# Search results

1. ### Additional boundary conditions for inclined flow?

Homework Statement I am solving an inclined flow problem, and am stuck. The problem is to find the volumetric flow rate of inclined flow in a square channel. Once I have the velocity profile, I can just integrate over that to get the flow rate. 2. The attempt at a solution Letting the...
2. ### Divergence of tensor times vector

Ah, that works well. Thanks!
3. ### Divergence of tensor times vector

(My question is simpler than it looks at first glance.) Here is Reynolds Transport Theorem: $$\frac{D}{Dt}\int \limits_{V(t)} \mathbf{F}(\vec{x}, t)\ dV = \int \limits_{V(t)} \left[ \frac{\partial \mathbf{F}}{\partial t} + \vec{\nabla} \cdot (\mathbf{F} \vec{u}) \right] \ dV$$ where boldface...
4. ### Maximum precision of deterministic measurements

Okay, I tend to have some weird thoughts, so bear with my odd question here. Suppose you have a collection of particles that obey Newtonian mechanics. For simplification, all particles are identical and can be assumed to be hard spheres that collide elastically. Each particle has a position...
5. ### What does the lost information in the wavefunction mean?

The wavefunction is defined on the domain of complex numbers. To find the probability of discovering a particle in a certain region, the amplitude of the wavefunction is integrated over that region. The problem is that you have an infinite set of complex numbers mapping to a single amplitude...
6. ### Electrons split in two?

Ah, that's what I was looking for. Thanks! You all can delete this thread.
7. ### Electrons split in two?

http://www.popsci.com/science/article/2012-04/first-time-electrons-are-observed-splitting-smaller-quasi-particles Sorry if this is old news or already posted somewhere, but could someone tell me more about this? (I know QM but not QFT, so if you can use QM terms that might be helpful). Thanks
8. ### Why is gravity special ?

That isn't really where I was going with this. If someone asks why two electrons repel, we can describe that using a model we've developed. If someone asks why there is a tide, we can give a reason involving the gravitational pull of the moon. And if someone asks why everything affects the...
9. ### Why is gravity special ?

Huh, okay. Thanks. A little over my head but I kind of think I know what you mean. I also thought of a better way to posit my question: Everything affects the gravitational field, but only certain things affect the electromagnetic field, the Higgs field, etc. Why?
10. ### Why is gravity special ?

Why is gravity "special"? (You may think this belongs in the General Relativity section, but the question really relates more to particle physics). As I understand it, anything with any energy whatsoever creates a disturbance in the gravitational field. So this means that the potential...
11. ### Composite particles de Broglie wave length

I too have wondered about this. My quantum mechanics professor used the example that a basketball has a very small wavelength, but if the individual particles that constitute the basketball have much larger wavelengths, well, then what's going on? (What does this mean experimentally?)
12. ### Superposition/Wave function inside blackhole

Hmm... this question does make me wonder though. Is a black hole a perfect example of a particle in a box?
13. ### Electron and the uncertainty principle

Actually, you CAN know both the position and momentum of a particle. But if you repeat the experiment many times again, and do it exactly the same way that you did it the first time, you will find that the standard deviations of your results adhere to the equation: \sigma_x \sigma_p \geq...
14. ### Uncertainty should be called as unpredictability

The word "uncertainty" leads to a lot of confusion. Say an electron is moving along, minding it's own business, and we decide to measure position and momentum. The way I (and many many others) interpreted it for the longest time was: (measured position - true position)*(measured momentum -...
15. ### Uncertainty should be called as unpredictability

I like "inconsistency principle" better, because identically prepared systems don't give consistent measurements :)

That's exactly* what I'm saying (minimal statistical interpretation) -- I don't see where we are differing. *Actually, I support the slightly stronger statement that the cat is "alive, dead, or something else". I mean, (and to further weird-ify Schrodinger's example), let's assume the cat is...

I've got a question. This describes an ensemble of multiple measurements. Which says nothing about one particular case for one particular cat. As far as I can tell, no experiment can be performed on one instance of a cat to determine its state because that would HAVE to involve a measurement...
18. ### Do particles have spatial extent or are they point-like?

Yeah, it does. That's how I set up the experiment... If he won't detect any electrons within Δt = (100 m)/c, then the domain that the electron wavefunction amplitude is integrated over is not infinity, which was exactly my point.
19. ### Do particles have spatial extent or are they point-like?

It seems to me that if this were true, then FTL communication would be possible. As a thought-experiment, consider an experimenter who has a container PACKED full of photons. He can release photons at will so that they collide with a nuclei, and via pair production, this produces an electron...

How would we set up an experiment to test that?
21. ### Do particles have spatial extent or are they point-like?

Yep, but what bothers me is that nothing can propagate faster than c, so how can the domain of an electron be infinity?

See, that's the absurdity that Schrödinger was trying to illustrate! Little did he realize is everyone would take on the position that the cat is simultaneously dead and alive. Experimentally, you can't say ANYTHING about that particular cat until you open the box and "measure" the result...
23. ### Ballentine on the quantum Zeno paradox

His book has far less errors than most textbooks describing quantum mechanics. I don't understand -- why is it non-standard? A professor can use whatever textbook he wishes to teach the class.
24. ### Loophole-free quantum steering

Was quantum entanglement predicted in theory before it was discovered experimentally?
25. ### The science behind the conversion of particles to other particles

...anybody else have any insight into this?
26. ### As per Japanese physicist (Masahiro Hotta), energy teleporation is possible

EDIT: Never mind. Not sure if what I posted was true.
27. ### The science behind the conversion of particles to other particles

The wave function measures nothing. A wave function completely specifies the state of a quantum-mechanical system. This function has the property that \Psi^{*}(\mathbf{r}_1, \mathbf{r}_2, t)\Psi(\mathbf{r}_1, \mathbf{r}_2, t)dx_1 dy_1 dz_1 dx_2 dy_2 dz_2 is the probability that particle 1...
28. ### Expectation value of momentum

Yep -- for a particle in a box. (Although I am assuming you meant to put an "n" in the argument of each sine function).
29. ### The science behind the conversion of particles to other particles

Hey thanks for replying! It doesn't quite answer everything though... The domain of a free electron or positron's wavefunction is infinite, so in a sense, they are always overlapping. Which means they would constantly be undergoing a collision, which does not happen. Is there any...
30. ### The science behind the conversion of particles to other particles

It seems kind of weird to me that particles convert between each other. As I understand it, if a positron and an electron "collide", two gamma ray photons are created, and the positron and electron are gone. 1st - What is meant by a collision? The positron and electron are each described...