How Would an Astronaut Falling Into a Black Hole Die? 412
ananyo writes "According to the accepted account, an astronaut falling into a black hole would be ripped apart, and his remnants crushed as they plunged into the black hole's infinitely dense core. Calculations by Joseph Polchinski, a string theorist at the Kavli Institute for Theoretical Physics in Santa Barbara, California, though, point to a different end: quantum effects turn the event horizon into a seething maelstrom of particles and anyone who fell in would hit a wall of fire and be burned to a crisp in an instant. There's one problem with the firewall theory. If Polchinski is right, then either general relativity or quantum mechanics is wrong and his work has triggered a mini-crisis in theoretical physics."
We must find out for sure! (Score:5, Funny)
Re:We must find out for sure! (Score:4, Insightful)
The problem is that we won't be able to observe what happens to them inside the event horizon. If you want to be sure, you have to go yourself.
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"if you want to be sure"... briefly, I suppose.
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That sounds like a youtube moment.
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Locate a black hole and start shooting monkeys at it! "Science can not progress without heaps [of monkeys]"
Isn't this how Planet of the Apes got started.... just saying... I, for one, welcome our new black hole traveling monkey overlords...
Re:We must find out for sure! (Score:4, Interesting)
Blackholes might not be that uncommon.
http://physicsworld.com/cws/article/news/2013/mar/15/micro-black-holes-could-form-at-lower-than-expected-energies [physicsworld.com]
There are even some theories that some ball lightning could be due to blackholes:
http://en.wikipedia.org/wiki/Ball_lightning#Black_hole_hypothesis [wikipedia.org]
Imagine a tiny blackhole with literally tons of charged particles beyond the event horizon (which is not far away for a tiny blackhole) in close very high speed orbit around it. Those particles might still be affected by magnetic fields, and how about their gravitational effect on the blackhole itself?
Perhaps some real physicists can explain what would happen in such a scenario.
Re:We must find out for sure! (Score:5, Informative)
I suspect that you're confusing gravity with density - as the black hole's event horizon gets bigger, the density gets lower. I can't remember exactly, but if the event horizon is somewhere around the radius of our solar system, you get an average density around the same as our atmosphere. The gravity's still a heck of a lot higher than 1g at the event horizon though.
Re:We must find out for sure! (Score:4, Interesting)
light can easily escape from 1g
Turns out it can't. Surprising, isn't it? The magnitude of gravity at the event horizon isn't why light can't escape - it's the fact that space itself is effectively rushing into the black hole. There aren't really any good intuitions to be had about conditions at the event horizon.
I'm not good enough to explain it well, but I think of it as the "time" direction points towards the singularity at the event horizon. No matter how good your engines are, you can't apply that thrust in a direction useful for escape.
Re: (Score:3, Informative)
No, light can most certainly escape from 1 G. Gravity IS the curvature of space. The Event Horizon is the point at which escape velocity = c.
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No, light can most certainly escape from 1 G.
Not necessarily. Imagine an infinitely large gravitational field (caused by an infinite object an infinite distance away, so that all field lines are parallel to each other). It should be obvious that the "escape velocity" at any point in that field is infinite (no matter how fast you are traveling, you will always stop and start "falling" at some point less than infinity).
Of course, thats a fictional example, but it's a reasonable approximation for an extremely large mass a very long distance away (such a
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The opposite of what you said is to make every variable 0, which yields invalid results just like your infinite variables yield invalid results. It's fine to speculate some numbers, but you can't use zero or infinity as those speculated numbers.
Not sure what you're even talking about, setting the numbers to 0 works fine (zero gravitational field is well defined, even if it doesn't exist anywhere). And deriving equations and examples from infinite cases is a routine practice in physics. Many equations are derived from such cases (indeed, quite often you find that assuming a non-infinite field makes deriving an actual equation impossible). If you like, you can pretend the field is simply incredibly large relative to the scale you are interested in.
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How does this compare with estimates of the masses of the largest quasars?
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No, light can most certainly escape from 1 G. Gravity IS the curvature of space. The Event Horizon is the point at which escape velocity = c.
G and g are different constants. g measures acceleration, not speed - g and c aren't comparable. Escape velocity is the minimum speed at which you'll "escape" to infinity without acceleration (from an ideal point mass), and it's a property of the mass, not your distance from the mass. Nothing to do with the event horizon.
You don't have to exceed the escape velocity of the Earth to reach the moon, if you have constant thrust. However, no amount of thrust will allow you to escape the event horizon once yo
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Escape speed is SQRT(2rg), where r is the radius and g is local gravity at that radius.
Which means that for escape speed = c and g = 9.8 m/s^2, r is somewhere around 177 light days.
Mass required to produce 1g at 177 light days is somewhere in the low trillions of solar masses.
So you'd need a honking big black hole (probably bigger than currently exists), but not an
Re:We must find out for sure! (Score:4, Interesting)
Hmm, working this out for myself:
The radius of the event horizon is:
R = 2GM/c^2
a = GM/R^2 = c^4/(4GM)
The units are right, so I think that's right. Setting a = g we get
M = c^4 / 4Gg ~= 3 * 10^42 kg ~= 1.5 * 10^12 solar masses
So, yeah, I was way off.
Still, a trillion-solar-mass black hole could possibly exist in the universe to lob monkeys at, I'm betting on the monkeys surviving the event horizon passage for a while.
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Last I checked, the time will slow down so much that you'd never hit the black hole (event horizon), that is, before the universe will end.
But that was "sometime bronze age" so I might be wrong.
Re:We must find out for sure! (Score:5, Interesting)
No matter the size of a black hole, gravity at the event horizon is finite. You could always in theory build rockets more powerful than whatever it is. It won't help you.
Newtonian acceleration determines how much gravity you feel, but not how you actually move, near a black hole, because space itself is effectively rushing across the event horizon.
I'm not good enough at this to explain it well, but as I replied to a sibling post, I think of it as if the time axis has rotated to point towards the singularity. As I understand it, the event horizon is where the time axis points at 45 degrees off the center, and no matter how hard you accelerate, you can't quite change your own vector more than 45 degrees off the time axis, so you're stuck.
Maybe we'll get a physics prof to wander past and explain this better!
Re:We must find out for sure! (Score:5, Informative)
No matter the size of a black hole, gravitational acceleration at the event horizon is c per Planck time. That's not "infinite", but it is maximal. Anything at the event horizon of a black hole will have its velocity increased by c toward the singularity as quickly as theoretically possible. You cannot build a rocket to put out that kind of acceleration in the other direction to keep you in place, because you cannot build a rocket to get you up to c at all, in any amount of time. Your talk about time axes sounds like it's an echo of a description of why you can't build a rocket to get up to c. It has nothing to do with black holes specifically, other than that you would need to get that fast to escape the event horizon of one.
If you were made of light, however, you would be moving at c, and you could orbit at the event horizon. If you're just above the event horizon, you could in theory get moving fast enough to orbit just outside of it. And in orbit, you don't feel any acceleration from gravity; you are free-falling around the black hole, and continually missing it. You could also have some flight path requiring 1g of constant acceleration to keep you from falling in. The size of the black hole doesn't matter for any of that; if you are anywhere outside the event horizon, you can find a flight path that will make you feel any amount of acceleration you want, for as long as you have fuel to maintain that kind of acceleration. (For an orbit, you feel zero acceleration, and so need no fuel and can maintain it indefinitely).
Where the size of a black hole does matter, and what I think you were thinking of in your earlier post about black holes of 100 solar masses or such, is tidal forces. These are the forces which pinch and stretch your body in uneven ways. Imagine you had a tetherball pole in the middle of a schoolyard. You stand far off to the east of it, facing it, with your arms outstretched. The lines from both of your hands, and your elbows, and your nose, toward the tetherball pole, are all roughly westward, so if you were to be pulled toward it, your whole body would be pulled more or less evenly. But if you stand right next to it, with your arms stretched out, your nose is pulled west, but your right hand is now north of it, and your left hand is south of it, so they get pulled south and north respectively, and the pole pulls your hands toward each other. If, like gravity, it also pulls harder the closer to it you are, it will pull your face toward it much harder than it will your hands, and make you smack your nose into it and then hit yourself as your hands fall in behind your head; while from a long ways away, all your body parts are pulled with about the same force.
Likewise with black holes. The closer you are to one, the more the different parts of your body (and spaceship, etc) are pulled in different directions and with different magnitudes. The farther you are from it, the more evenly everything is pulled. A very massive black hole has a very large event horizon, so at the event horizon, you are very far from the center of the black hole, and even though you are still experiencing the same acceleration you would feel at the event horizon of any black hole, it's all pulling you in more or less the same direction, so you could orbit there and suffer no ill effects. Around a small black hole though, even if you were orbiting just above its black hole and feeling no acceleration overall, the parts of you closer to it would need to orbit faster to maintain that effect and so would feel pulled and pinchedcompared to the parts of you further away from it, which would have more speed than they need to orbit and so tend to drift away from it. All in all you would feel pulled in every different direction and your body would be ripped apart. Around a larger black hole, even moving at the same speed to maintain orbit the same distance from the event horizon, all of you would feel roughly the same effects, so you wouldn't even notice them.
Quantum mechanics and relativity (Score:2)
We already know that QM and relativity can't both be true. Each theory is very good at predicting things in its realm, but they are mutually exclusive.
Re:Quantum mechanics and relativity (Score:5, Insightful)
This isn't true.
QM and *special* relativity get along just fine. When you combine them in a simple way you get predictions like antimatter, the fine structure of the hydrogen atom, and so on. If you do this in a more detailed way, using quantum field theory, you get the fantastically accurate predictions of quantum electrodynamics, the theory of quantum chromodynamics that can't be solved with pen and paper but which still gives accurate predictions when done on supercomputers, and so forth.
And there's nothing forbidding QM from playing nice with general relativity, either; we just don't know how it works yet. There are some models, like lattice quantum gravity, that seem quite promising.
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Whatever happened to M theory (the successor to string theory)?
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007 destroyed his sanity.
Re:Quantum mechanics and relativity (Score:5, Insightful)
And there's nothing forbidding QM from playing nice with general relativity, either; we just don't know how it works yet.
Translation: As currently formulated, at least one of quantum mechanics and general relativity is wrong, although like Newtonian mechanics or pre-relativistic optics, they will undoubtedly continue to be practical and very accurate approximations.
We knew this as soon as quantum mechanics was developed.
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We know no such thing. In fact both appear to be true, the problem being that we don't have an overarching theory that explains how that is so.
Gravitational time dilation (Score:2)
The astronaut dies of old age?
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Yes, because getting to a black hole will take a long time.
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Yes, because getting to a black hole will take a long time.
Your description of time is to general and relative.
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You mean spelling.
Re:Gravitational time dilation (Score:5, Informative)
Re:Gravitational time dilation (Score:5, Interesting)
Re:Gravitational time dilation (Score:4, Interesting)
This reminds me of the two unknowns: how can a black hole be created if the matter falling to it can never get there? The another one is of course: how can gravitons escape event horizon and attract anything?
I think good theorists can answer both - I cannot either.
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You got that exactly backwards.
Refer to Stargate SG-1 episode "A Matter of Time" (Season 2 Episode 16): "SG-10 is stranded on planet P3W-451, which is close to a newly formed black hole. The SGC opens the gate to find out what happened, but they cannot shut it down afterwards. Soon they realize that since the planet is near to a black hole, its intense gravity is causing time dilation, so if they do not shut down the gate very soon, it will destroy the SGC, and in time, the entire planet."
People o
Complimentarity Shlomplimentarity (Score:2)
The smart money is no-firewall and complimentarity is bunkum.
But I'm not smart, Polchinski is.
Disney knew this in 1979 (Score:5, Funny)
Bad headline (Score:5, Insightful)
TFA is an interesting article about a physicist apparently discovering an inherent contradiction between general relativity and quantum mechanics. The "black hole" stuff is really just the context that led to the apparent contradiction: the real issue is much deeper than that. It's depressing that the real underlying hypothesis isn't considered newsworthy, and the editor feels the need to lead with the "black hole" stuff.
Re:Bad headline (Score:5, Interesting)
Misleading (Score:2, Insightful)
The whole "what would happen to an astronaut" is the misleading sensationalist that's been pollution this site lately. It seems they're really going from "News for Nerds" to "Fox News for people who may buy computer and sciency stuff from places like Thinkgeek" (though thinkgeek is awesome BTW) in order to gain bigger audience.
End result is it drives away the core audience that used to make this site awesome, as it dumbs down the really interesting science parts beyond recognition.
Re:Misleading (Score:5, Informative)
The whole "what would happen to an astronaut"
...is part of a collection of classic thought experiments by real scientists which predate the internet. Your concerns are misplaced.
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That contradictions exist between Newtonian physics, relativity, and quantum mechanics is pretty much old news.
wow (Score:2)
That would certainly change the end of the movie [imdb.com].
no one escapes the Black Hole (Score:3)
i agree the reversed lower playfield can be a bit disorienting at first, but let's not get melodramatic -- since there are no outlanes in the gravity well, a quick SDTM drain is really the only way to die down there, and completing either bank of drop targets opens the re-entry gate anyway.
Why Waste an Astronaut? (Score:2)
Re:Why Waste an Astronaut? (Score:5, Funny)
well, technically, wouldn't the convicted murder BECOME an astronaut by definition the moment we shot him into space?
slashdot is really provoking the deep questions today.
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I wouldn't waste resources training the person.
Re:Why Waste an Astronaut? (Score:5, Funny)
Don't worry, I can fix that...
Now, Wikipedia says "In addition, a convicted murderer shot through space toward a black hole for experimental purposes."
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Shouldn't we use a convicted murderer or something?
They behave differently in a vacuum.
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"Just settle down out there, you'll get your $20"
~Cave Johnson
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Shouldn't we use a convicted murderer or something?
I think there would be plenty of volunteers for a one-way trip to a black hole -- volunteers more willing to make scientific observations than a death-row inmate forced to go.
Besides, what if the inmate banished from earth finds himself released by an atomic shockwave from a planet that his prison-ship flies near and he goes to that planet and finds that he has superpowers granted by the planet's sun, and he wreaks havoc on that planet as a super-villan until someone on the planet with super-powers to mat
Painfully (Score:2)
At this point all we have in conjecture as actually studying what would happen is for all intents and purposes impossible. Are you crushed, burned alive by everything else, toasted by radiation, spaghettified, or some other horrible fate?
The only thing that we /really/ know is that any possible fate you would have from falling into a black hole would be painful. Unless you are killed so quickly your body never has a chance to transmit the signals for excruciating pain. The bottom line is that we really don'
My theory (Score:5, Funny)
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Unicorns would stampede the astronaut as he enters the event horizon.
I think we can all agree the astronaut would die.
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Miniature giant space hamsters, actually. They're quite ferocious, and especially fond of eyeballs.
So the consensus is still (Score:5, Funny)
You may cross alive (Score:2)
I once read that if the black hole is big enough tidal forces will be minimal and you can actually cross the event horizon alive.
This theory has some merit as the universe itself is a black hole from a certain point of view.
Magnetic radiation (Score:2)
He'd be dead before got close to the thing.
only small BH rips you apart (Score:2)
You can't have infinite density (Score:2)
Infinite density = zero size and something with zero size no longer exists. If something has a presence in spacetime it will have some form of dimension. You can't have "something" that isn't actually there.
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To an outside observer he'd never die (Score:2)
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If Polchinski is right... (Score:5, Funny)
Umm... He's a string theorist, so...
Listen to Zombie Feynman kids: Unscientific [xkcd.com]:
Q: How Would an Astronaut Falling Into ... Die? (Score:2)
A. Very painfully
Wait, wait, I can answer this one (Score:2)
The astronaut would die of starvation or hypoxia long before they got to the Black Hole, given that the farthest we've sent an astronaut is 250,000 miles (a bit more than one light-second), and the nearest black hole is 1600 light years away, or 5E+10 times as far.
Leonard Susskind (Score:4, Funny)
First answer: Alone.
But I saw this rather interesting video of a lecture by Leonard Susskind : http://www.youtube.com/watch?v=pf0D8A0jRiY [youtube.com] ;)
It will probably not answer your question, but it's about black holes and they're very cool! Or hot. Depending on the observer
Re: Somebody, quick! (Score:5, Insightful)
The /. I knew and loved a decade ago is gone.
Re: (Score:2, Funny)
The /. we all knew and loved a decade ago was gone by 1997.
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That's more than a decade ago. But, in the Slashdot of yore, nobody could do math, so it's all good.
Re: Somebody, quick! (Score:5, Funny)
How would he die?
Of old age, on the multimillion year journey to the nearest black hole, I suppose.
But don't let me be the one to interrupt your little rec time, on the holodeck. ;-)
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That was when Slashdot IDs were negative numbers. Ahhh... I was so much older then, I'm younger than that now.
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Actually the thing that "crushes" the astronaut is the gravity differential over the length of the astronaut. In a "small" (let's say football-sized) black hole that difference is huge, and so the astronaut will get torn apart.
However with a supermassive black hole (and there's never been any other kind detected, they may exist briefly, but that makes the chances of encountering one very small), the differential at the event horizon is tiny.
As for the astronaut, you might think he might have trouble sending
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Nostalgia ain't what it used to be.
Re:Somebody, quick! (Score:5, Funny)
Leave your crappy sitcom references at the door and let the adults talk.
Take the time to read too, you might learn something that isn't some comic book fantasy.
Besides, if anyone knows the answer, it's Dr. Hans Reinhardt.
Re:Spaghetti (Score:5, Funny)
Re:Gravitational tides will kill you (Score:5, Informative)
Everybody repeat after me: "Black holes ain't yer friend. Don't try to hug them, you will die."
Re:Gravitational tides will kill you (Score:5, Funny)
Heck, considering what we know about the locations of black holes and the speed of manmade spacefcraft, old age will probably kill you before you get close enough to notice the gravity.
Everybody repeat after me: "Space is big. Don't mind Sarten-X, he is a jackass."
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Heck, considering what we know about the locations of black holes and the speed of manmade spacefcraft, old age will probably kill you before you get close enough to notice the gravity.
Everybody repeat after me: "Space is big. Don't mind Sarten-X, he is a jackass."
The trouble is that "what we know about black holes" is all theoretical and mathematical. No one has ever directly observed a black hole and thereby shown that these things even exist in the real world. Black holes were invented to explain present-day theories about the motion of stars and galaxies. The same is true of "dark matter" and "dark energy" and other dark fictions. Perhaps it is time to examine some of these widely held theories that require these mathematical fictions. At the center of these hyp
Re:Gravitational tides will kill you (Score:5, Informative)
Assuming you're not trolling, that's a nice story, but that's not how science works.
The trouble is that "what we know about black holes" is all theoretical and mathematical.
Usually, the first step in science is to observe something. In the case of black holes, our knowledge of their existence can be traced back to a few experiments [wikipedia.org], which provided pretty solid evidence against the prevailing theories of aether. The observation that doesn't match the expectation means that the theories aren't right, and must be changed.
In fact, many of today's experiments are simply re-running old trials, but with more precise technology. Rather than dropping rocks off a tower, we can measure how fast individual atoms fall, giving us a more exact understanding of gravity. Usually the results are a perfect match [wikipedia.org] for what's expected, but sometimes they aren't.
Black holes were invented to explain present-day theories about the motion of stars and galaxies.
Next comes the theory. Starting from the results of those experiments, Einstein hypothesized his theories of relativity, which are really little more than a collection of relationships derived from the assumption that the speed of light in a vacuum is constant. His theories explained the results of previous experiments, and importantly, provided a set of formulas that can be used to make predictions for future experiments.
Mathematics are very useful in describing measured experiments and observations in the physical universe. As soon as mathematics and computer simulations go beyond what is actually observed and measured, it no longer describes the real world were living in.
The relationships in the physical world are described with mathematics. Sometimes, when math is insufficient to easily describe a particular relationship, new mathematical forms [wikipedia.org] are invented to accommodate the real world [wikipedia.org]. Ultimately, though, every physicist knows that the mathematical models do not prescribe reality, but describe our understanding of it. Again, we use those models to predict the outcome of future experiments.
At the center of these hypothetical, theoretical black holes is this mathematical entity that has been called a "singularity". This is another mathematical fiction that can't exist in the known universe.
That depends on the rules of the known universe. in 1915, Karl Schwarzchild [wikipedia.org] transformed Einstein's theories of relativity into a form that would require black holes. This means that Einstein's formulas can only be correct if the universe allows black holes. If the universe does not allow black holes, then Einsteins formulas must be wrong - though less wrong than the aether theory they replaced.
Perhaps it is time to examine some of these widely held theories that require these mathematical fictions.
That's what experiments [arxiv.org] are [harvard.edu] for [harvard.edu].
No one has ever directly observed a black hole and thereby shown that these things even exist in the real world.
Black holes have been observed many times [harvard.edu].
In 1929 an astronomer named Edwin Hubble discovered that "red shift" of distant galaxies. Then he made the assumption (belief, faith) about the cau
Re:Gravitational tides will kill you (Score:5, Interesting)
All so-called "discoveries" of black holes are attributed to their supposedly enormous gravitational effects on their surroundings, but they never themselves have been found. The same is true of dark matter. The link you gave is all about how the gravity supposedly affects the surroundings of a black hole.
http://www.cfa.harvard.edu/seuforum/bh_reallyexist.htm [harvard.edu]
ALL the observations in that article can be explained by the operation of a force 36 orders of magnitude greater than gravity. This force is electromagnetism as evidenced by cosmic plasmas that can be accurately modeled not only with computers, but with real physical experiments in the lab. Most of the universe is not nicely electrically neutral, like here on earth, but consists of highly charged electrically active plasma. Most atoms in the universe don't have all their electrons nice and neatly orbiting their nuclei.
Scientists are observing immensely powerful cosmic rays and other radiation from many sources in the universe. All this radiation involves the electric force and has nothing to do with gravity. Scientists have postulated that there should be gravity waves and have spent gobs of money to try and detect these, but so far that has been money wasted since they have not found such waves. In addition, there are measurements of immense magnetic fields in space and on the sun. It is a firmly established principle of science, that magnetic fields can be generated easily by the motion of electric charges.
The large-scale universe is controlled by electrical forces that are far greater than gravity. Gravity is only a controlling factor in electrically neutral environments such as we have here in our corner of the universe. Even if only one atom in 100 billion loses one of its electrons, the force generated by this tiny charge imbalance is far greater than the gravity generated by those 100 billion atoms. You can verify that by doing an experiment right in your own home. Just pick up a few bits of Styrofoam with a charged glass or plastic rod. Charge the rod by rubbing it with a silk cloth. The electric charge on the glass rod will easily overcome the gravity generated by the entire Earth.
Re:Gravitational tides will kill you (Score:5, Funny)
If the astronaut gets across the event horizon, then he will never die relative to us. So, there really isn't a problem here as far as I can tell.
Re: Gravitational tides will kill you (Score:3)
Ahem, where was I before the new Slashdot mobile interrupted me?
To an outside observer, time stops at the event horizon. Nothing can ever fall through it. Someone falling in would see the universe speeding up, faster and faster, until time was progressing at an infinite rate by the time he hit the event horizon. Presumably either the black hole would evaporate or the universe would end before the infinite amount of time passed necessary for someone to reach the event horizon.
I don't really see the problem -
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Yeah, that sounds about right. The last time I read about this... somewhere... it really depended upon the size of the black hole.
Approaching a small black hole, the gradient in gravitational forces closer to the black hole means that e.g. diving head-first into a black hole would mean your head would feel a stronger gravitational pull than your feet and thus your body would be stretched and ripped apart.
Approaching a much more massive black hole with a larger event horizon could reduce that gravitation g
Re:Gravitational tides will kill you (Score:5, Interesting)
While yes, one of the things you would have to deal with is the incredibly hot material swirling around the event horizon which, in and of itself, should produce enough X-rays to fry you, I think this article is actually talking more about an actual characteristic of the event horizon, as opposed to what is in orbit around it, or even what is infalling.
In short, space is supposed to look the same to an observer no matter what side of the event horizon they are on. Instead, a special condition where you smack into something that is there beyond what you would expect from a black hole with infalling matter occurs. That "wall of fire" obviously consists of stuff that has entered the event horizon of the black hole, but it is structured in such a way as to form a highly energetic barrier that should not be there based on our current understanding of relativity or quantum mechanics.
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Perhaps you could cite what you are referring to. I know of no statement by Hawking that suggests gravity affects antimatter differently than matter.
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Actually this says that one member of the particle-antiparticle pair could fall into the black hole. It says nothing about which one would. Sometimes it could be the particle and sometimes the antiparticle. They are both treated the same by gravity. My understanding is that since the particle-antiparticle are separated by a tiny distance, sometimes one is inside the event horizon and is swallowed by the black hole leaving the other one to escape. Since they don't recombine, the one that is swallowed ha
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I don't understand. The standard view of antimatter is that gravity very much does affect it in some way equal to matter.
There are a few possibilities that need to be tested, such as if antimatter can cause antigravity in equal, but opposite proportion to how matter warps spacetime to generate gravity, or that antimatter might generate more or less gravity. However, this is only because we have yet to be able to test antimatter properly. The generally accepted hypothesis is actually that antimatter does
Re:Gravitational tides will kill you (Score:4, Informative)
The idea is that the two particles form, and one is closer to the black hole than the other. One of them barely falls in, while the other barely makes it out. No difference in how gravity effects them, just a difference in initial positions.
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I think they were asking why the one that escapes is always the one that ends up with positive energy, i.e. we never get 'reverse Hawking radiation' sucking up mass from the larger universe and adding it to the black hole. I vaguely know how this works, but my layman's understanding of QM isn't good enough for a decent explanation, and I don't want to lead others down the wrong path.
Re:Gravitational tides will kill you (Score:5, Informative)
Then why would the particle be affected differently than the antiparticle? Why wouldn't *both* fall into the black hole equally?
Both the particle and the antiparticle are affected equally by gravity, but gravity is the weakest force in nature. Think about it: a simple chair, held together by the electromagnetic force, supports you above the ground by counteracting the gravitational attraction of the entire Earth pulling you down.
Since virtual particle pairs start from vacuum, they are always created with equal but opposite momentum. This momentum can't be very big because the attraction between the pair (usually electromagnetic) has to be strong enough to quickly counteract that initial momentum (and bring the particles back together fast enough for them to still count as "virtual"). But just because the momentum can't be very big doesn't mean it can't be big enough for one particle to escape a black hole, if the particles happen to pop into existence with one of them pointing in just the right direction to escape. Hawking predicts that the odds are 50/50 on whether it's the matter particle or the antimatter particle that does the escaping; it has nothing to do with the particles responding differently to gravity.
(Keep in mind that the escaping particle doesn't have to rocket out in a straight line at escape velocity. Instead, it can take a few swings around the black hole in a rapidly decaying orbit, until it slingshots out on a hyperbolic path. The smaller the black hole gets, the more definite the position is for every matter/antimatter particle pair, and by Heisenberg's uncertainty principle applied to position-momentum, this makes it easier for one of the two particles to escape. A smaller black hole also has the bonus that, looking out from just above the event horizon, more directions point away from the black hole, giving more chances to escape.)
You could actually make a black hole that radiates away Hawking radiation with a bias toward antimatter over matter, or vice versa. It's easy: black holes can have an electric charge, so just electrically charge the black hole! Like charges repel, so if the black hole is positively charged, it will preferentially eject positrons instead of electrons. However, the absorbed electrons neutralize the black hole's electric charge, bringing it back to neutral and making the Hawking radiation return to a 50/50 ratio between matter and antimatter.
(We suspect that the universe has a small preference for matter over antimatter, and this is why the universe is made of matter. But this mostly happens for some heavy uncharged mesons, not for lightweight simple particles like electrons. Here, "heavy" means "high energy" means "unlikely to appear in Hawking radiation". So the radiation may not strictly be 50/50, but it should be very close.)
Size Matters (Score:3)
If you fall into a big enough black hole, you die by running out of air in your spacesuit.
Not only is the tidal stress less, but supermassive black holes tend to clear the vicinity of stuff, so if its not 'feeding' there is no radiation to fry you either.
Re: (Score:2)
Right, but this finding gives theoreticians something they can get to grips with in a much more tangible way than the hand-wavey incompatibility of QM and GR.
Re: (Score:3, Informative)
I thought that black holes were still theoretical. Or have they been scientifically proved, and I'm just an asshat?
They've been observed - just because there's theoretical work being done about something doesn't mean it hasn't been shown to exist.
Re: (Score:3)
Yes, black holes have not only been observed, but super-massive black holes have been discovered at the center of every galaxy we've checked.
Re:Black hole argument (Score:5, Informative)
Have we been to a black hole? No.
Have we taken photos of an actual black hole? No.
Have we seen gravitational effects that look exactly like what a black hole should have? Yes.
Do those gravitational effects calculate out as something of several to millions of solar masses in a tiny volume that can't exist in any non-black hole way that we are aware of? Yes.
Have we seen the radiation from an accretion disk falling into and being destroyed by a black hole as predicted? Yes.
Is a black hole what astrophysicists think it is? Probably.
Is a black hole what non-scientists (hollywood, general public, dentists, etc) think it is? Probably not.
Do you really exist? This is about black holes, but your existence is only a bit less theoretical than that of a black holes, though some of the specifics of either may not be what is generally thought about them.
And no, a black hole is not god dividing by zero. It's more likely an alien mad scientist multiplying by the square root of negative zero.
Re: (Score:2)
This doesn't mean that they're wrong; it means that the region of their applicability is bounded. Dealing with such bounds wasn't done in any formal way in Newton's time, but now we have an entire field of study, of "effective field theories", that are a rigorous way to understand how a complicated model behaves in some limit or other. (The example I am most familiar with is "chiral perturbation theory", which consists of pretending the world is made of protons, neutrons, and pions at low energy, knowing fu
Re: (Score:2)
In this case, you have two different theories predicting two different things. It is guaranteed that one of them (or maybe both) are wrong. The only question is: "which one is it?"
Re:They're all Wrong! (Score:5, Funny)
Actually, it is also possible that there is no such thing as a black hole - but cetain parts of the universe just suck. I have known some towns like that.
Re:He would die of shock (Score:5, Funny)
He would die of shock [...] And then her body would be torn asunder.
So you think a black hole would accomplish a gender change on the subject? Interesting theory.
Re: (Score:2)
(Joke!)
Don't be silly! You become a sheodinger's fireball!
Much like the alive and yet also dead cat of infamous repute, our stalwart and jaunty astronaught is in the *perfect* unobserved/unobservable condition!
He is both alive, and dead, at the same time! The schrodinger's cat is also alive, and dead from poisonous gas!
As such, he can simultaneously survive, be burned to a crisp, or be pulled apart like stringcheese, all at the same time!
Re: (Score:2)
Unless, of course, one's soul can exist in mere ashes, in which case the second option would be necessary for "you" to die.
Re:Well.... (Score:4, Informative)
"astronaut" - Someone on who has gone into space.
"fall" - 'to descend under the force of gravity"
"Into" - "to the inside of"; Also "toward or in the direction of:"
"black hole" - "an object in space so dense that its escape velocity exceeds the speed of light"
"die" - "to cease to live; undergo the complete and permanent cessation of all vital functions; become dead."
Or possible in this case: "to cease to exist" literally.
"Ass" - You.