# Search results

1. ### I Questions about ensemble interpretation of QM

I've been reading up on the ensemble interpretation (aka statistical interpretation) of QM and it's making a bit more sense to me that it did on the onset, but I still have some questions about how it is consistent with experimental observations of various QM experiments, especially...
2. ### I Force between parallel plates of set voltage

Hi PF, I have a setup with two plates that are connected to two different voltages and separated by vacuum. In my case, one plate is set at -10kV, and the other plate is set at -7.5kV. I know the area of these plates, the separation of the plates (which is much smaller than the plate area), and...
3. ### I Force between similarly charged plates

In a setup I am designing, I have two conducting plates of similar charge, separated by 1mm of vacuum. The "top" plate, which is mechanically fixed, is charged to -10kV. The other "bottom" plate, which is electrically isolated, but not mechanically fixed (can move toward the "top plate"), is...
4. ### I Lines of simultaneity in Twin Paradox spacetime diagram

I set up a Twin Paradox scenario and accompanying spacetime diagram to help better understand the resolution, but I had a question about the diagram I was hoping someone here could help answer. Please excuse the hastily drawn diagram! (Note: the ' frame corresponds to the outbound trip, the...
5. ### I Calculating thermal resistance across a metal flange

I've been using the following equation for thermal resistance to make basic calculations for a few different engineering designs: $$R_t = \frac{L}{kA}$$ Where L is the resistance path length, A is the cross-sectional area perpendicular to this path and k is the thermal conductivity of the...
6. ### Can lead shielding block beta particles?

I know lead is a great shield against gamma particles due to its extraordinary density, but I wonder if it can also block beta particles, or is it transparent to them due to being electrically conductive? Thanks ahead of time for your responses!
7. ### Is this reaction possible?

The equation is balanced, but would it actually work? NaOCH3 + CO2 + H2O → NaHCO3 + CH4O Or would the reaction simply ignore the water in the left hand side and go, 2NaOCH3 + CO2 → Na2CO3 + H2O + C2H4 Or perhaps a little of both? I'm just starting to teach myself Chemistry, so any insight...
8. ### Thermonuclear fusion in accretion disks?

I was wondering whether thermonuclear fusion could be achieved in accretion disks around black holes, or even neutron stars/white dwarfs. Seems like, in AGN at the very least, you would easily get the kind of temperatures and pressures necessary for thermonuclear fusion, perhaps even synthesis...
9. ### How can massless strings be the building blocks of matter?

To clarify, I'm not confused as to how massless strings can add up to make massive objects, I understand why that happens. My question has more to do with the speed at which strings move. If strings are massless, they must travel at the speed of light, correct? If so, then first off, what is the...
10. ### Schools To grad school (for physics) or not to grad school?

Hey PF! So I just finished my undergrad degree in Astrophysics, and I'm interested in going back to get my PhD. I really love physics, and I don't mind the kind of grind and time that it would take to be a successful PhD student. I'm not looking to get higher paying jobs after I get my PhD, I...
11. ### Spacetime is smooth after all?

Just came across this article, which details findings from the Fermi telescope that have an interesting consequence to quantum gravity theories: www.space.com/19202-einstein-space-time-smooth.html First, what do you guys think of this finding? Is it legitimate, or flawed? It's obviously...
12. ### Bernoulli Equation for Rotational Flow

Hi PF! I've been working on a research problem involving fluid dynamics, and I'm currently looking at a "bathtub flow". This is where water is draining through a hole, and we have a vortex. In a paper I have found dealing with this flow, the velocity potential was written as: \psi = Alnr + B\phi...
13. ### Quantum gravity - Planck's constant as a scalar field?

"Quantum" gravity -- Planck's constant as a scalar field? I was just reading about a fascinating new theory on the solution to the quantum gravity problem: http://arxiv.org/pdf/1212.0454.pdf I really like it, but I have one big problem with it: The author states that G = \frac{\hbar...
14. ### LaTeX Install custom Latex package for senior thesis!

Hi guys! I need some Latex help, so I'll try to be a descriptive as I can, I need to create a cover sheet for my senior thesis, and I'm trying to use the Latex format designed by my school, which uses a custom package called "ucscthesisbs" that I have to install in order to have the correct...
15. ### Linear vs. Angular Momentum

In classical mechanics, p = mv L = Iω These correspond to linear and angular momentum, respectively. They're both called momentum, but...they don't have the same units. Why is that?? How can we call them both momentum when they don't seem to represent the same physical quality? Can we set...
16. ### Transform of a Line Element

Homework Statement Transform the line element of special relativity from the usual (t, x, y, z) coordinates rectangular coordinates to new coordinates (t', x', y', z') related by t =\left (\frac{c}{g} + \frac{x'}{c} \right )sinh\left (\frac{gt'}{c} \right) x =\left (\frac{c}{g} +...
17. ### Proof of a Lorentz Transformation

Homework Statement Show that the following is a Lorentz Transform: \Lambda _{j}^{i}=\delta _{j}^{i}+v^iv_j\frac{\gamma -1}{v^2} \Lambda _{j}^{0}=\gamma v_j , \Lambda _{0}^{0}=\gamma , \Lambda _{0}^{i}=\gamma v^i where v^2 =\vec{v}\cdot \vec{v}, and \delta _{j}^{i} is the Kronecker Delta...
18. ### Surface area of a spherical cap

Homework Statement Calculate the area of a circle of radius r (distance from center to circumference) in the two-dimensional geometry that is the surface of a sphere of radius a. Show that this reduces to πr2 when r << a Homework Equations Surface area of a spherical cap = 2πah = π(r2 +...
19. ### Paradox of non inertial forces in relativity

Ok, so I've been thinking of a certain paradox in relativity that I can't seem to resolve: We have two observers, one in a "stationary" frame outside the Earth. This observer is looking down on Earth at another observer sitting at rest with respect to the surface of the Earth, but obviously...
20. ### The structure of strings

Quantum mechanics tells us that particles have a wave-like nature: their position, momentum and energy are not absolutely defined, and obey the Uncertainty principle. One thing that strikes me as peculiar in String Theory is how much internal structure string appear to have at the Planck...
21. ### Why is gravity the only force the causes time dilation?

We all know that in general relativity, there is the idea that the gravitational force and accelerating reference frames are very closely related. In GR, gravity acts through distortions of the space-time continuum, which causes phenomena such as redshift and time dilation. My question is this...
22. ### Coexistence of LQG and String Theory?

Can Loop Quantum Gravity and String Theory coexist? What if String theory was correct in its description of matter and 3 of the 4 forces, with the only difference from modern M theory being that there is simply no real particle called the graviton, and instead, gravity is as is described by LQG...
23. ### General Relativity vs. quantum gravity

Hey all! So, in my study of general relativity, I've come to understand that gravity is actually what physicists would have classically called a "fictitious force", in that it is a force derived from the fact that the observer is not in an inertial reference frame, like in the case of the...
24. ### Steady-State Temperature: Fourier Transform

Homework Statement Find the steady-state temperature in a semi-infinite plate covering the region x>0, 0≤y≤1,if the edges along the x axis and y axis are insulated and the top edge is held at Hint: Look for a solution as a Fourier integral. Homework Equations The Attempt at a...
25. ### Large rotating disk.

Imagine we have a spinning disk. Points near the center of the disk rotate slowly while those increasingly far out are moving faster. Now suppose we have a sufficiently large disk such that the points on the edge of it are moving relativistically, and would classically be reaching or surpassing...
26. ### Electrodynamics thought experiment

So I was thinking about E&M today, and specifically, how E&M relates to the ideas of relativity. Specifically, that magnetism is induced by a change in an electric field and vice versa. This got me thinking of some scenarios. In each, you have a particle emitting a constant magnetic field and...
27. ### At what redshift did the Universe beging accelerating?

Homework Statement Starting with the equation for a'', derive an expression for the redshift at which the deceleration of the Universe turned into acceleration. Your expression should contain only fundamental cosmological parameters at the present day such as \OmegaM0 and \Omega\Lambda0...
28. ### Escaping from Black Holes

I had a couple questions regarding the ability of objects and light to escape a black hole. 1) The even horizon is supposedly the boundary at which no object can escape from a Black Hole, as within this radius, the escape velocity is greater than c. This much I understand; If I throw myself...
29. ### Orthoganol matrices

Homework Statement Show that a product of orthogonal matrices is orthogonal. Homework Equations Orthoganol matrix: M-1=MT The Attempt at a Solution since A-1=AT A-1 and AT commute. commutable => symmetric => A-1AT=(A-1AT)T (A-1AT)-1=A-1AT/det(A-1AT) => (A-1AT)-1(A-1AT)=(A-1AT)2/det(A-1AT)...
30. ### Expanding Integrand into Power Function

Homework Statement The dilogarithm Li2(x) is a special function defined by the following integral Expand the integrand in a power series and integrate term by term, thereby deriving the power series expansion for Li2 about x=0 Homework Equations f(x)= f(0) + xf'(0) + (x2/2)f''(0) +...