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Déjà Vu

  1. Mar 19, 2003 #1
    I do not know if this belongs to philosophy. If not the mentor can move it.

    About a century ago the quantum theory was born. It claimed the atom was its domain. Molecules,and all bigger than molecules, were left to normal physics. Also, since a century, we have two systems of physical laws.

    In the past, from about 700 BC to about 1600, there were also two systems of physical laws, the earthly laws, governing earthly mechanics, and the heavenly laws governing the celestial mechanics. The frontier was the moon. The moon, and all above it, was governed by celestial mechanics.

    But whereas, in the past, there was a clear, nearly legal, separation of the two domains, the moon, now the separation is not well defined.

    For example, an electron in an atom is claimed to belong to QM. But when it is kicked out in a cathode and travels in a beam it obeys normal laws. Clearly, it passed from one system to the other.But where was the frontier?

    We know the moon and the artificial satellites orbit the earth following the earthly laws of Newton. The electrons in an atom seem to do the same, but some say they do not follow classical laws but special laws of QM. They say, as everybody can I see on Internet, classical physics can not, and may not, explain the atom because it belongs to QM and because, by normal physical laws, the electrons crash onto the nucleus of the atom.

    On the one side the instauration of a double system of physical laws is a step back to Copernic, Ptolemy, Aristotle etc..
    The Universality of the Physical laws has been claimed during antiquity. It has been defended by several scientists during the Middle Ages and was generally accepted since Newton. Now it is given up. A step backwards.

    On the other side I do not see why an electron should crash on the nucleus of the atom whereas the moon did not yet fall onto the earth.

    Can someone explain why an electron should crash on its nucleus and does not circulate about it in an elliptic or cicular orbit, as the moon and artificial satellites do , and why it is forbidden to explain an atom as a mini solar system.

  2. jcsd
  3. Mar 20, 2003 #2
    This is a FATAL mistake to make.

    An electron orbiting the nucleus has an electric charge. Its movement means it disturbs the electrical field around it and this disturbance will travel at light speed in vacuum. To put it simple, if we view electron from classical electromagnetics point of view it has to radiate electromagnetic waves. This radiation will in time consume the electron's kinetic energy and carry this energy in the space. Thus, electron will gradually lose its speed which is crucial for maintaining a stable orbit around the nucleus that exerts electrical attraction towards the electron. That's why electron "should" fall on the nucleus if we apply classical electromagnetics to it.

    Niels Bohr considered this situation and postulated what is famous as Bohr postulates. One of these postulates defines certain energy levels at which an electric charge, say an electron, is "happy" in a sense and despite its fast movement around the nucleus it will NOT radiate. Hence, it won't lose energy and won't fall on the nucleus. For the electron orbiting a Hydrogen nucleus (one single proton) this energy level is -13.6 eV. At this energy level, namely an Orbital, the electron moves all around the nucleus in a space defined by Schroedinger's equation without ever radiating which makes the Hydrogen atom stable.

    One would ask if the same thing won't happen for the Moon as its movement disturbs the gravitational field around it. Well, this is the core point in defining gravitational waves spreading in the gravitational field whose carrier particles are Gravitons. As far as I know, Gravitons haven't been yet detected. If Gravitons are proved empirically then we can consider the falling of the Moon in far future.

    Besides, Gravity has always been a rebellion. While we know electrical and magnetic dipoles, no gravitational dipoles have been discovered. Many somewhat strange features of gravity makes it difficult to be compared and formulated with other forces, although it was the first of the four forces to be noticed and formulated. Moreover, while other three forces have been unified, Gravity still resists all Physicists' efforts for making the Great Union possible.
  4. Mar 20, 2003 #3


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    Actually, structures much larger than atoms still require quantum treatment. Molecular structures are defined by hybrid electron orbitals. Superlattices exhibit quantum effects, such as the quantum confined Stark effect, and they are layered structures many atoms thick.

    There are actually many "domains" in physics. There is no magical divide between the quantum realm and everything else.

    If you are not dealing with charges, you can ignore the electro-magnetic realm. If velocities are small you can ignore relativistic effects. Sure, when you throw a ball up in the air and catch it there are interactions between the charges on the ball and the charges in the air and even the magnetic field of the Earth, but they are insignificant. There are relativistic effects on the ball's velocity, but again, they are insignificant. It is not that quantum effects vanish at some point, they become insignificant.


  5. Mar 20, 2003 #4


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    To put it even simpler: Electric force field is not conservative, while newtonian gravity is. Ie one comes from the gradient of a potential, the other no.
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