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5Algon's Shortform
3y
36
Book Review: To Explain the World
Algon7h20

Reading one of the articles on the site, I get the sense this guy has an axe to grind against Galileo. If I had to guess at my opinion after reading further, it would be that he's using asymmetric standards of evidence for arguments for/against the value of Galileo's work. 

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Algon's Shortform
Algon2d20

Some random notes on harvesting energy at stellar scales. Again, from Grand Futures.

 

Harvesting dark energy:
    Tying galaxies together: Anchor big rope to galaxies as they get pulled apart by dark matter. Build up elastic potential energy which can be harvested. Issue: inefficient. You get out < 10^{-39} times energy of rope. Needs negative energy density matter to give better efficiency. Not clear how you anchor rope to energy
    Letting particles expand apart: again, very tiny amounts of energy compared to mass energy of particles. So small it isn't clear if it's even a net return.

Dark matter: 
    Hawking radiation: takes a long time to see any returns. Very poor efficiency for black holes past 10^11 kg. Past that point, it is just neutrinos which are hard to capture. You can chuck in dark matter which isn't very usable and get interacting stuff back out.     

Neutrino capture:
    Lots of neutrinos running around, especially if you use hawking radiation to capture mass energy of black holes. So you might want to make use of them. But neutrinos are very weakly interacting, so you need incredibly dense matter to absorb their energy/convert them to something else. Too dense?

 

Some methods of extracting energy from ordinary matter using black holes.
  

 

Accretion discs: chuck in matter to orbit black hole, get very hot and transition into radiation. At most, 5% efficiency for stationary black holes, 43% efficiency for extremely rotating black holes. (With wormholes, you could get 51% efficiency). Very useful for converting matter we can interact with into energy. Not the most efficient but you don't need black holes to have angular momentum to do this, which is perhaps useful.

Penrose process: Extracts energy from angular momentum of black hole, a fair bit of which resides outside the event horizon in the form of frame-dragging spacetime. Have to drop in matter which gains energy, splits into new particles, some of which continue to fall in and others fall out. So not useful for dark-matter, which doesn't transition into ordinary matter. Has 20% efficiency at upper limits for the penrose process, but penrose like processes can get you >10x returns on mass-energy. But you need to use up the angular momentum of the black hole, which is boundedly large for a given mass. But you can get up to 50% for extremal charged black holes, and 29% for extremal rotating black holes. So this is good as long as you've got lots of spinning/charged black holes. Big black holes tend to spin reasonably fast, thankfully.
 

Black Hole Bombs: Another interesting way of extracting energy from black holes are superradiant instabilities, i.e. making the black hole into a bomb. You use light to extract angular momentum from the blackhole, kinda like the penrose process, and get energy out. With a bunch of mirrors, you can keep reflecting the light back in and repeat the process. This can produce huge amounts of energy quickly, on the order of gamma ray bursts for stellar mass black holes. Or if you want it to be quicker, you can get 1% of the black-holes mass energy out in 13 seconds. How to collect this is unclear. 

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James Camacho's Shortform
Algon3d20

I always liked this way of looking at the determinant. 

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That Mad Olympiad
Algon3d41

Wholesome. And at this point, I'd be happy if we got a future like this. 

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Stars are a rounding error
Algon3d20

Good catch. I meant when you dump in mass energy into a black hole, it eventually radiates it back out and about half of that radiation is stuff we can make use of: light, electrons, positrons, protons, neutrons etc. The other half is neutrinos.

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Don't Mock Yourself
Algon3d20

: ) I'm glad to hear that.

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Don't Mock Yourself
Algon5d62

Why? 

I agree the self-mockery is probably doing some work. But what it was ultimately doing for me, I could acquire elsewhere. Is the issue that you need to be able to come up with a replacement before you stop the self-mockery?

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I wasn't confused by Thermodynamics
Algon6d70

I agree with what you said. I'm curious what I wrote made you think I don't? 

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Buck's Shortform
Algon6d22

I'd be surprised if he had LW Rats in mind when he wrote that, but it's not impossible.

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What does it feel like to understand?
Algon7d20

Translation aids understanding, sure. I wonder if the graphical structure relating concepts in different fields determines what understanding feels like in each field.

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58Meditation is dangerous
6h
3
20Book Review: To Explain the World
1d
2
24Some astral energy extraction methods
2d
3
9Open Global Investment: Comparisons and Criticisms
2d
0
49What is Lesswrong good for?
Q
4d
Q
6
20Predictability is Underrated
4d
0
137Don't Mock Yourself
5d
14
26I wasn't confused by Thermodynamics
6d
3
20What does it feel like to understand?
7d
5
60Stars are a rounding error
8d
19
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