Wikipedia:Reference desk/Archives/Science/2020 April 26

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April 26

dish soap as solvent

I overcooked something at dinnertime so there is dried stuff stuck to the bottom of the pot. No big deal, soak it overnight then wash in the morning. Question: would squirting in some dish soap help the stuff dissolve faster? I do that sometimes but it's hard to tell by experiment, without a lot of repeated trials and a controlled amount of overcooking, soak time, etc. All of that defeats the simplicity of the basic plan of not having to pay attention to it while it soaks. Thanks. 2602:24A:DE47:B270:DDD2:63E0:FE3B:596C (talk) 07:34, 26 April 2020 (UTC)

In the interest of scientific progress you should overcome your aversity to careful experimentation. Now that so many more people have, overnight, become amateur cooks, this will be a great service to humankind. As dish soap serves as a powerful surfactant, I expect it will help to soak and dissolve the starch that serves as a glue, which otherwise might be shielded from the water by a coat of lipids. Using warm water also contributes by liquefying fats and making oils less viscous. For overnight soaking it may make little difference, though. If the bottom stuff is severely burnt and your pot is not made of aluminium, an additional table spoon of baking soda will do wonders.  --Lambiam 08:00, 26 April 2020 (UTC)

In my experience Bio washing powder makes dissolving baked on overcooked food much easier. Soak overnight. YMMV--Phil Holmes (talk) 08:58, 26 April 2020 (UTC)

Another proved technique is allow a dishwasher tablet to dissolve in the offending pot. Scope for a comparative study perhaps? Alansplodge (talk) 12:13, 26 April 2020 (UTC)

Just a clarification on terminology: In dish soap, the actual soap stuff (likely something like sodium lauryl sulfate or a similar compound) is a surfactant and detergent and not a solvent itself. The compound by itself is a waxy solid and not particularly good at dissolving anything. What soaps do is they make water a better solvent. The water is still the solvent, the soap just improves water's ability to dissolve things by both breaking up the surface tension of the water (the surfactant action) and by being amphiphilic, which basically means it has an end that 1/2 of it can dissolve in the dirt, and the other half can dissolve in the water, allowing the water to dissolve dirt it otherwise wouldn't very well (the detergent action). The water itself softens the grime; what the soap does is make it easier for the water to do its job. When I soak dishes, I always add a little soap to the water to speed things along. Periodic scrubbing and rinsing is good as well, as you sometimes need to remove the softened layer of gunk to expose more of the gunk to the soapy water. --Jayron32 13:02, 27 April 2020 (UTC)

Strains and sequences

Are strains and sequences two different things? I speak in respect of Severe acute respiratory syndrome coronavirus 2. I have heard there are over 6,000 sequences. Is this to do with how DNA reacts to the virus? I assume there are only a handful of known strains? I would appreciate it if someone could help clear this up for me :) Uhooep (talk) 12:21, 26 April 2020 (UTC)

It is quite possible that 6,000 samples of SARS-CoV-2 have been sequenced. They may be identical to each other or different. But "strain" only refers to a viral population sufficiently different from other viruses of the same species. Ruslik_Zero 13:37, 26 April 2020 (UTC)

The company deCODE genetics in Iceland is testing large numbers of people, initially only of high-risk cases but later by random sampling (currently 6% of the population), and is sequencing the SARS-CoV-2 genome of every positive test. As of April 14, 2020, they had sequenced SARS-CoV-2 from 643 samples.^[1] They find a high mutation rate which effectively allows them to reconstruct who infected whom. Clustering the collection of genomes into a small number of strains will always have something arbitrary: the choice of when to stop.  --Lambiam 04:12, 27 April 2020 (UTC)

Ringdown and no-hair theorem

"Immediately following the merger, the now single black hole will “ring”. This ringing is damped in the next stage, called the ringdown, by the emission of gravitational waves. The distortions from the spherical shape rapidly reduce until the final stable sphere is present, with a possible slight distortion due to remaining spin." - says our Wikipedia page.

What exactly is this ringdown? Is it a bad choice of words, so that the ringdown is just an echo, like the wobble in the membrane of a drum after the drum is stuck, or do post-merger deformations of (inside??) the black hole produce the waves? If the second, how does it square with the no-hair theorem (which says the black hole is completely described by about a dozen scalars) even if no overtones? 93.136.55.42 (talk) 15:54, 26 April 2020 (UTC)

This will be investigated by the proposed TianQin (Chinese: 天琴计划) space-borne gravitational-wave observatory consisting of three spacecrafts in Earth orbit. See Constraining modified gravity with ringdown signals: an explicit example, Phys. Rev. D volume=100 issue=8 at=084024, 14 October 2019. DroneB (talk) 17:47, 26 April 2020 (UTC)

Binary black hole § Ringdown: The article you were reading. Also no-hair theorem. From that article, the no-hair theorem is only conjectured for "stable" black holes. "Unstable" ones, like one immediately after a merger, may have more degrees of freedom. I'm afraid I'm not an expert on general relativity so I'm not sure what is involved in modelling these. Since it's difficult to observe mergers in detail most of this is based on mathematical models. And of course we can't observe anything beyond the event horizon. --47.146.63.87 (talk) 22:41, 26 April 2020 (UTC)

I would have written the content in the article you(s) have been reading. In the modelling section it becomes clear that what the ringdown is, is some sort of scattering of the gravitational waves from the late inspiral. Either similar to a simple echo, or an echo that has been twisted around by frame dragging by a spinning black hole. Because of the infinite redshift at the event horizon, you are never really going to observe a no-hair simple infinite age blackhole. Instead you are going to see a highly slowed down version of the close to final merger. The modelling can calculate what observers in different reference frames will "experience", but we are interested in the observer at infinity. I think the descriptions of echo are closer to the mark, than a vibrating ellipsoid. Graeme Bartlett (talk) 23:55, 26 April 2020 (UTC)

I asked an astro professor about something that a long time ago: if you had heavy objects (e.g. a binary star system) moving around inside the event horizon, could you detect that from the outside? He seemed to think yes. 2602:24A:DE47:B270:DDD2:63E0:FE3B:596C (talk) 00:09, 27 April 2020 (UTC)

well that would be a form of ring down, but you would never see the binary star pass the even horizon. Graeme Bartlett (talk) 12:43, 27 April 2020 (UTC)

That's pretty much why I'm asking this question, if the ringdown is the "echo" of pre-merger events that's fine, but if it's the echo of post-merger movements inside the event horizon, wouldn't that tell us something about the arrangement of matter inside the horizon? And wouldn't that then tell us something about the arrangement of matter before the merger and/or be some kind of a causality violation? 93.136.46.218 (talk) 15:08, 27 April 2020 (UTC)

Do the shapes bounded by each event horizon remain the same during the merging process? Or do they merge to form one joint event horizon that takes some time to settle down into a rotation-symmetric shape? And if so, might the latter process involve some form of oscillating? (The traditional concept of shape is ill-defined here, but the concept of rotational symmetry applies without difficulties.)  --Lambiam 19:13, 28 April 2020 (UTC)

Answering the original question: The no-hair theorem deals with stationary spacetimes, so strictly speaking it's not even applicable to the real world. But more practically speaking, the ringdown radiation follows an exponential decay in time - and approaching the no-hair state in such an exponential fashion seems to be what we get in reality. Icek~enwiki (talk) 14:09, 3 May 2020 (UTC)

I see. So this no-hair "violation" is predicted to only let us deduce that the observed black hole was disturbed by an interaction with another massive body, and nothing about its inner state, right? In other words, if two black holes with known 11 no-hair parameters merge, the result will be deterministic and we won't gain information that wasn't in the original no-hair parameters? 93.136.17.201 (talk) 17:17, 3 May 2020 (UTC)