Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

July 3

COVID vaccine mixing

I got my second shot the other day: the Moderna COVID-19 vaccine. My first shot, back in April, had been the Oxford–AstraZeneca COVID-19 vaccine, since that was the only one available at pharmacies in Ontario at the time (though a week later, they were discontinued amidst the ongoing concerns of rare side effects). The nurse who administered my second shot told me that I was in luck, since that combination was "the best". Is that true? I've done some searching, but it seems like most of the comparisons involve O-AZ vs. O-AZ/Pfizer (and the suggestion there is that the mixture is "as good or better" (ref. But what about O-AZ/Moderna? Matt Deres (talk) 14:16, 3 July 2021 (UTC)

Since Pfizer and Moderna are so similar, it's a good guess, but if you want proof, there's none yet. FWIW, the news that the J&J shot doesn't need a booster is based on a study of like 10 people, so I don't believe it yet. One shot of any vaccine is definitely insufficient. 74.64.73.24 (talk) 15:24, 3 July 2021 (UTC)

According to this news report, the German Standing Committee on Vaccination has stated that "current study results" show that the immune response generated after a mixed dose vaccination "is clearly superior."  --Lambiam 17:24, 3 July 2021 (UTC)

Though they did mean compared with two shots of Astra-Zeneca. Here’s the original in German. Cheers ⌘ 19:14, 3 July 2021 (UTC)

This UK study showed good results from a mix of AZ and Pfizer. Alansplodge (talk) 23:37, 3 July 2021 (UTC)

• From the above, the RKI does not reference any scientific study, and the BBC refers to [1]. Notice that the main page of that site says We ask that the media do not continue to contact researchers while this critical work is underway, and to use the media contact form for press enquiries., which makes me suspect they were unhappy with how the research was reported. From there, we get links to two actual publications, [2] and [3]. The former is an interim report on "reactogenicity" (= prevalence and importance of secondary effect) following the second injection, which is higher for a mixed vaccination.

The latter, published less than a month ago, compares all possible schedules of BNT (Pfizer-BioNTech, mRNA vaccine) and ChAd (Astrazeneca, viral vector vaccine). The endpoint is the (geometric) average of antibody (IgG) concentration in patient plasma 28 days after the booster (second shot). My interpretation of the abstract's figures is that ChAd/ChAd fares poorly compared to any scheme with at least one BNT; it is not so much that mixed vaccines are good but that pure ChAd is bad.

Please note that any interpretation rests heavily on the choice of endpoint. It might well be that "one month after booster" is precisely the time at which ChAd/ChAd is the weakest compared to others (daily antibody dosing would proably have been too intrusive to the study participants though). If you think "surely the choice of cutoff does not matter much" I would encourage reading this blog - for instance, check out their analysis of the original Pfizer or AZ trial results. Also, the study participants were all at least 50 years old, probably because of the recruitement period; it would be highly dubious to extend the results to younger populations.

Antibody levels are not a really good endpoint for clinical practice; as the OP's link says, what matters is vaccine efficacy i.e. whether one vaccination scheme really cuts infections or infection severity more than the other; while it is reasonable to expect that higher antibody counts means higher protection the link is far from direct.

Based on what I read, the only plausible argument to mix vaccines is at the population level under a vaccine supply constraint, because maybe two people vaccinated with a BNT+ChAd mixture fare better on average than two people with full BNT and full ChAd. Again, we do not know this: as far as I know nobody has run a mixed-vaccine efficacy study (of course, manufacturers are not going to fund a mixed-vaccine study). Frankly, if I were in a position to make such decisions, I would not greenlight vacccine mixing without data on efficacy, because I am absolutely not convinced the stronger side effects are worth it. Tigraan^{Click here for my talk page ("private" contact)} 10:42, 5 July 2021 (UTC)

Thank you. I suspected it was a bit early to make pronouncements like that. Further details on mixing here, inclduing "Of note is that the order of vaccines made a difference, with an Oxford-AstraZeneca/Pfizer-BioNTech schedule inducing higher antibodies and T-cell responses than Pfizer-BioNTech/Oxford-AstraZeneca, and both of these inducing higher antibodies than the licensed, and highly effective ‘standard’ two-dose Oxford-AstraZeneca schedule. The highest antibody response was seen after the two-dose Pfizer-BioNTech schedule, and the highest T cell response from Oxford-AstraZeneca followed by Pfizer-BioNTech." Matt Deres (talk) 13:51, 5 July 2021 (UTC)

July 4

Compared to other organisms, why only one human breed exist right now?

Statement: "Race is a socially constructed concept, not a biological one. It derives from people's desire to classify."

From the above statement, I can't call Race as breed, for example: German Shepherd, Rottweiler, Bull Dog, Pit Bull etc are existing dog breeds.

Compared to other organisms, why only one human breed exist right now? Rizosome (talk) 02:02, 4 July 2021 (UTC)

Have you tried reading the Breed article? It clearly explains that the word breed has no single, scientific definition, but is actually a "term of art". However, broadly speaking breed, like cultivar, generally refers to a result of selective breeding, and since humans aren't selectively bred (or farmed) the word isn't really appropriate. People don't generally like the word race either, but when discussing genetic and physical differences between different populations it's fine to refer to them as "racial characteristics". nagualdesign 03:57, 4 July 2021 (UTC)

Many languages use the same word for dog breeds as for unscientific racial classifications of humans. For example, German uses Rasse for both. English has two separate words, each with several generally somewhat vague meanings. In English, the term breed is not applied to humans for classification (except figuratively, as in, "bassoon players are a rare breed"). If Earth is in some future colonized by aliens, they may set up selective breeding programs to get differentiated human breeds comparable to the engineered classes of Brave New World. One of the senses of race is that of a subspecies, and one can ask why the species Homo sapiens has not split into subspecies. Such a split can only be expected if there are separated groups, not having contact for a very long time. In some science fiction stories set in the future this has indeed happened, like the Eloi and Morlocks of The Time Machine.  --Lambiam 09:36, 5 July 2021 (UTC)

A more elaborate and intentional version is in Jack Vance's short novel The Dragon Masters. —Tamfang (talk) 00:32, 7 July 2021 (UTC)

Note that "race" is occasionally used in reference to other species, specifically in the term "landrace". Nyttend backup (talk) 16:31, 7 July 2021 (UTC)

• There clearly are noticeable and statistically established genetic differences between human populations native to different areas of the world, even though this variation is small compared with the genetic variation within each population, and certainly not enough to limit interbreeding. It is a matter of semantics what term you apply to describe these different populations, although it is fair to say that if it were another animal species biologists might well have applied the terms subspecies or race for such geographically separated populations differing consistently in appearance. There were much greater genetic differences between modern humans, Neanderthals, and Denisovans, although also hybridisation between them. Sometimes these are called different subspecies, sometimes different species. Anyway, part of the answer to your question would involve examining why Neanderthals and Denisovans have gone extinct. Jmchutchinson (talk) 08:15, 8 July 2021 (UTC)

"it is fair to say that if it were another animal species biologists might well have applied the terms subspecies or race for such geographically separated populations differing consistently in appearance."

If you cannot be bothered to provide the OP with WP:reliable sources in answer to their query (you know, the only legitimate function you are meant to be providing on the reference desk), please at least do not attempt to fill the gap with your own random speculation based on a thimbles-full of actual scientific understanding. Putting aside for a moment that the "information" you are providing here is nothing more than parroted claptrap of the sort that eugenicists and other empirically naive racists have advanced since the 19th century, it's also just plainly, overwhelmingly debunked by consensus science, which has in fact investigated the matter at length with modern methods for many decades. No taxonomist and certainly no phylogeneticist with any degree of standing in the scientific community would even begin to advance the notion that the trivial differences in the genomic or phenotypical variances of modern Homo sapiens populations constitutes a "subspecies", let alone a large enough number to give such a "theory" anything even remotely approaching empirical validity.

And let me just head off any rejoinder that this observation "begs the question", because you were talking about a pet theory that this uniformity of scholarly opinion reflects "political correctness", or some other such social pressure that forces researchers to dogmatically embrace a different standard for phylogeny with our own species than we apply to others, in order totip-toe around race relations (which seems pretty clearly to be the implication of your comment): no, absolutely not. The uniformity of opinion is the result of exhaustive examination of this question, done with intellectual honesty, empirical rigor, and a faithful application of established and celebrated methodologies: facts you would have become aware of if you had used this space for its intended purpose and tried to find some relevant sources for the OP, rather than shooting from the hip based on your own lack of relevant expertise. Please, please think twice before answering any question in this space (especially questions that have the potential for a life-long impact on how a person coming here for information might view their fellow humans in fundamental respects) in which you are doing anything more than providing sources and maybe a little bit of extra text to contextualize them. This is WP:NOTAFORUM for you to make your best guess, stitch together scraps of your own knowledge to arrive at novel conclusions, or to speculate about alternative world realities based on your perception of the biases undergirding consensus science.

Rizosome, whatever you hear, here or elsewhere, there is one extant human species (Homo sapiens), and one extant subspecies of the clade, Homo sapiens sapiens, sometimes known idiomatically as "anatomically modern humans". If you are interested in this subject, I highly recommend Jared Diamond's The Third Chimpanzee: it is an exhaustive (but highly accessible to non-experts) look at exactly the area you are trying to probe with your recent questions here (the nature and place of humanity in relation to its closest taxonomic "relatives", living and dead, and the evolutionary path we took to our ecological niche over recent epochs, and the consequences for other hominids and our own genetic homogeneity). It is a little bit dated at this point, lacking some recent genetic and paleontological findings, but it is written specifically as a popular science primer to the subject, and I trust it will give you an effective leg-up in grappling with these topics. By contrast, I would not recommend relying too much on insights provided by random parties online, even here: we have many well-educated contributors here with more than passing knowledge in many technical fields, but my observation has been that when it comes to genetics and physiology, we have a dearth of qualified experts and a wealth of people willing to shoot off about pet theories, so take anything you hear here with a grain of salt.

In fact, with regard to a couple of your other posts here over the last week, I noticed more than a bit of confused information in the responses, which I would have liked to have corrected, had I been in a position to. But in a happy coincidence, at least one of these topics (the effect of melanin and phenotypical variations among human populations) is, as I recall, treated in The Third Chimapnzee, so I will trust in that much more eminent and articulate expert to help straighten the facts out for you. You seem to be going through a phase (which many who prefer a naturalist explanation of the world go through) where you are trying to reconcile the pressures of natural selection and how they normally play out with some interesting idiosyncracies of the human species. This is a moment that often separates people into two categories afterwards--those who can understand the nuances of human nature of physiology within legitimate naturalistic paradigms, and those who adopt simpler but less accurate racist frameworks--based on their initial motives, their willingness to put in the work, and (perhaps above all) the diet of information they are lucky enough to stumble upon. Needless to say, with that last one, the internet is an extremely mixed bag. Go forward with caution and skepticism, and good luck. Snow ^{let's rap} 21:47, 8 July 2021 (UTC)

1) From your tone, I think you must have jumped to the conclusion that I was saying that "subspecies" may fairly be applied to extant human populations. I was careful NOT to say that, and I know of no mainstream biologist or anthropologist today who would do so.

2) I nevertheless stand by the statement that you highlighted, that taxonomists routinely designate subspecies of other species on the basis of geographical differences in external appearance that are no greater than those we observe between populations of humans. Often the differences between named subspecies seem trivial to the non-specialist! Taxonomists are entitled to do so because there is no rigorous definition of subspecies (taxonomists do not even all insist that the variation is geographical). I often question whether the naming of subspecies on the basis of minor differences is useful, but this is common practice, partly because it is indeed a useful way to document geographical variation, partly because taxonomists like to name things, and nowadays also sometimes it is done to gain greater protection for a threatened population. For what it's worth, I am saying this as a professional taxonomist and geneticist myself and the editor of an established taxonomic journal.

3) My point in making this comment was to say that the words "race" and "subspecies" are poorly defined labels to describe levels of genetic variation. Scientists do not use the same criteria for defining a subspecies within the Hominidae as they use in many other organisms, such as moths or gulls for instance. That is an important component in answering the original question.

4) Besides these semantic matters, I am not sure whether we disagree about the biological facts. I think it is indisputable that there are genetic differences between geographic populations of modern humans. At least in the case of formerly long-isolated populations, like those in Australia, a suite of genetic differences covary with each other. But I emphasised that most genetic variation is within populations, not between. Do you disagree with any of that? Jmchutchinson (talk) 12:23, 9 July 2021 (UTC)

"Besides these semantic matters, I am not sure whether we disagree about the biological facts."

I don't doubt that you are correct in this assumption up to a point, but the nexus of disagreement happens to be on a very non-trivial distinction, and I continue to have concerns about how you are contextualizing the scientific consensus, the appropriateness of that speculation in a project space per WP:OR, and the message the OP is likely to take from that speculation.

"I think you must have jumped to the conclusion that I was saying that "subspecies" may fairly be applied to extant human populations. I was careful NOT to say that, and I know of no mainstream biologist or anthropologist today who would do so. . . . I nevertheless stand by the statement that you highlighted, that taxonomists routinely designate subspecies of other species on the basis of geographical differences in external appearance that are no greater than those we observe between populations of humans.

Yes, I do understand the distinction you were trying to make, but, bluntly, you are splitting the hair thinner than our policies allow. And for that matter, thinner than I think is responsible for a researcher in a context where they are trying to communicate scientific consensus rather than their own perspective on an issue--which you should not be doing on this project in any event, even (or perhaps especially) on the RefDesks. What those comments say in essence is "I acknowledge that the consensus of the expert opinions in this area are that there are non subspecies in anatomically modern human...however, I also feel that if those experts aren't applying the relevant methodologies in a fashion consistent how they are applied to other species, so that conclusion is dubious." Now the first part you are of course well in the clear to share with the OP. But the second part you are just not entitled to slip in there. With due respect to the fact that you are apparently well-educated in taxonomy, that doesn't give you a free pass on our ban on presenting original research on this project; that observation is simply not consistent with the consensus of reliable sources when it comes to the question of whether or not standard application of taxonomic and phylogenetic techniques renders into an observable existence of subspecies within Homo sapiens.

As with any article on this project, before you share information in this space, you need to ask yourself whether you can provide sources which support that claim. And, though you didn't provide any in this instance, even if you could find some references supporting those views, you should then ask yourself the second question of whether these sources, when put against the balance of consensus in the field, constitute enough WP:WEIGHT to warrant even a carefully worded corollary to the main statement. With respect, in this instance you have a pet theory which does not jibe with the consensus of experts in hominid taxonomy and phylogenetics, which consensus is said to be the result of the appropriate and scientifically rigorous application of standard methodologies, not mere anthropocentric bias, as you seem, in your expert opinion, to believe. I'm going to guess from your outside-looking-in skepticism of that consensus that your expertise is not in hominid species, but even if it was, it wouldn't matter here: you are not supposed to be sharing those opinions here unless through the vehicle of reliable sources--and even then, carefully within the framework of WP:WEIGHT. And when you ignore those rules, you are not sharing encyclopedic information (as it is defined by this project's policies) with the OP and others reading your comments, but rather your own speculation/original research, which is not what this space is for.

And yes, I do appreciate that what you have done in sharing your opinion is not unlike what happens on the RefDesks very frequently these days: speculation rather references has become the norm, rather than the exception here. But it's troubling normalization here doesn't make right under our policies--nor, bluntly does it make it intellectually honest or scientifically responsible.

"My point in making this comment was to say that the words "race" and "subspecies" are poorly defined labels to describe levels of genetic variation."

Hey, no doubt. And in numerous other contexts--an actual forum somewhere else online where we are not beholden to the same rules we are here; a conference; a walk across a campus; a dinner party--I'd undoubtedly love to have this conversation with you, and I think we would agree much, much more than we disagree. But that's not the context here. Here, we are meant to be summarizing what reliable sources say on the matter, not sharing our idiosyncratic, personal views with the world at large. There are many other forums for us to do that on--Wikipedia, including it's reference desk, has a more narrow lens.

"Scientists do not use the same criteria for defining a subspecies within the Hominidae as they use in many other organisms, such as moths or gulls for instance.

Well, that is a controversial take, and a complicated matter open to discussion amongst experts. But it is not the consensus of reliable sources, so, again (and at the risk of sounding like a broken record), not acceptable grist for the mill here.

"I think it is indisputable that there are genetic differences between geographic populations of modern humans. At least in the case of formerly long-isolated populations, like those in Australia, a suite of genetic differences covary with each other. But I emphasised that most genetic variation is within populations, not between. Do you disagree with any of that?"

No, I do not. The study of those differences is in fact one of the most robust fields in contemporary genetics and genomics. But "[significant] genetic differences" ≠ "subspecies". And the scientific consensus in this matter is clear: the differences in human genetic variation, whether related to easily observable phenotypical features or not, do not constitute evidence (or anything even remotely close to acceptable evidence) to support (or even suggest) the existence of extant subspecies in Homo sapiens. Period, end of story. Snow ^{let's rap} 01:18, 10 July 2021 (UTC)

User:Snow Rise, you again misrepresent me in saying that I think that extant human populations should be classified as subspecies: it should be clear from my comments that I think ape taxonomists have got it right, and that some other taxonomists are often too liberal in designating subspecies. You are also mistaken to say that it is controversial that the subspecies concept is used differently in different taxa: here's a supporting review (indeed we are both guilty of not citing relevant literature). See here for another nice review of the current usage of subspecies in zoology (focussing on butterflies). Jmchutchinson (talk) 05:48, 10 July 2021 (UTC)

• Other putative species would fall well into the best definition of "race" we have to work with, like Homo neanderthalensis and homo denisova, as well as homo floriensis. I've also previously pointed out that the facts that there is no such thing as magic and all these races have died off proves that the genre of real life is undoubtedly post-apocalyptic fantasy. ᛗᛁᛟᛚᚾᛁᚱPants Tell me all about it. 22:08, 8 July 2021 (UTC)

  What does this mean, if anything? What is "the best definition of 'race' we have to work with"?? The best taxonomic treatment of Homo neanderthalensis and Homo denisova within the genus Homo is unclear, and does not become any clearer by using terms that have no clear definition.  --Lambiam 10:09, 9 July 2021 (UTC)

  See Race (biology). It's usually considered close to, if not synonymous with subspecies. Note that the common definition of species includes the stipulation that different species cannot interbreed, whereas modern humans are known to have interbred with neanderthals and denisovians. So while neanderthals and denisovians are frequently called different species from modern humans, they do not actually meet the common criteria for being different species, making them subspecies. Which can be referred to as races. It's less clear whether there was any interbreeding with floriensis, but as they're frequently referred to as "hobbits", I couldn't very well leave them out. ᛗᛁᛟᛚᚾᛁᚱPants Tell me all about it. 14:42, 9 July 2021 (UTC)

July 7

Cell phone radiation.

New article came out about cell phone radiation and brain tumor. https://www.fox32chicago.com/news/new-uc-berkeley-study-draws-strong-link-between-cell-phone-use-and-cancer But I have 2 questions, is phone radiation from smartphones different than from flip phones? (These articles don't seem to ever make a distinction.). And is it different when the phone is on a conversation, vs. not on a conversation? Thanks. 67.165.185.178 (talk) 15:53, 7 July 2021 (UTC).

Phone on a conversation is definitely different from phone not on a conversation. That how the system works, you have to broadcast more when you are actually using the phone. Otherwise, it only has to ping the next tower nearby.

Use of smartphone vs. flip phone is relevant if you are using a different cellphone network standard (3G, 4G, 5G), which might be the case or not. Different phones might also induce a different use. Say, you hold your smartphone away from your ear to see the screen, use hands-free mode if it works well, or you use a headset. --Bumptump (talk) 16:29, 8 July 2021 (UTC)

Okay I have a 2nd question: smartphone also uses the radiation for Internet, that flip phones typically do not have? So is putting your head next to a smartphone that is using the Internet, comparable to putting your head near a laptop using wireless connection? Or is that still different radiation? 67.165.185.178 (talk) 19:24, 8 July 2021 (UTC).

4G, which is pretty standard for smartphones, uses LTE frequency bands. There are different bandwidth assigned depending on country.

WLAN, which is basically how we all connect wirelessly to our routers, most commonly uses the 2.4 gigahertz and 5.8 gigahertz bands. Each range is subdivided into a multitude of channels.

There are innumerable devices, besides wifi and 4G, using some share of the the radio spectrum: baby monitor, wireless speakers, toys, car alarms, garage remotes, radios proper, cordless phones, GPS, Bluetooth. The bandwidth they use is not only a technical question. They are licensed to work only within a certain range of frequencies. And they are regulated differently in different countries. But yes, in a specific country WLAN and 4G should have a different bandwidth. Bumptump (talk) 20:47, 8 July 2021 (UTC)

What is meant by uplink, downlink, and duplex spacing, columns, in the LTE_frequency_bands you posted? 67.165.185.178 (talk) 08:10, 10 July 2021 (UTC).

Uplink and downlink are explained on the notes A2 and A3 at the top of the columns - uplink is the frequency that the base station receives on, and downlink is its transmit frequency. Duplex spacing is the frequency gap between the uplink and downlink - which a little arithmetic makes plain.--Phil Holmes (talk) 09:30, 10 July 2021 (UTC)

Large ship fuel efficiency

How does the fuel efficiency of lake freighters compare with that of ocean freighters? Per tonne-kilometre/ton-mile, of course, since I assume the lake freighters are smaller because they don't need to be self-sufficient over the vast distances of the oceans. I found occasional resources that look at the fuel efficiency of lake freighters, e.g. [4], but unless I'm overlooking something, I didn't find enough numbers to calculate what I'm looking for. On one hand, an oceangoing ship can go wherever it wants to take advantage of good weather (cf. Trade winds#History) or avoid bad weather, while the size of the Great Lakes means that a lake freighter can't do that, and ships in the ocean can use currents (cf. Ocean current#Economic importance), while a lake freighter speeded by going downstream in the St Lawrence River has to fight the same current when returning upstream. But on the other hand, lake freighters only need to carry a small amount of fuel to reach their destinations, while oceangoing ships must use extra fuel to carry around the weight of the fuel that they need to reach their destinations. Nyttend backup (talk) 16:36, 7 July 2021 (UTC)

I haven't got exact numbers, but looking at engine power (which is a measure of fuel usage) and cargo capacity, both of which are mentioned on the infoboxes of many ships' articles, we can get a rough estimate. I looked at the numbers of MV Edwin H. Gott and Ever Given. Assuming the ships normally run at close to full power and have an engine efficiency of around 60%, and assuming bunker oil provides around 40GJ/m³, both have a daily fuel consumption of about 0.1% of their cargo capacity. The ocean-going ship is faster though, as is usual for container ships compared to bulk carriers, so per ton-kilometre it's more efficient. Despite going faster, which increases drag.

Carrying enough fuel to reach the destinations doesn't appear to be a problem for either of them. Carrying the fuel to cross an ocean only takes a few percent of their cargo capacity. There are other reasons why ocean going freighters are larger than lake freighters. Larger ships have less drag compared to their displacement, making them more efficient. Lake freighters cannot be that large, because:

• The largest ships only fit in a few ports. Ports are only made large enough for these ships if their cargo volume is huge, which is when they serve as a hub for a substantial part of a continent: Tianjin, Singapore, Rotterdam, Los Angeles, some others. As the North American Great Lakes cannot be reached by large ocean-going ships, they cannot serve as such a hub, so the ports can only handle modest ships.
• A low cargo volume means that, using large ocean-going ships, a port would be visited by few ships. This means that the cargo has to wait in port for a long time before a ship arrives to pick it up.
• On long distances, travel time is important. On shorter distances, loading time gets more important. Smaller ships (and the same applies to other modes of transport) allow for faster loading, as there's less to load. This is typically less important for bulk cargo.

On the other hand, lake freighters face smaller waves, so they can be made less strong and more streamlined, which is good for fuel efficiency. PiusImpavidus (talk) 10:21, 8 July 2021 (UTC)

Though not so good for ships like the Edmund Fitzgerald. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:13, 9 July 2021 (UTC)

July 8

Can laser beams have detectable surface gravity?

From the thingy that lets zero rest mass photons have relativistic mass? Sagittarian Milky Way (talk) 22:21, 8 July 2021 (UTC)

Generally, laser beams are not considered astronomical objects. I don't think the concept applies. Light beams in general bend under the influence of gravity (see Gravitational lens and Tests of general relativity § Deflection of light by the Sun), so they exert gravity themselves. They can also exhibit a repulsive gravitational effect.^[5]  --Lambiam 09:53, 9 July 2021 (UTC)

Has the gravity caused by a laser beam been detected in an experiment? Sagittarian Milky Way (talk) 15:21, 9 July 2021 (UTC)

A very high-power continuous wave laser is MIRACL, producing 1 MW in a 14 cm × 14 cm beam. That's an energy density of (10⁶ W)/(0.14 m)²/c = 0.17 J/m³, equivalent to a mass density of (10⁶ W)/(0.14 m)²/c³ = 1.9×10^-18 kg/m³. The density of air is around 1 kg/m³. Treating the beam as cylindrical for simplicity, the gravitational gradient at the surface is 2πGρ ~ 8×10^-28 s^-2 or 8×10-19 eotvos. To measure that in a year, you would need a gravitational gradiometer with sensitivity of 8×10-19 E × √(3×10⁷ s) ~ 4×10^^-15 E rtHz. Measurement techniques I can find are much less sensitive than this: [6], [7]. (The last linked paper shows that you can measure the gravitational field of a few lead bricks. But the energy density of a laser beam is much less than the rest-energy density of a lead brick.) As Lambiam points out, the gravitational field of a beam of light is not identical in GR to the gravitational field of a stationary mass of the same shape and energy density; these are ballpark order-of-magnitude considerations. --Amble (talk) 17:47, 9 July 2021 (UTC)

Of all the imperfections of reality (radiation pressure, slight magnetism of non-magnetic stuff, gravitational constant making Earthlike worlds too small..) at least it's nice to know that gravity from manmade light will have no detectable effect for awhile. Sagittarian Milky Way (talk) 21:44, 9 July 2021 (UTC)

July 10

Why UV rays is good for health if it is higher frequency than 5G?

• Ultraviolet rays from the Sun are high-frequency and can be dangerous.

Source

Why UV rays is good for health with such higher frequency? Good means here Rizosome (talk) 15:25, 10 July 2021 (UTC)

You just quoted something saying it wasn't good for your health. You seem to have answered your own question by showing your question is false. While it is an oversimplification to say that UV is dangerous, you haven't presented anything suggesting it is good for your health. --OuroborosCobra (talk) 15:36, 10 July 2021 (UTC)