## Gravity-temperature musings by Toffo

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schapel
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:Does the radiation not gain energy on it's way down, and does that not decrease the time to heat the pizza to appropriate temperature?

No, photons do not gain energy as they're traveling towards a black hole. Energy is conserved. When an object falls, its potential energy is converted to kinetic energy, but the total energy remains constant unless something does work on the object. I think as a photon approaches a black hole its wavelength becomes shorter, but the energy for this to happen came from the potential energy that was already present in the photon.

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### Re: Gravity-temperature musings by Toffo

Toffo wrote:
gmalivuk wrote:Viewed from position p, it takes the same amount of time to heat the pizza according to your own argument (you just said the pizza spends 5 minutes where time dilation is 2, which works out to looking like 10 minutes from position p).
Nothing was viewed from the point of view of the pizza ... the 5 minutes heating time is 2.5 minutes heating time according to the time dilated pizza.
Then you're simply wrong about what happens, even in your incorrect view that Hawking radiation comes from the event horizon. (As I've said numerous times, if it came from the horizon itself, it would be infinitely dilated and those photons would never leave.)
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Toffo
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### Re: Gravity-temperature musings by Toffo

schapel wrote:No, photons do not gain energy as they're traveling towards a black hole. Energy is conserved. When an object falls, its potential energy is converted to kinetic energy, but the total energy remains constant unless something does work on the object. I think as a photon approaches a black hole its wavelength becomes shorter, but the energy for this to happen came from the potential energy that was already present in the photon.

I kind of like that way of thinking. What happens to energy of an object that is lowered down using a winch? What happens to energy of an object that is lifted up using a winch?
Last edited by Toffo on Mon Jan 04, 2016 4:56 am UTC, edited 1 time in total.

SDK
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### Re: Gravity-temperature musings by Toffo

That's work: the force of the winch has now been applied over a distance.
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Toffo
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### Re: Gravity-temperature musings by Toffo

gmalivuk wrote:As I've said numerous times, if it came from the horizon itself, it would be infinitely dilated and those photons would never leave.

Interesting point there. Energy cannot move faster than the speed of light, so if energy in an object falling into a black hole is ever going to come back from there, then the energy better not follow the object.

If there's lot of energy inside some radius, then a black hole forms, after that no energy is inside that radius and no energy enters inside that radius. This way all energy is able to radiate away.

So Hawking radiation comes from somewhere ... let's say from radius 2R, it comes from there and it propagates to an object hanging near event horizon ............. and the object is fried.

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### Re: Gravity-temperature musings by Toffo

You should not make the big smiley face, because you have painted yourself back into a corner where you are reaching a conclusion which you have been repeatedly told is wrong. You seem eager and delighted to find ever new ways to be wrong. Why is this? This is trouble.
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Toffo
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### Re: Gravity-temperature musings by Toffo

Hey here's some kind of argument why objects hovering near event horizon get fried:

An object hovering near event horizon receives some radiation, the energy source of that radiation is the black hole.

It's important to realize one thing: You can't accelerate the evaporation of a black hole, doing so would violate laws of thermodynamics.

So putting energy absorbing objects near a black hole must decrease the energy that radiates to infinity from the black hole. Now if the radiation absorbing objects absorb all energy that the black hole emits, the objects absorb energy at the same rate that the black hole emits energy. Which rate feels very fast for such objects that are very time dilated. Right?

gmalivuk
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:Hey here's some kind of argument why objects hovering near event horizon get fried:

An object hovering near event horizon receives some radiation, the energy source of that radiation is the black hole.
No.

How many times do we have to tell you Hawking radiation doesn't (and logically can't) come from the horizon itself?
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Toffo
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### Re: Gravity-temperature musings by Toffo

A black hole stores all information that is in the stuff that the black hole absorbs on the event horizon of itself.

The stuff must contain the energy needed to store the information in the stuff, I mean enough energy to create new event horizon area, where the new information can be stored, must be in the stuff.

So, not very surprisingly small black holes don't absorb long wavelength radiation.

But what if we store information in a radio wave by first producing a continuous wave and then cutting lots of holes of different sizes on the wave, and send that into a black hole? How does a black hole deal with that? I mean, that radio wave that we sent into the black hole has little energy and lot of information. Right?

gmalivuk
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### Re: Gravity-temperature musings by Toffo

If we cut lots of holes in a wave, we add a bunch of higher frequency features.
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Toffo
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### Re: Gravity-temperature musings by Toffo

Let's consider two drum solos with following macro states:

A: 100 hits on the drum, one minute duration
B: 100 hits on the drum, one hour duration

In drum solo B the pauses, or holes, between the hits have larger state-space, or how do we say correctly... there is more room into which the hits can diffuse, if some composer decides to move the hits around randomly.

For any reader wondering what is the point of this, let's say I'm trying to design a thing with high information content and low mass, and then I will try to feed that thing to a black hole. And the point of that is: To see how things work.

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### Re: Gravity-temperature musings by Toffo

Whatever analogies you want to come up with, it remains a mathematical fact that cutting holes in a long wave is equivalent to adding high-frequency elements to that wave.

For example, if you have a 1Hz wave, and you "cut holes" in it every 10ms, then you no longer have a 1Hz signal, you have a modulated 100Hz signal. And it takes energy to cut those holes in it.
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Toffo
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### Re: Gravity-temperature musings by Toffo

Of course we would do the hole making in a really smart way. Large holes with smooth edges, and so on and so forth.

But I have solved the problem: Let's say we play a drum solo on the membrane that is said to be one planck-length above the event horizon of a black hole. (just because the word membrane fits this drum analogy)

Every bit of information does not have to be recorded in the black hole, as there is Hawking radiation that can also record some information, particularly about long compositions.

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### Re: Gravity-temperature musings by Toffo

If they're long holes with smooth edges, then you're not adding as much information and you're doing it at a lower frequency, but you're still raising the information, energy, and frequency of the wave. A modulated 10Hz sine wave and a modulated 100Hz square wave both carry a lot more energy than a simple 1Hz sine wave.

As for the broader information paradox, I somehow doubt you're going to solve it with thought experiments about drum solos...
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Toffo
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### Re: Gravity-temperature musings by Toffo

Question: Is it possible to capture 1 kg of Hawking radiation, then compress it to a small volume, then lower it to the black hole that emitted it, without increasing the mass of the black hole more than 1 kg?

In other words: Is Hawking radiation emission a reversible process?

I feel there may be some complaints about measuring radiation in kilograms ... 1 kg of Hawking radiation is that amount of Hawking radiation that causes a mass loss of 1 kg of a black hole that radiates that radiation.

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### Re: Gravity-temperature musings by Toffo

You'd be limited by your ability to capture the energy in the radiation.
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Toffo
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### Re: Gravity-temperature musings by Toffo

If I have some radiation in a container, I can extract energy from the radiation by:

If I do some 1 then I can do less 2.

What happens if I try to do 2 after doing 1? A physicist attached to the container will report that no change has occurred as the container was lowered.

Hmmmm ... the lowering takes so much time that a black hole emits more radiation than we are putting in ... or the radiation has to do work against the pressure of Hawking radiation if the radiation tries to expand. Something like that happens when we are lowering radiation into a black hole.

BUT what if we use an almost a black hole instead of a black hole??

Would a solar panel on the surface of a cool neutron star allow us to make electricity out of cosmic background radiation??

Hypnosifl
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:In other words: Is Hawking radiation emission a reversible process?

Yes, in the sense that if you put a black hole in a mirrored box, you can have an equilibrium where the black hole neither gains nor loses mass because the energy it loses from Hawking radiation is balanced by the energy it gains when those same photons later bounce off the mirrors and back into the black hole. This is mentioned on p. 4 here for example.

Toffo
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### Re: Gravity-temperature musings by Toffo

If an object is very entropic, lowering it into a black hole trying to extract all of its energy must somehow fail. The way it fails is that the event horizon moves towards the object, which reduces the energy we can extract.

That motion of event horizon is caused by the mass of the object. So if we could cut the object to many small pieces, lowering those pieces one by one would be a method to extract some extra energy. This attempt to cheat must fail too.

When we cut an entropic object to pieces we add energy to it. Potential energy. So if we pack lot of entropy in a small volume, then it's difficult for a piece of that entropy to leave that area. Do we agree?

Hypnosifl
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:If an object is very entropic, lowering it into a black hole trying to extract all of its energy must somehow fail. The way it fails is that the event horizon moves towards the object, which reduces the energy we can extract.

I don't understand, why would lowering an object into a black hole allow you to extract energy from it, regardless of what happens to the horizon? What specific energy extraction apparatus are you thinking of?

Toffo
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### Re: Gravity-temperature musings by Toffo

Hypnosifl wrote:I don't understand, why would lowering an object into a black hole allow you to extract energy from it, regardless of what happens to the horizon? What specific energy extraction apparatus are you thinking of?

Potential energy of the object is extracted when the object is lowered into a potential well by using a winch and a cord. Potential energy of a object with mass m seems to be mc2.

See this:
http://www.scholarpedia.org/article/Bekenstein_bound
Search word "cord" for a short discussion about extraction apparatus.

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### Re: Gravity-temperature musings by Toffo

But the energy you're "extracting" is just the gravitational potential energy, and why would entropy affect that?
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### Re: Gravity-temperature musings by Toffo

Also rest mass and potential energy are completely different things.
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Toffo
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### Re: Gravity-temperature musings by Toffo

gmalivuk wrote:But the energy you're "extracting" is just the gravitational potential energy, and why would entropy affect that?

The entropic object attracts the entropic event horizon. When the horizon and object meet, the object plunges into the black hole, and some gravity waves are emitted outwards, and much more of those waves go into the black hole. The energy of these waves came from potential energy, so there exists this inefficiency when trying to extract potential energy from a black hole and an entropic object.

If an object has entropy, then it has mass, which will hinder potential energy extraction, as described above.

If an object has entropy, then it has mass, which will make cutting the object an potential energy increasing process, if the object is also small.

There should also be something that hinders extraction of potential energy from objects that are entropic and large, I guess. ...Well these objects have the extra potential energy, so they have some extra mass, which deforms event horizon, which produces gravity waves, which are mostly lost into the black hole. So no problem here, I hope.

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### Re: Gravity-temperature musings by Toffo

Toffo wrote:
gmalivuk wrote:But the energy you're "extracting" is just the gravitational potential energy, and why would entropy affect that?

The entropic object attracts the entropic event horizon.
Are you treating entropy and mass as equivalent?
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Hypnosifl
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:
gmalivuk wrote:But the energy you're "extracting" is just the gravitational potential energy, and why would entropy affect that?

The entropic object attracts the entropic event horizon. When the horizon and object meet, the object plunges into the black hole, and some gravity waves are emitted outwards, and much more of those waves go into the black hole. The energy of these waves came from potential energy, so there exists this inefficiency when trying to extract potential energy from a black hole and an entropic object.

No gravitational waves need necessarily be emitted when things fall into a black hole--if you have a spherically symmetric shell of dust that contracts inward due to gravity until it falls through the event horizon, for example, no gravitational waves will be emitted according to Birkhoff's theorem.

Even for a non spherically symmetric case where gravitational waves may be emitted, why would you expect the energy we can extract to depend on the system's internal entropy? I think you are overgeneralizing from the fact that you can't extract as much work from higher-entropy systems than lower-entropy ones of the same composition. Think of it this way, if you have a bound system at some distance away from a source of gravity, the total number of states of the system should be possible treated as a product of (all possible internal states of the bound system)*(all possible positions of the bound system's center of mass in the external gravitational field, along with all possible states of electromagnetic and gravitational waves in the surrounding space). Since entropy is proportional to the logarithm of the number of possible states a system can be in, the total entropy of the system should be possible to treat as a sum of some definition of "internal" entropy which has nothing to do with the position in the gravitational field or waves outside the system's boundaries, and an additional "external" entropy due to the object's position in the gravitational field and the gravitational and electromagnetic waves around it, which might be emitted as it falls (in fact, from what I understand emission of radiation is absolutely essential for a system to continue to collapse after it has reached the size where it becomes "virialized", see here and here for details). It seems to me that these two types of entropy would be totally independent--and if your energy-extraction method depends only on converting gravitational potential to kinetic energy as in the cord-and-winch method you described, and not on converting any of the internal potential energy within the bound system, then it should be limited only by the second type of entropy, the first type of entropy due to the object's internal states should be totally irrelevant. The second type of entropy does increase as the object falls in and possibly emits electromagnetic and/or gravitational waves, but I don't think it would increase by a different amount when you drop in an object with low internal entropy than when you drop in an object with high internal entropy.

Toffo
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### Re: Gravity-temperature musings by Toffo

gmalivuk wrote:Are you treating entropy and mass as equivalent?

Well I thought about it - but no.

Edit:

Ok now I thought about it some more, and now I'm equating those things again: Entropy bends space and has inertia, that's why we say that black holes have mass. Also "potential entropy" bends space and has inertia. That's why we say a rock has mass.

If we have 1 kg of mass, then we potentionally have entropy: Bolzman's constant * 1 kg * c2 / temperature of a 1 kg black hole.

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### Re: Gravity-temperature musings by Toffo

Toffo wrote: Entropy bends space and has inertia

No.
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schapel
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:Ok now I thought about it some more, and now I'm equating those things again.

This is clearly wrong, as mass (or more correctly, mass-energy) is conserved, but the entropy of a system can increase (i.e. is not conserved).

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### Re: Gravity-temperature musings by Toffo

Hypnosifl wrote:No gravitational waves need necessarily be emitted when things fall into a black hole--if you have a spherically symmetric shell of dust that contracts inward due to gravity until it falls through the event horizon, for example, no gravitational waves will be emitted according to Birkhoff's theorem.

Even for a non spherically symmetric case where gravitational waves may be emitted, why would you expect the energy we can extract to depend on the system's internal entropy? I think you are overgeneralizing from the fact that you can't extract as much work from higher-entropy systems than lower-entropy ones of the same composition. Think of it this way, if you have a bound system at some distance away from a source of gravity, the total number of states of the system should be possible treated as a product of (all possible internal states of the bound system)*(all possible positions of the bound system's center of mass in the external gravitational field, along with all possible states of electromagnetic and gravitational waves in the surrounding space). Since entropy is proportional to the logarithm of the number of possible states a system can be in, the total entropy of the system should be possible to treat as a sum of some definition of "internal" entropy which has nothing to do with the position in the gravitational field or waves outside the system's boundaries, and an additional "external" entropy due to the object's position in the gravitational field and the gravitational and electromagnetic waves around it, which might be emitted as it falls (in fact, from what I understand emission of radiation is absolutely essential for a system to continue to collapse after it has reached the size where it becomes "virialized", see here and here for details). It seems to me that these two types of entropy would be totally independent--and if your energy-extraction method depends only on converting gravitational potential to kinetic energy as in the cord-and-winch method you described, and not on converting any of the internal potential energy within the bound system, then it should be limited only by the second type of entropy, the first type of entropy due to the object's internal states should be totally irrelevant. The second type of entropy does increase as the object falls in and possibly emits electromagnetic and/or gravitational waves, but I don't think it would increase by a different amount when you drop in an object with low internal entropy than when you drop in an object with high internal entropy.

A vehicle loaded with lot of low entropy fuel accelerates itself to speed 0.99 c - No laws of physics violated. Right?

A vehicle loaded with lot of high entropy fuel accelerates itself to speed 0.99 c - Laws of physics are violated, as entropic fuel energy turned into non-entropic kinetic energy. Right?

One example of high entropy fuel is black holes. Fusing black holes generates energy. Black holes are so entropic that only 1/2mc2 of energy can be generated from fuel with mass m.

You see the above is an example of the rule that you can not fuse entropic stuff and extract lot of energy. So as I have been saying there must always be some mechanism that prevents dropping entropic stuff into a black hole and getting too much energy out.

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### Re: Gravity-temperature musings by Toffo

What, in your own words, do you think "entropy" means?
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### Re: Gravity-temperature musings by Toffo

Entropy

Let's say we have a bucket full of hot water, and a bucket full of cool water. Now let's call those buckets fuel tank A and fuel tank B respectively. Now the energy in the fuel tank A has some 'entropy', as the temperature is not infinite, and the matter in fuel tank B has some 'entropy' as the temperature is not zero.

The 'entropy' in the fuel tanks will prevent us to extract all the energy of the fuel, where 'all' in this case means all the heat energy that fuses with the cool matter.

Fuel

Hydrogen - oxygen, that's a fuel, it can propel vehicles

Heat energy - matter without heat energy, that's another fuel, it can propel vehicles

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### Re: Gravity-temperature musings by Toffo

You have not explained what you think entropy means, you've just provided an example of some things with some entropy.

In particular, you have not said anything yet that supports your idea that entropy curves space, because the two buckets of water have exactly the same amount of rest mass, and it's energy, not entropy, that makes the hotter one have slightly more total mass-energy.
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:A vehicle loaded with lot of low entropy fuel accelerates itself to speed 0.99 c - No laws of physics violated. Right?

A vehicle loaded with lot of high entropy fuel accelerates itself to speed 0.99 c - Laws of physics are violated, as entropic fuel energy turned into non-entropic kinetic energy. Right?

Sure, if a system is at maximum entropy, it can't convert heat into linear kinetic energy of the center of mass using internal reactions alone, although some external force can still accelerate it.
Toffo wrote:One example of high entropy fuel is black holes. Fusing black holes generates energy. Black holes are so entropic that only 1/2mc2 of energy can be generated from fuel with mass m.

Where does that equation come from? It doesn't ring a bell. And when you say "fuel with mass m" do you mean the black hole has mass m, or the thing you drop into it has mass m? If the latter then you aren't really getting the energy from the black hole itself, but rather to the potential energy of the combined system that includes both the black hole and the thing initially at some distance away from it, and this combined system may not be at maximum entropy even if the black hole's internal entropy is maximized for its mass (see below for more on this point).
Toffo wrote:You see the above is an example of the rule that you can not fuse entropic stuff and extract lot of energy. So as I have been saying there must always be some mechanism that prevents dropping entropic stuff into a black hole and getting too much energy out.

But you can't consider the black hole alone, you have to consider the entropy of the combined system that includes both the black hole and the other system you want to drop into it. This combined system will have lower entropy when the system is at its initial distance than it does after it's been absorbed into the black hole (perhaps emitting some radiation as it is pulled inwards, so you have to include that radiation in the entropy too). And as I said before, the total entropy of the combined system involves a sum of A) the system's own internal entropy, and B) entropy due to its position relative to the black hole (the number of position and momentum states the system's center of mass can have at different radii and potential energies) along with entropy due to any radiation emitted. The total entropy of the system would also include C), the internal entropy of the black hole, although we can forget about this for now. My point is that when you say "dropping entropic stuff", you seem to be talking purely about A), the "internal" entropy of the stuff being dropped (whether it has internal temperature differences, for example). But since your method of extracting energy using a winch doesn't rely at all on converting any of the system's internal potential energy into kinetic energy, only in converting gravitational potential, the internal entropy is totally irrelevant, all that matters is B), which increases by exactly the same amount regardless of whether the thing you drop in has high internal entropy or low internal entropy. Do you disagree with this logic? If so, which is the first step in my argument above that you would take issue with?

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### Re: Gravity-temperature musings by Toffo

Hypnosifl wrote:But you can't consider the black hole alone, you have to consider the entropy of the combined system that includes both the black hole and the other system you want to drop into it. This combined system will have lower entropy when the system is at its initial distance than it does after it's been absorbed into the black hole (perhaps emitting some radiation as it is pulled inwards, so you have to include that radiation in the entropy too). And as I said before, the total entropy of the combined system involves a sum of A) the system's own internal entropy, and B) entropy due to its position relative to the black hole (the number of position and momentum states the system's center of mass can have at different radii and potential energies) along with entropy due to any radiation emitted. The total entropy of the system would also include C), the internal entropy of the black hole, although we can forget about this for now. My point is that when you say "dropping entropic stuff", you seem to be talking purely about A), the "internal" entropy of the stuff being dropped (whether it has internal temperature differences, for example). But since your method of extracting energy using a winch doesn't rely at all on converting any of the system's internal potential energy into kinetic energy, only in converting gravitational potential, the internal entropy is totally irrelevant, all that matters is B), which increases by exactly the same amount regardless of whether the thing you drop in has high internal entropy or low internal entropy. Do you disagree with this logic? If so, which is the first step in my argument above that you would take issue with?

Yes I disagree with that logic.

I have a computer simulation of an ideal black hole power plant somewhere, this kind of thing:

let there be two black holes and one empty energy storage device
loop until one black hole has zero energy:
calculate temperatures of black holes
calculate Carnot-efficiency of an engine when the two temperatures are those we calculated
take a little bit of energy off of the smaller black hole
add efficiency*energy to the storage device
add energy - the energy that went to the storage device to the bigger black hole
endLoop

print energy in energy storage device
print energy of the black hole with non-zero energy

Using my simulator I have found out that fusing two same mass black holes can release at most about half black hole's worth of energy. So the released energy is only about 1/4 of the total energy of the two black holes, not 1/2 as i said earlier.

doogly
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### Re: Gravity-temperature musings by Toffo

Simulations tell you nothing if you are encoding your misunderstanding of the physics into the algorithms.
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gmalivuk
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### Re: Gravity-temperature musings by Toffo

Toffo, you've explained how your (inaccurate and poorly designed) simulation causes you to disagree with Hypnosifl's conclusion, but you were asked which part of Hypnosifl's *resoning* you disagreed with.

It's clear you don't understand what entropy is or how it relates to gravitational energy, so you really shouldn't trust some old "simulation" you put together one time.
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Hypnosifl
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### Re: Gravity-temperature musings by Toffo

Toffo wrote:let there be two black holes and one empty energy storage device
loop until one black hole has zero energy:
calculate temperatures of black holes
calculate Carnot-efficiency of an engine when the two temperatures are those we calculated
take a little bit of energy off of the smaller black hole
add efficiency*energy to the storage device
add energy - the energy that went to the storage device to the bigger black hole
endLoop

What physical mechanism are you supposing to "take a little bit of energy off" a black hole? I know it's possible to extract rotational energy from a rotating black hole by the Penrose process, but I can't think of a method that would allow you to extract the energy contained in a non-rotating black hole (though you could extract potential energy from a combined system of a black hole and some mass far away by something-like the rope-and-winch method you suggested...likewise if you have a temperature difference between the Hawking radiation and some external system, that's another form of potential energy you could use to do work using a heat engine, but if the external system was hotter then it would lose heat energy and some would be converted to work while some would go to increasing the black hole's energy, and if the external system was colder than the system would heat up and no more work could be done by the heat engine once it reached the same temperature as the black hole).

Toffo
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### Re: Gravity-temperature musings by Toffo

Here's a mechanism, or whatever, of getting energy out of a black hole:

http://www.nature.com/nature/journal/v2 ... 030a0.html

Oh yes, maybe I should tell what my simulation simulates. We take one of those Hawking radiation reflecting containers, put one small and one large black hole in there and wait ... after some time small black hole has evaporated and big black hole has absorbed the evaporated radiation. As there is a radiation wind there, we can put a radiation wind turbine there and get some electric energy out of that contraption.

doogly
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### Re: Gravity-temperature musings by Toffo

Are you simulating general relativity and quantum field theory, or just two counters?
LE4dGOLEM: What's a Doug?
Noc: A larval Doogly. They grow the tail and stinger upon reaching adulthood.

Keep waggling your butt brows Brothers.
Or; Is that your eye butthairs?