I'm sorry but for the most part question simply doesn't make any sense, it's merely using big words without any indication they're understood, so I have no choice but vote to close as "unclear what you're asking". I would start by reading answers to questions on Astronomy tagged under black-hole and supermassive-black-hole first, since many of them are already discussing human experience, but there is no way that you could "fall into a black hole and experience it", and by the time you'd be able to "perceive" gravity gradient on your own body, you'd be long dead too.

Sorry about the big words, feel free to edit if you can make the question use simpler language. And thanks for the tags. I've looked at all the existing questions and nothing covers this in my view. I guess I'm interested in the timeline for a hypothetical "immortal" (or spacesuit-wearing) astronaut falling into a black hole. How long after being able to clearly see the lensing would you pass the event horizon? Why, for example, do you say you'd be long dead before you'd perceive a gravity gradient?

I'm happy to agree that this is probably on the fringes of the sort of questions this site is for, in which case I'd appreciate suggestions for a more appropriate site to ask it.

To perceive gravity gradient means you'd actually be able to detect different gravitational force on your own body, meaning e.g. different one in your own feet than in your own head. It does not mean that you'd simply feel increased gravity. Which you wouldn't anyway, if you're in free-fall towards the black hole. Problem with perceiving gravity gradient is that we don't have any sense for that, so it could only be inferred through other side-effects. Most of which would kill you before you'd be aware of any such gradient in those ~ 2 m (depends how tall you are).

Site to ask would likely be Physics, but I suggest asking it in a manner that you understand, so answerers can follow that and write answers accordingly. Strictly technically, human experience in space exploration is also on topic on Space Exploration, but again, the question should be answerable and clear. I have problems understanding what has gravitational lensing (microlensing?) to do with falling towards a black hole? And you also seem to misunderstand what "event horizon" is, which is clearly answered several times here on Astronomy.

Yep, that's my understanding of a gravity gradient too. It's those side effects, and the times you'd experience them that I'm interested in. By the time you feel a gravity gradient, you'd presumably be accelerating very quickly toward the black hole, so how long do you have left at that stage?

hey there ;)

Hi!

I'm confused about why you think I'm using words and terms I don't understand. Could you give me specific examples?

I obviously want to ask a clear question (and I don't wanna seem like an idiot...)

Perhaps you think this is a bad question (maybe in addition to being asked badly)?

Well "gravity gradient" for one, I'm not entirely sure you understand what would involve actually feeling it, it's not like we have any sensors for it. And by the time you'd "feel" like being pulled by your legs or something like that, you'd be long gone because of that gradient working on your entire body, including your brain... so... well, by the time you'd have a chance to develop a headache there wouldn't be anything left in the head to feel it with

I understand the "experience" of a gravity gradient would simply feel like a stretching of your body...

I feel pretty confident I understand that ...

@aaaidan your whole body, your internals inclusive... it wouldn't be "artificial gravity" but true gravity, every single particle with rest-mass larger than 0 would be affected by it

My question is about what you're saying there: that by the time you'd have a headache, your brain would be a mushy piece of spaghetti?

@aaaidan No, that'd come later, first you'd just lose consciousness due to lack of oxygen and too low blood pressure, and that would be way before you'd be able to "feel" it by any other means

Ah. So if you were in a space suit, say.

so ... no experience

@aaaidan doesn't matter, we don't have any anti-gravity suits

No, not an anti-gravity suit, a space suit.

you could reduce impact of pressure gradient, not gravity gradient

Yeah, so I guess I'm trying to put aside the fact that you can't breathe in space, and that it's deadly cold and depressurised.

by say using in-suit compression or alike

Yeah sure. The suit has an internal earth-like pressure.

And it's air conditioned, and all that.

I mean like fighter pilots use, whatever those are called, pressure garments I believe

Ah okay. Sure, maybe.

Do you think you understand my question though, now?

you could reduce impact of pressure gradient loss of rapid changes by simply reducing blood inflow to lower torso for example... but even then only for a few moments

"only for a few moments"?

How many moments?

@aaaidan I understand your question, but there's not much to answer in terms of "experience", you'd be dead before your point one

You'd be dead before being able to see the lensing?

What would kill you?

@aaaidan not long, a few 10 seconds perhaps? and it still wouldn't work against gravity gradient

@aaaidan reduced level of fluids in your brain

or a cardiac arrest, whatever would come first

Right - this is close to the sort of answer I'm looking for...

Do you think my question, as it stands, is clear enough to get these sort of answers?

And aside from that, do you think it belongs on astronomy?

@aaaidan The question isn't bad on its own, I just think you're overthinking it and suggesting some order that isn't really such as you put it. The second half of your points don't make any sense, there's nothing to "experience" past the event horizon, and even way before that. So any answers would have to deal with a lot more than is actually required.

Ah okay. I guess it was unclear to me that you'd definitely be dead before the event horizon, but thinking about it now that's kinda obvious.

I'd just ask it more in a sense "how close to a black hole would be a safe distance" and "what would you die of if you crossed that point"

but then it's not really for Astronomy

not that it ever was, mind you

Ah, good to know.

So, physics, you think?

space exploration?

@aaaidan physics only if you clearly define what effects you consider "unsafe" and at what level... you can't just ask for "when would I get a headache" but I guess you could ask "when would my cranial fluids start reducing to an unsafe (and you specify volume change, say in %) level if I'm in a legs first free-fall towards a black hole"

Cheers.

@aaaidan well human experience is OK on Space.SE, safety and health even, but I can't think of a good way to ask it in such a way that it wouldn't be considered "bike shed fodder" (sorry for the choice of words, I didn't coin them)

Heh, fair enough. It's a difficult question to answer definitively. Is that what mostly annoyed you about this question?

(if it's fair to say you were annoyed)

perhaps if you keep it simple enough, like in my short examples

@aaaidan it didn't "annoy" me, if it did I wouldn't be chatting here with you about it... I just think that some of the words chosen didn't make any sense or were misused, like for example "celestial sphere", "experience / feel gravity gradient", "cross the event horizon" in terms of "experience", even "falling into a black hole" again as an experience.

We do have some answers on what black holes are, and reading them should help you understand there is no way you'd be able to "experience" anything even way before the event horizon, which is the point at which not even light can escape the strength of the gravitational pull.

I feel reasonably confident about my usage of all those terms, though. Are you game to talk about them? We discussed feeling the gravity gradient before, as the sensation of your body being stretched...

@aaaidan There wouldn't be any "sensation" of it before it would be too late... think of it this way: you don't feel gravity because you're in a free-fall, but you would suffer effects of gravity gradient long before you'd be able to "perceive" it by any means that are naturally given to us. We simply don't have any sensors to measure it. My main problem with your question is actually that you base it around "human experience" which does by necessity require being conscious

Oh, right. I sorta get what you're saying now. That even a subtle gravity gradient would drain the blood outta your brain (or push too much up there, if you're going in head first) well before you would feel a "stretching" feeling.

Is that what you mean?

Small gravity gradients are fine, our body can deal with them, but we don't really "feel" them. So there's no conscious experience. Problem with falling into a black hole is however, that by the time the pressure gradient would be large enough to "feel" it (say as if someone was pushing on your legs), part of your body would experience time slower than the rest of it. Your body simply wouldn't be able to function. And that's way before that would even happen.

You have to remember we're only musing over a significant enough gravity gradient that it would be felt at length of your body... we're not talking about the ever accelerating velocity of your body falling towards a black hole. You wouldn't feel that as gravity at all, you'd be in a constant free-fall, you'd think it's just empty space and you're floating in it

Yep, I understand velocity can't be felt in free-fall. Just thinking about that time dilation thing...

(Now that may not be appropriate use of the term!)

@aaaidan heh, maybe time dilation gradient?

basically, you'd be asking "what curvature in spacetime can a human body tolerate"

Well, yeah I guess that's part of the question I want to ask. But what @astromax just said is particularly interesting to me:

So, given a heavy enough black hole, you could cross the event horizon and stay conscious (because the gradient would only be mild at that point)

But what you said before about the time dilation gradient ... that's another matter altogether. Is the time dilation gradient a function of the gravity gradient? Does a subtle gravity gradient necessarily mean time flows at a similar rate throughout your body?

@aaaidan in terms of distance yes, since we're talking about a change in curvature in a constant size body (well, hopefully more or less constant, but you get what I wanna say)

@aaaidan No

@TildalWave No?

@TildalWave Crossing the event horizon is necessarily lethal?

@aaaidan Yes, but that's irrelevant... you can't cross event horizon and even have consciousness, let alone keep it. Let's just just ponder on this quote off Wiki for a moment: "boundary in spacetime beyond which events cannot affect an outside observer"

so there is no information that can be shared beyond that point

@TildalWave Ah. That sounds like a bit of a problem for consciouness.

@aaaidan indeed

So ... what's the deal with that? If you're not torn apart by the gradient, why can information not move around normally?

I guess that's something I can try to research on my own.

well, you'd have problems way before that, but let's assume for a moment a micro black hole where you could approach relatively close to its event horizon without being affected ... but you really don't wanna step over that threshold

So that's kinda the thing about what @astromax was saying: the larger the black hole, the less dangerous the gradient up to the event horizon.

What is it about that threshold (other than you definitely can't escape) that's so special?

@aaaidan well yes, the event horizon radius would be much larger, so relative to its curvature, you'd be of a much smaller length

Are we sure that by "outside obvserver" wikipedia doesn't mean someone watching from a safe distance?

@aaaidan that doesn't change anything for how you framed your question. You didn't ask how it would look like to others, you asked how it would feel like for you that are on your way towards the black hole

for others, there would be significant time dilution and it would seem like you're really taking your time

and you'd become stretched (but not for you)

@TildalWave you'd appear stretched, yeah.

@aaaidan well eventually you'd be literally stretched, not just to the outside observer... but till a certain point your physics wouldn't change, everything would seem "normal"

@TildalWave Heh ... being literally stretched would appear quite different to "apparently stretched" I'd say...

up till the point your body could tolerate it, which is debatable because I'm not even sure something else could kill you before you lost intracranial pressure

@aaaidan you wouldn't care by then anyway, and your friends from the outside would see you just as before for up till they die of old age

well, depending on the mass of the black hole again

@TildalWave Yeah, I concede that point now I think - you'd be well unconscious before your skeleton was dismembered, etc...

@TildalWave Yep, what I'm wondering is that maybe that "information barrier" thing just means you can't possibly transmit information to objects not in the "falling" reference frame, or something. You know? It just seems like a weird discontinuity in ... physics.

At the time you cross the horizon of a really large black hole, although the gradient isn't dangerous, you are travelling at some ridiculous speed... Surely your frame of reference is intact as you cross the horizon?

This is where even I would say I'm out of my depth...

@aaaidan It is, and it's not an easy concept to wrap one's head around so yeah, we see many such questions, some specific enough to be answerable, some too broad or speculative (yours?), and some really ... well, you know. Yours is intriguing in a way, but when I was considering posting an answer, I simply didn't know where to start. So one way would be splitting it into smaller chunks, or just using less words so answerers have less to "trip over" ;)

@TildalWave Great advice, thanks. I needed to ask a question about how to ask a question, it seems.

@TildalWave Although, @astromax seems to think he understands enough to write an answer. It'll be interesting to see if it's satisfying... ;)

@aaaidan Well we could certainly use more questions, but that's not why I suggested it... what I meant is, when you're asking a question and you realize you're not sure about one point you're using in it to demonstrate a problem, then stop, ask about that first. Otherwise there's too many things to address and you either won't get an answer because nobody would take the time for it, or it will be be closed as "too broad" or "unclear"

Most of this would fall into Physics scope tho, some might be suitable for Biology even (human physique, tolerance threshold, etc.) and if you'd be curious how to get there or how to protect yourself against X,Y then I guess Space Exploration

@TildalWave Right, I understand what you're saying I think: make sure you understand the components of the question you're asking. But I didn't feel uncertain about any points in my question. Maybe I should have been, which is another problem I guess. But you've not convinced me (yet) that I was misusing terms or phrases.

← 106 messages moved from Discussion between aaaidan and TildalWave

OK, now let's superping @astromax, see if he has a few minutes to spare :)

brb in 2 min

Ok... so now I thought it wouldn't be a bad question asking at what distance to a black hole would one lose consciousness... problem is, I'm not a medical expert so I haven't a clue how much of intracranial fluids one can lose (or putting it otherwise, what pressure change could one be conscious through) before losing consciousness

I think it's safe to assume we don't have to take compressibility of water into account, since there's plenty of body cavities that could expand to hold excess fluids way before that would be an issue

so the body would be not much more than a hermetically sealed tube filled with n% of liquids and the rest is sea-level air density of whichever gasses we don't care about for the physics of it

at least for maths that should suffice

I think the easiest would be to find some gee force on human body studies, or assume some reasonable arbitrary value, say up to 3 gee max

so... this leaves us with... at what distance to n-mass black hole is there a 3g gravity gradient over a distance of 2 meters

does that make sense?

@aaaidan ? I'm not sure if you had write access here before, but I've now added you to the list so you should now

@TildalWave Yeah that makes sense!

Those equations would probably well answer the parts about "feeling the gradient" and "reaching a lethal gradient".

Right, would you want to ask this over at Physics? Something tells me I forgot about something in my reasoning now, but I'm frankly too tired to see it...

Sure, will do.

@aaaidan well I'm pretty certain you'd lose consciousness when that'd happen, lethal would come a bit later... not too much tho

So ... that question, "how do I calculate the gravity gradient between two distances from a black hole" wouldn't belong on astronomy?

@aaaidan Try to be a bit more specific, ask about naturally found black holes that we know exist (to avoid speculation and so they have minimum mass to use in calculations)

@TildalWave I know it's a physics-heavy question, but "The study of celestial objects" seems to cover this well. Is astronomy more for telescopes and star-gazing?

@aaaidan not sure... perhaps if you found a way to make a case for it in the question itself that would apply to astronomy as a science, then yes, otherwise probably better over at Phy.SE

@TildalWave I wonder if asking this (astronomy-related) question at physics will be deemed too "high level".

@aaaidan No, black holes are on scope, but I'm not sure about the applicability / usability of any answers to such a question ... it's just not usable for astronomers. Unless you can make a case for it, that is

@aaaidan definitely not too high level

@TildalWave cheers

@aaaidan no problem ;)

@TildalWave Ah, so this is site has a practical emphasis?

@aaaidan Hmmm, no I wouldn't put it like that, not any more than any other SE site. For example cosmology is on-topic, theoretical astronomy, etc.

@TildalWave I find that a bit confusing, then that this "sub question" wouldn't be reasonably asked here?

problem is, when you put it like you first did, that it becomes more of a problem of human endurance, tolerance thresholds of human physique, which is biology. And after we've established those parameters, it's more or less just physics... and applicable to other cases than what an astronomer would be interested in too

Here's that sub question, btw... physics.stackexchange.com/questions/90581/…

@TildalWave Yeah, I kinda muddied the waters with the biological aspects, I see now.

@TildalWave But, biology aside, I'd say the physics of a black hole would fit more in "astronomy" than in "physics", no? I dunno. I could go either way...

More importantly, perhaps, you'd know better than me!

@aaaidan Could be here too IMO, but I'm just a single man, we're kinda running a democracy here LOL

Holy moley, stack exchange is amazing... that edit approval thing, mathjax, chat....

this is insane.

@aaaidan welcome to the club :) we're all insane here and it's contagious too

frankly, it is overwhelming at first ... but you eventually either start appreciating local culture and get drawn into it or you don't and you're just a passer by ... SE is a bit like marmite in that sense, but I find it for the good reasons so far. For example, if you didn't really care about your question, you'd just let it die slow death from neglect ... but you did care, and you'll get some answers, and some you perhaps already did

I'm here about a year, a bit less and I've learned a great deal on many things. Mostly what I'm interested in from before, but also on some that I didn't even know I am

Maybe we should rename this chat into "The Asylum" ? :)))

Sounds like a corrective psychology chat room to me...

talking of insanities, it's 7 a.m. in my stretch of the woods and I haven't slept yet ... again! (I do that often) So... @aaaidan you have a good time and I'll see you around ;)

Oh wow. I used to get to do that.

Night.

Or "sleep well"

Wakey, wakey. Anyone around?

@TildalWave Hi, I just checked Astronomy.SE right now, otherwise I would have attempted to respond quicker. This is the first time I'm participating in a discussion, so if I'm not responding in the correct way (responding to this comment rather than starting a new one at the bottom), please let me know. My response to all of this is though there are many things about black holes that are mysterious (namely, what happens after the event horizon) are all well and good,

(cont'd) but they are irrelevant to the question I believe @aaaidan is asking. The effects on different observers and the distortion on space and time due to these objects thought to be well known. One can ask how long it takes an infalling observer to reach the event horizon (even if it takes an infinitely long time and the infalling observer is infinitely redshifted according to another observer). One can ask about the tidal gravitational field and stresses it would put on the human body as

@aaaidan Compared to what? :-) scifi.stackexchange.com

(cont'd) somebody approaches (not crosses; I was careful not to say that originally) the event horizon of a black hole. These are all calculations we can actually do in cosmology are therefore are appropriate for this site - regardless of its hypothetical nature. Hypothetical doesn't necessarily mean it's a bad question. The foundations of scientific theory rest upon initially hypothetical questions which are then tested experimentally.

Hello @astromax. Welcome to The Revolution.

Why thank you. But, what do you mean when you say The Revolution? Am I missing an important pop-culture reference here? :)

@astromax Perhaps. I think I was actually confusing at least two different, unrelated references. I was actually thinking of "Welcome to the real world." from The Matrix and it came out wrong.

Thanks for checking in on the black hole question. And for using small words that those of us who are non-physicists can understand.

@Donald.McLean Ah, I see. Maybe you can answer this. Are there standard operating procedures in place on how to participate in these chat sessions? I'm assuming that since I was notified to the existence of a chat referring to something I said (by using @astromax), that these are not always real-time discussions.

@Donald.McLean Absolutely, I'm not an expert in black holes, but I do enough General Relativity to know that its effects upon space and time are known (though not necessarily simple to carry out) calculations. I try to make things as easy to understand without having to know every last bit of formalism and jargon.

@astromax You are correct in that chat is a temporally flexible construct. Feel free to participate in whatever way works for you. I tend to check in on chat periodically whenever I am on a computer for long periods (such as at work).

@astromax Formalism I could probably handle. My dad is a chemist and amateur mathematician. Jargon gets confusing though.

@Donald.McLean Excellent. I agree, Jargon is an important issue on sites like these. I bet that a substantial fraction of the comment section of questions and answers are due in large part to a disagreement of jargon. That's why I'm excited to see something like chat where these things can be hashed out. Anyway, that's just my two-cents. I'll wait for @aaaidan and @TildalWave to respond to my comment about why I think this is a relevant question for Astronomy.SE.

Jargon is good. Makes you sound smart :p

@ManishEarth You've obviously never had to work with someone who had a degree but was, nonetheless, a complete idiot.

@Donald.McLean He's still a student, everyone with a degree higher than his is either totally awesome at this point, or he's never heard of them :)

@astromax Oh I agree that a lot of what being asked in the question is relevant to Astro.SE, I never had any disputes regarding scope. But it was worded awkwardly, which might throw off course potential answerers and take a lot of their time to describe what he wasn't as interested in as some other points we later established during our chat. So what I primarily wanted to establish was what the question really is, without trying to suggest what I'd like to ask if it was mine. Quite tricky...

...especially since we later established that it hides many sub-questions in it that might be even a better fit for some other SE sites, since they're broader applicable than merely astronomy as a science (as wide as that might be in definition). Could be also asked here tho, after we cleared the biology / medical part of it.