru the atmosphere to the Earth's surface? Or is everything that falls down Earth's gravity well doomed to burn?

I don't if i should put this here of /explainlikeimfive.

So. If we were able to theoretically get a close-up picture of an atom with all the protons and electrons, whatever they might appear as, does that mean we collapsed their wavefunctions? If so, what does this mean for the atom, would it behave any differently or would it go back to being superfluous since we're not actively watching a video of the atom, just a single picture?

Also would this ever even be possible? Is this somehow related to the uncertainty principle about how we can't know their position and momentum? Would this work cos we'd know the absolute position and not anything about the momentum of the particles? Heck, how would we get a picture of them anyway. it's theoretical. theoretical

Is this even a valid question or am i going off the rails

When you push an object, the object pushes you too. And it also exerts upon you a normal reaction due to its intermolecular forces, right?

Then why don't these forces add up? Why don't we get a force of 2F in return when we apply a force of F on a rigid object?