PDA

View Full Version : Is it possible to engineer anything useful with black holes in our universe?



Ryan Fenton
2009-Apr-14, 09:23 PM
First off, first time poster, long-time fan of Phil Plait - saw him at a James Randi Amazing Meeting, and have enjoyed his input every time I've seen him since.

I posted these questions over at the PhysicsForums.com forums on astrophysics, they linked me to the Penrose Process (http://en.wikipedia.org/wiki/Penrose_process), but that wasn't quite what I was looking for, then I remembered BadAstronomy, and was shocked I didn't think of asking here first, especially considering the science/fiction/physics connection!

Anyway, I'm working on making the backstory for a fiction I've been thinking about, and I'd like to get a better understanding of theoretical black hole physics for that story.

The way I understand black holes so far is that they have a position, a mass, a rotation vector (including speed), and a charge. They also eject (hawking) radiation effectively as heat, as a way of expressing entropy thanks to quantum particle interactions. The rate this hawking radiation escapes is fairly static compared to the mass of the black hole, meaning that small black holes can lose their entire mass quickly compared to larger black holes which can take longer to lose all their mass than the heat death of the rest of the universe.

My questions:

1. Can hawking radiation be directional at all, or is it only expressed as a temperature around a black hole with completely random output?

2. (related to 1) Is it possible for hawking radiation to impart any kind of velocity on a black hole, or are the effects of the radiation completely isolated from what is inside the event horizon?

3. Is it possible for any quantum tunneling or similar effects to target anything inside a black hole? Put in other words, if quantum particles involved in a black hole's interactions can force something out of the black hole, can a similar effect started out of a black hole have an effect inside?

4. Is there any theoretical use for hawking radiation? If a black hole can act as a "heat battery" outliving the rest of the output of the universe, could that long-stored heat energy purchased at great expense be used to lengthen the theoretical lifespan of the presence of solid matter in the universe, even if entropy takes it's toll the entire time? Would it ever be enough energy to maintain an orbit around a large black hole for any amount of matter?

5. Is there a maximum possible value for the charge a black hole can hold? Would this be enough for two or more long-lasting black holes to hold eachother out of range of their respective event horizons for a long period of time? Or would the same effect prevent further charged particles from entering the event horizon in the first place?

Basically, I'm wondering how a society/intelligence that was thinking about the extremely long term could possibly use black holes as engines to "refresh" matter and thus information for the maximum amount of time. Are black holes a viable way of "paying" entropy in order to stay in the game of existence longer than would otherwise be possible? Can one "aim" a black hole's facing or position using any outside effect, or are they totally isolated from anything we can affect behind the event horizon?

Thanks for any input!

Ryan Fenton

slang
2009-Apr-14, 11:47 PM
I'll take a stab at the questions, but I'm hardly qualified except for some enthusiastic reading... IOW don't take as gospel :)


The way I understand black holes so far [...]

Seems ok, I didn't see anything outrageous there.


1. Can hawking radiation be directional at all, or is it only expressed as a temperature around a black hole with completely random output?


I don't think there's any directionality to it, but maybe the magnetic field and jets do something with the created particles.


2. (related to 1) Is it possible for hawking radiation to impart any kind of velocity on a black hole, or are the effects of the radiation completely isolated from what is inside the event horizon?

If it's random as I think, and there's only the jet influence on them, then that jet action will probably cancel out on both sides. So, no.


3. Is it possible for any quantum tunneling or similar effects to target anything inside a black hole? Put in other words, if quantum particles involved in a black hole's interactions can force something out of the black hole, can a similar effect started out of a black hole have an effect inside?


I know nothing about quantum tunneling. Hopefully someone else may have something to say here :) I don't feel confident to say anything in response to question 4 and 5 either.

Hope this helps, if not to answer then at least to start discussion.

trinitree88
2009-Apr-15, 11:15 AM
Garbage disposal for PCB's, nuclear waste, and old teddy bears.:shifty:

TampaDude
2009-Apr-15, 11:48 AM
Garbage disposal for PCB's, nuclear waste, and old teddy bears.:shifty:

^ this

timb
2009-Apr-15, 12:29 PM
Surviving low-mass primordial black holes are energy sources. Two black holes can produce gravitational radiation, whatever that's good for. A lift that goes up and down to just above the event horizon could be used as an alternative to a refrigerator, or a cure for boredom. According to Wormhole dynamics in spherical symmetry (http://arxiv.org/abs/0903.5438), a blackhole can be converted to a wormhole, but I'd take that cum grano salis.

Cougar
2009-Apr-15, 03:46 PM
First off, first time poster, long-time fan of Phil Plait...

Welcome to the board!


The way I understand black holes so far is that they have a position, a mass, a rotation vector (including speed), and a charge. They also eject (hawking) radiation effectively as heat...

Hawking radiation, if it exists, doesn't come from inside the event horizon. It comes from near, but outside, the EH. It is a bit of tricky theorizing how it reduces the mass of and eventually evaporates a black hole. Eventually here means many, many times the current age of the universe.


1. Can hawking radiation be directional at all, or is it only expressed as a temperature around a black hole with completely random output?

Random.


2. (related to 1) Is it possible for hawking radiation to impart any kind of velocity on a black hole, or are the effects of the radiation completely isolated from what is inside the event horizon?

Isolated.


3. Is it possible for any quantum tunneling or similar effects to target anything inside a black hole? Put in other words, if quantum particles involved in a black hole's interactions can force something out of the black hole, can a similar effect started out of a black hole have an effect inside?

As mentioned above, Hawking radiation isn't coming out of the BH.


4. Is there any theoretical use for hawking radiation? If a black hole can act as a "heat battery" outliving the rest of the output of the universe, could that long-stored heat energy purchased at great expense be used to lengthen the theoretical lifespan of the presence of solid matter in the universe, even if entropy takes it's toll the entire time? Would it ever be enough energy to maintain an orbit around a large black hole for any amount of matter?

Hawking radiation itself is pretty theoretical. I'm not coming up with any theoretical uses of Hawking radiation....


5. Is there a maximum possible value for the charge a black hole can hold? Would this be enough for two or more long-lasting black holes to hold eachother out of range of their respective event horizons for a long period of time? Or would the same effect prevent further charged particles from entering the event horizon in the first place?

I could be wrong, but I don't think the charge of a BH is going to be overcoming the gravitational infall.


Basically, I'm wondering how a society/intelligence that was thinking about the extremely long term could possibly use black holes as engines to "refresh" matter and thus information for the maximum amount of time.

Kip Thorne, in his book Black Holes and Time Warps, Einstein's Outrageous Legacy [1994] puts forward (in a little sci-fi Intro) a way to use a very large black hole as an energy source. Sorry, I forget exactly what the mechanism was. :o It wasn't Hawking radiation.

rommel543
2009-Apr-15, 05:03 PM
The Hawking Radiation comes from a pair of particles/anti-particles, that physics theorizes, are being created all over the universe all the time. Normally this pair once created instantly destroys itself due to gravitational attraction. If the pair is created near the EH of a black hole, the anti-particle would be drawn to the stronger attraction of the black hole and destroy a particle in the BH. The now orphaned particle of the pair would then be emitted as thermal radiation.

An idea for the practice use of a black hole would be that of a dynamo. The extreme speeds in the ergosphere would do nicely to power a massive generator. The frame dragging also causes magnetic and gravitational waves which could possible power energy generators or possible galactic 'sling shots' that crafts could use to travel between galaxies.

Ryan Fenton
2009-Apr-15, 05:04 PM
Welcome to the board!


Thank ya!



Hawking radiation, if it exists, doesn't come from inside the event horizon. It comes from near, but outside, the EH. It is a bit of tricky theorizing how it reduces the mass of and eventually evaporates a black hole. Eventually here means many, many times the current age of the universe.


Yup - that's the exact aspect I'm looking for with my fiction. I'm looking for a plausible mechanism to use a black hole to act as a battery to allow matter to exist many times longer than the expected shelf life of matter in the universe.



Random.


I've heard that x-rays at least show a direction going out of black holes, is this related to such theoretical hawking radiation?



Isolated.
...
As mentioned above, Hawking radiation isn't coming out of the BH.


The way I understand the current amalgam of theories, the black hole, like the rest of the universe, is following a path to an entropy-exhausted state. The black hole, however, seems to bank it's mass into a single blob, and pays the cost of entropy over a much longer time.

Whether it's bunched strings reaching a stable state, or whatever, the current models show the black holes evaporating at a fairly constant rate (see the 1st law of black hole dynamics.)

Whether the radiation is "emerging" from the mass of the black hole or not, there is an interaction there between the pool of mass, and the radiation coming out.



Hawking radiation itself is pretty theoretical. I'm not coming up with any theoretical uses of Hawking radiation....


I'm wondering what a story one could tell to speculate on what can be done with those facts. Basically, if you've ever been annoyed by the misuse of science in a fiction, this is someone questioning what a good guess would be that isn't disingenuous - while still being speculation.



I could be wrong, but I don't think the charge of a BH is going to be overcoming the gravitational infall.


Yeah - that certainly makes sense. Charged fields and such aren't going to compete against something that pulls the very fabric of reality into a shape that traps light, over such huge distances.



Kip Thorne, in his book Black Holes and Time Warps, Einstein's Outrageous Legacy [1994] puts forward (in a little sci-fi Intro) a way to use a very large black hole as an energy source. Sorry, I forget exactly what the mechanism was. :o It wasn't Hawking radiation.


Most of the mechanisms I've seen have relied on throwing matter into the black hole to get some lesser amount of energy in return. In my fiction, I'm considering how to use output of a super-massive black hole to allow matter and information to continue to exist in the universe for a couple orders of magnitude longer.

Since I can't rely on a supply of matter, if there is any directional energy coming out of the black hole, then you'd have a potential long-term power source that can be used to do any number of things over time, assuming it is sufficient to allow a stable orbit for a given amount of matter, and enough energy to renew the matter being used.

If there's no useful directional radiation, and no plausible way to use the black holes, then that's fine - I can work with another universe if needed, it's just much less inspiring. I was just looking for input on what the best information we had so far.

Thanks again!

Ryan Fenton

rommel543
2009-Apr-15, 05:20 PM
I've heard that x-rays at least show a direction going out of black holes, is this related to such theoretical hawking radiation?

The x-ray emission is caused from the destruction of matter near the EH. As it's dragged around the BH the matter is being ripped apart at the atomic level and heated to plasma levels. This super heated matter emits the x-rays. There is also the gamma radiation emitted from the poles of the BH.

Ryan Fenton
2009-Apr-15, 05:59 PM
Thanks for the info - googled some papers, and did a quick read.

Hmmm... here's another dynamic following the same trend - black hole jets:

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/990923a.html

Basically, all these methods require a larger portion of mass to go into the black hole, in order to create a much lesser ejection of mass/energy in return.

The next best mechanism I can think of would be to simply accumulate potential energy, to refresh matter in a minimal fashion - but that would not scale well, and would only multiply the existence of matter a very limited number of times. This is because you'd have to "recharge" the matter of the batteries you use each time, leaving you with you with an extremely small fraction of the matter you had before each time.

Maximizing the long game for the existence of information is an interesting subject in any case.

Ryan Fenton

TampaDude
2009-Apr-15, 06:18 PM
The x-ray emission is caused from the destruction of matter near the EH. As it's dragged around the BH the matter is being ripped apart at the atomic level and heated to plasma levels. This super heated matter emits the x-rays. There is also the gamma radiation emitted from the poles of the BH.

So, I presume an advanced interstellar civilization could use those accretion disks as a power source, either by utilizing an existing accretion disk or creating one. The amount of power available from such an accretion disk generator would be enormous, orders of magnitude greater than the power output of our entire planet, would it not?

rommel543
2009-Apr-15, 06:23 PM
Honestly, if it's just a matter of energy collection then utilizing the power from a star would be far simpler than attempting to collect the energy from a black hole. I think the utilizing that power for other than energy collection would more likely.

TampaDude
2009-Apr-15, 07:00 PM
Honestly, if it's just a matter of energy collection then utilizing the power from a star would be far simpler than attempting to collect the energy from a black hole. I think the utilizing that power for other than energy collection would more likely.

Wouldn't the radiant flux from the accretion disk be greater for a given mass than that of a star? Just wondering.

rommel543
2009-Apr-15, 07:20 PM
If a race had the technology to collect energy from a black hole, I'm sure the output from it would be far greater than that of a star. I'm just saying it would be more practical to collect from the fusion energy of the star than the dynamics of the black hole. I'm just thinking that the requirements just to create and maintain the energy collection around the black hole, the race could create collectors around thousands of stars and still have less issues and equal energy.

TampaDude
2009-Apr-15, 07:32 PM
If a race had the technology to collect energy from a black hole, I'm sure the output from it would be far greater than that of a star. I'm just saying it would be more practical to collect from the fusion energy of the star than the dynamics of the black hole. I'm just thinking that the requirements just to create and maintain the energy collection around the black hole, the race could create collectors around thousands of stars and still have less issues and equal energy.

Okay...I see your point...Dyson Spheres FTW... :D

RalofTyr
2009-Apr-15, 11:11 PM
If you could reverse gravity, it would be a great accelerate.

Also, miniature black holes would make an excellent weapon.

timb
2009-Apr-15, 11:30 PM
The Hawking Radiation comes from a pair of particles/anti-particles, that physics theorizes, are being created all over the universe all the time. Normally this pair once created instantly destroys itself due to gravitational attraction. If the pair is created near the EH of a black hole, the anti-particle would be drawn to the stronger attraction of the black hole and destroy a particle in the BH. The now orphaned particle of the pair would then be emitted as thermal radiation.


That explanation is wrong. For one thing the force that draws subatomic particles together is not gravitation, and for another your explanation creates something from nothing. Adding antimatter to a black hole makes it more massive. You'd need to add particles with negative mass to make the black hole smaller.

Disinfo Agent
2009-Apr-16, 12:58 PM
Kip Thorne, in his book Black Holes and Time Warps, Einstein's Outrageous Legacy [1994] puts forward (in a little sci-fi Intro) a way to use a very large black hole as an energy source. Sorry, I forget exactly what the mechanism was. :o It wasn't Hawking radiation.Is the process mentioned in the article here (http://www.bautforum.com/astronomy/87066-lenticular-galaxy-reveals-spinning-black-hole.html) what you mean?

Cougar
2009-Apr-16, 07:58 PM
Is the process mentioned in the article here (http://www.bautforum.com/astronomy/87066-lenticular-galaxy-reveals-spinning-black-hole.html) what you mean?

Hmm. I don't think so, but I really just don't remember.

Cougar
2009-Apr-16, 08:38 PM
Maximizing the long game for the existence of information is an interesting subject in any case.

Well, I can only suggest more reading: Leonard Susskind's new (2008) The Black Hole War, my battle with Stephen Hawking to make the world safe for quantum mechanics. [Love that title!] I'm only about half way through, so I'm not sure how he defeats Hawking's early assertion that the information falling into a black hole is NEVER recovered....

Noclevername
2009-Apr-17, 04:52 AM
Long-term storage facility, using time dilation. You'd need a supermassive BH to minimize the tidal effects, with a minimal accretion disk, just whip something into a stable orbit and come back when you need it. Just make sure you have a quick-in-and-out plotted, or it may take a few millenia to retrieve your belongings...

rommel543
2009-Apr-17, 03:09 PM
That explanation is wrong. For one thing the force that draws subatomic particles together is not gravitation, and for another your explanation creates something from nothing. Adding antimatter to a black hole makes it more massive. You'd need to add particles with negative mass to make the black hole smaller.

My mistake, I was going by a simplified view of the Hawking radiation. It's the strong force that cause the particles to interact. However, the theory is that vacuum fluctuations in space cause the creation of the particle-antiparticle.


A slightly more precise, but still much simplified, view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes.
http://en.wikipedia.org/wiki/Hawking_radiation

timb
2009-Apr-17, 10:00 PM
My mistake, I was going by a simplified view of the Hawking radiation. It's the strong force that cause the particles to interact. However, the theory is that vacuum fluctuations in space cause the creation of the particle-antiparticle.


http://en.wikipedia.org/wiki/Hawking_radiation

There's nothing in the explanation you quoted about the anti-particle falling into the black-hole while the particle escapes. According to the standard model of Hawking radiation the emitted particles are as likely to be anti-matter as matter. The wikipedia article you linked to says



A slightly more precise, but still much simplified, view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle that fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process, the black hole loses mass, and, to an outside observer, it would appear that the black hole has just emitted a particle. In reality, the process is a quantum tunneling effect, whereby particle-antiparticle pairs will form from the vacuum, and one will tunnel outside the event horizon.

DrRocket
2009-Apr-18, 02:14 AM
Basically, I'm wondering how a society/intelligence that was thinking about the extremely long term could possibly use black holes as engines to "refresh" matter and thus information for the maximum amount of time. Are black holes a viable way of "paying" entropy in order to stay in the game of existence longer than would otherwise be possible? Can one "aim" a black hole's facing or position using any outside effect, or are they totally isolated from anything we can affect behind the event horizon?

Thanks for any input!

Ryan Fenton

There is enough controversy surround the details of black hole physics, including the information problem, that I think it is fair to say that any engiineering involving them is quite a long way off.

BUT, it is equally clear that they would make a wonderful resort for politicians.

Cougar
2009-Apr-18, 04:37 AM
A slightly more precise, but still much simplified, view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle that fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole).

These "simplified" and "slightly more precise" explanations of Hawking radiation seem overdone to the point of misleading, but I guess even Kip Thorne, Feynman Professor of Theoretical Physics at Cal Tech, says there are different ways to picture evaporation. He goes on to state that the tidal gravity near the horizon pulls the photons apart with a huge force, feeding great energy into them. The increase in photon energy is sufficient to convert them into real photons and have enough energy left over to give back to the neighboring, negative energy regions of space (where the virtual photons borrowed from). The photons, now real, are liberated from each other. One coincidentally falls in the hole, the other does not. The one that escapes carries away the energy (that is, the mass) that the hole's tidal gravity gave to it. The hole, with its mass reduced, shrinks a bit.

Cougar
2009-Apr-18, 04:58 AM
In reality, the process is a quantum tunneling effect, whereby particle-antiparticle pairs will form from the vacuum, and one will tunnel outside the event horizon.

I haven't heard this explanation before. Maybe I'm not well enough read, but every explanation I've heard or read discussing Hawking radiation has the virtual particle pairs appearing outside the event horizon. They don't come from inside the hole.

But I like the tunneling explanation. It seems a lot more straightforward than the "Hawking radiation" explanation, whichever it is. Tunneling was coined when experimental physicists kept detecting particles where they shouldn't be. Heisenberg uncertainty. Seems apt.

mugaliens
2009-Apr-18, 05:18 AM
Aside from the previously mentioned duty of a BH being the universe's most perfect toxic waste dumps, spaghettifying matter down to the subatomic level, they make terrific slingshots, particularly with two tethered masses, one of which drops into the black hole, slingshoting the other around it.

Of course engineering the tether that could withstand the stress is another matter...