Pentcho Valev
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Is our definition of entropy unique?
3 votes

It can be proved that, if the definition is $\delta S=\delta Q_\text{rev}/T$, the entropy is a state function for an ideal gas (a different definition would not ensure "statefunctionness"). That was ...

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Carnot engine (theorem) Proof
1 votes

First of all, we took irreversible engine and carnot engine. we stated that irreversible is more efficient than carnot one. then we disproved it by contradicting 2nd law. all fine now. Not so fine. ...

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Transforming absolute temperature into electricity via ions?
1 votes

Perpetual-motion machines of the second kind converting ionic thermal energy into electricity do exist - see this: http://scitation.aip.org/content/aip/journal/apl/103/16/10.1063/1.4825269 ...

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The Carnot engine and entropy?
1 votes

Here is an oversimplified presentation of Clausius' 1850 argument: Premise: Heat can never pass from a colder to a warmer body SPONTANEOUSLY. Conclusion: Heat can never pass from a colder to a ...

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Entropy and reversible paths
1 votes

There is an implicit but crucial assumption in thermodynamics (your calculations are based on it): Any irreversible process can be closed by a reversible process to become a cycle. If it is false, ...

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Hypothesis of Lorentz-Fitzgerald contraction
1 votes

http://books.google.com/books?id=JokgnS1JtmMC Banesh Hoffmann, Relativity and Its Roots, p. 106: "The effect is mutual. Each of us finds the other's lengths in the direction of our relative motion ...

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Maxwell and special relativity
0 votes

Maxwell's 19th century theory posited that the speed of light does vary with the speed of the observer: John Norton: "That [Maxwell] theory allows light to slow and be frozen in the frame of ...

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What were the findings of the Pound-Rebka Experiment?
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The Pound-Rebka experiment demonstrated that the velocity difference (acceleration) of photons is "identical to that which a material object would acquire in free fall", as predicted by Newton's ...

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What does the second law of thermodynamics really mean?
0 votes

Here is vigorous motion of water in an electric field, obviously able to produce work - e.g. by rotating a waterwheel: "The Formation of the Floating Water Bridge including electric breakdowns" ...

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Einstein's relativity of simultaneity - train
0 votes

There is often confusion about this thought experiment because textbooks fail to explain how the two observers "see" simultaneity or lack of it. One can imagine that either observer possesses so many (...

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GR. Einstein's 1911 Paper: On the Influence of Gravitation on the Propagation of Light
0 votes

There is a subtlety here. The impression is that in 1911 Einstein confirmed Newton's prediction (the speed of light falling towards the source of gravity varies like the speed of ordinary falling ...

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Definition of Second Law of Thermodynamics
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0 votes

Why do we state that Second Law of Thermodynamics holds only for isolated systems? Because this is a theorem deduced by Clausius in 1865: http://philsci-archive.pitt.edu/archive/00000313/ Jos ...

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Refraction and how light bends
0 votes

Newton believed that light was a stream of particles - near the boundary between two substances unbalanced forces of attraction act on them and the light ray is bent. See this: http://www.antonine-...

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Can the second law of thermodynamics be written as $\delta Q \leq T \mathrm{d} S$?
Accepted answer
0 votes

The second law of thermodynamics cannot be written in this way because the inequality in question is not even wrong (the entropy term is not defined). The entropy is only definable for irreversible ...

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According to special relativity, has the future already happened?
0 votes

If the moving clock runs slow (more slowly than the stationary one), then the future already exists, in the sense explained here: Thibault Damour, in http://www.bourbaphy.fr/damourtemps.pdf: The ...

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Is the deformation of spacetime, elastic deformation or plastic deformation?
0 votes

Your question makes no sense if, as theoreticians almost universally believe nowadays, spacetime does not exist and has to be "retired": https://www.youtube.com/watch?v=U47kyV4TMnE Nima Arkani-...

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Time dilation of a body A with respect to B
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Special relativity predicts that either clock runs more slowly than the other, as judged from the other clock's system: http://www.people.fas.harvard.edu/~djmorin/chap11.pdf David Morin, ...

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Reciprocal Time Dilation in Special Relativity
0 votes

Yes, Einstein's postulates entail symmetrical (reciprocal) time dilation, but in 1905 Einstein deduced, invalidly (in the sense that this does not follow from the postulates), asymmetrical time ...

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Did Newton argue that particles speed up when entering a more dense medium?
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"From this source, I gather that he did argue that the light particles sped up when entering a more dense medium. However, it just doesn't make sense." It does make sense. They enter the medium at a ...

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Special Relativity, 2nd Postulate -- Why?
0 votes

Maxwell's theory had predicted that the speed of light varies with the speed of the observer. Initially (prior to Fitzgerald and Lorentz advancing the ad hoc length contraction hypothesis) the ...

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If a light beam is sent tangent across earth would it curve at 9.8 $\rm m/s^2$?
-1 votes

Yes the light beam would curve at 9.8 m/s2, as per Newton's theory: To see why a deflection of light would be expected, consider Figure 2-17, which shows a beam of light entering an accelerating ...

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Twin paradox in SR
-1 votes

In 1918 Einstein informed the world that, as the traveling clock (twin) turns around and experiences acceleration, a HOMOGENEOUS GRAVITATIONAL FIELD emerges. This homogeneous gravitational field ...

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Understanding a quote about the speed of light in a gravitational field
-1 votes

"To see why a deflection of light would be expected, consider Figure 2-17, which shows a beam of light entering an accelerating compartment. Successive positions of the compartment are shown at ...

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Postulate of constancy of speed of light in vacuum
-1 votes

"I want to emphasize that light comes in this form - particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you probably ...

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Relativity and time
-1 votes

Einsteinians systematically contradict special relativity when it comes to the traveling observer's time: Brian Greene: "If you're moving relative to somebody else, time for you slows down." https:/...

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Is the absolute speed of light invariant or its speed relative to us?
-1 votes

Yes before the Michelson-Morley experiment they believed that the speed of light was independent of the speed of the source but varied with the speed of the observer. In 1887 (prior to FitzGerald and ...

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Twin Paradox: Why does't the traveling twin measure faster-than-light photons on Earth?
-1 votes

In 1918 Einstein informed the world that, during the turning-around acceleration, a HOMOGENEOUS gravitational field appears: http://sciliterature.50webs.com/Dialog.htm Albert Einstein 1918: "A ...

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Is Carnot's theorem equivalent to the Second Law of Thermodynamics?
-1 votes

Carnot's theorem IS the second law of thermodynamics - the Kelvin-Planck version can be derived from it. "Entropy always increases" is just camouflage - the statement is not even wrong. I have ...

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How can Entropy Distinguish Reversible and Irreversible Process if It is a State Variable?
-1 votes

You say "if entropy is a state variable", but is it? "Entropy is a state function" is a fundamental theorem in thermodynamics. Clausius deduced it from the assumption that any cycle can be ...

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In relativity, how does a traveller "catch up" in time after coming to a rest with respect to a stationary observer?
-1 votes

All along, Alice observes Bob's clock, more precisely, stationary clocks that she meets, synchronous with Bob's clock, running slower than her clocks, according to special relativity. The last ...

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