# All Questions

0answers
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### Is it believed that all UV completions have “Maldacena duals”?

I have heard occasional rumors that effective field theories have gravity duals. For example, I've been told that UV momentum cutoffs in N=4 SYM become finite radii in AdS. I've heard speculations ...
1answer
108 views

### How do I calculate how something should stay in position under gravity?

Excuse me if this too simple a question - I'm not a regular (consciously) user of physics. I have a ship in space and it is under the effect of three moons. The ship can rotate and thrust to move ...
4answers
1k views

### Why does a tire produce more traction when sliding slightly?

It is well known in racing that driving the car on the ideal "slip angle" of the tire where it is crabbing slightly from the pointed direction produces more cornering speed than a lower slip angle or ...
2answers
135 views

### Suggestions on a particular arXiv publication on math needed for theoretical physicists [closed]

I'm going to start my PhD in a year and I'll be taking a gap year doing other stuff. But I also wanted to fill in the gaps in my math knowledge and I came across an arXiv publication called ...
1answer
2k views

### Does gravity affects temperature reading of a mercury thermometer?

I remember when I was in primary school, the science teacher put me in charge of a mercury thermometer. I do not quite understand the mechanics behind except that mercury expands when it is hot and ...
1answer
410 views

### what's the center of mass for triatomic-molecule system

My text use the following example to explain the center of mass. There are three balls (mass $m$) sitting in the origin, at $x=l$ and $x=2l$, each two mass are connected with a spring of constant $k$. ...
1answer
328 views

### Deriving the conservation of mass in a perfect fluid

I have a problem on a homework assignment. I will write the question and then what I have so far. I just want some guidance on what I am doing wrong (or right). Any help would be greatly appreciated: ...
1answer
98 views

### Can the fuzzball conjecture be applied to microscopically explain the entropy of a region beyond the gravitational observer horizon?

In this article discussing this and related papers, it is explained among other things, how the neighborhood of an observer's worldline can be approximated by a region of Minkowsky spacetime. If I ...
3answers
221 views

### Effects of surface roughness on specularity

Say you have a piece of glass, which looks specular if propery cut/polished. But if you sand the surface using say sand paper, it will look hazy and glossy. I'm wondering how much surface roughness ...
2answers
963 views

### Distance of objects in car mirrors

We've all seen that label on our passenger side mirrors that says, "Objects in mirror are closer than they appear." Why is this? Further, why does it only apply to the passenger side mirror, and not ...
3answers
5k views

### Which will stop first a heavier car or a lighter car?

If the friction from brakes, wind resistance and all such factors remain constat, which will stop first? A heavier car or a lighter car? How will the momentum of the car and graviational pull on a ...
0answers
318 views

### Why did increasing the Ackermann geometry in my race car make it faster in corners?

Ackermann geometry is used to account for the different radius arcs that the front tires follow when the steering wheel is turned from center. It's often expressed as a percentage: e.g. 25% Ackermann, ...
1answer
134 views

### At the smallest level, how do things move?

When we see something moving on a screen it's usually just pixels being turned off at one location and turned on at another. For example: This would render a dot moving from A to C. Turn on pixel ...
0answers
256 views

### Dimensional regularization and IR divergences and scale invariance

I want to know if dimensional regularization has any issues if the theory has IR divergences or is scale invariant. Does dimensional regularization see "all" kinds of divergences? I mean - what ...
1answer
820 views

### Has anyone on Earth ever seen the dark side of the moon and if so where are the pictures? [duplicate]

If the Moon rotates then we should see the dark side right? But as far as I know the Moon only shows one side to Earth, how can this be if it is rotating?
1answer
399 views

### If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal?

Free field theories are definitely local in . In the interaction picture, we can decompose the fields into creation operator modes and annihilation operator modes. The product of operators can be ...
6answers
3k views

### Why isn't temperature measured in Joules?

If we set the Boltzmann constant to $1$, then entropy would just be $\ln \Omega$, temperature would be measured in $\text{joules}$ ($\,\text{J}\,$), and average kinetic energy would be an integer ...
1answer
179 views

### Electromagnet, ideal turns depending on ohm

More turns -> stronger field more turns -> longer copper wire longer copper wire -> more resistance(ohm) at what turn does the resistance make the electromagnet weaker? - I want to make an ideal ...
1answer
359 views

### confusion on quantum field theory [closed]

Having read Art Hobsons paper on Quantum field theory, he states " the field collapses into a field of atomic size" This seems to be stating that each field quanta is a different quantum field? Like 2 ...
1answer
144 views

### Units for physical constants

Someone told me that units for $G$ and $\epsilon_0$ (gravitational constant and Coulomb's constant) are placed there simply to make equations work dimensionally and that there is no real physical ...
1answer
158 views

Dilemma The uncertainty principle of energy and the 2nd law of thermodynamics don't add up : the uncertainty principle of energy says that $\Delta \tau \cdot \Delta E \ge \frac{h}{4\pi} = ... 0answers 202 views ### About the seesaw mechanism I was reading about the seesaw mechanism in my Lecture notes and got a technical question. See for example http://www.lhep.unibe.ch/img/lectureslides/9_2007-11-30_SeeSawMechanism.pdf page 13. There ... 1answer 554 views ### Accessible microstates of harmonic oscillator in microcanonical enemble While reading up on statistical physics, I am going through the calculation of the partition function of the harmonic oscillator in the microcanonical ensemble. The result for the partition function ... 1answer 240 views ### The paradoxical nature of Hawking radiation [duplicate] The definition of a classical black hole is when even electromagnetic radiation can not escape from it. Why then can Hawking radiation be emitted from semi-classical black holes? What is difference ... 1answer 386 views ### Planes of graphite crystal on diffraction experiments When doing electron diffraction on graphite (a popular experiment for students at universities) always diffraction at these two planes with distances$d_1$and$d_2$are observed: But a plane ... 1answer 340 views ### Angular Momentum Addition Theorem If I have, for example a particle with$s = 3/2$and$\ell = 2$, what are the allowed values of$j$? I'm slightly confused because I know that$j = \ell + s$, so surely there is only one allowed ... 1answer 76 views ### Schriffer Wolff Transformation - for first order change in eigenvalues Step 1 Let me formulate the problem to convey my notation. I have a matrix$A$which is hermitian - and is diagonalisable by a transformation $$U_A A\,\,U_A^{-1} = A_{diag}$$ Now the matrix is ... 1answer 230 views ### Space time curvature real or theoretical (mathematical)? Assuming one were in a capsule of some kind, with no window or instruments, and you swung into the gravitational field of a massive object (planet). Assuming no atmosphere to provide friction, could ... 3answers 112 views ### is frictional force right or wrong an experiment to disprove the statement--"frictional force is irrespective of the surface area in contact." take a x rs note. fold it in a half and put it in the pocket of a shirt. then invert the ... 1answer 264 views ### Is the Hilbert space of$\phi^4$theory known? Consider free, real scalar field theory in$d=1+3$dimensions:$H = \frac{1}{2} \partial_\mu \phi \partial^\mu \phi + \frac{1}{2} m^2 \phi^2$. The Hilbert space of this theory is known; it is just ... 2answers 75 views ### About hubble observatory and distant galaxies [duplicate] According to Hubble observatory, the age of universe is 14 billion years. But, the distant galaxies are about 40 billion light years. How could that simply be possible? That means the information that ... 1answer 388 views ### Angular Momentum Addition Theorem - Sanity Check Looking back at my quantum mechanics notes, the angular momentum addition theorem is listed as:$j=j_1+j_2,j_1+j_2-1, ..., |j_1-j_2| $(Using conventional notation) , but I'm a little unsure how to ... 3answers 352 views ### Will Cone standing on its tip, without any other force other than gravity topple? A cone standing on its tip is considered to be in unstable equilibrium as a slightest force could topple it. So, if the cone is stood on its tip with no other force other than gravity (and the ... 1answer 109 views ### Prove an action expansion's even-indexed terms have to be integrated, where the odd-indexed terms are only derivatives of the potential (WKB) After assuming a wavefunction of a form: $$\psi \approx A \exp{\left(i \frac{S(x)}{\hbar}\right)}$$ and letting $$S = \hbar^0 S_0 + \hbar^1 S_1 + \hbar^2 S_2 +...$$ The odd-indexed terms of the ... 2answers 2k views ### Given Angle, Initial Velocity, and Acceleration due to Gravity, plot parabolic trajectory for every “x”? Given any Angle -> 0-90 Given any Initial Velocity -> 1-100 Given Acceleration due to Gravity -> 9.8 Plot every x,y coordinate (the parabolic trajectory) with cartesian coordinates and screen pixels ... 2answers 1k views ### What kind of cooling mechanism could be used in outer space? This question arises out of this question on Quora - Apollo 11: 1969 Moon Landing: Did Neil Armstrong really land on the moon? I'm convinced with most of the explanations provided in the first ... 0answers 53 views ### Book suggestion : geometric approach to electromagnetism [duplicate] I´m looking for a book on electromagnetism that is introducing the topic from a geometric point of view, focusing more on the theoretical structure than on the application. 2answers 331 views ### If the moon was rapid enough would it be able to orbit the earth from a close distance? If the moon was close in orbit that it's surface was like 100 km away from the earth's surface. And it had a large enough angular velocity will it be able to hold orbit? If this was possible, is ... 1answer 5k views ### Kubo Formula for Quantum Hall Effect I'm trying to understand the Kubo Formula for the electrical conductivity in the context of the Quantum Hall Effect. My problem is that several papers, for instance the famous TKNN (1982) paper, or ... 2answers 3k views ### The Spectral Function in Many-Body Physics and its Relation to Quasiparticles recently, I stumbled accross a concept which might be very helpful understanding quasiparticles and effective theories (and might shed light on an the question How to calculate the properties of ... 2answers 918 views ### What are the units of these virial coefficients? I'm reading some papers for calculating the vapor pressure of alkali metals as a function of temperature, and I've come across some familiar-looking virial expansions, but when I tried to work out the ... 1answer 225 views ### Straightforward questions about calculating SUSY F-terms So in the Lagrangian for a SUSY theory we have the F-terms, which I have seen written (e.g., in Stephen Martin's SUSY primer) as$F^*_i F^i$where$F^i = \frac{\partial W}{\partial \phi^i}$. I ... 2answers 1k views ### Quantization of orbital angular momentum Probably a very simple question, but I can't find the answer on the Internet. I know nearly to nothing about quantum mechanics, but in statistical physics I'm confronted with the idea that the orbital ... 0answers 100 views ### References for Understanding Minahan's N=4 SCFT review This is about the same paper as this thread: Some questions about chapter I.1 (by Minahan) of the "Review of AdS/CFT Integrability" but it was never answered. I have some different ... 1answer 319 views ### If I have a rectangular loop moving through a magnetic field, which way will it go? If I have a rectangular loop moving through a magnetic field, which way will it go? A uniform magnetic field (say it's pointing into the page) A square/rectangular loop of wire moving into the field ... 2answers 2k views ### The difference between the Wannier function and atomic orbit in a tight binding model In a tight binding model, we usually start from the atomic orbits and linearly combine them to get the wave function of the crystal energy band. My questions are: Since this kind of tight binding ... 0answers 117 views ### How does one write eigenstates of field operators in terms of particle states in scalar field theory? I am reading the first paper in Schwinger's QED anthology, where he discusses his action principle. In this, he writes down states that are simultaneous eigenkets of the field operators at all points ... 4answers 3k views ### Are quantum mechanics calculations useful for engineering? I heard it's is pretty tough to get results for more than a few quantum particles. Are quantum mechanical calculations useful at all for any technology that is being sold? Or do they use ... 1answer 201 views ### How does one find the wave velocity and the phase speed? While I was studying beats, I tried to find a displacement function of any particle in the most generalized form. I ended up with $$y=2A\sin(\pi(t-x/v)(f_1+f_2))\cos(\pi(t-x/v)(f_1-f_2)).$$ Now, ... 1answer 519 views ### Simultaneously commuting set How does one determine the members of an simultaneously commuting set (of operators)? For example, I have read that for orbital angular momentum, the set is {$H,L^2,L_z\$}. How does one know that these ...

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