advanced_notions:black_hole
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advanced_notions:black_hole [2018/03/14 14:33] jakobadmin [Layman] |
advanced_notions:black_hole [2018/12/19 11:02] (current) jakobadmin ↷ Links adapted because of a move operation |
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| ====== Black Hole ====== | ====== Black Hole ====== | ||
| - | <tabbox Why is it interesting?> | ||
| - | |||
| - | <blockquote>Among those of us who think about space and time | ||
| - | professionally, black holes play a central role. [...] Beyond the fascination they hold for astronomers, | ||
| - | black holes are important to science for other reasons. They | ||
| - | are a central object of study for those of us who work on | ||
| - | quantum gravity. __In a sense, black holes are microscopes of | ||
| - | infinite power which make it possible for us to see the physics | ||
| - | that operates on the Planck scale.__ | ||
| - | |||
| - | <cite>Three Roads to Quantum Gravity by Lee Smolin</cite></blockquote> | ||
| - | <tabbox Layman> | + | <tabbox Intuitive> |
| + | {{ :advanced_notions:bhhorizon.png?nolink&400|}} | ||
| - | A black hole is a region of space and time where light cannot escape because gravity is so strong. This is possible because [[theories:classical_theories:special_relativity|light always moves with the same velocity]] in the vacuum and therefore cannot move so fast as would be required to escape the black hole. In addition, no object or thing can move faster than with this speed of light, and therefore nothing can escape a black hole. | + | A black hole is a region of space and time where light cannot escape because gravity is so strong. This is possible because [[models:special_relativity|light always moves with the same velocity]] in the vacuum and therefore cannot move so fast as would be required to escape the black hole. In addition, no object or thing can move faster than with this speed of light, and therefore nothing can escape a black hole. |
| As a result, no light and nothing else can emerge from the black hole. | As a result, no light and nothing else can emerge from the black hole. | ||
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| * A great discussion of Black Holes in layperson terms can be found in Chapter 5 of Three Roads to Quantum Gravity by Lee Smolin | * A great discussion of Black Holes in layperson terms can be found in Chapter 5 of Three Roads to Quantum Gravity by Lee Smolin | ||
| + | * See also the short video series by Minutephysics: | ||
| + | * [[https://www.youtube.com/watch?v=sgIqRwvaBw4|How We Know Black Holes Exist]] | ||
| + | * [[https://www.youtube.com/watch?v=t-O-Qdh7VvQ|The Unreasonable Efficiency of Black Holes]] | ||
| + | * [[https://www.youtube.com/watch?v=brmjWYQi2UM|The Black Hole Tipping Point]] | ||
| + | * See also [[http://mentalfloss.com/article/84683/black-holes-field-guide|Everything You Ever Wanted to Know About Black Holes]] by Dank Falk | ||
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| - | <tabbox Student> | + | <tabbox Concrete> |
| **Black Hole Entropy - Bekenstein's law** | **Black Hole Entropy - Bekenstein's law** | ||
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| <cite>Three Roads to Quantum Gravity by Lee Smolin</cite></blockquote> | <cite>Three Roads to Quantum Gravity by Lee Smolin</cite></blockquote> | ||
| - | **Hawking Radiation** | + | **Black Hole Temperature - Hawking Radiation** |
| + | |||
| + | //see also [[advanced_notions:hawking_radiation|Hawking Radiation]]// | ||
| In the beginning, many people did not take Bekenstein's ideas about the entropy of a black hole seriously, because of the following reason: | In the beginning, many people did not take Bekenstein's ideas about the entropy of a black hole seriously, because of the following reason: | ||
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| where $k_B$ is the Boltzmann constant, $c$ the speed of light, $G$ the gravitational constant, $\hbar$ the reduced Planck constant and $M$ the mass of the black hole. | where $k_B$ is the Boltzmann constant, $c$ the speed of light, $G$ the gravitational constant, $\hbar$ the reduced Planck constant and $M$ the mass of the black hole. | ||
| - | This formula shows why black holes are so important and intersting. In this little formula everything comes together: | + | This formula shows why black holes are so important and interesting. In this little formula everything comes together: |
| * Quantum mechanics, in the form of $\hbar$ | * Quantum mechanics, in the form of $\hbar$ | ||
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| where $M_\odot$ is the mass of the sun. In words this means that black hole with a mass equal to the mass of our sun would have a temperature of only $10^{-8}$ K. If the black hole is heavier, the temperature gets even tinier. | where $M_\odot$ is the mass of the sun. In words this means that black hole with a mass equal to the mass of our sun would have a temperature of only $10^{-8}$ K. If the black hole is heavier, the temperature gets even tinier. | ||
| - | <tabbox Researcher> | + | <blockquote> |
| + | Far from a black hole, spacetime is "flat" and you can calculate the configuration of quantum fields that we think of as "the vacuum" (empty space). | ||
| + | |||
| + | You can do the same thing for "empty space" near the edge of a black hole. | ||
| + | |||
| + | However, what Hawking did was show that the "empty space/vacuum" configuration near the event horizon was *different* from the one far from the black hole. Moreover if you started with fields in the vacuum configuration near the black hole, far from the black hole, they'd look exactly like a thermally radiating system. That is, by bending spacetime, the black hole made the vacuum itself radiate away energy. The source of this energy is the black hole's mass, and eventually this process (Hawking radiation) would cause the black hole to evaporate. And there is still so much we don't understand about what all this means. We still don't really know where the entropy of a black hole is coming from. But Hawking made the connection explicit: there is a black hole entropy, it's proportional to the surface area, and it's enormous. [...] (There's another way to describe Hawking radiation as "virtual particles near the horizon, one falls in, the other escapes." That's not even really morally incorrect, but its slightly more accurate to think of the vacuum changing.) Anyway, Hawking radiation allows one to show that the maximum entropy ANY volume can have is the entropy of a black hole contained in the volume. Since the entropy of a black hole is set by the surface area, this means the maximum entropy of a volume goes like the area. That's sort of nuts, because it means if I make a room 2x larger in each dimension, I can fit $2^3=8$ times as much stuff, but only 2^2=4 times as much entropy ("information" loosely speaking). So somehow, the information in volume is encoded in the surface area of the volume. This is the "holographic principle" and I don't think we have a great idea of what it means about how our Universe is put together. Anyway, Hawking radiation is a fascinating thing. And it is the opening step in a really interesting area of physics that seems to be saying something very deep about how the Universe works. I'm not sure what. | ||
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| + | <cite>[[https://twitter.com/physicsmatt/status/973780542452793344|Matthew Buckley]]</cite></blockquote> | ||
| + | |||
| + | <tabbox Abstract> | ||
| <note tip> | <note tip> | ||
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| | | ||
| - | <tabbox Examples> | + | <tabbox Why is it interesting?> |
| - | --> Example1# | + | <blockquote>Among those of us who think about space and time |
| + | professionally, black holes play a central role. [...] Beyond the fascination they hold for astronomers, | ||
| + | black holes are important to science for other reasons. They | ||
| + | are a central object of study for those of us who work on | ||
| + | [[theories:speculative_theories:quantum_gravity|quantum gravity]]. __In a sense, black holes are microscopes of | ||
| + | infinite power which make it possible for us to see the physics | ||
| + | that operates on the Planck scale.__ | ||
| - | + | <cite>Three Roads to Quantum Gravity by Lee Smolin</cite></blockquote> | |
| - | <-- | + | |
| - | --> Example2:# | + | <tabbox History> |
| + | [[https://arxiv.org/abs/1805.02302|Jacob Bekenstein and the Development of Black Hole Thermodynamics]] by Robert M. Wald | ||
| - | <-- | ||
| - | |||
| - | <tabbox FAQ> | ||
| - | | ||
| - | <tabbox History> | ||
| </tabbox> | </tabbox> | ||
advanced_notions/black_hole.1521034425.txt.gz · Last modified: 2018/03/14 13:33 (external edit)
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