I just finished A Brief History of Time, the updated 10th anniversary edition. I know Hawking is one of the world's foremost experts on black holes.

But . . .

I noticed a rather huge inconsistency.

One of the sections where I learned something new (that's why the inconsistency bugs me) was his description of black hole event horizons. He describes a rather elegant proof that, in order for the event horizon to be the event horizon, all of the photons must be moving exactly parallel to each other. The consequence, of course, is that the event horizon of a black hole could never grow smaller.

He then has several diagrams that show how the event horizon would grow through the black hole accumulating mass or through merging with another black hole.

Great.

The very next chapter, however, details how, due to the spontaneous creation of particle-antiparticle pairs near the event horizon, black holes do, indeed behave like hot bodies obeying the 2nd law of thermodynamics: they radiate energy proportional to their size.

Super.

Except that he then proceeds to prove that, since the energy being radiated is invariable positive, then the energy the black hole absorbs (through capturing the antiparticles) is negative. Black holes, therefore, have a life expectancy and radiate their energy over time.

Thus growing smaller, and eventually exploding at a certain minimum energy. He cites evidence that this happens.

My question: given his earlier demonstration that the event horizon cannot shrink due to the exactly parallel path of photons, what happens as the black hole loses energy?

Logically, the event horizon must shrink, because space-time warps increasingly less as the black hole grows smaller. What happens to the parallel photons? They ought to be emitted as a laser, which is no more than coherent (parallel) photons of a given wavelength.

I'm confused.

Did anyone else note the inconsistency?

If not, did anyone else see something I missed that might explain the apparant contradiction between the idea that the event horizon cannot shrink and the idea that black holes actually shrink?

{MusicMatch won't play that, for some reason}

Since space inside a blackhole is not the same as outside, its possible that it is just converted into something different whenever there is excess photons lying around.

This is purely speculation on my part of course.

I think, however, he has a different definition of how the event horizon is "growing smaller" then how it goes away as a black hole dissapates.

Or maybe I need to read the book. Heh.

"Oh, there's so much I dont know about astrophysics. I shoulda read that book by that wheelchair guy!" -H.S.

Of course we all know the bet that Hawking made, right? Hawking bet that the thing the planet was orbiting (Think it was in Sygnus. Maybe..) was NOT a black hole. He lost the bet, of course.

His explanation was: "If it was not a black hole, then all of my life was wasted in pursuit of it. When I made the bet, I thought that if It wasnt a black hole, then at least I would have the consolation of winning the bet" .. Paraphrased, maybe.

Thats my intelligent post for the decade.

Loosely speaking, a black hole is a region of goddamn space that has so much fucking mass concentrated in it that there is no way for a shit slinging goddamn nearby object to escape its motherfucking gravitational pull. Since our best theory of gravity at the moment is Einstein's general theory of relativity, we have to fucking delve into some results of this theory to understand black holes in detail, but let's fucking start off slow, for you fucking gimps out there, by thinking about gravity under fairly simple circumstances can make your mothers cunt swell up like a big wad of yeasty goodness.
Suppose that you are standing on the surface of a goddamn planet like some fucking dumbass. You throw a fucking rock straight the fuck up into the air. Assuming you don't throw it too hard like a goddamn asshole, it will rise for a while, but eventually the acceleration due to the planet's gravity will make it start to fall the fuck down again. If you threw the rock hard enough, though, you could make it escape the planet's gravity entirely. It would keep on rising for fucking forever. The speed with which you need to throw the rock in order that it just barely escapes the planet's gravity is called the "escape velocity." As you would fucking expect,DUH! the escape velocity depends on the mass of the planet: if the planet is extremely massive, then its gravity is very strong, and the escape velocity is high. A lighter planet would have a smaller escape velocity. The escape velocity also depends on how far you are from the planet's center: the closer you are, the higher the escape velocity. The Earth's escape velocity is 11.2 kilometers per second (about 25,000 m.p.h.), while the Moon's is only 2.4 kilometers per second (about 5300 m.p.h.).

Now imagine an object with such an enormous goddamn oncentration of mass in such a small radius that its escape velocity was greater than the velocity of light. Then, since nothing can go faster than light, nothing can escape the object's gravitational field. Even a beam of light would be pulled back by gravity and would be unable to escape. Well goddamn.

The idea of a mass concentration so fucking dense, like your mom, that even light would be trapped goes all the way back to Laplace in the 18th century. Almost immediately after Einstein developed general relativity, Karl Schwarzschild discovered a mathematical solution to the equations of the theory that described such an object, by lighting his fucking balls on fire. NO SHIT! It was only much later, with the work of such people as Oppenheimer, Volkoff, and Snyder in the 1930's, that people thought seriously about the possibility that such objects might actually exist in the Universe. (Yes, this is the same Oppenheimer who ran the Manhattan Project,asshole, EARN some history, okay?) These researchers showed that when a sufficiently massive star runs out of fuel, it is unable to support itself against its own gravitational pull, and it should collapse into a black hole. HOW DO YOU LIKE THOSE APPLES? Slappy.

In general relativity, gravity is a spooky manifestation of the curvature of spacetime, like in Ghostbusters but it can kill you. Massive objects distort space and time, like your moms fat ass distorts the fucking couch cushions, so that the usual rules of geometry don't fucking apply anymore. Near a black hole, this distortion of space is extremely severe and causes black holes to have some very strange properties. In particular, a black hole has something called an 'event horizon.' No NOT the SHITTY movie. This is a spherical surface that marks the boundary of the black hole. You can pass in through the horizon, but you can't get back out. In fact, once you've crossed the horizon, you're doomed to move inexorably closer and closer to the 'singularity' at the center of the black hole.

You can think of the horizon as the place where the escape velocity equals the velocity of light. Outside of the horizon, the escape velocity is less than the speed of light, so if you fire your type R rockets hard enough, you can give yourself enough energy to get away, and live to be cool in your Type R shit box anotherday. But if you find yourself inside the horizon, then no matter how powerful your shitty Type R rockets are, you can't escape. EVEN if your rocket was Type R, you'd still be fucked, ricey. Havent you been paying attention?

The horizon has some very strange geometrical properties. To an observer who is sitting still somewhere far away from the black hole, the horizon seems to be a nice, static, unmoving spherical surface. But once you get close to the horizon, you realize that it has a very large velocity. In fact, it is moving outward at the speed of light! That explains why it is so fucking easy to cross the goddamn horizon in the inward direction, but fucking impossible to get the fuck back out. Since the horizon is moving out at the speed of light, in order to escape back across it, you would have to travel faster than light. You can't go faster than light, and so you can't escape from the black hole.

(If all of this sounds very strange, don't worry. It is strange. The horizon is in a certain sense sitting still, but in another sense it is flying out at the speed of light. It's a bit like Alice in "Through the Looking-Glass": she has to run as fast as she can just to stay in one place.)

Once you're inside of the horizon, spacetime is distorted so much that the coordinates describing radial distance and time switch roles. That is, "r",as in R-eeverderchee, the coordinate that describes how far away you are from the center, is a timelike coordinate, and "t" is a spacelike one. One consequence of this is that you can't stop yourself from moving to smaller and smaller values of r, just as under ordinary circumstances you can't avoid moving towards the future (that is, towards larger and larger values of t). Eventually, you're bound to hit the singularity at r = 0. You might try to avoid it by firing your rockets, but it's fucking futile, have you NOT been comprehending this, shit ape?: no matter which goddamn direction you try to fucking run, you can't avoid your future. Trying to avoid the center of a black hole once you've crossed the horizon is just like trying to avoid next Thursday, or that syphillitic parapalegic whore at the mall, goddamn how I hate her.

Incidentally, the name 'black hole' was invented by John Archibald Wheeler(oralse), and seems to have stuck because it was much catchier than previous names. Before Wheeler came along, these objects were often referred to as 'frozen stars.' I'll explain why below.

How big is a black hole?
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There are at least two different ways to describe how big something is. We can say how much mass it has, or we can say how much space it takes up. Let's talk first about the fucking masses of black holes, and NO black holes are NOT catholic, shithead.

There is no limit in principle to how much or how little mass a black hole can have. Any amount of mass at all can in principle be made to form a black hole if you compress it to a high enough density. We suspect that most of the black holes that are actually out there were produced in the deaths of massive stars, like Marilyn Monroe and Cher, and so we expect those black holes to weigh about as much as a massive star. A typical mass for such a stellar black hole would be about 10 times the mass of the Sun, or about 10^{31} kilograms. (Here I'm using scientific notation: 10^{31} means a 1 with 31 zeroes after it, or 10,000,000,000,000,000,000,000,000,000,000.) Astronomers also suspect that many galaxies harbor extremely massive black holes and Waffle Houses at their centers. These are thought to weigh about a million times as much as the Sun, or 10^{36} kilograms.

The more massive a black hole is, the more space it takes up. In fact, the Schwarzschild radius (which means the radius of the horizon) and the mass are directly proportional to one another: if one black hole weighs ten times as much as another, its radius is ten times as large. A black hole with a mass equal to that of the Sun would have a radius of 3 kilometers. So a typical 10-solar-mass black hole would have a radius of 30 kilometers, and a million-solar-mass black hole at the center of a galaxy would have a radius of 3 million kilometers. Three million kilometers may sound like a lot, but it's actually not so big by astronomical standards, you dumb ass, this is physics and shit, not grocery baging for fagots. The Sun, for example, has a radius of about 700,000 kilometers, and so that supermassive black hole has a radius only about four times bigger than the Sun.

What would happen to me if I fell into a black hole?
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Let's suppose that you get into your shitty Type R spaceship and point it straight towards the million-solar-mass black hole in the center of our galaxy. (Actually, there's some debate about whether our galaxy contains a central black hole, but let's assume it does for the moment.) Starting from a long way away from the black hole, you just turn off your rockets and coast in. What happens?

At first, you don't feel any gravitational forces at all. Since you're in free fall, and your cool ass Type R sticker can still save you, every part of your body and your spaceship is being pulled in the same way, and so you feel weightless. (This is exactly the same thing that happens to astronauts in Earth orbit: even though both astronauts and space shuttle are being pulled by the Earth's gravity, they don't feel any gravitational force because everything is being pulled in exactly the same way.) As you get closer and closer to the center of the hole, though, you start to feel "tidal" gravitational forces. Imagine that your feet are closer to the center than your head. The gravitational pull gets stronger as you get closer to the center of the hole, so your feet feel a stronger pull than your head does. As a result you feel "stretched", like that big asshole of oralse, (This force is called a tidal force because it is exactly like the forces that cause tides on earth.) These tidal forces get more and more intense as you get closer to the center, and eventually they will rip you and your shitty Type R rice rocket apart.

For a very large black hole like the one you're falling into, the tidal forces are not really noticeable until you get within about 600,000 kilometers thats like 42 feet for you lame ass americans, of the center. Note that this is after you've crossed the goddamn horizon. If you were falling into a smaller black hole, say one that weighed as much as Marlon Brando, tidal forces would start to make you quite uncomfortable when you were about 6000 kilometers away from the center, and you would have been torn apart by them long before you crossed the horizon. (That's why we decided to let you jump into a big black hole instead of a small one: we wanted you to survive at least until you got inside.)

What do you see as you are falling in? Surprisingly, you don't necessarily see anything particularly interesting, like your sex life. Images of faraway objects may be distorted in strange ways, since the black hole's gravity bends light, but that's about it. In particular, nothing special happens at the moment when you cross the horizon. Even after you've crossed the horizon, you can still see things on the outside: after all, the light from the things on the outside can still reach you. No one on the outside can see you, of course, since the light from you can't escape past the horizon.

How long does the whole fucking process take? Well, of course, it depends on how far away you start from. Let's say you start at rest from a point whose distance from the singularity is ten times the black hole's radius. Then for a million-solar-mass black hole, it takes you about 8 minutes to reach the horizon. Once you've gotten that far, it takes you only another seven seconds to hit the singularity. By the way, this time scales with the size of the black hole, so if you'd jumped into a smaller black hole, your time of death would be that much sooner.

Once you've crossed the horizon, in your remaining seven seconds, you might panic and start to fire your souped up type R rockets in a desperate attempt to avoid the singularity. Unfortunately, it's hopeless, since the singularity lies in your future, and your shitty Type R rice rocket is really a goddamn hunk of space flying shit, and there's no way to avoid your future. In fact, the harder you fire your rockets, the sooner you hit the singularity. It's best just to sit back and enjoy the ride, asshole.

My friend Penelope is sitting still at a safe distance, watching me fall into the black hole. What does she see?
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Penelope sees things quite differently from you, because of here semen encrusted eyes. As you get closer and closer to the horizon, she sees you move more and more slowly. In fact, no matter how long she waits, she will never quite see you reach the horizon, but this is really because she is blowing your friend John, cause you went off to fly into a goddamn black hole, shithead.

In fact, more or less the same thing can be said about the material that formed the black hole in the first place. Suppose that the black hole formed from a collapsing star. As the material that is to form the black hole collapses, Penelope sees it get smaller and smaller, approaching but never quite reaching its Schwarzschild radius. This is why black holes were originally called frozen stars: because they seem to 'freeze' at a size just slightly bigger than the Schwarzschild radius.

Why does she see things this way? BECAUSE she is a WHORE. The best way to think about it is that it's really just an optical illusion. It doesn't really take an infinite amount of time for the black hole to form, and it doesn't really take an infinite amount of time for you to cross the horizon. (If you don't believe me, just try jumping in shithead! You'll be across the horizon in eight fucking minutes, and crushed to death mere seconds later.) As you get closer and closer to the horizon, the light that you're emitting takes longer and longer to climb back out to reach Penelope. In fact, the radiation you emit right as you cross the horizon will hover right there at the horizon forever and never reach her. You've long since passed through the horizon, but the light signal telling her that won't reach her for an infinitely long time.

There is another way to look at this whole business. In a sense, time really does pass more slowly near the horizon than it does far away. Suppose you take your shitty Type R spaceship and ride down to a point just outside the horizon, and then just hover there for a while (burning enormous amounts of fuel to keep yourself from falling the fuck in). Then you fly back out and rejoin that cocksmoking whore Penelope. You will find that she has aged much more than you during the whole process;sucking cocks all the lie long day, time passed more slowly for you than it did for her.

So which of these two explanation (the optical-illusion one or the time-slowing-down one) is really right? The answer depends on what fucking system of coordinates you use to describe the black hole. According to the usual system of coordinates, called "Schwarzschild coordinates," you cross the horizon when the time coordinate t is infinity. So in these coordinates it really does take you infinite time to cross the horizon. But the reason for that is that Schwarzschild coordinates provide a highly distorted view of what's going on near the horizon. In fact, right at the horizon the coordinates are infinitely distorted (or, to use the standard terminology, "singular"). If you choose to use coordinates that are not singular near the horizon, then you find that the time when you cross the horizon is indeed finite, but the time when Penelope sees you cross the horizon is infinite. It took the radiation an infinite amount of time to reach her. In fact, though, you're allowed to use either coordinate system, and so both explanations are valid. They're just different ways of saying the same thing.

In practice, you will actually become invisible to Penelope before too much time has passed. For one thing, light is "redshifted" to longer wavelengths as it rises away from the black hole. So if you are emitting visible light at some particular wavelength, Penelope will see light at some longer wavelength. The wavelengths get longer and longer as you get closer and closer to the horizon. Eventually, it won't be visible light at all: it will be infrared radiation, then radio waves. At some point the wavelengths will be so long that she'll be unable to observe them. Furthermore, remember that light is emitted in individual packets called photons. Suppose you are emitting photons as you fall past the horizon. At some point, you will emit your last photon before you cross the horizon. That photon will reach Penelope at some finite time -- typically less than an hour for that million-solar-mass black hole -- and after that she'll never be able to see you again. (After all, none of the photons you emit *after* you cross the horizon will ever get to her.)

If a black hole existed, would it suck up all the matter in the Universe?
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FUCK, no. A black hole has a "horizon," which means a region from which you can't escape. If you cross the horizon, you're fucking doomed to eventually hit the singularity. But as long as you stay outside of the horizon, you can avoid getting sucked in. In fact, to someone well outside of the horizon, the gravitational field surrounding a black hole is no different from the field surrounding any other object of the same mass. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects.

What if the Sun became a black hole?
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Well, first, let me assure you that the Sun has no intention of doing any such thing. Only stars that weigh considerably more than the Sun end their lives as black holes. The Sun is going to stay roughly the way it is for another five fucking billion years or so. Then it will go through a brief phase as a big ass red giant star, during which time it will expand to engulf the planets Mercury and Venus, and make life quite uncomfortable on Earth (oceans boiling, atmosphere escaping, that cunt Penelope sucking even more cocks, that sort of thing). After that, the Sun will end its life by becoming a boring ass white dwarf star. If I were you, I'd make plans to move somewhere far away before any of this happens, like Amsterdam, I also wouldn't buy any of those 8-billion-year government bonds.

But I digress. What if the Sun *did* become a black hole for some reason? The main effect is that it would get very dark and very cold around here, WOW, this is SO much like your sex life, huh? The Earth and the other planets would not get sucked into the black hole; they would keep on orbiting in exactly the same paths they follow right now. Why? Because the horizon of this black hole would be very small -- only about 3 kilometers -- and as we observed above, if you can comprehend what you fucking read, as long as you stay well outside the goddamn horizon, a black hole's gravity is no stronger than that of any other object of the same mass.

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Jacked from Drysart's old thread

*runs away*

quote:

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Delphi had this to say about pies:
That does seem to contradict itself.. Hrm.

I think, however, he has a different definition of how the event horizon is "growing smaller" then how it goes away as a black hole dissapates.

Or maybe I need to read the book. Heh.

"Oh, there's so much I dont know about astrophysics. I shoulda read that book by that wheelchair guy!" -H.S.

Of course we all know the bet that Hawking made, right? Hawking bet that the thing the planet was orbiting (Think it was in Sygnus. Maybe..) was NOT a black hole. He lost the bet, of course.

His explanation was: "If it was not a black hole, then all of my life was wasted in pursuit of it. When I made the bet, I thought that if It wasnt a black hole, then at least I would have the consolation of winning the bet" .. Paraphrased, maybe.

Thats my intelligent post for the decade.

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That part about the bet was funny.

Incidentally, Rush has a kickass song called "Cygnus X-1" also.

The deal about the paralles photons was important. If they weren't all exactly parallel, then there would be collisions, and their paths would change either outward (impossible) or inward, eventually spiraling into the singularity (also impossible, since that would mean there was no event horizon at all). Ergo, all of the photons at the event horizon must be exactly parallel to each other.

If the event horizon shrinks, however, it seems to me that the parallel photons would jet off in a laser beam tangent to the previous event horizon because space-time was no longer sufficiently warped to hold them and, since any other trajectories inside the event horizon ought to spiral into the singularity, the event horizon would go away.

But Hawking also points out that there is no such thing as a naked singularity. The explanation for that gets a bit technical/metaphysical.

Indeed, if you haven't read it, the book is an excellent primer on the nature of the universe as observed by modern science.

That reminds me of the other odd thing: gravitons.

He mentions that the forces we observe--gravity, electromagnetism, the strong and weak nuclear forces--act through the exchange of quantum particles.

Gravity, however, acts instantly, AFAIK. To do so, however, gravitons would have to travel FTL. Which is, of course, not possible.

Hawking doesn't bother to explain that apparent contradiction, either. Even the later stuff on string theory begs the question of how gravity can act instantly over long distances. Or if it even does.

quote:

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Bloodsage had this to say about (_|_):
Thanks!

That reminds me of the other odd thing: gravitons.

He mentions that the forces we observe--gravity, electromagnetism, the strong and weak nuclear forces--act through the exchange of quantum particles.

Gravity, however, acts instantly, AFAIK. To do so, however, gravitons would have to travel FTL. Which is, of course, not possible.

Hawking doesn't bother to explain that apparent contradiction, either. Even the later stuff on string theory begs the question of how gravity can act instantly over long distances. Or if it even does.

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{Add:}

I don't think this part is exactly correct:

quote:

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The horizon has some very strange geometrical properties. To an observer who is sitting still somewhere far away from the black hole, the horizon seems to be a nice, static, unmoving spherical surface. But once you get close to the horizon, you realize that it has a very large velocity. In fact, it is moving outward at the speed of light! That explains why it is so fucking easy to cross the goddamn horizon in the inward direction, but fucking impossible to get the fuck back out. Since the horizon is moving out at the speed of light, in order to escape back across it, you would have to travel faster than light. You can't go faster than light, and so you can't escape from the black hole.

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Unless that's meant to be a far-fetched explanation of what radically curved space-time might look like.

Chalesm?

Anyone else into astrophysics?

quote:

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nem-x had this to say about Cuba:
For a very large black hole like the one you're falling into, the tidal forces are not really noticeable until you get within about 600,000 kilometers thats like 42 feet for you lame ass americans

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Love that part :P

Actually I think it breaks down to the notion of quantum foam. Know what that is? essentially if you break reality down to the smallest level, you get this stuff they call quantum "foam", with the "bubbles" in the foam being comprised of, in theory, hyperspacial tubes. Was an interesting Nova on it, discussing FTL movement, teleportation, and most of all time travel.

quote:

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Ja'Deth Issar Ka'bael had this to say about Robocop:
if Gravitons moved faster than light, then they'd be a form of tachyon.

Actually I think it breaks down to the notion of quantum foam. Know what that is? essentially if you break reality down to the smallest level, you get this stuff they call quantum "foam", with the "bubbles" in the foam being comprised of, in theory, hyperspacial tubes. Was an interesting Nova on it, discussing FTL movement, teleportation, and most of all time travel.

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I agrees with Ja`Deth. At such a level where the event horizion occurs, normal relative physics cease to apply and quantum mechanics take over. Their behaviors might possibly account for the inconsistancies you see. Alice in Quantumland is an excellent read for learning the basics of quantum mechanics. That's about all I can offer, because I'm still majorly f*cked up from getting my wisdome teeth yanked.

As for the photons, could think of it sort of as a shell. Electrons in an atom aren't on set orbital paths. They form shells, and in theory the only thing keeping the electrons in the same shell from ricocheting off from each other is the fact they've all got the same polarity, right? But at the same time, they can't blow outward.

Photons of the event horizon could be in the same sort of state, maybe. Constantly radiating outward, reflecting off of whatever's getting sucked into the black hole, but against a pull like that OF a black hole, it's futile. The "running constantly to stay in one place" analogy fits, especially when you consider that space/time is warped severely. Since none of the photons escape anyway, it doesn't matter if they do careen into one another. It's like having a series of metal balls on the end of chains, which you then fire from a series of guns...once they reach the extent of the chain, they might clatter against one another at the end of their reach, but none of them actually get any farther than the others.

My thoughts, anyway. I'm a mad scientist, though, we don't concern ourselves with stuff like that. Just what explodes and what doesn't.

Well, because I'm not at home, I don't have my copy of A Brief History of Time, so I'll have to wing it from memory. It's been a while since I've read it, so if I say anything directly contradicting something written in the book, just point it out to me.

If I remember the concept of the parallel photons at the event horizon correctly, the resolution that I formed in my head dealt with the fact that there is a constant inflow of photons, some small percentage of which will always be trapped at the exact event horizon. As the black hole's mass shrinks (Which it must, from the radiated energy) The mathematical event horizon (that point at which the escape velocity is c ) shrinks as well. The photons, which were at the event horizon, now are some miniscule distance away. They begin their escape, (though through a very tight spiral outward, as the escape velocity that close would be very close to c. They are no longer "true" event horizon photons.

However, at the same time, there is a constant influx of photons from other stars, some percentage of which are at the exact right trajectory to orbit at the event horizon. These form a new parallel set of photons at the event horizon, maintaining the layer of photons.

The heart of this interpretation is that I take it that when he says the event horizon can't grow smaller, he only means the photon barrier, not the actual mathematical event horizon (which he states must shrink according to blackbody radiation). When the mathematical event horizon shrinks, the old photon layer is no longer the event horizon, only a set of photons very slowly spiraling outward. The new photons aquired are now the barrier at the event horizon.

Thinking about this now, I would even bet that the parallel paths would maintain the same direction over time. The near-parallel spirals would probably knock away any photons that were captured in the wrong direction, as the black hole only shrinks at a slow, constant rate.

I'll readily admit that most of this comes from my own mind creating mental models, and has little to no basis from what the book says. However, it seems to work, at least for as much I can remember since I last read the book. The basic argument I see is that the mathematical event horizon must shrink, because of the constant loss of math, and so therefore the photons that were parallel must be freed. That doesn't mean the barrier must beak down, as long as there is still an influx of new photons. This whole problem is probably because of both the order the ideas were discussed, and the order the ideas were discovered. The "never shrinks" statement may just be left over from before they knew they actually did. The statement can still apply in a fashion, when speaking of the physical photon layer, but it can no longer be speaking about the actual event horizon.

As for gravitons, you're pretty much on your own there. I have very little clue how they work. I think their main problem is that in the theories, they don't quite fit in; we have no real data to work with for them to figure out what's going on.

First, gravitons must be massless. By that, I mean truly massless, not just massless in the sense that photons have no rest mass. As an example of how that changes things, gravitons have no problem moving around as if that black hole wasn't even there. They fly in or out without problem, affecting things nearby. That's only the start of their oddities.

Unfortunately, I see the exact same contradition in the book you did. On one hand, we have talk of those time cones, how nothing can possibly communicate information faster than the speed of light. I can't remember where he mentioned the FTL travel, but it is ringing a familiar bell. Could you please quote it here, so I can be reminded, since I can't get to my copy of the book?

I have to come to the conclusion, though, that gravity isn't instantaneous, regardless of what the quote is. If it is instantaneous, then gravitons would violate relativity, in several very major ways. For one, there's the old experiment of two astronauts aproaching eachother at relativistic speeds. Each sees the other's watch going slower than their own, and both are correct. However, if gravity was instantanous, the one of the astronauts could agree to make some kind of gravity disturbance (moving a planet, etc) at exactly 3 minutes after the meeting. An instantanous message would violate the laws which say that both are correct in the speed of the others clock, violating relativity. The heart of relativity is "different reasons for the same result" but with instantanous messages, the result would be forced to be different.

I didn't explain that experiment very well, but if you know the initial experiment I'm talking about, I think you can probably puzzle out what I mean. Of course, on the other hand Quantum mechanics almost necessitates FTL travel, thanks to Feymann's "takes every possible path to the destination" (someday we'll get them to work together ... someday) So maybe gravitons can. After all, gravity isn't a normal particle, it's (in at least one sense) a disturbance in space-time. A space-time disturbance isn't a particle, or a wave in the traditional sense, so perhaps it, of all things, could exceed light.

This time, the contradiction may not be Hawking's fault. Gravitons lie on that thin border between quantum mechanics and relativity; it is a subatomic particle that fuels the force that relativity deals with. It sits exactly where all our theories break apart. Like I said, I have very little idea about these things, and I have to wonder if anyone truly does.

And since this thing is probably already an ungodly size (I refuse to scroll up to see how big it is), I'll add an old question of my own from Hakwing's book. You mentioned how a black hole takes in the antiparticles of particle-antiparticle pairs, and shoots out the particle, shrinking and generating particles just as it needs to. However, I always wondered; why does it only absorb anti-particles from these pairs? wouldn't it absorb an equal number of normal particles, balancing out the mass? There's no reason why the black hole should favor anti-particles, so why wouldn't it get an equal number of both, leaving the same net mass?

I hate only being able to deal with physics in layman's terms, I'm sure that's where nine out of ten contradictions pop up. Only one more year until my first quantum mechanics class, then maybe I'll be able to answer many of my own questions.

ABHoT is showing its age...

Pika???

And 'Deth!

Perhaps it is merely the chronological order in which he discusses the ideas that creates the seeming contradiction. The editor may have simply missed the sentence telling us that the new knowledge superseded the old.

On FTL travel, Hawking dismissed it completely. Even for virtual (completely massless) quantum particles. He was able to show, quite convincingly, that the ability to move FTL was inextricably linked to the ability to travel in time, setting up all sorts of contradictions, not the least of which was the observable curvature of space-time and the uniform distribution of matter, which don't seem to allow such.

I seem to remember, though, that general relativity is coming under increasing pressure recently. Several astronomical observations seem to show objects moving FTL--I forget their NGC numbers.

Hmmm. I must investigate further.

Thanks for the food for thought, everyone!

Especially Motiak: I missed the funee the first time, 'cause I read it "Tony Hawk"!

Why oh Why did I drop out of college..

Er, I probably wont explain it well, but here goes:

Take two particles. One particle must spin the exact opposite way of the other. Now, send one off to some distant galaxy (or heck, across the block if your time measurments are that good) and then, at a predetermined time, change the rotation of one particle.

Instantly (Yes, Instantly! ) the other particle changes its rotation to be exactly opposite of the other one.

This could be a basis for a teleporter system. Simply take two particles, send one to where ya want to go. Then change the particle spin in a pattern describing matter (Might take a while, but hey..). It could be a long distance telephone at FTL speed. That'd be kewl.

Of course you'd have to solve the problem of destroying the original and making the new one, but if we can figure that out, We could travel in time, i'll bet.

Geez you guys need hobbies.
http://www.towerhobbies.com

hehe rmember when he was on the simpsons.. that ownd

homer is my hero

[ 01-04-2002: Message edited by: Lawgiver Cadga ]

quote:

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And since this thing is probably already an ungodly size (I refuse to scroll up to see how big it is), I'll add an old question of my own from Hakwing's book. You mentioned how a black hole takes in the antiparticles of particle-antiparticle pairs, and shoots out the particle, shrinking and generating particles just as it needs to. However, I always wondered; why does it only absorb anti-particles from these pairs? wouldn't it absorb an equal number of normal particles, balancing out the mass? There's no reason why the black hole should favor anti-particles, so why wouldn't it get an equal number of both, leaving the same net mass?

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That, I understood. I've been wondering about that myself.

quote:

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Delphi had this to say about Reading Rainbow:
Information travelling FTL is possible, and has been proven.

Er, I probably wont explain it well, but here goes:

Take two particles. One particle must spin the exact opposite way of the other. Now, send one off to some distant galaxy (or heck, across the block if your time measurments are that good) and then, at a predetermined time, change the rotation of one particle.

Instantly (Yes, Instantly! ) the other particle changes its rotation to be exactly opposite of the other one.

This could be a basis for a teleporter system. Simply take two particles, send one to where ya want to go. Then change the particle spin in a pattern describing matter (Might take a while, but hey..). It could be a long distance telephone at FTL speed. That'd be kewl.

Of course you'd have to solve the problem of destroying the original and making the new one, but if we can figure that out, We could travel in time, i'll bet.

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This is actually a common misperception regarding quantum mechanical effects. According to Nobel prize winner and discoverer of the quark, Dr. Gell-Mann. He explains it in The Quark and the Jaguar, but I don't remember the details.

But hawkins thinks on many differant lvls so he might have been thinking of something totally differant.
i sure would like to meet the man and just hang out and play video games with him

Could we stick to discussions on String Theory ... plz K thanx!

Edit: The above statement has been brought to you by the Society of Stupid People for More Funny Physics.

[ 01-04-2002: Message edited by: Woody ]

It's an energy thing. Antiparticles have less energy than regular particles (negative, as a matter of fact). In the extremely curved space-time near the event horizon, antiparticles lack the energy to escape in all cases where the regular particle is captured, although in some cases where the antiparticle is captured, the regular particle may have enough energy to escape.

Thus, black holes absorb more negative energy than positive, and emit only positive energy. They therefore lose mass.

As for strings, things get a bit bizarre when we go there. Like the fact that they require many dimensions--as opposed to our standard four--in order to exist. But the math shows that the extra dimensions are extremely curved.

What initial conditions would curve some dimensions, but not others?

Strings also don't solve the problem of gravity's apparantly instantaneous effects: rather than particles moving FTL, you have waves on a string moving FTL. Same problem, though.

Strings do, however, explain some things better than general relativity.

Me -->