# Tag Info

27

1915 On November 25, nearly ten years after the foundation of special relativity, Einstein submitted his paper The Field Equations of Gravitation for publication, which gave the correct field equations for the theory of general relativity (or general relativity for short). Actually, the German mathematician David Hilbert submitted an article ...

20

The list of topics can be found here (in Russian, of course). Nowadays students are examined by collaborators of Landau Institute for Theoretical Physics. Each exam, as it was before, consists of problems solving. For every exam there is one or several examiners with whom you are supposed to contact with to inform that you're willing to pass this particular ...

19

In the following arXiv article Landau's Theoretical minimum, the author details personal experiences on being one of 42 students ever who passed it, as well as some details of the examination. He also mentions some questions in passing, from which I gather most of them were similar to the exercises and examples of his famous books. Quote: Landau gave ...

18

in the late 1960s, the strongly interacting particles were a jungle. Protons, neutrons, pions, kaons, lambda hyperons, other hyperons, additional resonances, and so on. It seemed like dozens of elementary particles that strongly interacted. There was no order. People thought that quantum field theory had to die. However, they noticed regularities such as ...

15

There have only been 3 recorded deaths that occurred in space (that is, greater than 60 miles above the Earth). The crew of the Russian capsule Soyuz 11, died when their capsule depressurised during preparations for re-entry. It wasn't known they had died until the re-entry capsule was opened on Earth as communications had been lost with the capsule during ...

14

First of all, it would be preposterous to think that there was a simple recipe that Newton followed and that anyone else can use to deduce the laws of a similar caliber. Newton was a genius, and arguably the greatest genius in the history of science. Second of all, Newton was inspired by the falling apple - or, more generally, by the gravity observed on the ...

14

The first estimate of Avogadro's number was made by a monk named Chrysostomus Magnenus in 1646. He burned a grain of incense in an abandoned church and assumed that there was one 'atom' of incense in his nose at soon as he could faintly smell it; He then compared the volume of the cavity of his nose with the volume of the church. In modern language, the ...

13

Gugg's answer is thorough (+1 :-), and the answer to your question is probably "yes". However Hilbert acknowledged that he had merely added the last step to a long process and therefore that he had no claim to have invented General Relativity. It's tempting to think of GR being revealed to the world in a single stunning paper, but this isn't the way it ...

12

I will exaggerate a bit, but in physics, proof in the sense of mathematical proof is irrelevant. Even if all of Einstein's deductions of the formula were wrong, it still turns out that empirical evidence supports $E=mc^2$. Now, without the exaggeration, mathematical deduction is important in physical theories because it shows us how conclusions and ...

12

The Dirac equation implies negative energies as well as positive. This is due to energy-momentum relation $E=\pm \sqrt{m^2+p^2 }$. If we replace $E$ and $p$ by operators $E\to i\frac{\partial }{\partial t}$ and $p\to -i\nabla$ we get the Klein-Gordon equation $(\Box+m^2)\phi=0$ for scalar (spinless) fields $\phi$. The problem with this equation is that it ...

12

If you don't like complex numbers, you can use pairs of real numbers (x,y). You can "add" two pairs by (x,y)+(z,w) = (x+z,y+w), and you can "multiply" two pairs by (x,y) * (z,w) = (xz-yw, xw+yz). (If don't think that multiplication should work that way, you can call this operation "shmultiplication" instead.) Now you can do anything in quantum mechanics. ...

12

The wording of the question suggests that the electrons were the first objects or particles whose charge required the people to establish the sign convention. But that's obviously not the case. The electron was discovered by J. J. Thomson in 1897 but for much more than a century before that moment, people had already been studying electric (and magnetic) ...

11

The idea of the existence of galaxies is certainly not new, and quite a bit older than the field of modern astrophysics. In 1750, Thomas Wright, an English astronomer correctly speculated that the Milky Way was a flattened disk of stars and that some of the nebulae astronomers viewed in their telescopes were separate "Milky Ways". In 1755 Immanuel Kant ...

10

There's no such thing as verifying a theory "to complete exclusion." One of the key principles of the scientific method is that theories can't be proven by experiment, only supported (or disproven as the case may be). The scientific reality is that quantum mechanics, like any other theory of its caliber, has been supported by countless experiments, so we ...

10

As far as I know, nuclear fission was already understood at the time, so was all the competition between the american team and the german team to develop the bomb first, a mere matter of engineering? Only some very, very basic knowledge about the physics of nuclear fission was available at this time. I'll give a few details about this below. Also, ...

9

Tesla was an engineering giant but it is true that in most cases, he was just a crackpot when it came to theoretical physics. This "theory of gravity" is one of the major ones. It wasn't really connected with gravity - the attraction of objects to the Earth etc. with a universal acceleration - by anything else than a wishful thinking. As expected for the ...

9

The excitement behind various claims is somewhat excessive. First, the Mayan astronomers, see e.g. Mayan astronomy at this page, didn't use any armillary spheres or sextants as others did. Their observations were made with naked eye and they were depicting positions of planets with crosses. The accuracy of the Venus' position after a synodic 584-day cycle ...

9

which particular observation, made us think that it could be the other way around Retrograde motion must be a prime candidate. As seen from Earth against star background, Mars occasionally slows down and goes backwards. Our moon doesn't. It probably became clear to people constructing orreries that heliocentric models were enormously simpler and more ...

9

(Attn: non-seriousness ahead.) Since Helen, whose face could launch a thousand ships is the unit of beauty (as in a millihelen is a face that could launch one ship), perhaps Edison could be the unit of jerkishness. I base this, of course, on an entirely unbiased source.

9

The number of stars that are visible depends heavily on local conditions. Under perfect conditions (e.g. a mountain area with minimal atmospheric turbulence) and with perfect eyesight, one would be able see stars as faint as magnitude 6.5. Of course, conditions are usually not ideal. According to this site, there are 1500 stars brighter than mag 5.0 4800 ...

8

Historical issues I suppose; indeed current definition of ampere is rather stupid (force between two cables in vacuum) in light of the fact it could be done with number of elementary charges per second. Candela is even worse, because it involves properties of average human eye (so called "luminosity function") -- so in principle it changes instantaneously as ...

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