Recent content by George K

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    Does AC form a closed loop circuit?

    No, I didn't mean that. Read my answer more carefully. I said: "Electrons will not "come up" from the ground by themselves. You should, also, connect the - pole of the battery to the ground in order to form a closed loop for the current to flow." In my example the + pole is connected to the one...
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    Does AC form a closed loop circuit?

    Don't be confused. Always there must be a closed loop for a current (DC or AC) to flow. The voltage (as provided by a voltage source) is just the "tendency" of the electrons to flow. But the electrons will never flow unless -somehow- the two poles of the voltage source form a closed loop. This...
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    I See How Andromeda Would Look if It Were Brighter

    I think that the artist used this photo: http://www.universetoday.com/30289/andromeda-galaxy/ This photo is just flipped, rotated and scaled. (I can't find how this Andromeda's photo has been produced but it seems to be a combination of different captures through a telescope, as the several...
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    I See How Andromeda Would Look if It Were Brighter

    If you read the text you'll see that the artist took a typical image of Andromeda and added it to the original photo, but in an appropriate scale (i.e. 3 times wider than the moon is).
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    A Two Black Holes' collision thought experiment

    Once, someone had asked two interesting (though absolutely hypothetical) questions: 1) What should happen during the collision of two BHs, one consisting of matter (BH+) and the other consisting of antimatter (BH-)? Should they form a larger BH or should they be annihilated? My personal...
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    I See How Andromeda Would Look if It Were Brighter

    Hi everyone. The next link shows how the Andromeda should look like (from the Earth's surface) if its stars were much more brighter than they are (or if we could have a super-vision). http://www.iflscience.com/space/what-andromeda-would-look-night-if-it-were-brighter It seems so amazing as I...
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    Does light always travel at light speed?

    How do you know that are not valid?
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    Does light always travel at light speed?

    Yes, of course, the incident light is interacting with a whole region of the lattice. (The interaction with the single atoms is a rather wrong and misleading explanation.)
  9. G

    Does light always travel at light speed?

    That's exactly what I meant. E.g. the propagation velocity of an AC signal on a wire is (somewhat less than) c. It doesn't matter if the signal's wavelength is very large and the wire's length is very small (i.e. much smaller than the signal's wavelength). The propagation velocity is always the...
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    Does light always travel at light speed?

    I've never thought of that (i.e. the light wavelength compared to the distance of the atoms in a solid medium). That's a good point. However, is it correct to assume that the light-wave doesn't travel at speed c if its full wavelength is not "completed" through its travel? (It's like to say that...
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    B Can a black hole event horizon grow at the speed of light?

    That was very interesting. Thanks. :smile:
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    B Can a black hole event horizon grow at the speed of light?

    Thank you for your reply. Unfortunately, at first, I was confused but now the whole issue is perfectly clear. :smile:
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    B Can a black hole event horizon grow at the speed of light?

    I think that you mean (in simple words) that the gradual increment of the BH's spacetime curvature -caused by an infalling object- will not let the light of an "event just outside of the EH" to escape, even before this object reaches the EH. Is this correct? (Please confirm.)
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    B Can a black hole event horizon grow at the speed of light?

    Thanks for your reply. I had also thought the scenario of the "spherically symmetric shell of matter falling into the hole", as this is a scenario where no bouncing of the EH will occur (of course in the case of an ideally spherical and homogeneous shell of matter). I think that (at least) I was...
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    B Can a black hole event horizon grow at the speed of light?

    The question is: What is the exact moment that an outside observer can verify that the mass of a BH has been increased? I know that, essentially, all the mass of a BH is concentrated upon its singularity. So, I suppose that an actual increment of the BH's mass (as observed by an outside...
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