8
votes
3answers
2k views

Maxwell's Demon Constant (Information-Energy equivalence)

New Scientist article: Summon a 'demon' to turn information into energy The speed of light c converts between space and time and also appears in e=mc^2. Maxwell's Demon can turn information supplied ...
5
votes
4answers
949 views

How would I calculate celestial body characteristics without a priori knowledge?

Without any a priori knowledge of the mass, speed, distance, and size of local celestial bodies (aside from Earth's size), what can I calculate and how from my "backyard" through observation? Edit: ...
1
vote
1answer
2k views

What is the direction of the friction force on a rolling ball?

Suppose you have a solid ball on a horizontal table. What is the direction of friction force when the ball I pushed horizontally and starts rolling? Why is the direction of friction as it is? Which ...
59
votes
9answers
5k views

Is Angular Momentum truly fundamental?

This may seem like a slightly trite question, but it is one that has long intrigued me. Since I formally learned classical (Newtonian) mechanics, it has often struck me that angular momentum (and ...
4
votes
3answers
849 views

What are some approaches to discrete space-time used in modern physics?

This thought gave rise to some new questions in my mind. What are the consequences for: How would it affect duality i.e. particle, wave property of photons? How does this statement affect the ...
8
votes
3answers
256 views

What categorical mathematical structure(s) best describe the space of “localized events” in “relational quantum mechanics”?

In a recent (and to me, very enlightening) paper, entitled "Relational EPR", Smerlak and Rovelli present a way of thinking about EPR which relies upon Rovelli's previously published work on relational ...
20
votes
4answers
3k views

How do you calculate the anomalous precession of Mercury?

One of the three classic tests of general relativity is the calculation of the precession of the perihelion of Mercury's orbit. This precession rate had been precisely measured using data collected ...
3
votes
2answers
1k views

What is up and down conversion in photonics?

I have heard the terms up and down conversion in photonics/photovoltaics articles. What do the terms mean?
8
votes
3answers
6k views

Why does the water level equalize in a series of tubes?

Say I have a series of tubes (not the internet) looking like this, where w represents water: ...
6
votes
3answers
2k views

Constraint force on a rod

I really hope someone will take a quick look at the following, I would just love to better understand it... This exercise is from Arnold's "Mathematical Methods of Classical Mechanics", p. 97 in the ...
4
votes
2answers
864 views

Question about moment of inertia and velocity

First off, I swear this is not homework. I'm doing some practice problems because I got an exam coming up. I'm stuck on this one: I figured I would use energy conservation for this problem. So since ...
4
votes
3answers
540 views

Energy of the electron-muon reaction

Lets see the reaction: $e^- \mu^- \to e^- \pi^- \nu_\mu \;\;\;\;\;\;\;\;\;\;\; {(1)}$ I suppose, that this reaction occurs as follows $e^- \mu^- \to e^- \mu^- \pi^+ \pi^- \to e^- \pi^- \nu_\mu$ Is ...
8
votes
4answers
6k views

Is Dr Quantum's Double Slit Experiment video scientifically accurate?

I'm fascinated by the fundamental questions raised by the Double Slit Experiment at the quantum level. I found this "Dr Quantum" video clip which seems like a great explanation. But is it ...
6
votes
2answers
2k views

How to calculate a ballistic trajectory for a suborbital flight?

I'm trying to calculate the initial launch angles and velocity of a projectile (atmosphere's effects can be neglected), assuming that I know the lat/lon coordinates of both the launch and the ...
33
votes
9answers
11k views

Can Jupiter be ignited?

Our solar system itself contains two candidate "Earths" One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...
10
votes
10answers
2k views

What is the most efficient way to destroy the universe? [closed]

Don't worry... I won't actually do it, just would like to know how.
7
votes
2answers
401 views

Notation for Sections of Vector Bundles

(Reformulation of part 1 of Electromagnetic Field as a Connection in a Vector Bundle) I am looking for a good notation for sections of vector bundles that is both invariant and references bundle ...
-4
votes
1answer
160 views

Amount of 2 amperage [closed]

I have 2 equation describing the alternating amperage $I_1$ and $I_2$. I need to get amount of these amperages. My equations: $$I_1=10\sin(\omega t+30)$$ $$I_2=20\sin(\omega t-50)$$ How can i make ...
-3
votes
7answers
3k views

Does Quantum Physics really suggests this universe as a computer simulation? [closed]

I was reading about interesting article here which suggests that our universe is a big computer simulation and the proof of it is a Quantum Physics. I know quantum physics tries to provide some ...
13
votes
3answers
2k views

Mathematics of AdS/CFT

To date, what is the most mathematically precise formulation of the AdS/CFT correspondence, and what are the most robust tests of the conjecture?
11
votes
1answer
354 views

How many atoms per light year does light encounter when traversing interstellar space?

Interstellar space is pretty empty but there a small number of of atoms (mostly hydrogen?) floating around. How many atoms per light year would a photon encounter while traversing interstellar space?
26
votes
13answers
3k views

Suggested reading for renormalization (not only in QFT)

What papers/books/reviews can you suggest to learn what Renormalization "really" is? Standard QFT textbooks are usually computation-heavy and provide little physical insight in this regard - after my ...
10
votes
3answers
2k views

Electromagnetic Field as a Connection in a Vector Bundle

I would like to know more about Ehresmann connections in vector bundles and how they relate to the electromagnetic field and the electron in quantum mechanics. Background: The Schrödinger equation ...
24
votes
12answers
3k 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). ...
2
votes
3answers
163 views

What condition is fulfilled by the path of a mass sliding down a lumpy hill?

Suppose I have a hill that goes up and down unevenly. It's frictionless, and I want to slide a point mass down the hill. I am interested in the path it takes. (By "path" I mean the trail it leaves ...
5
votes
4answers
666 views

Help fill in my understanding of the Polywell fusion reactor

Polywell is a proposed new type of fusion reactor, which is designed to use magnetic fields to overcome the problems with the Elmore-Tuck-Watson fusor. I'm trying to understand exactly how it works. ...
4
votes
5answers
630 views

If the size of universe doubled

My question is silly formulated, but I want to know if there is some sensible physical question buried in it: Suppose an exact copy of our universe is made, but where spatial distances and sizes are ...
1
vote
1answer
2k views

Relativistic speed/energy relation. Is this correct?

The relativistic energy-momentum equation is: $$E^2 = (pc)^2 + (mc^2)^2.$$ Also, we have $pc = Ev/c$, so we get: $$E = mc^2/(1-v^2/c^2)^{1/2}.$$ Now, accelerating a proton to near the speed if ...
4
votes
4answers
751 views

Are the physical laws scale-dependent?

If you read the article "More Is Different", by P.W. Anderson (Science, 4 August 1972), you will find a deep question: are the physical laws dependent of the size of the system under study? As an ...
1
vote
4answers
1k views

Is gravity a vector or tensor function and does gravity have velocity or is it instantaneous?

If gravity exists quantumly it must take up space, have frequency, velocity, etc. Perhaps gravity is too fine a frquency for detection.
4
votes
4answers
390 views

Which gets you first when you are falling into a black hole, the black hole singularity or the cosmic background radiation?

If you look up while you are falling into a black hole you see the universe blue shifted, that is, you see the universe moving quickly forward in time compared to your local time. Since this effect ...
23
votes
14answers
3k 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 ...
5
votes
5answers
2k views

Is it possible to destroy proton in proton-proton collision?

Or in proton-electron collision. To destroy is to turn into other particles, not baryons. In context of the baryon asymmetry.
3
votes
3answers
5k views

What is the relation of sound propagation to air pressure?

Hi there i am wondering, air is making sound propagate. So in vacuum there is no sound. but what is the relation of pressure to sound volume? is it linear? if i have a source of sound and lets say i ...
20
votes
7answers
2k views

Is it possible to blur an image in such way that a person with sight problems could see it sharp?

If someone has short or long sight, is it possible to tune image on a computer monitor in such way, that a person could see it sharp as if they were wearing glasses? If not, will 3d monitor make it ...
2
votes
2answers
295 views

Why isn't the ISS electrically charged?

If metal moves in a magnetic field It creates a current so when the ISS or any other satellite/object charged so that if you connected a light/ put it in a circuit/ it would light up? also why doesn't ...
3
votes
2answers
674 views

What is an “Idea” in terms of time space and matter? [closed]

If the physical world we know is made of matter stretched in time and space and some forces affecting it, what would be an Idea, pure Information or something similar. Does those things don't exist ...
4
votes
3answers
395 views

How do molecules vibrate after collision?

The difference between kinematics and dynamics that Grisha pointed to in his answer comes up in a similar but slightly more complicated case: Consider (in 1D) two point-like particles connected by a ...
3
votes
2answers
927 views

logarithmic wind speed profile

Under some atmospheric stability condition, over flat terrain, it has been observed for a while that the ratio between wind speed at height $h_1$ above the earth and the wind speed at height $h_0$ is ...
6
votes
7answers
950 views

Evolution in the interpretation of the Dirac equation

As I understand, Dirac equation was first interpreted as a wave equation following the ideas of non relativistic quantum mechanics, but this lead to different problems. The equation was then ...
18
votes
4answers
2k views

Is it possible to observe interference from 2 independent optical lasers?

It seems that if the coherence length of a laser is big enough, it is possible to observe a (moving) interference picture by combining them. Is it true? How fast should photo-detectors be for ...
30
votes
17answers
3k views

Why does one experience a short pull in the wrong direction when a vehicle stops?

When you're in a train and it slows down, you experience the push forward from the deceleration which is no surprise since the force one experiences results from good old $F=m a$. However, the moment ...
33
votes
9answers
3k views

Is a “third quantization” possible?

Classical mechanics: $t\mapsto \vec x(t)$, the world is described by particle trajectories $\vec x(t)$ or $x^\mu(\lambda)$, i.e. the Hilbert vector is the particle coordinate function $\vec x$ (or ...
1
vote
4answers
345 views

Why is it so hard to accelerate macroscopic objects?

It seems all we're capable of accelerating currently are atomic particles. Why can't we, say, accelerate a clock to relativistic speeds?
7
votes
8answers
2k views

Is it possible to make glasses that make everything brighter, but do not magnify or focus?

Corrective glasses are usually intended to help focus light on your retina. Supposing I had good vision already, but simply wanted more light, could I make glasses that would send more light into my ...
1
vote
3answers
351 views

Where do atoms go after collision?

[I edited the question according to Mark's and Grisha's answers.] Consider two point-like particles of equal mass colliding centrally in 2D. The final directions of the momenta of the two particles ...
2
votes
1answer
555 views

Two-point correlation function for planar Potts model

Fastest known method for computing Potts model partition function (Bedini and Jacobsen's "A tree-decomposed transfer matrix for computing exact Potts model partition functions for arbitrary graphs, ...
5
votes
1answer
732 views

Equilibrium and movement of a cylinder with asymmetric mass centre on an inclined plane

A cylinder whose cross section is represented below is placed on an inclined plane. I would like to determine the maximum slope of the inclined plane so that the cylinder does not roll. The mass ...
3
votes
4answers
276 views

Chosing a reference frame in which the earth is at rest and doesn't rotate

We may choose a non-rotating earth as our reference frame and ask ourselves: how about the planetary and stellar motions. A star at a distance of 10 million light years would turn around the earth in ...
6
votes
5answers
1k views

Nano-particle or Molecule?

What's the difference between something being labeled a "nano-particle" or it being called a "molecule"?

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