Hawking Radiation Full of Sh!%???

YO-Blah,

I have NEVER Completly agreed with Hawking Radiation even though one of my #1 corrospondents seems to take it as gospel (Machio Kaku). The way I understand it, in the ‘Quantum Foam’ that is everywhere, there is always Particles and antiParticles forming and annihilating each other. When this happens close to the Event Horizon of a ‘Black Hole’, one of the pair MAY be sucked into the BH, while the other leaves on a long, Scenic journey of the unniverse. Now, I agree that ‘Hawking Radiation’ exists, BUT what I DONT agree with is that it would make the ‘Black Hole’ ‘Evaporate’ over time…According to the books by S. Hawking that ive read, the only reason that ‘Hawking Radiation’ makes Black Holes evaporate is: ‘The Energy Has To Come From Somewhere’…IE from within the BH…WTF!!! The Energy appears outta nowhere (the ‘ZERO-POINT ENERGY’ of the Quantum Foam…) If it apears outta nowhere then WHY does it need to take its energy outta something (ie the Black Hole)???

I THINK BH’s force the production of energy outta the ‘Quantum Foam’ around da event horrizon. Sure they ‘Make’ positive Energy but…WHY does it have to come from outta da Black Hole???

Im just an SF writer lookin for answers…
-Blah

Law of conservation of matter/energy. Basically, you can’t get something for nothing.

I dunno. I’d reckon that virtual particle/antiparticle pairs are created from nearby “rest state” energy, no matter where they are (if they’re in the middle of a rock, they’re created out of the rock’s rest energy, for instance). So when a particle/antiparticle pair is created on the event horizon and doesn’t annihilate, that’s a tiny chunk of rest energy that the black hole just lost.

That’s conjecture on my part, however, so take it with a big ol’ grain of salt.

There’s also another mechanism creating Hawking Radiation, quantum tunneling of particles. IOW, a wave function on the threshold of the event horizon has a finite chance of being on the other side, thus a certain amount of radiation breaks free of the black hole all the time.

Oww… Please. Spelling and grammar.

The way you understand it is not altogether correct. Virtual particles do not form out of the energy of a ‘quantum foam’. They form because of the uncertainty principle. Conservation of mass and energy can be violated on a sufficiently small time scale, producing a particle/anti-particle pair. When this happens on the boundary of a black hole, one is absorbed into the black hole and the particles cannot recombine. Therefore energy has been used to create them, which comes out of the black hole. I don’t know the exact details - some of the physics involved is quite complicated - but this is a reasonably accurate ‘layman’s interpretation’ of it.

Further, there is at the moment no experimental evidence for hawking radiation. If you don’t accept the theoretical reasons for it then your only real reason for accepting it is that you think it’s a neat idea. If you do accept the theoretical reasons for it, then the black hole evaporates. You can’t have it both ways.

Just a word, BlahMan. The task of the SF writer isn’t to correct perceived mistakes in the physics of the day.

Most people read SF for the story, not for the science, since they don’t know a whole lot about science anyway.

There is no observational evidence for Hawking Radiation. That’s part of the reason Hawking hasn’t won the Nobel for it.

It is a clever theory, though. For reasons that I shan’t go into here, black holes have to have a non-zero entropy. This is problematic if you view GR-considerations of the black-hole solution for the Field Equations. Hawkings answer can also be expressed in the form of vacuum energy density that has to exist because of the fact that the black hole represents and unobservable location, in effect, it’s a “hole” in spacetime. Hawking radiation is a solution to this quandry. The quantum foam explanation is really a whole lot of fancy wording (as is the “borrowing” of mass from the blackhole by the virtual particle pair that has tunnelled into existence). What is really going on is simple conservation of energy, believe it or not. Hawking radiation allows for some of the nasty effects of black holes to be explained away rather nicely. This is why you should buy it.

Wow… What a great sales pitch. I want me one now! Does Sainsbury’s stock hawking radiation?

Yo,

I finally got around to reading ‘A Brief History of Time’ last night (took me 4 hours :frowning: ) . Hawking gives 3 possibilities for Hawking radition: 1: The Particle Anti-Particle forming right next to the Event Horrizon. 2: Quantum Tunneling Effect (I agree with this one) 3: I dont really rember this one but it was unusual.

For #1, Hawking seems to say that when a particle from the pair falls into the BH, it will always become an antiparticle with negative energy, therefore it will lower the energy inside the BH. Also if an anti-particle jets away from the BH, it will become a particle. Sounds a little hokie and contrived to me.

As for the spontaneous generation of Particle/Anti-particle pairs, this is supposedly because of the Heisenburgh Uncertainty Principle (which I also dont agree with). Apparently no single point in space can have 0 energy, because that would mean you would know the precise value of a field and its rate of change which cannot be known at the same time, similar to a particles position and velocity.

Speaking of which, the Heisenburgh Uncertainty Principle: The more accuratly you determine a particles position, the less accuratly you can determine its velocity. The ‘why’ of this is because in order to measure a particle, you must either bounce another particle off it or have the particle hit something, ie a detector. Both of which would alter the particle. I agree with that part of it, but the part I dont agree with is the part that says this happens NO MATTER WHAT WAY you measure it. What if you could measure it in some passive way, for example by detecting the ‘M-Rays’ it gives off, M-Rays being ‘Magic Rays’, ie some type of undiscovered radiation or a ripple in the geometry of one of the higher dimensions, what I mean is some way we dont know about yet. This way would not alter the particle in anway, yet the HUP says you still wouldn’t be able to measure both. Like most of the revolutionary physics of today, the ‘why’ seems very contrived. Also the HUP is self-validating. If you ‘read between the lines’ of the HUP, it pretty much says that there is NO WAY to measure all the attributes of a particle…period.

D. Simmons: My goal is to be a ‘Hard’ SF writer, ie stay as close to Science Fact as possible. I personally enjoy this type better, plus it is a little educational.

-Blah

P.S. I would like to appologise to everyone for the poor spelling, grammer, etc of my OT, I was a little drunk (actually I dont remember starting this thread…) I came home from a heated debate of Hawking Radiation at my local bar and wanted to get some more input (NO I didnt drive back) . Almost everyone there takes the words of Hawking and Co. as gospel, and wont for one nano second even think that he could be wrong.

P.S.S. Has anyone seen my other OT? The one about antigrav and FTL travel? I seem to have lost it…

NM I found it :slight_smile:

Well, about HUP being wrong, here goes. IANAP but I do like the field. Anyway, if I understand correctly, there is no passive way to view very small particles. Actually, thinking about it for a bit there is no passive way to view any object. Let’s take the moon for an example. We see the moon by light bounced off the moon itself. The light comes from the sun. At the same time the light from the sun has mass according to e=mc2. So observing the moon using the light of the sun affects the path of the moon since the light has mass and two masses hitting each other will deflect each other to a point. In the case of observing the moon the mass of the light hitting the moon is trivial compared to the mass of the moon itself but there should be some effect. (I seem to remember reading somewhere that the mass of all the light hitting the earth at any given point of time was roughly equal to the mass of a piece of paper) So we can track where the moon is pretty closely but what we see is delayed by the speed of light according to e=mc2. If I remember correctly the moon is about 8 light seconds from the earth, though that number is probably wrong. Anyway, the point I am trying to make about HUP is that, according to HUP and e=mc2, our observations are always going to be off because we can never see anything in real time and we cannot gauge the effect light has on objects in real time. By the time the light we see which pinpoints the location of the moon hits our eyes the moon has already moved on with the effect of the light on it’s path. The smaller the objects you are trying to view the greater the rate of error since the particles will have more equal masses.

As far as your M-Rays idea goes, there is a simple problem with it in my eyes. The problem is that first, M-Rays haven’t been found and, second, your magical M-Rays couldn’t exist and at the same time convey any information. Point the second is the big one. For example, let us say there is a “Slee particle” that exists but never comes in contact with any other particle in the universe. Since the Slee particle doesn’t interact with any other particle there is no way to confirm the particle exists of gather information from the particle itself because it doesn’t interact with the universe.

Then again, IANAP, and I could be very wrong.

Slee

That bar needs a TV.

Science “fact” at any time can be considered as what the scientific establishment agrees is supported by the available evidence. Hawking’s theories about mini-black holes and radiation from them etc. isn’t yet “scientific fact” and so should not be part of science fiction that is as “close to science fact as possible.”

Maybe a Dink Stover at The Institute For Advanced Study type of story could have Dink proving, or disproving as the case may be,(while the prettiest girl around looks on admiringly) Hawking’s speculations in spite of opposition from all of those surrounding him.

Should I quit my day job now, or wait awhile?

Blah… you are taking the smarmy version of QM to heart way too much. The Heisenberg Uncertainty Principle is endemic, not simply a result of bouncing rays of particles. This is because the position and momentum operators do not commute with each other. You see, that’s the way quantum mechanics works. You have states and operators. The operators act on quantum states (which can be superimposed) to give you an observable (if they are a Hermetian Operator) or some other quantity (if they are not a Hermetian Operator).

All of this may sound like mumbo-jumbo, but it’s the mathematical formalism behind the magic. I’m not sure there is a better way to explain it. If you are up on your mathematics (that is you know enough multivariable calc to not be scared by gradients and you know enough linear algebra to understand what orthogonal bases means) then you can go ahead and wade through a text like Griffiths Introduction to Quantum Mechanics which will explain the math behind the uncertainty principle.

In any case, the reason that measurement is so often mentioned with regards to Heisenberg’s Unvertainty Principle is because it was first proposed as a way to get around the fact that position and momentum did not commute. “What if” the enterprising skeptic like yourself would begin, “I could MEASURE the position and the velocity exactly! Then I would have violated the formalism and we’ll have to throw out the theory.”

“Ho-ho!” says the experimentalist, “you have to do your measurements using something… light, M-rays, I don’t care what. You have to do it with something. And wouldn’t you know that that measurement ends up altering the state enough so that the position and the momentum are NOT known as well as you’d like.”

"But what if we measure it

Won’t that do the trick?" Well, guess what, it will not. We already have thought of such weirdness… looking at the radiation of particles and triangulating backwards. It turns out that anytime a particle emits something that is observable, it changes. If we use that emmission to determine well, say, the position of the object, we will end up, sadly, with the velocity undetermined to a certain level. That’s just the way the world works. We have looked at quantum-entangled triplets, and such, having looked at one of the particles positions, one of the particles momenta, but calculating back we find that in doing so we have altered the quantum state just enough to have the uncertainty return in particle #3. It’s exceedingly frustrating, but it’s by no means contrived. Nature is just set up in this way to thwart our desires in this arena.

Also, Hawking’s treatment of his radiation is done for a general audience in his book. It utilizes the quantum foam idea and weird concepts such as quantum pairs tunnelling out of nothingness. If you are uncomfortable with that, you can look at it a different way. Take the vacuum to have an energy density. What? you say, How can the vacuum have an energy density? Well, it does. We can see it through various treatments. For example, the Casimir Effect. If we know this density exists, and we know that a black hole has to have entropy, then if we change reference frames we will see a difference in the energy near the event horizon because of either length contraction (the vacuum appears larger in extent in some rest frames) or because of time dilation (we will end up seeing more energy signal per unit time in some rest frames). The way to counter this paradox is to allow for some type of radiation that when added up with the vacuum energy density will give us, very neatly, the right answer. Therefore relativity remains intact near black holes with entropy.

If this stuff is a bit too much, feel free to ask more questions and we’ll try to get to the bottom of your misunderstanding. I feel that, in terms of physics, emulation of Feynman is of the utmost importance. Anyone should be able to, if given enough information, wrap their head around what physics tells us.

Uh…what does IANAP mean?

Yo,

JS Princeton:

Emulation of Feynman…Writing squiggly lines on bar napkins??? (A rip on him NOT you…) The heart of my…suggestion…was the ‘why’ of the HUP. The way I understood it, like I said, you must bounce something off the particle, etc etc. You’re saying that it ‘is’ because thats what the math says. Math is my weakest subject, I barely managed to get a C in calculus and even then I never understood nor remembered any of it. The only way I got that grade was because of all the extra credit I squeezed out of the teacher by making computer programs that showed visually the various concepts, etc. (wow that was along time ago…) I guess my biggest thing is that I distrust mathematically derived laws of physical things. Yes, I know that Math is ‘reality distilled’…But where did the equations come from? Just numbers and letters strung together in mathematically correct ways? Did some hindu god/goddess send them to your dreams?

Anyway, so what you’re saying is that even if some entirely passive way, discluding how a particle is changed by emiting radiation, is found there STILL would be no way to tell both, just because thats what the math says. Im sure the math is right but what is the math based on? And what is that based on?

I guess my biggest thing is that almost all of human knowledge seems to be a ‘Tower Built On Sand’ if the foundation is bad, the whole tower has no right to stay standing. What I mean is EVERY scientific theory, etc, seems to be based on at least one assumption, usually on many assumptions, or other theories which have assumptions, etc. What if even one of any of those assumptions are wrong? Then the whole tower comes tumbling down. It seems to me like almost every theory takes the previous theories as gospel, without even considering what the prev. theory was based on and its assumptions.

The scientific method is about explaining observations and changing or retracting theories based on more observations. It seems to me like all the current theories have forgotton the 2nd part of the method, and mainly focus on the first part of it, the explaining, and then look for observations that agree with the explaination. Well, if you look for something expecting to find it you usually do. Any time they do try to change the theory, they seem to do so in a very contrived way (Oh yah, how about Cosmological Constant or ‘Higgs particles’…that will explain why our theories dont agree with our observations…)

Also it seems like alot of physics is filled with statements like ‘such in such acts in such a way that it appears like’. Can anyone say: “The planets orbit around the earth in such a way that they APPEAR to orbit the sun”. I guess in my mind it all comes down to ‘something-ology’ (the study of knowledge and its roots…what is it called? There have been several popular threads here about this…) I think all of human knowledge needs to be carefully examined and ‘rethunk’ from the beginning. Where am I going with this…I have no idea…Im just venting…

Sorry about all that, I was just venting all of the days stress and frustrations in a scientific way…im sure im very wrong about all of that…
-Blah

I Am Not A Physist

blah-Man…

We’ll get you there, don’t worry.

You are worrying right now about the roots of science. This is an epistemological (that’s the word you were looking for) game rather than a practical one. Also, you have the justification a bit backwards. Science doesn’t pick and choose which observations justify itself. It uses all observations to come up with theories and the BEST theories suggest further tests that would falsify themselves.

Let’s consider the development of quantum mechanics and HUP. It was really all instigated, you see, by the condundrum of the blackbody spectrum. The thermodynamical relationship of a blackbody radiating energy blows up as you approach zero energy. That is, there should be an infinite number of low frequency, high wavelength photons pouring out at us from everything if classical physics is right. We can measure such things and find them not to be true. What Planck found was that if you allow for quantum states that the photons have to be in (in other words, there is NOT a continuum of states), then you will necessarily get a spectrum that agrees with observation.

Okay, but Planck didn’t know WHY this was the case. Before we get to the next point, we have to mention some things about wave-particle duality. This was discovered pretty much independent of quantum mechanics. It had actually been a war of sorts back when Newton was around. Newton thought light was a particle, the French thought light was a wave. Ultimately the French won by using interference patterns of light to show that they couldn’t be particles, for how could a particle interfere with itself? (Temember this, it’ll come in handy later.) Now comes the photoelectric effect. This effect was measured in the 19th Century and found that light actually carried momentum. How does a WAVE that is massless carry momentum? Very confusing! Furthermore, de Broglie showed that if a wave like light could carry momentum, than any PARTICLE that carried momentum could be shown to be a kind of wave. Huh? Confusing!

So here’s problem number two: the atom. An electron spinning around a nucleus should give off radiation if it is in a classical E&M system. This would imply it looses momentum and goes spiralling in toward the center. In fact, if you calculate classicaly the age of an atom using this idea, you’ll find that atoms can’t exist for very long at all. They just degenerate! What’s the resolution to this? Again, the Bohr atom relies on the quantization of electrons in so-called orbitals. If the electrons are only allowed to be in places where they don’t destructively interefere with their waves. But electrons are particles, you say. Rightly so, but remember de Broglie? He gave us this wonderful way of making anything with momentum (including electrons) into waves. So it seems that Bohr was onto something.

Okay, so now we have to deal with Schrondinger. All of these facts were known about the world, but they didn’t seem to go together. That is, until Schrondiger decided to write down a peculiar wave equation that had as solutions both the Blackbody Spectrum and the Bohr Atom (with some minor additions that actually make the model BETTER than Bohr’s). Since you claim to be math-phobic, I’m not going to write down the equation (you can look it up for yourself if you wish). However, it deals with the following concepts: Wavefunctions; a system of states (think HARMONIC reasonances) for a given waveparticle (remember that waveparticle duality again), and operators; mathematical manipulations of the states that give you a property of the system you are looking at. Observables (that is anything you can measure) are a particular kind of operator that acts on a state to give you… not an answer, but a whole slew of answers that are each assigned a probability. This is the weird thing about having “states” instead of objects: you can measure one time and get one answer, and then you can measure another time the same wavefunction and get a different answer. Remember the problem of getting particles to interfere with themselves? Well, it’s no longer a problem because if they are in more than one state they can add and subtract to give you the peaks and valleys of an interference patter, even though you thought all along that the thing was a particle! In fact, there is no such thing as “particles” or “waves” in quantum mechanics. They are grouped together under one catagory: waveparticle.

A DIRECT consequence of this formalism is the Heisenberg Uncertainty Principle. Why? Well, it happens that both position and momentum are operators (as they are observable). Whenver you have two different operators, it is fair to ask the question, does it matter which order I operate in? In other words, if can I multiply first and then add or can I add and then multiply and does it make a difference. Sometimes the answer is “yes, it makes a difference” and sometimes the answer is “no, it makes no difference”. For the case of the position and momentum operators the answer is, “yes, it makes a difference.”

In other words, there is no way for you to measure the position and the momentum at the same time and get an arbitrarily good measurement on both. Scientists have been dreaming up ways around the uncertainty principle for ever, and EVERY SINGLE TIME IT IS TESTED, it has been found to hold true. Likewise, Scientists have been dreaming up ways to get around wave particle duality. You may have heard of Young’s Double Slit Experiment? Done with electrons,. it is a pefect example of how it is impossible to divorce quantum mechanics from observation.

You ask the question, what is all this math based on? The truth of the matter is it was based upon fundamental observed properties of the universe. It would be so much NICER if the universe didn’t behave quantum mechanically, but we just don’t see it doing that. Perhaps someday, in the future, someone will come up with a better theory that will incorporate all that quantum mechanics explains and do an even better job. Until that day, QM is the best we got.

You mention being worried about the “contrived” nature of science. You’re going to have to explain your worries better than that. To some extent, all of science is contrived. We see something, and we try to quantify it. Then we look for relationships between the quantities. We postulate a relationship that suggests other observations we can make. We go and make those observations. Sometimes we find, to our delight, that the observations confirm the postulate (the hypothesis). This happens with every relevant observation ever made and you have a theory. Sometimes it doesn’t work out and it’s back to the drawing board. Your mentioning of the Higgs Boson and the Cosmological Constant (dark energy: which, by the by, has direct consequences on Hawking Radiation) are two theories that are currently under considerable scrutiny. They both predict very particular things about what we SHOULD see if we look in the right place. Scientists are racing to look in those places to either confirm or deny these theories. Both of them stand up to the scrutiny that they explain all previous observations. (Did I say all? Yep, I mean all that are recognized as valid by the scientific community. If you wish to argue with the tests of validity or why the community gets to decide, that’s another thread.) We may find them to be lacking or wrong in some way, in which case it’s back to the drawing board. They are contrived ideas only from the standpoint that they are directly related to what we observed and not necessarily DEDUCED from axiomatic expressions (the way math is deduced). However, they have to be rigorous (you can’t have in your theory that 2+2=1.e5) and consistent. If you think that the scientific process in general is flawed, you’d probably be best to jump on one of the other threads that discuss this topic.

Okay, that just about does it. Hope this has opened a few more windows. Keep pushing if it doesn’t.

Schrondinger? Did I write Schrondinger?

Yes, yes you did, JS. But please! Don’t let that stop you! I’m learnin’ a lot here!

:smiley: