# All Questions

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### Could we recharge the sun's “batteries”?

From this link: The Sun is 4.6 billion years old and is estimated to live in this stable phase another 4.6 billion years. Since the Sun is a star, once it reaches the end of its lifetime, it ...
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### What is the error on measuring the phase of a sine wave?

Let's say I have a wave, with frequency $\omega$ and phase $\phi$, of the form: $$y(t) = 1 + A \sin(\omega t+\phi)$$ where $A < 1$. I have measured this wave N times, and we can assume these ...
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### Does the definition of the SI unit “second” require that possible perturbation of primary frequency standards should be measured?

The definition of the SI unit "second" is stated as The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground ...
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### How do adhesive and cohesive forces affect surface tension? [closed]

Surface tension appears at the interface of two immiscible fluids if the cohesive force of attraction is more than adhesive force. What will be the physical effect if the adhesive force is more than ...
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### Fluid dynamics - Water level in a container

An open container is being filled with water from the top at a constant volumetric flow rate $300 \frac{cm^3}{s}$. At the same time, water is leaving the container trough a circular whole at the ...
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### Why does a string remain taut in circular motion

Lets say an object is tied to a string and it is being swung in a circle: In this case, the tension of the string acts as a centrifugal force that keeps the object moving in a circle. However, if ...
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### Question on circular motion — car turning on road

Lets say a car is turning on a road that has friction. I made this small diagram where the two parallel lines indicate the tires of the car. In order for the car to keep turning in a circle, there ...
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### What is a superfluid in field theoretic terms?

I'm wondering how one precisely defines a superfluid in terms of the effective field theory description. In Nicolis's paper http://arxiv.org/abs/1108.2513 there seems to be an extremely simple ...
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### If a planetoid was wet and you spun it would the water move to the equator?

If the moon was alone in space and covered in X feet of water and it began to rotate would it displace to a bias along the equator?
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### Kallen–Lehmann spectral representation for an arbitrary spin

Let's have Kallen–Lehmann spectral representation for the scalar theory: $$\tag 1 D(p) = \int \limits_{0}^{\infty} d(\mu^{2})\frac{\rho (\mu^{2})}{p^{2} - \mu^{2} + i\varepsilon}.$$ We can represent ...
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### Why should a (physical) principle be applicable to different systems in different positions in space and time?

This is a question with a philosophical, as well as physical, flavor. Why should a physical principle (or a description of one), be applicable to different systems that can be in different positions ...
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### Probability and the propagator

Due to the Wiki article, "...In quantum mechanics and quantum field theory, the propagator gives the probability amplitude for a particle to travel from one place to another in a given time, or to ...
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### Basic question on the Aharonov-Bohm effect

I have a very basic question on the Aharonov-Bohm effect. Why is the curve integral $\oint_\Gamma {A}\cdot d{r}$ non-zero ? $\Gamma$ is the "difference" of both paths $P_1$ and $P_2$. If the ...
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### What is the percentage of stars that are massive enough to end their lives in a supernova?

I have been searching for the percentage of stars that are massive enough to end their lives as a supernova but couldn't get any result. As far as I know, a star has to be at least 8 times more ...
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### Physical Role of Batter in Baseball

Physically, what is the role of a batter in baseball? My question is inspired by How does the speed of an incoming pitch affect the speed of a baseball after it's hit? The answer to that question, ...
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### Where do $X_0^{-d}$ and $G'_r$ come from in Polchinski Eq. (6.2.13)?

I have a question about deriving Eq. (6.2.13) in Polchinski's string theory book volume I. It is claimed that Now consider the path integral with a product of tachyon vertex operators, A_{S_{2}...
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### O(N) sigma model at large N

I would like to better understand the main principles of large-N expansion in quantum field theory. To this end I decided to consider simple toy-model with lagrangian (from Wikipedia) \$ \mathcal{L} = ...