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Comment by drx | Hacker News Reader

TFA says "they had heard and recorded the sound of two black holes colliding a billion light-years away" and "1.2 billion years ago".

And from the paper: "The source lies at a luminosity distance of 410+160-180 Mpcc corresponding to a redshift z=0.09+0.03-0.04.". (https://dcc.ligo.org/LIGO-P150914/public) Which corresponds to 1.337+0.522-0.587 billion ly (or between 750.2 million and 1.859 billion ly).

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Oops, missed that. Thanks!

Looks like there are roughly three million galaxies within a billion light years. Seems like lots of space for black hole pairs to live in. I suppose over the coming years, these gravity wave observatories will nail down just how common they are.

So that's wayyyyyyy outside our galaxy? Any idea how many galaxies fit into a 1 billion ly sphere around the milky way? I'm guessing a shit ton, which makes the detection of a bh merger seem more realistic to me.

That's some serious range!

It was mentioned during the press conference today that gravitational waves are not affected by interstellar/intergalactic dust the same way light is. In theory, once our detectors are good enough we should be able to use gravitational wave astronomy to peer all the way back to the big bang!

So, we'll finally be able to hear what god said at the start of the universe?

This is a beautiful premise for a mind bending book.

I'm sure He either said "let there be light" or "gee, that's funny...."

I'd prefer either "what does this button do?" or "shit, don't press that!".

Those are what you get when you figure out how to construct a machine that looks to the future and can hear what God says at the end of the universe.

"I clicked print and nothing happened!"

If these waves travel at the speed of light shouldn't the distance and time match up...?

Not if space time it'self is stretching while the light is in transit.

This would be true in a static universe, but, during the 1.2 billion years the waves have been traveling, the universe was experiencing accelerating expansion.

For example, the edge of the observable universe is about 46.5 lightyears away, while the universe is thought to be 13.8 billion years.

https://en.wikipedia.org/wiki/Observable_universe#Misconcept...

is about 46.5 lightyears away

I assume you mean 46.5 billion?

Yeah, thanks! I can't edit it any more, unfortunately.

That's around 1/60th the diameter of the observable universe!

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