Wikipedia:Reference desk/Archives/Science/2022 January 18

= January 18 =

Omicron vs. common cold
Is there data comparing the infectiousness of omicron covid against the common cold? What are the data I should be searching for aside from R_0, vaccine effectiveness and country prevalence statistics? I'm trying to make a Bayesian estimate, assuming I would experience omicron and cold the same way, what would be the likelihood that a given disease I experienced was omicron. 31.217.7.231 (talk) 16:25, 18 January 2022 (UTC)
 * This is difficult to answer as there is no such thing as the "common cold." What we call the "common cold" can be any of 200+ different viruses, and by different, I do not mean different strains. I mean different viruses that can differ from each other as much as we (humans) differ from a banana. --OuroborosCobra (talk) 16:39, 18 January 2022 (UTC)
 * As noted above, and as can be seen from the article Common cold, the term is not really a medically rigorous term. It generally means any viral upper respiratory infection (inflammation of the mucosa of the nose, sinuses, larynx, etc.) and while there have been over 200 different viruses associated with colds, there are likely many many more, pretty much any idiopathic infection that meets the basic symptoms of the common cold is called "the common cold".  Making any broad statements about infection rates, duration, virulence, transmissibility, etc. of such a thing is basically impossible.  -- Jayron 32 17:12, 18 January 2022 (UTC)
 * It is meaningful to ask about the prevalence of symptoms, not due to COVID-19, that one would have self-diagnosed as a case of the common cold in the pre-COVID-19 era. Most adults used to have such symptoms say twice a year, mostly in the colder season (at least, outside of the tropics), lasting typically for one or two weeks. So with an onset in winter season, I'd estimate the prevalence of new cases attributable to of the common cold for an adult at somewhat over 2/365, somewhere in the ballpark between 0.5% and 1%, and of any ongoing cases at 4% to 8%. However, the same measures that reduce Re for COVID-19 also reduce it for the transmission of common-cold viruses, so these numbers are useless for making a Bayesian estimate. --Lambiam 18:01, 18 January 2022 (UTC) [Added clause "not due to COVID-19".  --Lambiam 10:23, 19 January 2022 (UTC)]

How far does SETI institute broadcasts?
How far do they go?

Is it only inside the milky way galaxy, is it going a bit outside it?

Thanks, 79.176.222.75 (talk) 23:55, 18 January 2022 (UTC)


 * I believe the first Active SETI broadcast was in 1962. So the signal has reached less than 60 lightyears, and is targeted at a specific nearby star in our Galaxy.
 * There haven't been any Active SETI transmitions targeted outside the galaxy. It'd be pointless. We don't have any transmitters that would realistically reach that far, and even if we did, the signal would take 2.5 Million years to arrive. Humanity would probably be extinct by the time they got our message.
 * But none of that answers your exact question. I can't find a source that exactly says this, but I'm pretty sure the SETI Institute itself has never broadcast a signal. They concern themselves with listening.   The broadcasts were made by other groups. ApLundell (talk) 00:14, 19 January 2022 (UTC)
 * That's almost certainly correct. The SETI Institute - that is to say, these people - a non-profit research organization, located in the Silicon Valley - "The SETI Institute" - (and to be circumspect, there exist other individuals and organizations who also conduct scientific research relating to the topic of SETI) - but The SETI Institute does not (currently) directly fund or operate transmitters.  The folks who hang out at SETI, or are directly employed by the Institute, frequently have multiple institutional affiliations.  (After all, it's kind of hard to earn rent-money while you're out looking for space-aliens - not impossible, but merely improbable).  Transmissions and transmitters do exist, and could indirectly be affiliated with a person who has an affiliation with ... and so on, ad infinitum, - but the institute itself is not presently directly paying for or operating any large "Active SETI" project.  Notable examples of "active" transmissions, for the express purpose of intentionally sending a signal only-for-the-purpose-of-SETI... are actually quite rare.  Like so many other things we find in space science - who's gonna pay for it?  Rather, it's much more common to find "SETI" (the concept) as an inspirational tag-along that rides in the backseat of a project that satisfies a clearly different scientific objective.  And for this reason, it's very common to find "SETI" (the Institute) as a partner, affiliate, or "not-actually-affiliated-in-any-documented-fashion-because-the-scandal-it-might-cause-could-crush-the-public-support").  But if you hang out in Silicon Valley, you'll find SETI is conveniently located only a short lunch-break walk away from many other places that one may draw a paycheck while building giant radios and supercomputers.
 * Here's a review of what SETI Institute is actively doing right now - the Q3 2021 Activity Report. In addition to over 50 peer-reviewed scientific publications, several Mission Highlights include collaborations with other institutions to design and scope scientific instruments on future spacecrafts and ground stations.
 * Nimur (talk) 17:32, 19 January 2022 (UTC)
 * Or - tackling this question from a different approach: the question of how far the broadcasts go is actually a great SETI question. If we put a finer technical point on it - how do we pose the question - and myself, being a "Signal Processing" kind of person, would look at it this way.  Everything you do - even just sitting around being not-absolute-zero - causes photon emissions.  If we build a big antenna that absorbs photons, how can we know whether any particular photon that we receive actually came from you?  This is a pretty subtle question of physics and statistics, which is actually what SETI is entirely about!  We might start putting some caveats: it's pretty challenging to know anything when we receive one single photon.  In fact, we can't even know for sure whether we actually received one or zero photons... - so the reception of the minimum amount of physically-possible signal is not, itself, actually "proof" of any signal at all!
 * Thus is born the discipline of statistical signal processing; or, stated a bit informally, how do we build machinery so that we can yield the highest statistical confidence for any query we wish to pose about a particular physical process? I mean, the rat-hole that I personally like to chase down is how the mathematical machinery of error correction codes interplay with the particular physical processes affecting our machinery: there are ways for us to select "better" codings for signals if we expect them to propagate as electromagnetic waves, and further nuances if we expect those waves to travel through the unique environment of interstellar space, and so on, and so on,...
 * Technically we can build a wave that propagates from here to the end of the universe - traveling at the speed of light. But the farther it goes, the fewer photons we expect to find traveling in any particular direction.  What exactly happens when the expectation value drops below one photon - which is the minimum quantized amount of energy that can exist?  I think there's some spooky answers that depend entirely on whether anything receives that signal, and whether this prevents somebody else from receiving the same signal on the other side of the universe.  After all, there's only one photon, ... right?  ... right?
 * Somehow, deeply and profoundly, this weird question links back to the earlier weird question - you really honestly can't know if you've received zero or one photons. If that - by inductive extension to every-number-larger-than-one - doesn't lead you in to a bit of a nihilistic melancholy, you're probably not thinking hard enough about it.
 * Nimur (talk) 17:44, 19 January 2022 (UTC)


 * In theory, across the entire universe. In practice, inverse square decay and absorption will diminish the signal to a point where it is in practical terms undetectable. Where that point is depends on which broadcast (how much power they used), and what the sensitivity of the hypothetical detection equipment is. Here's what SETI say. The current absolute limit is a 100 light years or so, given the speed of light. Ballistic missile radar signals have actually been more powerful in general, so would actually probably be more likely to be detected (dependent on wavelength). I'm surprised our article on Active SETI doesn't mention this. Fgf10 (talk) 00:17, 19 January 2022 (UTC)