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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 ...
  • 109
-4 votes
6 answers
6k 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 ...
  • 1,211
22 votes
3 answers
4k 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?
  • 2,770
10 votes
1 answer
671 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?
  • 953
47 votes
14 answers
13k 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 ...
18 votes
4 answers
5k 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 ...
26 votes
10 answers
5k 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). ...
1 vote
3 answers
198 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 ...
6 votes
4 answers
974 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. ...
  • 5,458
7 votes
5 answers
1k views

What if the size of the Universe doubled?

My question has a silly formulation, 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 ...
  • 4,901
5 votes
1 answer
21k 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 of light,...
  • 3,659
9 votes
5 answers
2k 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 ...
  • 550
2 votes
5 answers
2k views

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

If gravity exists quantumly it must take up space, have frequency, velocity, etc. Perhaps gravity is too fine a frquency for detection.
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12 votes
4 answers
1k 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 ...
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27 votes
16 answers
6k 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 I'...
6 votes
7 answers
5k 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.
  • 2,020
10 votes
3 answers
23k views

What is the relation of sound propagation to air pressure?

I am wondering, air makes sound propagate. So in a 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 let's say I am in a ...
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35 votes
9 answers
15k 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 ...
  • 1,415
4 votes
2 answers
387 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) orbits, is it charged such that if you connected a light, in a circuit, it would light up? ...
  • 6,739
4 votes
2 answers
2k 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 ...
  • 187
5 votes
3 answers
638 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
2 answers
2k 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 $...
7 votes
7 answers
1k 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 ...
  • 4,676
22 votes
4 answers
5k 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 ...
  • 584
43 votes
17 answers
5k 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 ...
53 votes
9 answers
7k 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 $x^\...
6 votes
3 answers
1k views

List of Scattering Phenomena

While at lunch with my lab group we got into discussion of the different types of scattering phenomenon that we encounter in everyday life and physical experiments. We ended up listing about a dozen ...
1 vote
4 answers
516 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?
8 votes
11 answers
8k 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
3 answers
408 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 ...
3 votes
1 answer
723 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, ...
7 votes
2 answers
2k 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 ...
4 votes
4 answers
454 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 ...
  • 6,521
7 votes
5 answers
4k views

Nano-particle or Molecule?

What's the difference between something being labeled a "nano-particle" or it being called a "molecule"?
  • 171
7 votes
3 answers
3k views

Books for linear operator and spectral theory

I need some books to learn the basis of linear operator theory and the spectral theory with, if it's possible, physics application to quantum mechanics. Can somebody help me?
4 votes
2 answers
2k views

Does the friction force change directions with a change in reference frame?

In a basic friction problem with Block $A$ sliding on top of Block $B$ , the direction of the friction force is usually explained as being simply the opposite of the direction of motion. So if Block $...
27 votes
2 answers
2k views

Why is tape so hard to rip when it is not broken, but so easy once there is the tiniest cut in it?

Question says it all. Ripping a piece of tape along the width is tough, stretches the tape, messes it up, etc, but if you put the tiniest nick at the top, it rips without any problems. Why is that?
  • 555
6 votes
3 answers
514 views

What is necessary for a causal set to be manifold-like?

A causal set is a poset which is reflexive, antisymmetric, transitive and locally finite. As a motivation, there is a programme to model spacetime as fundamentally discrete, with causal sets ...
5 votes
3 answers
3k views

Is it possible/correct to describe electromagnetism using curved space(-time)? [duplicate]

Comparing the simples form of the forces of both phenomena: the law of Newton for gravitation $V\propto \frac{1}{r}$, and the Coulomb law for electrostatics $V\propto \frac{1}{r}$, one might think ...
  • 1,415
12 votes
3 answers
11k views

What determines the color of a pure substance and is it possible to predict it?

I have always wondered why salt is white, water is clear and gold is, well, gold. What determines the color of a substance? Does it have something to do with the electrons? And is it possible to ...
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1 vote
1 answer
680 views

2 Electricity generator connected

I'd like to know (my knowledge at physics are realy poor) what would happen if I've got a generator connected to another generator and both of them generating electricity for a house or whatever. ...
  • 121
12 votes
5 answers
7k views

How do neutron stars burn? Is it decay or fusion or something else?

What makes a neutron star burn, and what kind of fusion/decay is happening there? What is supposed to happen with a neutron star in the long run? What if it cools, then what do the degenerated matter ...
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3 votes
3 answers
297 views

Material resistency to lasers beam

Keeping the average power constant, why some materials are more eager to be damaged by pulsed laser with respect of C.W. lasers, or viceversa? When i talk about pulsed lasers i think for examples of ...
  • 577
12 votes
10 answers
20k views

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 ...
  • 403
51 votes
3 answers
14k views

Why doesn't this perpetual motion machine using the buoyant force work?

I realize this isn't possible, but I can't see why not, especially if you change the model a little bit so that the balls simply travel through a tube of water on the way up, rather than exactly this ...
  • 521
8 votes
4 answers
25k views

What causes hot things to glow, and at what temperature?

I have an electric stove, and when I turn it on and turn off the lights, I notice the stove glowing. However, as I turn down the temperature, it eventually goes away completely. Is there a cut-off ...
  • 5,860
8 votes
4 answers
1k views

Chance of objects going against greater entropy?

My book uses the argument that the multiplicities of a few macrostates in a macroscopic object take up an extraordinarily large share of all possible microstates, such that even over the entire ...
23 votes
6 answers
89k views

Can the coefficient of static friction be less than that of kinetic friction?

I was recently wondering what would happen if the force sliding two surfaces against each other were somehow weaker than kinetic friction but stronger than static friction. Since the sliding force is ...
  • 74.1k
291 votes
18 answers
74k views

Why does kinetic energy increase quadratically, not linearly, with speed?

As Wikipedia says: [...] the kinetic energy of a non-rotating object of mass $m$ traveling at a speed $v$ is $\frac{1}{2}mv^2$. Why does this not increase linearly with speed? Why does it take so ...
28 votes
9 answers
17k views

Why can you have shiny black objects?

Knowing black is supposed to be the "color" (I don't want to get into the color/hue/shade debate, please) that absorbs light. how does one manage to have shiny black surfaces? I know about "gloss ...
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