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bio website motls.blogspot.com
location Czech Republic
age 40
visits member for 3 years, 10 months
seen 14 hours ago

Hi, I am a string theorist and a publicist.


18h
answered Why is 0 $\nu \beta\beta$ decay often written with electron emission and not positron?
2d
awarded  Nice Answer
2d
revised What is the luminosity of the Milky Way galaxy?
added 284 characters in body
2d
answered What is the luminosity of the Milky Way galaxy?
Nov
25
answered Irreducible Representations from Cartan Matrix
Nov
24
comment What kind of invariants are proper time and proper length?
You may also talk about the proper distance between the two world lines of the two end points of the rod (the maximum - because of the Lorentzian signature - distance between any selected pair of points on these two lines). If you do so, this proper distance is again an invariant, and it's equal to the length of the rod at rest. But just the "length of the rod" isn't the common "width of the strip" in the spacetime. In non-rest frames, the "length of the rod" is measured along a slanted direction across the strip, so it's shorter $\gamma$ times, @Frank
Nov
24
comment What kind of invariants are proper time and proper length?
Dear Frank, the length of a rod is not called a proper length. The proper length has an extra adjective and it always refers to the scalar length between two particular events (points) in the spacetime. The length of a rod is frame-dependent (i.e. it is not invariant under Lorentz transformations) because in different frames, the length of a rod is interpreted as the proper length of different line intervals, due to the relativity of the simultaneity.
Nov
23
awarded  Nice Answer
Nov
21
answered The integral is zero! $\int \frac{\mathrm{d}^d k}{(2\pi)^d} = 0$
Nov
21
comment About the Ether Theory acceptance
Even the claim that one needs quantum fields is debatable. One may describe the whole QFT Hilbert space in terms of particles only, so that the vacuum is really unique and empty, and one doesn't "need" to talk about quantum fields at all.
Nov
21
comment About the Ether Theory acceptance
Aether may sound as anything that fills the vacuum, @WetSavannaAnimalakaRodVance. After all, the classical notion of "aether" - which used to be synonymous with "quintessence" - was some sort of a spirit. But since Newton, "aether" was used as a hypothetical material composed of particles. Newton was actually trying to explain gravitation via aethers of different densities etc. Those things culminated in the 19th century when the aether had very playful models with gears and wheels, by FitzGerald and others...
Nov
19
awarded  Nice Answer
Nov
16
comment The physical definition of work seems paradoxical
Dear @bobie, I am OK enough with your answer not to compete, especially because I know that I would get much fewer votes because almost no one reads old questions... The quadratic relationship is natural but people considered other dependences as well, and were actually confusing the momentum with energy for quite some time, and before Newton, the right questions weren't even formulated to be able to decide what is right and what is wrong. Moreover, in special relativity, the simply quadratic relationship becomes inaccurate.
Nov
15
comment The physical definition of work seems paradoxical
@Bobie: Coriolis was also the first man who coined the term "work" for the force integrated over distance, en.wikipedia.org/wiki/Gaspard-Gustave_Coriolis - The knowledge behind the concept of "kinetic energy" isn't just some vague guess about a power attributed to some mysterious "living force". What matters is the right interpretation or the well-defined framework that allows to decide whether something is right or wrong, and Leibniz had nothing of the sort. It's more wrong (but similar) to cite him as the originator of KE than to quote Lorentz as the father of special relativity.
Nov
15
comment The physical definition of work seems paradoxical
@Bobie: I didn't mean just "your" personally – I meant "your" in the plural, counting everyone who prefers historical speculations over the obvious physics content. The relevant physics knowledge equivalent to kinetic energy should be assigned to Newton, and the particular formula $mv^2/2$ may only be attributed to the first person who was actually using the correct laws - i.e. post-Newton - and it happened to be Gaspard-Gustave Coriolis. Lord Kelvin and Thomas Young coined the name "kinetic energy" later. But everything before Coriolis were fairy-tales about "living forces".
Nov
15
comment The physical definition of work seems paradoxical
Dear Bobie, it interests me but I totally disagree with your interpretation. Leibniz said mathematically wrong things about all these energy-related questions so I just won't count him as a "discoverer" of the concept. Any agreement with the reality - the right power of the velocity etc. - is a coincidence.
Nov
14
comment Why does smashing a TV remote load its batteries?
If the lithium ions cause an insignificant or tiny redistribution of the locations of lithium vs the electrolyte, then the capacity of the battery (energy or charge per unit mass) is also insignificant and tiny! You can't really separate these things. In lithium-ion batteries, there are no electrons flowing through the electrolyte - it is an electron insulator - and it's only the ions that make the current and ions are heavy because they include the nuclei. You can't make this motion negligible for efficient batteries - it's how they work!
Nov
14
comment The physical definition of work seems paradoxical
An even better idea, @Bobie - it is indeed -a in some other words. Lots of mess. ... Otherwise there's nothing inherently "Newtonian" about energy and work. The detailed formulae change but there are still quantities under these names that are related but not synonymous - both in relativity and quantum mechanics. The existence of these quantities, and their changes, is due to the time-translational symmetry of the laws of physics (Noether's theorem) which doesn't need to make any "classical physics like" assumptions.
Nov
13
revised The physical definition of work seems paradoxical
added 2 characters in body
Nov
13
comment The physical definition of work seems paradoxical
You're right, @Bobie! I thought it was international because -a is the right declension in plural in Latin. But the 1st case in Latin is synonymūs, I guess, not synonyma! ;-) So it's indeed just some Czech idiosyncrasy based on declension of "město" (town). You can still find "are not synonyma" via Google on 92 pages, including Wikipedia main pages. ;-)