
When You Fall Into a Black Hole, How Long Have You Got? - Pr0
http://blogs.scientificamerican.com/critical-opalescence/2012/12/14/when-you-fall-into-a-black-hole-how-long-have-you-got/
======
iwwr
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>

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-
or...](http://www.technologyreview.com/view/423608/planets-could-orbit-
singularities-inside-black-holes/) 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.

~~~
ars
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.)

~~~
Tloewald
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.

~~~
ars
The object can not suddenly switch from moving straight to a curve. That's
what I mean. In order to curve something must cause it to do so, but there are
no lateral forces on it (or more accurately the forces in all directions are
exactly balanced).

~~~
jbri
It is still moving in a straight line. Large amounts of gravity tend to
distort spacetime, such that a "straight line" appears bent to a distant
observer.

It's the same phenomenon as what causes gravitational lensing.

~~~
ars
Gravity curvature works fine at ordinary masses too. Take a rock, throw it
directly away from the earth.

It's not moving in a curved line, it's moving straight - from the POV of a
distant observer as well.

In order to curve it must have some lateral motion relative to "down".

~~~
gruturo
Different effect. A rock is actually following a curved trajectory through
ordinary space. Light always goes straight - but in these extreme
circumstances space itself is curved. You can easily verify this by looking at
said curving rock: the fact that you can see it without distortions (or at
all) implies that its region of space has insignificant curvature and the
light from the event is reaching your eyes is an easy indication of it.

Ordinary masses bend space nowhere nearly enough. The Sun bends space just
_barely_ enough for the effect to be observable in a solar eclipse (it was
used as a verification of Einstein's theories) by causing stars behind it to
appear ever so slightly out of place when its disc is just about to overlap
them. The light from these stars is NOT being bent - it keeps going in a
straight line, but the Sun's gravity slightly alters the very idea of straight
in its immediate vicinity. The effect is a tiny distorsion, about 0.00048
degrees.

And the Sun is not exactly small.... but it's not dense enough to have a
strong effect. Nothing in our everyday experience is. If you could stuff all
of its mass into a tiny volume then in its immediate vicinity you could
experience this.

------
alecst
My friend told me: "Looking out from [falling into] a black hole you see the
life of the universe pass before you. That means if you've managed to fall
into a black hole, no one in the history of the universe cared enough to
rescue you."

~~~
bithive123
Isn't that equally true of any kind of hole?

~~~
alecst
Black holes fudge with time and other holes don't.

------
omegant
Complete ignorant question: there is always the discussion of "falling" in to
a black hole, but could it be possible to "hang" something from outside the
event horizont?(given an infinitely strong and quite long wire). If so, could
it be possible to send any signal outside? Is it possible for a particle to
vibrate in a radial axis away from the blackhole once inside the event
horizont?. Does a particle follow in an orbit around the black hole once
inside the event horizont? Or the acceleration towards the center is so big
that is a vertical fall? I think that this last question is somehow replied on
the article but I can't understand it. Amazing topic indeed!.

Edit: some corrections.

~~~
yaks_hairbrush
> Complete ignorant question: there is always the discussion of "falling" in
> to a black hole, but could it be possible to "hang" something from outside
> the event horizont?(given an infinitely strong and quite long wire).

It's a good question, because it exposes some subtle assumptions being made.

The string breaks, because you cannot have an infinitely strong wire in a
universe that allows black holes. If we could have such a wire, black holes
would not be formed, since the wire's material would be able to resist being
crushed into a black hole. Therefore collapsing stars would compress into this
material rather than into black holes, and there would be no black holes.

Once inside the event horizon, every path leads to the singularity. You cannot
get further away from it, and you cannot orbit it (or otherwise keep distance
constant).

~~~
astrodust
All that the math suggests is that the escape velocity from inside the event
horizon is beyond the speed of light, so it's physically impossible.

It doesn't seem impractical to be able to establish an orbit inside that
radius, though, even a highly elliptical one, provided this orbit never slings
you back out. It just seems if your orbit decays even slightly, you'll never
be able to recover, leading to the inevitable conclusion of being pulled
directly into the singularity.

~~~
yaks_hairbrush
Inside an event horizon, orbiting implies traveling faster than c from your
reference frame. No can do.

(Note: this applies to an electrically neutral non-rotating black hole.)

~~~
astrodust
Since the event horizon itself is supposed to be a fairly non-event to cross,
why can't you just fly in a lazy circle around a large black-hole at a
relatively "safe" distance and maintain an orbit that's decaying only very
slowly?

------
psykotic
Greg Egan's Planck Dive short story is worth a read:
[http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...](http://gregegan.customer.netspace.net.au/PLANCK/Complete/Planck.html)

------
teilo
I love how Physics is like the biggest, grandest game of Sudoku ever played.
You can get so far, certain that everything is about to fall into place, and
then you reach a contradiction. And what better place to find the
contradiction than at the event horizon of a black hole. Good stuff.

~~~
javert
If you reach a contradiction, it means you've done something wrong. To me,
this article is a partial confirmation of earlier suspicions that the physics
community has lost touch with reality.

~~~
shmageggy
The history of science shows your conception is a bit too stringent. It sounds
a bit like Popper's extreme views on falsification in philosophy of science,
whereby a theory must either pass every empirical test that is thrown at it,
or be flatly rejected. The history of science (Kuhn, etc) shows that this is
just not how it works. In general, when a theory fails a test it is tweaked
and revised to accord better with the data, and sometimes (usually after the
theory gets much more complex) a new, usually simpler, revolutionary theory
replaces it. Now, since we can't go toss stuff into black holes, theoretical
physics at this level is more like pure math, where the "observations" are the
calculations of the theorists. When the calculations don't add up and a
contradiction is found it doesn't mean that they've lost touch with reality.
On the contrary, they are bringing their theories into closer congruence with
reality.

~~~
javert
_A theory must either pass every empirical test that is thrown at it, or be
flatly rejected._

Well, that's how reality actually works. Statements about reality are either
true or false. How many physicists would even agree with that? Therein lies my
distrust of modern physics, or at least part of it.

I'm no fan of Popper, though.

 _The history of science (Kuhn, etc) shows that this is just not how it
works._

I'm no fan of Kuhn either, though. He also probably wouldn't agree with my
litmus test of "Statements about reality are either true or false."

~~~
shmageggy
This seems to be at odds with your reply to the sibling comment. If Newtonian
physics is incomplete, then the statements it makes about reality are,
strictly speaking, wrong. Yet to flatly reject Newtonian physics would be
silly, since it clearly has some aspect of truth to it, having been useful not
only in practical tasks, but as a platform for building more complete accounts
of physics. Analogously, modern physics may have contradictions and is clearly
"wrong" at some level, yet it is remarkably good at explaining lots of
empirical phenomenon, and we would probably be much worse off if we scrapped
the whole enterprise and started over from first principles rather than
building on what we have until the next breakthrough. Your litmus test may be
right, but that's no way to do science. Lastly, since you aren't a fan of
Kuhn, do you prefer any one else's account of philosophy of science?

------
archivator
Here's a not-so-scientific but rather fun YouTube video on the topic:
<http://www.youtube.com/watch?v=3pAnRKD4raY>

------
satori99
All this Blackhole talk reminds me of the excellent Frederick Pohl novel,
Gateway. And its sequel Beyond the Blue Event Horizon. Both of which deal with
humans interacting with these regions of the universe for the first time.

<http://en.wikipedia.org/wiki/Gateway_%28novel%29>

------
kyllo
The event horizon is the point where the gravitational pull is pulling you at
nearly the speed of light so that there is no possible escape velocity for any
particle that has mass, correct?

I'm no physicist, but if gravity were to act on a human body with that much
force, wouldn't the force alone kill you? I imagine the force of the pull
would be stronger than the force holding together the atoms that make up the
tissue of your body, and you would disintegrate into a stream of particles
accelerating toward the singularity. Am I way off here? If a smaller object
approached an object of such great mass that not even light can escape its
gravitational pull, wouldn't the smaller mass's particles inevitably be
funneled into a single-file line until they are absorbed into the singularity?

~~~
jbri
How much gravitational force does the Sun exert on you? Do you feel any of it?

A constant gravitational field doesn't change anything - everything is
accelerating the same amount, in the same direction. What can cause problems
is the _difference_ between the gravitational field at two different points
(for example, when a planet gets too close to a star, it can be torn apart due
to the force exerted on the near side being much greater than the force
exerted on the far side). But this isn't the same as the overall strength of
the field, and a sufficiently large black hole could have a very survivable
field gradient at the event horizon.

~~~
kyllo
Oh ok, so what I described (the atoms of your body being stretched apart by
tidal force) will eventually happen, but not necessarily until quite a while
after you cross the event horizon, if the total mass of the black hole is
great enough. Thanks for the explanation.

------
ableal
_"[...] observers who are freely falling—whether into a black hole or toward
the ground—don’t feel the force of gravity, [...]"_

They will if there's enough of a gradient and the observers are not ideal
points.

Many years ago, Larry Niven wrote a story
(<http://en.wikipedia.org/wiki/Neutron_Star_%28short_story%29> ) where tidal
forces killed observers trying to orbit a neutron star.

~~~
teilo
Yes, but in a sufficiently massive black hole, it is still possible to pass
the event horizon unscathed. Thus, the paradox still exists.

------
deltasquared
I wouldn't worry so much about the event horizon so much as what is right
outside of it.

The tidal forces and the x-rays resulting from said forces are pretty much
lethally intense.

<http://chandra.harvard.edu/chronicle/0104/tidal/index.html>

~~~
pdonis
The X-rays don't come from "tidal forces" by themselves, they come from tidal
forces acting on matter falling into a black hole.

~~~
astrodust
Doesn't "tidal force" dictate that it's acting on something? What is a force
if there's nothing for it to act against? Just as it takes two to tango, you
can't have a force without two participants at opposing ends.

~~~
pdonis
_Doesn't "tidal force" dictate that it's acting on something?_

Tidal gravity is equivalent to spacetime curvature, so it's there whether or
not there is matter falling into the hole; the term "tidal force" is sometimes
used to refer just to that fact. But X-rays won't be produced unless enough
matter is falling in and being acted on by the tidal force. If there were no
large quantities of matter falling in, a very small object like, say, an
astronaut in a rocket ship, could fall in and not encounter any X-rays, but
the tidal force would still be there (and could potentially pull his ship and
him apart). I wasn't sure if that distinction was clear.

~~~
astrodust
I'd always understood that tidal forces were related to objects large enough
to have a measurable differential in orbital period from one side of the
object to the other.

In the ordinary universe this often plays out on small moons in a low orbit
around very large planets such as Jupiter.

A definition (<http://en.wikipedia.org/wiki/Tidal_force>): "The term _tidal
force_ is used to describe the forces due to tidal acceleration." You can't
have acceleration without an object being accelerated.

Not trying to split hairs here, but to try and establish if it's possible to
have a force that's not acting on anything.

~~~
pdonis
_I'd always understood that tidal forces were related to objects large enough
to have a measurable differential in orbital period from one side of the
object to the other_

This is one way of looking at it, but it's not very general. The more general
way of looking at it is to look at two nearby "test objects" (meaning objects
so small that they don't affect the gravitational field enough to make a
difference), both in free fall, that start out at rest relative to each other.
If they don't stay at rest relative to each other, then tidal gravity is
present.

The term "tidal force", on the more general view, refers to forces felt by
objects that are _not_ allowed to follow the free-fall paths that tidal
gravity is trying to make them follow. For example, consider a small piece of
the Earth on the side facing the Moon, and another small piece on the side
opposite the Moon. If these two pieces of matter were in independent free-fall
orbits, they would separate due to the tidal gravity produced by the Moon.
Since the two pieces of matter are _not_ independent--they are both attached
to the Earth--they both feel a "tidal force" because they are being prevented
by the rest of the Earth from following the "normal" free-fall orbit they
would follow due to the Moon's gravity if they were not attached to the Earth.

 _if it's possible to have a force that's not acting on anything._

If you don't like using the term "force" when there's no object feeling the
force, then you can just use the term "tidal gravity", as I did above, to
refer to the underlying spacetime curvature that, when objects _are_ present
to feel the force, causes "tidal force". So tidal gravity can be present even
when there is no object feeling tidal force due to the tidal gravity.

------
patrickgzill
The rest of your life?

------
PaulHoule
It's not any more possible to get into a black hole interior than it is to get
out because black holes don't have an interior.

~~~
teilo
They have an event horizon. Everything past that is inside the black hole.
Things absolutely can and do pass the event horizon. That is how the mass of
the black hole increases. That is also the problem the article is addressing.
This creates a paradox in that it allows a single quantum particle to be poly-
entangled - something that is not allowed by our current understanding of
quantum mechanics.

Therefore, what really happens? No one knows for sure. If the no-drama
principle correct (which is implied by Einstein's theory of gravity), in that
you cannot feel gravity when you are in free-fall, you pass through the event
horizon just fine, and then die when you are torn apart by tidal forces. (Of
course, the tidal forces kick in outside the event horizon in smaller black
holes - but that's beside the point). If the no-drama principle is correct,
then there is a fundamental and insoluble contradiction in our understanding
of physics. That's the point of the article.

~~~
PaulHoule
No, stuff that falls inside the black hole stacks up around the event horizon,
which really grinds stuff up to the planck scale and transforms it to maximum
entropy hawking radiation.

falling into it, it has enough degrees of freedom to put you into any kind of
virtual reality, so you might experience falling into a singularity or somehow
travelling into an "asymptotically flat spacetime" but I'm certain that the
classical picture of a black hole is completely wrong.

~~~
teilo
And you are welcome to be as certain as you wish. But I would point out that
without black holes having an interior, there can be no Hawking radiation in
the first place. Your statement is therefore internally inconsistent.

~~~
PaulHoule
there might be something "on the other side" but there's no reason to believe
that it has a 3+1 signature or is anything like the space we know at all.

~~~
pdonis
_there might be something "on the other side" but there's no reason to believe
that it has a 3+1 signature or is anything like the space we know at all._

There is plenty of reason to believe that, if a horizon does form, the region
of spacetime on the other side will be spacetime, not something completely
different.

There are some (speculative) reasons to believe that quantum effects might
possibly prevent horizons from ever forming, but that would mean there is no
"other side".

------
stephengillie
I get this feeling we'll see idiot daredevils doing "black hole falls" in 300
years. They'll be posted on YouHoloTube or whatever video display system we're
using then.

