Warp Drive - A Nice Idea While It Lasted?
Monday June 15, 2009
A few weeks ago, I mentioned a new warp drive possibility based on string theory, a variant of the Alcubierre drive. A new set of calculations performed by a team of Italian scientists, however, have proposed that a warp drive engine would eventually fail. The massive energy required to manipulate spacetime in the correct way would, according to their calculations, result in a rupture in the fabric of the universe when the massive energy running the drive runs out. This rupture could result in either an explosion or a black hole that might swallow up nearby planets, but it's unclear from the paper which result is more likely ... that depends on certain fundamental properties of our universe which are still being explored by theoretical physicists.
Comments
“The only real beef I have is to point out that Maxwell’s Equations include among them Faraday’s law of induction, …”
Ummm…so what? Faraday showed that the electric and magnetic fields (which had previously been viewed as separate phenomena) were linked; Maxwell surmised (what we now call) the displacement current, and by doing so completed the linkage and predicted the propagation of electromagnetic waves.
The Nobel Prize to Arthur Holly Compton (1927)
Early in 1923 Arnold Sommerfeld visited the USA and wrote to Bohr: “The most interesting thing ..is the work of Compton in St Louis…. After it the wave theory of X-rays will become invalid.”
Compton had followed up an observation that some parts of X-rays were scattered away from the beam direction with a longer wave length than the incoming radiation. He measured the shift in wave-length very accurately. The shift is impossible to understand on classical wave theory. Compton’s own explanation for the scattering process was as in terms of a collision between two particles – one being a free electron, the other a photon.
Arthur Holly Compton
Based on quantum theory and relativistic kinematics Compton calculated what shift of wave length to expect on this theory using the laws of energy and momentum conservation. His measurements agreed perfectly with the predictions. Compton used an X-ray spectrometer for accurate measurements of the wave-length of the scattered radiation, which consists of two components – one shifted and one with no shift. The shifted component is due to scattering against free or almost free electrons, so that they may recoil, thereby taking up momentum and a sizeable amount of energy, whereas the unshifted component is due to scattering against bound electrons, in which case the whole atom or even crystal takes up momentum but only a negligible amount of energy.
The understanding of how such a spectrometer as used by Compton functions is based on the wave theory of X-rays. By this he found that X-rays scatter as particles. This fact illustrates clearly the dual nature of light.
Compton was awarded the Nobel Prize for Physics in 1927, sharing it with C.T.R.Wilson for his cloud chamber, with which Wilson had observed the recoil electrons from the X-ray beam, thus giving strong support for the validity of the Compton process.
Did the Academy now finally award the prize for the discovery of the particle nature of light? The answer is no.
In the evaluation report one finds a sentence saying that Compton’s theory must now be considered obsolete in view of the latest theories. Thus the particle picture is not accepted.
The position taken by the Nobel Committee is understandable, since at the time of Compton’s Nobel Prize there was no good theory for the differential cross section based on the photon concept. Such theories were still in the future. But there were theories based on the wave picture, treating both the electrons and the X-radiation as waves, also giving the correct wave length shift.
The Compton effect had been assessed by the Nobel Committee already in 1925 and 1926 and had found the theory very unsatisfactory. However, in 1927 that had changed. The new evaluation was carried out by Carl Wilhelm Oseen, professor of Mechanics and Mathematical Physics at Uppsala University. He did a thorough study for the Committee. He began by recalling the great interest by which Compton’s discovery in 1922 had been met, much due to the theory offered by Compton himself. He writes (my translation from Swedish) “it is not surprising that the agreement of this theory with observations inspired with less critical representatives for theoretical physics the thought that, the lengthy fight between the wave theory and the corpuscular theory would be nearing its end. Compton’s discovery was by these scientists taken as the decisive proof for the truth of the corpuscular theory. If these expectations had been fulfilled, the discovery by Compton would undoubtedly had marked a decisive turning point in the development of the whole of the radiation theory”. Oseen set out to show that this is not so. His view was that the new effect, discovered by Compton, is nevertheless, very important.
Oseen describes how the Bohr theory had fallen by 1925 and that the Compton effect had nothing to do with that. He mentions how matrix-mechanics and wave-mechanics have entered the stage without inspiration from the Compton effect. The oldest theories for the Compton effect were given by Compton, and ‘Debijes’ (Debye) and Woos. Being based on the theory of light quanta “they have been of value to experimental research, but must now be considered obsolete in view of the latest theories”. Oseen mentions several such newer works, especially that by Gordon and a recent one by O. Klein, based on the wave theory, treating both electrons and light as waves. They all arrive at the same equations for the conservation of energy and momentum between the scattered wave and the recoiling electron as originally derived by Compton assuming a two-particle collision. “The basis for the Compton-Debije theory is thus found, this time not as a hypothesis but as a consequence of the atomic theory,” is a conclusion by Oseen, which justifies his judgement of the former being obsolete. These wave mechanical treatments, furthermore, also gave formulae for the intensity vs scattering angle (i.e. differential cross section) in much better agreement with measurements than the classical wave theory prediction.
Oseen summarised by saying that the revolution during the last 18 months had been independent of Compton’s discovery and that the new direction for the revolution had moved opposite to the one expected after Compton’s discovery. The new theory is a wave theory in a higher degree than any previous theory. Using the new theory it has been possible to give a qualitatively and quantitatively correct account of the Compton effect.
The Committee emphasised that the Compton effect is nevertheless important, since it once more and very clearly and convincingly demonstrates that the classical theories are not applicable in the realm of atomic physics and that it offers a valuable and welcome possibility to test the new ideas.
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whereas the unshifted component is due to scattering against bound electrons, in which case the whole atom or even crystal takes up momentum but only a negligible amount of energy.
)!!! i’m new to responding to articals [and no physicist], but this sparked my interest and its statement on momentum with not much energy!
If people, really do have this gift why would they brodcast it and try to make money off of it? I sure wouldn’t want to it is something special and sacred to my heart, but its your life do what you will, I was just curious.
Nick – The point you make is certainly valid … which is why I made it in the original article. Maxwell’s Equations include the Faraday Law as a subset … they are a more complete formulation of the work begun by Faraday. In the article, my intention (which clearly wasn’t effective from your standpoint) was just to point out that there was some level of redundancy, but I quickly pointed out that they were still distinctly useful elements of electrodynamics. You seem to have caught the first part but missed the second, which I blame on my own lack of clarity.