Wikipedia:Reference desk/Archives/Science/2023 October 1

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October 1

Variables affecting national fertility rates

I have a proposal for a scientific study, but I don't know enough about statistics to do the study myself. Specifically, I am wondering if it can be shown that the prevalence or legal status among worldwide nations of birth control, pornography, homosexuality, and other sexual behaviors historically considered 'non-traditional' have any effect on national fertility rates. How could I go about forwarding this idea to someone who can do a study? Wiki Crazyman (talk) 01:54, 1 October 2023 (UTC)

This is not at all a simple question, and I think you are probably going about this the wrong way/a way impossible to get meaningful results. You are going to need to speak to, work with, and get data not only from sociologists, anthropologists, and historians (these first three might also have something to say about throwing around words like "non-traditional" about the variables you listed), but also experts in fields like fertility health, epidemiology throughout history, and many, many other fields. Not only are all of the things you have listed happening at the same time, but potentially far greater other variables as well. For example, how much of a population is reaching adulthood to even have children? If many die before adulthood, then there will be pressures to have higher birthrates. That's just one example. How about a war having a huge impact on the population of one biological sex? What about the impacts of famines or climatic events? It is generally difficult to determine correlation or causation when you have more than one changing variable, very difficult when you have three, and even more difficult when trying to do so while attempting to control for a myriad of other outside influences like those I've listed. I would remind you that a "traditionally conservative" (and that's a bad use of the term) country, Russia, experienced a marked decline in its fertility rate at the very same time that the Russian Orthodox Church was massively returning to general public life with the fall of the Soviet Union. There were many other confounding variables, such as a sharp collapse in the economy, lowered support for public healthcare, the loss of a portion of its male population at normal child raising age due to war, and many other issues that all had impacts on birthrate. You aren't likely to get a meaningful result by setting out already deciding what your independent variables are going to be (indeed, it is even worth asking if those practices you listed are independent variables with fertility rate depending on them, or if their incidence and practice are the dependent variables that respond to the fertility rate of a given population; you can't just assume it's one way or the other). You are better off first studying things like historical trends and working to determine what influenced those specific trends, instead of starting already thinking you know. --OuroborosCobra (talk) 03:06, 1 October 2023 (UTC)

Meta-answer: very few (if any) scientific fields are lacking in "study ideas". The hard part is actually making the study in a proper way.

The first step in any of these is "look up if others have not already done it". A 30 second Google Scholar search turns up this article which did (attempt to) disentangle the various effects of economics, religious views, and so on. Any serious research should take that previous publication (and others) into account - either attempting to replicate its results, question implicit hypotheses, or study something else entirely. Tigraan^{Click here for my talk page ("private" contact)} 13:21, 4 October 2023 (UTC)

Crustaceans becoming insects

If crustaceans have 10 legs and insects developed from crustaceans, how did they end up with only 6 legs?? Did 4 legs evolve into anything?? If so, what did they evolve into?? Georgia guy (talk) 14:28, 1 October 2023 (UTC)

Does Arthropod#Segmentation help? Martin of Sheffield (talk) 14:52, 1 October 2023 (UTC)

Lots of crustacians have many legs or ten legs. And caterpillars have lots of legs too. The common ancestor of crabs and flies was perhaps twice as long ago as the rise of the dinosaurs and didn't have to look particularly like anything today. A lot of things can happen in deep time. NadVolum (talk) 15:19, 1 October 2023 (UTC)

• As a general principle, it's a bad idea to say "<current group> evolved from <other current group>". They may both have evolved from the same thing, but that last common ancestor can be a lot different to either. Also there are some body structure (leg pairs on arthropods being an example) where it's just not that hard for the total number to vary (over evolutionary time). Andy Dingley (talk) 17:30, 1 October 2023 (UTC)

  Our article Pancrustacea states that several molecular studies support a phylogeny in which hexapods, including insects, are derived from crustacean ancestors, so then cladistically insects are crustaceans, just like birds are dinosaurs.  --Lambiam 20:44, 1 October 2023 (UTC)

• But is our hypothesised Pancrustacean ancestor a crustacean? Was it (by any stretch of the imagination) "a crab"? A common mis-implication from cladistics, especially when the names are similar like this, is my original point: although it's true that the ancestor is a pancrustacean, this shouldn't be taken to mean that it resembles anything like what we'd regard today as a modern example crustacean. Morphologically modern birds are far closer to coelurosaurs. Andy Dingley (talk) 21:34, 1 October 2023 (UTC)

  Regardless of the answer to these questions, the statement vindicates the OP's contention that insects developed from crustaceans. The clade Pancrustacea would have been named just "Crustacea" but for the fact that in traditional taxonomy, mainly based on morphology, Hexapoda were excluded from Crustacea. Look at the phylogenetic diagrams in Pancrustacea and note that not a single one contains a subphylum "Crustacea". Note also that in each of these diagrams Hexapoda is a subsub...subclade.  --Lambiam 06:45, 2 October 2023 (UTC)

• Segmentation, including in arthropods, is often governed by HOX genes. A very small alteration in HOX genes can easily result in a different number of legs, just as long as the number is still even. It can even result in some fun things, like legs growing out of where you would expect antennae. --OuroborosCobra (talk) 21:29, 1 October 2023 (UTC)

• The arthropod head problem Andy Dingley (talk) 21:34, 1 October 2023 (UTC)

Hashtag: Very High Energy, Particle accelerator, Blueshift

Besides the well-known device - which "accelerates particles" to ultra-velocity and above - in order to charge them with very high energy, is there also an analogous device - which "shifts the color of photons" to ultra-violet and above - in order to charge them with very high energy?

2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 23:30, 1 October 2023 (UTC)

Not that I can think of. If you want to make high energy (i.e. high frequency, which is the same thing) photons, you generate them at the desired frequency, rather than trying to add energy to existing photons. The Hermes III experiment at Sandia National Laboratory claims to be the most powerful gamma ray generator in the world.[1] PianoDan (talk) 03:20, 2 October 2023 (UTC)

Thanks. It seems that Hermes III is weaker than Z Pulsed Power Facility, which is the successor of the former, isn't it? 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 08:10, 2 October 2023 (UTC)

This is a tough thing to do. very small changes can be done via Optical modulators using electro–optic effects. Nonlinear optics using multiple photons, can do Second-harmonic generation or Third-harmonic generation to generate ultraviolet. And it appears that High harmonic generation can generate X-rays. Graeme Bartlett (talk) 03:32, 2 October 2023 (UTC)

Thanx. 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 08:11, 2 October 2023 (UTC)

Thank you all. Assuming the very high velocities generated by particle accelerators have no upper bound (at least theoretically), do you think gamma ray generators (like those built in Sandia National Laboratory) can also generate any chosen frequency (at least theoretically)? 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 08:19, 2 October 2023 (UTC)

No, a human engineered system will have limits. For natural gamma rays see Ultra-high-energy gamma ray which says that 1.4 PeV is the highest energy detected so far. A 100,000 PeV photon would interact with the Earths magnetic field to produce a pair of particles. For an even bigger imaginary limit, if the whole mass energy of the universe was used to make one photon, its energy could not be exceeded. Some consider that the Planck energy is a limit. Graeme Bartlett (talk) 10:16, 2 October 2023 (UTC)

Please notice that I've added "theoretically", just to make sure that one should not consider any practical limits human engineered sustem usually has. As for the Planck energy, It's approx. one billion Joule, so it can't be a limit, because there are many objects whose energy exceeds this limit. Just as the Planck momentum, being approx. six kg m/s only, is not a limit of momenta in the universe. So it seems that the only theoretical limit is the energy of the whole universe, right? What about intermediate exact values of energy, like pi (3.14...) Joule? Again, I'm asking theoretically. 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 11:24, 2 October 2023 (UTC)

The velocities produced by particle accelerators absolutely have an upper bound, namely the speed of light. Electrons approach this limit so quickly that all you're basically doing to the velocity as you add energy to electrons in an accelerator is adding "9"s to the end of 0.999...*c. PianoDan (talk) PianoDan (talk) 15:01, 2 October 2023 (UTC)

I'm referring to a limit of energy. 2A06:C701:7466:7300:ED6A:AA06:3CDA:BB2 (talk) 15:16, 2 October 2023 (UTC)

Using the mass–energy equivalence, the mass of a photon with an energy of 3.5 GJ (about 22×10²⁷eV) is such that the corresponding Schwarzschild radius is larger than its wavelength. Does this give a limit on the energy of a photon?  --Lambiam 22:32, 2 October 2023 (UTC)

You can always transfer to a reference frame where this photon's energy is below that value — nothing happens in that reference frame, therefore nothing happens in the original frame. This is a good example of why the mass-energy relation should not be applied to centre-of-mass motion (or whatever you'd call it in the case of a photon). A limit would have to come from considerations about the emission process, or generally about the interaction of photons/the electromagnetic field with matter. --Wrongfilter (talk) 06:18, 3 October 2023 (UTC)

1. Do you think you can calculate the limit you suggest? This may help.

2. As for user:Lambiam's comment you have rejected, I think the core of Lambiam's quesion is simple: Does a photon's wavelength have any lower bound, e.g. the Planck length (being approx. 10^-35 m)? Please notice this question is quite equivalent to my original question about whether a photon's energy (in a given reference frame) has any upper bound. Maybe this important question, at least about the wavelength, deserves a thread of its own. 2A06:C701:7446:D900:1D55:57C:4F3F:3A51 (talk) 07:36, 3 October 2023 (UTC)

ad 1.: I do not know what that limit would be. I only know that it cannot come from the photon in isolation.

ad 2.: My answer is no, based on the theory of relativity. Again, interactions, possibly with the quantum structure of spacetime or more simply with the matter distribution in the Universe, could change the answer. It might be that the photon picture is too simplistic, however, and there might be more in the full theory of quantumelectrodynamics.

I was mainly challenging the argument with the Schwarzschild radius. If that radius depended on "relativistic mass", it would be frame-dependent. What would it look like anyway? Spherical? In which frame? The event horizon of an ordinary (non-rotating) black hole is spherical only in its rest frame, but non-spherical in a frame where the BH is moving (same for its gravitational field). --Wrongfilter (talk) 08:11, 3 October 2023 (UTC)

Do you think a photon's wavelength may be less than the Planck length (being approx. 10^-35 m)?

A photon's relativistic mass depends on the photon's momentum only, hence on the photon's wavelength only. Are you sure this momentum/wavelength, the photon has, depends on the reference frame? 2A06:C701:7446:D900:1D55:57C:4F3F:3A51 (talk) 10:45, 3 October 2023 (UTC)

Around the Planck length, quantum gravity effects become important. Perhaps the speed of photons like this will be lower than the speed of light. In reference frames that move with respect to each other, there can be a Doppler shift that affects the frequency measured, and thus wavelength, momentum and energy. In a gravitational field, the photons will also change energy and be shifted. Graeme Bartlett (talk) 11:15, 3 October 2023 (UTC)

OP's recent thought: If no wavelength can be shorter than the Planck length, then no photon can have energy higher than 12.3 billion Joule (hence no photon can have a relativistic mass higher than 0.13675 milligram), so no gamma ray generator can generate a photon whose energy is higher than that limit. 2A06:C701:7446:D900:1D55:57C:4F3F:3A51 (talk) 17:37, 3 October 2023 (UTC)