20
votes
2answers
184 views
Post-doc advice for a low publication grad student
As a grad student, I have a single publication, a conference proceeding, to my name. So, my question is what do I need to do to obtain a post-doc position? Obviously, my references are going to be ...
20
votes
4answers
3k views
What if the LHC doesn't see SUSY?
A question in four parts.
What are the main problems which supersymmetry purports to solve?
What would constitute lack of evidence for SUSY at the proposed LHC energy scales (e.g. certain predicted ...
20
votes
6answers
2k views
How fast a (relatively) small black hole will consume the Earth?
This question appeared quite a time ago and was inspired, of course, by all the fuss around "LHC will destroy the Earth".
Consider a small black hole, that is somehow got inside the Earth. Under ...
20
votes
3answers
238 views
An entropy of the Wigner function
Is there an entropy that one can use for the Wigner quasi-probability distribution?
(In the sense of a phase-space probability distribution, not - just von Neumann entropy.)
One cannot simply use ...
20
votes
6answers
1k views
Rotation angle of a giant lily when a child crawls on its rim
Below is a picture of Giant Water Lily. Scientific Name: Victoria Amazonica. Leaves of some of these could be as big as 3 m diameter and carry a weight of 45kg spread evenly and can support a child. ...
20
votes
2answers
2k views
Why is the sky not purple?
I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of ...
20
votes
8answers
2k views
Why doesn't the bike fall if going with a high speed?
Why does the bike fall when its speed is very low or close to zero and is balanced when going with a high speed?
20
votes
4answers
2k views
Why is the bell, well, bell shaped?
What is the significance about the bell shape, when its hit at the rim it rings/produces sound better than other shaped objects? If so could anyone explain a little bit on it.
EDIT: From the ...
20
votes
2answers
83 views
experimental bounds on spacetime torsion
Did Gravity Probe B provide any bounds on Einstein-Cartan torsion? is a non-zero torsion value at odds with the results regarding frame-dragging and geodetic effects?
20
votes
3answers
786 views
+50
From where (in space-time) does Hawking radiation originate?
According to my understanding of black hole thermodynamics, if I observe a black hole from a safe distance I should observe black body radiation emanating from it, with a temperature determined by its ...
20
votes
3answers
781 views
Lie theory, Representations and particle physics
This is a question that has been posted at many different forums, I thought maybe someone here would have a better or more conceptual answer than I have seen before:
Why do physicists care about ...
20
votes
4answers
745 views
Is there a Lagrangian formulation of statistical mechanics?
In statistical mechanics, we usually think in terms of the Hamiltonian formalism. At a particular time $t$, the system is in a particular state, where "state" means the generalised coordinates and ...
19
votes
12answers
2k views
Is it possible for information to be transmitted faster than light by using a rigid pole?
Is it possible for information (like 1 and 0s) to be transmitted faster than light?
For instance, take a rigid pole of several AU in length. Now say you have a person on each end, and one of them ...
19
votes
6answers
2k views
Could there be a star orbiting around a planet?
I wonder if there ever could be a star (really small) which may orbit around a planet (really big)?
19
votes
8answers
2k views
Starting a physics Ph.D. at 60?
Decades ago I was in a physics Ph.D. program, made a hash of things, and quite rightly was dropped from the program. Since then I've had a very satisfying career as a computer programmer, and picked ...
19
votes
14answers
2k views
Learning physics online?
I'm thinking of following some kind of education in physics online. I have a master degree in Computer Science and have reasonable good knowledge in physics. I would like a program of 1-2 years and ...
19
votes
3answers
126 views
Does entropy measure extractable work?
Entropy has two definitions, which come from two different branches of science: thermodynamics and information theory. Yet, they both are thought to agree. Is it true?
Entropy, as seen from ...
19
votes
1answer
705 views
Why does it take so long to get to the ISS?
I don't understand why when first launched Space X's Dragon capsule had to orbit the Earth many times in order to match up with the ISS? Was this purely to match it's speed, or to get closer (as in ...
19
votes
5answers
2k views
Do photons gain mass when they travel through glass?
Please correct me if I'm wrong, but I believe that photons slow down when travelling through glass. Does this mean they gain mass? Otherwise, what happens to extra kinetic energy?
I understand now ...
19
votes
2answers
62 views
Kerr Geometry, Separability and Twistors
One of the remarkable properties of the Kerr black hole geometry is that scalar field equations separate and are exactly solvable (reducible to quadrature), even though naively it does not have enough ...
19
votes
12answers
2k views
Will a ball slide down a lumpy hill over the same path it rolls down the hill?
Suppose I have a lumpy hill. In a first experiment, the hill is frictionless and I let a ball slide down, starting from rest. I watch the path it takes (the time-independent trail it follows).
...
19
votes
6answers
1k views
Do Maxwell's Equations overdetermine the electric and magnetic fields?
Maxwell's equations specify two vector and two scalar (differential) equations. That implies 8 components in the equations. But between vector fields $\vec{E}=(E_x,E_y,E_z)$ and ...
19
votes
10answers
874 views
What is the difference between a measurement and any other interaction in quantum mechanics?
We've learned that the wave function of a particle collapses when we measure a particle's location. If it is found, it becomes more probable to find it a again in the same area, and if not the ...
19
votes
1answer
983 views
Why does this object periodically turn itself?
See this video about 30 sec in. http://www.youtube.com/watch?v=dL6Pt1O_gSE
Is this a real effect? Why does it seem to turn periodically?
Can it be explained by classical mechanics alone?
Is there a ...
19
votes
2answers
46 views
Bell polytopes with nontrivial symmetries
Take $N$ parties, each of which receives an input $s_i \in {1, \dots, m_i}$ and produces an output $r_i \in {1, \dots, v_i}$, possibly in a nondeterministic manner. We are interested in joint ...
19
votes
1answer
33 views
What is known about the classification of N=4 SCFTs with central charge 6?
I was talking about K3 surfaces with some physicists, and one of them told me that the N=4 superconformal field theories with central charge 6 are expected to be relatively scarce. In particular, one ...
19
votes
4answers
2k views
Why is the angle of the wake of a duck constant?
Why is the angle of a wake of a duck constant? And why are some conditions on the water depth necessary?
I realize that this question turns up in google searches, but I did not see a good discussion. ...
19
votes
5answers
1k views
Could gravity be an emergent property of nature?
Sorry if this question is naive. It is just a curiosity that I have.
Are there theoretical or experimental reasons why gravity should not be an emergent property of nature?
Assume a standard model ...
19
votes
9answers
6k views
How did Newton discover his second law?
I've always assumed/been told that Newton's 2nd law is an empirical law — it must be discovered by experiment. If this is the case, what experiments did Newton do to discover this? Is it related to ...
19
votes
3answers
548 views
Why wet is dark?
When something gets wet, it usually appears darker. This can be observed with soil, sand, cloth, paper, concrete, bricks ...
What is the reason for this? How does water soaking into the material ...
19
votes
3answers
573 views
Why is gravity such a unique force?
My knowledge on this particular field of physics is very sketchy, but I frequently hear of a theoretical "graviton", the quantum of the gravitational field. So I guess most physicists' assumption is ...
19
votes
1answer
278 views
State of Matrix Product States
What is a good summary of the results about the correspondence between matrix product states (MPS) or projected entangled pair states (PEPS) and the ground states of local Hamiltonians? Specifically, ...
19
votes
6answers
1k views
Massless charged particles
Are there any massless (zero invariant mass) particles carrying electric charge?
If not, why not? Do we expect to see any or are they a theoretical impossibility?
19
votes
3answers
362 views
How much information about the scale of a waterfall can be obtained from its sound?
Is it possible to constrain the height, volume flow, or distance of a waterfall from the quantitative analysis of a high-quality recording of its sound?
As an aside, the simulated sounds of fluid ...
19
votes
1answer
66 views
Any use for $F_4$ in hep-th?
In high energy physics, the use of the classical Lie groups are common place, and in the Grand Unification the use of $E_{6,7,8}$ is also common place.
In string theory $G_2$ is sometimes utilized, ...
19
votes
1answer
658 views
What nonlinear deformations will a fast rotating planet exhibit?
It is common knowledge among the educated that the Earth is not exactly spherical, and some of this comes from tidal forces and inhomogeneities but some of it comes from the rotation of the planet ...
19
votes
2answers
541 views
Theoretical penetration limit for evanescent waves
Consider a problem in classical electrodynamics, when a monochromatic beam experiences total internal refraction when traveling from a medium with $n>1$ to a medium with refractive index $1$ - see ...
19
votes
2answers
633 views
Covariant Description of Light Scattering at a fastly rotating Cylinder
Let us consider the following Gedankenexperiment:
A cylinder rotates symmetric around the $z$ axis with angular velocity $\Omega$ and a plane wave with $\mathbf{E}\text{, }\mathbf{B} \propto ...
19
votes
4answers
389 views
Paradox?: What is the form of radiation experienced by a harmonically accelerated observer?
Theory predicts that uniform acceleration leads to experiencing thermal radiation (so called Fulling Davies Unruh radiation), associated with the appearance of an event horizon. For non uniform but ...
19
votes
3answers
514 views
Is gecko-like friction Coulombic? What is the highest known Coulombic $\mu_s$ for any combination of surfaces?
Materials with large coefficients of static friction would be cool and useful. Rubber on rough surfaces typically has $\mu_s\sim1-2$. When people talk about examples with very high friction, often ...
18
votes
4answers
1k views
Would you be weightless at the center of the Earth?
If you could travel to the center of the Earth (or any planet), would you be weightless there?
18
votes
5answers
134 views
Given a photo of the Moon, taken from Earth, is it possible to calculate the position of the photographer's site?
Given a photo of the Moon, taken from Earth, is it possible to calculate the position (Earth longitude and latitude) of the photographer's site?
I am thinking about photos taken with a normal camera ...
18
votes
6answers
2k views
Does Godel preclude a workable TOE?
Godel's incompleteness theorem prevents a universal axiomatic system for math. Is there any reason to believe that it also prevents a Theory of everything for physics?
Edit:
I haven't before seen ...
18
votes
9answers
847 views
What is the simplest way to prove the Earth is round?
Assume you've come in contact with a tribe of people cut off from the rest of the world, or you've gone back in time several thousand years, or (more likely) you've got a numbskull cousin.
How would ...
18
votes
3answers
1k views
Do two beams of light attract each other in general theory of relativity?
In general relativity, light is subject to gravitational pull. Does light generate gravitational pull, and do two beams of light attract each other?
18
votes
5answers
1k views
Does Heisenberg's uncertainty under time evolution always grow?
Recently there have been some interesting questions on standard QM and especially on uncertainty principle and I enjoyed reviewing these basic concepts. And I came to realize I have an interesting ...
18
votes
4answers
1k views
Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem?
Stephen Wolfram's A New Kind of Science (NKS) hit the bookstores in 2002 with maximum hype.
His thesis is that the laws of physics can be generated by various cellular automata--simple programs ...
18
votes
3answers
174 views
Geometric Langlands as a partially defined topological field theory
I have heard from several physicists that the Kapustin-Witten topological twist of $N=4$ 4-dimensional Yang-Mills theory ("the Geometric Langlands twist") is not expected to give
rise to fully defined ...
18
votes
2answers
129 views
Does 4D N = 3 supersymmetry exist?
Steven Weinberg's book "The Quantum Theory of Fields", volume 3, page 46 gives the following argument against N = 3 supersymmetry:
"For global N = 4 supersymmetry there is just one supermultiplet ... ...
18
votes
3answers
3k views
If both radio waves and gamma rays can travel through walls
and they are on opposite ends of the electromagnetic spectrum, then why can't light travel through walls which is right in the middle of the spectrum?
This question has already been asked here. ...
