All Questions

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Cameras in Voyager probes

I've always wondered about the cameras in the space probes, especially in the Voyagers. 1) What kind of cameras do they have? Digital? (What kind of sensor and megapixel count?) Analog? (Do they ...
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How many earth-sized planets have been discovered outside the solar system?

How many earth-sized planets have been discovered outside our solar system? Is there a combined registry of them anywhere? Where might I look for more information?
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How can I read density fluctuation from microwaves?

The Cosmic Microwave Background Radiation shows temperature differences. The red and yellow areas are warmer. The green and blue areas are cooler. For example consider this picture of CMBR ...
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Why does charge conservation due to gauge symmetry only hold on-shell?

While deriving Noether's theorem or the generator(and hence conserved current) for a continuous symmetry, we work modulo the assumption that the field equations hold. Considering the case of gauge ...
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What geological properties of the earth could we deduce by measuring magnetic field strength and direction?

I wonder if it is of any use for a geophysicist, if we measure the magnetic field strength and direction of the earth. Could we make valid statements about the composition of the the earth, earth ...
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What is the spatial mode of light or the spatial mode of a massive particle?

I'm extremely confused by what physicists mean by the spatial mode of light. I am also equally if not more confused by what the spatial mode of a massive particle is. Can anyone help me out by ...
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How to get “real-time” temperature from sensor?

The following is LM35 Thermal response time in air The following is temperature reading from LM35 sensor. Horizontal axis is time in sec. So this is not "real-time" temperature graph. The ...
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What's so special about wave solutions of EM?

Maxwell's equations allow for wave solutions via oscillations between electric and magnetic field content. Couldn't we generate electric waves also if that solution didn't exists? Imagine there was ...
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How does the position of lift affect the stability of the lifted object?

Consider this example: Treat G as 10. The blue blocks provide lift of 10N, or -1KG. The red block has a weight of 20N, or 2KG. The black bar has no weight. All have their center of gravity in ...
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Question on inflation

I have two particular questions regarding the inflationary scenario. They are: 1.) What is the physical origin of the inflaton field? 2.) Why has the potential of the inflation field its particular ...
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Intensity of light

If we have 2 beams of light with equal intensities, but with different frequencies, wouldn't the one with the higher frequency generate more power? If so, how come the intensity, which is in $W/m^2$, ...
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How does the evaporation of a black hole look for a distant observer?

Let's assume an observer looking at a distant black hole that is created by collapsing star. In observer frame of reference time near black hole horizon asymptotically slows down and he never see ...
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re-defining the question, field quanta size in field theory? [duplicate]

Possible Duplicate: confusion on quantum field theory I asked are field quanta infinite in extent and I keep getting back that its the probabibility distribution. But this is a normal ...
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Basic classical mechanics question

A and B are in a lift. The mass of the lift is 250kg. As it moves upward, the floor of the lift exerts a force of 678N and 452N on A and B, respectively. The tension in the cable of the lift is 3955N. ...
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Field quanta- infinite in extent? [duplicate]

Possible Duplicate: confusion on quantum field theory Are field quanta infinite in extent as stated in Art Hobsons paper? What does this even mean? I've not seen any electrons or atoms that ...
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Bernoulli's equation and reference frames

So I was thinking about this while driving home the other day. I've never been quite clear on why when you drive with the windows down air rushes into your car. I thought this might be explained by ...
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Estimating atmospheric friction by measuring the change in velocity of a ball thrown straight upwards

Imagine I throw a ball straight upwards with some velocity $v_1$, and filming the ball with a camera, I can estimate a velocity $v_2$ (along the same vector) after the ball has moved a distance $D$. ...
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Capacitance per unit area and CMOS case

In a modern 0.35μm CMOS processor, the gate oxide thickness is around 80Å = 8nm. This gives us a capacitance per unit area of $430nF/cm^2$ I am not getting how one gets this capacitance per unit ...
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Charge carrier injection in heterostructures - help with concept definition

I have this report to do on "Charge injection in heterostructures". I have been searching and reading but I still have some trouble with the basics, i.e. defining the concept. As far as I understood ...
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Physical meaning of magnetic length

What is the physical meaning of magnetic length $\ell_B=\frac{\hbar c}{e B}$ in 2D electron system under magnetic field? When $\ell_B \longrightarrow a$, where $a$ is the lattice constant, does that ...
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Is there a background independent closed string field theory?

Analogous to the background independent open string field theory by Witten. If there isn't, what are the main stumbling blocks preventing its construction?
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Do Killing spinors know global information?

The conformal Killing spinor equations on $R\times S^3$ in Minkowski signature are $$\nabla_\mu \epsilon=\pm \frac{i}{2}\gamma_\mu\gamma^0\gamma^5\epsilon$$ whose solution ...
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Generalized Complex Geometry and Theoretical Physics

I have been wondering about some of the different uses of Generalized Complex Geometry (GCG) in Physics. Without going into mathematical detail (see Gualtieri's thesis for reference), a Generalized ...
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Are there rigorous constructions of the path integral for lattice QFT on an infinite lattice?

Lattice QFT on a finite lattice* is a completely well defined mathematical object. This is because the path integral is an ordinary finite-dimensional integral. However, if the lattice is infinite, ...
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equivalence of wave equations

I wonder if the following 2 PDEs are equivalent: $$\frac{\partial^2}{\partial t^2}\psi(\vec{r},t)-c(\vec{r})^2\nabla^2\psi(\vec{r},t)=s(\vec{r})\delta'(t)$$ subjects to zero initial conditions ...
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The direction of electric field in a diode

Why electric field pointing to left? (The middle area is depletion region.) (This is without any external electrical voltage applied.)
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Course advice for someone interested in strings and mathematical physics [closed]

I'll be doing Introductory General Relativity and Graduate Quantum Mechanics II next semester. I still need to choose 2 (or maybe 3, but I don't want to overload too much) from the following: ...
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Can we model gravitation as a repulsive force? [closed]

This question is actually related to my earlier question ("what is motion"). The fact that objects move a lot in the universe and that the universe is expanding, can imply that gravity is a repulsive ...
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Shapes of galaxies

I've heard most of galaxies are spiral or ellipsoid shaped. Is it true? If true, then why they form in such shapes? How did arms of the spiral galaxies form?
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Why are so many forces explainable using inverse squares when space is three dimensional?

It seems paradoxical that the strength of so many phenomena (Newtonian gravity, Coulomb force) are calculable by the inverse square of distance. However, since volume is determined by three ...
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Christoffel symbols and affine connection

What is the difference between the "affine connection" (S. Weinberg, Cosmology) and "Christoffel symbols?"
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How much can AdS/CMT tell us?

I will begin my research on AdS/CMT, however I find AdS/CMT is only a phenomelogical method, so I want to know can AdS/CMT give some results the condensed matter physicists can not give, or even ...
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Local Fermionic Symmetry

That is perhaps a bit of an advertisement, but a couple of collaborators and myself just sent out a paper, and one of the results there is a little bit surprising. We found (in section 6E) a fermionic ...
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Does the complex 3-sphere have a complex structure modulus?

This question has a flavor which is more mathematical than physical, however it is about a mathematical physics article and I suspect my misunderstanding occurs because the precise mathematical ...
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Is ghost-number a physical reality/observable?

One perspective is to say that one introduced the ghost fields into the Lagrangian to be able to write the gauge transformation determinant as a path-integral. Hence I was tempted to think of them as ...
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Does anything exist in the intergalactic space?

I am a part time physics enthusiast and I seldom wonder about the intergalactic space. First, it is my perception that all(almost all) the objects in the universe are organized in the forms of ...
An important aspect of the AdS/CFT correspondence is the recipe to compute correlation functions of a boundary operator $\mathcal{O}$ in terms of the supergravity fields in the interior of the ...