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Comment by ben_w | Hacker News Reader

Frustratingly, when I tried to ask on Physics Stack Exchange if you could hear a gravitational wave and if so how powerful it would have to be, I managed to simultaneously have the question closed as a duplicate with a link to someone saying “yes” without saying how powerful, and find the top answer on my question was “no”.

https://physics.stackexchange.com/questions/560833/could-a-h...

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Hi Ben, as the person who initially flagged your question as a duplicate, I'm sorry. I can see why this was frustrating. I'll try to provide a more detailed answer here.

According to a 1948 paper by Bekesy [0], a human ear can detect sounds through several mechanisms. In a gravitational wave, since the whole head would vibrate, sound would reach the ear by bone conduction through the skull. Fortunately, this also happens to be the most sensitive mechanism. The smallest vibration amplitude detectable by bone conduction is about 4 x 10^-9 cm at around 3 kHz. If a typical skull is about 17.5 cm from front to back, that gives a minimum detectable wave amplitude h (the fractional expansion and contraction of spacetime) of about 2 x 10^-10.

The frequency of the gravitational waves produced in a collision between a neutron star and a small black hole turns out to be pretty close to an optimal match for the human ear. To estimate the amplitude, the first black hole collision detected at LIGO produced a strain of about 10^-21 at a distance of 410 Mpc. (The events in the article were smaller, but within the same order of magnitude.) Thus, since the amplitude scales as 1/r, the gravitational waves from the collision in the article would have been theoretically audible at a distance of about 400 AU or 40 billion miles.

Alas, attempting to test this calculation experimentally would incur certain practical difficulties. Notably, you would be vaporized by gamma radiation from the collision several seconds before the gravitational waves became audible.

[0]: https://asa.scitation.org/doi/10.1121/1.1906433

Hacker News once again proving to be the king of social networks.

Or at least the royal court where you can bump into the squires and get your issue resolved without the plebeian bureaucracy.

This is amazing. What are the chances you'd find this?

Great reply!

Awesome, thanks for the detailed response!

why not post this answer to physics.stackexchange.com?

The question is currently closed, so I can't post a new answer. I voted to reopen it, and I've edited the title to focus on the aspect of the question that is not adequately answered by the duplicate.

Be careful when you do this. It is easy to want to change a question you can't answer into one that you can, but you really have no idea what the original poster was asking. I had a question changed into something extremely idiotic by dilettantes who thought they knew what they were doing.

Fortunately, the person who asked the question is here (me), and it’s cool :)

What got removed from my original was effectively “could a human even hear this in principle?”, with my thoughts at the time being “or would you require an gravitational wave intensity so great that the energy of the gravitational waves would be enough to spontaneously collapse into a black hole?”

400 AU from a (stellar mass) black hole-neutron star merger isn’t going to be that intense, and is therefore implicitly gives me my answer (even if the environment itself would be deadly for other reasons).

(400 AU is ~ 10x-15x the distance to Pluto)

>"Notably, you would be vaporized by gamma radiation from the collision several seconds before the gravitational waves became audible"

How much lead shielding would you need to survive such a thing? Would standing on the far side of an Earthlike planet absorb the gamma rays?

You'd need a lot of shielding. A planet is about the right order of magnitude, though it's still not clear that a human could survive. You wouldn't die of acute radiation poisoning; a few thousand km of rock would be enough to absorb the gamma rays. At 400 AU, you wouldn't immediately boil to death, either. Part of the collision-facing surface of the planet would be converted into plasma and ablated into space, which would insulate the rest of the planet from the worst of the heat.

My guess is that you'd still die from shock waves propagating through either the atmosphere or the planet itself, but it's difficult to predict the exact effects.

Could the black hole itself shield you from the radiation while but not the gravity waves?

In the right scenario the neutrinos would kill you. Aside from everything else. Read somewhere you would need a light year of lead to stop them

Are neutrinos produced in these mergers?

I think it was a super nova.

> I'll try to provide a more detailed answer here.

Maybe you could provide a more detailed answer THERE instead?

In the recent Netflix documentary, "The Edge of All We Know" about the project to capture the first image of a black hole, there is a segment where they talk about what two black holes colliding might sound like, and they play a simulation of that sound. It was quite interesting.

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