3115: Unsolved Physics Problems

Unsolved Physics Problems

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Title text: 'Tin pest' makes more sense to me. Tin just doesn't want to be locked down in a shape like that. I get it. But why would any metal want to grow hair??

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Explanation

This comic is part of the Unsolved Problems series and follows 2943: Unsolved Chemistry Problems and 2529: Unsolved Math Problems. Quantum gravity is the problem of determining how gravity interacts with the physics of quantum mechanics. There are contradictions between the two theories as currently understood. Gravity is described by the theory of general relativity and is well-characterized at large scales, while quantum mechanics is also well-understood and well-characterized but is easiest to observe at very small scales. This scale discrepancy makes it hard to conduct an experiment that includes both phenomena, leading to a wide range of unifying theories that are difficult to experimentally confirm or refute. In this comic, the question is specifically what part time plays in quantum gravity, but this is left vague and open-ended by considering several different options that may or may not be mutually contradictory.

The second issue, the gallium anomaly, is an example of a precise experiment to understand a specific phenomenon, namely a deficit of germanium (⁷¹Ge) when gallium (⁷¹Ga) is bombarded with neutrinos (ν_e). The difference between the expectation and reality is small but statistically significant, and indicates our models of physics are inaccurate. One possible explanation is the creation of sterile neutrinos, a theoretical type of neutrino outside of the standard model that would only interact with other matter gravitationally, making them essentially impossible to detect directly and one of the proposed explanations for the nature of dark matter.

Millimeter-long zinc whiskers on zinc-coated steel

The third problem concerns zinc whiskers — a phenomenon that at first sounds extremely strange, and the mechanism for which is not fully understood, in which a piece of metal (in this case zinc) can 'grow' hair-like filaments on its surface. Hair is usually thought of as an organic structure, and spontaneous change in a block of metal is not a problem most people would expect (leading to an off-panel character to ask whether it is a joke). For an inorganic object to grow hair seems both magical and grotesque, so Randall considers this phenomenon cursed. Metal whiskers can cause problems in a lot of electronics, where metal hairs create unwanted electrical connections or act as antennae. In particular, they can degrade performance of rechargeable batteries. Since electronic devices are ubiquitous, the prevention of metal whiskers is a challenge that affects us widely, while it is hard to see how the other two issues affect most people. The problems caused by metal whisker growth also support the "cursed" descriptor. Lead has been widely used as an additive to solder for whisker prevention, but lead is toxic and has in fact been banned in the E.U. for most electronics.

The title text mentions tin pest — a transformation which causes deterioration of formed tin objects into a powder in a chilly environment. Randall considers this an understandable rebellion of the tin against being forced into shapes that we want it to take, whereas he cannot understand the motivation of zinc to grow hair. In reality, metallic elements do not have motivations and intentions. The actual cause of tin pest is that solid tin has two forms (allotropes) with different crystal structures. β-tin is white, metallic, and malleable, and the more stable at temperatures above 13.2°C; α-tin is grey, non-metallic, and brittle, and is stable at temperatures below 13.2°C. When an object is made from tin, it's generally done at higher temperatures, where it's easily worked, resulting in the β crystal structure. If such an object is then left at lower temperatures, it eventually spontaneously changes to the α crystal structure, but the transition causes it to disintegrate. Impurities in the tin can lower the transition temperature, or prevent the disintegration from occurring at all. Tin pest was famously responsible for the destruction of the tin pipes of pipe organs in churches, when those churches were allowed to get cold below the transition temperature at times they weren't being heated.

A similar spontaneous reorganization in crystal structure is one possible factor in the growth of metal whiskers. Preferred crystal shapes can be strongly influenced by subtle factors of temperature and impurities, and atoms and molecules can slowly rearrange even in solids. If a solid mass is in the form of extremely tiny crystals that precipitated quickly, atoms and molecules can depart from the surfaces (especially the edges and corners) of the smallest crystals and redeposit on larger crystals. Impurities that were trapped by the original rapid precipitation tend to be released in the process, caught between the growing purer crystals.

Transcript

The Three Types of Unsolved Physics Problem

[Each physics problem is in a separate panel]

Vague

[A Feynman diagram of two particles interacting via the electromagnetic force is to the right of Cueball. The diagram is drawn on a curved surface]

Cueball: What is the nature of time in quantum gravity? Is it a background parameter, a dynamic aspect of spacetime, or an emergent phenomenon?

Precise

[A scientific instrument and a nuclear reaction equation of gallium-71 becoming germanium-71 are to Megan's left. The equation says: ⁷¹Ga + ν_e → ⁷¹Ge + e^- .]

Megan: Why does the S.A.G.E. Gallium Neutrino Capture Experiment produce only 75% as much germanium as predicted?

Cursed

[A rectangular block of zinc, with whiskers growing out of it, is visible to the right of White Hat]

White Hat: Why does some metal randomly grow hairs?

White Hat: It keeps causing short circuits and we have no idea what's going on.

Voice from off-panel: Is this a joke?

White Hat: No! Please help!

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Discussion

I didn't notice that the linked paper on zink whiskers was from NASA at first, but it was immediately apparent that an American wrote it... The style is super American. "Oh, no! People who chose to read this paper won't get it unless I write really big and EMPHASISE words." It's a very "I Can't Believe It's Not Butter" style of naming margarine, so to say. Kapten-N (talk) 07:23, 15 July 2025 (UTC)

The linked pdf is not a scientific paper, but a slide presentation. I think especially for safety-related presentations it is not uncommon to go a bit over the top with "be aware that this seemingly harmless effect can have serious consequences" -- especially if the risk is seemingly low, but the possible damage is really high. --134.102.219.31 08:25, 15 July 2025 (UTC)

@Kapten-N, your Ameriphobia is duly noted. 76.216.164.118 14:20, 15 July 2025 (UTC)

It seems that there is a typo on the second panel about the Gallium anomaly. According to Wikipedia "The resulting production of 71Ge was calculated in 2005 to be 79% of expected", not 75%. Should this be mentioned? Rps (talk) 12:12, 15 July 2025 (UTC)

Unremoved background on the middle title: The middle title has unerased lettering with a slightly different style. 92.40.191.220 (talk) 08:41, 15 July 2025 (UTC) (please sign your comments with ~~~~)

You know, Hair Metal is a thing. Just sayin'. 92.184.140.165 12:39, 15 July 2025 (UTC)

If metal inexorably produces hair and unwanted behaviour, which I believe it does, could you explain to me why rock doesn't? 2001:1C00:31C:0:90DD:6826:AA7C:C80F 19:57, 15 July 2025 (UTC)

Because it absolutely refuses to be in any way vulnerable to scissors! 92.23.2.228 22:55, 15 July 2025 (UTC)

If we can't explain why metal grows hair, why would you think we could explain why rocks don't? DL Draco Rex (talk) 19:23, 16 July 2025 (UTC)

An (overly) simplified explanation: Rocks frequently are made out of multiple different chemicals which are less likely to all behave the same way when mixed together than in a pure sample of an element like Zinc or Tin. In the explanation it notes that mixing different chemicals into Zinc or Tin (an alloy, but I'm simplifying) can change the behavior and prevent the "hair" from growing. Tomb (talk)

If you look closely where it says ‘precise’, it looks like Randall traced it! Broseph (talk) 12:44, 15 July 2025 (UTC)

The zinc whiskers are similar to joke in 3112: Geology Murder where the

dagger-shaped object precipitated within the wound

KingPenguin (talk) 02:19, 16 July 2025 (UTC)

A rare case where gallium is the somewhat normal behaving metal. RegularSizedGuy (talk) 13:00, 16 July 2025 (UTC)

First-year chem lab on purification by recrystallization. We started with human gallstones — I don't recall if we had the actual "stones" and crushed them or even just dissolved them whole, or started with the powdered material. This material was dissolved in the smallest amount of boiling solvent that would do the job, giving a dark brown solution. The solution was cooled in an ice bath, and the cholesterol precipitated out (leaving some still in solution, which reduced the yield). The crystals were filtered out, very pale beige. The procedure was repeated, and the resulting crystals were white/colourless. One interesting observation was that the crystals that came out of the first stage were wide flat thin plates, but the second stage gave long needle-like crystals. Same materials, same solvent, same temperatures, same procedures and handling... but the concentrations of the impurities in solution completely changed how the crystals grew. BunsenH (talk) 17:13, 17 July 2025 (UTC)

I would add that some fields like avionic and medicine are still allowed to use lead in solder because while lead is toxic, NOT using it could easily cost more lives in such cases. -- Hkmaly (talk) 23:07, 22 July 2025 (UTC)
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