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Problems with The Universe

  1. Aug 13, 2010 #1
    I just watched the latest episode of "The Universe", on the History Channel.

    Yipes, they made a lot of gross errors!

    They explained why matter is solid when it's composed of mostly empty space: Using an electric box fan, they showed that pingpong balls go through it when the blades are not moving. They said the hub is like the positive nucleus, and the blades are the electrons. It was said that "standing still" they don't keep anything out, but when spinning (he turns on the fan) it now fills out the space and prevents the balls from passing through.

    When they said that matter is mostly empty space, they showed an illustration of simple planetary-model atoms, far far apart like a diffuse gas. In reality, those electron shells are touching or bound together to make the solid. The "emptiness" was portrayed at the wrong level!

    The Earth was morphed-in from a bar magnet, showing the magnetic field is like the Earth is a big magnet. But they showed the N at the Earthly north pole. If the Earth were a big bar magnet, the S would be at the top, so the N's on our compass needles are attracted to it.

    Particles from solar flares are radioactive? I thought they were mainly protons and electrons.

    They said that the plasma is magnetic, and that's why it's deflected via the Earth's magnetic field.

    They said that if the geomagnetic field faded or reversed, our compasses would not work, and GPS would not work either.

    Sunspots are holes where the sun dimples down, and a solar flare is where material rushes out of this central bore (the body of the black spot) like a geyser! The "solar flare" arcs across and somehow connects with another one (it didn't say if they both squirt and meet in the middle, or of the first plume dives back down the other hole) to form the loops you see at the edge of the sun.

    Jupiter's magnetic field extends out for 4 million miles.

    The classic picture of iron filings around a magnet: this was explained as a way to visualize the "lines" that are really there. They got the basics wrong, but I can see how they were leading up to the way magnetic lines behave in the sun.

    I don't remember what else -- it just kept on going, with almost every scene being incorrect somehow. Anyone have more?
     
  2. jcsd
  3. Aug 13, 2010 #2
    Almost everything in your above list is correct. The ones that aren't are completely fair simplifications for the general public.
     
  4. Aug 13, 2010 #3

    diazona

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    I don't know, I think they could at least have showed the Earth's magnetic field in the proper orientation, and maybe colored in some electron clouds in the atom model. But to be fair, "solidness" is not exactly the easiest thing to explain in non-technical terms.

    Then again, I didn't see the show, so maybe I should keep my mouth shut :wink:
     
  5. Aug 13, 2010 #4
    lol, I don't think that's a necessary prerequisite.

    But I really disagree about the magnetic field, if anything the scientific convention of magnetic fields is what's incorrect, not the earth's field--which is based on historically clad nomenclature. The "top" of the earth is 'north,' so the magnetic pole on that side is also 'north.' Some genius just decided that whichever direction of a bar magnet points towards that pole is also 'north.' ;P
     
  6. Aug 13, 2010 #5

    diazona

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    Well, yeah, I can agree with you there, that the convention is confusing. It probably would have made more sense to use other terms that aren't related to geographical direction.

    But actually, what came first was people deciding that the end of a bar magnet which points north should be labeled "north." It made perfect sense for several centuries, until (according to Wikipedia) William Gilbert first postulated that the Earth itself was a giant magnet in 1600. I'm sure after that happened, it didn't take too long for someone to realize that the north end of the Earth had to have the same polarity as the end of a bar magnet which points south. Of course, by that time they were pretty much stuck with the "north" and "south" labels, so they had to say that the Earth's south magnetic pole was the one at the north end of the planet. The alternative would have been decreeing that the end of a bar magnet which points north should actually be relabeled the "south" end, and that would have confused a lot of people. Probably even more than the current system.
     
  7. Aug 16, 2010 #6
    How is the balls and fan bit "correct" or at least "fair simplification"?
     
  8. Aug 16, 2010 #7

    alxm

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    On a related historic note, 'B' for the magnetic field comes from borealis.

    But yes, the whole 'atoms are mostly empty space' stuff is pretty lousy if you ask me. The is no meaningful distinction between 'empty' and 'occupied' when you're talking about particles that have no definite location.

    Besides being the truth, that's a far more interesting fact than the claim that atoms are 'mostly empty'.
     
  9. Aug 16, 2010 #8
    Their magnetic reference is no more odd than using current flow conventions to reflect "positive" current movement.

    The only one I did not get was the GPS comment...I can tell you from first hand experience navigating a boat in magnetically anamolous areas of Maine (US east coast) my two GPS systems continued to provide my correct position and heading.....

    They implied compass navigation would be interrupted by a pole reversal...but did not explain .....I suspect they meant the new (reversed) N and S poles would likely be in different relative positions from the opposite ones today....the inner Plasma would likely move and shift about....
     
  10. Aug 16, 2010 #9
    You see, they weren't actually saying that atoms are "balls and fans." They were using what we call an "analogy." See: http://en.wikipedia.org/wiki/Analogy. Analogies have been used since the ancients to explain difficult concepts. The use of analogies is similar to that of "comparisons," "metaphors," "similes," "allegories," and "parables." They can all be used to produce insight in otherwise obscure subjects.

    Note that here, I neglected to employ an "analogy," so as to not confuse you further.
     
  11. Aug 16, 2010 #10
    I really can't see a way in which the ball-and-fan thing is helpful under any circumstance. I used to think that's why material was solid, I don't know who told me it. What's the analogy? A mostly empty space can impart a force? It's completely misleading.
     
  12. Aug 17, 2010 #11
    I've actually always wondered that, thanks!

    The significance of 'mostly empty space' is exactly that particles don't have a definite location, and more importantly, that the entire concept of "size" and the pool-ball notion of particle physics is entirely subjective.

    Its important to realize that when you touch something, its not nano-scopic billiard-balls colliding and therefore not moving further. Instead its E&M interactions between elusive collections of energy we term 'particles.'

    ~~~~~~~~~~~~~~
    As for everyone who's suggesting that 'mostly empty space' isn't even accurate: that's ridiculous. The covalent radius of a hydrogen atom is something like
    [tex]
    R_H \approx 10^{-11} \textrm{ - } 10^{-10}
    [/tex]
    The charge radius of a proton, on the other hand, is
    [tex]
    R_p \approx 10^{-15}
    [/tex]
    Thats a factor of a hundred million difference in 'volumes.'
    Now, the electron's radius
    [tex]
    R_e \lesssim 10^{-22}
    [/tex]
    in advance of objections (see: http://iopscience.iop.org/1402-4896/1988/T22/016/).

    So the 'size' of the electron, which generates the effective barrier between atoms, is a whopping 22 orders of magnitude smaller in effective volume than a hydrogen atom. So how exactly is it inaccurate to say that what we think of as 'matter,' if you look at the constituent particles, is 'mostly empty space'?
     
  13. Aug 17, 2010 #12
    I didn't know there was a "size" of an electron.
    Thought that all fundamental particles are essentially "size-less"
     
  14. Aug 17, 2010 #13

    sophiecentaur

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    At School, were were told that the end of a bar magnet that pointed to the North was called a "North Seeking Pole", not a "North Pole". There could be no confusion that way because the South Pole of the Earth is also a NSP.
     
  15. Aug 19, 2010 #14
    You don't have to be condescending. I certainly know what Analogy is. I just don't see how this analogy is useful or valid. Electrons don't repel other atoms because they are moving rapidly around the nucleus. Are you saying that is the case?
     
  16. Aug 19, 2010 #15
    But the "size" of the bound electron is exactly that of the resulting atom. It is the concept of size that is funny. In no cases do we really have the same concept of size like we use in our familiar world. It's more like the territory of a lion: it's staked out a zone of space, and affects things that overlap that space.
     
  17. Aug 19, 2010 #16
    What if the motion of the fan blades is an "analogy" for the delocalization of the electrons--mostly due to QM effects, but yeah, a classical concept of velocity can't be entirely excluded from that. As I showed earlier (above), the fundamental "size" of an electron is (in this context) negligible. If electrons weren't delocalized around nuclei, the effective size of atoms would be many orders of magnitude smaller and therein their interactions with other atoms.
     
  18. Aug 19, 2010 #17
    That's just not the case. That would be the same as saying the "size" of jupiter is that of its orbit (even though the Bohr model is incorrect), because its tidal and gravitational interactions over large time scales extend that far.

    An electron "cloud" or "occupied orbital" is not the same as an electron.
     
  19. Aug 19, 2010 #18

    alxm

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    That's a charitable interpretation to say the least. Most people hearing the claim that 'atoms are mostly empty space' aren't learning quantum mechanics. Most people's image of the atom is that of the Bohr model, which most certainly does give people the idea that there's nothing 'between' the electron and the nucleus.

    As for the rest of your objections, that was handled by JDługosz already.

    That is the case. And it underlines what JDługosz said, 'size' on the macroscopic scale has no meaning at the subatomic scale. There is no 'shell' around the atom giving it a particular radius, and any definition of such radius is merely a convention or convenience (such as the Bohr radius, or charge radius), with no real resemblance to macroscopic 'size' which is quite definite.

    It certainly is, as far as the electron's "size" and location and every single observable property of it are concerned. What's the 'size' of a delocalized electron? It can be detected in several places simultaneously.
     
  20. Aug 19, 2010 #19
    seriously misleading.....Of course "size" has meaning on the sub atomic scale....not the same as our classical macroscopic understanding.....but clearly observables which makes such things "real"....

    For a particle in a bound state, there is a vanishing probability of finding the particle at infinity.....the particle is localized in a finite region; in a unbound state, that particle does not remain localized in a finite region...the eigenfunctions do NOT vanish at infinity....

    Another interpretation of "size" comes from scattering observations....

    and yet another, perhaps less direct, in nulcear reaction calculations via nuclear cross sections...http://en.wikipedia.org/wiki/Nuclear_cross_section
     
  21. Aug 19, 2010 #20

    alxm

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    I don't see how this is 'seriously misleading' when I made the point in the same post that 'sizes' are used. But I disagree that they are not clearly 'observable'. They're calculated from observed values in accordance with some definition that was defined into existence.

    E.g. The Bohr radius is the radius of greatest total electronic density in the non-relativistic hydrogen atom, not accounting for reduced mass effects. You could define it as the radius that encloses 90% of the electronic density or 50% or whatever you like.
     
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