[ExI] Gravitational Waves Detected By LIGO!

Anders Sandberg anders at aleph.se
Thu Feb 11 17:16:20 UTC 2016

Depends on the number of civs per galaxy, and whether they are checking 
for black hole binaries. A rough calculation suggests that this could 
wipe out biospheres across a galaxy:

If we assume the energy release was around 10^50 J over a second, then 
the power per square meter at distance d is 10^50/(4 pi r^2) Watts. So 
the criticial distance if the danger power is P is r=sqrt(10^50/4 pi P). 
If we assume a megawatt/m^2 is enough to cause biosphere damage, then 
the distance is 298,000 lightyears. To wipe out more advanced 
civilizations I would expect a much higher P; for a gigawatt the range 
is 9,400 lightyears - bad in the central part of a galaxy, but not even 
covering it.

So if you are an optimist about civilizations, then you should expect a 
fair number to have at least had to flee over long distances from this.

I wonder if one can make a gravity wave powered sail? I doubt it, since 
most matter is too transparent to the gravity waves to get any decent 
coupling. But black holes sometimes get a 1000 km/s kick from mergers.

On 2016-02-11 16:34, Giulio Prisco wrote:
> I'm wondering how many zillions of sentient beings died as a result of 
> the black hole fusion event.
> On Feb 11, 2016, at 5:13 PM, John Clark <johnkclark at gmail.com 
> <mailto:johnkclark at gmail.com>> wrote:
>> On Sept. 14
>> ​ ​
>> at 4am the LIGO
>> ​ detector in ​
>> Livingston
>> ​ Louisiana  ​
>> detected a burst ​
>> ​ of gravitational waves, ​7 milliseconds later the LIGO detector in 
>> Hanford Washington detected the same thing. The possibility of this 
>> being due to chance is
>> vanishingly small
>> ​ . What they detected was 2 black holes circling each other at 250 
>> times a second, one was 36 times the mass of the sun and the other 29 
>> times. The entire signal only lasted for a fifth of a second.
>> http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html 
>> J ​ohn K Clark
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Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University

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