# All Questions

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### Spontaneous symmetry breaking and 't Hooft and Polyakov monopoles

What is spontaneous symmetry breaking from a classical point of view. Could you give some examples, using classical systems.I am studying about the 't Hooft and Polyakov magnetic monopoles solutions, ...
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### Using Einstein's Relativity: Who is younger?

Suppose we have a person A and a person B. Person B travels very close to speed of light and never returns. He's constant in speed. Then, we can say two things: B is younger than A. A is younger ...
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### what is expectation values of this anti-commutator?

what is expectation values of this anti-commutator? $$\langle \{ \Delta \hat x,\Delta \hat p\} \rangle$$ where the $\Delta \hat p=\hat p-\langle \hat p \rangle$ and $\hat p$ is momentum operator and ...
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### How could scientists know how far a star or galaxy is from us?

How do astronomers measure how far a star (or galaxy) is away from the earth? How would they know that it has taken 13 million years for light to travel in space before it reaches us?
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### Is the U(1) gauge theory in 2+1D dual to a U(1) or an integer XY model?

The compact U(1) lattice gauge theory is described by the action $$S_0=-\frac{1}{g^2}\sum_\square \cos\left(\sum_{l\in\partial \square}A_l\right),$$ where the gauge connection $A_l\in$U(1) is defined ...
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### Why is it that when you pick up a cup from a stack of solo cups too quickly, they stick together?

Intuitively I think it makes sense but can somebody explain very clearly to a non-physics person why it is that when you pick up a cup from a stack of solo cups very quickly, the cup below it seems to ...
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### Circular motion period equation

The equation, $$a_c=\frac{4\pi^2r}{T^2}$$ Can be expressed as: $$F_c=\frac{m4\pi^2r}{T^2}$$ I am confused as to how to arrive at this second equation, and the relationship between these two ...
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### What would it feel like to touch a frictionless surface

Assume there is a completely frictionless surface. Would touching such a surface be possible? If so, what would it feel to the touch?
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### In relativity, what is the difference between a rod that is perpendicular to direction of motion and a rod parallel to the direction of motion?

In Feynman's Lectures on Physics , chapter 15, page 6 he writes about 2 identical, synchronized light signal clocks. These are clocks that consist of a rod (meter stick) with a mirror at each end, and ...
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### Could the Periodic Table have been done using group theory?

These three questions are phrased as alternative-history questions, but my real intent is to understand better how well different modeling approaches fit the phenomena they are used to describe; see 1 ...
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### Must the derivative of the wave function at infinity be zero?

I came across a problem in Griffiths where the derivative of the wave function (with respect to position in one dimension) evaluated at $\pm\infty$ is zero. Why is this? Is it true for any function ...
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### The (co)algebra for the (co)monad of a light switch

If we take a light switch to embody an entire category, we could take the light switch to be a set with two elements and the morphisms are all endofunctions. Let's say, for fun, that we define the ...
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### Euclidean Geometry in Classical Thought - Realization or Representation?

First post! :] This has been bothering me for a while now: [Taken from John J. Roche's "The Mathematics of Measurement: A Critical History"] When physico-mathematicians in the seventeenth ...
384 views

### How can a body be transparent?

How can a body be transparent? I need the theoretical explanation for the same. Has anybody succeeded in doing that practically?
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### Why is radioactive decay dependent on amount of substance available?

Radioactive decay is an attribute of unstable nucleus. When we represent it in equation, we don't involve any macroscopic attribute of substance. But still, rate of radioactive decay is proportional ...
523 views

### Natural Units and the Nuclear Radius

In a paper I'm looking at and also in a similar program, the authors note that the nuclear radius $R$ is given in "natural units" as $R = 3.11\times 10^{-3}\;A^{1/3}$. This has me slightly confused, ...
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### Spin-ice materials with strong quantum fluctuations

Spin-ice materials are insulating materials where spins form a 3D pyrochlore lattice and have a frustrated magnetic interaction. The spin dynamics in most spin-ice materials is very classical and has ...
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### At what g is terminal velocity not terminal?

How weak would gravity need to be in order for a human to reliably survive the terminal velocity of falling through air? (Context: watching scifi on a space station with a variety of artificial ...
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### what is difference between these two expectation values?

what is difference between these two expectation values $\langle \hat A \hat B\rangle$ and $\langle \hat B \hat A\rangle$? where the $\hat B$ and $\hat A$ are two operators.
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### extracting energy from cosmological expansion

This question is a more concrete reincarnation of an old question about energy conservation in GR. Are there mechanisms to extract energy from the cosmic rate of expansion? putting some extremely ...
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### Nature of orbit due to central force! [duplicate]

Possible Duplicate: Kepler problem in time: how do two gravitationally attracting particles move? How do we get the shape of orbit under the condition that Force is centrally directed ...
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### Current scope of Chaos theory and non-linear dynamics? [closed]

I am a physics undergrad interested in stuff like dynamical systems, chaos theory etc. Is there ongoing research in these fields? I am talking about pure research and not applications to things like ...
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### Intrinsic structure of electron

The electron contains finite negative charge.The same charges repel each other.What makes electron stable and why does it not burst? Is it a law of nature that the electron charge is the smallest ...
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### How to tell whether a physics theory is beautiful?

A lot of physicists would have agreed that General Relativity is a beautiful theory. My question is that, what really makes a physics theory beautiful? Is there any criteria that a theory must ...
214 views

### Unexpected potential energy increase during Tic-Tac drop

I dropped a Tic-Tac: (no worries, it happened before), and I noticed as it bounced on the floor that it would first jump 20 cm high, and at the next bounce for instance 50 cm high. Shouldn't it ...
163 views

### How do Kolmogorov scales work in shear thinning fluis?

My understanding of Kolmogorov scales doesn't really go beyond this poem: Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity. ...
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### Do wormhole exits require matter? If not, would they change the edge of the universe?

As a layperson who watches way too many theoretical physics and astronomy documentaries, I've seen the folded-piece-of-paper analogy of wormholes a bajillion times. Usually they explain that black ...
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### Can atmospheric hydrogen be collected for use?

Just what the title states. Free hydrogen accumulates in the exosphere. At high altitudes there are large volumes of open space between molecules - which would be a hindrance to collection. Would ...
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### When I connect in series two floating capacitors, one charged and the other not charged, does current flow?

Suppose I energize one capacitor by connecting it across a battery, allowing it to achieve some potential difference V0 across its plates, then disconnect it and allow both of its leads to float in ...
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### Does infrared light pass through active shutter glass?

The glasses that we use for 3D viewing, do they allow infrared light to pass through them? Infrared rays pass through normal glass right? I need the pupil illuminated through infrared LEDs so I need ...
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### Quantum Mechanics by Dirac

I took quantum mechanics from our school's electrical engineering department. It was a grad level class designed for students working in device physics, thus it covered a lot of materials: from the ...