151–160 of 839 posts
What happens when you actually fall inside a black hole and what is the singularity. I never really understood what happened really when the guy fell inside it in Interstellar and how come he started seeing all those photos. I just accepted it as Hollywood bs. I know my question is based on a movie but would still like to know what will someone witness (assuming of course they somehow live)
Entropy. Sometimes you read that it's a measure of randomness; sometimes, information. Aren't randomness and information opposites?
Let's use an analogy of a remote observation post and with a soldier sending hourly reports:
0 ≝ we're not being attacked
1 ≝ we're being attacked!
The entropy, denoted H(X), measures how uncertain the central command post have about the message before they will receive, or equivalently, the information they gain after receiving the message. The peace time messages contain virtually no information (very low entropy), while wartime 50-50-probability messages contain H(X)=1 bit each.
Another useful way to think about information is to say "how easy would be to guess the message" instead of receiving it? In peacetime you could just assume the message is 0 and you'll be right 99.99% of the time. In wartime, it would be much harder to guess---hence the intuitive notion that wartime messages contain information.
I find most explanations of the Equivalence Principle that lies at the foundation of General Relativity to be very lax. To wit, the idea is that you cannot distinguish whether you are in an accelerated frame or in a gravitational field; alternatively stated, if you’re floating around in an elevator you don’t know whether you’re freefalling to your doom or in deep sideral space far from any gravitational source (thoug…
Why bicycles stay upright. For every authoritative-sounding, in-depth explanation, there is an equally plausible, yet conflicting and contradictory alternative.
I find most explanations of the Equivalence Principle that lies at the foundation of General Relativity to be very lax. To wit, the idea is that you cannot distinguish whether you are in an accelerated frame or in a gravitational field; alternatively stated, if you’re floating around in an elevator you don’t know whether you’re freefalling to your doom or in deep sideral space far from any gravitational source (thoug…
If you think it's sneaky to "implicitly" assume they're in the same direction, I would point out that this is no different from assuming they have the same magnitude. It would be kinda dumb to say "well this 1m/s^2 acceleration can't possibly be equivalent to gravity because gravity is 9.8m/s^2, so the statement is obviously wrong and they're trying to trick me!!"... same thing for direction.
What happens when you actually fall inside a black hole and what is the singularity. I never really understood what happened really when the guy fell inside it in Interstellar and how come he started seeing all those photos. I just accepted it as Hollywood bs. I know my question is based on a movie but would still like to know what will someone witness (assuming of course they somehow live)
Quantum spin. Electrons aren't really spinning, right? But why do we call it spin? I know it has something to do with angular momentum. What are the possible values? Is it a magnitude or a vector? Is there a reason we call it "spin" instead of "taste" or some other arbitrary name? How do you change it? What happens to it when particles interact?
Annoyingly I've always struggled with the precise definition of spin, but to my understanding angular momentum is only conserved if you take spin into account as well. Being quantum mechanical there is some ambiguity in the direction, but in principle it is a vector (except it's a superposition of several vectors, and this superposition is also equal to superpositions of different vectors, I think there is usually on…
Do you know an example of a process that moves angular momentum from one kind of spin to the other?
Earlier quoted context omitted.
It directs air moving horizontally downwards, by conservation of momentum the wing must get additional upwards momentum, called lift.
That can't be the explanation, otherwise wings wouldn't need to be curved - flat wings could fly, as long as they're tilted to redirect the air.
Earlier quoted context omitted.
What follows is very hand-wavy, and the renormalization sibling post may touch on it. An answer is that the d->0 approaches infinity presumes a nice, continuous analytic function. If d->epsilon, you can't get to that singularity. There was an equivalent problem in the E/M space with "The Ultraviolet Catastrophe" [1], which turned out to go away if you assumed quantization. I'm not going to claim this is a perfect ana…
This is definitely related, though not the whole story. Quantization did get rid of some infinities, but as GP kind of states, it also introduced others. My comment focuses on what we do for those.
I believe the poster's general premise to be false. While renormalization may be useful in resolving infinities in general, I don't think it's necessary for this one.
You can't commute the dp*dx of a Hamiltonian to be zero in a quantized world, so if gravity has quantum properties, you don't need to worry about what happens when d -> 0. There is no "0" distance.
Quantum spin. Electrons aren't really spinning, right? But why do we call it spin? I know it has something to do with angular momentum. What are the possible values? Is it a magnitude or a vector? Is there a reason we call it "spin" instead of "taste" or some other arbitrary name? How do you change it? What happens to it when particles interact?
It is techinically a two-component spinor, which is why the direction of the spin 'moves' if you measure it along different x,y,z axes. It is also quantized unlike a normal vector: All fermions have quantized half-integer spin magnitudes and all bosons have integer magnitudes.
Magnetic fields can be used to change the spin.
When particles interact, opposing spins tend to pair up in each electron orbital which cancels the magnetic field. This is why permanent magnets must have unpaired electron orbitals.