2
votes
3answers
293 views

Proof of Connected Diagrams

If $Z[J]$ is the generating functional for the path-integral, could any prove (or more reasonably, refer me to a proof) that $$W[J]\equiv\frac{\hbar}{i}\log\left(Z[J]\right)$$ "generates" only ...
2
votes
2answers
351 views

Is it possible to design a large permanent magnet that creates a multi-Tesla field?

Is it ever possible to create a LARGE magnet (in meters wide/long) that could potentially create a powerful magnetic field?
2
votes
1answer
81 views

Amateur thoughts on QM theory at celestial scale

Some amateur scientist asked me that why can't one just simply apply the entire theory of QM at atomic scale to "quantize" celestial system with a different choice of $\hslash$, which he believed can ...
2
votes
2answers
248 views

Why are results of Bell's experiments considered to “break realism”?

Related to my previous question (Why would classical correlation in Bell's experiment be a linear function of angle?), as a newbie in quantum mechanics, I am also unable to find the reason to why ...
2
votes
3answers
632 views

Describing a circular current loop as delta functions

It would be really nice to see how Jackson got eqn 5.33 on his example problem for finding the vector potential of a circular current loop $$ ...
2
votes
2answers
191 views

How “unnatural” is the universe? [closed]

Looking to read up on the impact the discovery of Higgs boson has on the String Theory I came upon these two paragraphs in an article about the Higgs boson Nobel Prize: One possibility has been ...
2
votes
3answers
613 views

Intuitive explaination for why higher engine compression ratio is more efficient?

Intuitively to me it seems likes increasing compression ratio would require more work to compress the gasses before ignition, so you'd just end up getting back what you put in - like a spring. What am ...
2
votes
2answers
147 views

Fluid flow at mach 1

fluid-dynamics is not my preferred discipline, yet I have been landed with this problem and just seeking some clarification. I have a nozzle at the end of a tube, with 8 holes in it, and we are going ...
2
votes
3answers
872 views

How was Newton able to guess that gravitational force is inversely proportional to distance squared?

This question is puzzling me since I learnt about the gravitation law in school. Why did Newton guess/assume that gravitational force is inversely proportional to the square of distance? Did he ...
2
votes
1answer
243 views

Landau's derivation of a free particle's kinetic energy- expansion of a function?

I was reading a bit of Landau and Lifshitz's Mechanics the other day and ran into the following part, where the authors are about to derive the kinetic energy of a free particle. They use the fact ...
2
votes
2answers
307 views

CPT invariance of Dirac equation

We know that Dirac equation is \begin{equation} ( i \partial _\mu \gamma ^\mu - m ) \psi ~=~0. \end{equation} How can we show that Dirac equation is invariant under CPT transformation?
2
votes
1answer
28k views

Calculation of pressure from flow rate of water

Anybody kindly help me to find how to calculate pressure in bar from flow rate. I have a pipe and from that I am transferring water at a constant flow rate of 5ml/min. At this flow rate, with a 0.5 cm ...
2
votes
1answer
132 views

Where does this delta of zero come from?

It is common when evaluating the partition function for a $O(N)$ non-linear sigma model to enforce the confinement to the $N$-sphere with a delta functional, so that $$ Z ~=~ \int d[\pi] d[\sigma] ~ ...
2
votes
3answers
264 views

Momentum acceleration in space?

I'm an engineering student and have a few ideas to bat at the scientific community. First premise is based upon common sense. I understand that if I am standing on a skateboard on a relatively smooth ...
2
votes
1answer
118 views

Does the Higgs Boson “operate” inside, outside, or throughout the volume of an Atom?

Is the Higgs force exchanged by particles within the atomic structure, or is the Higgs force exerted on individual particles, at the quantum scale, independent of their atomic coorelations?
2
votes
1answer
2k views

Please explain the flaw in this picture [duplicate]

So I saw this picture on my google+ feed and I immediately know why it wont work. But I'm having trouble explaining to myself and others exactly why. Without using anything overly complex, can anyone ...
2
votes
1answer
91 views

Attractive higgs force and inflation

Inflation was the extreme accelerating expansion of the universe, see here: http://en.wikipedia.org/wiki/Inflation_(cosmology) It worked in a similar way to dark energy but was so strong it would ...
2
votes
1answer
106 views

Quantum numbers in QFT

In nonrelativistic quantum mechanics the state of a system is characterized by a vector of a Hilbert space. To characterize a state we need a complete set of commuting observables, and once we have ...
2
votes
2answers
157 views

Drude model: A concerning approach to $\tau$ hurts Ohm's Law

Here's the question. Between two points, $a$ and $b$, if an object is accelerated between them, it will cross the distance between them in time $t=\sqrt{2\frac{d}{a}}$. So, if the acceleration is ...
2
votes
3answers
78 views

Can we measure rates in real time?

I know what it means to say that my position is "X" at a particular moment in time. I can easily take a picture of my motion and observe my exact location at the instant the picture was taken. That is ...
2
votes
2answers
763 views

Evaporative cooling in a tropical environment

I am an architect and am trying to understand the effects of evaporative cooling in a humid climate for buildings. I would like to use the example of a zeer pot for my question. I have read ...
2
votes
4answers
149 views

Drake's equation

Some years ago i read about this equation that helps us estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. Now, i am wondering if there are results ...
2
votes
1answer
137 views

Are these guard rails truly strong enough?

I'm lay about physics, but I'd like to learn about it behind this question. A friend criticises and claims that the single strip of traffic barriers (as shown below) would fail and is useless. For ...
2
votes
1answer
680 views

Why do i see bright red hand when i place flashlight behind my hand?

When I place a working flashlight behind my hand, I see my hand bright red because of the light. So my question is, why do I only see red light after transmission even if incoming light from the ...
2
votes
1answer
792 views

Would white light waves act as same as monochromatic waves in double slit experiment?

Would white light waves act as same as monochromatic waves in double slit experiment? If not, what pattern would be seen on the screen?
2
votes
1answer
439 views

Is speed of light invariant in different inertial frame?

Don't get angry at me. I believe in special relativity just as any scientist would. But reading this article http://arxiv.org/abs/0708.2687 I realize that actually I haven't done any experiments on ...
2
votes
1answer
145 views

If a window in a plane cabin breaks will a bunch of water vapor form?

If a plane has some windows broken mid-flight (ie open) will the plane suddenly be full of water vapor because of the difference of pressure?
2
votes
1answer
207 views

Schrödinger evolution for a Klein-Gordon equation

I have a problem with the transition from quantum relativistic wave equations (specifically Klein-Gordon equation) to QFT, since a lot of assumptions seem implicit. For example I have a problem with ...
2
votes
4answers
807 views

How does buoyancy work?

I realised, reading another Phys.SE question about balloons moving forwards in an accelerating car that I don't really understand how buoyancy works. Particularly concerning, for a SCUBA diver. The ...
2
votes
1answer
144 views

From where randomness comes from and why it exists? [closed]

I recently began to study statistics and probability and I have two questions: Where does randomness come from? What is the source of randomness? Why does the randomness exist? Is it possible to ...
2
votes
2answers
118 views

Is an object's color/shine/texture dependent on its electrons only? If electrons are same then why are there so many different colors?

when we look at an object be it a metal or a non-metal are we looking at its electrons only, so then if all electrons are same then why do different chemicals or elements or objects have different ...
2
votes
3answers
270 views

Does processing for a quantum computer take place in other universes?

Apologies in advance if my question seems misinformed. I am a software developer, and neither quantum mechanics nor physics are my specialties. From ...
2
votes
1answer
98 views

What is the exact relation between a real oscillating body's time period with time?

I took an empty bottle and placed it on the floor, then tilted the bottle to one side such that the the displacement caused a disturbance in its balance but not enough to completely tilt it over. The ...
2
votes
1answer
115 views

Where does the steam pressure go?

Lets say you build a steam boiler and then you connect several turbines to the boiler in series. What limits the number of turbines that you can connect to the boiler in this way? In my mind, it ...
2
votes
2answers
88 views

Can eddy currents be extremely reduced?

Is it possible to create a certain design of a conductor to reduce eddy currents greatly? So that the magnetic "breaking" can be reduced? Is it even possible for the force generated by the eddy ...
2
votes
3answers
2k views

Which is stronger, wire rope or chain?

Assume they are the same material with the same weight, which is stronger?
2
votes
2answers
278 views

Do individual photons increase entropy as they travel?

If I draw a control volume around a single light wave traveling through empty space, is entropy increasing as it goes? How is the degradation of the quality of energy manifested?
2
votes
3answers
1k views

Curl of an electromagnetic wave

I can't understand the concept of the curl of an electromagnetic wave. $$ \nabla \times E = -\frac{\partial \textbf{B}}{\partial t} $$ All of the examples I find show a current through a conductor, ...
2
votes
4answers
1k views

Can causality be violated?

A common justification for prohibiting many unusual phenomena such as faster than light travel is that if they were possible, causality would be violated. Let's define causality as: You cannot ...
2
votes
2answers
97 views

Does geodesics from solving full field equations are same as path from energy-momentum tensor?

As we know, if we had an energy-momentum tensor in all space-time we could obtain the metric tensor by solving field equations. Also i think if we had an energy-momentum tensor then we have ...
2
votes
2answers
105 views

Orthogonality in curved space/spacetime

When are two vectors orthogonal in curved spacetime? From wikipedia: "In 2-D or higher-dimensional Euclidean space, two vectors are orthogonal if and only if their dot product is zero, i.e. they ...
2
votes
1answer
413 views

Surely proper time expands like proper space?

The FRW metric at the origin $r=0$ is simply given by: $$ds^2 = -dt^2 + a^2(t)\ dr^2$$ Setting $dt=0$ gives us an element of proper distance $ds$ given by: $$ds = a(t)\ dr$$ Thus we get the well known ...
2
votes
1answer
226 views

Conserved charges given conserved current via Noether's theorem

Let $j^{\mu}_{a}$ be the conserved current associated with an infinitesimal symmetry transformation, cf. Noether's theorem. The conserved charge associated with $j^{\mu}_{a}$ is $$Q_a = \int d^{d-1}x ...
2
votes
1answer
595 views

Why do whips crack?

Whips have been discussed in a previous question last year. I wish to ask a further question on the subject. (I can not comment or reply to the previous question since I am a new member here and my ...
2
votes
1answer
406 views

Tension in an Atwoods machine conceptual?

Assuming $T_1$ is the force that acts on box $1$ and $T_2$ is the force that acts on box $2$. Exactly what causes the Tension? Why does $T_1 = T_2$? The problem is we are told to memorize that ...
2
votes
1answer
301 views

The Helium mass fraction from the Big Bang Nucleosynthesis

In Perkin's book Particle Astrophysics (page 144): I do not understand how one comes to the following expression (the second equality with $r$) for the Helium mass fraction due to the Big Bang ...
2
votes
2answers
688 views

Is every material able to exist in every state of matter?

I was shocked while reading Kittel's "Introduction to Solid State Physics", that the solid state of noble gases is a well described and makes one of the fundamental achievements of solid state ...
2
votes
3answers
164 views

Quantum mechanics scattering theory

When an electron absorbs energy and jumps to the another excited state by absorbing the photon and why it is always said that the electron will come back to $\hbar\omega/2$? Why doesn't the electron ...
2
votes
2answers
187 views

Is tea weaker if you make it in a half full cup of water?

Imagine you put a tea bag in a cup and half fill it with boiling water. Then after one minute you take the tea bag out and then fill the cup up to fill with hot water. Will the tea be weaker than if ...
2
votes
1answer
364 views

Gravity, a weak force?

Why is gravity such a weak force? It becomes strong for particles only at the Planck scale, around $10^{19}$ $\text{GeV}$, much above the electroweak scale ($100$ $\text{GeV}$, the energy scale ...

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