Wikipedia:Reference desk/Archives/Science/2020 August 22

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August 22

Tears

what is the evolutionary advantage of children having tears that stream down their faces when they cry? Thanks. — Preceding unsigned comment added by 2A00:23C6:6884:6200:CD3A:16A0:165D:8FF8 (talk) 11:37, 22 August 2020 (UTC)

Their parents (or others) can see they want attention, and then assist them. Graeme Bartlett (talk) 12:11, 22 August 2020 (UTC)

While some scientists believe that human crying is an evolutionary trait, others believe it is behavioral. Therefore, it may well be a mix and fall into the nature vs nurture world. While it is accepted that humans are the only animals that cry with tears, there is evidence that pets, primarily dogs, can learn to mimic the behavior with positive reinforcement. 97.82.165.112 (talk) 13:23, 22 August 2020 (UTC)

Some hypotheses:

Why Cry? Evolutionary Biologists Show Crying Can Strengthen Relationships.

Teary-Eyed Evolution: Crying Serves A Purpose

Why Only Humans Shed Emotional Tears : Evolutionary and Cultural Perspectives

We also have an article, Crying. Alansplodge (talk) 14:03, 22 August 2020 (UTC)

Can we stabilize a radioactive nuclei?

We know that some nuclei exist for only a limited time.

1. why same configuration atoms decay differently?

2. can it be that the positions of the nucleons makes the difference?

--Exx8 (talk) 17:01, 22 August 2020 (UTC)

Well for one thing, I would think a stronger gravitational field might make a difference. Although I have no idea whether or not anyone has ever bothered to test that hypothesis. Otherwise, yes, I would agree that the specific configuration of nucleons would likely effect the process. No reference for that either, unfortunately. Earl of Arundel (talk) 18:17, 22 August 2020 (UTC)

@Earl of Arundel: That's not correct. There's no way to stabilize radioactive nuclei, with one exception: nuclei that decay only by electron capture can be stopped from doing so by simply removing all the electrons around it (i.e. completely ionizing it). This is possible only for a select few radioactive nuclei, though. In one exceptional case, a technically-metastable nuclear isomer is stabler than its ground state (in practice, stable), namely Tantalum-180m, but converting the ground state to that is not a simple matter of rearranging nucleons–that is close to impossible to do in a surgical manner.

Stronger gravity only would make a neutron star. So you can argue that neutronium can be stabilized that way, but it doesn't help for any other nuclide.--Jasper Deng (talk) 18:27, 22 August 2020 (UTC)

What I meant was that an unstable isotope might decay slower near the surface of Jupiter for example. Or has that sort of thing already been tested for? Earl of Arundel (talk) 18:46, 22 August 2020 (UTC)

Gravity is by far the weakest of the four fundamental forces. It's almost irrelevant for the purposes of radioactive decay.--Jasper Deng (talk) 19:44, 22 August 2020 (UTC)

The questioners may be thinking of Gravitational time dilation, which would do it from an outside observer's perspective.John Z (talk) 20:17, 22 August 2020 (UTC)

Well there you go. So I was inadvertently correct. But seriously, without incontrovertible proof I don't think anyone can say for sure that large gravitational fields have absolutely no effect on (non-relativistic!) decay rates. Earl of Arundel (talk) 21:18, 22 August 2020 (UTC)

Decay rates assume the same frame of reference as the radioactive nucleus, so special relativity is irrelevant.--Jasper Deng (talk) 21:26, 22 August 2020 (UTC)

Some people are trying to find out if decay rates can change eg "Fluctuations in measured radioactive decay rates inside a modified Faraday cage: Correlations with space weather". Possibly neutrons and neutrinos have an effect. Also they mention a near zone effect. You may also wish to consider atmospheric electricity - the electric field in the air, negative or positive ions in the atmosphere, amount of carbon-14 around, and the magnetic field. These might affect your measurements, but only really affect the decay rate at some super-extreme. Graeme Bartlett (talk) 22:35, 22 August 2020 (UTC)

Please see (and update as necessary) Radioactive decay#Changing decay rates. DMacks (talk) 04:47, 23 August 2020 (UTC)

Just by the way, there's no such thing as "a nuclei". The singular is "nucleus". --Trovatore (talk) 22:49, 22 August 2020 (UTC)

Maybe a misuse similar to the frequent treating of "media" as a singular. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:56, 23 August 2020 (UTC)

Welcome to this (ouch, according to a grammatical number criteria) phenomena.  --Lambiam 12:07, 23 August 2020 (UTC)

Question 1: Do you mean, "why do some nuclides have more than one decay mode"? In a nutshell, an unstable nuclide can "try" to decay through any mechanism it's "allowed" to decay by. The full answer involves complicated quantum mechanics: quantum numbers and eigenstates. Both the parent nuclide and the decay products have to have the "right" parameters for a certain interaction, or else it can't happen. Question 2: nucleons bound in a nucleus don't have separate "positions". A nucleus is not a bunch of teeny balls stuck together like Legos; it's a composite particle that is its own thing. It's not possible to say "proton number seven is right here at this spot". Our human intuition is wired for our familiar macroscopic world where solid things are solid and come in chunks, but the quantum realm is not like that at all. --47.146.63.87 (talk) 06:04, 24 August 2020 (UTC)

There's an explanation here [1] which I understand in parts, while this [2] is more readable. 2A02:C7F:BE12:7100:F94B:2D97:BB69:D6AF (talk) 12:07, 24 August 2020 (UTC)

The first one is rubbish (arXiv is not free of cranks promoting their private "theories", in this case "the presence of cosmic expansion velocities in extended objects"). --Wrongfilter (talk) 12:57, 24 August 2020 (UTC)