Physics Weekly Newsletter
Physics Weekly Newsletter

Top new questions this week:

Was Titanic's captain's decision correct?

I just saw a documentary on Titanic. Someone in that documentary told Captain Smith "Shall we close the water tight doors, sir?" and the Captain replied "No, let it be open. Let the water …

water metals  
asked by Amit Joki 22 votes
answered by Floris 35 votes

Why doesn't dark matter affect planetary motion?

If the universe is made up of ~95% dark matter, and it interacts only gravitationally then why didn't Newton and Kepler discover it before ? Why does it show itself only in the radial velocity profile …

orbital-motion solar-system dark-matter  
asked by user44330 18 votes
answered by DavePhD 12 votes

Wouldn't angular momentum of a binary star system decrease?

Consider a binary star system, as these stars go around one another they would emit gravitational waves. Since, the graviton is a spin 2 particle. Wouldn't the angular momentum of the stars decrease? …

general-relativity gravity angular-momentum quantum-gravity stars  
asked by Anant Saxena 14 votes
answered by WetSavannaAnimal aka Rod Vance 21 votes

What if photons are not the fastest particles?

Einstein originally thought that special relativity was about light and how it always travelled at the same speed. Nowadays, we think that special relativity is about the idea that there is some …

special-relativity photons faster-than-light tachyon  
asked by user132181 10 votes
answered by Jim 21 votes

Can nowadays spin be described using path integrals?

In Feynmans book, "Quantum mechanics and Path Integrals" he writes in the conclusions (chapter 12-10) With regards to quantum mechanics, path integrals suffer most grievously from a serious …

quantum-mechanics spin path-integral  
asked by asmaier 10 votes
answered by Robin Ekman 4 votes

What's the relationship between $SL(2,\mathbb{C})$, $SU(2)\times SU(2)$ and $SO(1,3)$?

I'm a beginner of QFT. Ref. 1 states that [...] The Lorentz group $SO(1,3)$ is then essentially $SU(2)\times SU(2)$. But how is it possible, because $SU(2)\times SU(2)$ is a compact Lie group …

special-relativity group-theory lie-algebra representation-theory spinors  
asked by user34669 10 votes
answered by Edward Hughes 5 votes

How is the Plane of the Solar System oriented to the Sun's motion through space?

How is the Plane of the Solar System oriented to the Sun's motion through space: parallel, perpendicular, or some other angle?

astronomy solar-system  
asked by user44430 8 votes
answered by John Rennie 9 votes

Greatest hits from previous weeks:

How can you weigh your own head in an accurate way?

I read some methods but they're not accurate. They use the Archimedes principle and they assume uniform body density which of course is far from true. Others are silly like this one: Take a knife …

mass everyday-life measurement home-experiment  
asked by metacompactness 78 votes
answered by twistor59 84 votes

What is the relationship between kinetic energy and momentum?

I can't seem to figure out the relationship between $E_k$ and $p$ or $F$. I understand that the units are pretty different. But for example: A bullet with a mass of 10.0g is moving at the speed of …

homework energy energy-conservation kinematics momentum  
asked by Dan the Man 6 votes
answered by Lagerbaer 15 votes

Can you answer these?

R-symmetry commutator

I've seen the claim made several placed; Terning's "Modern Supersymmetry" p. 5 on N=1 SUSY algebra states it as well as anyone: The SUSY algebra is invariant under a multiplication of $Q_\alpha$ …

supersymmetry lie-algebra  
asked by wittensdog 4 votes

What is the meaning behind the neutrino oscillation parameter?

As far as I can tell, there are 6 parameters that describe how a neutrino oscillates: 2 mass squared differences, 3 mixing angles and another parameter I don't understand at all (delta). Thus I have …

particle-physics neutrinos beyond-the-standard-model  
asked by user44391 2 votes

Polar Decomposition of a Complex Scalar Field

People often write a complex scalar field via polar decomposition. What does this parametrization precisely mean? To be more explicit consider the following Lagrangian of a complex scalar field with …

quantum-field-theory coordinate-systems  
asked by JeffDror 5 votes
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