# All Questions

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### A database for review literature in theoretical physics

Is there a database somewhere of the review literature (especially the most cited papers) in theoretical physics? I know about Spires but unfortunately it is not working. When I open a page it says ...
701 views

### Combined Gravitational Force Vectors in a Spherical Coordinate System

Asking a question here is quite intimidating for me -- while I love Physics, my high-school understanding only allows me to go so far... I've been trying to solve this problem for the last couple of ...
60k views

### Would time freeze if you could travel at the speed of light?

I read with interest about Einstein's Theory of Relativity and his proposition about the speed of light being the universal speed limit. So, if I were to travel in a spacecraft at (practically) the ...
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### Say we're driving a bike and suddenly hold the brakes?

It's easy for me to imagine that if we brake the front wheel then there is a chance that I'll flip. On the other hand if I brake the back wheel, there is no way it'll happen no matter how fast I ...
3k views

### Regarding possibility of infinitely many spatial dimensions

Recently I was taking a look at a video explaining the existence of fourth spatial dimension and thereupon that infinitely many spatial dimensions are possible. Also it showed that what Einstein told ...
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### Is the classical Doopler Effect, for light shift, $1-v/c$, exact? What is it an approximation of?

Is the classical doopler effect for light shift equal to $1-v/c$ exact or an approximation of a classical formula? I know that it is an approximation of the relativistic formula, but what was the ...
40k views

### Has any permanent magnet motor been proven to run?

I have read lots of articles about permanent magnet motors, some of which claim the possibility and other which refute it. Is it possible to have a permanent magnet motor that runs on the magnetic ...
479 views

### How can there be a quantum field theory that predicts all particle masses?

Say I have a theory with only one (energy) scale, e.g. one given by the fundamental constants $$\epsilon=\sqrt{\dfrac{\hbar c^5}{G}}.$$ In this case, where I can't compare to something else, is ...
266 views

### Loudspeaker frequency response dip

I'm trying to determine the reason for a dip in the frequency response curve of my loudspeaker. I have a loudspeaker mounted on the inside of an enclosure, and a 100mm ID tube mounted in-front of the ...
1k views

### What is the relationship between string net theory and string / M-theory?

I've just learned from this one of Prof. Wen's answers that there exists a theory called string net theory. Since I've never heard about this before it picks my curiosity, so I`d like to ask some ...
825 views

### Thermodynamics of cooking rice

The question is whether (1) cooking rice in a pot of boiling water for an hour and then leaving the pot (of water and rice) to cool to room temp heats my house the same amount as compared to (2) just ...
215 views

### Validity Of the Drake Equation [closed]

The Drake Equation is designed to estimate the number of Planets possibly having intelligent life forms existing in our Galaxy. But I don't see how it's justified. As far as we know, Earth is the only ...
538 views

### Physical Explanation of Being Able to “Think” [closed]

This may look like a philosophical question, but I'm looking for physical explanations (if there's any), that's is why I'm asking it here. What is the ability of thinking? We are all creatures ...
166 views

### What is the mean field value of a scalar field with spontaneously broken symmetry in a scattering event?

Consider you have a quantum field theory that undergoes spontaneous symmetry breaking at some critical temperature. It doesn't necessarily have to be a continuous symmetry that's broken, I don't think ...
166 views

### Hydrostatic forces

I've started learning hydro static force system right now. I have problem understanding one thing. In the picture I'm looking for the forces on the black lines: A part is making the purple force above ...
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### Variational wavefunctions and “spread” of potential in quantum mechanics

A particle in a box has an energy that decreases with the size of the box. In the general case, it is often said that a variational solution for a "narrow and deep" potential is higher in energy than ...
83 views

### Adaptive Optics Capability in the Visible Range

Telescopes with adaptive optics (AO) have been in use for several decades. To my knowledge, the lowest wavelengths utilized are in the near-infrared. It's known that Fried parameters are smaller for ...
Playing around with the four acceleration $$\left(\gamma^4_u \frac{\vec a\cdot\vec u}{c^2}\vec u +\gamma^2_u\vec a,\, \gamma^4_u\frac{\vec a\cdot\vec u}{c}\right)$$ I found the time part for frame' ...