Wikipedia:Reference desk/Archives/Science/2022 July 7

= July 7 =

Strength of wines
Most wines are 12.5% or maybe 12% ABV. Why is this? Thanks 86.184.26.44 (talk) 20:08, 7 July 2022 (UTC)
 * Because that's the point at which historic strains of yeast died or became inactive. Some modern strains will tolerate a higher concentration. Martin of Sheffield (talk) 20:17, 7 July 2022 (UTC)
 * Thank you so much. Is this explained in any article? And what about lower ABVs - do they use different yeasts? Thanks. 86.184.26.44 (talk) 20:33, 7 July 2022 (UTC)
 * "There are several factors that affect the alcohol content of wine including the style of wine, quality level, and climate where the grapes grow." This webpage implies that wines under 10% ABV have had their fermentation process deliberately halted somehow, and thus have remaining sugar. Then wines up to 11.5% have more complete fermentation but are from grapes with less sugar in the first place, perhaps due to a cooler climate or deliberately picked when less ripe. Card Zero  (talk) 20:44, 7 July 2022 (UTC)
 * Thank you. Is all this included in any Wikipedia article? It looks very useful. 86.184.26.44 (talk) 21:10, 7 July 2022 (UTC)
 * I think Wikipedia might be lacking a detailed breakdown of the factors leading to different strengths of wine. Fermentation in winemaking gives an upper limit of 15%. Card Zero  (talk) 21:33, 7 July 2022 (UTC)

Would travelling to different points in time but in parallel universes actually be compatible with the laws of physics?
I apologize if I sound really stupid here, but I've got a question: Would travelling to different points in time but in parallel universes actually be compatible with the laws of physics? Conventional time travel seems like it would be impossible due to the grandfather paradox, but what about moving from one universe to another, parallel universe at a different point in time, as per the multiverse theory? In such a scenario, you wouldn't literally be meeting people from your own universe's past, but rather from another parallel universe's past at the point in time where that universe branched off from our own universe in a separate direction of its own. Does that make sense? And is this actually compatible with the laws of physics?

68.4.99.100 (talk) 20:41, 7 July 2022 (UTC)


 * Yes, this is speculated about in The Fabric of Reality and The Beginning of Infinity. Other physicists may disagree.
 * One wrinkle is that the universe you arrive in has to be a special version of the past, in that it must contain you as a newly-arrived time-traveller. Card Zero  (talk) 20:48, 7 July 2022 (UTC)


 * Yeah, obviously you entering this parallel universe at some past point in time will create a universe split, with the branching off of a new parallel universe. 68.4.99.100 (talk) 22:21, 7 July 2022 (UTC)
 * Here "universe" is strictly speaking equal to "instant in time".
 * "Timelines", arbitrary strings of related universes, aren't anything in particular, but that's also something "universe" may be used to mean, mainly because a person can't live in a single instant. I mean you want to say "travel to a universe" and not just mean an instant.
 * Every physically possible universe (instant) exists, including those with no past and no time-travellers, pointlessly.
 * Every one of them has vast numbers of possible alternate next instants. The language of "create a split" is thus a bit awkward, since the splits exist. It wouldn't even be right to say they "pre-exist": there is no outer time for time to take place in, so time-related language can't apply to time. They aren't created, they don't already exist, they just exist. I'm not sure whether there's supposed to be anything special about instants which we would call causally related: I suspect they have no particular property to relate them, other than humans liking to arrange them conceptually in a sequence. Card Zero  (talk) 22:42, 7 July 2022 (UTC)


 * Well, is it theoretically possible to travel in-between parallel universes? I mean other than simply going forward in time the regular way. 68.4.99.100 (talk) 22:46, 7 July 2022 (UTC)
 * Yes. Exactly by what means, especially by what non-fatal means, is a detail, but yes. Wormholes, or something hand-wavy like that. Card Zero  (talk) 22:53, 7 July 2022 (UTC)
 * Is there any evidence for the existence of multiple universes? --←Baseball Bugs What's up, Doc? carrots→ 23:32, 7 July 2022 (UTC)
 * QM is said to be evidence of such, but the many-worlds interpretation is one of fifteen Interpretations of Quantum Mechanics. Modocc (talk) 23:39, 7 July 2022 (UTC)
 * There's the experiment with the single photon causing an interference pattern with its parallel-universe counterparts, if you interpret it that way. Double-slit_experiment, Double-slit_experiment. Card Zero  (talk) 23:41, 7 July 2022 (UTC)
 * I think that the moment we start "interpreting" is the exact moment that we start to play fast and loose with the definitions of the natural-language words: "time," "point," and "universe" —
 * If I may paraphrase another encyclopedia, Being and Becoming in Modern Physics - the advantage offered by physics is that it offes analytical tools to sharpen our answers to metaphysical questions, rather than to rehash the same metaphysical ambiguities that have had little resolution despite millenia of informed debate. In other words, let's not dull the answer, which is really quite clearly and sharply no: what is being described (time travel) is not consistent with any observed behavior in any experiment we contrive, or ever have contrived; and it's pretty reasonable for us to make the leap of inductive generalization and say "it ain't possible, not here, no how."  Physicists like sharp answers, and though we can and do immerse ourselves in details, the details should not cloud our conclusions.
 * I also think if we start with a cogent definition for each of these words - "time", "space," "universe," "travel," ... and then we apply modern physics (specifically, the conduction of controlled experiment with quantitative, repeatable conclusions that can be modeled with mathematical expressions - the scientific method) ... we can study these as interactions and phenomena that meaningfully map to our natural language understanding of them.
 * If we do that, we conclude that "time travel" is quite weakly defined; but we can talk about causality and causal relations, and we can express strong rules based on observation. To translate into plain English - "no, you can't travel backward in time" - not in one or many universes.  In fact, it's quite problematic to express a strict empirically-validated definition for what "many universes" should even mean!
 * We can use mental gymnastics to contort words, and redefine "past" and "future" in manners that fray these words from the thread of normal conversational usage... but, we're physicists: we prefer to reserve our mental gymnastics tricks and relegate them to clever u-substitutions in delicate integral analyses.  Let's leave the plasticity of the English language to the language experts, and let's not try to find ways to u-substitute "time travel" when we really mean "time-evolution of an ensemble of electron state-vectors."  This is not "time travel" as it is known to the casual speaker of the English language, and nobody benefits when we confuse people with abused terminology.  Not professional physicists, not casual enthusiasts, and not the general public.
 * I feel that dwelling on interpretations and linguistic vagueness actually detracts from the real study of physics, which is at its core the methodical and mathematical study of real actual reality. Ambiguity in language is a simple error that we can quickly resolve using precise terminology - and once we move beyond that phase, then we can actually move the conversation to an interesting topic.  Whether that topic is "mind-expanding mathematical methods," "interesting empirical observations from the lab," or "really worthy questions of teleology and metaphysics" depends on personal taste - but I think many people get stuck at the ambiguity-stage, sucked into a decade-old badly-worded "interpretation debate" that's fundamentally a false dichotomy perpetuated by poor word-choice, and probably attributable to bad translations of real physics communications between scientists who spoke and wrote in different native languages.
 * Nimur (talk) 04:53, 8 July 2022 (UTC)
 * "travelling" like this breaks the conservation of mass law in physics as a human body vanishes from one universe, and then appears in another. Graeme Bartlett (talk) 08:17, 8 July 2022 (UTC)
 * The problem is solved bureaucratically by decreeing that every time immigrant shall register at Hotel Hilbert. Philvoids (talk) 15:00, 8 July 2022 (UTC)
 * Hilbert, not to be confused with his cousin Filbert, who's a nut. --←Baseball Bugs What's up, Doc? carrots→ 15:37, 8 July 2022 (UTC)
 * I'm thinking I might have got the "no past" part wrong. I was inferring that as a way to explain how the time traveller just pops into existence, but I vaguely remember that the destination universe has to contain whatever a "time machine" is. So I suppose that provides a physical mechanism for the entry of the time traveller into the universe, and universes don't suddenly appear in arbitrary states without some kind of origin event. Card Zero  (talk) 16:00, 8 July 2022 (UTC)
 * Can the parallel universe contain something else such as a wormhole instead of a time machine? 68.4.99.100 (talk) 05:04, 9 July 2022 (UTC)
 * Since it's fictional, it can contain anything you want. --←Baseball Bugs What's up, Doc? carrots→ 07:13, 9 July 2022 (UTC)
 * Perhaps. Our article on the possibility of wormholes is quite extensive with published physics' references. For example "...armed only with arbitrarily small quantities of ANEC violating matter...", per Traversable wormholes with arbitrarily small energy condition violations Modocc (talk) 14:21, 9 July 2022 (UTC)
 * But doesn't the conservation of mass rule only apply to closed systems, which would not be the case here? 68.4.99.100 (talk) 05:55, 10 July 2022 (UTC)
 * Parallel universes? 67.165.185.178 (talk) 03:07, 14 July 2022 (UTC).