# All Questions

1answer
200 views

### Considering the wave function is not 'real', what is interfering?

I find the idea of the wave function being 'just' a collection of numbers (probabilities) quite alluring, and elegant in explaining away the whole 'collapse' business (see Luboš' answer to this ...
0answers
290 views

### Does positronium have a stable crystalline phase?

This is a long shot, but while the 100YSS conference is going on at Houston, i haven't been able to get a grip on myself and think in other, more mundane and short-term rewards as normal people do. ...
0answers
17 views

### Formulas for compressibility of solids (physics) [duplicate]

Possible Duplicate: Formulas for compressibility of solids I have a question which is technically a physics question, but since I have yet to find a good physics forum which accepts Latex, ...
2answers
111 views

### Has there been any serious work in how the world would look if basic physical laws were changed?

Has there been any serious work in investigating how the world would look if certain basic physical laws were changed? Like if gravity or electromagnetism laws were changed to have different ...
2answers
330 views

### Is it possible to have faster-than-light movement in General Relativity?

The speed of light as the maximal possible speed is build into Special Relativity as a premise of the theory. However I know of no such premise in General Relativity. When looking at two stars laying ...
4answers
334 views

### How does the Hubble Redshift work?

I am a little confused about the workings of the Hubble Redshift. I do understand the classical Doppler-effect, however in special relativity the velocity of light c is a natural velocity limit. So ...
1answer
141 views

### Loopy lightning

What causes lightning to follow the path it does ? picture from BBC news: http://news.bbcimg.co.uk/media/images/62891000/jpg/_62891901_untitled-1copy.jpg main page: ...
1answer
117 views

### Spike when wavefunction collapses

So, when wavefunction collapses, there is a spike occuring. Does this mean that there are parts with the continuous probability of 0? (For example, x position from -9 to -3 has probability of 0, while ...
1answer
464 views

### What is the difference between infrared heat and “regular” heat?

In Feynman's terms temperature is the speed at which atoms are 'jiggling'. Now, let's suppose I've just eaten a sizable dinner, and my body temperature just got a tad up. Am I emitting more photons in ...
1answer
83 views

### Waves travelling with water flow

Suppose I use a tool to create a circular wave in the river. If there are two fish swimming 1m from the source (2m from one another), they will both feel the wave at the same time. What will happen ...
1answer
2k views

### Ideal gas law, pressure increase and temperature

If I had a container, full with air, and I suddenly decreased the volume of the container, forcing the air into a smaller volume, will it be considered as compression, will it result in an increase in ...
0answers
142 views

### quantum field theoretic models of decoherence

I am interested in whether there is a field theoretic description (there is, so what is it?) of the tensor product (aka density matrix) model of open quantum systems. In particular, I am interested in ...
2answers
679 views

### Are the protons and neutrons in the nucleus arranged in any particular way?

I was wondering this: suppose you have two oxygen atoms. They will both have 8 protons and 8 neutrons in the nucleus (at least if they are the most common isotope). Now, will all those particles be ...
2answers
3k views

### How do you calculate angle of projection?

At what angle the projectile should throw with initial velocity v in order to reach distance d? discard the air resistance, only gravitation acts. So far I got the equations for horizontal and ...
5answers
610 views

### Where does the “g” force that pilots experience come from?

I understand that it has to do with acceleration. Say a pilot does a quick maneuver and experiences a force of 5g. What exactly is happening here? And what is this force relative to? If someone ...
2answers
137 views

### Force to use in harmonic oscillation through the inside of a planet

I am to find an equation for the time it takes when one falls through a planet to the other side and returns to the starting point. I have seven different sets of values - mass of object falling, mass ...
1answer
407 views

### How did Copernicus establish the relative distance to the superior planets?

I understand that the relative distances to the planets had been calculated using various methods since ancient times, and, in particular, that the assumptions of the Copernican model of the Solar ...
3answers
326 views

$$\frac{d}{dt}\int \limits_{A} \mathbf B d \mathbf A = \int \limits_{A} \left( \frac{\partial \mathbf B}{\partial t} + \mathbf v (\nabla \cdot \mathbf B ) + [\nabla \times [\mathbf v \times \mathbf B ... 3answers 381 views ### Why there is electromagnetic resistivity in vacuum? I cant understand that. If there isn't a material that makes it hard to pass, why there is a resistivity in vacuum? 6answers 8k views ### What causes an electric shock - Current or Voltage? Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ... 1answer 131 views ### Could this fountain, under the right conditions, technically be able to lift me up? There is a big fountain in a lake in my city. I was talking with a friend and we were wondering whether it would be able to lift me up. I sent a few emails and obtained information about the ... 4answers 1k views ### Reason for the Gaussian wave packet spreading I have recently read how the Gaussian wave packet spreads while propagating. see: http://en.wikipedia.org/wiki/Wave_packet#Gaussian_wavepackets_in_quantum_mechanics Though I understand the ... 3answers 250 views ### In what way do Cooper pairs of electrons bond and stay bonded in superconductors? I understand how electrons initially move into another's vicinity, but nowhere can I find a fathomable answer to this. Also, does the pairs forming 'a condensate' mean a Bose-Einstein condensate? 2answers 5k views ### Why do objects with different masses fall at the same rate? [duplicate] Possible Duplicate: Confused about the role of mass Today we were in our Literature class talking about the Renaissance and the Enlightement and our teacher also said that scientific ... 4answers 1k views ### Does a material exist that reduces a magnetic field without being affected by the magnetic field itself? Consider a common bar magnet, magnet 1 resting on a surface with its North pole facing up. Suspended distance y above it ... 3answers 111 views ### What will be the shape states of water in a centrifuge in 0G Consider the concept of these videos http://www.youtube.com/watch?v=Zip9ft1PgV0&sns=em and http://www.youtube.com/watch?v=cUhgKFV5Ri4&sns=em but set in a zero gravity environment and in a ... 1answer 57 views ### What mechanism produced the baryon excess in the universe? A baryon is a composite subatomic particle made up of three quarks (as distinct from mesons, which comprise one quark and one antiquark). Baryons and mesons belong to the hadron family, which are the ... 0answers 123 views ### Electroweak Symmetry Breaking Electroweak symmetry breaking is manifested by the nonzero masses of the weak W and Z bosons, and requires the existence of a Higgs boson or some other yet unseen mechanism. To solve the problem of ... 1answer 293 views ### What gives matter Gravitational Mass? [duplicate] Possible Duplicate: Does the equivalence between inertial and gravitational mass imply anything about the Higgs mechanism? In Higgs mechanism, Higgs field, which likes syrup, slows down ... 4answers 337 views ### Is there any quantum interpretation which isn't “crazy” at all? [closed] Is there any quantum interpretation which isn't "crazy" at all? Exponentially many parallel worlds in MWI, superdeterministic conspiracies, and/or nonlocality in hidden variables, idealism and the ... 2answers 370 views ### Lever Mechanics - How to formulate an ideal lever launch Let's say I have a simple lever as shown below, and the lever is massless and the pivot is frictionless and there is no air resistance. I'm thinking the cradle for the projectile would have to have a ... 1answer 173 views ### What is relation between Holographic principle and Hologram? What is relation between Holographic principle and Hologram? The holographic principle is a property of quantum gravity and string theories which states that the description of a volume of space can ... 1answer 151 views ### Wavefronts and phase velocity faster than c Lets assume we have parallel wavefronts in a glass of water: and we put an inclined rod on the water surface: related to a very small inclining, Vy velocity is greater or much greater then Vx ... 1answer 240 views ### Is it possible that nuclear fission contributes to climate change? This is probably a really stupid question, please forgive me. Is it possible that the use of nuclear fission on earth contributes to the increased energy in the Earth's system as according with the ... 1answer 97 views ### converting daily global radiation into hourly values I would like to convert daily global radiation into hourly solar radiation. While I do not know the terms, I tried using below equations I found in the papers but I have negative radiation values ... 1answer 242 views ### Does string theory provide a physical regulator for Standard Model divergencies? In other question, Ron Maimon says that he thinks string theory is the physical regulator. I did not know that string theory regularize divergencies. So, Q1: How does string theory regularize the ... 4answers 1k views ### How to prove that proper orthochronous Lorentz transformations form a group? Proper orthochronous Loentz transform are Lorentz transforms that satisfy the conditions (sign convention of Minkowskian metric +---)$$\det \Lambda=+1, \qquad \Lambda^0{}_0 \geq +1.$$How to prove ... 1answer 139 views ### Zero entropy change If you put a object in contact with a heat reservoir that is infinitesimally higher in temperature than the object and allow equilibrium to be reached the entropy change is zero right? 1answer 223 views ### Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? Magnetic monopole predicted by Dirac nearly a century ago was found in spin ice as quasi-particle(2). My question is Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? (I ... 2answers 257 views ### Force and Natural Units Today in my Physics lecture I suddenly thought of something. We all know that gravitational force is proportional to the two masses and inversely proportional to the square of the distance between ... 1answer 71 views ### Modeling falling spheres The following situation interests me and I was wondering if there is software to model it? A large set of n spheres of uniform density and discrete sizes, mass proportional to volume, are dropped ... 1answer 210 views ### How do I measure the temperature of a tiny water droplet? How do I accurately (+/- 0.1 degrees Celsius or better) measure the temperature of a small (5 to 50 microliter) water droplet without noticeably affecting its temperature? The mass of a thermistor or ... 1answer 238 views ### Relativistic contraction for a wave packet and uncertainty on momentum Consider an electron described by a wave packet of extension \Delta x for experimentalist A in the lab. Now assume experimentalist B is flying at a very high speed with regard to A and observes the ... 1answer 188 views ### Distance and displacement of an object on a straight line [closed] I had this homework problem, but don't actually know if what I did is right, or that I even read the problem correctly. Can someone please tell me if this is the right interpretation of the problem ... 2answers 953 views ### Gentle introduction to twistors When reading about the twistor uprising or trying to follow a corresponding Nima talk, it always annoys me that I have no clue about how twistor space, the twistor formalism, or twistor theory works. ... 2answers 84 views ### Is the magnetic field of a white-dwarf merely residual? Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures? Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is ... 2answers 210 views ### What is the most natural classical polynomial complexity class that includes all of BQP and NP? Since we know that there are some oracle problems which can be solved on a quantum computer, but not on an NP machine with the same oracle, the idea of nondeterministic (i.e. infinitely parallel) ... 0answers 78 views ### Searching for a specific Feynman quote [closed] Pardon that this is strictly speaking not a question about physics but about a quote about physics, but I'm not sure where else to turn to. A while back I read a quote by Feynman in which he says ... 1answer 2k views ### Work on ideal gas by piston Imagine a thermally insulated cylinder containing a ideal gas closed at one end by a piston. If the piston is moved rapidly, so the gas expands from V_i to V_f. The expanding gas will do work ... 1answer 306 views ### How much does the curvature of space change the volume of Earth by? If we assume space is flat the volume of Earth is:$$ V = \frac{4 \pi R^3}{3} = \frac{4 \pi (6378.1 km)^3}{3} = 1.086 \times 10^{21} m^3  The Einstein field equations, however, predict that the ...

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