# All Questions

779 views

### Retrodiction in Quantum Mechanics

To focus this question let us consider first classical mechanics (which is time-symmetric). Given a final condition (and sufficient information) one can calculate the system conditions of an earlier ...
650 views

### What is generating the hydrogen that has exploded in the Fukushima reactor?

The explosions at the Fukushima nuclear reactors were caused by a build of hydrogen. I was wondering where this hydrogen came from. This question Fukushima - Isn't the hydrogen presence a proof ...
228 views

### Mechanical momentum of the EM field in a continuum?

Given an uncharged continuum the EM field produces no force on it. Yet in a discrete system we know that atoms are not uncharged locally and momentum can be exchanged due to the electric field(Which ...
307 views

### Fukushima - Isn't the hydrogen presence a proof of meltdown?

As I understand, the hydrogen is produced by water thermolysis, which need quite high temperature. This temperature is close to previously observed corium temperatures. So: Is the eutectic ...
4k views

### What does it mean to say that mass “approaches infinity”?

What does it mean to say that mass "approaches infinity"? I have read that mass of a body increases with the speed and when the body reaches the speed of light, the mass becomes infinity. What ...
517 views

### A water drop in a falling lift

Consider a lift, which is at rest in an homogeneous gravity field. There is a thin layer(with thickness $h$) of water on the floor of the lift. At some moment a single cable, supporting the lift, ...
1k views

### What is the source of high-frequency squeal in faulty CRT monitors and TV, and what is physics of generating this sound?

Sometimes old faulty CRT monitors generate nasty high-frequency squeal sound. What element might be responsible for generating such sound? I have heard that it might be dry electrolytic capacitor; ...
131 views

### Binding Energy of He

The graph of nuclear binding energy is relatively smooth going from H to U, except for He4 (alpha particle). Why is He4's binding energy so anomalously high compared to its neighboring isotopes?
2k views

### Can a nuclear reactor meltdown be contained with molten lead?

If lead can absorb or block radiation, would it be possible to pump molten lead into a reactor core which is melting, so that it would eventually cool and contain the radiation? Is there something ...
627 views

### Alternative theories to the big bang?

Hey all, are there any theories out there on the origins (or infinite existence of) the universe beside the big bang that actually adhere to current scientific knowledge and fact?
2k views

### In superluminal phase velocities, what is it that is traveling faster than light?

I understand that information cannot be transmitted at a velocity greater than speed of light. I think of this in terms of the radio broadcast: the station sends out carrier frequencies $\omega_c$ but ...
553 views

### London penetration depth

Which type two s-wave superconductor has the smallest London penetration depth? What is l_lamda ?
2k views

### Why does amount of protons define how matter is?

My question might sound convoluted but my mind is twisting right now so my apologies in advanced. Why is it that when I have one proton and one electron it is Hydrogen a clear flammable gas, and ...
486 views

### What Would be the Experimental Signature of Composite Leptons?

So far, the quarks and leptons appear to be fundamental particles. But they're complicated enough that there's always been some speculation that they might be composite. What experimental evidence ...
1k views

### Is it Possible to Determine Radiation Levels Using Satelites?

Given recent events in Japan, this got me wondering. Is it possible to determine radiation levels reliably not having Geiger counters near the possible radiation contaminated zone? According to ...
962 views

### Uses of the 'Golden Ratio' in Physics

What are some physics applications of the golden ratio? $$\varphi~=~ \frac{1+\sqrt{5}}{2}~\approx~ 1.6180339887\ldots$$ Does it ever function specifically as a constant in any formulas or theorems? ...
151 views

### Applicability of Baxter's method for IRF models

In a interaction-round-a-face model of $n^2$ particles in a lattice, a weight $W(a,b,c,d)$ is assigned to each face in the lattice based on the spins $a,b,c,d$ (listed say from the bottom-left corner ...
681 views

### Giant string in space

I saw an interview with Ed Witten, where he said one way to confirm string-theory is to observe a giant string floating in space, left over from the Big-Bang. How does one observe such a string, does ...
608 views

### Why didn't Newton have a cosmological constant

Einstein initially added the Cosmological Constant because (if I get this right) it seemed to him that the universe should be static. I agree that back then this would have been an obvious assumption. ...
248 views

### Power Spectral Density of constant speed data in a car

I recently calculated the PSD of the vibration data in a car at constant speed. I would like to know what this means and what if I calculate PSD of the vibration data in a car for the total journey ...
236 views

### The speed of light also applies for 'distance' materials?

The question is hard for me to put into one sentence so please try to completely read the example: If I had a stick that is 1000KM long and I would push it forward with 1 millimeter in lets say... ...
528 views

154 views

### Readings of the detectors at Japan and Izu-Bonin-Mariana Trenches

Given the relevance of this subduction system, I would expect that a wide range of detectors (temperature, vibration, seismometers, whatever) are deployed in the depth of these trenches. What would be ...
206 views

### The size of the planets

What calculations were done to discover the size of all the planets?
1k views

### How are light and time related?

So, from what I understand: Special Relativity says that light is always observed moving at the speed of light (c). If some object had a velocity of (3/4)c, and the object had some sort of clock ...
303 views

### References on the physics of anyons

Anyone know some good introductory references on the physics of anyons?
2k views

### Why should optical fibers be thin?

What are the reasons that optical fibers have to be thin (small radius of the fiber)? Is there a good picture which explains this in detail?
3k views

### Why can one bend glass fiber?

Why can one bend glass fibers without breaking it, whereas glasses one comes across in real life is usually solid? Is there also a good high-school level explanation of this?
4k views

Why do optical fibers usually have a cladding? Ok, if you put make a bundle of optical fibers this prevents that light leaks from one fiber to another fiber in contact. However, are there other ...
162 views

### How good is current tsunami prediction?

We all know that predicting tsunami and earthquake is difficult, with too many variables involved. But with the advent in data collection and computing power and better models, one should be able to ...
536 views

### “Work” when biking up a hill

So, when biking, I noticed that when going up hills, it was less tiring if I went up them more quickly. This is not total Work done as is Force * Distance, as that should be the same. But the longer ...
261 views

### What happens if I charge a a Li-ion battery with non-nominal voltage?

Suppose that I have a li-ion battery with voltage 10V (and some capacity, say 1000mAh). Can I charge it completely using 5V voltage? What will hapen if I charge it with 12V voltage? Edit: Found the ...
515 views

### What is the formula for the relativistic ellipse?

If an astronomer moves at relativistic speed, the stars and constellations are distorted. He sees the stars towards which he is moving blue shifted, while the ones he's moving away from are red ...
554 views

### What is the exponential form gamma matrix for a general rotation and boost?

It would be nice to have a cute method that uses Lorentz transformations of basis vectors by exponential transformation using gamma matrices. To avoid confusion, let's assume -+++ signature. Given ...
312 views

### is the sun itself moving

I just thought of an interesting question.Is the sun actually moving? I have learnt that the way the lunar landers and the space ships of the Mercury and Apallo missions moved and controlled their ...
412 views

### Can PEPS explain the holographic principle in quantum gravity?

Condensed matter physicists have shown using quantum information that in many condensed matter systems, entanglement entropy only scales as the area of the boundary, and not the volume. This is the ...
557 views

### What are the modern marvels in Physics that seem crazy but true? [closed]

What are the modern marvels in Physics which are crazy but true? Ideas which are ridiculed and dismissed in the beginning but passed the test of time?
454 views

### Is Weyl invariance absolutely necessary for string worldsheets?

The Polyakov action for a string worldsheet has Weyl invariance. In the conformal gauge augmented with Weyl gauge-fixing, we can always impose a flat worldsheet metric in Minkowski coordinates. The ...
1k views

### Find true anomaly given period, eccentricity and time

Is it possible to find the true anomaly of an object in a Kepler orbit given the orbital period of the object, the orbital eccentricity and the time? Assuming a two body system and the mass of the ...
1k views

### Electro Magnetic Waves can cause matter displacement?

After watching this video: http://www.youtube.com/watch?v=j1jIjx0XF_U The experience is made with a speaker that generates a sound wave or mechanic wave. Can you use this to establish a link to ...
202 views

### Density/distribution of Eigenvalues

In various articles (I am here talking about specially the ones related to string theory etc.) I have seen the discussion on density and distribution of eigenvalues. I want to know why do we use them ...