B Can anything work (including human brains) inside a black hole?

[Manan]

TL;DR Summary

Popular descriptions say you could be inside a very large black hole (assuming you could shield yourself from radiation etc), but how is that possible?

Popular descriptions say you could be inside a very large black hole (assuming you could shield yourself from radiation etc), but things MUST move only one direction towards the singularity correct?

Meaning, let's say you're facing the singularity and your back is to the event horizon. Everything must move in one direction only - including air molecules, bodily fluids (e.g blood) and even electrical signals in your neurons. E.g you can't have a functioning system (not even electrical equipment, let alone a human body) where things are only doing in one direction. Your heart couldn't pump blood, your neurons would only conduct electrical signals one way? Or am I misunderstanding what happens inside (or even anywhere near) a black hole?

 

[PeroK]

TL;DR Summary: Popular descriptions say you could be inside a very large black hole (assuming you could shield yourself from radiation etc), but how is that possible?

Popular descriptions say you could be inside a very large black hole (assuming you could shield yourself from radiation etc), but things MUST move only one direction towards the singularity correct?

Meaning, let's say you're facing the singularity and your back is to the event horizon. Everything must move in one direction only - including air molecules, bodily fluids (e.g blood) and even electrical signals in your neurons. E.g you can't have a functioning system (not even electrical equipment, let alone a human body) where things are only doing in one direction. Your heart couldn't pump blood, your neurons would only conduct electrical signals one way? Or am I misunderstanding what happens inside (or even anywhere near) a black hole?

The singularity is more like a point in time. It's not a point in space. It's more like everyone is moving inevitably towards next Tuesday.

 

[Manan]

Right, which makes it even more impossible right? Because a blood cell going to the back of your head would require it to go backward in time?

 

[Ibix]

Right, which makes it even more impossible right? Because a blood cell going to the back of your head would require it to go backward in time?

No. The singularity is, as PeroK says, a moment in time. Just as every bit of you is approaching tomorrow morning now, if you were inside a black hole every bit of you would be approaching the singularity. Your brain works fine here, and it would there too. For a while, anyway.

 

[Nugatory]

Right, which makes it even more impossible right? Because a blood cell going to the back of your head would require it to go backward in time?

No. Right now it is 5:00 PM where I am now, and whatever direction I move in, I’m going to get to 6:00 PM, blood cells and all. Same thing inside the event horizon, all spatial directions point forward in time so the blood cells going one direction in an artery and then coming back in the other direction are both still moving forward in time.

 

[Manan]

No. Right now it is 5:00 PM where I am now, and whatever direction I move in, I’m going to get to 6:00 PM, blood cells and all. Same thing inside the event horizon, all spatial directions point forward in time so the blood cells going one direction in an artery and then coming back in the other direction are both still moving forward in time.

Hmm, so can you move towards the event horizon once you are past it? If you can't, then why can your red blood cell?

I guess conceptually I have to go back and figure out the new axis.

 

[Dale]

let's say you're facing the singularity and your back is to the event horizon

How do you face tomorrow?

your neurons would only conduct electrical signals one way?

Your neurons only conduct signals to the future anyway. Never to the past.

 

[Ibix]

Hmm, so can you move towards the event horizon once you are past it? If you can't, then why can your red blood cell?

The event horizon is a null surface - from the inside it recedes from you at the speed of light. So no, you can never get closer to it.

The singularity is not a place in space, and the event horizon isn't really one either, not in the naive sense. You are free to move as you like inside an event horizon because there is no spatial direction pointing towards or away from the singularity, and the event horizon is always moving away from you faster than you could move.

 

[Manan]

Ahhh, that is starting to make more sense conceptually. Thank you. So what happens AT the event horizon? Meaning when I am outside of it and falling in, and half my head is inside the event horizon while the other half is outside?

 

[Ibix]

Ahhh, that is starting to make more sense conceptually. Thank you. So what happens AT the event horizon? Meaning when I am outside of it and falling in, and half my head is inside the event horizon while the other half is outside?

You pass through it quickly. Or you try to stop yourself and the force you apply tears your in two.

 

[Manan]

Thank you all.

 

[Manan]

Sorry, one follow up question. Since it's a moment in time, I assume that moment in time would be very 'short' (not sure how time would 'feel' inside a black hole) given the 'speed' you'd be accelerating at?

So if its a very very large black hole (say largest we've measured), how much 'time' would it take to get from crossing the event horizon to "meeting" the singularity.

 

[Dale]

There is actually an interesting paper on this topic which gives a strategy for a person in a rocket to maximize the proper time.

https://arxiv.org/abs/0705.1029

In this paper Lewis and Kwan show that after you cross the horizon you have only approximately a time $R/c$ where $R$ is the Schwarzschild radius. The maximum possible is $\pi/2=1.571$ times that value.

 

[Manan]

That's really cool! So if R of the largest black hole (per google search) had a R of 1949*10^14, that would be t = 975 174 632, which I assume is in seconds? If so, that's 30 years of proper time.

 

[renormalize]

If so, that's 30 years of proper time.

Your value of R is way too big. According to https://en.wikipedia.org/wiki/Supermassive_black_hole, the mass of Ton 618 is about 41 billion solar masses with a Schwarzschild radius (https://www.calctool.org/astrophysics/schwarzschild-radius) of 1.2 x 10¹⁴ m. Dividing by c and multiplying by pi/2 gives 4 x 10⁵ sec or a bit over 7 days.

 

[jbriggs444]

Your value of R is way too big. According to https://en.wikipedia.org/wiki/Supermassive_black_hole, the mass of Ton 18 is about 41 billion solar masses with a Schwarzschild radius (https://www.calctool.org/astrophysics/schwarzschild-radius) of 1.2 x 10¹⁴ m. Dividing by c and multiplying by pi/2 gives 4 x 10⁵ sec or a bit over 7 days.

I suspect that the $1,949 \times 10^{14}$ figure had a comma intended as a decimal point. The first source I googled up presented it that way. That is a factor of 1000 error in interpretation.

In addition, it appears that estimates on the mass of TON 618 vary. The Wiki article includes two figures.

From this, the mass of the central black hole of TON 618 has been estimated to be at 66 billion M

A more recent measurement in 2019 by Ge and colleagues which utilizes the C IV emission line, an alternative spectral line to Hβ, using the same data reproduced by the earlier paper by Shemmer found a lower relative velocity of the surrounding gas of 2,761±423 km/s, which indicate a lower mass for the central black hole at 40.7 billion M☉, consequentially lower than the previous estimate.

 

[Nugatory]

So what happens AT the event horizon? Meaning when I am outside of it and falling in, and half my head is inside the event horizon while the other half is outside?

If you had a rocket propulsion unit attached to your head and used it to hold your head outside of the horizon while your feet were inside the horizon, one of two things would happen: either the propulsion unit is not strong enough (and the closer to the horizon your head is, the greater the required force, so we’re talking infinite force as you get arbitrarily close) so your head falls through the horizon despite the best efforts of your propulsion unit; or the propulsion unit is strong enough to tear your body in two and the head stays outside while the feet keep falling.

If your head does pass through the horizon, nothing remarkable happens and you won’t even notice the horizon as you pass through it. You’re looking at your toes, meaning that light reflected from them is reaching your eyes. Before your toes cross the horizon, light from them starts outside the horizon and reaches your eyes just as it would if there were no black hole (aside from redshift and time dilation effects). After your toes have fallen through the horizon there’s no way light reflected from them can reach your eyes outside the horizon; but that doesn’t matter because your head is falling through the horizon as well, and it meets the “outgoing” light from your toes once through the horizon. The net effect is that you’re never not seeng your toes, just as if there was no black hole involved.

 

[Orodruin]

TL;DR Summary: Popular descriptions say you could be inside a very large black hole (assuming you could shield yourself from radiation etc), but how is that possible?

Or am I misunderstanding what happens inside (or even anywhere near) a black hole?

You are misunderstanding what happend inside a black hole. Moving towards the singularity is more like progressing into the future than moving in a spatial direction. You are current progressing into the future. Does that prevent your brain from working?

 

[martinbn]

Imagine a spherical formation of stars with Earth at the center. The stars a falling towards us. Before they are near an event horizon will form and expand towards the stars, so we will be inside the horizon well before anything noticeable happens. We could be in this scenario right now. Does your brain work?

 

[SiennaTheGr8]

Your value of R is way too big. According to https://en.wikipedia.org/wiki/Supermassive_black_hole, the mass of Ton 618 is about 41 billion solar masses with a Schwarzschild radius (https://www.calctool.org/astrophysics/schwarzschild-radius) of 1.2 x 10¹⁴ m. Dividing by c and multiplying by pi/2 gives 4 x 10⁵ sec or a bit over 7 days.

7 days is a lot longer than I'd realized is feasible. I wonder how much time you'd have (in this scenario) before the tidal forces became uncomfortable; I have a summer vacation to plan...

 

[Dale]

That's really cool! So if R of the largest black hole (per google search) had a R of 1949*10^14, that would be t = 975 174 632, which I assume is in seconds? If so, that's 30 years of proper time.

I didn't do that final calculation, but a useful approximation is that the Schwarzschild radius of the sun (divided by $c$) is about $10 \mathrm{\ \mu s}$. Since the mass of a black hole is often reported in units of solar masses, you can just multiply that number by $10 \mathrm{\ \mu s}$ to get the radius divided by $c$.

 

[PAllen]

7 days is a lot longer than I'd realized is feasible. I wonder how much time you'd have (in this scenario) before the tidal forces became uncomfortable; I have a summer vacation to plan...

Seems like a very interesting end of life plan. I’ll never get to tell anyone, but I’LL know what’s really there before I pass.

 

[Ibix]

7 days is a lot longer than I'd realized is feasible. I wonder how much time you'd have (in this scenario) before the tidal forces became uncomfortable; I have a summer vacation to plan...

Search "ouch radius" in this forum.