Carrock

I agree... I did not expect to find this definition of heat. So heat can't flow from cold to hot. Got it. According to all the references I could find I'm wrong here as well, but I can't see why. e.g. from https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics How can any system be in thermal equilibrium, or be measured to be in thermal equilibrium with another system unless 'heat flows from hot to cold' is part of the zeroth law? Alternatively, 'heat flows from hot to cold' could be part of both laws, but that is messy at best. If (plausibly) the second law cannot be formulated without some version of the zeroth law then the zeroth law should surely not rely on part of the second law. As my thermodynamics is (obviously) rusty, I expect I've overlooked something obvious.

But is that so ? The change in entropy going from state A to state B is always the same, irrespective of the path between A and B since entropy is a state variable and thus a function of the state of the system alone. It make no difference whether that path is reversible or irreversible. ............................... For any completely isolated system we are restricted to adiabatic processes since no heat can either enter or leave the sytem. For a reversible process in any such system dq=0, hence ΔS is also zero, which means that S is a constant. Thus if one part of the system increases in entropy another part must decrease by the same amount. You cover "in an isolated system entropy need not increase." I'll assume ideal, classical conditions, including an ideal gas. An (old) example of "in some isolated systems entropy can increase:" You have an x cubic units sealed container of ideal gas, inside an empty sealed container of y cubic units. A side of the smaller container is 'instantaneously' removed without otherwise affecting the system. The gas irreversibly expands and comes to equilibrium in the y cubic units container. No work has been done so the temperature has not changed. The entropy has increased by the factor ln(y/x).

I don't regard "of its own accord" as very scientific... From my water example, does the heat associated with warm water molecules not accompany those molecules spontaneously/of its own accord when they become vapour? I would regard your statement as entirely accurate for systems referred to in the zeroth law. I was basically objecting as politely as I could to studiot's second law, which is a duplicate of part of the zeroth law. The zeroth law involves thermal equilibrium and is needed to define temperature. It's impossible (I think) to have stable thermal equilibrium without the explicit/implicit assumption or law that heat flows from hot to cold in the systems relevant to the zeroth law. "heat will not flow continuously from a warmer body to a colder one" is also accurate. Both are non equilibrium systems. I am assuming they are finite. I brought entropy into it because because I thought you gave a hasty, inaccurate version of the second law. It is very easy to get tripped up by all the ifs and buts in thermo.

Maybe oversimplified, therefor misleading? Particularly "of its own accord" - rather anthropomorphic. alternative: Zeroth law: If two systems are isolated except for a heat permeable wall then heat will flow from hot system to cold system. (If the two systems do not change over time and there is no net heat flow they are at the same temperature.) 2nd law: In an isolated system entropy will increase or remain the same. Heat can flow from cold to hot provided total entropy does not decrease. An example is water evaporating into air at the same initial temperature. The higher energy water molecules leave preferentially, lowering the temperature of the remaining water and warming the air. (Intended to complement earlier posts.)

Nope. Wave guides are not one way guides of R.F. energy. You're thinking of circulators, which rely on permanent magnets. edit or using half wave transformers etc to interface with spark gaps etc used for switching.

Sort of. First user starts downloading from source server. Second user gets partial downloads from source server and from first user, who has already downloaded part of file. Third user downloads from source, first and second users. First user can now download from source, second and third users. And so on... My post was only a response to the OP's second sentence. i.e. I felt his first sentence unnecessarily limited his options. Sensei: "Torrent is rather not an option, if you want to redistribute your own legit software, to worldwide clients." BitTorrent is an option for every major Linux OS worldwide download; users are requested to download with BitTorrent or similar to reduce server load.

Free software such as BitTorrent is available to reduce server load. It's (I think) only useful if several users are downloading the same file(s) simultaneously.

Archbishop James Ussher used biblical research to calculate day 1 of creation as 23rd October 4004BC. Did he get it wrong?

I believe that lack of evidence is definitely proof of nonexistence when it has been sufficiently sought after. If anti-matter bodies existed in the universe, then there would be huge anti-matter/matter explosions of energy, which simply don't exist. You're just making things up. CP violation is a subject of current research and certainly hasn't been 'sufficiently sought after.' If you'd read the reference I gave - https://en.wikipedia.org/wiki/CP_violation#Matter–antimatter_imbalance you wouldn't find anything to even hint at the existence of 'anti-matter bodies.' No evidence exists of presumed stable particles such as antielectrons (aka positrons) or antiprotons decaying. Such particles can be contained indefinitely.

Really? CP-symmetry violation produces matter/antimatter asymmetry. The currently known violations are insufficient to produce the observed asymmetry but lack of evidence is not proof of nonexistence.

Good to know there wasn't one.

Not that each has competence in different activities?! Or am I insufficiently evolved to appreciate your joke!?

Enthalpy, you seem to be refuting things I didn't write, partly by agreeing with things I did... As spires are a relatively low part of the total cost, it's a reasonable speculation that the materials, build quality or foundations were considered inadequate for the extra weight. Thanks for the expansion... You seem to be suggesting nothing was learned from those failures and the builders of Notre Dame etc were just lucky. Really? When I referred to builders' competence I was referring to collective competence. This would include judgment of whether many nonstandard constructions were adequate. I still believe modern architects would not do as well as the builders unless you allowed them to use some modern technology e.g. pencil and paper. I didn't mention architects as they were as rare as hens' teeth... From https://en.wikipedia.org/wiki/Architect Gotta wonder if the next fire will be hot enough to ignite aluminium...

There would have been less damage if the modern (19th century) tower hadn't collapsed into the building. Often 'obvious' improvements like extra towers etc weren't included because the builders knew that such constructions could overload the building or cause serious damage in a fire etc. Very old buildings still in use often are and sometimes have to be somewhat modified over the years, but the default assumption should be that as they still exist the builders were competent.

Do old buildings in the US all have these fitted then or something? All the old US buildings have these fitted. They're not considered cost effective for modern buildings i.e. less than 500 years old.

Also, are you aware of the relationship between the amplitude and the intensity of a sound wave? Hint: they are not directly proportional.

Complementary to studiot's post: Most metals have a thin layer of oxide which usually prevents any direct metal to metal contact. If there is any metal to metal contact it's usually a very small area (due to uneven/contaminated surfaces) and any bonds can easily be broken. I have read that in space, where the above is less significant, accidental welding of two metal surfaces is a significant safety issue.

An additional hint in the OP.

If it's possible to get a loosely aggregated large icy body into low orbit, it might be possible to separate it with explosives into sufficiently small fragments to melt during entry. Any larger fragments could similarly be reduced in size. Very speculative idea, and even if it becomes possible, any miscalculation could be disastrous.

Yours was a good response to my rubbish post. I misinterpreted the paper, the red mist descended and I pressed 'Submit Reply' without engaging brain...

Old mains clocks, such as mathematic may have, had a synchronous motor and were dependent on mains frequency for accuracy. IIRC they had a tendency not to start, or to run backwards, so they were likely designed to work at lower than normal voltage, so that they'd be reliable at normal voltage. So the dimmed bulb may be normal, while the clock continued to run on a very low voltage.

I realised I'd got it wrong, too late to edit my OP; I didn't make that clear enough. Or that I had realised is consistent with any valid QM interpretation. (The referenced book is behind a paywall; how 'environment' is defined is of course crucial.) Clarification: You appear to be referencing an unspecified paragraph from "Hawking, S. W. Particle creation by black holes. Commun. Math. Phys. 43, 199–220 (1975)." As I didn't quote from it, I don't think a cited reference has much relevance to the quality of the citing article. Don't know where you got that from... Congratulations on the cheerleading. +1 In summary: nothing in the paper appears to depend on a particular interpretation. I originally thought it did.

I suppose on second thoughts that paper is a pretty normal Copenhagen interpretation; it's just the scale of the superposition that's unusual.

From https://www.nature.com/articles/s41467-019-08426-4 Another quote from that paper: Ouch. From a reference from that paper: Joos, E. et al. Decoherence and the Appearance of a Classical World in Quantum Theory. (Springer, Berlin Heidelberg, 2003). So a whole paper with quantified maths about an arbitrary split between quantum superposition and a purely classical environment i.e. no superposition of different 'records.' This would only be valid if the Copenhagen interpretation was a distinct theory rather than an interpretation. Dubious theory isn't confined to SF speculation section...

The disinformation and ad hominem attacks go on.... Manning initially approached Assange. Whether Assange did anything more with Manning than most investigative journalists (not whistleblowers) would do is very questionable at present. The difficulty for the U.S. was/is finding a charge which would not also apply to a few million other journalists. The relatives of victims of the war crimes in Iraq and elsewhere who would otherwise never have known what happened likely have a different view on what is in the public interest than you do. Perhaps, like Hillary Clinton, you think the harm he did to the democrats outweighs this? Chelsea Manning was convicted and had her sentence commuted by Obama. She's now 'enjoying' her freedom during an indefinite prison sentence, much of her time in solitary confinement. A somewhat disproportionate sentence for an unnecessary witness? Secret justice is often more expedient than disappearing people.