[ExI] Gravitational Waves Detected By LIGO!
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
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
>> 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.
>> J ohn K Clark
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>> extropy-chat at lists.extropy.org <mailto:extropy-chat at lists.extropy.org>
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Future of Humanity Institute
Oxford Martin School
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