81–90 of 129 posts
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It actually is true thought, that some supermassive blackholes have a density thats pretty close to that of water, and their event horizons are very very gentle.
I think this is only the case if you consider the mass density to be uniform within the event horizon, which isn't true.
"The fabric of space-time" — I hear this a lot, but what does it mean? Does it mean that space and time are a "fabric"? What is such a fabric made of? The idea that space and time are actual objects, instead of intellectual constructs, has always struck me as wrong. (I'm not a physicist.)
It's usually referred to as a fabric because in general relativity, spacetime is dynamic, as if it were on a fabric that could stretch and contract in response to the density of matter occupying it. This is where the rubber-sheet analogy comes from. As for what it is made of, that is one of the great open questions in theoretical physics right now, but also possibly where the analogy breaks down. Because of Lorentz I…
After watching, I have a question, please forgive if it is ridiculous or displays some fundamental problem with my layman's understanding of the subject.
If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"? Would every black hole within our observable universe contain information from all light cones within the observable universe? In other words, would different black holes contain different information?
Does my question make sense?
Earlier quoted context omitted.
It's usually referred to as a fabric because in general relativity, spacetime is dynamic, as if it were on a fabric that could stretch and contract in response to the density of matter occupying it. This is where the rubber-sheet analogy comes from. As for what it is made of, that is one of the great open questions in theoretical physics right now, but also possibly where the analogy breaks down. Because of Lorentz I…
Thanks for linking to the video, it was the most informative handling of the subject I have seen. After watching, I have a question, please forgive if it is ridiculous or displays some fundamental problem with my layman's understanding of the subject. If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"? Would every black hole within our observable universe contain info…
However, as for black holes containing the same information, our universe is expanding uniformly at an accelerating rate, and this results in cosmological horizons beyond which objects are moving faster than the speed of light (with respect to the frame of reference). Therefore, black holes in different galaxies shouldn't be able to have access to the same light cones without compromising the principle of locality. Although, if you believe that entangled black holes in different galaxies would lead to the same singularity ("ER=EPR" [1][2]), this becomes more complicated and is way out of my depth.
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Nima Arkani Hamed | Unification and Fundamental Phyics: A Status Report 9-21-2018
[0]: https://www.youtube.com/watch?v=pXYvFMqwbhc
Leonard Susskind Public Lecture | "ER = EPR" or "What's Behind the Horizons of Black Holes?"
[1]: part 1: https://www.youtube.com/watch?v=OBPpRqxY8Uw
[2]: part 2: https://www.youtube.com/watch?v=uiG_EtVQu5o
I've seen a couple of articles about this guy recently and they both struck me as weirdly credulous given the apparently complete lack of evidence supporting his theory and the fact that approximately no other scientists seem to find it credible.
There's a moment at which every scientific theory is only thought credulous by a single person.
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Thanks for linking to the video, it was the most informative handling of the subject I have seen. After watching, I have a question, please forgive if it is ridiculous or displays some fundamental problem with my layman's understanding of the subject. If time becomes space-like, and space becomes time-like, can we think of black holes as "time stars"? Would every black hole within our observable universe contain info…
I'm not an expert either, but according to the treatments I've seen on GR, the flipping of time and space inside of black holes is just an artifact of the choice of coordinates, and can be fixed by changing your coordinate system. However, there are some ideas based on holography for solving the black hole information paradox that posit that it doesn't even make sense to talk about the inside and outside of a black h…
One point that was made in the video was that inside a black hole, space is collapsing faster than light. This seems like more than a change to coordinate system? Doesn't this mean that time is also moving faster than light? Could time effectively become "solid" at the singularity, with all events within the black hole's light cone at a single point in time, but in infinite space(ignoring Hawking Radiation)?
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After all the big discoveries (and personalities) of the 20th century, physics has seemed to be relatively quiet lately. So people are eager for the next big and dramatic change to our understanding. And that's what George Chapline is offering the pop sci press.
If what LIGO achieved is not loud enough for the 21st century, then we are probably doomed. It is a NEW kind of telescope that has not even been utilized for 1% of its potential. PS: I'm not arguing with your statement, you have all the right to think that way. Maybe even people who lived during Einstein's earlier times thought the same for their previous century.
The problem is that it is REALLY hard to describe to the layman just how excruciatingly difficult it is to do what LIGO does.
I like to think that I know a thing or two about electrical engineering and quantum mechanics, and even I probably don't get just exactly how amazing LIGO is.
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If what LIGO achieved is not loud enough for the 21st century, then we are probably doomed. It is a NEW kind of telescope that has not even been utilized for 1% of its potential. PS: I'm not arguing with your statement, you have all the right to think that way. Maybe even people who lived during Einstein's earlier times thought the same for their previous century.
Yes, and there are also neutrino telescopes. I wait for the detection of an high energy neutrino event from beyond the CMBR. I think the opportunity, our understanding of physics and technology give us right now are immense. The fact that general relativity and quantum mechanics havent been reconciled by now only means that this is probably a very hard thing to do. But it doesn't mean that 'phyics is dead'. [0]: http…
My (non-physicist) understanding of this, is that neutrinos from then will be quite low energy now, due to the expansion of the universe(?), and so not detectable by the method IceCube uses. There is a minimum energy required, in part because the charged particles generated by the neutrino interaction need to be moving faster than the speed of light in water (or whatever the detection medium is) for there to be Cherenkov radiation generated and then detected.
That said, I would love to see a response from a more knowledgeable person!
I've seen a couple of articles about this guy recently and they both struck me as weirdly credulous given the apparently complete lack of evidence supporting his theory and the fact that approximately no other scientists seem to find it credible.
Here is one of his recent papers: Emergent Relativity https://arxiv.org/pdf/gr-qc/0302028.pdf
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Yea that's a part of the string theoretic calculation, that some of these higher dimensions are different than the three we're accustomed to. They're curved and swirled and weird. It's pretty unclear that they're real, but it's an interesting idea
Indeed. The usual layman example is that a string has two dimensions when you're close enough to it that it resembles a cylinder, but only one when you zoom out far enough that it becomes a line.