sethoflagos

The bottom line here is Kirchoff's Law of Thermal Radiation which is often expressed as: If this were not true then there could be spontaneous nett heat flow from a cool body to a hotter one which simply doesn't happen. However, the proviso 'in thermal equilibrium' is key since 'arbitrary bodies' can have widely different emissivities at different wavelengths corresponding to different equilibrium temperatures. This is where the misunderstandings arise. Taking an arbitrary example quote from https://en.wikipedia.org/wiki/Emissivity Here the absorptivity is with reference to thermal equilibrium radiation at the surface temperature of the sun, whereas the emissivity is with reference to local thermal equilibrium in the vicinity of the collectors. The collectors are NOT in thermal equilibrium with the surface of the sun. Without the temperature difference, there would be no loophole to exploit. Okay so far. But note that emission by the antennae is NOT independent of the temperature of the antennae, The receiver does not reradiate incident solar radiation because it is not at the same equilibrium temperature. Therefore there is an asymmetry between absorption and emission that can be exploited. But refer to the relevant paragraph in https://en.wikipedia.org/wiki/Optical_rectenna The proposal neglects to consider the equivalence of absorptivity and emissivity at thermal equilibrium. So it falls foul of Kirchoff's Law, and by logical extension, the 2nd Law of Thermodynamics.

As I understand it, the theorical maximum efficiency from a 2nd Law point of view is 1 minus the temperature ratio of absorber over emitter. This yields something like 85% for solar spectrum conversion. Trying to convert near ambient spectrum IR would yield zilch I suspect as the antenna would be emitting about as much as it absorbed.

Imagine the current generated is used to charge a battery. Losses are generated by the required electrode overpotentials and internal Ohmic resistance of the cell resulting in radiation of waste heat to the environment. An overall picture of the thermodynamics can be found here. Closely related is Thermodynamic bounds on Work Extraction from Photocells and Photosynthesis which connected a lot of loose strings for me at least. Attached. Well worth a read imho. Photocells and Photosyntesis.pdf

Given that current generation PAC-2/3 interception missiles can top Mach 4, their speed deficit against say Avangard and Starry Sky-2 hypersonic glide vehicles is perhaps less of a challenge than keeping track of these highly manoeuvrable devices as they actively evade defence systems. That they achieve their impressive success rates via direct kinetic impact (rather than nearby fragmentation) I find quite staggering. Perhaps the real test will come with the future deployment of the BrahMos II Russian/Indian scram jet powered hypersonic cruise missile which will be capable of Mach 8-ish.

Just running with Weinreich's quip about the difference between a language and a dialect (https://en.wikipedia.org/wiki/A_language_is_a_dialect_with_an_army_and_navy).

AFAIK they never controlled a Navy, so I guess so.

We call it 'the universe' We call it 'space'. The pressure is <10-6 Pascals which is a near-perfect vacuum by earthly standards Mott-Gurney shrapnel distributions apply to this sort of 'big bang' The uniform shrapnel distribution we see on the larger scale is more suggestive of free gas expansion. ie there wasn't any shell casing involved. Photons emitted from a uniform shrapnel distribution? Do you think photons emitted by the shrapnel can only travel in the same direction as the shrapnel?

You can recycle all of it back into 'useful energy' in principle if you have a handy heat sink at absolute zero and lots of time to realise near-reversible thermodynamic processes. Trouble is the 'ifs'. They tend to cost a lot of capital. y

To emphasise this point, the Kelvin was redefined in May 2019 as: ... though perhaps the wikipedia article should clarify that it's strictly one degree of freedom of thermal energy change rather than the total change.

Except for your tardis.

You miss my point entirely. A precambrian rabbit would predate anything we believe remotely capable of giving birth to the first rabbit by half a billion years. 'Our history' as we understand it supports a pretty clear picture of the growth of the tree of life supported by millions of well-documented data points with not one single notable exception. If subterfuge and misidentification etc. could be ruled out, we are left having to explain the existence of a genuinely identified item not of its rightful time. For those seeking evidence of time travel, anachronistic artefacts like precambrian rabbits (or 1st Dynasty Tricorders etc) are precisely the sort of hard evidence they would be looking for.

To paraphrase JBS Haldane (albeit in a slightly different context)

I'm not sure you fully appreciate: a) how impossible your question is to answer in the absence of any information regarding the amount and composition of what you are attempting to mix. b) how technically deep the answer you seek may be even given full disclosure of what you are attempting to do. I've attached an open access brief summary paper 'A General Review of the Current Development of Mechanically Agitated Vessels': Jaszczur & Mlynarczykowska, Processes, Aug. 2020 to give you an idea of the basics. It runs to 39 pages and references no less than 309 sources. (downloadable from https://www.mdpi.com/2227-9717/8/8/982) This is not a topic you can at all usefully summarise in a single forum post. The answers you seek will be in there somewhere, though not necessarily in an easily digested form. However, if you can narrow down the scope of your OP, one or other of us should be able to help clarify. processes-08-00982-v2.pdf

As a postscript for those who are interested in how deep the rabbits have dug this particular burrow. Replacing the Latin alphabet with a phonemic alternate more suited to the English language is not a new idea. The best known is perhaps the Shavian alphabet produced under the bequest of the playwright George Bernard Shaw. According to https://en.wikipedia.org/wiki/Shavian_alphabet 48 letters might sound a lot for an alphabet, but Shavian doesn't use capitalisations, so it's actually shorter than our standard orthography. Being phonemic, @studiot and I would use different spellings for 'bath': bib-are-thigh vs bib-ah-thigh for example. Another difference may be that I don't have a 'strut' vowel in my dialect so I would spell 'up' not as up-peep (which sounds somewhat illegal anyway), but as wool-peep. It would actually make for a very concise orthography. Standard written English is significantly more concise than most languages, but Shavian would further trim the character count of most texts by about 30% due mainly to the elimination of digraphs and clusters like 'ough' and 'ght'.

A nod's as good as a wink to a blind man 🤐

Thanks, @MigL. Matter of picking the correct wording in the main. Is the end of time a singularity? Have to sleep on that one. That and would we see a step change in CMBR intensity when it comes around for the second time? Do you mind if I ignore everything after 'but'? It's late and the rest is way off the point I was trying to make.

Say Alice observes a time interval of 1 year and space interval of 1 light year between two events. If Bob sees a time interval of 1 million years between between those events is the following not true: Bob's space interval = sqrt (Bob's time interval2 + Alice's space interval2 - Alice's time interval2) = 1 million light years Hence, presuming the technology was available to detect CMBR radiation as the age of the universe tended towards infinity would not the source of that radiation tend towards being infinitely distant? ie infinities in the time intervals spawn infinities in spatial intervals.

Substitute axis/axes with interval/intervals. Are we good now?

Yes - and each observer has their own world line which is typically rotated from the other's point of view according to their relative velocities such that the proper time interval of one is seen at least in part as part of the space interval of the other. Does that help? I'm sort of uncomfortable trying to explain the mechanics of coordinate transformation to a mathematician 🤨

You've framed this discussion so far in terms of the (understandable) difficulty in envisaging a spatially infinite universe. Do you have the same difficulty in envisaging temporal infinity? If the expansion of our universe has (as seems likely) no means of reversing then how can time (in the forward direction) be anything but infinte? And if so, that sounds like a good prima facie case for the infinity of space-time in at least one dimension. But if space-time is only infinite in OUR time dimension what impact would this have on far distant observers for whom our time axis is transformed into the spatial axes of their local coordinate system? We must all agree on the observed spacetime interval between two events (because causality) and while I'm admittedly no mathematical expert and speak with only some slim understanding of SR, it does appear that an infinity in any one dimension of spacetime implies infinities in all. Is the 'fade to grey' option on the table? The impression I get is that the boundaries of spacetime are either infinities or singularities. Taking the time dimension again, but this time in the reverse direction, when we run the film backwards we end up in a singularity and all hell seems to break loose. Same deal with black holes. I'm not saying that our squeamishness towards infinity is akin to a fear of sailing of the edge of the world into the bottomless abyss. But it might be. A bit. Personally I experience less angst over infinity than I do singularities. Not that counts as evidence for one or the other. I'd say the balance of the argument is a bit better than 50:50 subject to whether or not you can give my spacetime interval argument a good caning.

When an allele changes its frequency of occurrence in a population, is it because of adaptive pressure or just chance? The mechanism is the same either way: individuals with that particular allele just happened to have a greater or lesser mortality/reproductive success than the population mean for some period. So to me it seems that genetic drift is not some fundamentally different 'process' to evolution by natural selection. Rather they are two sides of the same coin. Given that the thrust of the OP is specifically related to the overall behaviour of complex systems; systems where we typically expect emergent properties of the whole to dominate over action at the level of the individual; systems where we typically expect the whole to be greater than the sum of the parts; I think we should be more wary than usual of the reductionist splitting of pertinent parts. None of the parts exist in isolation. The OP is concerned with some apparent similarities in the development or 'evolution' of increasing diversity with time in a wide variety of disparate complex systems such as nucleosynthesis, earth's mineral composition and life. While I think the article over-eggs the pudding to a certain extent: two unifying features struck me as I read it. 1) The Arrow of Time is a major factor in all cases therefore the 2nd Law of Thermodynamics is a dominant factor. Nothing else in physics has this feature. 2) Pound for pound, systems with more types of 'thing' have significantly higher entropy than those with less so what is driving the diversity of these systems? Given a temperature gradient and a few basic building blocks to get the ball rolling the 2nd Law of Thermodynamics will (eventually) build any new structures it is possible to build quite spontaneously, and use these as building blocks for constructing yet more. (Sorry, I've a bit of a thing about the 2nd Law) Anyway, that's the pattern that the authors are picking up on.

Isn't it pretty well established that 'evolvability' is itself under strong selective control? And that genetic drift, the ability of a population to lose non-vital alleles at some optimal rate as a kind of spring cleaning exercise is all part and parcel of that evolvability? Genetic drift is a particularly interesting case wrt the OP as it represents a steady source of decline in the diversity of a complex system running counter to the main thrust of the linked article. Perhaps the message of genetic drift is to remind us that non-transitory structures in complex systems require sufficient energy flow passing through the system to maintain their low entropy configuration. Of course, Dawkins has pointed out that these structures are not confined to living forms but also include the evolution of their extended phenotypes such as beaver lodges, weaver bird nests, termite mounds and AI technology.

Not sure what the issue is with 'bath' - other than my version will be a lot shorter than yours. It still follows the rule: unvoiced for endings of nouns and adjectives; voiced for verb endings. So bathe has the silent 'e' to lengthen the 'a' and voice the 'th'. Compare breath/breathe; tooth/teethe; cloth/clothe etc. A key one where I suspect we will differ is that I don't voice the ending of 'with' which is the older form that you Southerners forsook for some strange reason.

Just to correct some erroneous assumptions made above, the following quotation from Wikipedia entry https://en.wikipedia.org/wiki/Eth is worth reading The distinction between voiced and unvoiced 'th' has never been made in English by its representation as 'th', thorn or eth. They are simply alternates for the same pair of sounds. It's a common misunderstanding. In principle, you can go through a Beowulf manuscript swapping all the thorns for eths and vice versa, and still claim with some justification that you'd not introduced any spelling mistakes. Whether the sound is voiced or unvoiced is governed by a) common contemporary usage (always) and b) the adjacent vowel sounds (usually). Not by its orthography.

I've not looked at this for quite a few years, but for sure, in Britain the UKAEA and Defence industries were active in the field and that stuff rarely makes it into the public domain. You could try looking at what CERN have on this.