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All given metrics are for orthonormal-basis. 2 dimensional spacetime : I saw that Minkowski Metric looks like this : $$\pmatrix{-1 & 0 \\ 0 & 1}$$ or $$\pmatrix{1 & 0 \\ 0 & -1}...
Is it plausible to desire a "universal" calendar applicable everywhere in our universe? Must calendars be based on solar systems (Must calendars be "relational")? It might be that the universe "...
Are there areas in the observable universe which surely cannot contain galaxies with planets that can support life as we know them?
Two weeks ago, my carry on worked perfectly. But last week the detachable wheels stopped rotating smoothly, when I tried to glide my carry on. The wheels budge JUST A TAD when you push them hard, b...
I was wondering what's the physical meaning of Laplace operator. $\vec\nabla$ actually represent a field. I had seen that Laplace operator is written as $\vec \nabla \cdot \vec\nabla=\nabla^2=\Delt...
I saw following equation in Griffiths EM $$V(r)=-\int_\mathcal{O}^r \vec E \cdot d\vec l$$ While the surface was closed but not symmetrical circular. At first I was thinking $\mathcal O$ was repr...
If I have a rocket with some known number of engines $n$, each producing thrust with arbitrary direction $T_n$ and center of thrust $r_n$, the total thrust amount and direction $T_{total}$ is equal...
What is "disorder" in entropy? Entropy is measurement of "disorder". (Some says it's not "disorder") I had read "disorder" and "order" of entropy in my book. But I was wondering what "order" ...
I am not sure if it is suitable in the site. I am asking the question here cause Olin and Celtschk said it here. They told me to use unit in every "single line" (Nope! They didn't say like it. Oli...
I was reading about Ether, Maxwell and Young-double-slit experiment. I got a question about Ether law. Let me say what I read about Ether Law. Suppose, a boat is traveling with Adverse of Water ...
I was introduced to a somewhat novel derivation of the ideal gas law that starts by thinking about the number of microstates of an ideal gas, $\Omega$. Say we have a gas with a single particle in a...
I had a thought that crossed my mind a while back that went something like this: It's a cool thing measurements exist, if there wasn't, there'd be trouble and we'd be counting atoms if we could....
I have recently heard of Apsidal Vectors. I was searching about it through internet. I had found the video in YT. I had found similar question in PF. But, the PF answer wasn't clear to me. I am jus...
Since, there's no book category currently so, I am asking it here. And, It can be moved to that category later. I want to start learning now so, I don't want to wait. Which book is best for Clas...
$$F=F(q,p,t)$$ $$\frac{dF}{dt}=\frac{\partial F}{\partial q}\frac{\partial q}{\partial t}+\frac{\partial F}{\partial p}\frac{\partial p}{\partial t}+\frac{\partial F}{\partial t}$$ $$=\frac{\part...
What is semiholonomic is? Holonomic actually means two point can be expressed by a equation. Non-holonomic can be expressed but, not properly. Holonomic e.g. $r^2-a^2=0$ Non-holonomic e.g. $r^2-a...
$L=T-U$ Here, $L$ is Lagrangian. T is kinetic energy. U is potential energy. But, what Lagrangian actually is? I know what Holonomic and non-holonomic is. But, I was thinking what the Lagrangian re...
In my notes from University the reason a material can exhibit superconducting properties is at really low temperatures electrons form Cooper pairs of which the electrons of the Cooper pairs have lo...
How to derive the Lagrangian differential force? $$\frac{d}{dt}(\frac{\partial L}{\partial \dot{x}})+\frac{\partial L}{\partial x}=0$$ I was trying to do something. $$L=T-U=\frac{1}{2} m\dot{x}^...
If planet 9 exists, is it correct to say that it is a "dark planet"? By "dark" here I mean to a planet that doesn't reflect enough light to easily be seen from normal telescopes (in the current co...
We know that electrons always repel electrons. But, if somehow they collide, then what will happen? I found a related question of above one in Quora. An incoming electron can instead make them ...
What will happen if an electron and a proton collide? They attract each other inside an atom. But, why they don't collide inside atoms? Does the "boundary" of the nucleus push them away? depends...
This gravitational field we move inside has some distance L after which it becomes 0.Before L it is just like any gravitational field. Suppose we move inside that gravitational field.The accelerat...
Would a colony on earth's moon need to be deeply underground to ensure more natural gravity (by getting closer to its core)?
I was reading "Introduction to classical Mechanics" by David Morin. In that book they wrote that The third law says we will never find a particle accelerating unless there’s some other particle ...
In signal processing, are signals modeled in only one way (digitally or analogously) or are there some signals which can be modeled in both ways?
We have place a charged particle of 2C with mass 2kg, 1mm above a current-carrying wire of 1A.The charged particle has an initial velocity of 100m/s The magnetic field of the wire for simplicity w...
I have heard the physicist Laurence Krauss claiming that he believes that the universe is flat. Okay, but if we take four astronomers and we put one in the north pole, one in the south pole, one i...
I stumbled these pictures on Quora, and I'm assuming they were real. Wouldn't the supporter (person whom gun is mounted on) suffer hearing loss? Wouldn't the barrel burn his ear? I'm assu...
Suppose we have an electric dipole of charge Q+ and Q-.The charges of the dipole are fixed (they cant move closer to each other than they already are).If we place a test particle at some distance r...
How can I turn this floor lamp into a reading light? I want all light exiting upwards from the lamp shade to point down. Do I just buy a mirror and put it on top of the lamp shade? Then the mirror...
I am having trouble understanding what a cosmic inflation is. Please try to suffice an explanation for non physicists / non formal students for physics / general audience. I understand that an ...
Should Earth's moon colonies being deep underground ensure natural heating? By natural I mean "non artificial" i.e. not from "artificial" air conditioning. The question is based on the thought th...
Decibel level listed of solfege. Do Re Mi Fa So La Ti Do 24 27 30 32 36 40 45 80 I saw that whispering decibel level is around 40. And, normal voice level is ...
In Srednicki's proof of the spin-statistics theorem for scalar fields ("Quantum Field Theory", section 4), he considers interaction terms, added to the free Hamiltonian, that are Hermitian function...
Is this advice correct? Are they alluding to Freezing Point Depression? Adding salt to tap water lowers the Crystalloid's freezing point. Pour 3 tbsp (51 g) of salt into each of your 3 plast...
Please see the images below. I owned these Mykita John glasses for three years, which feels short for glasses to break! Every day, I fold them them before placing it on my night stand and going to ...
In 1970, the USSR began drilling at the Kola Super-deep Borehole. The target depth was 15,000 meters; The stated areas of study were the deep structure of the Baltic Shield, seismic discontinuit...
I'm not asking about cleaning human organs here. This handheld power scrubber looks like your average rotary toothbrush! Indubitably I know that a toothbrush's brush head can be far gentler than...
Let's say we have a single plate with liquid on both sides rising up due to surface tension. The meniscus formed has a radius of curvature $R$. I'm trying to find the excess pressure, i.e, the pre...
My optician counselled me I don't recommend a 1.74 index with a metal grooved frame, like the one you want from ic! Berlin, because the edge will be less resilient and be more susceptible to chi...
I don't understand either of these Reddit comments that are still too complicated. Please simplify? Alfenhose An interesting phenomena, it is because the brain doesn't store what you saw during ...
The major advantage of Alternating Current is that it can be transmitted to large distances without significant losses, which is not possible in Direct Current. Had economical superconducting wire...
I have a question about the discussion of constrained Lagrangian systems in the book Mathematical Aspects of Classical and Celestial Mechanics by Arnold et al. (section 1.2.5). The Lagrangian syst...
I asked this question on Stack Exchange, and didn't get an answer, but maybe someone here will be able to help. In non-relativistic quantum mechanics, the normalization condition for position eige...
In special relativity, spacetime coordinates are normally given as $$(ct, x, y, z) \tag{S}$$ with the metric being either $$g = \operatorname{diag}(-1,1,1,1) \tag{+}$$ or $$g = \operatorname{d...
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