Wikipedia:Reference desk/Archives/Science/2017 November 15

= November 15 =

Positronium diameter
In the book "Parallel Worlds" Michio Kaku writes that in the Dark era of the universe intelligent life might survive by being based on positronium atoms which would be 10^12 parsecs in diameter. How come these atoms would be so huge when Wikipedia says that nowadays they're the size of an ordinary hydrogen atom? 93.136.80.194 (talk) 08:13, 15 November 2017 (UTC)
 * When positronium is in an excited state it becomes bigger. It does decay, but the higher the state, the longer its life time. It does not have to be so big to last a long time. This would be termed a Rydberg atom. Some may combine together to form Rydberg matter. A solid positronium chunk of matter based on this would be less dense than air. Graeme Bartlett (talk) 12:31, 15 November 2017 (UTC)
 * Let me try to understand your question: In a the author writes about  and now you want us to explain it? You'd have to ask the author.  It's their imagination.  Explaining the fictional scientific concepts in real science terms is always a futile exercise.  -- Jayron 32 13:32, 15 November 2017 (UTC)  Sorry for the misunderstanding.  Carry on.  -- Jayron 32 16:06, 15 November 2017 (UTC)
 * FYI, Parallel Worlds is intended as a work of popular science non-fiction. That said, I don't know the answer to the IP's question or whether he is accurately describing what is presented in the book.  Dragons flight (talk) 14:46, 15 November 2017 (UTC)
 * The book is on archive.org) (apparently legally), search for 'positronium'. Positronium also mentions this, with a link to a paper. Basically, they are talking about the distant future when the density of matter in the Universe is extremely low and after nucleons (protons and neutrons) have decayed away (if protons do decay). In such an environment huge positronium "atoms" can be stable over a long time scale (small positronium atoms would annihilate quickly) and seem to be the only thing that is still around if this scenario is correct. --Wrongfilter (talk) 15:56, 15 November 2017 (UTC)
 * So arbitrarily large atoms can be created? Why 10^12 pc then? 93.136.80.194 (talk) 19:52, 15 November 2017 (UTC)
 * "Atom" is a funny word here, and it depends on what you mean by an "atom". Positronium has some properties like an atom, in that it is metastable enough at current conditions to be studied, it forms chemical bonds with other atoms, etc.  Indeed positronium hydride has been created long enough to be studied; the half-life of positronium being longer than some transuranium isotopes.  But it isn't really an "atom", if you mean "A group of nucleons surrounded by an electron cloud".  What it is is an electron and positron with enough quantum pressure to keep them in the same general area long enough to have consistent properties.  The question being asked (and answered) by the 10^12 parsecs answer is something akin to "at what distance will a bound electron-positron pair be such that the quantum pressure keeping them apart would be sufficient to prevent them from collapsing together and annihilating?" and apparently that answer is "a trillion parsecs"  I don't know the specifics of the math here, but that's how I interpret the result.  Now, since this thing would only really be able to exist in a state that large if there were literally nothing else left to interact with it in ways that may disrupt its stability, that would be a very empty universe indeed. But I think that's the point, the author is looking for some sort of matter which would still exist.  As long as you have matter, you can store information, and if you can store information, you're not yet at the end of time.  -- Jayron 32 20:16, 15 November 2017 (UTC)
 * I see, thanks. 93.136.80.194 (talk) 20:33, 15 November 2017 (UTC)


 * I think "neutrino nuggets" make for a much more interesting speculation in this direction - hmmm, I thought we had an article... anyway, the general idea is that all the light fast-moving particles that don't interact with anything in a given era of the cosmos eventually tend to slow down as the overall temperature decreases, while their interactions at increasing distances become relevant as much longer time scales become of interest.  It's thought that there can be interesting "neutrino chemistry", which due to high speeds and poor interaction is presently not readily accessible to us for study. Wnt (talk) 16:45, 19 November 2017 (UTC)

Baked Beans
It is well known that baked beans can cause flatulence. According to the article this is "due to the fermentation of polysaccharides (specifically oligosaccharides) by gut flora, specifically Methanobrevibacter smithii. The oligosaccharides pass through the small intestine largely unchanged; when they reach the large intestine, bacteria feast on them, producing copious amounts of flatus."

1) Of the carbohydrate content of baked beans, what percentage is actually polysaccharides? For example, this can from Heinz says 11.4g of carbohydrate per 100g. How much of that is polysaccharides?

2) When the polysaccharides are feasted on by bacteria, how much of it gets absorbed by the human body or wasted?

Thanks 91.47.17.210 (talk) 10:09, 15 November 2017 (UTC)
 * See "Polysaccharide from Dry Navy Beans, Phaseolus vulgaris: Its Isolation and Stimulation of Clostridium perfringens",, a wonderful research paper that discusses both the polysaccharide content of a few bean varieties, and also gives measurements for how much gas is produced. What a world! SemanticMantis (talk) 17:34, 15 November 2017 (UTC)

Baked beans and polysaccharides
I read something recently that made me wonder about baked beans and flatulence. It is well known that baked beans can cause flatulence. According to the article this is "due to the fermentation of polysaccharides (specifically oligosaccharides) by gut flora, specifically Methanobrevibacter smithii. The oligosaccharides pass through the small intestine largely unchanged; when they reach the large intestine, bacteria feast on them, producing copious amounts of flatus."

The questions are:

1) Of the carbohydrate content of baked beans, what percentage is actually polysaccharides? For example, this can from Heinz says 11.4g of carbohydrate per 100g. How much of that is polysaccharides?

2) When the polysaccharides are feasted on by bacteria, how much of it gets absorbed by the human body or wasted?

Thanks, SemanticMantis (talk) 19:34, 15 November 2017 (UTC)


 * I have found a suitable reference on the topic, but I'm curious to see what anyone else can dig up on question 2). Polysaccharide from Dry Navy Beans, Phaseolus vulgaris: Its Isolation and Stimulation of Clostridium perfringens",, a wonderful research paper that discusses both the polysaccharide content of a few bean varieties, and also gives measurements for how much gas is produced. What a world! SemanticMantis (talk) 19:34, 15 November 2017 (UTC)


 * WP:POINTY "When one becomes frustrated with the way a policy or guideline is being applied, it may be tempting to try to discredit the rule or interpretation thereof by, in one's view, applying it consistently. Sometimes, this is done simply to prove a point in a local dispute. In other cases, one might try to enforce a rule in a generally unpopular way, with the aim of getting it changed.


 * "Such behavior, wherever it occurs, is highly disruptive and can lead to a block or ban. If you feel that a policy is problematic, the policy's talk page is the proper place to raise your concerns. If you simply disagree with someone's actions in an article, discuss it on the article talk page or related pages. If mere discussion fails to resolve a problem, look into dispute resolution.


 * The proxy for whom you have made yourself a proxy can always post under his real identity in 60 days from the time he was blocked. Hopefully that addresses your problem, SemanticMantis. μηδείς (talk) 04:03, 16 November 2017 (UTC)
 * I had figured it was the banned user Light Current. ←Baseball Bugs What's up, Doc? carrots→ 04:13, 16 November 2017 (UTC)

Off topic shouting. Take it to the talk page if you must SemanticMantis (talk) 13:41, 16 November 2017 (UTC)

It's already on the talk page, and it is on-topic. ←Baseball Bugs What's up, Doc? carrots→ 15:31, 16 November 2017 (UTC)}}

This is off topic for the Refdesk, so I'm opting for a hat here. Wnt (talk) 16:47, 19 November 2017 (UTC)