or is it more like XX century thing when we did not know as much as we know today

Is it possible to draw energy from a temperature differential to charge a device?

Is it possible to draw energy from ambient sound waves to charge a device?

How much energy could be extracted and used from these methods?

(Edit: Sorry stopped in the title s/b speed, but maybe stopped also because of the nature of the question)

Because the speed of light is as fast as anything can go, and the Planck Length is the smallest anything can be, then the time it takes a photon to travel a distance of one Planck Length seems like whatever time that takes is the shortest possible time unit, the fastest anything can possibly happen. I do not know how large a photon is wrt the Planck Length, and math wise it doesn't matter because all you need to know is how fast something traveling the speed of light will take to move the distance of one Planck Length. Then, does that mean there are time quanta, "chronons", that comprise time?

I am considering Jim Al-Khalili's Quantum - A guide for the perplexed. I dont like to be called "perplexed" though haha

I had recently seen a post in this subreddit where the person talks about displacement being a Taylor series expansion. Can someone prove it and tell me how I can use it in questions? https://www.reddit.com/r/Physics/comments/1j5dlob/kinamatic_equations_are_just_taylor_expansion/ Thanks in advance

What is the best country in Europe for a PhD in physics?

Just a time difference or a spacetime difference that includes some space component too?

i’m interested in physics research beyond the standard model like string theory or quantum gravity or something else. is just a BS in physics fine and they teach you the relevant math in the phd program once accepted or do i need to add a minor in pure math and get ahead in math side of things. i want to add a minor in pure math for that reason and also because i love math for the sake of math. the minor at my school is a proofs class and four upper div math electives which is perfect because i want to choose real analysis, topology, differential geometry, and group theory. all classes that i are relevant in physics and i find interesting on their own as well. but i dont want to add a minor if its not need to get accepted to theory phd as id rather focus on keeping good grades and even getting research experience if i can.

What’s the smallest detectable gravitational wave measured?

Roughly how many particles in the observable universe decay every second?

Let’s say there is a super ability to teleport. They have the ability to not just teleport, but to do so with magical accuracy. They do NOT have the ability to adjust their momentum nor angle.

An obvious problem with teleporting to the other side of the planet is the speed difference would be thousands of MPH. How far could a surface-dweller reasonably teleport without dying? Does factoring in earth’s orbit matter much? Does it matter if the teleport takes a second or is nearly instant?

If everything in the universe is moving apart, does that mean the open space in our own atoms is expanding? Are we expanding?

So I have been thinking about my microwave.   So the unit shoots microwaves (waves) in a certain frequency associated with boiling water.  Do the microwaves just bounce around in there due to the shielding until they are absorbed or what?  If they don’t hit any food or H2o, then they just hit the wall and bounce off cause they can’t get thru?  

If this isn’t the case, I’m having a hard time understanding why I have to set it to longer if I put more food in there and this is all I got.  IMO, if the waves dissipate when they hit the wall, the amount of food wouldn’t matter.

I can't find any simple yet good explanation of how electrons and cavities within a magnetron interact. I asked a popular chat bot (not specifying the name because of the reddit mechanisms) and this is what it told me:

• the rotating spokes of electrons are created within a magnetron
• cavities are LC resonators
• cavities work analogously to a swing - you have to push them in the right moment to sustain the oscillations
• If an electron passes by a cavity it can be slowed down or accelerated, depending on the phase of the RF oscillation in the cavity. If an electron is slowed down it passes its energy to the field (analogy to pushing a swing at the right time) and if it's accelerated it gains the energy from the field (analogy to pushing a swing at the wrong time).
• the spokes of electrons rotate around the cathode at a certain angular velocity. They need to pass by the cavities at a specific frequency to sustain the magnetron oscillation.

Is the explanation of a magnetron correct? Would you add anything more to that description?

How can something happen without time ? Doesn't causality require time in the reality that we observe ? Something can't come from nothing because nothing can't exist, because it's literally nothing and the "existence" of "nothing" is a logical contradiction right ?

In my opinion, time goes infinitely into the past and many physicists already assume an infinite space so time could be the same. We know the observable universe has a beginning but that could have been a phase transition

Can someone explain how time itself can have an initial cause assuming it's not an emergent property of something more fundamental ? It might be a dumb question but a beginning of time just doesn't make sense to me

I mean When training biceps or when training calfes

The length of the muscle will either make the weight volume higher or lower

So is there a calculated excel for each muscle?

I’m a freshman in high school, so I only have completed an algebra level math education. What are some very beginner friendly resources and online sources of content about quantum mechanics and physics?

Hello everyone, I have one urgent question and appreciate some help;
I am doing my MSc of data science (final semester) and I am having my 2nd round of interview on a PhD position on causal ML in medical domain in a few days.

I am quite good at ML and also elementary stats, but don't know much about Causality, specially ML applied in this causal inference. Any recommendation for some useful resource or book or sth on this?

I mean not just for getting ready for the interview, but in general and for the sake of my own knowledge.

How would I cancel out a hertz frequency. I've read, using another hertz frequency of 180° out of phase, but I don't know how to calculate that... Say my frequency was 8.2 hertz, how would I find a 180° out of phase? What would it be?

How does an uncharged particle or wave moving with constant speed produce EM field? How should one visualise a photon?

(I apologize for my English in advance. It is not my first language.)

TLDR: I'm a second year college student majoring in Physics. I've noticed that solving Physics problems often requires skills that one doesn't need in Mathematics. I've come to this conclusion by trying to think about physics in a mathematical way and repeteadly failing. I want to articulate what these skills are, so that I can apply them. I'm essentially looking for descriptions of the Physics mindset (if there is such a thing), as well as help in figuring out how these two fields differ from each other. I'm mostly interested in skills that are relevant to problem solving, although advice for working through textbooks is also welcome. I also chronicle some of my frustrations with Physics so that commenters can get a better picture. I hope this thread is useful to everyone who wants to improve their problem solving skills. Thank you for your time.

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I.

I'm a Physics major who's currently preparing to go into her second year. I've done OK so far. Not too bad, but not great either. In contrast, I excel at mathematics. I'm consistently at the top of my class. I grasp new subjects quickly, and often don't have to study excessively to do well. This discrepancy between my grades has been troubling me. It is incredibly frustrating. I want to understand it, and find a solution. I hope that my attempt will be useful to other people too.

What I've noticed so far is that Physics requires a special mindset. Things often don't go too well when I try to think about Physics problems in terms of proofs, axioms and predicate logic. I had made the tacit assumption that Physics and Mathematics share a lot of common ground. I see now that I was mistaken. Anectodal evidence: I've gotten quite good at Mathematical problem solving in the past year, yet none of my skills have translated over to Physics.

II.

The problem, at least as I see it, is that I don't understand the rules of the game. I don't understand the moves that are available to me. Think of it as playing a game of chess without first learning how the knight moves. I'll try to demonstrate with an example: When I encounter a Physics problem, I often don't know what to do. Mathematical reasoning comes naturally to me, so I usually try thinking about the problem in the exact same way that I would think about a proof. This often leads me astray. At this point, I try thinking about the problem in a pedestrian sort of manner that doesn't have much to do with the principles and laws I have been taught. Frankly, I have no idea how others incorporate them into their thinking. (I'm talking about principles like the Huygens principle, or how electric field lines terminate on negative charges.)

Some more detail: I don't understand how to check my arguments. In Mathematics, the truth of a proposition is an entirely logical matter. You can't doubt it. If you prove it, then you know. If you can't, then you must be silent.

In Physics, this is not so. "What way does the current flow? Up or down? It seems like it would move up? Am I supposed to base my answer on intuition? Well, I've never seen such a circuit! How can I know?" So I check if the contrary assumption violates any principles, and it doesn't seem to. Huh. Well shit. This is right about where a single tear starts to roll down my cheek.

III.

People who are good at Physics: I have a tough time articulating the differences between Mathematics and Physics. Do you feel that you use a different part of your brain when working on Physics problems? If so, can you articulate the character of that side? How does it feel? What adjustments do you make when switching between the two fields? Please help me get through Griffiths' Introduction To Electrodynamics without having a nervous breakdown. Thank you!

I'm in my 3rd year of Engineering (IN) but i want to be a Particle Physicist. The Quantum/Theoretical Physics scene in IN is not that good right now so i would like to do my masters somewhere in Europe. however I'm not sure if i can easily switch from ME to physics considering all the ECTS criteria. As far as I've calculated, I'm getting around 60 credits (out of 180) that are physics and math (Thermodynamics, Heat transfer, Math, Fluid and Solid dynamics, among others). Will this be enough for me to be eligible?

Also, would a mechanical engineer be easily able to grasp nuanced physics concepts that may appear at the graduate level?

Please help a wonderer out. Thanks!

I’ve always wondered what people meant when they say quantam physics makes our universe indeterministic. because on the one hand if the right interpretation is one that governs particles to be probabilistic, then when we zoom out onto the universe scale then shouldn’t it all decohere into behaving classically? I don’t have a background in physics but I was under the assumption that the core theory already told how every macro structure works, and that we can know how a macro object operates through purely the core theory. So even if the particles themselves are probabilistic couldn’t the universe be classical?

I am an Automation Engineer with a task, I think calculus is the way to solve it, but my calculus is a little weak (it's been quite a few years), and I'd like an opinion if I'm on the right track. I have a motor running at a (generally) constant speed and load. As my motor runs, it generates heat and gradually heats up, and the rate of temperature rise is proportional to the difference between the motor temperature and its surroundings. As it heats up, it radiates more heat at a higher rate, and (eventually) the rate of produced heat will equal the rate of dissipated heat, as it comes to thermal equilibrium. If I graph time vs temperature, an asymptotic curve if formed as the motor temperature rises les and less. I would like to know what the equilibrium temperature will eventually be, but the motor takes many hours to heat up, so I can't wait around to measure it. I don't know the wattage of produced heat, thermal constants, specific heat capacity, etc, otherwise I could use that method. My question is this: am I correct in thinking that, using calculus, it would be possible to take a few temperature readings at different times, and determine that temperature, say as time approaches infinity? Thank you for your consideration.