Things I learned in physics class
POSTED BY: BadgersHat
UPDATED: Friday, August 12, 2005 15:00
VIEWED: 25158
PAGE 8 of 11
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While QM doesn't tell you where each specific electron is going to strike a phosphor (in the classic two-slit example), the results of firing thousands of individual electrons results in a distribution that exactly matches the mathematical prediction. (Or am I misunderstanding or otherwise over/understating this point?) This predictive power makes QM the most successful theory ever devised by Man. (Everybody agrees on this point, so I'm not even going to make that a question.)
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As you said, the math is undeniably descriptive of a level of reality that is incredibly bizarre when compared to the 'macro' world of our existence (which corresponds more closely with Relativity), and I wouldn't be typing this on a computer were the predictive powers of QM 'untrue'.
So far, so good. What you may not realize, though, is that Relativity is the second most successful theory in human history, judged by that same imperical standard. What's facinating about that fact is that, as far as we know so far, there is no way for both QM and Relativity to both be correct.
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Thanks for understanding and -- I'm begging you -- please correct anything I've said that is either incorrect or misleading, not only for myself but for others who might be following this with some interest (like TiPpY). You can even call me an idiotic poser if you'd like, so long as you enumerate specifically where I've gotten it wrong. I'm seeking deeper understanding and a greater depth of perspective, which can only be gotten from honest and unafraid discussion with others ...
I certainly don't see anything wrong, as far as it goes. The odd thing is, when I learned this stuff in undergraduate school, the missing "how" did bug me. Somewhere along the line, I've discovered, it stopped. My new theory is that we really don't have as much of an emotional need for knowing "how" as we think we do. Rather, what we need is a sense of being right. The only reason we care about "hows" is because it helps us cope when we learn that what we thought was true is not. Whenever science presents us with an observed fact that we would not have anticipated, learning how that happened returns us to a sense of security, I think.
Back in undergraduate school, I think I lost that need for "how" completely. I spent a lot of time explaining QM and Relativity both to my peers in other disciplins, and I got a lot of "how comes." Often, my answer was just "because that's how the universe is, as it turns out." I mean, once you learn that the value of pi is irrational because it was randomly determined during the big bang (and all randomly determined numbers are irrational, because irrational numbers are dense in the real number field), there's not much left that can't be satisfactorily answered that way. Sometimes it turns out that effects to have causes, and it's fun to investigate those cause-effect chains. But it's just the nature of logic that, if you follow the chain far enough, you eventually come to the end--the effect without a cause. The first time or two, that's unsettling, but you get used to it.
P.S. You also need to keep an open mind. It's also the nature of science that, sometimes, everything you think you know turns out to be wrong. However successful QM and GR are, tomorrow they could still be proved totally wrong.
P.P.S. My favorite recent example of the unexpected observed fact are the macroscopic quantum effects seen in the gravity wave studies. They've been measuring the momentum of some gravity wave detectors to such ludicrous levels of accuracy that their position has become uncertain, on a macroscopic scale. I first heard a talk about it at IU when I was in grad school, before they'd done it. It was a popular subject of speculation: what on earth would something like that look like, to the naked eye. I mean, measuring photons in electron cascade devices is a pretty concrete physical event, but let's face it, it still FEELS about the same as an experiment in a computer generated alternate reality. It
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To all:
Thank you very much for providing your perspectives. Since the conversation seems to be getting more 'normalized' I'm tempted to just sit back and let y'all 'riff'. Please don't stop. I've got a blender full of margueritas and it's 'birthday week' at my house...
To QBeam:
Yeah, I was aware of the successes of Relativity. As tough as it might have been for some classical Newtonians to accept at the time, the theory has a certain, "Doh! How could we have not seen that?" quality to it. Very aesthetically pleasing and the fact that it may be summed up so simply (i.e., E=mc², or as originally written, "m = L/c²") adds to its beauty. Correct me if this is mistaken, but I've read that GR has become a model for physical laws, because of this attribute of simplicity. There is some expectation that the fundamental laws of the universe will ultimately be found to be simply elegant.
The fact that the greatest minds of our and previous generations have been questing for TOEs and GUTs has not escaped my attention, either. The problem, as you stated, is that while QM and GR are remarkably successful, they are also mutually incompatible. I'm betting that neither framework is wrong, per se, but that both are subsets of a larger, as yet undiscovered framework, similar to the way that Newtonian mechanics is not wrong, it's just not as complete as Einsteinian Relativity. To clarify and avoid trouble: I've read that Newtonian physics is a functional subset of Relativity.
The gambling man in me says that neither of the apparently incompatible theories of the very small and the very large is wrong, just that they are both part of something larger. The gambler also says y'all are going to find it, hopefully in my lifetime. I think that'll be a special day...
But speaking of the incompatibility of QM and GR, here's a genuine question in my mind, the answer to which I haven't a clue: Has anyone got a firm idea or even an approximate guess as to when the changeover occurs, wherein QM effects stop being the rule and GR takes precedence? I reckon it's got to be larger than an atom (since you still get 'quantum leaps' in the electron shell) and yet smaller than the "Planck mass" (roughly put, about the mass of an amoeba or "some fleas" according to Wikipedia, which is definitely in the realm of the directly observable). So does anybody have information about the precise changeover point?
Your 'P.P.S' only makes this question more beguiling, since you reported QM effects may -- under the right circumstances -- be writ large enough to be viewed with the naked eye. And you actually observed the superposition(?) of the detector yourself?! Could you take me to work with you someday? I'd give a lot to see that.
Are there any write-ups on the phenomenon available on the web? When you say "gravity wave detectors" do you mean as in LIGO or GEO 600? Are the detectors themselves integral to the experiment or just handy objects near a laser interferometer? Is any of this work related to Raymond Chiao's proposed EM radiation-to-gravitational radiation conversion apparatus, or did that whole thing turn out to be snake oil? I have so many questions! Just give me an effective search term, if not an actual link...
Adding your observation to the 'changeover point' question, has anybody begun thinking about what mechanism caused the quantum effect to be extended to a human scale? Is it simply because the detector was so precisely measured in one of two corresponding attributes, that the other (position, in this case) necessarily became more uncertain? What would happen if human observers were thus measured; would using conscious observers as the subjects of the precision measurement change the results in any way, and I wonder what they would see, should they begin to become 'fuzzy' in position like the detector? I hereby request more data...
Respectfully,
zoid
P.S.
What would happen if you put Schrödinger's cat inside the gravitational wave detector? :sm
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@Zoid:
Know what, I wrote this long elaborate post explaining, blah, blah, blah. But, 
it, I have no interest in trying to explain something that will be mis-interpreted... again. I really think that you think you know what I'm about (and are quite off the mark BTW) and read that into what I write instead of reading what I write (yes, I'm guilty of this from time to time as well).
So, I'll just state it simply.
If you are so inclined re-read my posts, you are definitly reading something that isn't there.
I also must note that in the last thread you did (by implication) presume authority (and explicitly after that). Before that, we go along.
This alone should tell you that we can get along and what pushes my buttons.
Also, all my posts regarding your behaviour primarily reference that other thread. If you continue asking questions as you have here (minus the passive aggressive holeness), we'll get along fine. With the holeness, expect people (not just me) to behave offended/irritated/etc from time to time. Act as in the last thread, expect problems as in the last thread. ie To expect different results from the same behaviour is insane.
That is all that I have to say about that. Hopefully it has been put to rest.
Zoid wrote:
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Or how about one or two of those predicted but experimentally unobserved (as yet) particles? "Inquiring minds want to know".
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The colliders are being built as we speak that will help answer that (ie CERN and I think that Fermi Lab is as well.). At least, as far as I know they're still being built. Never know with the gov's today.
Daikath wrote:
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If someone in the scientific community is openly religious he is often not taken seriously
by other scientists.
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I don't know what you've heard but I've never heard anything of the sort; neither has the wife. Any examples?
----
"Canada being mad at you is like Mr. Rogers throwing a brick through your window." -Jon Stewart, The Daily Show
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Originally posted by zoid:
Very aesthetically pleasing and the fact that it may be summed up so simply (i.e., E=mc², or as originally written, "m = L/c²") adds to its beauty..
E=mc^2 is, in Einstein's words (man I hope this quote is right...) "the most important upshot of the special theory of relativity". The equation is not a 'summing up' of special rel.
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Your 'P.P.S' only makes this question more beguiling, since you reported QM effects may -- under the right circumstances -- be writ large enough to be viewed with the naked eye. And you actually observed the superposition(?) of the detector yourself?! Could you take me to work with you someday? I'd give a lot to see that.
Sorry, I don't work in that lab, either; my report is second-hand. Actually, I first heard this described in a talk by a panel that was on CSPAN, or CSPAN2, I don't remember which. I was rivetted, since, like I said, I'd heard that they'd expected to be able to observe macroscopic QM effects at the talk at IU.
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Adding your observation to the 'changeover point' question, has anybody begun thinking about what mechanism caused the quantum effect to be extended to a human scale? Is it simply because the detector was so precisely measured in one of two corresponding attributes, that the other (position, in this case) necessarily became more uncertain? What would happen if human observers were thus measured; would using conscious observers as the subjects of the precision measurement change the results in any way, and I wonder what they would see, should they begin to become 'fuzzy' in position like the detector? I hereby request more data...
Yeah, it sounds to me like you're thinking of the "changeover point" incorrectly. It's not like there are two different physical realms, in which two different sets of laws apply. There's no arbitrary line dividing "large" and "small."
Rather, I suggesting thinking of it as another example like the wave/particle duality of light. When you run certain kinds of tests, light acts like it's made up of particles. When you run other kinds of tests, it acts like it's waves. The truth is, neither is entirely correct--they're just both different aspects of light's true nature. Those tests are interesting because they appear to filter out one of those aspects, but it doesn't mean that other aspect doesn't still exist. The metaphore I use when I give talks to humanities-type groups is to consider your house. If you stand outside at the curb and look, you see one thing. If you go inside and look around, you see something that looks completely different. If you showed some person who'd never seen any kind of building before two photos, one from the curb, and one from sitting on your couch, it might be hard for him to concieve that he was seeing pictures of the same thing, right? But because you understand so much more about the true nature of your house, it makes sense to you--you're just seeing two different aspects of something that's really far more complex than either picture reveals.
I expect that QM and GR are exactly like that. QM problems, like interferometry problems, are designed to observe one aspect of the behavior of mass and energy, and to filter out the other. And vice versa. Both are equally true at all times, and in all circumstances. Just like when you're standing at the curb, looking at your house, that other view from your couch is still there--you're just not seeing it, at that moment, because the limitations of the human mind restrict you to one perspective at a time.
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I'm somewhat leery of entering this fray, but there is definately something facinating about the difference in the perspectives on "science" that you and Zoid are expressing. So here goes.
Anyone who thinks that science isn't totally immersed in faith and irrational belief is profoundly confused. "Science" is merely a certain way of answering questions, and scientists are just a group of people who treat that method as the correct way of answering at least one set of questions. It is a peculiar feature of our civilization today that most people believe that "science" gives "knowledge," and everything else you think you know is just "belief."
The trouble is, the scientific method is horribly constrained. Human beings simply cannot get by in this world, without accepting many, many things without insisting on scientific verification. Its an interesting thought-problem. How many things do you take on faith each day, before you even make it into the lab (or whereever you go to do your job)?
Anyway, I quickly learned that, as a sub-culture, scientists are every bit as prone to irrational assumptions and emotional attachment to ideas as anyone else. In fact, they might be worse than average, because they tend to be skilled at rationalizing. I think I first started to figure this out my senior year in undergraduate school. I was taking a seminar called "current topics in physics," and I had to prepare a talk on the hole in the ozone layer. So off I went to talk to various lab groups who were doing research on the subject. To get me started, I had a specific question in mind: "If CFCs emitted by man are the principle cause of ozone depletion, why is there a hole in the southern hemisphere, but not in the northern hemisphere?" After all, something like 95% of human CFC use was concentrated in the northern hemisphere, and, for the most part, air from one hemisphere doesn't mix with air from the other. I figured this was such a basic problem for the whole field that there would be a simple, well-known answer. I was wrong--lab after lab, no one had any idea. In model after model, everyone just assumed that human emissions were spread evenly between the two hemispheres. Bizarrely, no one seemed to think this was a problem.
Lesson number two came quickly thereafter, when I found out that the reason there were so many lab groups doing one type of research or another was that the easiest way to get federal funding for your project was if the word "ozone" appeared in the title of your proposal. To make a long story short, I discovered that a whole lot of the scientists I was interviewing were simply adopting on faith a position that was not just unproved, but that appeared to be false, based on the best evidence at the time, for the very human reason that doing so made it a lot easier to get paid. It was quite disillusioning, but heck, I couldn't even blame them.
And here's another interesting data point. The vast majority of my physics professors have been devout Christians. This was in stark contrast to my profs in other scientific disciplins--especially biology/chemistry, which was nearly uniformly populated with bitter atheists.
And you better believe that those biologists/boichemists/chemists' emotional investment in their atheism influenced their scientific reasoning. I can't tell you how many times I heard one of these types pontificating about how Christianity was foolish, because they could completely explain the origin of species through evolution. For those who've never considered this argument (how is that possible?), there are two problems with this argument. Firstly, only a specific sub-faction of Christians believe in creationism, and only some of them think it's an important part of Christianity. Secondly, and more amusingly, it's simply not the case that evolutionary science can (at least yet) explain the origin of species. There are several practical problems (such as irreducible complexity), that we don't fully understand yet. Consequently, if you believe that evoluti
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Originally posted by QBeam:
So let me pull all this together in a thesis. I think Zoid has made a valid point, by identifying different factions of scientists. The nature of science appears to be such that we always have more questions than answers. And the idea that science is all about deductive reasoning is a fiction that results from focusing only on the part of science that gets published in the finished papers. The truth is, the most important part of what happens in science is what happens before the experiment ever gets run. Because there's never enough time or money to test every hypothesis, those scarce resources get allocated according to what the scientists collectively believe will be most fruitful--in other words, based on unscientific guesses. Finally, for reasons that are obvious, I expect, when scientists talk to each other, or to non-scientists about their community, they're usually talking about those non-scientific guesses, because they are emotionally invested in their particular favority guesses. After all, people don't waste time talking about things they don't care about.
I disagree with a lot of your conclusions here.
First, the things that I do agree with. Yes, scientific funding is very important (work can't continue without the money), and often times scientists will use the "popular" and "sexy" buzz words which makes things sound exciting. But just becuase they sell their work with them, doens't mean they dominate the scientific method that they'll be using. "Mention ozone and you'll get money." It's true, but its mostly jaded and a little misleading. It's not like their work has no effect on what they're selling, it just may not be "significant" in the vein that most people think. Yes, there's a significant bit of marketing going on, it stinks, but unfortunately, there's still a whole lot of politics involved.
But, it's, in my opinion, "what happens before the experiments get run" is certainly not the most important part. What gets decided upon for future research projects really isn't based on "non-scientific guesses". Just the opposite. There's so much fighting over funding, you really can only get money to look at something that you're absolutely assured of seeing. In fact, most people end up doing a good deal of the work before they put in the grant and experiment proposals, just so they can show good cause that it's worth the investor's money. Additionally, while the actual money is handed out by people who know nothing about science, there are many many committees whose sole job it is to look at the scientific validity of their propositions. If they were based on "non-scientific guesses", they wouldn't be funded. (Insert quip/argument for/against string theory here).
And sure, while scientists may be emotionally involved in their own hunches and beliefs about where science should go yet, if there was a clear and decisive evidence as to the next obvious option, the opposition wouldn't get the money. This has happened to people in the past. The other groups either adapt or fade away. You certainly have to pick a direction and run with it, and often times you really want yor theory to pan out. But doing this is really just putting all your eggs in one basket, and Darwin assured us that that's likely to kill off half the species...
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Quote:
Originally posted by QBeam:
Rather, I suggesting thinking of it as another example like the wave/particle duality of light. When you run certain kinds of tests, light acts like it's made up of particles. When you run other kinds of tests, it acts like it's waves. The truth is, neither is entirely correct--they're just both different aspects of light's true nature.
It's not just 'like' the wave/particle duality of light, it IS wave/particle duality. Particles like electrons have associated wavelengths, just as photons have associated momenta. The 'changeover' (if you want to call it that) occurs when the particle in question is so massive that its associated wavelength is too small for us to perceive its wave-like properties.
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But, it's, in my opinion, "what happens before the experiments get run" is certainly not the most important part. What gets decided upon for future research projects really isn't based on "non-scientific guesses". Just the opposite. There's so much fighting over funding, you really can only get money to look at something that you're absolutely assured of seeing. In fact, most people end up doing a good deal of the work before they put in the grant and experiment proposals, just so they can show good cause that it's worth the investor's money. Additionally, while the actual money is handed out by people who know nothing about science, there are many many committees whose sole job it is to look at the scientific validity of their propositions. If they were based on "non-scientific guesses", they wouldn't be funded. (Insert quip/argument for/against string theory here).
I'm afraid I don't agree. Yes, much money gets cycled through scientific review committees. But I have no idea why you think this means that they won't fund research based on unscientific guesses. As I said, scientists often formulate their opinions based on unscientific guesses.
Let me give you a concrete example, to illustrate my point. (No sense talking past each other.) Consider the research grants that were proposed for SIS/UBS in the mid 90s. SIS and UBS (and a few other material) are a natural tissue graft material that is derived from internal organs, usually pigs. In a nutshell, you get rid of the cellular parts, and keep the collagenous part in as close to its native state as possible. The original idea (in the late 80s) was to use it to make artificial blood vessels to replace blocked or damages ones. In the 90s, researchers at Purdue got the idea of using it as a wound dressing. Their preliminary results showed that it actually induced healing. But for years, scientific review boards refused funding, for the simple--and highly unscientific--reason that people who'd never tried it would not believe that it was possible.
So there it is: funding decisions being made on purely unscientific guesswork. It's not even like they didn't have access to the preliminary data that showed it worked. They just chose to believe that the data was more likely faked or anomolous, rather than consider the possibility that you could heal a diabetic ulcer with pig guts.
The ozone problem I described is another example, of course. The whole field of global climate change has degerated into pseudoscience, because of the huge emotional investment of just about everybody involved, on both sides.
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It's not just 'like' the wave/particle duality of light, it IS wave/particle duality. Particles like electrons have associated wavelengths, just as photons have associated momenta. The 'changeover' (if you want to call it that) occurs when the particle in question is so massive that its associated wavelength is too small for us to perceive its wave-like properties.
Ha! Good point.
In fact, that's kinda what I'm saying. It's not too hard to get your mind around this peculiarity in the case of photons. Or maybe its just that we grow up being trained to understand and accept it. (How old were you the first time the wave/particle duality was explained to you?) The question is, will the rest of the universe turn out to be equally comprehensible? I expect that it will. (My completely unscientific opinion, based on preference for believing the universe is elegant.)
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