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visits member for 2 years, 11 months
seen 10 hours ago

16h
comment Can FTL-Communication between two points in the same frame of reference break causality?
I like your answer & didn't even think of the conservation of energy bit!
17h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@Torge It's true that the frame in which communication is occuring is not the frame in which the three objects all have zero velocities (zero velocity=vertical blue line), but you can solve this by supposing that the earth, observation 1, and aliens, all constantly send out probes w/ the required velocities in both directions, ready to send and receive at any time. The message jumps from the earth, to its probe, to another probe (at rest wrt this one), to the aliens. So that presents no obstacle.
17h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@Torge I think you are misinterpreting the Minkowski diagram. en.wikipedia.org/wiki/Minkowski_diagram . Each blue line is an object. Each object is at rest with respect to the others.
17h
comment Reaction force explanation?
possible duplicate of How can I stand on the ground? EM or/and Pauli?
18h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@JohnDuffield I agree with everything you've said, except for "the animation is misleading", "this is a non-answer", and "this conversation isn't dumb".
19h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@JohnDuffield This is a dumb conversation. I say, "Supposing X, Y." Then you say, "not Y." Then I say "true, but supposing X, Y." Nothing new has been said.
19h
comment Best twin paradox trajectory for constant acceleration rocket?
Welcome to physics stackexchange! I think this question is a bad fit for the website at the moment, because it shows insufficient research effort. Take the equation at the end of joshphysics's post here physics.stackexchange.com/questions/75487/… and piece together three such paths, and then integrate to get the proper time, then use calculus to minimize/maximize whatever parameters you want. Start doing that, and once you get stuck at a conceptual difficulty, you can ask that question here.
19h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@Torge I updated the diagram. Note that this is a Minkowski diagram ( en.wikipedia.org/wiki/Minkowski_diagram ). "Outpost 1" is just a line in spacetime (ref. to the new diagram), and it can be viewed in whatever frame you want to view it in. By special rel., the laws of physics should be equivalent in all these frames.
20h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@JohnDuffield True, and in-line with everything in my post. The question is how and why do things break when you try to wiggle special relativity around with notions of FTL communication, and that is what I am discussing.
21h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@Torge added an illustration of the diagram I'm referring to.
22h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@JohnDuffield on the supposition that changing your state of motion changes whether or not very-rapid communication can occur, changing your state of motion changes whether or not very-rapid communication can occur. On the supposition that very-rapid communication can occur and on the supposition that special relativity holds, you get a causality paradox which can be illustrated with a spacetime parallelogram. I need to use a reference frame/state of motion as my privileged coordinate system, else I can't define any notion of instantaneous communication between earth/alpha centauri.
22h
comment Can FTL-Communication between two points in the same frame of reference break causality?
@Torge the fun thing about the universe is that it doesn't care what you think is pointless or not :D I think my ** comment addresses your concerns. I'll draw a diagram to help you out.
23h
comment Can FTL-Communication between two points in the same frame of reference break causality?
I think this answer is bad. The OP is asking "what would known physics predict about FTL communication, and does FTL communication contradict it?" This answer doesn't address that.
2d
comment What is special about quantum entanglement?
possible duplicate of Quantum entanglement vs classical analogy
2d
comment Is Wikipedia's definition of angular velocity incorrect?
@kalkanistovinko Yes I suppose they would! That's a topic for another question. It's explained poorly in the wiki article en.wikipedia.org/wiki/… . But in practice I've never seen that definition of angular velocity used -- you usually specify a frame with Euler angles, construct a base change matrix $R(\theta,\varphi,\psi)$ in which all particles of the rigid body are fixed, and go from there.
2d
comment Solving for the firing rate of a model neuron
@dbliss oh. Well then maybe Oussama's use of erfi is correct.
2d
comment Solving for the firing rate of a model neuron
Seeing as how the author refers to $\sigma_V$ as the "effective standard deviation in the voltage", and seeing as how yes, $\mathrm{erf}(x)=c \int e^{-u^2}\mathrm{d}u$. I'd guess that it should be $\int e^{-x^2}(1+\mathrm{erf}(x))\mathrm{d}x$. It could be a typesetting issue because that seems like too big of an error.
Aug
29
comment How to determine the angular velocity of a particle with mass $m$ and charge $q$ in a constant B field?
That's just the form of the equation. $\bf f$ could be the momentum or the velocity (doesn't matter), and $A$ should have units of inverse time.
Aug
29
comment How to determine the angular velocity of a particle with mass $m$ and charge $q$ in a constant B field?
I don't think you've shown sufficient research effort in this problem! Two tips: 1. the question likely intends for you to set $\vec{E}=0$. 2. restrict $\vec{v}=\vec{p}/m$ to a plane, and write out the resulting system of ordinary differential equations to the two by two matrix equation $\dot{\bf f}=A\cdot \bf f$ where $f$ is your two row column vector, and $A$ is a matrix.
Aug
25
comment modelling the sound wave of a guitar string with an equation
@ja72 fun simulation!