Material flexibility is something that is often overlooked in everyday life, but I’ve been a little curious about how it works and what is going on at the molecular level. Some materials can temporarily bend and then snap back to their original position or break. Some materials bend permanently after a certain threshold force is applied. To set teeth straight, orthodontists feed a wire through tooth braces, which the teeth initially bend, but the wire tries to bend back to its original position over time.

What determines these properties? I assume heat plays an important role, and I assume the effectiveness of heat varies. Why? Finally, is there any way to predict the bendiness of a compound (or alloy) based on the bendiness of their elements?

I’ve seen a number of science communicators say that objects don’t pass through each other because of electrodynamics. The general story is, the nucleus of the atoms repel because of electric charge. You look at the Coulomb force and as distance goes to zero, the force between them goes to infinity. So atoms can’t touch there’s an infinite Coulomb force repelling them.

But then other science communicators say that the electric repulsion between atoms isn’t actually enough to keep them apart, and it’s actually the Pauli exclusion principle. You can’t have electrons in the same spin state occupy the same space. So, they can’t touch therefore your hand can’t pass through a wall.

But this confuses me because if an atom is mostly empty space, can’t the nucleus just “slide past” another one? I thought quarks and electrons are point-sized. They’re volume-less. So how can they ever touch at all?

All of this really confuses me. Why can’t my hand pass through a wall? Is it electrodynamics? Is it the Pauli exclusion principle? What’s going on?

I saw a lot of heavy equations regarding this concept, which I fear I can't understand, so can someone make it easier for me to digest .... thanks

Hi, I'm a software engineer who loves science, especially theoretical physics.

First of all, the context of my idea: I was watching a Neil deGrasse Tyson StarTalk episode on YouTube, as I sometimes do, and in this one, Neil talked about the connection between entangled particles in space acting like wormholes. He mentioned that these links are, in some fundamental way, necessary for the universe to exist.

And that’s when I had this thought. The universe, as described by General Relativity, is like a 4-dimensional sponge or fabric that bends due to the mass of objects, altering the natural paths of things passing through. At the same time, quantum entanglement describes quantum threads that the universe somehow needs at a fundamental level.

So, what if those threads were actually the basic building blocks of spacetime itself? Instead of being a smooth, continuous fabric, spacetime could be made up of discrete quanta.

That’s basically my idea. I don’t have a background in theoretical physics, but this thought has been on my mind for about a month, and I at least need to know if it’s completely wrong (and hopefully understand why).

Thanks for reading this! Feel free to ask me anything if I wasn’t clear on something. I’m not a native English speaker, so please don’t be too harsh.

so we say that slope is the ratio of the change in vertical and horizontal then can we represent it in the form of a vector or can we say that slope is a vector ??

thanks

Hello, so basically its as the title says. My Hamiltonian will be probably around 2^7 dimension, and I was thinking if I should just try to diagonalise it or if there are some more efficient ways

I have a basic grasp of the idea, but I have one question. Imagine a man that is a normal human being and another man that moves at light speed. The normal man challenges the man that moves at light speed to a race to the point in front of them. According to general relativity the faster one goes the slower time moves relative to their surroundings? Like in that Twin paradox. So the faster one moves the slower they move through time right? So then the man moving at light speed would lose? Because the man moving at light speed would move through time differently and depending on how much time he spends at this speed, the normal man may age a couple years? Even though logically you'd think the fatser one would win the race. It's so incredibly confusing. I have more questions, but I'm keeping it short. Care to enlighten me?

I'm given a rod of negligible mass that is rotating about a point at the center of the rod. Compare the kinetic energies if a solid disk is attached to the rod some radius R from the point of rotation verse if the disk is attached to the center of the rod at the point of rotation.

In case 1, it seems like the disk is really orbiting around the center of the rod. Therefore, it should have only translational kinetic energy of 0.5mv^2.

in case 2, the disk is effectively, rotating about a central axis, so it has only rotational kinetic energy of 0.5Iw^2 with I = 0.5mr^2.

Subbing I into KE formula gives me KE of .25m(r^2)(w^2). Then subbing in v for rw, I get rotational kinetic energy for case 2 of .25mv^2.

The key for this problem (might be wrong?) gave a completely different answer by comparing the inertias stating that case 1 has inertia of I(cm) + mr^2 and case 2 has inertia of I(cm). I'm assuming cm is center of mass. Then the conclusion is that Case 1 has kinetic energy greater than case 2. My first issue with this is that it is stated that the rod has negligible mass ... what am I missing or could this key be incorrect?

So I'm a 15 year old electrical engineering student, 1st year. Currrntly reading AoSP introduction to Algebra/Quadratics and in mine school we're currently learning 'logic' - something with conjunction, disjunction,implication, negation etc.

I really like Physics, but I find the boundaries of calc and the majority of algebra limiting. Is it wise to learn only some parts of mathematics that I will need in specific equations? For example The theoretical minimum book by susskind gives a brief explanation of for example limits and derivatives. I also may do some exercises on it myself to get a better grasp at it.

Of course I will learn everything from the bottom up, this is just an temporary measure until I reach calc in AoSP books.

Thanks for the help in advance! I'm also looking for someone to guide me, someone who wants to teach someone. After all the best way to understand something is to teach it. I just don't want to make some fundamental mistakes in self learning stuff, that will drag me down later.

In other words, are all waves the same "stuff?"

So my understanding is that time essentially stops for you (or at least the particles of you) if you enter a black hole. Or as Brian Cox says it, you "go to the end of the universe." But if time has stopped inside then how can the black hole have a velocity?

I assume we can track a motion of the black hole relative to us, so the core of the black hole has a direction and a velocity. But that means the core is moving and that means it is moving through time as well, so how can time be stopped?

I don't know if I'm explaining that well, but hopefully someone gets me.

When we talk about the universe expanding, are we talking about

A. The distance between every atom is growing larger

B. The space in which an atom consumes is increasing

C. Galaxy are set in motion travelling away from each other but the what they are made of remains the same size.

D. None or a combination of the above.

All of this might just be nonsense, but here goes my theory. We know that light particles don't experience time and they are observed only when they interact with other materials( I think), right? What if our soul or something equivalent is similar to that and can only be "observed" when it comes into contact with something? Also, what if similar to multiverse theory, where all the universes are squished in the same space but vibrating at a different frequency, all of time is also a single point? And what we observe as time passing or life we are living is the soul just interacting with time and all our life is happening in an instance. Also, a lot of cultures and civilizations have the concept of reincarnation and what if this was the soul interacting with time and all the reincarnations are happening at the same time in a quantum state, multiple lives are being lived at the same time within the same instance but due to our brains inability to comprehend the working of time we think these are happening at different times? So, basically what I mean is, our soul is in a quantum state where it sometimes interacts with things and these instaces of interaction are the lives we live and all these lives are happening in the same instance. This is just me rambling, but I want to know how much of this could be true or if this is entirely bull sh*t.

I've seen once the definition of Fermat's Principle as follows: The light's trajectory is such that the time it travels between 2 points is minimum, maximum or stationary. But I've never seen any example for the stationary or maximum times. Someone can clarify this for me/give me one example.

Think about it from it's perspective. A photon only "sees" what's in-front of a certain cone of vision that lays in it's path of travel.

Since it's been flung at c, and gravity can't travel faster than c, that would mean the photon is perpetually being "sucked" in one direction, with the gravity behind it no longer being of any influence, and the gravity in front of it having an exaggerated effect. Excepting, of course, when an object in it's cone of vision interacts with it in some way. Catching it for whatever reason, or redirecting it towards it's new path.

Or, and I wrong in that thinking?

Edit: Yea, wrong thinking

Despite the speed of light, the warped space is already present. Gravity from "behind" the photon will have an effect on it, as the light still needs to travel through already acted upon spacetime.

Honestly, I'm a little lost in the mathematical sauce here. It has been stated around the internet that QFT lacks a formal mathematical basis, but I have not studied quantum field theory, although I have studied undergraduate quantum mechanics.

I am curious what sorts of functions QFTs generally use because analytic functions obey the identity theorem while smooth nonanalytic functions do not, and I am wondering if there could exists near-identical universes except for the nonexistence of some specific object or planet. Basically, would it be (meta?)physically possible for an object to not exist in, or to essentially be removed from, a 3 dimensional time slice.

I'm worried I'm becoming a redditor-crackpot-physicist-philosopher that doesn't even know enough to ask a valid question but thinks he know things.

This may be a bit of a vague mathematical physics question, so please let me know if there is a better place to post this.

It is well known that orange cats have a communal braincell [1], and that any orange at any given time is unlikely to get access to it. If I lock an orange cat into a box, will the cat be in a superposition of having and not having the braincell?

[1] r/OneOrangeBraincell

I’m a bit confused about the mechanics here and could really use some clarification. Here’s the scenario:

I have a closed system with a piston filled with air, and I’m lifting the piston up. My question is: Am I doing work on the system, or is the system doing work?

What aspect of a battery makes it that it can do 9J/C (in a 9V battery) of work compared to a 1.5V only being able to do 1.5J/C across the terminals?

Is it the chemical reactions that populate the negative terminal with lots of electrons, with a 9V battery having a greater concentration of electrons on the terminal creating lots of repulsive forces? Or something to do with the electric field strength?

Another thing about batteries I wanted to clarify. So I know that the current is carried by free electrons in the conductor. However at the end of the circuit these free electrons are going into the positive terminal (negative in conventional current). Therefore does the negative terminal replace that free electron from its own source of electrons?

I looked up this question and a lot of the time read that the battery doesn't supply any electrons and it's entirely those in the conductor so I'm very confused.

Hey I was just wondering if it is possible that there were planets before that fell into sun and if we could tell. I dont know if something can even be considered a planet if the orbit is unstable but to my understanding what makes the ellipse shape of the orbit is basically because the planets are "falling" towards the sun but missing it and then being pulled for another round by the suns gravity (very simplified) so it should be possible with enoug time that eventually a planet (most likely the closest one first) hits the sun. And also what would happen then? Since the sun is a gas giant would the planet just be absorbed or vaporize before even touching it. And lastly would there be a way to detect such a collision that happened before humanity existed since there wouldnt be a crater because of the fact that the sun is made of gas, correct?

Hi, in 13 and in middle school. In one of our classes we're starting to learn more of an intro to physics and gravity. It seems like I'm the only kid in the class who understands it. And the only kid in class that enjoys it. My teacher already knows that I'm not the greatest at learning, and she thinks it's good that I finally found a class I'm interested in. But since I'm the only kid in class who likes it and understands it I don't wanna look like a need, unless that's a good thing? I have no idea. Just thought I'd reach out to people WAYYY smarter then me lol

So this is more a belief question, I'm at the end of my physics bachelor's, and to me it seems like many ends where physics is may (!) be dead ends. Obviously that may be completely wrong, and someone may come up with a great solution, but as far as I'm aware, math is incomplete, and there are unsolvable problems in math, so why shouldn't there be some in physics? The 3 body problem is an example, it isn't analytically solvable, but that's fine because approximation methods work great.

But there are cases like Quantum-chromo-dynamics, or even QED, where there are only approximation methods (like perturbation calculation), and those perturbation series just diverge, and our theories kinda break apart.

As far as I know there are no particular reasons on why physics should be solvable, or unsolvable, so both options seem realistic, and I tend to believe that it may just not worky but would be interested in other physicist opinions and reasoning about that.

Edit: When I'm talking about solvable I'm not 100% sure what I mean by that myself. Something that I would called solved is f.e. the harmonic oscillator, you have a problem, and an exact solution.

Something that is only approximated is in my view solved, when we can calculate it to arbitrary precision with simply more calculation power (only calculation power that is actually feasible).

Something where we don't know how it really works would be completely unsolved.

I am a bit confused by why this is the case, and the more I looked into quantum entanglement, the less I can find a solid basis for this implication.

In entanglement, two particles that are separated by a very large distance can remain correlated. Physicists have already discovered that this cannot be explained by local hidden variables. In other words, the particles do not simply have pre determined correlated states that are merely “revealed” upon measurement.

This seems to leave only three options:

a) the correlation is explained by some sort of mechanism/hidden variable that would have to be explicitly non local

b) there is no further “explanation” (Copenhagen interpretation) and the non local correlations that we see remain even after particles are separated do not have a further cause explaining why one outcome occurs instead of another, and why the correlation remains. One could perhaps classify this as a sort of fundamental, nonlocal randomness

c) all possible outcomes are realized (many worlds)

I am refusing to see why b) is not the least likely and why a) (along with c)) are often not widely believed, even if we do not have a theory yet. Given that we do see a non local correlation, why is it so out of the question that a non local cause results in this, or that the universe is fundamentally nonlocal? Presumably, this has to do with violations of relativity, but why are we so sure that it is not violated?

Either way, b) seems to literally be the equivalent of saying “there is no further explanation for why there is a consistently observed correlation that remains among particles separated by large distances”. One can perhaps say that this already is explained by the joint wave function of the particles, but that does not tell you which one of multiple joint outcomes will occur, or how. The equation is merely an abstract entity just saying the same thing: that there is a nonlocal correlation. It doesn’t tell us why a certain outcome is occurring instead of another or how this non local correlation remains.

It would be like if someone noticed that every time I jump off a balcony, I fall, and that those two things are correlated, and then someone else said “well, there just isn’t any further explanation for why this happens”. How can something that isn’t even a complete scientific explanation/theory be a viable option in the first place?

I think my question is slightly flawed, assuming that GRGs are all one thing and that we'd know their density well enough to do an integral, but regardless, let's assume it's just a big cylinder of light that's a few light seconds long.

The gravity well can't be in front of the GRB, or I guess it might be able to if the speed of light in the vacuum of space is slightly less than c, but then would the gravitational wave be going slower as well? I don't know.

Would it create a gravitational wave? Like a plane going mach 1 it makes a kinda-wave?

hi! so im making a countdown to an event in js, i have a meme option to make the countdown account for time dilation at 99% speed of light, basically the event is in 10 days but imagine if you were travelling in a spaceship going at 99% speed of light and you wanted to catch the event, does the ~7.09 times time dilation mean the countdown should be 10/7.09 days or 10×7.09 days?

thank you!

Hi, I'm an undergrad that likes physics in general, not just a specific topic, I will finish my degree this year and I have decided to pursue a masters in quantum computing/technology, mainly because I like computers, AI and quantum mechanics.

The thing is that during my degree I took clases based on what I like so I took clases on nanotechnology, astrophysics, QFT, cosmology, etc. Just to let you know, my final thesis is in astrophysics and I'm going to start an internship in cosmology, and yet I decided that I like more quantum physics.

My question here is, How hard is to change to a branch after the PhD? I just want to know how plausible it is to think I can, if I want, to start doing research on astrophysics, or cosmology.

Thanks for reading.

I have a physics exam this week and thankfully its online, is there any websites or software that will calculate the questions for me entirely? I really need to pass this exam and would appreciate any help. Thanks :)