Wikipedia:Reference desk/Archives/Science/2021 May 27

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May 27

Altering the viscosity of air to shift the wavelengths of visible light?

Greetings!

I've been studying various topics relating to optics as well as to the refractive index of dry air, and something has now befuddled me.

I know that, under controlled conditions, one can shift the wavelengths of visible light rays (400 nm to 700 nm) just slightly enough that they can cancel each other out and create interference patterns. I also know that—under high temperatures—distant objects can appear "blurry" and distorted to an observer, owing to the viscosity of the air causing light rays to refract. If you'll permit me, however, then I have a thought exercise that I'd like to share.

Imagine a cubical box (30 cm × 30 cm × 30 cm) that is closed on 5 sides and open on just one end. If somebody wanted to distort the visible-light rays entering the box through the open end, then could he do so by changing the viscosity of the air inside the box? i.e., does any process exist that could alter the visible light so that an observer looking into the box would see either total darkness or an extremely distorted sight?

Namely, if someone placed a toy, doll, or other object well inside said box, then could anyone engineer the air on the box's open end so that the aforementioned object would become either invisible or completely indistinguishable to a person looking right at it—even in bright light?

Thank you. Pine (talk) 11:44, 27 May 2021 (UTC)

First of all, I need to correct one wrong thing you stated, which is "high temperatures—distant objects can appear "blurry" and distorted to an observer, owing to the viscosity of the air causing light rays to refract". This is not really correct. Such blurriness and distortion is caused by convection currents that cause air of different densities to rise and fall in chaotic and unpredictable ways, and it is those convection currents that cause the blurriness. Also, "changing the viscosity of air" is not a direct thing. There's no "magic viscosity changing process" or device or anything like that. Under normal, human conditions (i.e. any temperature you'd live through), air's viscosity is only dependent on temperature; so it really makes no sense to discuss the effect of viscosity on optics. It's a pointless detour. It is much better to talk about density, which is also dependent on temperature; for a closed system like your box, you can use the ideal gas law (PV=nRT) and the average molar mass of air (MM = m/n) re-arrange the two equations to get d = (P/RT)*MM. In reality, this means you can reduce the calculation to just two values: pressure and temperature. Here is a javascript calculator set up to do that for you. You plug in a few numbers (pressure, temperature, wavelength, and CO2 and H2O amounts; those two gases will have the greatest variability in affecting the average molar mass of dry air, which is essentially a fixed N2/O2 mixture.) and viola. No need to muck around with viscosity (which is pointless) or even density (which is the property that really matters, but which you don't actually need to calculate directly because of the ideal gas law). --Jayron32 12:09, 27 May 2021 (UTC)

Maybe you could use an unbelievably loud, exactly tuned sound to set up a standing wave in your box that would create the desired interference. Abductive (reasoning) 15:04, 27 May 2021 (UTC)

If you put a black hole in the box, no light can come out. But using standard optics, if there is a path from a light source to a reflective spot inside the box to the eye of an observer, some light from the source will indirectly reach the observer's eye. To obtain some form of interference, apart from the fact that you need strictly monochromatic and coherent light, you need to create different paths from the source to the reflective spot. The density variations you can make are too small and also too unstable to do the job.  --Lambiam 22:14, 27 May 2021 (UTC)

Thanks to everyone for the prompt responses!

Pine (talk) 18:39, 28 May 2021 (UTC)

Resolved

Engineering question.

My dad recently paid a company to install solar panels to his rooftop. They 1st has to assess whether the roof was strong enough to hold it. How do they do such a thing? I'll also transcend into a simpler question: suppose you stack heavy books on a chair. What is the science that determines how heavy the chair can hold, and how precise can it go, like whether the chair will collapse in a few years, or a few weeks? What kind of engineering would cover this? Structural? 67.165.185.178 (talk) 15:07, 27 May 2021 (UTC).

Simple measurements of things like the number and orientation of the supporting members of the roof, known as a truss, as well as the quality of materials, how well maintained they are, etc. Depending on how well supported your roof is, it may or may not need additional supports to handle the weight of the solar panels. The inspectors will likely access the attic space between the ceiling and the roof, to ascertain how it was built and if the existing truss can support the weight. There are going to have already been engineers who have determined construction standards based on how well certain trusses are expected to hold certain loads. This fits broadly into the field known as beam analysis, and just by inspecting how the truss for your roof is built (the number, type, and orientations of the beam in question) they can determine if the roof meets established codes for adding additional solar panels. --Jayron32 18:06, 27 May 2021 (UTC)

Okay it is a flat-roof. Other than that, as soon as I found that out, and asked the next employees the next time, they said "oh, we're electricians, we're only here to do the electricity part" so they didn't know the answers lol. 67.165.185.178 (talk) 18:10, 27 May 2021 (UTC).

Even flat roofs need a truss system to be supported; they'll just be rectangular trusses rather than triangular or pentagonal in shape. See examples here for example. The truss system for any building, even without an attic space you could stand up in, should be able to be inspectable, as that area needs to be able to be insulated, and contains ductwork, electrical conduits, etc. There will be some access point or points between the ceiling and roof for an inspection to be made. --Jayron32 18:18, 27 May 2021 (UTC)

This may be true for most buildings in the US, but I have seen flat-roofed houses with no space between the ceiling and the roof; the roof consisted (below the waterproof decking) of boards over wall-to-wall beams; the underside of the boards was the ceiling. Nowadays, architects and civil engineers use apps to calculate the weight a construction can bear, based on the finite element method and characteristics of the materials used.  --Lambiam 21:59, 27 May 2021 (UTC)

That's entirely true; it depends on the local codes at the time the building was built. Still, there are ways to elucidate things like the beam structure between the roof and ceiling, even if it is a simple joist array with a ceiling slapped on the bottom and a roof laid directly on top. Stud finders will do the trick. --Jayron32 12:21, 28 May 2021 (UTC)

Crudely, if you know how old the house is you know what wind and snow loads it was designed for in that jurisdiction. If it appears to be designed in accordance with industry practice at the time, then for a domestic installation that is probably good enough to make a decision. For larger installations some calculations may be necessary. The field is called structural engineering. Greglocock (talk) 22:16, 27 May 2021 (UTC)

Can anaerobic bacteria be produced from aerobic bacteria?

Bacteria reproduce by splitting in half, right? Can anaerobic bacteria be produced from aerobic bacteria? 67.165.185.178 (talk) 15:09, 27 May 2021 (UTC).

Binary fission produces genetically identical offspring both to each other and to the original/lost parental cell excepting the normal random mutations or errors that may occur. If the parental bacteria is incapable of living in an anaerobic environment, the two identical offspring bacteria aren't going to be. Of course over a very long time frame, you could get anaerobic bacteria from aerobic ones via the accumulation of mutations as evolution tells us can happen but this isn't something that will generally happen in a single generation. (To be clear, it isn't just from fission that this happens.) You can come up with special very likely artificial circumstances where anaerobic respiration is prevented by something which only requires a small number of mutations to resolve. In this case, you could end up with a situation where one or both offspring can live in an anaerobic environment but the parental one could not. But this could also just easily happen without fission. Note also in practice on earth, if some bacterial "species" develops the ability to live in an anaerobic environment it previously didn't have, it's I'm fairly sure it's significantly more likely this arose mostly from bacterial conjugation or some other process rather than a simple accumulation of mutations. Also a number of bacteria are facultative anaerobes meaning although they grow better in an aerobic environment, they can survive in an anaerobic one as well. With such bacteria, if you move the offspring to different environments, they will adjust, but of course this also applies to the original parental cell. (Although frankly, it's often a bit weird to talk about a single bacteria in circumstances like this.) 17:09, 27 May 2021 (UTC) Nil Einne (talk) (sorry sig failure)

The shorter answer is "Can dandelions be produced from lobsters" is roughly how the original question reads. The term "bacteria" covers a bewildering array of life forms. Taxonomically and cladistically, bacteria taken as a group are as diverse and vast as the entirety of eukaryotic life, which covers everything from amoebas to oak trees to elephants. In terms of bacteria, the categories of "aerobic" and "anaerobic" are rather broad categories (that do not strictly match up with any particular taxon or clade of bacteria per se), but rather refer to ends on a continuum of Microbial metabolism, and as noted above, bacterial species exist with any number of metabolic processes, some of which have multiple such processes, all of which likely evolved many times over history. The long, slow, gradual slog of evolution means that, over time, you can have anaerobic bacteria evolve from aerobic ones, but this is not likely the sort of thing you can sit and watch happen naturally. Given gene editing technology like CRISPR, there are a LOT of things you can engineer bacteria to do in a lab, including something like what the OP is asking about, but simply watching bacteria reproduce assexually and waiting to see an anaerobic bacteria grow from an aerobic one, no, that is not going to happen, anymore than my initial example of a lobster giving birth to a dandelion. --Jayron32 17:56, 27 May 2021 (UTC)

Okay here's my analogy. You wear socks inside shoes for some time, at the end of the day take them out, they smell a little. Isn't that the smell of anaerobic bacteria? And you flip your socks inside-out and let them sit overnight, by the next morning most of the smell is gone. And I'm arguing bacteria is not a gas, so they did not float away. So I'm arguing the bacteria were anaerobic and therefore destroyed by oxygen (so dead bacteria do not smell, living bacteria smell, is my 2nd argument). What is the contradiction? If they were aerobic bacteria, the smell of socks would not have gone away as easily or quickly, so I think they were anaerobic. 67.165.185.178 (talk) 18:14, 27 May 2021 (UTC).

Okay, here's my analogy: You have a farm, and when you drive by in the morning, you see cows feeding in a field. You drive by later in the evening, and you see horses feeding in the same field. Did the cows turn into horses, or do you have different populations of animals for each observation? --Jayron32 18:21, 27 May 2021 (UTC)

Well after you shower, your feet are in aerobic environments. Or from the socks point of view, your socks are in aerobic environments, so bacteria around there should be aerobic. So maybe, there are small traces of anaerobic bacteria, that lay dormant? And then being inside socks and shoes for hours, the anaerobic bacteria populate? That's the last theory I can think of. 67.165.185.178 (talk) 18:45, 27 May 2021 (UTC).

The bacterium that makes your socks smell like Limburger is probably Brevibacterium linens, which is strictly aerobic.^[1] There may be endospores of anaerobic bacteria laying dormant, such as those of Clostridium butyricum. Immerse your feet in oil, and they may wake up, but unless you are wearing boots that are sealed airtight, there will be way too much oxygen in the environment to their liking.  --Lambiam 21:43, 27 May 2021 (UTC)

Possibly relevant to this conversation are facultative anaerobic organisms, which is not at all uncommon among bacteria. Many that I have worked with, such as staph or E coli, are capable of both aerobic and anaerobic respiration. When oxygen is present, they use the more efficient aerobic respiration, but when incubated without O2, they switch. --OuroborosCobra (talk) 18:52, 27 May 2021 (UTC)

injectable monitoring devices

I have heard many times that people are afraid to get vaccinated because Microsoft (or whoever) have miniature tracking devices in the vaccines. Do we even have the technology to make tracking devices that small? I know we can put microchips in our pets, but I'm sure they are too big to hide in a vaccine. 70.26.18.24 (talk) 22:34, 27 May 2021 (UTC)

I don't have the technology, but how can we know that "they" don't have it? Because of fundamental scaling limits, any such "nanochips" cannot be based on CMOS technology. See further the article Beyond CMOS.  --Lambiam 07:22, 28 May 2021 (UTC)

Those people who are afraid to be tracked, usually carry with them 24/7 a smartphone with active GPS function, upon which they are tracked anyway since years. So there is no point in injecting any microsomething in them. This just by the way. Technically in a receiver/transmitter the electronics can be as small as you like but it needs some kind of antenna and this antenna makes a large part of a microchip for pets and can hardly be miniaturized any more. But as already said, why laboriously inject them something at high cost if they carry voluntarily an extremely efficient tracking device which they have paid themselves for? 2003:F5:6F02:C00:3480:EE69:3CE5:7302 (talk) 11:46, 28 May 2021 (UTC) Marco PB

The microchips that we put in our pets are not tracking devices, they are passive integrated transponders. They don't contain a battery and do not transmit anything unless an RFID reader is brought within close proximity. They're also a little larger than a grain of rice. A tracking device requires a power source to transmit data over a long distance and, like a mobile phone, would need to be regularly recharged. A battery small enough to pass through a hypodermic needle probably wouldn't hold enough power to last a single second. nagualdesign 18:58, 28 May 2021 (UTC)

Conspiracy theorists don't let facts and logic get in the way. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:53, 28 May 2021 (UTC)

They'd probably explain away nagualdesign's argument by saying that the devices use advanced technology supplied by the shapeshifting Reptilians, and he's part of the cover-up. The nym "nagual design" is a dead givaway! {The poster formerly known as 87.81.230.195} 2.121.163.176 (talk) 20:46, 28 May 2021 (UTC)

Shussshhh! nagualdesign 22:54, 28 May 2021 (UTC)

These are the types of characters that probably think Fantastic Voyage is a documentary. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:00, 29 May 2021 (UTC)

Any documentary featuring Raquel Welch is worth watching :-) MarnetteD|Talk 13:53, 1 June 2021 (UTC)

Our government couldn't even make a working "test-and-trace" app, so how they think they're going to conjure up that kind of technology, I can't imagine. Alansplodge (talk) 10:20, 30 May 2021 (UTC)

Thanks everyone. I was disappointed to learn that Fantastic Journey was not a documentary! 70.26.18.113 (talk) 03:21, 1 June 2021 (UTC)

But was Innerspace a documentary? --Jayron32 13:38, 1 June 2021 (UTC)

Pfft.. They didn't have that technology in 1987! But was Ant-Man a documentary?? nagualdesign 18:22, 1 June 2021 (UTC)