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A comment on Black Hole Propulsion as Technosignature.

Re:Black Hole Propulsion as Technosignature by simonh on Thursday March 07, 2019 @12:47PM (#19330191)
The problem with firing lasers at a black hole light years away is beam spread. Using the biggest best telescopes we currently have, at our admittedly miserable technology level, the tightest beams we can project on as close a target as the moon are kilometres across. Even if we were to create a mirror as wide as a planet to create a beam, it would be many, many times that wide by the time it reached the binary system. It would be further diverged by the slingshot round the black hole (or neutron star), and diverge further again on it’s way back to the spacecraft. I don't see any way such a system could be made practical.
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Re:Black Hole Propulsion as Technosignature by survivaletc on Thursday March 07, 2019 @03:05PM (#19331755)
This is part of a short series on Centauri Dreams, starting with this article: https://www.centauri-dreams.org/2019/03/04/pondering-the-dys...

As it says in that article,

> Such concepts obviously imply an interstellar civilization capable of reaching the objects in the first place. But once there, the energies to be exploited would be spectacular.

The paper discussed in these articles is not proposing that we puny current Earthlings fire lasers at the closest binary black hole systems. It's exploring the possibility of getting close enough to such a system to make this technique useful.

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Re:Black Hole Propulsion as Technosignature by _Microft on Thursday March 07, 2019 @01:15PM (#19330515)
If you have the technology to reach the nearest binary blackhole ("you just have to pay the one-time fee of the cost to reach the nearest binary black hole system", at 16:12 min in this video: https://youtu.be/rFqL9CkNxXw?t=972 ), you can most likely deal with the mirror/energy harvesting problem as well.
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Re:Black Hole Propulsion as Technosignature by kristianp on Thursday March 07, 2019 @07:10PM (#19333962)
You would have to be fairly close to the black hole in question to do this. A distance of r=3 MG/c² according to Stuckey '93 [1], which is referred to in the paper referenced [2] in the article. Skimming the articles, I can't see any reference to how sensitive to error in aiming this would be.

[1] The Schwarzschild black hole as a gravitational mirror https://sci-hub.se/https://doi.org/10.1119/1.17434 [2] http://coolworlds.astro.columbia.edu/halodrive_preprint.pdf

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Re:Black Hole Propulsion as Technosignature by 781 on Thursday March 07, 2019 @02:12PM (#19331135)
A civilization using this method might not use optical systems to focus the beam like we do, but might individually fire precisely aimed photons.
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Re:Black Hole Propulsion as Technosignature by thatcherc on Thursday March 07, 2019 @02:27PM (#19331290)
You'll have a similar problem due to the Uncertainty Principle. Even a single photons will experience the same kind of diffraction as a beam of photons, limiting the degree to which you can aim it.
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Re:Black Hole Propulsion as Technosignature by rickycook on Thursday March 07, 2019 @03:58PM (#19332335)
assuming that we got that right and didn’t just misunderstand what we are seeing (or assuming that there’s no “side channel” to know how to correct for it)

we also can’t get to a black hole, so for this civilisation it’s safe to assume they have a significantly better understanding of physics than us. we don’t know what we don’t know

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Re:Black Hole Propulsion as Technosignature by gus_massa on Thursday March 07, 2019 @05:30PM (#19333228)
The reason that makes it imposible to avoid the dispersion even of a single photon is not technological, it's a theoretical reason. You can't solve it with more advanced technology, you must change the laws of Physics.

It is sure that the current laws of Physics are incomplete, and some may even be wrong, but this effect is so fundamental and the proof is so simple that I doubt it will change.

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Re:Black Hole Propulsion as Technosignature by arisAlexis on Thursday March 07, 2019 @06:46PM (#19333820)
why is our technology miserable? do you know of a better benchmark out there? if not I would assume this is the most advanced technology <ever>
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Re:Black Hole Propulsion as Technosignature by klyrs on Thursday March 07, 2019 @07:58PM (#19334219)
I work with physicists and engineers. The physicists think the equipment is miserable because it doesn't fit their idealized models. The engineers think that their tech is the best because nobody is doing it better. As a mathematician, I can see that both groups are consistent in the application of their assumptions, and both sets of assumptions have utilitarian foundations.
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Re:Black Hole Propulsion as Technosignature by simonh on Friday March 08, 2019 @02:13AM (#19335747)
This is literally a discussion about detecting interstellar civilisations using black holes for near light speed travel, and similar technologies we might develop in the future. I am posting in that context.
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Re:Black Hole Propulsion as Technosignature by arisAlexis on Friday March 08, 2019 @06:27AM (#19336649)
me too since we developed a framework to think about ways to detect more advanced civilizations than us that may not exist. My context is that we are very advanced. But you seem convinced that we are miserable and I guess our difference is pessimistic vs optimistic rather than objective.
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Re:Black Hole Propulsion as Technosignature by simonh on Friday March 08, 2019 @09:26AM (#19337695)
At every point in human history, current Human technology has been the best technology ever developed. It's a completely useless perspective because it always gives you the same answer under every circumstance that has ever existed.

The discussion we are having now gives an eternal objective reference point - the technology required to exploit the gravitational energy of binary black holes. How advanced would you say our current technology is, compared to that reference point?

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Re:Black Hole Propulsion as Technosignature by arisAlexis on Tuesday March 12, 2019 @05:09AM (#19366444)
I don't find this fruitful. Compared to infinite possible intelligence that creatures could conceivably reach either here or other worlds or machines, Einstein was extremely stupid. What good of a convo does it make?
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