6 ms·

Well, given that you can't travel backward once you've crossed the event horizon, can neural signals travel in a direction opposite the center of the singularit

by iwwr 14y ago

Well, given that you can't travel backward once you've crossed the event horizon, can neural signals travel in a direction opposite the center of the singularity? Meaning, once neural and sensory activity stops then you are dead, even if your body has not yet experienced the crushing gravitational effects. You are dead as soon as you cross the event horizon. Though it may be possible to design some machines that can do computation in this unidirectional fashion. Consider something like: http://en.wikipedia.org/wiki/Rule_110 http://en.wikipedia.org/wiki/Rule_110 Another possibility is finding a really enormous black hole, large enough that stuff can live inside it: http://www.technologyreview.com/view/423608/planets-could-orbit-singularities-inside-black-holes/ http://www.technologyreview.com/view/423608/planets-could-or... Of course, humans are not wired topologically to survive in such an environment, but if there is an energy source and computing restrictions are followed, it may be possible to grow a civilization inside an event horizon. A 1 trillion solar mass black hole would have an event horizon at about half a light year, enough room for a few solar systems, depending on our good luck.

SilasX 14y ago
Interesting: to have a working brain or computer inside the event horizon, you would have to set it up so that all the information flows must move along surfaces whose points are all equidistant from the center (except for write-only operations, which could move centerward).
gizmo686 14y ago
I don't think that is an issue, as you are not supposed to be able to detect if you are under a gravitational influence. I suspect what happens is that becuase all of your brain is being accelerated towards the center at the same rate as the neural signals, it would continue operating normally.
- monochromatic 14y ago
  Tidal forces would be a problem though (if not at the event horizon, then at least increasingly so as you approach the singularity). Basically, whatever part of you is closest to the singularity experiences more gravity than the parts that are farther away.
jlgreco 14y ago
I think once the entire brain was in the event horizon it could continue to work more or less normally. Things past the event horizon should be able to travel in the direction of it, though they will always turn back before actually crossing it. Now, a brain that was only half across would have some trouble as you describe I think. If you crossed it fast enough maybe no part of the brain would have enough time to realize it was isolated? I suspect if you are falling in faster than anything in your body was moving in the opposite direction nothing would be noticed.
- yaks_hairbrush 14y ago
  I think (note: I am not a cutting-edge theoretical physicist) that the brain would work fine against both of these effects. First, I'm not sure it's possible for the brain to be half-way across an event horizon. When an in-falling object nears the event horizon, the horizon "dimples" in response to the changing gravitational field caused by the object's mass. Second, once inside the horizon, it is true that messages cannot be sent opposite the direction of the singularity. However, your entire brain is moving toward the singularity, and therefore neural communication does not require messages to be sent away from the singularity. >Things past the event horizon should be able to travel in the direction of it, though they will always turn back before actually crossing it. According to the best of my understanding, if you're inside the event horizon, every direction you look leads to singularity. There are no paths away from the singularity.
  - iwwr 14y ago
    Not all your brain would be the same distance from the singularity. So when trying to send a signal from a nearer part to a farther part, you are prevented. The brain cannot function.
    - yaks_hairbrush 14y ago
      > Not all your brain would be the same distance from the singularity. True, but you are not standing still. You are moving. Accelerating, in fact. No messages need to be sent away from the event horizon for the brain to work.
DenisM 14y ago
>it may be possible to grow a civilization inside an event horizon Maybe that's where we are already :)
sramsay 14y ago
"once neural and sensory activity stops then you are dead, even if your body has not yet experienced the crushing gravitational effects." One of the few "no brainers" in quantum physics.
fargolime 14y ago
A massive enough black hole could contain our entire observable universe. An observer crossing the event horizon of a black hole needn't notice anything special either. That's the theory anyway. Black holes are disproved using the theory itself and rock-solid logic, here: finbot.wordpress.com/2008/03/05/no-black-holes/ Of course I'm using a throwaway account because people love to assume that any science not coming from an academic source is both false and crackpotish, evidence be damned. (This unscientific behavior that pervades our society is the strangest thing to me. Especially among hackers, who are otherwise highly logical.) It's generally accepted among astrophysicists that black hole theory forms a physical paradox called the information loss paradox, a contradiction with quantum mechanics, a much better tested theory. No black hole has yet been definitely observed (despite media harping to the contrary), and Einstein's theory itself explains all suspected black holes without predicting them to be black holes. Sorry to pop anyone's sci-fi bubble!
- trhtrsh 14y ago
  Wow, nice job cramming several "I'm a crackpot" indicators in there, instead of just sharing your ideas.
- othermaciej 14y ago
  The post you linked actually does look like crackpottery, and your endorsement of it looks like crackpottery too. Highlighting how your point of view is suppressed by mainstream science just makes it seem more like crackpottery. The basic mistake in this whole argument is that there is no such thing as an inertial frame or near-inertial frame that crosses an event horizon. An inertial frame outside the event horizon will appear to be fully outside it from within the frame, even if extended. Event horizons can exist in GR even without black holes, for example, an accelerating observer sees an apparent horizon or Rindler horizon, where signals beyond it will never reach him. But there is no near-inertial frame that, from within the frame itself, appears to cross the Rindler horizon.
  - pdonis 14y ago
    there is no such thing as an inertial frame or near-inertial frame that crosses an event horizon. Sure there is. Consider an object falling into the black hole; you can set up a local inertial frame around the event of that object crossing the horizon and it will work just fine even though it straddles the horizon. What you can't have is a static inertial frame that crosses the horizon; i.e., you can't have one that stays at the same radius, even for an instant. The inertial frame I described above is infalling--i.e., an observer at rest in the frame is falling into the hole. But there is no near-inertial frame that, from within the frame itself, appears to cross the Rindler horizon. Yes, there is. This is even easier than the black hole case because you can have a Rindler horizon in flat spacetime, where all inertial frames are global--they cover the entire spacetime, including the region behind the Rindler horizon. I should note that I do not mean to imply that the "finbot" article linked to is correct; it isn't. As I described above, inertial frames that straddle the horizon can be constructed, and they are perfectly consistent with the equivalence principle.
yk 14y ago
> Well, given that you can't travel backward once you've crossed the event horizon, can neural signals travel in a direction opposite the center of the singularity? This is essentially the 'no drama' assumption the article is about. It means roughly, that there is no way to detect that you did cross the event horizon. And therefore the brain still works fine.
neolefty 14y ago
It's more about escape velocity. Your neural signals would not be able to escape to an observer "outside" the black hole -- I mean outside most of its gravitational influence -- but they could move around locally. The larger the black hole, the smaller the tidal forces at the event horizon, so with a large enough black hole, a human body would be fine.
ars 14y ago
This is actually one of the problems with black holes, the event horizon is listed as an impenetrable barrier, but if you emitted light (which is in principle no different from an electrical impulse) from just under the barrier what prevents it from traveling past the barrier and away? And don't tell me that it curves away because that would be a violation of conservation of momentum. It also can't travel directly up then back down, because light can't do that - at the moment of reversal it's not traveling at the speed of light. And the light particle can't evaporate (i.e. red shift into nothingness) by loosing all its energy to the blackhole because that would be a violation of conservation of angular momentum (every photon caries some angular momentum). So what happens to it? I should mention that after studying all the physics that I could understand I do not believe black holes exist. (Super massive objects might, like the observed objects in the center of galaxies, but not as black holes.)
- simcop2387 14y ago
  My suspicion (ie no facts) would be that either the light just does make it to the event horizon to leave because of time dialation effects, or we can't answer it because our math breaks down at the horizon so we can't say anything about the universe past it.
  - pdonis 14y ago
    the light just does make it to the event horizon to leave because of time dialation effects No, the light does make it to the horizon. our math breaks down at the horizon No, the horizon, and the spacetime inside all the way down to the singularity, can be described perfectly well mathematically.
- Tloewald 14y ago
  Gravity causes or is (depending on how you look at it) curvature of space so the light goes "straight" but doesnt leave. Sorry if that means it "curves away" but that's what having an escape velocity greater than the speed of light means. And what does that have to do with conservaton of momentum? If i throw a rock upwards it curves away rather than leaving the solar system — momentum is still conserved and the rock has much more than a photon.
pdonis 14y ago
once you've crossed the event horizon, can neural signals travel in a direction opposite the center of the singularity? They don't have to for your brain and nervous system to continue functioning. Suppose you are falling feet first towards the singularity, and your feet send a nerve signal to your head. From your viewpoint, the signal travels up your body normally. But from the "god's-eye" viewpoint, the nerve signal from your feet to your head just falls towards the singularity more slowly than your feet and head do, so your feet fall away from the signal and your head catches up with it.
- ars 14y ago
  Am I falling faster than light? At the moment of the crossing, does the floor of the spaceship look dark? If I can see the floor, then light from the floor is passing the horizon and entering my eye.
  - pdonis 14y ago
    If I can see the floor, then light from the floor is passing the horizon and entering my eye. No, it isn't. Consider a ray of light emitted by the floor just below the horizon, and suppose that your eye is just above the horizon when it is emitted. By the time that ray of light reaches your eye, your eye will have fallen below the horizon. So your eye will see the ray of light just fine.
    - pixl97 14y ago
      I'm not sure about the just fine. If you were not in a complete free fall you'd be smooshed (I'm guessing W = m · g is nasty at black hole gravities). I guess my question is how fast you'd be traveling by the time you got near/in the even horizon. Anywhere close to 'c' and things would look a lot different.
      - pdonis 14y ago
        If you were not in a complete free fall you'd be smooshed (I'm guessing W = m · g is nasty at black hole gravities) If you are trying to "hover" at a constant altitude above the black hole's horizon, then yes, the acceleration you would feel increases without bound the closer to the horizon you try to hover. But if you're falling into the hole you clearly aren't "hovering"; it is perfectly possible to fall in while feeling only 1 g by adjusting your rocket power properly. The tidal gravity at the horizon might be very large, or very small, depending on the mass of the hole. If it's large enough, yes, tidal forces would tear you apart by the time you reached the horizon. But that would happen even if your center of mass was in free fall. I guess my question is how fast you'd be traveling by the time you got near/in the event horizon. Relative to what? There is no absolute answer to "how fast" you are going; velocity is relative.

by iwwr 14y ago

SilasX 14y ago

Interesting: to have a working brain or computer inside the event horizon, you would have to set it up so that all the information flows must move along surfaces whose points are all equidistant from the center (except for write-only operations, which could move centerward).

gizmo686 14y ago

I don't think that is an issue, as you are not supposed to be able to detect if you are under a gravitational influence. I suspect what happens is that becuase all of your brain is being accelerated towards the center at the same rate as the neural signals, it would continue operating normally.

monochromatic 14y ago
Tidal forces would be a problem though (if not at the event horizon, then at least increasingly so as you approach the singularity). Basically, whatever part of you is closest to the singularity experiences more gravity than the parts that are farther away.

jlgreco 14y ago

I think once the entire brain was in the event horizon it could continue to work more or less normally. Things past the event horizon should be able to travel in the direction of it, though they will always turn back before actually crossing it. Now, a brain that was only half across would have some trouble as you describe I think. If you crossed it fast enough maybe no part of the brain would have enough time to realize it was isolated? I suspect if you are falling in faster than anything in your body was moving in the opposite direction nothing would be noticed.

yaks_hairbrush 14y ago
I think (note: I am not a cutting-edge theoretical physicist) that the brain would work fine against both of these effects. First, I'm not sure it's possible for the brain to be half-way across an event horizon. When an in-falling object nears the event horizon, the horizon "dimples" in response to the changing gravitational field caused by the object's mass. Second, once inside the horizon, it is true that messages cannot be sent opposite the direction of the singularity. However, your entire brain is moving toward the singularity, and therefore neural communication does not require messages to be sent away from the singularity. >Things past the event horizon should be able to travel in the direction of it, though they will always turn back before actually crossing it. According to the best of my understanding, if you're inside the event horizon, every direction you look leads to singularity. There are no paths away from the singularity.
- iwwr 14y ago
  Not all your brain would be the same distance from the singularity. So when trying to send a signal from a nearer part to a farther part, you are prevented. The brain cannot function.
  - yaks_hairbrush 14y ago
    > Not all your brain would be the same distance from the singularity. True, but you are not standing still. You are moving. Accelerating, in fact. No messages need to be sent away from the event horizon for the brain to work.

DenisM 14y ago

>it may be possible to grow a civilization inside an event horizon Maybe that's where we are already :)

sramsay 14y ago

"once neural and sensory activity stops then you are dead, even if your body has not yet experienced the crushing gravitational effects." One of the few "no brainers" in quantum physics.

fargolime 14y ago

A massive enough black hole could contain our entire observable universe. An observer crossing the event horizon of a black hole needn't notice anything special either. That's the theory anyway. Black holes are disproved using the theory itself and rock-solid logic, here: finbot.wordpress.com/2008/03/05/no-black-holes/ Of course I'm using a throwaway account because people love to assume that any science not coming from an academic source is both false and crackpotish, evidence be damned. (This unscientific behavior that pervades our society is the strangest thing to me. Especially among hackers, who are otherwise highly logical.) It's generally accepted among astrophysicists that black hole theory forms a physical paradox called the information loss paradox, a contradiction with quantum mechanics, a much better tested theory. No black hole has yet been definitely observed (despite media harping to the contrary), and Einstein's theory itself explains all suspected black holes without predicting them to be black holes. Sorry to pop anyone's sci-fi bubble!

trhtrsh 14y ago
Wow, nice job cramming several "I'm a crackpot" indicators in there, instead of just sharing your ideas.
othermaciej 14y ago
The post you linked actually does look like crackpottery, and your endorsement of it looks like crackpottery too. Highlighting how your point of view is suppressed by mainstream science just makes it seem more like crackpottery. The basic mistake in this whole argument is that there is no such thing as an inertial frame or near-inertial frame that crosses an event horizon. An inertial frame outside the event horizon will appear to be fully outside it from within the frame, even if extended. Event horizons can exist in GR even without black holes, for example, an accelerating observer sees an apparent horizon or Rindler horizon, where signals beyond it will never reach him. But there is no near-inertial frame that, from within the frame itself, appears to cross the Rindler horizon.
- pdonis 14y ago
  there is no such thing as an inertial frame or near-inertial frame that crosses an event horizon. Sure there is. Consider an object falling into the black hole; you can set up a local inertial frame around the event of that object crossing the horizon and it will work just fine even though it straddles the horizon. What you can't have is a static inertial frame that crosses the horizon; i.e., you can't have one that stays at the same radius, even for an instant. The inertial frame I described above is infalling--i.e., an observer at rest in the frame is falling into the hole. But there is no near-inertial frame that, from within the frame itself, appears to cross the Rindler horizon. Yes, there is. This is even easier than the black hole case because you can have a Rindler horizon in flat spacetime, where all inertial frames are global--they cover the entire spacetime, including the region behind the Rindler horizon. I should note that I do not mean to imply that the "finbot" article linked to is correct; it isn't. As I described above, inertial frames that straddle the horizon can be constructed, and they are perfectly consistent with the equivalence principle.

yk 14y ago

> Well, given that you can't travel backward once you've crossed the event horizon, can neural signals travel in a direction opposite the center of the singularity? This is essentially the 'no drama' assumption the article is about. It means roughly, that there is no way to detect that you did cross the event horizon. And therefore the brain still works fine.

neolefty 14y ago

It's more about escape velocity. Your neural signals would not be able to escape to an observer "outside" the black hole -- I mean outside most of its gravitational influence -- but they could move around locally. The larger the black hole, the smaller the tidal forces at the event horizon, so with a large enough black hole, a human body would be fine.

ars 14y ago

This is actually one of the problems with black holes, the event horizon is listed as an impenetrable barrier, but if you emitted light (which is in principle no different from an electrical impulse) from just under the barrier what prevents it from traveling past the barrier and away? And don't tell me that it curves away because that would be a violation of conservation of momentum. It also can't travel directly up then back down, because light can't do that - at the moment of reversal it's not traveling at the speed of light. And the light particle can't evaporate (i.e. red shift into nothingness) by loosing all its energy to the blackhole because that would be a violation of conservation of angular momentum (every photon caries some angular momentum). So what happens to it? I should mention that after studying all the physics that I could understand I do not believe black holes exist. (Super massive objects might, like the observed objects in the center of galaxies, but not as black holes.)

simcop2387 14y ago
My suspicion (ie no facts) would be that either the light just does make it to the event horizon to leave because of time dialation effects, or we can't answer it because our math breaks down at the horizon so we can't say anything about the universe past it.
- pdonis 14y ago
  the light just does make it to the event horizon to leave because of time dialation effects No, the light does make it to the horizon. our math breaks down at the horizon No, the horizon, and the spacetime inside all the way down to the singularity, can be described perfectly well mathematically.
Tloewald 14y ago
Gravity causes or is (depending on how you look at it) curvature of space so the light goes "straight" but doesnt leave. Sorry if that means it "curves away" but that's what having an escape velocity greater than the speed of light means. And what does that have to do with conservaton of momentum? If i throw a rock upwards it curves away rather than leaving the solar system — momentum is still conserved and the rock has much more than a photon.

pdonis 14y ago

once you've crossed the event horizon, can neural signals travel in a direction opposite the center of the singularity? They don't have to for your brain and nervous system to continue functioning. Suppose you are falling feet first towards the singularity, and your feet send a nerve signal to your head. From your viewpoint, the signal travels up your body normally. But from the "god's-eye" viewpoint, the nerve signal from your feet to your head just falls towards the singularity more slowly than your feet and head do, so your feet fall away from the signal and your head catches up with it.

ars 14y ago
Am I falling faster than light? At the moment of the crossing, does the floor of the spaceship look dark? If I can see the floor, then light from the floor is passing the horizon and entering my eye.
- pdonis 14y ago
  If I can see the floor, then light from the floor is passing the horizon and entering my eye. No, it isn't. Consider a ray of light emitted by the floor just below the horizon, and suppose that your eye is just above the horizon when it is emitted. By the time that ray of light reaches your eye, your eye will have fallen below the horizon. So your eye will see the ray of light just fine.
  - pixl97 14y ago
    I'm not sure about the just fine. If you were not in a complete free fall you'd be smooshed (I'm guessing W = m · g is nasty at black hole gravities). I guess my question is how fast you'd be traveling by the time you got near/in the even horizon. Anywhere close to 'c' and things would look a lot different.
    - pdonis 14y ago
      If you were not in a complete free fall you'd be smooshed (I'm guessing W = m · g is nasty at black hole gravities) If you are trying to "hover" at a constant altitude above the black hole's horizon, then yes, the acceleration you would feel increases without bound the closer to the horizon you try to hover. But if you're falling into the hole you clearly aren't "hovering"; it is perfectly possible to fall in while feeling only 1 g by adjusting your rocket power properly. The tidal gravity at the horizon might be very large, or very small, depending on the mass of the hole. If it's large enough, yes, tidal forces would tear you apart by the time you reached the horizon. But that would happen even if your center of mass was in free fall. I guess my question is how fast you'd be traveling by the time you got near/in the event horizon. Relative to what? There is no absolute answer to "how fast" you are going; velocity is relative.