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Thread: The Official Cricketweb Science Thread!

  1. #1636
    International Captain Ruckus's Avatar
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    Just saw another science video that blew my mind...was a talk by Brian Cox called 'A night with the stars'. Apparently as an implication of the Pauli exclusion principle, because no fermions can share the same quantum state, it means everything in the universe is connected; i.e. changing the state of one electron alters the state of every other electron. From basic first year chemistry I was already aware of that principle and the concept of quantum states/numbers, but I always thought it only applied to electrons in individual atoms (and that electrons in different atoms could share the same states). But according to him that isn't the case. As soon as he said it, I automatically thought he must have accidently implied something he didn't mean to....but I researched it a bit and on a physics forum the very topic was being fiercely debated, and it turns out he responded on the very same forum to rebut some of the criticisms directed at him. He first posted this link as a more detailed analysis:

    Double Well.html

    And then responded with this afterwards:


    Quote Originally Posted by Brian Cox


    Dear all,

    Let me add a bit more by way of clarification, because I think it's interesting. I've already posted a detailed analysis of the behaviour of a two proton - two electron system, and shown how the exclusion principle leads to a covalent bond in a Hydrogen molecule. Let me paste a couple of pages from my book The Quantum Universe - to save you having to buy it - and annotate it in a couple of places.

    In the book, we do the double well as I posted previously.

    This is how we describe the situation:

    "It seems that we must conclude that the pair of identical electrons in two distant hydrogen atoms cannot have the same energy but we have also said that we expect the electrons to be in the lowest energy level corresponding to an idealised, perfectly isolated hydrogen atom. Both those things cannot be true and a little thought indicates that the way out of the problem is for there to be not one but two energy levels for each level in an idealised, isolated hydrogen atom. That way we can accommodate the two electrons without violating the Exclusion Principle. The difference in the two energies must be very small indeed for atoms that are far apart, so that we can pretend the atoms are oblivious to each other. But really, they are not oblivious because of the tendril-like reaches of the Pauli principle: if one of the two electrons is in one energy state then the other must be in the second, different energy state and this intimate link between the two atoms persists regardless of how far apart they are.
    This logic extends to more than two atoms – if there are 24 hydrogen atoms scattered far apart across the Universe, then for every energy state in a single-atom universe there are now 24 energy states, all taking on almost but not quite the same values. When an electron in one of the atoms settles into a particular state it does so in full “knowledge” of the states of each of the other 23 electrons, regardless of their distance away. And so, every electron in the Universe knows about the state of every other electron. We need not stop there – protons and neutrons are fermions too, and so every proton knows about every other proton and every neutron knows about every other neutron. There is an intimacy between the particles that make up our Universe that extends across the entire Universe. It is ephemeral in the sense that for particles that are far apart the different energies are so close to each other as to make no discernable difference to our daily lives.

    This is one of the weirdest-sounding conclusions we’ve been led to so far in the book. Saying that every atom in the Universe is connected to every other atom might seem like an orifice through which all sorts of holistic drivel can seep. But there is nothing here that we haven’t met before. Think about the square well potential we thought about in Chapter 6. The width of the well determines the allowed spectrum of energy levels, and as the size of the well is changed, the energy level spectrum changes. The same is true here in that the shape of the well inside which our electrons are sitting, and therefore the energy levels they are allowed to occupy, is determined by the positions of the protons. If there are two protons, the energy spectrum is determined by the position of both of them. And if there are 1080 protons forming a universe, then the position of every one of them affects the shape of the well within which 1080 electrons are sitting. There is only ever one set of energy levels and when anything changes (e.g. an electron changes from one energy level to another) then everything else must instantaneously adjust itself such that no two fermions are ever in the same energy level.

    The idea that the electrons “know” about each other instantaneously sounds like it has the potential to violate Einstein’s Theory of Relativity. Perhaps we can build some sort of signalling apparatus that exploits this instantaneous communication to transmit information at faster-than-light speeds. This apparently paradoxical feature of quantum theory was first appreciated in 1935, by Einstein in collaboration with Boris Podolsky and Nathan Rosen; Einstein called it “spooky action at a distance” and did not like it. It took some time before people realized that, despite its spookiness, it is impossible to exploit these long-range correlations to transfer information faster than the speed of light and that means the law of cause and effect can rest safe.

    This decadent multiplicity of energy levels is not just an esoteric device to evade the constraints of the Exclusion Principle. In fact, it is anything but esoteric because this is the physics behind chemical bonding. It is also the key idea in explaining why some materials conduct electricity whilst others do not and, without it, we would not understand how a transistor works."

    We then go on to 3 wells, and then to 10^23 or so - which is the situation in small lump of silicon - and show that this multiplication of very closely-spaced energy levels, (correction added - the occupation of which is governed by) the Pauli principle, is the origin of the conduction and valance bands - i.e. the key to understanding how transistors work (which we also describe).

    I'll admit that we just state that causality is preserved without proof in the book. The notion of causality in quantum field theory is actually a tricky one - there is a large literature on it if you do a search on Spires. But the description of the Universe as a single potential well, with an associated energy level spectrum, is surely valid unless one introduces new physics, which is not mandated by experiment - and I remind you that this rather counter-intuative picture is necessary at a macroscopic level (admittedly transistor-sized and not universe-sized) in order to understand the conduction and valence bands in semiconductors.

    The more "presentational" question posed by some on the forum - namely that one shouldn't say that everything is connected to everything else for fear of misinterpretation - is interesting. In my view, the interpretation of quantum theory presented above is not only valid, but correct in the absence of new physics - and therefore everything IS connected to everything else. I was very careful to point out in the lecture that this does not allow any woo woo ****e into the pantheon of the possible, as I think I phrased it.

    My general position is that when communicating with the public we shouldn't spend our time triangulating off nutters. I'm having to deal with this in spades in my current series, Wonders of Life, where it is tempting to try to give creationists no ammunition at all by avoiding areas of doubt when describing the origin of life and the evolution of complex life on Earth. My strategy is to ignore such concerns, because these people shouldn't occupy any of our time! If we tried to take account of every nob head on the planet, we wouldn't have time to make the programs or write the books.
    I'm not gonna lie...I barely understand either of the above rebuttals, but nevertheless the conclusion he draws does seem to be consistent with what he said on the tv program - e.g. "In my view, the interpretation of quantum theory presented above is not only valid, but correct in the absence of new physics - and therefore everything IS connected to everything else."

    There's one thing I would like someone to clarify if possible, though...does anyone know if this kind of connection on a universal scale is implicated to be physically real or simply a connection that is an inevitable result of uncertainty (i.e. the result of mathematical ambiguity rather than necessarily a 'real' thing)?
    Last edited by Ruckus; 08-05-2012 at 09:08 AM.

  2. #1637
    Global Moderator Spark's Avatar
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    But the description of the Universe as a single potential well, with an associated energy level spectrum, is surely valid unless one introduces new physics, which is not mandated by experiment - and I remind you that this rather counter-intuative picture is necessary at a macroscopic level (admittedly transistor-sized and not universe-sized) in order to understand the conduction and valence bands in semiconductors.
    Would like to see a proof before I believe him. Big claim.
    Last edited by Spark; 08-05-2012 at 08:49 AM.
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  3. #1638
    International Captain Ruckus's Avatar
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    what's a single potential well?

    Edit: if cannot be answered in 20 words or less, just forget about it haha
    Last edited by Ruckus; 08-05-2012 at 08:55 AM.

  4. #1639
    Global Moderator Spark's Avatar
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    A box, more or less. A perfect box if we talk infinite square well.


  5. #1640
    State Captain Lostman's Avatar
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    Quote Originally Posted by Spark View Post
    Would like to see a proof before I believe him. Big claim.
    This isn't a logical conclusion to make from even a simple QM introduction?
    I understand that logic=/=QM at most times, but it just seemed like the natural conclusion to make...
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  6. #1641
    International Captain Ruckus's Avatar
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    On a more philosophical level, do people think that there will be a point (and maybe even sometime soon) where, because of overwhelming complexity and/or uncertainty, science will no longer be a meaningful endeavour (at least in certain areas)? It's kind of like, what happens if they find solid proof of something like a multiverse, or seemingly the scale of the universe or the number of elementary particles in it appears infinite? Would there be any point to pursuing the 'truth' anymore if it seems like it will be a never-ending story? Of course there are always practical applications of science (sometimes very indirect), but I don't really see how the discovery of something like a multiverse would ever offer more than a feeling of awe. And I'm all for science for the sake of discovery and wonder (that imo is it's most important purpose), but will there be a stage when even that side to it becomes meaningless, simply because everything starts to get so far removed from everyday reality it no longer is worthwhile to pursue it?

  7. #1642
    The Wheel is Forever silentstriker's Avatar
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    No - at least not for me. There're two separate points you brought up - one, will it ever become so complicated that human beings are unable to understand it? Possibly, there's no way to know. So far the most surprising thing about the universe is how eminently not complicated it is. There's no reason to believe that a chimp only a few million years removed from swinging on trees ought to be able to discern its basic laws, but that's where we're at.

    The second point is whether it will become 'not worthwhile'. I am not sure what this means. Most of astrophysics of the 20th century have been completely removed from everyday life. And the pursuit of science seems to be unworthwhile to a lot of people, and always has been. But there're still plenty of scientists pursuing it, and always will be. Some people are just driven curiosity about the universe, and always will be.
    Quote Originally Posted by KungFu_Kallis View Post
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  8. #1643
    International Captain Ruckus's Avatar
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    Quote Originally Posted by silentstriker View Post
    No - at least not for me. There're two separate points you brought up - one, will it ever become so complicated that human beings are unable to understand it? Possibly, there's no way to know. So far the most surprising thing about the universe is how eminently not complicated it is.
    Not necessarily just complicated, but perhaps even 'not able to be understood' no matter how intelligent the being is. Science has always been a journey of humility, and I think that would actually be, in a somewhat contradictory sense, a satisfying conclusion if one day it were simply not possible to understand nature any further because of some fundamental constraints.

    Quote Originally Posted by silentstriker View Post

    The second point is whether it will become 'not worthwhile'. I am not sure what this means. Most of astrophysics of the 20th century have been completely removed from everyday life. And the pursuit of science seems to be unworthwhile to a lot of people, and always has been. But there're still plenty of scientists pursuing it, and always will be. Some people are just driven curiosity about the universe, and always will be.
    Yes and no. Most of the stuff has been either directly or indirectly relevant to questions regarding the origins of our universe. One could argue that is removed from everyday life, because of the immense scales involved - whether that be size or time or whatever. But nevertheless, if the question of our existence was confined to perhaps a single universe following from something like the big bang, then it still seems to me a very meaningful question. However, if it gets to the stage where there is concrete evidence of a multiverse and then multiple multiverses and then multiple multiverses in nth dimensions etc. etc. etc. (silly example, but you get the point) I would begin to wonder whether questions of our, and the universe's, existence have any meaning at all any more - it's kind of like if there are seemingly infinite possibilities, using whatever you can come up with in your imagination is essentially just as meaningful as whatever the 'reality' actually is.

  9. #1644
    The Wheel is Forever silentstriker's Avatar
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    Quote Originally Posted by Ruckus View Post
    Not necessarily just complicated, but perhaps even 'not able to be understood' no matter how intelligent the being is. Science has always been a journey of humility, and I think that would actually be, in a somewhat contradictory sense, a satisfying conclusion if one day it were simply not possible to understand nature any further because of some fundamental constraints.
    It's possible and we're already hitting those up. If that ever happens overall, for me personally, it would be highly disappointing almost to "what's the point of living?". I'm glad I'm not alive at such a time but I can definitely see why others would like something like that.
    Quote Originally Posted by Ruckus View Post
    Yes and no. Most of the stuff has been either directly or indirectly relevant to questions regarding the origins of our universe. One could argue that is removed from everyday life, because of the immense scales involved - whether that be size or time or whatever. But nevertheless, if the question of our existence was confined to perhaps a single universe following from something like the big bang, then it still seems to me a very meaningful question. However, if it gets to the stage where there is concrete evidence of a multiverse and then multiple multiverses and then multiple multiverses in nth dimensions etc. etc. etc. (silly example, but you get the point) I would begin to wonder whether questions of our, and the universe's, existence have any meaning at all any more - it's kind of like if there are seemingly infinite possibilities, using whatever you can come up with in your imagination is essentially just as meaningful as whatever the 'reality' actually is.
    Well I'm not sure if there is a functional difference between knowing what happened 12 billion years old vs. trying to find out what happened and if there was anything prior to the bang. I think it's a bit of an artificial difference to say that knowing about another galaxy is any different to knowing about other universes. Both will never be visited by man an I don't see the difference fining out about it to be any different. But that's me personally - obviously what you find interesting is up to you. However your last sentence is key - there could be a point where our theories are unable to make testable predictions (eg string theory ) - and at that point it's not science as far as I'm concerned even if those theories are 'true'.
    Last edited by silentstriker; 08-05-2012 at 12:25 PM.

  10. #1645
    Global Moderator Spark's Avatar
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    Quote Originally Posted by Lostman View Post
    This isn't a logical conclusion to make from even a simple QM introduction?
    I understand that logic=/=QM at most times, but it just seemed like the natural conclusion to make...
    Aren't you making an assumption about the boundedness of the universe by saying so?

  11. #1646
    International Debutant shankar's Avatar
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    Quote Originally Posted by Ruckus View Post
    Yes and no. Most of the stuff has been either directly or indirectly relevant to questions regarding the origins of our universe.
    I don't think this is true. The questions have been about the nature of the universe at earlier and earlier times but not about the origin of the universe itself. That appears to be a meaningless question to me. What is meant by 'origin' of the universe?

  12. #1647
    The Wheel is Forever silentstriker's Avatar
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    I assume it means WTF happened prior to 10^-43s post big bang...

  13. #1648
    Global Moderator Spark's Avatar
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    I think that's a meaningless question as well tbh.

  14. #1649
    The Wheel is Forever silentstriker's Avatar
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    Quote Originally Posted by Spark View Post
    I think that's a meaningless question as well tbh.
    Well, it's possible that it is, as I've mentioned before, due to density and time issues, but I don't think you can make that conclusion for sure until we have better theories.

  15. #1650
    International Debutant shankar's Avatar
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    As I understand it, our equations only 'work' upto t1=t0+10^-43s. We can't ask the question - "What happened before that time?" because the question presumes that "before t1" is a meaningful entity to talk about.



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