# Tag Info

6

In at least one history I've read about Einstein's early life -- sorry, I don't recall the name of the book -- the author claimed that even back when Einstein was in Gymnasium (high school), he pondered a simple thought experiment: What would an electromagnetic wave look like if one traveled along beside it at the speed of light? The answer from ...

12

There was no problem with electromagnetism. The problem was that Maxwell's equations are invariant under Lorentz transformations but are not invariant under Galileo transformations whereas the equations of classical mechanics can be easily made invariant under Lorentz transformations. The question was: how to reconcile both in a universe in which Maxwell's ...

4

Maxwell's equations of electromagnetism predicted that light would travel with a constant velocity c. The question is - a velocity c with respect to what? It was thus supposed that it must be with respect to an ether which was at absolute rest in the universe. It then followed from the Galilean transformation that absolute uniform motion with respect to ...

0

The responses given so far are fairly accurate however, the question you should be asking goes to the experimental proof for the kinetic energy formula. Mathematically, the formulas for work and kinetic energy seem to function perfectly as taught. Unfortunately, there are at least 2 or 3 situations where it does not. No physics teacher ever looks at these ...

2

You've already got some answers, but nobody mentioned Noether's Theorem yet. Noether's theorem maps a conserved quantity to each continuous symmetry. The relevant continuous symmetry needed to prove the conservation of energy is the one that leaves the laws of nature invariant, meaning the laws of physics don't change with time. Each continuous symmetry ...

13

As you probably know, Newton thought that energy is linearly proportional to velocity. The second law's original formulation reads: "Mutationem motus proportionalem esse vi motrici impressae" = "any change of motion (velocity) is proportional to the motive force impressed". This law, which nowadays is wrongly interpreted as: $F = ma$ (there is no ...

0

I suspect, though I'm not sure, that a nineteenth century French mathematician and scientist, Gaspard-Gustave Coriolis, is your man. He was the first to define the notion of "work done" and even kinetic energy. His wiki reads: In 1829, Coriolis published a textbook, Calcul de l'Effet des Machines ("Calculation of the Effect of Machines"), which presented ...

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The master of the law of energy conservation was Hermann von Helmholtz (1821-94). See his classic 1847 paper "Über die Erhaltung der Kraft," translated into English as "On the Conservation of Force." (He called energy force.)

3

Based on some "google research" I get the impression that the popularity of the perfume thought experiment stems from a 1975 Scientific American article written by David Layzer called The Arrow of Time. The article featured this figure visualizing the thought experiment: Of course, the notion that the second law of thermodynamics implies an asymmetry ...

1

Henri Poincaré, in discovering limit cycles, used a thought experiment containing a box with a partition. One side had a gas, and the other didn't. When the partition was removed, the gas would diffuse through the opening and occupy both sides of the container. He first published works describing limit cycles somewhere in 1881-1882. I am unsure if he ...

5

Heavy water is an effective moderator for the production of $^{239}$Pu, which is a possible active ingredient of a fission bomb. The heavy water itself is not used in the final weapon. The allies realized that this might work - and they decided to set back any attempt by the Nazis to create a plutonium based atom bomb by depriving them of the moderator ...

2

I am not an expert on nuclear technology or weapons but the Wikipedia page on the plant and it's destruction provides some clues. Ultimately there were many potential methods that might be used to design a weapon. It was known at the start of the war that bombarding Uranium with neutrons resulted in nuclear fission which could be chained together. Heavy ...

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There is a much better description here of Fizeau's nineteenth century experiment. Some of the key features that enabled Fizeau to succeed: A lens to collect the light from the source A collimating lens to prevent the light diverging during its journey A large diameter beam to minimise broadening of the beam by diffraction More lenses to focus the light ...

0

There are problems mathematically with point particles, pointy surfaces, and the like. Point particles can be made to go zooming off with infinite velocity in finite time. Systems that violate the Lipschitz conditions can be set up, creating non-deterministic classical mechanics problems. These are conceptual problems. We use point particles because real ...

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Quoting from wikipedia http://en.wikipedia.org/wiki/Wave_function_collapse "The concept of wavefunction collapse was introduced by Werner Heisenberg in his 1927 paper on the uncertainty principle, "Über den anschaulichen Inhalt der quantentheoretischen Kinematic und Mechanik", and incorporated into the mathematical formulation of quantum mechanics by John ...

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