Hacker News Reader

Comment by perihelions | Hacker News Reader

Huh, so you can hear things explode in space, after all. If you're close enough to a warp field doing funny things, the gravitational wave strain would create audible-frequency artifacts, as it wiggles your eardrums at frequencies close enough to the audible.

They derive an equation for estimated strain as a function of distance from the warp bubble collapse. How does strain translate to sound intensity, in the situation where a gravitational wave is driving sound pressure waves, and/or directly wiggling eardrums?

View on HN

One of the reasons I no longer ask questions on Physics stack exchange:

1. I asked "how powerful" such waves would have to be to be audible.

2. I directly linked to another question whose accepted answer said "these waves can wiggle your ear drum"

3. Got my question closed as a duplicate but the link was to different question that only asked "is it possible" (and accepted the answer "yes") without there being any answer to the "how powerful" part.

4. Got an answer which said "no, never".

Of course, I can now get an infinite supply of confusing contradictions from ChatGPT, and because I ask questions from a position of ignorant curiosity, I'm equally incapable of discerning which of the mutually incompatible responses I get is definitely incorrect regardless of if it comes from an LLM or a trained physicist.

The moderation on SE is abysmal, but it's the best moderation around for such a large, universally accessible, user-submitted knowledge store.

A better form of moderation exists in the form of whatever they were doing before, when you could ask a question and get an answer.

At one point SE was my most used resource. As of now I haven't used SE at all for I think four years. Why would you, when so much of the site's content is outdated and the moderators enforce that situation?

That's for sure. It's been... five, six years? Since last time I visited any of those sites and found relevant information. Not for lack of trying, but it's all outdated or incomplete.

I find that weird, so maybe we're in different spaces. SO often comes up with relevant answers to my queries, and I'll click them if they seem helpful. They aren't always available and when they are they aren't always useful, but I still end up on it at least once or twice a month.

"Marked as a duplicate of an outdated post" has been a common complaint since the 2000s, the only "before" was when the site was brand new.

I even checked to make sure I wasn't misremembering things - here's someone complaining about the same thing in 2011: https://old.reddit.com/r/programming/comments/cm02a/you_cant...

That doesn't really show that it was a common complaint given it accrued zero Reddit agreement points.

The situation now is also much worse than it was, because answers could be two years out of date then and beyond a decade out of date now.

I quit when I realised I would be scrolling by walls of jQuery answers for the foreseeable future if I kept using the site, not worth the waste of my time.

In the old days, moderators were encouraged to update the old post. Many stopped to do that when people complain their post were edited by others, or the votes goes to wrong person because it was edited.

I was an moderator in very early days.

Afaik, this is the policy since day one. It was aimed to be a FAQ site -- not just a question-answer site.. That's why it have community answer, allow the same poster answering his own question, encourage duping, allow other people to update/correct an existing answer,etc.

Back in those days:

1) Moderator knew the subject.

2) Most questions are "frequent" enough to qualify as FAQ.

3) When duped, the old answer is less likely to be outdated (because the site was new)

I worked this out once!

Gravitational waves obey the inverse-square law much like most radiation does (and subject to some constraints about weird spatial geometry, but most of their propagation is going on in open flat-ish space, so we can ignore that).

GW150914, the first gravitational wave observed, had an amplitude of about 4 times 10^-22 [1], i.e., differences changed by a factor of about that. Typical sound displaces the eardrum by on the order of half a micron or so [2], with the threshold of hearing at about 100 nm. The inner ear's shape is curved, but linear length is on the order of 10 mm [3] (it curves around so the total length is longer, but the gravitational wave would be transverse along its length).

A 100 nm displacement on a 10 mm length is a relative change of (100 x 10^-9) / (10 x 10^-3) = 10^-7, that is, 4 times 10^-17 times larger than the gravitational wave detected. That gravitational wave was emitted at a distance of about 410 Mpc [1], and so we can solve:

(d / 410 Mpc)^2 = 4 x 10^-17

d^2 = 4 x 10^-17 * (410 Mpc)^2

d = 2 parsec.

Granted, this is at the limit of hearing for a very brief sound (the sound was only in the human audible range for about a tenth of a second). You'd need to be perhaps 10 times closer - about 20,000 AU - for it to be a loud sound under these assumptions.

Of course you wouldn't be around to hear it for very long because you're 20,000 AU from one of the most energetic events in the cosmos, but hey, you'd hear a brief "click". Totally worth being vaporized.

[1] https://en.wikipedia.org/wiki/First_observation_of_gravitati... [2] https://biology.stackexchange.com/questions/79963/how-far-do... [3] https://www.verywellhealth.com/inner-ear-anatomy-5094399

4 times 10^-17 doesn't sound right... 2.5 times 10^14 I think?

EDIT: the CALCULATIONS are right, but they're based on an incorrect assumption. As a poster further down this thread corrects me, while the energy of a GW obeys inverse-square, the amplitude is just inverse. I can't edit my original post, but the corrected calc is here.

There is also a typo in my post where there's 10^-7 instead of 10^-5, but the calculations are done correctly.

That corrected assumption gives:

    d_audible / d_actual = 4 x 10^-17 x 410 Mpc = about 500,000 km

or about the distance to the Moon.

----

Strain drops off as 1/r, not 1/r^2

Oh. Well, silly me. I did double check that it's inverse-square, but apparently not deeply enough - the energy is, but the amplitude isn't. Which makes sense if I think about it a little more (it's basically a spring, so energy ~ displacement^2)

For other readers, this poster's correction is right, here's an astronomy SA thread on it. https://astronomy.stackexchange.com/questions/34761/why-does...

I swear, the one time I try posting outside my areas of expertise :D

Sorry I hyperfocused on the value but it's really the context which makes it confusing:

> 10^-7, that is, 4 times 10^-17 times larger than the gravitational wave detected

which doesn't sound right. (Like saying "X is 0.1 times larger than Y" when X = 10Y.) The ear displacement is 2.5×10^16 larger than the gravitational wave, no?

(Also I think 10^-7 should be 10^-5 in the quoted phrase, as per your reply above.)

> (Also I think 10^-7 should be 10^-5 in the quoted phrase, as per your reply above.)

Yeah, you're right, I had a typo in one of the intermediate numbers (the rest of the calcs used the correct number). Turns out I was just wrong overall though, not because of a typo but because of an incorrect assumption. Energy goes as 1/r^2, but amplitude is only 1/r, so the correct value is much smaller (it's about the Earth-Moon distance).

> 10^-7, that is, 4 times 10^-17 times larger than the gravitational wave detected which doesn't sound right. (Like saying "X is 0.1 times larger than Y" when X = 10Y.) The ear displacement is 2.5×10^16 larger

A is 2.5x10^16 larger than B is equivalent to B is 4x10^-17 larger than A, although I get what you mean by the phrasing being weird. "times the size of" would've been better than "larger".

> Totally worth being vaporized.

Agree. We should list of all kinds of similar endeavors. I volunteer to be dropped at PSR J0108-1431

This is the minimum for the drum to move, but sound is also about a frequency no ? Do gravitaional waves have the right one ?

They do. The signal in question peaked at around 250 Hz, so in the bass range of human hearing.

But as noted in other posts the post you're replying to was based on an incorrect assumption - there's a corrected value in one of the comment threads, and the distance for it to be audible is much closer than originally posted, roughly the Earth-Moon distance.

On this point I recall when the gravity wave detector first detected a black hole merge, which is of course a LOT of mass and power. It was in the hearing range so they played a .wav. It unironically sounded exactly like a "PLOP" drop of water falling in a bucket - an irony that such a big event and a small event sound so similar.

This is both not surprising and surprisingly amazing

Why would you ever consider asking an LLM a question like this though? They just make plausible-sounding things up, even if sometimes they're correct.

If you tell it to use wolframalpha it could probably do some ballpark spherical cow physics.

Amazing comment for two reasons:

The idea of asking an LLM to generate code for a more rigorous but still high-level language is under-explored. This way you can experiment with AI - but at least have an intermediate code artifact that you can review and test before it gets published! Exposing the raw token stream is reckless.

I had never heard of "spherical cow" science before but I love the imagery.

You really are one of today's lucky 10,000!

For anyone else: https://en.wikipedia.org/wiki/Spherical_cow

Meta reference: https://xkcd.com/1053/

Because with an LLM you can walk away confused for only a fraction of the frustration and time of the old way.

Why? Same reason I'd ask a student in the second year of a degree — knows more than I do.

> They just make plausible-sounding things up, even if sometimes they're correct.

This is indistinguishable from my experience described above.

I think the point of the comparison with LLMs was to disparage StackExchange, I don't think they disagree with your view of LLMs

It was closed as a duplicate because you asked 3 separate questions in your post, and the most prominent one (the title) was a clear duplicate of the original. I doubt it would have been closed if you had asked only "how powerful would the waves have to be?"

It's the same cognitive disconnect that comes up with Wikipedia and Debian too.

People often add more facts to Wikipedia and complain when they get deleted. The misconception is that wikipedia is where facts go, whereas, Wikipedia is specifically trying to be a tertiary source, where all the facts can be traced back to primary sources and all the analysis can be traced back to secondary sources.

People often complain that Debian testing gets almost no updates at all for six months every two years. The misconception is that it's a general rolling release distro, whereas, testing is specifically trying to become the next stable release and needs to have a freeze period.

People often complain that stack exchange deletes their questions. The misconception is that it's a site to ask a question and get an answer, whereas, stack exchange is specifically trying to produce a 1:1 mapping between specific questions and answers.

There's a saying in business that "you're not in the business you think you're in; you're in the business that your customers think you're in". If any of the above wanted to pivot, into what their less-informed users think they are, they'd do great at it, but their (sometimes inconvenient) organizational goals are what produces the high quality that made them all popular in the first place.

> ...produces the high quality that made them all popular in the first place

Agree with everything you said in general, but you lost me at the very end in the context of this thread. Hard to equate Stack Exchange as a "high quality" destination. It was probably true in the first few years after inception, but years of tug war between "the business they think they're in" vs. "the business their users think they are" have made a terrible experience for said less-informed users.

When given an alternative (e.g. LLMs, ironically probably trained on their own content, but without the snarkiness and self-righteousness of their mods), users seem to be voting with their clicks [1].

[1] https://meta.stackexchange.com/questions/387278/has-stack-ex...

> but their (sometimes inconvenient) organizational goals are what produces the high quality that made them all popular in the first place.

Plainly not true for either Wikipedia or Stack Exchange. The rules came later, once the rules lawyers showed up to help everyone understand that those sites needed to change because they were too useful for people. This might be ancient history, but the debates that raged on for the Wikipedia editors are important. There were people who thought Wikipedia should be what we all think it should be, and they'd been there since the beginning... but they were more interested in adding missing content to Wikipedia. The exclusionists though, who to a much lesser degree hadn't been there since the beginning, thought it more important to be more prestigious than Britannica, a paper encyclopedia, for their own egos or something. And they formulated rules that they believed would get them there. And more or less the same thing with SE, though it's a private business and less a open source project than Wikipedia. Every once in awhile you'll find a 15 or 20 year old question/answer, and you'll be gobsmacked by how just "nice" it was. There was room to go off topic a little, room to provide solutions rather than answers, and so on. Though, many of those are getting deleted now days. Wouldn't want the replicants to get any ideas about how SE is supposed to work.

The disconnect is that when the core group of users was much smaller, those places acted to some extent like a real world community of people, even if no one knew anyone and no one recognized anyone else's face. Because they were a community, people wanted to be helpful. If someone had a question that was difficult to find the correct wording for, others were willing to interpret and answer the interpretation. They really wanted to be helpful. But now the group of users is much too large, and instead of wanting to be helpful, they want to compete. No one can rack up 400,000 reputation being helpful. They can't rack that up if others are being helpful. And it doesn't feel like a community, so they don't ever feel like they should be helpful.

What a horrible policy to classify as dupe the more informative question. A better approach would be to close the original question instead, with the original answers merged, color coded, and inserted the original question as a quote block at the top.

>I no longer ask questions on Physics stack exchange:

Lately, on the science fiction stack exchange, they've been opening new questions that are duplicates, then closing my old questions/answers as the duplicate, so they can point farm their own newer ones that naturally get more traffic while making sure mine are dead and can't get more upvotes. When you check dates, mine are all timestamped years before theirs.

I do remember the day Stack Exchange was announced (on reddit maybe), and I thought to myself how great it would be compared to Expert Sexchange... little did I know.

Sometimes I like to go on StackExchange, find questions I'm deeply knowledgeable in and where people are saying things like "it can't be done" and reply with a code example doing the thing.

I find it deeply pleasing when I witness this in any domain. It's like watching a magic trick :)

I really don't understand how people can answer questions they are not 101% sure of the answer, on a public site like that. I mean, informal chat with a colleague? Sure. But to go on SO and do it, it's unthinkable for me.

If they're like me (I'm weird, but I think in this case it's likely), then they may be both confident and wrong at the same time.

My brain doesn't seem to index many examples of my own wrongness, even though I have more than once thought "this would be a good mistake to remember", and the worst that I can remember is under an NDA (very confident and very wrong), so the only example I can give is a currently ongoing personal error:

I've spent the last 5 years improving my German substantially, but the whole time I've been trying to estimate my current skill level and gotten the same answer, B1.

While LLMs and people are questionable in their ability for one-shot answers to complex things, with an LLM you can at least ask questions ad-nauseum all the way down the tree, ask for sources, ask it to be self-critical, think step-by-step, etc. From there, you'll at least be armed with more knowledge to ask better questions, whether to an LLM or a person. I think it's also a good exercise in figuring out how to break complex things down into smaller parts, and figuring out what questions to ask -- especially important if it's something where you barely know where to start.

Humans have a tendency to over-value their personal experience and cite their limited knowledge sets, beliefs, and intuitions as fact, and will probably tend to only show you the info that aligns with that.

I guess I'm biased, but for the most part, I don't think the error rates between people and LLMs are significant enough for me to want to deal with the human ego, versus an AI with infinite patience. There are certainly equally intelligent and gracious people, but I don't think they hang out much on Stack Exchange (or much of the popular internet, really)

Gravitational waves would "wiggle" all of you the same way, so not sure how they would do something different for one part of your body, so you could hear it.

Would it even wiggle the eardrums relatively to the rest of your head? Intuitively it seems that would only happen if the wavelength is exactly right, but at that wavelength the frequency would be inaudible because the speed of light is so high.

It can move soft tissues relatively to the skull bone, resulting in changes of pressure detectable by eardrums.

So those whooshing sounds of spaceships in sci-fi movies/series were real after all ...

But surely it isn't wiggling the tissues by sound waves passing through matter, but by vibrating space time itself?

The skull shouldn't be able to resist gravity waves any more than soft tissues or 10km of lead?

When a gwave passes through, since the space contracts or expands, you get changes in density, since bone and soft tissue are different densities, there should still be a pressure differential that can be heard.

It does not directly change density of matter afaik, only exerts gravitational pull, same as Earth does, and that in turn influences the body. But unlike Earth's it rapidly changes in magnitude and direction.

I imagine the sound of the hull + everything else shuddering would probably dominate the perceived sound from eardrums or direct excitation of the air.

The hull is in a vacuum, and so are the eardrums.

What part of the question or the premis stipulated that the eardrums are in vacuum? Who cares if the eardrums of a dead human vibrate?

The hull and all other parts of the ship or suit around the eardrums would all also vibrate.

The idea is that the eardrums are not vibrating due to the air - so such medium is irrelevant to the question.

GP specifically said "hear things explode in space".

can't argue with that

If we are talking about manned spacecraft, I would expect the interior of the hull to be held at 1 atm.

> the gravitational wave strain would create audible-frequency artifacts

Pretty sure this is only true if the spaceship (or the disturbance it causes) is ~100 miles across, like neutron stars and black holes are. If it’s much bigger or smaller, the frequencies will be shifted correspondingly shifted.

This is stretching my imagination to a point where I don't have any practical understanding of the physics behind it.

Would the eardrum be "wiggled" in the same way as a normal mechanical wave? Does the gravitational wave apply force on the eardrum?

Can I touch a gravitational wave and feel it?

That ringing in your ears you get once in a while... ?

I'm curious about this, sometimes also when one ear suddenly sounds different for a short time.

That's one of the little hairs in your ear dying. You're literally hearing the sound of your hearing deteriorating.

Well, that or earwax.

Source? A brief perusal around the internet seems to indicate this is an urban legend.

> the gravitational wave strain would create audible-frequency artifacts

That reminds of a considerably softer-sci-fi plot device from Earth by David Brin, where (somehow) gravitational waves of the right "tuning" could kill humans (via some kind of Roche-limit or spaghettification phenomenon) but not most other living things.

Someone calculated that one of the LIGO detections (of a black hole merger) would have been audible from about 1 AU away. Of course, you would be fried, too. But it's still interesting.

Imagine how much ridicule would a SF author in the XX century will get for suggesting his characters "hearing" FTL ships arriving into their solar system.

Only if the characters take it for granted.

That's one of the few situations where some good expospeak can make things better. If it's established the FTL travel is specifically audible in that universe because of some gravitational eardrum-wiggling snenanigans, it would just be a perfectly valid, probably quite interesting mechanic in that universe.

In the late 90s and early 00s you could totally have handwaved a hard SF scenario where gravitational waves from a Warp drive. Einstein calculated gravity Waves in 1911, and we saw the first evidence of them in the decay of a 1970s binary pulsar. Alcubierre published his warp spacetime in 94.

So there would have been room for hard SF space opera authors to sell the idea, like Stephen Baxter, Peter F Hamilton, or Alastair Reynolds.

Granted, it's amazing that now we can actually /simulate/ the sound of arriving warp ships! I imagine this will very quickly show up in short stories!

Now Star Wars makes sense, thanks!

Reply on news.ycombinator.com