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  1. 4 points
    In a sense, getting to massless SM particles could be achieved by increasing the temperature in some region. But it would be more like an activation of the frozen Higgs field than a blocking. It is easier to explain coming from the high-energy side (high temperature), since that is the standard explanation for the Higgs mechanism: The Higgs proto-field (*) can be considered as an additional particle class to a Standard Model in which all of the other Standard Model particles are massless (**). It interacts with most of the other particle fields. But it also has a weird self-interaction which causes the energetically lowest state to not be at "no proto field" but at "some value of the proto-field". At low temperatures, where the Higgs proto-field is just lying around in its minimum, this means that the dynamic interaction terms of the Higgs proto-field with the other particles become some dull interaction of those particles with some sticky stuff that seems to lie around everywhere (***). In the mathematical description of the Standard Model time evolution, the associated terms that originally were terms of a dynamic interaction now become the mass terms for the other particles. If the minimum was at "no field", they would simply drop out (****). This "low-energy" limit actually covers almost all of the temperature ranges we can create on earth, and only recently did we manage to even create and see a few excitations of the Higgs proto-field around its minimum in specialized, very expensive experiments (-> confirmation of the Higgs-Boson at the LHC). So technically, I think we are very far away from creating the "massless particles" state in an experiment. But there is no theoretical reason why this would not be possible (*****). But as described, I would understand it to be less of a shielding of the Higgs field and more of an activation. And as a state with such a high amount of interaction between the fields. So I am not even sure if the common view of a few particles flying through mostly empty space and only rarely kicking into other free-flying particles would still make sense. Remarks: (*) I would just call it Higgs-field(s), but since the paper you cited seems to explicitly avoid using the name at this stage I may be wrong about common usage of the terms. Haven't been working in the field for over ten years. So I have invented the term proto-field for the scope of this post - it is also easier to understand than "doublet of complex scalar fields". (**) This is not exactly true because the particles are mixed and get renamed under the Higgs mechanism. But I'll pretend that does not happen for the sake of providing an answer that is easier to understand than reading a textbook. (***) Sidenote: In this state, the few excitations of the Higgs proto-field around its minimum are the infamous Higgs Boson. (****) Which is why you can always invent new fields that just happen to have no effect on anything we can see but magically make your particle cosmology equations work at very, very high energies (****) Except for the fact that some people still expect new physics and associated new particles at such high temperatures, which then again would have mass from another Higgs-like mechanism
  2. 2 points
    QFT. KJU has already gotten what he wants... He's been recognized as a world leader... He's been given a seat at the table among the "league of nations," and he's now been platformed as a peer. He's been taken seriously by the world, is meeting with the most powerful countries of US and China, and it has legitimized him as a powerful person who has made N.Korea a player. Everything else is just gravy at this point. Kim got what he wanted the moment Trump agreed to meet. Sure, KJU's been discussing specific industry investments from the US into NK with Pompeo, but that's all secondary to his push to develop nuclear weapons in an attempt to be taken seriously by the world. He's solidified his place, been praised by the POTUS as a great chairman, elevated instead of treated like the teapot dictator he is. They got what they wanted already, and the US keeps losing more and more credibility. Are you tired of all that winning yet?
  3. 2 points
    My hobby in my retirement is painting big-wave surfing scenes. I haven't made hardly any money from it yet. When I started using an airbrush it gave more realism to my pictures. My avatar photo, by Robert Brown, is famous, a giant 77-foot wave ridden by Mike Parson at Cortes Bank (100 miles off the coast of San Diego, CA) on 1-5-2008. See the actual photo here and read all about it: https://www.nytimes.com/2008/01/09/sports/othersports/09surf.html But the problem with that photo is the smaller wave in front of it blocks our view of the trough, so for my painting of that same wave I removed the wave blocking our view of the trough: https://john-kaelin.pixels.com/featured/cortes-bank-xxl-1-5-2008-john-kaelin.html See all my artwork at "biggestwaveseversurfed.com" which takes you to this web site: https://john-kaelin.pixels.com/ Recently a new world record for "biggest wave ever surfed" was established at Nazare, Portugal on 11-08-2017 by Rodrigo Koxa at 80 feet tall. What about Ken Bradshaw's 80 footer at Log Cabins on 1-28-1998? Well, that was not photographed, only some grainy video was shot from a mile away. http://www.swellnet.com/news/rearview-mirror/2018/01/28/condition-black-january-28th-1998 The video of the new world record is not much help because you can hardly see what is happening: https://www.bing.com/videos/search?q=rodrigo+koxa+nazare&view=detail&mid=D41B67AF5A72B9621951D41B67AF5A72B9621951&FORM=VIRE
  4. 2 points
    You have a lot to learn my young padawan, the real answer is "it makes your arse look great".
  5. 2 points
    Some scientists think they have solved the mystery https://arstechnica.com/science/2018/05/nasas-em-drive-is-a-magnetic-wtf-thruster/ "Even with a power of just a couple of Watts, the EM-drive generates thrust in the expected direction (e.g., the torsion bar twists in the right direction). If you reverse the direction of the thruster, the balance swings back the other way: the thrust is reversed. Unfortunately, the EM drive also generates the thrust when the thruster is directed so that it cannot produce a torque on the balance (e.g., the null test also produces thrust). And likewise, that “thrust” reverses when you reverse the direction of the thruster. The best part is that the results are the same when the attenuator is put into the circuit. In this case, there is basically no radiation in the microwave cavity, yet the WTF-thruster thrusts on. So, where does the force come from? The Earth’s magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal). The current in the cable experiences a force due to the Earth’s magnetic field that is precisely perpendicular to the torsion bar."
  6. 2 points
    I agree. They shouldn't be. Like music and reason shouldn't be enemies. Because they are completely separate things. The problem comes when people insist that their faith means that reason must be wrong (e.g. Creationists etc).
  7. 2 points
    Not a bad summary +1 though I would probably describe unsmoothness as anistropic.
  8. 2 points
  9. 2 points
    Whenever discussing stars we also need to take into consideration all the other "stuff" that formed in addition to the star. I have no doubt that the first Population III stars would have had planets, asteroids, comets, and everything else we find in solar systems. However, it has been suggested that these first stars would have been massive, anywhere from 100 to 1,000 solar masses. If that is true then these first stars would have had very short lives indeed. Perhaps just a few million years. While that may be sufficient time to produce the first 26 elements on the Periodic Table, it is far too short a time for life to develop. At best life would just be getting started, only to be wiped out by the resulting hypernova when the Pop III star dies. I think life has its best shot beginning with Pop II stars. The metal-poor stars in the halo of our Milky Way, for example, have been dated to 12+ billion years. Since we only have one example to go by, it is rather difficult to say with any certainty how long it takes to evolve beyond primordial life. I would imagine that it very much depends on the conditions. On Earth it took just over 700 million years before life first appeared, and then another 3.3+ billion years before we get to the Cambrian. That is a long time for a planet to remain relatively stable. Too long for any star with greater than just a couple of solar masses. Given that Pop. III stars would have been short lived, the Pop. II stars would have formed shortly after the Pop. III stars. Certainly within the first billion years after the Big Bang. Therefore, I would not rule out the possibility of life being 12.8+ billion years old. Source: The Formation of First Stars. I. The Primordial Star-forming Cloud - The Astrophysical Journal, Volume 564, Number 1, 2002 (free preprint)
  10. 2 points
    Ok magnetism is primarily due to the net magnetic moment alignment of electrons, which involves spin. Every electron has a magnetic dipole moment. In most materials the alignment cancel each other out. However certain materials such as hematite the net alignment is imbalanced. Here is a rather lengthy 633 page article that has excellent coverage of magnetism. This will greatly help you in your physics course. It will detail several highly important details such as the Currie temperature etc. https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.dsf.unica.it/~fiore/libricorsoptr/coey-magnetism.pdf&ved=2ahUKEwj7puu4-pTbAhUeHGMKHVdgBO0QFjAAegQIBxAB&usg=AOvVaw01a_57WGwNznR89qLB3zxW The article is essentially a one stop resource for pretty much anything you will need to know or want to know about magnetism and why certain materials have greater magnetic susceptibility and others don't. How this ties into spin orbitals etc. It also details Maxwells equations etc. Rather than give snippets of details which would be unavoidable via strictly questions and answers on a forum this will provide you a comprehensive and rather detailed understanding of magnetism.
  11. 2 points
    You might want to rethink that
  12. 1 point
    I don't think that it is entirely accurate. Based on various articles on NK, it seems that the Kim's position is far more precarious than one might imagine. The purges and assassinations were means to strengthen his internal power and there are reported worries regarding military coups, especially when he leaves the country. Now, NK has again stated that they are open for talks any time, thus placing the blame squarely at the US. Thus Kim has effectively eased pressure on NK and made the US president look bad. These are huge wins for Kim who can use his external wins to cement his position. I suspect the wedge between SK and US is one of the biggest wins for NK, in this respect.
  13. 1 point
  14. 1 point
    This is how coast line of Sunda shelf looked like in Upper Paleolithic: Extend it to the entire world coast line, e.g. 20k years ago, till now.. and you will have answer for Flood Myth. If increase of temperature, because of global warming, will continue melting ice, you will have Flooding v2.0.
  15. 1 point
    The distinction I make between faith and hope/wishful thinking is in the willingness to change one's life for the belief. I can hope there is something for my consciousness to continue into after the death of my body without doing anything different in my life. Faith, however, often requires great sacrifices and strictures on lifestyle based only on the strength of the belief.
  16. 1 point
    Hi Oliver, I take it you don't live by the sea? If you did you would be used to the fact that things don't last. Cars, bridge steel, metal lamposts rust more quickly, aluminium corrodes, even stainles steel does not last indefinitely. Non metal materials don't fare any better In the water fibreglass boat hulls are subject to absorbing salt water and swelling, becoming jelly like.
  17. 1 point
    No, you did not... HCl is stronger acid than acetic acid. You can make weaker acid from salt of weaker acid and stronger acid, but not reverse. e.g. C2H5COONa + HCl -> C2H5COOH + NaCl
  18. 1 point
    If it's not covered by the Standard Model, it's not a particle. 1st of all, what do any of us know confidently about anything outside the standard model? 2nd of all, what are you trying to say with this?
  19. 1 point
    The evidence is pretty strongly in favour of dark matter being some form of matter. Whether it is a particle yet to be detected or something else is unknown. But, certainly, there are non-matter particles with mass; W, Z and Higgs bosons. Well, unless there is some alternative theory that says they can't have charge... But I can't see how that would mean they would have to be made of known type of matter. The same is true of Schwarzschild black holes. No. These are completely different things. Hawking radiation is created at the event horizon. It exists even in the absence of matter around the black hole; it is purely a function of the existence of the event horizon. In fact, our only chance of detecting it would be if there was a small and almost completely isolated black hole close enough to make detailed measurements of. Polar jets on the other hand come from the accretion disk outside (quite a long way outside) the black hole. Well, dark matter obviously isn't. As to what happens inside a black hole; we don't know. You might be interested in this, though, as an alternative: https://www.quantamagazine.org/how-fuzzballs-solve-the-black-hole-firewall-paradox-20150623/
  20. 1 point
    Look at the mass difference between the target and the result, e.g. O-16 and O-15 + neutron. E = mc^2 That will tell you the minimum energy you must add. But anything involving an accelerator is ultimately going to be very inefficient and probably not produce net energy. You have to be able to collect the material on the cheap, as we do for fossil fuels, wind and solar (which are all, ultimately, solar), fission, or get fusion technology working.
  21. 1 point
    We're very well aware of many of the limitations of QM. And we're really racking our brains about them. Also, not a scientific argument. We're not 99%. I don't mean to be arrogant, but I expect most people here, especially professional physicists, to be among the 1% of the smartest people in the world, some maybe even in the .1%, which would mean they have an IQ around 140-150. So, if you want to use real physics arguments, I'm sure we'll understand you. But you also have to recognize that if they say there's a serious problem, or an array of serious problems, with your theory, that pouting and whining won't promote your theory. What dogma? Regarding your finger and its light-bending abilities, check out this mind-bending video on youtube. You may be talking about it in the way you describe. I am certainly not. Since Photons don't carry a charge, their movement doesn't create a magnetic field, either, and the only way they could interact with other photons in a classical mechanical manner would be collision, and thereby impulse transfer. I haven't ever heard (or read, for that matter) of any such observation of this manner of photon-photon interaction. Photon-electron and photon-nucleotide, yes, but not photon-photon. If photons could exchange momentum with eachother as described by newtonian mechanics, even if the probability were ever so slight, by the abundance of photons bathing our reality we would have noticed. And for reasons already explaned, a Photon is NOT A ROTATING DIPOLE
  22. 1 point
    YaDinghus, welcome, I think you will be an asset to the forum. +1
  23. 1 point
    Faith imho is pretty much the same as hope. It's not a matter of because, but of in spite. To try in spite of the odds, to carry on in spite of the hardship. This can be inspired in the best cases, and deluded in the worst. To the oppressed, it's the source of their defiance, to the oppressors, the source of their authority (here hope not so much)
  24. 1 point
    oh great just great is that where QM got the term " state " lol particle/system state/property based on economics lol works for me
  25. 1 point
    Money is useful to regulate the dispensation of scarce resources. Basically, it's a rationing system. What we call economy is an emergent system from this rationing function and human psychology, and in this system, money is a basic resource, and value an essential property. I guess you could compare it to a Field in QM, where Money is the exchange boson for the force (value) exchange
  26. 1 point
  27. 1 point
  28. 1 point
    The only assumption I made was about it being mentioned before that nothing you've described is out of the normal parameters for human empathy, and that's why I said "probably". The rest are observations based on your writing, which is all I have to go by in this discussion. I "picked" that one segment to quote strictly because it held examples of what I find to be faulty reasoning. In science terms, you've removed your falsifiability. The way you pose your explanation for this phenomenon, you can never be shown to be wrong (and again, I'm not saying you are, just saying you aren't presenting objective support for it).
  29. 1 point
    https://phys.org/news/2018-05-alma-most-distant-oxygen-universe.html Astronomers find evidence for stars forming just 250 million years after Big Bang May 16, 2018, National Radio Astronomy Observatory Not long after the Big Bang, the first generations of stars began altering the chemical make-up of primitive galaxies, slowly enriching the interstellar medium with basic elements such as oxygen, carbon, and nitrogen. Finding the earliest traces of these common elements would shed important light on the chemical evolution of galaxies, including our own. New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the faint, telltale signature of oxygen coming from a galaxy at a record-setting distance of 13.28 billion light-years from Earth, meaning we are observing this object it as it appeared when the universe was only 500 million years old, or less than 4 percent its current age. For such a young galaxy, known as MACS1149-JD1, to contain detectable traces of oxygen, it must have begun forging stars even earlier: a scant 250 million years after the Big Bang. This is exceptionally early in the history of the universe and suggests that rich chemical environments evolved quickly. Read more at: https://phys.org/news/2018-05-alma-most-distant-oxygen-universe.html#jCp ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: the paper: https://www.nature.com/articles/s41586-018-0117-z The onset of star formation 250 million years after the Big Bang: Abstract: A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang1,2,3. The abundance of star-forming galaxies is known to decline4,5 from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD16, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< Hmm, interesting in as much as would or could it be suggested that extrapolating the evidence for early star and element formation, one could reasonably suggest that life via abiogenesis may have also arisen early? Obviously not life on Earth but an early form of universal life and abiogenesis. Perhaps the foundation of another discussion/debate in another more appropriate forum?
  30. 1 point
    I was wondering when scientist figured out when oxygen took a place in evolution. When did they know that oxygen was a byproduct before it was essential for life. At what time did they figure out that oxygen came later?
  31. 1 point
    It seems almost engineered that these men reject intellectual arguments, don't care about being healthy or educated, and generally vote for those who actually make it harder for the working class to get by. They support the butcher with his thumb on the scale who has been pushing inferior meats cut way past the bone for years, just because the other butchers try to serve everyone fairly. It's a long con that has been very successful for the worst extremist capitalists. They've removed most of the help a government can provide, and then they made the People afraid of the government. Very handy when POTUS needs to remove the FBI's credibility.
  32. 1 point
    Evidence based explanations for god didn’t work out very well for you last time you tried (you got banned till Christmas) so now you’re trying to use philosophy to convince yourself of the necessity of a creator. Philosophy is o lot more flexible than evidence based science so you might actually last a little longer this time with your inevitable god rants but make no mistake, you will fail as long as you will not provide viable, comfirmed evidence for your religious stance, good luck though.
  33. 1 point
    I think there's an issue here where people say faith when they mean trust, and the meanings are different. One can trust science and trust a doctor, rather than have faith in them.
  34. 1 point
    Abiogenesis came before bacteria. Those gazillions of opportunities to make complex chemisty made chemistry with enough attributes of life to become the living precursors to more complex forms. Just to be clear, I wasn't suggesting bacteria - which are complex and sophisticated lifeforms with a lot of evolutionary history - got assembled from primordal sea chemistry in one extraordinary and unlikely chemical occurrance. Umm, that is unless you count the precursor life forms as extraordinary and unlikely chemical occurrances.
  35. 1 point
    He and his team have decided not to attack the facts, but to attack the fact finders. He knows the legal challenge is secondary to the political one. I feel confident Mueller already has evidence of criminal activity from Trump and his cronies, lots of it, too. He got help from Russia, probably from the Saudis, and his campaign “officials” actively sought it. His campaign manager changed the republican platform to help Russia. China invested in his properties to get help on trade. The gratf and corruption is there, but the president is the head of the justice department. Can the justice department indict or convict the individual with the authority to prevent them from doing so? Can the courts intervene, or does the constitution keep those powers separate? This is the constitutional “crisis” people are referring to, but none of it matters. I don’t think Mueller will indict him. I think he’ll hand a very well supported, extremely solid evidence based report to Congress so THEY can act. This isn’t a legal issue, IMO. It’s a political one, and that’s part of the reason the midterm elections later this year in November are so critical. Who has power in Congress will ultimately dictate who has control of the Oval Office and accompanying executive powers.
  36. 1 point
    The association between BMI and health risks isn't anymore telling then age, genetics, and lifestyle are. BMI is just a superficial way to guess at what is going on with ones diet and lifestyle. Provided one has a good diet, active lifestyle (relative to age), and feels healthy their BMI probably isn't important. That said it has been my experience that people simply are not honest with themselves about their diets and activity levels or are totally ignorant of them. In such cases a generic standard (BMI) is useful in creating a standard for those otherwise have known. Where I work we actually get weighed in a couple times a year at a minimum. As a collateral responsibility I work with people who miss their weight. In my experience the overwhelming majority of people who are over their BMI are so because they are fat. In 12yrs of working with those who weighed in over I have never seen where someone simply had too much muscle. I think people use the too much muscle excuse to deny the simply truth that they are fat. When Arnold Schwarzenegger won his first Mr. O he measured 186 cm (6'1) tall at 107kg (236lbs) in weight. Admittedly he was also using steroids. Yet I have known many men over the years heavy as or heavier than 107kg who are no taller than 186cm who insist it is all muscle which would mean they are more muscular than a competition ready Arnold Schwarzenegger cycling steroids. While it is true some athletes pack on weight for their sport it is also true that most are fat. Athletic skill positions seldom ever require artificial weight. It is generally the the known skill position where one benefits from size and in those non-skill positions the sizes typically includes lots and lots of fat.
  37. 1 point
    The one that all men’s fate hangs in the balance of - Does this make my butt look big?
  38. 1 point
    You might want to actually read Penrose instead of relying on misquotes. This topic is discussed in "Road to reality" Chapter 27. (Which I am currently reading after advice from members on this forum.) It is not the most accessible book, but this Chapter is quite readable. His conclusion is that any theory about an origin of the universe should be able to explain why the initial entropy is so low, not the opt-out "A wizard did it". He even explicitly says so.
  39. 1 point
    Indeed. His explanation is that the universe is cyclic and so there is no start or creation of the universe to worry about: https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology Do you realise how stupid this logic is? It is like saying: "I saw something that I couldn't identify. Therefore it was an alien spaceship."
  40. 1 point
    Scientist with the right equipment can do it using mass spectrometer. Elements can be identified by their spectral lines. This method is used by astrophysicists it learn what is composition of stars.
  41. 1 point
    Or can you? Is the question about free will vs determinism? In which case, maybe you can't control the future: whatever decision you make (to have a drink or not have drink) may have been predetermined. Even the fact that you change your mind after reading this, to prove that you can, was also predetermined. ... ... As was the fact you have just changed it back again
  42. 1 point
    I can control whether I’ll have a drink tonight, I can’t control whether I will win 365mln in the Euro Jackpot tonight. There are various levels of controling the future, I can make decisions which have a 100% binary outcome on the future...like for example I won’t be driving after having drinks tonight which renders a 100% outcome that I will not hit anybody while drunk tonight. On the other hand I can only partially control some aspects of the future.
  43. 1 point
    As Studiot correctly pointed out asteroids would be a poor starting point. However that being said, asteroids are made of minerals and ice commonly found on Earth. So studying the different properties of those minerals here on Earth is sufficient. We would be happy to help guide you in learning how electromagnetism and gravity differ from one another but also as pointed out we need an understanding of what level of teaching to start at. Lets start with Studiots questions then work from there... By the way it is a great act of character to admit when one is wrong or doesn't fully understand something. I wish far more posters did the same so +1 for that. I have far greater respect for posters who honestly wish to learn than those making grandiose assertions. When thinking over the comments made by both Studiot and Swansont I would recommend you start thinking of iron in particular. Iron does not normally exhibit a magnetic field but if you apply a current can be made into a magnet. The questions Studiot asked relate to this phenomenon. (it also relates to why certain astronomical bodies has a magnetic field while others do not)
  44. 1 point
    okay. I don't account for them, I'm asking to learn. I wonder what the average composition of such an asteroid is?
  45. 1 point
    Are you going to get upset when someone points out that any religious belief that stems from reason isn't religious (I'm a staunch atheist, but I will believe the same thing if you show me that it's based in rational thought) so the only things that are based on religious faith are not rational?
  46. 1 point
    Raider5678 has been suspended for six months at his own request, in order to pursue employment and educational opportunities in a less tempting and more focused manner. We wish him all the luck in the world, and hope to see him back in time for the holidays.
  47. 1 point
    Why is not a science question. But if you look at available evidence, one could put together a decent argument that a planet with life on it needs at least one species that can leave to spread life to other planets.
  48. 1 point
    Humans evolved to be just good enough. Not extraordinarily good. Not exceptionally bad. A fair turn of speed. Excellent endurance. Good enough eyesight. Hearing. Some sense of smell. A very big brain. Plus the important thing you need to remember about humans is that they always run in packs. One human alone was weak. Fifty together were superior. What is also important is that at the time Humans really got going there was nothing else standing in their way. All the environmental conditions were ripe. Humans had the vital capacity to quickly adapt to a changing environment. The final factor was that people learned to adapt the environment to their needs rather than just blending in. The rest is history.
  49. 1 point
    It is known that chlorine is produced when electrolysis of seawater or sodium chloride solution.My question, what is first produced, or in which form chlorine will be the first evolved; 1- as chlorine gas form that starts to dissolve in the salt solution? or; 2- as an aqueous form which will start to escape the solution after reaching saturation limit?all answers are very much appreciated. Thanks, Shadi
  50. 1 point
    More likely a work of art. There are other examples. https://en.wikipedia.org/wiki/A_Book_from_the_Sky