studiot

This is correct and known as Earnshaw's Theorem. https://en.wikipedia.org/wiki/Earnshaw's_theorem This theorem originally applied to electric charges, but was later extended to bodies in other potential fields.

Another clear Eise explanation. +1

You are correct that the glasshouse warming is more complicated since there is also a conduction and convection mechanism. Radiation still dominates at night however. This article is very readable. https://www.gi.alaska.edu/alaska-science-forum/how-do-greenhouses-work

I agree with this statement. But this makes no sense to me. If the lower atmosphere (ie the air directly above the ground) absorbed the incoming IR and only radiated 50% down to the ground as you seem to suggest that surely would result in a cooling compared to what would happen if the absorbing gases were not there so 100% reached the ground ?

Surely that depends upon what you mean by macroscopic tunnelling ? It's the electrons that do the tunnelling, and a significant number of them at that. Is that enough to be macroscopic ?

Thank you for that, I had never heard of it before today's search. The reference I gave is a US government document dated 2017

The basis of the greenhouse effect in greenhouses is worth noting. It is also worth noting that greenhouses come in two varieties. Heated and Cold. That is with internal heaters and those just warmed by the sun's rays. The Earth corresponds to the Heated type as already noted. So the light of the Sun is of a frequency determined by the temperature of the surface of the Sun, by Stefan's Law. Most of it arrives at the glass at a very low angle of incidence, nowhere near its 'critical angle' where it might be reflected. When it falls on the ground or benches inside the greenhouse its energy is absorbed. The ground and benches are at the internal greenhouse temperature and also radiate 'light' as very much longer wavelength EM radiation. It is also known that the critical angle increases with increasing wavelength. So the outgoing radiation strikes the glass at or above the critical angle and is reflected back into the greenhouse. It is also this longer wave radiation that is reflected back to ground in the atmosphere.

Since this thread is about Carnot Efficiency and the Carnot Cycle refers to and was conceived as using only reversible processes I thought I would look around and post this link to a modern publication that claims to achieve Carnot efficiency for an irreversible process, notable the Feynman Ratchet. https://pubmed.ncbi.nlm.nih.gov/28878219/ The paper is downloadble as a pdf at 2.9M I haven't had time to study it properly yet, but it doesn't seem to avoid mentioning the standard proof of Carnot via a proposed more efficient engine leading to a contradiction. It is worth noting that there is no such thing as an ideal hot or cold reservoir in the real world. The best we can do it to take something where the heat content of the reservoir is many orders of magnitude greater than the heat being used in the engine.

What amazes me is your total refusal to pay attention to important matters others say to you. For instance, what do you actually know about the history of the subject ? Do you actually hate the French ? You have persisted with some incredible slurs upon Carnot. Why slurs ? Because your version is not possible. Carnot published his cycle in 1824, when Clausius was exactly 2 years old. Clausius published his most famous thermodynamic work in 1850, in which he discussed Carnot's earlier work mathematically and indeed provided a mathematical basis for it, replacing Sadi's Physics basis. Do you know either of their reasoning ? This stuff is a matter of Historic record. https://mathshistory.st-andrews.ac.uk/Biographies/Clausius/ https://mathshistory.st-andrews.ac.uk/Biographies/Carnot_Sadi/

I'm sorry I still don't understand this or how it is related to my post that you replied to. As a refresher, my post concerned bargaining power. Those under shariah law have exactly zero bargaining power, as I have already noted. Economically speaking, have you tried bargaining lately in Tescos ? It is not a free market.

There you go again. Preaching fallacies, to those who know more than you do, Instead of reading properly what they are saying. Seth has told you and I have highlighted what he told you and tried to reinforce that he specified the direction not the amount of heat transferred. And yet here you go again trying to change the subject to the amount. A total waste of others' time and effort.

Well I have a major disagreement with the claim I have emboldened. This is a fine example of what two experts (+1 each) have been trying to tell you. You do not know enough to understand exactly what they are saying to you. The energy level has exactly zero bearing on the direction of heat flow. This is a simple case of. If A > then B heat flows from A to B. If A = B no heat flows.

I can't see why anyone should give you a negative rep for these questions so I have reversed them. +1 also to exchem for introducing some scientific sanity here. I am suprised you are only offering these oversimplistic responses to someone who is perhaps a youngster trying to understand climate change. @CrystalMagic To answer you questions and offer some further information about the subject. The fundamental driver for the average surface temperature of the Earth is the balance between energies reaching the Earth, energies leaving the Earth and energies being transported within the Earth. None of these three energy flows have ever been constant. As a result there have been periods when the Earth's surface has been warmer than at present and also colder than at present, both on average. Climate is the result of the fact that the average surface temperature is the average of a very uneven distribution of temperature and also the three energy flows. Climate is the response by the Earth's fluid environments (Atmosphere and Ocean) to this uneven distribution towards evening this out. The processes of climate are affected by many factors including the two you have asked about. The last major volcanic eruption, Krakatoa in 1883, cooled the Earth for about a decade becasue the dust released in the atmosphere reflected back some solar energy before it reached the surface. And yes, as sensei says there were bigger and better eruption a long time ago. As to your second question, yes the Earth has warmed and cooled many times before the present as the actual prevailing position of that energy balance shifts. The shifts occur over periods of hundreds of years, thousands of years as well as the millions sensei mentioned. We are currently in a period between two much colder periods commonly called ice ages. Please indicate if you have further interest when you reply.

So what about my shadow ? That occupies points where, by definition, nothing happens. And the shadow is made of nothing, again by definition. Also if you are going to claim that the points are but abstract and only come into existence when something happens then you also need to establish whether or not the points and their nature depend in any way upon the something that happens. A real can of worms.

Some are some are not. I think Seth was referring to those that are. You should listen to him and answer his questions properly. He is/was a pretty good engineer. I don't any response to his question about the working fluid. The term 'working fluid' has a particular meaning to an engineer and may be imaginary or representational depending upon the configuration of the machine. This is because Carnot and the 2nd Law refer to a working fluid undergoing a cyclic process. They do not apply directly to non cyclic processes This is of fundamental importance and would be asked by any engineer working on a heat engine.

So you haven't really shown that they 'don't exist' - whatever that means. I don't know of any human who has tried and failed to move from one 'real ' point to another through the empty space between them, where you seem to claim there are no points. As a matter of interest two different scientific definitions of the word 'event' have been introduced in this thread. One is the Physics (relativistic) definition which means point in space, occupied or not and regardless of 'whether anything happens there ' The other is the statistics definition which seems to fit how you intend to use the word. This does indeed define points in 'event space' as an individual instance of something happening. Event space is by nature discrete, though we postulate underlying abstract continuous spaces in some cases.

Perhaps if you could elaborate further we could explain. What sort of line on each representation do you mean ? You realise that the mapping from one to the other may result in a straight line becoming curved and vice-versa ? Also it depends upon just how long the lines are.

Are you suggesting that the peoples in Australia did not come from 'the African Cradle' ? As a matter of interest you map appears to show that man never reached India ? Only half a mistake really. The nomads of the steppes pushed both east and west, and into south northern India at one time or another. It's just that the older cultures in India and China were stronger and better at resisting that the weaker cultures in Europe.

If it doesn't exist, how can you identify it to demonstrate that it doesn't exist ? Further how can you tell that nothing happens there ? These are really similar questions to those Genady has already put. Indeed so, but Riemann has already taken that into account. Translation from German by Spivak, adapted by McCleary. So was the birth of Topology and topological manifolds.

I am aware of the work of Prigogine and of Szilard. But I am not aware that anyone has proven the need for either deletion or the actual physical embodyment of mathematics. As far as I am concerned, the Mathematics existes and existed quite independently of any physical use or discovery. I do not support the suggestion that symbols written say 1000 years ago should be erased or deleted, otherwise the equations of entropy that I write today, or even just conceive of but not write down, would somehow become unbalanced. In my opinion they are totally unconnected. But we are getting further and further from the OP question which was about large numbers and my observation that since there are no limits to the number of point in a region of space we can assign a different number to each one without limit. We simply need to follow a Peano curve 1,2,3,4,5... to accomplish this. Since one one the basic tenets of number theory is that we can take any number proposed as the largest and increase it by various means. We can repeat this indefinitely. Each repetition we will uniquely identify a new largest 'number'.

I don't follow your objection. Please elaborate, perhaps with an example or two. As regards units, since entroy difference refers to the difference between states in a space it follows that any system that possesses multiple states can have an entropy, defined by multiplying the statistical entropy of the states (which is a pure number) by the units of those states.

Thermodynamic entropy is indeed a function of energy (and temperature) It has units (dimensions) of energy per degree K. Information entropy is dimensionless. Probably the most interesting distinction is given by Caratheodory in his version of the 2nd Law. As far as I know, Information entropy admits no such restriction on the states and consequently does not require the second law. Clearly since it it not directly concerned with energy it does not require the first law either. Another commonly mixed up pair of terms is information and meaning. Take the letters in alpha order A D E M N O R S Form one of the 1024 (with replacement) possible 10 letter 'words'and you have a 1 in 1024 chance of getting RANDOMNESS. How many more have meaning ? This is rather like the difference in economics between price, cost and value or worth.

I have no quarrel with proper capitalism. But I don't see how your reply to my post you quoted has anything to do with my point. As regard value, here is a parable about value. Due to Stafford Beer. Take 1lb of apples. Something of intrinsic worth in its own right. Give it to a top chef and he will turn it into something worth significantly more. Give it instead to an ill suited work experience person who may well loose all of its original value let alone add to it, in the mess they make.

Well as I understand the Aboriginals in Australia they are some of the most (or perhaps longest) undisturbed humans on the planet. Yet the maps show they are quite different from the Polynesians, Maoris and South American indigenous peoples. Yet Australia (the nearest parts) is thousands of miles closer to SE asia than New Zealand or most of the pacific islands. So why did they not get to Australia first or even at all ?

I wouldn't until I knew what sort of entropy you were talking about. It is unfortunate that the same word (ie entropy) is used for both phenomena, unlike my example which clearly distinguishes. Beltrami has a good discussion of different sorts of 'entropy' in his book What is Random ? Chance and order in Mathematics and Life.