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It was the observation that atoms have "size". Rutherford's alpha-particle experiment had shown that the nucleus was incredibly small, very much smaller than the distances between atoms, bringing about the "solar system" idea, which right away came into question because such atoms would produce synchrotron radiation and the electrons would rapidly decay from their orbits. So, every nanosecond that the universe has not tuned itself into powdered neutronium is evidence against electrons in "orbit". I think it was Laue who then proposed that the electrons must be bound very close to the nucleus (somehow). Making the atoms very sharp points, and separated from each other by vast distances (relative to their size). However, if the electrons really were confined to very sharp points, then the x-ray diffracted intensities from things like perfect rock salt crystals would not fall off with increasing sin(theta)/lambda. They would be relatively constant (much like the scattering profile of Rutherford's experiment). This was explained away as thermal vibrations "blurring" the atomic positions, making them look like they have "size", and causing the spots to fade with increasing resolution. What Debye showed was that the temperature-dependence of this falloff was insufficient to give the atoms zero size, even when extrapolated to absolute zero (yes, they had liquid air in 1914), and this residual "size" was still comparable to bond lengths. That meant the electrons really were distributed in a "cloud" very far from the nucleus, and apparently not falling in. The only explanation is that the electron must be de-localised. And that is a quantum effect. I always thought that the paper Debye (1914) Ann. Phys. 348, 49-92 is perhaps one of the most remarkable in all of science. It is the original reference for the B factor, the Lorentz factor, and also the paper that ended determinism. At least, that is how I understand it. I had to return my English translation of the Debye paper to the library. I'll order my own copy. -James Holton MAD Scientist On Fri, Apr 19, 2013 at 2:38 PM, <[log in to unmask]> wrote: > James > > In 1915, I thought Debye and Scherrer were testing for interference > between the electrons in different orbits within atoms. This was in order > to test the Bohr model. They got rings but they were powder diffraction > rings. The method never did identify planetary type orbitals. However Debye > eventually adjusted his aims and the method did become useful despite "the > requirement for objects to force themselves into ordered arrays" > > Was there some other key observation Debye made in 1915 which you refer to? > > Colin > > > > > -----Original Message----- > From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of > James Holton > Sent: 19 April 2013 18:27 > To: ccp4bb > Subject: Re: [ccp4bb] popular piece on X-ray crystallography > > Because there is never more than one photon "in flight" at any given time. > Even at 1 photon/s, we still eventually get spots. > > Atoms also don't emit synchrotron radiation, despite there being charged > particles accelerating around their little "orbits" in there. > > But yes, in 1913, people were still hoping there was another explanation > for these two observations, other than that pesky quantum theory. It was > in 1915 that Debye made the key observation that collapsed determinism as > we knew it. I don't think he was very happy about that. > Neither was Einstein. > > -James Holton > MAD Scientist > > On 4/19/2013 9:43 AM, Tim Gruene wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > > Hash: SHA1 > > > > Hello Bernhard, > > > > could you explain this? A photon is the exchange particle of the > > electromagnetic force, i.e. as soon as you have more than two charged > > particles interacting there is more than one photon - why is it > > incorrect to use the term "multi-photon process" in the context of > > X-ray diffraction? > > > > Cheers, > > Tim > > > > On 04/19/2013 06:19 PM, Bernhard Rupp (Hofkristallrat a.D.) wrote: > >> However, a reviewer could reject the method on theoretical grounds > >> - the explanation of X-ray diffraction as a multi-photon process is > >> not correct.... > >> > >> BR > >> > >> -----Original Message----- From: CCP4 bulletin board > >> [mailto:[log in to unmask]] On Behalf Of Peter Artymiuk Sent: > >> Friday, April 19, 2013 7:11 AM To: [log in to unmask] Subject: > >> Re: [ccp4bb] popular piece on X-ray crystallography > >> > >> Just to clarify, Jeremy was not being serious, but imagining what an > >> awkward / obnoxious grant reviewer might have said in 1913. But your > >> points would be valuable in rebutting such a view > >> > >> Pete > >> > >> > >> > >> On 19 Apr 2013, at 11:28, Navdeep Sidhu wrote: > >> > >>> Dear Pet, > >>> > >>> On the contrary, far as I know, nature seems to require most solids > >>> we see around us to be crystalline. And much of the rest is either > >>> gaseous or plasma. Hence, by the reasoning proposed, we are led to > >>> suspect a different conclusion: that it's studies dealing with the > >>> remaining state that have "little general applicability as the > >>> requirement for objects to force themselves into" the disordered > >>> arrays of the liquid state "is an absurd limitation." (However, I'd > >>> support funding it nevertheless.) > >>> > >>> Best regards, Navdeep > >>> > >>> > >>> --- On Fri, Apr 19, 2013 at 10:14:04AM +0100, Peter Artymiuk > >>> wrote: > >>>> Another of my colleagues, Jeremy Craven, is an NMR spectroscopist > >>>> and > >> bioinformatician. He is in referee mode at present and comments: > >>>> > >>>>> From: Jeremy Craven <[log in to unmask]> Date: 19 April > >>>>> 2013 10:05:18 GMT+01:00 To: Peter Artymiuk > >>>>> <[log in to unmask]> Subject: Re: Fwd: popular piece on > >>>>> X-ray crystallography > >>>>> > >>>>> I suspect this technique will have little general applicability as > >>>>> the > >> requirement for objects to force themselves into ordered arrays is an > >> absurd limitation. I would not support funding it. > >>>>> Jeremy > >>>> > >>>> I fear he may be right > >>>> > >>>> best wishes Pet > >>>> > >>>> > >>>> > >>>> > >>>> On 19 Apr 2013, at 09:53, David Briggs wrote: > >>>> > >>>>> Following on from that - readers may be interested in Stephen > >>>>> Curry's post in the Guardian, regarding the Crystallography > >>>>> exhibit at the London Science Museum. > >>>>> > >>>>> http://www.guardian.co.uk/science/occams-corner/2013/apr/19/1 > >>>>> > >>>>> > >>>>> > > regards, > >>>>> Dave > >>>>> > >>>>> ============================ David C. Briggs PhD > >>>>> http://about.me/david_briggs > >>>>> > >>>>> > >>>>> On 19 April 2013 09:44, Peter Artymiuk > >>>>> <[log in to unmask]> > >> wrote: > >>>>>> Dear all > >>>>>> > >>>>>> In Britain there is a free newspaper that you can pick up on > >>>>>> buses > >> called the Metro. My colleague Geoff Ford pointed out this short > >> feature on the history X-ray crystallography in last Monday's Metro > >> newspaper. I think it's rather good. > >>>>>> http://www.cosmonline.co.uk/blog/2013/04/14/conquering-realm-invi > >>>>>> si > >>>>>> > >>>>>> > > ble > >>>>>> best wishes Pete > >>>>>> > >>>>>> > >>>>>> > >>>>>> Prof Peter Artymiuk Krebs Institute Department of Molecular > >>>>>> Biology & Biotechnology University of Sheffield Sheffield > >>>>>> S10 2TN ENGLAND > >>> > >>> --- Navdeep Sidhu Departments of Structural Chemistry & Pediatrics > >>> II University of Goettingen Office Address: Institute of Inorganic > >>> Chemistry Tammannstrasse 4 37077 Goettingen Germany > >>> Email: [log in to unmask] Phone: +49 551 39 33059 Fax: > >>> +49 551 39 22582 Dept. Homepage: http://shelx.uni-ac.gwdg.de/ > >>> --- > >> Prof Peter Artymiuk Krebs Institute Department of Molecular Biology & > >> Biotechnology University of Sheffield Sheffield S10 2TN ENGLAND > >> > > - -- > > - -- > > Dr Tim Gruene > > Institut fuer anorganische Chemie > > Tammannstr. 4 > > D-37077 Goettingen > > > > GPG Key ID = A46BEE1A > > > > -----BEGIN PGP SIGNATURE----- > > Version: GnuPG v1.4.12 (GNU/Linux) > > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ > > > > iD8DBQFRcXQyUxlJ7aRr7hoRAm2MAJ92WHxpnCeuwTDw/kcc6Qdy4ynBpgCgooRr > > MN2Rm2CU2N95Sz4Epd0lEj8= > > =Ai1+ > > -----END PGP SIGNATURE----- > > -- > This e-mail and any attachments may contain confidential, copyright and or > privileged material, and are for the use of the intended addressee only. 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