French, you're starting to frustrate me again. Listen. Radioactive nuclei do act independently. Each one decays at random. If you observe a single, isolated atom of plutonium or whatever, it will decay at a random moment. You will never be able to devise any experiment that can predict the moment of decay. This much I have already said. Now, there is no difference (in the context of radioactivity) between two billion isolated plutonium atoms, each in its own little box, and a lump of two billion plutonium atoms in one box. From the standpoint of the radiation emitted, the two are equivalent. Each atom decays randomly. When you observe a large number of atoms decaying, you will see a probability distribution emerge. When you flip a coin, it lands on heads or tails at random. When you observe a large number of coin flips, you begin to recognize that the chance is 50/50. - Warren
In thinking about Quantum Theory, it is important to realize that our minds have been conditioned by millions of years of evolution in the Classical World. All the processes and objects which can perceived by our unaided senses conform to the laws of classical physics. Our Classically trained minds are not capable of visualizing Quantum World processes and objects, which conform to a fundamentally different type of law. I do not believe in a deterministic universe, even though it seems more consistent with my intuitive feelings about the Classical World. For most practical purposes in my day to day life, the deterministic view works quite well. However, I am aware of many devices which obey weird Quantum Laws. Unless I am willing to believe in magic and computer fairies, I am forced to believe in Quantum Randomness and other weird notions. As long as I believe that my computer works according to some scientific laws, I have to accept Quantum laws, since classical deterministic laws do not apply. In view of the experimental evidence, the probabilistic view fits very well, and the deterministic view is out of step with reality. Frencheneesz: There are very basic problems in discussing Quantum Theory with you due your view of what is being said by the QT experts. First, the Uncertainty Principle is not saying that there is a practical problem in making exact measurements. It is saying that it is impossible for a Quantum Object to have an exact position and an exact momentum at the same time. It is saying something about the nature of Quantum Objects. While there are practical problems with making extremely precise measurements, this is not the point. What you post implies that you view the Uncertainty Principle as being a statement about the fairly obvious fact that exact measurements are impossible. For example, consider the following two statements posted by you. Even in the 19th century, when most (all?) of the scientific community believed in a deterministic universe, it was realized that exact measurements could not be made. The Uncertainty Principle is saying that even if it were possible to make exact measurements, we would never discover a Quantum Object with an exact position and an exact momentum at the same time. It also states that an experiment which causes momentum to be accurately (not exactly) known will cause position to become less accurately known. This is a property of the Quantum Objects, not a measurement problem. An implication of the Principle is that exact measurements are impossible in principle as well as practice, but this is not the point of the Principle. Weird effects result when quantum objects begin to approach the state of having an exact momentum or position. You really need to understand the implications of the Bose-Einstein condensate, which is an example of quantum weirdness as a consequence of the Uncertainty Principle. Temperature is actually a measurement of particle velocity. The higher the temperature, the faster the particle motion & vice versa. As atoms are cooled to nearly absolute zero, their momentum becomes very close to zero due to having nearly zero velocities. As the momentum gets closer to an exact value (namely zero), the position and particle identity both become extremely blurred, and the group of atoms act as a single quantum object with some weird properties. This is a consequence of the Uncertainty Principle predicted by Bose & Einstein. Imagine a group of dancers becoming motionless when the music stopped. Suppose that every time the music stopped, you could no longer see the individual couples on the dance floor, but could only see a weird blurry object occupying the entire dance floor. Would your mind be boggled by this phenomenon? Would you be able to find a reasonable explanation for it? That is analogous to what happens when atoms become almost motionless, and is a consequence of the Uncertainty Principle. To me it is incredible that Bose & Einstein predicted the results of this experiment more than 50 years before it was possible to perform it. You seem to consider a random process to be one with unknown deterministic laws governing it, implying the existence of such laws. This happens to be the view of many brilliant men who developed the mathematics of probability and statistics at a time when the world was considered to be deterministic in principle, if not in practice. As long as you have this view of processes which obey statistical laws, you are working with a hidden axiom that deterministic laws exist. As a result of this unexamined axiom, your disbelief in Quantum Randomness is similar to a religious faith, which ignores experimental evidence. You also seem to have no appreciation of the nature of processes governed by statistical laws. Are you aware that there are many different types of random processes? My MathCad7 software provides about 20 pseudo random number generators. This is because there are many different types of random processes, with each type producing a different type of data. Random means more than unpredictable or haphazard. Individual events in a random process are unpredictable, but a random process can result in predictable overall behavior. Radioactive decay is used to determine dates for various objects, and it does an excellent job. Quantum tunneling is the basis for various workable electronic devices. Both of these processes obey statistical laws. The mathematics of probability and statistics were developed based on various axioms relating to uncaused events, by men who believed that every event had a deterministic cause. The first men in this discipline were interested in analyzing 17th century gambling games. They considered the mathematics to be a substitute for unknown deterministic laws. Their thought processes started along the following lines. During a period of over 300 years, the mathematics of probability and statistics became a rich, mature, and useful discipline. Our intuition strongly suggests that dice, coins, and roulette wheels are governed by deterministic laws, which cannot be used due to practical problems relating to collection of the necessary data and the complexity of the required calculations. This viewpoint works on the assumption that deterministic laws exist, even though they might be unknown and/or impractical. It seems like a reasonable point of view. As Quantum Theory matured, it became obvious that various Quantum processes were far simpler than casino games of chance. There seemed to be no lower layer of complexity providing an environment in which deterministic laws could act. The experimental data strongly suggested capriciousness, discontinuousness, and other weird behavior. Some of the workers in this discipline began to question the assumption that every event had a deterministic cause. On one hand they had a logically consistent field of mathematics based on assumptions about uncaused random processes. On the other hand, they had a lot of experimental evidence about processes which conformed very precisely to that mathematics. They began to question the assumption that every event had a deterministic cause. Determinism just did not seem to apply to the Quantum world, and the probabilistic view became accepted. At the Quantum level, this does not seem hard to accept, until you realize that it implies lack of determinism for the Classical World, which is based on Quantum phenomena.
The uncertainty principle doesn't state that you can't measure the exact position and momentum of a particle. It states that the particle doesn't have an exact position and momentum. Its position is 'smeared out' over a region. You can't measure the exact position because there isn't an exact position to measure, no matter how perfect your measurement device.
good lord...has anybody ever heard of variables... how constipated can one person er..(or a couple) get...Please Register or Log in to view the hidden image! :bugeye: Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image!
"The allowed precision is so enormous that we literally can't detect the Heisenberg uncertainty principle operating at macroscopic scales." I forgot to reply to this before. If you say that the precision here (in macroscopic world) is why the QM effects are not observed, then what makes you say that even if we had unlimited presision that we would still see uncertainty effects? "What makes you think QM prohibits it? Eh? " I guess it doesn't, but it does imply a more fundemental level. If all particles are composed of strings, then thats lower than the level we can detect now. "QM does not tell you WHY the particle does what it does -- QM predicts the outcome of experiments. There is no experiment that can tell you WHY a particle does what it does." There must be some hypothetical explanations, right? "I've explained this like three times now. Quit acting like you don't understand it!" I understand what you mean when you use the Uncertainty principle. You seem to say the principle still works without the neccessity of bad precision. Why then does the principle mention precision at all? Why doesn't it just leave it out? The precision seems to have somewhat of importance sinse everyone uses it in their definition of the term. "Radioactive nuclei do act independently." Read my statement again. I didn't contest this. I was saying that the particles in the nucleus act independently. You know, protons, neutrons... You aren't going to tell me that protons and electrons "fuse" into one large fundemental nucleus particle, are you? If the particles in the nucleus act independently, then the "randomness" of nuclear decay depends on the "randomness" of aspects of the particles that make up the nucleus. If I was understanding you correctly, you implied that the nucleus acted as a whole and had no more fundemental factors determining its decay. I will tell you, I DO understand you, I DO know what you are trying to say. When I contradict you, I am understanding, yet disagreeing. I know what YOU mean by the uncertainty principle, I know what YOU mean when you talk about randomness. BUT I also pay attention to what I think, there is a wide gap between disbelief and ignorance. Dinosour: "First, the Uncertainty Principle is not saying that there is a practical problem in making exact measurements. " Yes yes. I realize what you mean when you use it. What you don't realize is that when I ask questions or make statements, I use your OWN comments against you whenever possible. This is not to say I don't understand what you think, but I use your writing in a way that is full circle. "As the momentum gets closer to an exact value (namely zero), the position and particle identity both become extremely blurred, and the group of atoms act as a single quantum object with some weird properties. " Well, I don't know much about the condensate, but It seems to me that it would make sense for the particles to "act as one" because they are so close together. The lack of heat makes the particles bounce away from eachother much much less, therefore they are closer, and the closer they are, the more we see it as one particle. As I recall, bose-einstein condensate is the product of bring ATOMS down to near 0 K. ATOMS are composed of many smaller particles that we don't exactly know are doing inside an atom. The particles inside an atom at near 0 may well do wacky things that produce the wacky effects you see in the condensate. You are running by the theory that sinse we cannot see inside the bubble, then the bubble's pressure is an integral part of the universe (yet if we cut the bubble we find that the pressure is due to air).
Frencheneesz Not even close I'm afraid. If what you said was true then any substance taken to near absolute zero would exhibit this behaviour. It is reasonably easy (compared to previously) to cool things down to with a millionth of a Kelvin. Low temperature physics labs do it routinely nowadays. Yet only a very few substances exhibit Bose-Einstein Condensate behaviour. Think about that for a moment. I mean really think about it. It implies the explanation is non-trivial. And the explanation has a lot to do with the Copenhagen interpretation. It goes like this. Particles, and aggregates of particles called atoms, have a property called spin. Spin is similar to, but not the same as angular momentum. Spin is of course a quantum number calculated from probabilistic wave functions. Turns out there are two possible spins allowed by particles, and atoms. You can have half-integer spin, calcaulated from Fermi-Einstein Satistics, or integer spin, calculated from Bose-Einstein Statisics. You can see where this is going I hope. Particles with half-integer spin are called fermions and have the property that no two particles in a closed system can have the same spin. Electrons are fermions and as I said before this is what dictates the energy levels of electrons in an atom. Atoms like He<sup>3</sup> have an aggragate half integer spin so are fermions. If you super-cool this only one atom can be in the lowest possible energy state. Others have to occupy higher energy states, larger spin values. This is observed. Particles with integer spin are called Bosons. These have the property that particles in a closed can have the same spin. For some reason all the force carriers are bosons and most particles are fermions. So, an atom like He<sup>4</sup> has an aggragate integer spin. Supercool a quantity of this and all the atoms can exist in the lowest possible energy states. It also means their wave functions are indistinguishable. It looks like a single object or single atom. Right, you claim to understand all this and yet disagree. I want you to think very closely about this. This behaviour was predicted from understanding the Copenhagen Interpretation. It has been experimentally verified now, over 60 years ater it was predicted. Most of the predictions of QM, based on its probabilistic nature, have been verified and ithas been used to develop many useful techcological tools, as repeatedly pointed out. If you still fail to accept the findings of QM ater all this, then you are in a state of denial. Further debate on this topic is no longer possible since nothing any of us can say can dissuade you from your stance. Irregardless of the swathes of evidence supporting QM and disproving your worldview.
QM is a theory. An extremely successful theory. The theory, in addition to predicting the results of thousands of experiments, predicts this. No, I'm sorry -- it doesn't imply a more fundamental level. It implies that the fundamental level is probabilistic. You will have to get over your cultural bias. Why do there need to be explanations? Once again, can you explain WHY a triangle has 180 degrees? Or why it happens that momentum is conserved in macroscopic systems? Or why there are only two kinds of electric charge? In any event, QM doesn't provide any "explanations." Nor does any other theory. The philosophers can deal with it. The word 'precision' does not imply manmade measurement equipment. Webster's declares that 'precision' means only: "The ability of a measurement to be consistently reproduced." This says nothing of humanity. There are two kinds of imprecision: that which is imposed fundamentally by quantum mechanics, and that which is caused by manmade imperfect machinery. Quantum mechanics literally dictates that particles do not have precise momenta and positions simultaneously. All of your hand-waving and bullshitting has not resulted in any better theory. You don't like quantum mechanics, yet you don't understand it on even a conceptual level. In the case of beta and gamma decay, certainly, the nucleons themselves are individually responsible. In the case of alpha decay, it is the "vibrational" modes of the nucleus as a whole that causes the decay. Essentially, an alpha can tunnel its way out of the strong force potential well. Many times when you 'disagree' you're actually misusing fundamental, important pieces of quantum mechanics. It would seem that you do not actually understand those pieces, since you misuse them so readily. So you're using the Socratic method. However, you've shown us nothing so far. You kick and scream and wail and bitch and moan, yet you have not shown us wrong in any way. You constantly say things like "well, I just don't believe that" when you finally get cornered and your pet illusions are proven wrong. You need to give this crap up. You're bordering on being a religious zealot. You have to wake up and accept physical evidence. "Close together?" The density of Helium-4 is not much different in fluid and superfluid phases. As a result, we must conclude the atoms are approximately the same distance apart. Therefore, we must conclude that the phenomenon of superfluidity has little to do with density. Sorry, no. Sorry, no. A Bose-Einstein condensate is a phase of matter. Superconductors are also a form of Bose-Einstein condensate in which the half-integral-spin electrons form Cooper pairs with integral spin (bosons) and condense. Superconductivity continues to be discovered at higher and higher temperatures, now well above the boiling point of liquid nitrogen. There is no indication that Bose-Einstein condensation requires low temperatures. Could you be any less scientific? I don't see that he's doing anything like this at all. Please explain. - Warren
"QM is a theory. An extremely successful theory. " Point taken, but let me remind you that the mathmatics are the successful ones. Our picture of the subatomic world is only a description of what the mathmatics predict. "it doesn't imply a more fundamental level. " I'm not going to argue with you, but when was the last time you heard someone decting a "string"? "In any event, QM doesn't provide any "explanations." " Ok, I can accept that. "Webster's declares that 'precision' means only: "The ability of a measurement to be consistently reproduced." " Well, how about "exact" as in "It is saying that it is impossible for a Quantum Object to have an exact position and an exact momentum at the same time."? It doesn't look from THAT definition that the uncertainty principle deals with randomness. Using the definition of precision it seems like you are implying that some sort of observation is impossible to reproduce consistently which might imply randomness. Am I right? "In the case of alpha decay, it is the "vibrational" modes of the nucleus as a whole that causes the decay. " In any case, each individual particle has its own movement. Are you denying that, in alpha decay, that the particles in the nucleus act separately? "Sorry, no." Alright, I can accept facts. I can understand that particles could be acting on probabalistic properties, but what I have a real problem with is when you apply randomness to "large" particles that obviously are composed of smaller ones (radioactive decay). The only way that I could see radioactive decay be entirely and independently random is if all the particles in the nucleus combine into one super-particle as you were telling me about the neutron. If the nucleus is composed of particles AND the particles have to be ejected for radioactive decay to have happened, THEN the radioactive decay depends entirely on the properties and interactions of the smaller particles inside it and any randomness that can be attributed to them.
I don't think I need to be reminded, but thanks. I have no idea what you're getting at. I don't think string theory has really been a part of this discussion. This is incorrect. Particles DO have exact positions and momenta. You can measure them to any amount of decimals you'd like. You can get an exact measurement. Then, if you put the system back in the same state, and measure again -- you'll get a DIFFERENT, exact number. And the next time, too. The spread is what's referred to as a lack of precision, and you cannot measure anything more precisely (i.e. repeatably) beyond the precision given by the uncertainty principle. Yes, that's it. Yes, I'm denying that. There are many examples. A free neutron decays with a half-life of about 15 minutes. However, there are many hundreds of stable isotopes known -- the neutrons inside don't decay. Why? Because (in very qualitative terms) the rest of the nucleons interact with the neutron, and squelch the beta process. An isolated nucleon DOES behave differently than a nucleon in a nucleus. This is not good logic, French. Think about a system composed of two coins, each being flipped once a second. If you watch the composite system, you'll see a particular variety of random behavior. If you look more closely, you'll see two coins, each of which is also obeying a particular variety of random behavior. Neither picture is "more correct." You can think of the system as two independent coins, or one "coin assemblage" with its own behavior. The nucleus is no different. There are behaviors at the level of the nucleon that are specific to each nucleon, and then there are larger-scale behaviors that depend on the interactions between nucleons. - Warren
"This is incorrect. Particles DO have exact positions and momenta. " Alright, but some of your coarguers would disagree. That quote I had in there was not of my contruction. It might have been theds.... I'm not quite sure though. "Yes, I'm denying that." "Why? Because (in very qualitative terms) the rest of the nucleons interact with the neutron, and squelch the beta process. An isolated nucleon DOES behave differently than a nucleon in a nucleus." Ok I see what you're saying. Never the less, science is there to find the inner workings of anything. We do not just stop at saying that humans have any sort of random probabilities of having any of the millions of alleles, but we go further to show what particles are working together to produce such an effect. If there ARE smaller parts to an alpha-decay nucleus, then it is the particles' interactions inside that "have" the randomness, and not exactly the nucleus as a whole. Each particle in the nucleus would contribute its own randomness to the randomness of the whole, just as protons and electrons contribute to the properties of an atom while retaining their own.
I doubt they will disagree. You don't seem to fully appreciate the difference between 'exactness' and 'precision.' As I've said about a hundred times now, it seems that some particles, like the leptons, truly are fundamental. It also seems that they are probabilistic. It seems Nature is so. A nucleon cannot undergo alpha decay (an alpha, by the way, is a He-4 nucleus, composed of two protons and two neutrons). Only a nucleus as a whole can undergo alpha decay. The nucleus as a whole has its own set of behaviors, which, you could say, are built from the behaviors of the individual particles. In any event, your statement makes no sense. One coin flipped in isolation shows randomness. A system of two coins flipped together also exhibits randomness. It seems that, like many of the things you bring up, this issue is merely semantic. - Warren
"I doubt they will disagree. You don't seem to fully appreciate the difference between 'exactness' and 'precision.'" I do appreciate it. You clarified that for me already. If you would look up at the statement by dinosaur above "nasor" 's post, you will find that he wrote the quote I had written. "A system of two coins flipped together also exhibits randomness." So what you are saying is that you don't care weather more fundemental factors contribute to a certain randomness (nucleus), and so need not understand anything more?
No. I was trying to express to you the fact that are interactions at many different levels -- not just one. - Warren
"I was trying to express to you the fact that are interactions at many different levels -- not just one." ok... But the reason there is random on that "higher" level is BECAUSE of the smaller factors that exibit certain behavior. You cannot call flipping two coins a fundemental randomness. You need to eventually find the factors producing effects. If something is composed of more than one fundemental part, then any properties of the whole are because of the fundemental parts. Therefore, In ANY nucleus, the randomness of any sort of decay will be based on the state of the particles inside it.
Whaddya mean, let a thread like this die? Hello. This is my first post here, and this thread (which I found doing a search on the behavior of liquid in a vacuum, if you can believe that) is the first I have read here... I explain that because reading this thread, and then replying to it probably will seem like the very pinnacle of irritating behavior to the many people who put so much time (and clearly, not a little frustration) into it-- if I didn't explain myself. The fact is, until today, and my reading of this thread, I didn't know that Sciforums existed. Yes, I did read the whole thing, every last bleeding word. In fact, having read the whole thing is exactly why I have to reply to it-- after all that, and having so many thoughts I would have interjected at various points along the length of it, I can't just let it go without saying anything about it. The first thing I'd like to address is actually the original topic of this thread! Although I could hardly believe the range of topics and the breadth of discussion here, the only thing I started out wanting to reply about was the question of the speed with which fire travels. Actually, the reason I started out to read it all in the first place was to make sure no one else said what I have to contribute about the original fire question! Incidentally (because it seems to come up eventually) I have much larger grounding in philosophy than physics or other "hard" sciences-- but since so many of the implications of what was discussed here are so at home in the philisophical world, I figure I'm in good company. (who was it that said in here, "leave that to the philosophers"? --that one made me laugh) Okay, so the original question was, "How fast does fire travel?" Well, just to have the semantics out of the way, fire propogates through a medium-- I don't want to even start using a word like "travel" around here! Please Register or Log in to view the hidden image! And, as someone already pointed out (in one of the few replies that actaully addressed fire), fire is a chemical process. So, the speed with which fire propogates through the medium that is burning is dependent (naturally) on the medium. Fire propogates at one speed through pure oxygen, as gas (for example) and at another speed through a cloud of gasoline vapor-- and at still another speed through your dear old Aunt Edna. To measure the speed of fire (which someone satirically suggested you go and do-- but it's really not so farfetched!), one can lay out a long line of whatever-it-is you're going to burn, set one end on fire, and time the length of its passage to the other end. In point of fact, this is what is done; and it is why the speed of fire's propogation through certain media is quite well-known. Obviously, there's a large difference between doing this type of thing in a lab, and marching out to your local football field with a can of gas and a stopwatch-- for the record, the info I'm about to spout is from the laboratory style of experimentation, and not the okay-now-light-the-stuff variety. So, what speed does fire travel at? Well, I can answer specifically, but only for those media which fire's speed-of-propogation is specifically known. Those media are mostly explosives. So, your answer(s) is(are): Black Powder: 1,312 feet per second Lead Azide: 13,400-17,000 fps Lead Styphnate: 17,100 fps Mercury Fulminate: 11,500-21,100 fps Tetracene: 13,100 fps Amatol: 14,800-21,100 fps Ammonal: 17,700 fps Ammonium Nitrate: 3,300-8,200 fps Ammonium Picrate: 22,500 fps Astrolite: 26,200 fps C-4: 26,400 fps Cyclotol: 25,900-26,400 fps Flex-x: 22,300 fps HBX (Torpex): 22,700-23,700 fps HMX: 29,900 fps Kinepak: 21,100 fps Minol: 19,100-19,700 fps Nitrocellulose: 21,900 fps Nitroglycerin: 25,400 fps Nitroguanidine: 25,100 fps Octol: 27,500-28,300 fps Pentolite: 24,500 fps PETN: 27,200 fps Picratol: 22,900 fps Picric Acid: 19,000 fps RDX: 26,800 fps Tetryl: 25,800 fps Tetrytol: 24,000-24,200 fps Torpex: 24,600 fps Tritonal: 21,200-22,000 fps The differences in speed, and the range (within a particular explosive) of speeds are due to differences in the chemical makeup of that explosive. Also, although most people have heard the term "high explosives," almost no one knows to what that refers. Well, now you can impress all your friends at parties: it is the speed of detonation that determines whether an explosive is "high" or "low" (now, you didn't think there'd be high explosives without low ones, didja?). In this list, really only Black Powder and Ammonium Nitrate qualify as "low explosives" (generally taken to be anything less than about 7,000 fps detonation speed). Although there are a bunch of comments I am interested in making about the overall thrust of this thread, and where the basic disconnect lies between the "understands" and the "understand-nots" (if you will), I will let it go for now... and possibly revisit it another time. I'm also passingly interested in whether or not I will recieve death threats for having reawakened this long-and-for-some-thankfully-dead thread just so I could put my two cent's worth in. Regardless of these questions, I find that I can retire with the smug satisfaction that comes from knowing that I, and only I, have actually addressed, and answered, in concrete, real numbers, the original question of this thread. So, to all my headily-scientific and infinitely knowledgeable new friends here at Sciforums, I leave you now with this solemn, final thought: Nyah-nyah, na-nyah-nyah
Isarmann: How dare you muddy up an abstract discussion with experimental facts that actually provide a good answer to the question posed? Somebody here will find a way to get you for that. Others: This guy is weird. He read all the prior posts to avoid wasting our time with a redundant post.
Re: Whaddya mean, let a thread like this die? To make a chemical explosion you need two components - a fuel and an oxidizer. You can let the atmosphere be the oxidizer but that produces what we'd simply call a fire. I had thought that the speed of a fire was what the original post - but the topic has drifted since then. Anyway, you can, alternatively, mix the fuel with a solid or liquid exidiser to produce what we normally consider an explosive. Strictly, low explosives don't detonate - they just burn. They don't produce a shock wave. High explosives detonate, i.e they produce a shock front that runs ahead of the flame front. Cheers, Ron.
I'm glad Isarmann drop in his understanding of how fast fire spreads. I'm sure that for a fair experiment you would have to "balance" the very compounds, as some might include oxidizers over others. The reason I mention that is just to add that Altitude might alter speeds (Although so miniscularly that you probably wouldn't notice. Reason: Pressure) Still it's good to see how this thread has evolved.
