Wikipedia:Reference desk/Archives/Science/2023 March 23

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March 23

Why are so many scientific names of USA named after the first British colony?

Wouldn't X. americana have been a better size than virginianus/virginiana for most of these range-based species names? Sagittarian Milky Way (talk) 16:08, 23 March 2023 (UTC)

Linnaeus 1753 and Linnaeus 1758 maybe? fiveby(zero) 16:38, 23 March 2023 (UTC)

I think you are starting from a faulty premise. These are more likely to be locality names than range names. That is,they were named for where they were discovered. In that case, the moe restricted name would be preferred. Even if they were meant as range names, the full range of the species would have been unknown and unknowable at the time of naming. Thus a more restricted name might still be preferred.--User:Khajidha (talk) (contributions) 02:14, 25 March 2023 (UTC)

Entropy and the "cosmic battery"

The second law of thermodynamics says that entropy always increases. Does that mean that the universe has a "battery" that started at 100% at the Big Bang and will go down to 0% at the heat death of the universe 10¹⁰⁰ years later? If so, then the cosmic battery percentage would decrease by 1 every 10⁹⁸ years, so it would decrease by 10^-98 every year and the current cosmic battery percentage would be (100-13.8*10^-89)%. GeoffreyT2000 (talk) 17:20, 23 March 2023 (UTC)

The hypothesis of Heat death of the universe (see article) stems from the ideas of Lord Kelvin. It's possible to conceive of the universe starting with a finite amount of Thermodynamic free energy (see article), all available to perform work like a kind of battery. Thereafter all thermodynamic processes left to themselves are, by the 2nd Law, causing irreversible increases in Entropy that can be understood as disorder from which no more work can be extracted. The OP's calculation of the "present state of the cosmic battery" yields a value that both assumes a constant exponential decay rate and depends on the whole universe being somehow treatable as a single thermally isolated system history. Philvoids (talk) 20:16, 23 March 2023 (UTC)

The OP uses a linear formula: percentage remaining is $(1-A/(10^{100}~{\text{y}}))\times 100\%,$ in which $A=0.138\times 10^{9}~{\text{y}}$ stands for the current age of the universe. What with the accelerating expansion of the universe, it is not clear that in this battery model a constant rate of discharge can be given a theoretical basis.  --Lambiam 22:51, 23 March 2023 (UTC)

Is there a theory that the universe actually spends the vast majority of its time in an extremely high entropy state, only occasionally becoming ordered in accordance with the Poincaré recurrence theorem (like a universe-scale Boltzman brain), and then the 2nd law of thermodynamics is only a statistical pattern that brings the universe from its current low entropy state back to normal? (The current low entropy state could be explained by the anthropic principle.) This seems like the expected behaviour mathematically, so why isn't it more commonly stated? Is there some conflict with quantum physics or the expansion of the universe? 135.180.244.18 (talk) 06:34, 24 March 2023 (UTC)

The are various Cyclic models which I guess are loosely similar Nil Einne (talk) 17:26, 24 March 2023 (UTC)

As far as I can see a problem with that is that a state where we are all destroyed in a very short time is the most probable if we are the product of a random chance like that. But in fact the universe is fairly like around us as faras we can see to billions of light years away. NadVolum (talk) 18:29, 24 March 2023 (UTC)

We can only observe the observable universe, which appears to be expanding, but if the universe is infinite, it may be locally expanding here and there while contracting elsewhere. There may likewise be occasional pockets of low entropy in an ocean of high entropy, and assuming random fluctuation some of these pockets will inevitably be as large as our observable universe. The arrow of time will symmetrically be directed away from the temporal valley of a low-entropy pocket; elsewhere, time is not oriented one way or another. An argument against this theory, if we may call it that, is the unimaginably low probably of finding oneself in such a temporary pocket of order in an ocean of chaos hidden behind the horizon. On the other hand, the probably of finding oneself in the midst of an ocean of chaos is zero, since the notion of observation has no meaning there. Like the various multiverse theories, the Boltzman brain, Last Thursdayism and solipsism, no conceivable experiment can falsify this – but neither can its negation be falsified experimentally.  --Lambiam 21:07, 24 March 2023 (UTC)

It feels like we should be careful here ... it is, after all, a question couched in thermodynamics. A battery stores potential energy and this energy can be extracted to do work. Batteries store chemical potential energy (for all of the more common types of batteries, anyway). Chemical energy is one form of stored potential energy - this is, we hope, obvious to anyone who passed muster in high school science class! But perhaps less obviously: stored potential energy is not the only type of thermodynamic potential! Entropy has a complex relationship with energy, and this question is inquiring about the mechanisms that drive processes at cosmic scales! As posed, the question asks if the entropy of the universe is like the energy in a battery. Well, ... "no!" The energy of the universe is like the energy of a ... battery. The entropy is a related, but different, quantity from the energy. One relationship is quantified using the equation for Helmholtz free energy, which tells us something about how we can obtain work from a closed system. We can extract work from energy; we can extract work from entropy; we can extract work from a combination of them. (There is also an unsolved question about whether the universe is well-represented as a "closed thermodynamic system" ... or not! I don't pretend to have the answer!) The point is, batteries have stored energy; batteries also have entropy; universes have both entropy and energy. Any particular physical process can be described as work being done; sometimes that work is driven by potential energy; sometimes that work is driven by an entropy change; and these two are fundamentally different, at the macroscopic and microscopic scales. Nimur (talk) 18:57, 24 March 2023 (UTC)

That is carefully shadowboxing the OP's question that doesn't actually suggest the entropy of the universe is like the energy in a battery. The OP instead lays the basis for a novel all-embracing cosmic Calendar in which all dates that ever existed are expressible in decaying positive percentage measures. However the large number of digits of resolution needed to distinguish between, say yesterday from today and tomorrow, makes the scheme impractical. Philvoids (talk) 17:00, 27 March 2023 (UTC)

If it covered all events as well it'd be like the map in Sylvie and Bruno which was a mile to the mile but they'd never spread it out because the farmers objected it would cut out the sun ;-) NadVolum (talk) 20:51, 27 March 2023 (UTC)

Courtesy link: Wikipedia:Reference desk/Archives/Science/2019 February 9#Arrow of Time. 2A00:23C3:9900:9401:7816:B61:458D:EFF3 (talk) 16:20, 29 March 2023 (UTC)

RNA

What is the difference between coding and noncoding mRNA or "micro RNA"? 2A02:908:424:9D60:A147:51B5:31C9:EE80 (talk) 22:05, 23 March 2023 (UTC)

Basically the same as between coding and non-coding DNA. The coding parts consist of sequences of codons (triplets of bases) that code for amino-acids (see DNA and RNA codon tables) such that the resulting sequences of amino acids are chained together to form polypeptides, the backbones of proteins. The non-coding parts are the other parts – which does not imply they have no function, as earlier mistakenly thought.  --Lambiam 22:37, 23 March 2023 (UTC)