6
votes
1answer
248 views

What would gravity be like on a hemispherical planet?

On a hemispherical world half the size of Earth (ignoring that the planet should break apart and become a smaller sphere) what would the gravity be like? How would it change as you traveled from pole ...
0
votes
1answer
109 views

Entropy, Mass and Brane gravity

Does string theory state as vibrational entropy increases, mass increases? Related: What is a D-brane? Reference: Cambridge Relativity
4
votes
2answers
228 views

What counts as a measurement?

In quantum mechanics, an elementary particle does not have a well defined position until a measurement is performed on it (right?). Such a "measurement" is any sort of interaction with other ...
18
votes
3answers
843 views

Direct observations of a black hole?

I'm not very knowledgeable about physics generally, but know that nothing can escape a black hole's gravitational pull, not even light (making them nearly invisible?). My question is: What has been ...
2
votes
1answer
315 views

Power dissipated in resistor

Suppose one has a circuit consisting of an inductor $L$ and resistor $R$ in series where $L$ and $R$ are known, passes an alternating voltage of frequency $\omega$ through it and that one wishes to ...
8
votes
2answers
665 views

Do you pay more for gas when the day is warmer?

Found this at the gas station yesteday - got me thinking...
12
votes
1answer
630 views

Is this a quaternion representation of the equations of motion of General Relativity?

In The Quaternion Group and Modern Physics by P.R. Girard, the quaternion form of the general relativistic equation of motion is derived from $du'/ds = (d a / d s ) u {a_c}^* + a u ( d {a_c}^* / ...
3
votes
0answers
174 views

Some more questions on conformal spinors of $SO(n,2)$

This is somewhat of a continuation of my previous question. I had stated there that a conformal spinor ($V$) of $SO(n,2)$ can be created by taking a direct sum of two $SO(n-1,1)$ spinors $Q$ and $S$ ...
1
vote
1answer
226 views

why does perpendicular motion to the direction of someone' s approach does not affect the distance between them

I was reading about the the four turtles/bugs math puzzle Four bugs are at the four corners of a square of side length D. They start walking at constant speed in an anticlockwise direction at all ...
1
vote
1answer
401 views

Combining Multiple Light Sources

Ok, Lets say I have two point light sources A and B. Each light source has a power Pa and Pb, and is distance Da and Db away from a point P on a plane. I can calculate the amount of luminosity at ...
3
votes
1answer
350 views

Set theory, category theory, realism and the recent “reality of the wavefunction” papers

I will add a better phrased question here. Do we need to consider quantum foundations to form a quantum theory of gravity? The kind of foundational question I am thinking of is expressed in the ...
1
vote
1answer
253 views

Why Higgs particle is the root of all elementary particles?

The Higgs boson is a hypothetical elementary particle predicted by the Standard Model (SM) of particle physics. It belongs to a class of particles known as bosons What Will Happens If physicist Find ...
0
votes
1answer
1k views

Triangulation for Astronomical Distances

How can triangulation be used to calculate the approximate distance to very distant celestial bodies like stars, globular clusters, etc.? And can it be used to measure the distance to a Black Hole? ...
5
votes
2answers
306 views

Modeling stochastic process with frequency-dependent power spectrum

I'm trying to model of Johnson-Nyquist noise propagation in a nonlinear circuit. An ideal (linear) resistor can be modeled very nicely by the Fokker-Planck equation (equivalently, the drift-diffusion ...
3
votes
1answer
140 views

Moons of the planets

What is the phenomena behind gas giants like Jupiter and Saturn having a large number of moons as compared to other planets. Were the present state moons a part of their parent planet long time ago ?
12
votes
3answers
654 views

Why does spin have a discrete spectrum?

Why is it that unlike other quantum properties such as momentum and velocity, which usually are given through (probabilistic) continuous values, spin has a (probabilistic) discrete spectrum?
0
votes
2answers
575 views

The measurement of $g$ and air resistance

Suppose I am trying to determine the value of the acceleration due to gravity by simply dropping objects from a ledge. If I did not account for air resistance, would the acceleration due to gravity ...
1
vote
1answer
433 views

How fast was the universe expanding during the inflationary period?

Compared to how fast it is expanding in the post-inflationary period (now)
3
votes
1answer
238 views

Hamiltonians and Lagrangians, Euclidean and Hyperbolic: Are they related?

The Lagrangian of a system is the difference between its kinetic energy $T$ and potential energy $V$, and is relativistically invariant: $L = T - V$ The Hamiltonian of the same system is the sum ...
6
votes
1answer
170 views

If a fundamental theory exibits e.g. a mirror symmetry, in what sense it the underlying geometry real?

Are the more recently discovered symmetries in string theory such that the theories based on mirroring geometries are absolutely the same from an observable point of view? I have mirror symmetry ...
3
votes
0answers
89 views

Relating the deformation of Calabi-Yau metrics and the conformal quantum field theories

(v2) As I read e.g. in this question, the nice holonomy group features of Calabi-Yau manifolds are valuable regarding supersymmetry (I suspect because it's a symmetry involving the target manifold, ...
2
votes
1answer
224 views

In a neutron star - what force keeps the neutrons from getting closer and closer? [duplicate]

Possible Duplicate: Why do neutrons repel each other? What I mean is that the neutrons are attracted to one another via gravity, so what force keeps them from collapsing to form a "neutron ...
0
votes
1answer
1k views

How positively charged protons remain glued to each other while they should repel each other out of nucleus? [duplicate]

Possible Duplicate: Protons' repulsion within a nucleus How positively charged protons remain glued to each other while they should repel each other out of nucleus?
2
votes
2answers
182 views

Relativistic mass as seen by different observers

Imagine there are two observers $A$ and $B$ and a particle $P$. $A$ and $B$ are at about the same point, $P$ is some distance away. From $A$'s point of view, $P$ has velocity $V$ and $B$ has ...
2
votes
2answers
270 views

Understanding Dynamic light scattering

I'd like to understand the physics of dynamic light scattering experiment. In particular I want to understand the basic relation between relaxation time $\tau_q$ and the diffusion coefficient $D$: ...
3
votes
2answers
2k views

Charge distribution on a plate of Capacitor with Dielectrics .

I had this Homework Problem with a capacitor (parallel plate) that has a group of 3 dielectrics between it like so : Now We were asked to find the equivalent capacitance and the distance of ...
0
votes
3answers
1k views

How to determine an exponential acceleration curve?

I've always been not so bad in mathematics, but I'm terribly bad at physics. For me, abstract concept are totally understandable, but when it come to reality, I'm lost ! So, for my job, I need to ...
1
vote
1answer
337 views

Quantum gravity and relevant/irrelevant operators

I am familiar with the casual dichotomy in QFT between coupling with positive dimensions in energy implies relevant operator on one side and negative dimension implies irrelevant operator on the other ...
7
votes
3answers
101 views

Rotationally invariant body and principal axis

Suppose a rigid body is invariant under a rotation around an axis $\mathsf{A}$ by a given angle $0 \leq \alpha_0 < 2\pi$ (and also every multiple of $\alpha_0$). Is it true that in this case the ...
2
votes
1answer
438 views

How much is important the role of Planck length in the strings theory?

this is Planck length: $$\ell_p=\sqrt {\frac {G.\hbar}{c^3}} .$$ How much is important the role of this length in the strings theory? is this planck's length or newton's length! or maybe both of ...
7
votes
1answer
768 views

Entropy increase and end of the universe

While taking thermodynamics our chemistry teacher told us that entropy is increasing in day by day (as per second law of thermodynamics), and when it reaches its maximum the end of the world will ...
3
votes
1answer
674 views

Cases in which angular velocity and angular momentum point into same direction

I know that angular momentum $\vec{L}$ and angular velocity $\vec{\omega}$ of a rigid body doesn't point into the same direction in general. However if your body spins around a principal axis, ...
1
vote
2answers
599 views

Are the laws of physics objective or subjective? [closed]

The laws of physics have often been taken to be objective statements about reality, but are they? Suppose Bob is a smart computer programmer with access to a super-duper-supercomputer. In it, he ...
0
votes
1answer
1k views

Operators and Commutator Definitions

I have several problems with General Definitions of an Operator and Commutator : the product of operators is generally not commutative: $$\hat A \hat B \not= \hat B\hat A .$$ what is this means ...
8
votes
3answers
343 views

Intuitive explanation for the de Broglie / Planck relations

A friend asked me to explain "why" a particle's energy is proportional to it's frequency, i.e: $$E=h\nu$$ The reason this result is so un-intuitive, is that in the macroscopic world, A wave's energy ...
1
vote
0answers
72 views

The sound of coffee [duplicate]

Possible Duplicate: Why does the sound pitch increase on every consecutive tick at the bottom of a filled cup of coffee? A colleague suggested this experiment this morning : Get a cup of ...
4
votes
2answers
584 views

How can one feel cold without touching it?

Let me explain. My shower is inconsistant in how hot it gets. Whenever I turn on the shower, I always put my hand really close to the water, but not touching it, so I can feel the heat radiate from ...
1
vote
1answer
72 views

Weather Radar Interpretation - Radial Rays

I was browsing the NEXRAD radar feeds (I'm not an expert, just figuring them out) and I came across the following signature (visit the link to view the radar image) http://cl.ly/3n0y0p0g2M0K2B313g3U ...
5
votes
5answers
9k views

Is all kind of light same speed?

Is there any speed difference between blue or red light? Is there ever a speed difference? Or does all types of light move at the same speed?
0
votes
1answer
65 views

What kind of light is needed to light up Venus?

Let's say I would want to light up Venus, such that we can see Venus all day long and not have to wait for a Venus Transit. What kind of light would I need for it? How powerful would it need to be?
1
vote
1answer
122 views

What is a good reference for the mechanical properties of materials at cryogenic temperatures?

I want to research various the properties of various materials, namely tensile strength at cryogenic temperatures (~20K). I was wondering if a freely available database of material properties exists.
3
votes
4answers
2k views

Does the mass of an object change as it moves away from the earth?

The mass of a helium nucleus is less than the mass of two isolated protons and two isolated neutrons. When the component hadrons are assembled, this mass is lost as energy ($E=mc^2$). This makes it ...
3
votes
1answer
330 views

Loop of wire in a varying magnetic field

Let us suppose we have a loop of wire with some definite resistance in a magnetic field. Let the magnetic field be varying. This varying magnetic field will st up an EMF in the wire. My questions are ...
2
votes
1answer
2k views

Which are other anomalies like Divergence of 1/r^2?

As one might have learned in the basic science (ex. Electrodynamic theory), when we apply the divergence theorem to the vector function like 1/r^2 with it pointing in the radial direction (like ...
3
votes
3answers
4k views

Does friction decrease as objects move faster against each other?

I was told that the faster two objects move against each other, the less the friction between them would be… compared to if they were moving slower. In physics class, we always use the coefficient of ...
5
votes
2answers
916 views

The multiverse of eternal inflation

I don't have a clear picture of what is "by definition" the multiverse appearing in the models of eternal inflation. A long time ago I heard that it is a quantum state, but in the cosmology books I ...
6
votes
1answer
301 views

Naturalness and experiments

Is there an example where model building that is motivated only by Naturalness, has led to experimentally verified observations? If the question is unclear, or if the reader wants more elaboration, ...
2
votes
2answers
731 views

how to measure activation energy of fission?

i heard that fission activation energy of (235)U is less than of neutron separation energy of (236)U so this must the reason that (235)U is fission able $$E_s+(236)U\to (235)U+n$$ in this interaction ...
3
votes
2answers
809 views

quantum explanation of doppler effect

How would quantum mechanics explain doppler effect? And just for curiosity, is there any effect similar to doppler effect occuring at quantum level?
3
votes
2answers
2k views

How are the CPU power and temperature caculated/estimated?

From Wikipedia The power consumed by a CPU, is approximately proportional to CPU frequency, and to the square of the CPU voltage: $$ P = C V^2 f $$ (where C is capacitance, f is ...

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