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When Geiger and Marsden shot alpha particles at their metal foils, they noticed only a tiny fraction of the alpha particles were deflected by more than 90°. Most just flew straight through the foil. This suggested that those tiny spheres of intense positive charge were separated by vast gulfs of empty space. Most particles passed through the empty space and experienced negligible deviation, while a handful struck the nuclei of the atoms and bounced right back.

Rutherford thus rejected Thomson's (plum) model of the atom,and instead proposed a model where the atom consisted of mostly empty space. (Geiger-Marsden experiment).

As an analogy I want to use an thought experiment with a "modified" peach containing a tiny kernel, where the kernel would have a much greater density than the peaches fruit.

  • If one shoot (with a not very precise gun and from a long distance) another such kernels towards the peach mostly the kernels are going through the fruit and doesn't get deflected. Only if the shoot was by randomness directed to the tiny peaches kernel mostly a noticeable deflection takes place.

  • If one would be able to shoot small marbles from the peaches fruit of the diameter of the peaches kernel towards the peach there will be a different result. Since the density of this marbles according to our thought experimental setup is of low density the marbles will be deflected from the boundary of the peach.

Rutherford thus rejected Thomson's model of the atom, and instead proposed a model where the atom consisted of mostly empty space, with all its positive charge concentrated in its center in a very tiny volume, surrounded by a cloud of electrons (Geiger-Marsden experiment).

If Rutherford had repeated the gold foil experiment with electrons he would have get a result, in which the electrons will get reflected at low kinetic energies and only on higher energies get through the foil. Performing at least a time measurement to compare the time of flight of electrons through the foil and without the foil one will see that the foil electrons are slower the electrons not passing the foil. The high energy electrons passing the foil somehow get influenced from the foil atoms and by this are not going through empty space.

From this can be concluded that the empty space is a miss-interpretation. What says the theory and what are empirical facts (phenomena) which shows that the proposed "peach" model is not holdable?

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  • $\begingroup$ Dear physicists, please avoid circular references like "it was introduced by Rutherford or it is written in books and that's why it has to be so" $\endgroup$ – HolgerFiedler Feb 26 '17 at 18:39
  • $\begingroup$ Hi Holger, More importantly than the possible typos below, the empty space idea is not necessarily the correct way to view electron density regions, or am I missing something? Sorry if I am misunderstanding your point :) You say Performing at least a time measurement to compare the time of flight of electrons through the foil and without the foil one will see that the foil electrons are slower the electrons not passing the foil. Do you mean "a one time" /single experiment and "are slower than". $\endgroup$ – user146020 Feb 26 '17 at 19:01
  • $\begingroup$ Hi @Countto10 It was a little bit difficult to describe in a short way how high energy electrons move in a chain reaction through the foil. But it is enough to show that there is an influence. How to show? Let single electrons through the foil to a sensor and measure the time of flight. Do the same without foil. There will be a time difference and this will be the evidence that high energy electrons passing through the foil are going through not-empty space. Beg my pardon for my English and feel free to correct it, please. $\endgroup$ – HolgerFiedler Feb 26 '17 at 19:08
  • $\begingroup$ The bulk of the space in atoms hasn't been "empty" since 1925 or 1926—excepting of course in popular articles. Keep in mind that this experiment predates the development of quantum mechanics and the interpretations of it at the time are therefore lacking in any understanding of the subtleties of that theory. See also: physics.stackexchange.com/questions/126512/… $\endgroup$ – dmckee Feb 26 '17 at 19:08
  • $\begingroup$ Secondly, the level of timing precision needed for the experiment you suggest is at the sub-nanosecond level even assuming electron speeds comparable to that of a walking human (and in more realistic estimates at the sub-picosecond or even sub-femptosecond level). Nanosecond scale timing is easy enough today, but wasn't possible until many decades after Geiger and Marsden did their work. Femptosecond time of flight isn't possible even today. $\endgroup$ – dmckee Feb 26 '17 at 19:14

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