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  1. 5 points
    At which point, I have to post this: https://what-if.xkcd.com/1/ Spoiler: it doesn't end well
  2. 4 points
    My little bother just ate all the Scrabble tiles and his poop made more sense than you do.
  3. 3 points
    Just to add to what has already been said by other contributors here: 1. First and foremost, the notion of "gravitational potential" can only be defined in spacetimes that are stationary (more precisely: those which admit a time-like Killing vector field) and asymptotically flat. It cannot be generalised to more general spacetimes, which makes it useless so far as a general model for gravity is concerned 2. Gravitational potential itself is not an observable, only differences in potential can be observed and measured. This is because the potential has a gauge freedom, in that one can freely choose where the zero point is, without affecting the physics. The same is not true for the speed of light, hence the relation above is trivially and obviously wrong, since it equates two quantities that cannot physically and numerically be equal, on fundamental grounds. 3. A varying speed of light would constitute a violation of Lorentz invariance. This symmetry has been experimentally and extensively tested with modern equipment to extremely high precision, both here on Earth and in the vacuum of space - needless to say, no such violations have ever been found. Given the degree of precision of these tests, any variability in the speed of light can effectively be ruled out far beyond the usual 5 sigma threshold. 4. A variable speed of light would also break CPT symmetry, which underlies the Standard Model of Particle Physics. Since we continue to successfully use and test this model in particle accelerators on pretty much a daily basis, any variability in c can also effectively be ruled out on that ground. 5. Neither classical Maxwellian electrodynamics nor quantum electrodynamics allow for varying values of permittivity and permeability (in the same medium of course). Hence the notion of a varying speed of light is actually in direct contradiction to what we know about electrodynamics. 6. As has been pointed out on another recent thread, a scalar field theory such as this one is fundamentally incapable of capturing all required degrees of freedom of gravity; there is more to gravity than just time dilation! I could probably go on, but these are the points that immediately come to mind without thinking about the issue too much. I'll leave it at this.
  4. 3 points
    Disclaimer: Black hole not visible, southern hemisphere required. https://www.theregister.com/2020/05/06/nearest_black_hole_earth/
  5. 3 points
    You mean calling him a "racist"? That is no more "name calling" than referring to someone a "physicist" or a "plumber". Name calling implies an insult. "Racist" is a title he earned all by himself. I don't see what is to be gained by dancing around words to spare people's feelings. This place is not a quilting circle. So there is the "status quo" and there is "your way". Some people feel there are other means to change the status quo, and they don't involve allowing others a platform to share hatred and bigotry. I allow no room in my heart for showing understanding for racism. Hatred of others based on the color of their skin is never acceptable to me. I will not stand by while others spew hate without calling them out. There is a reason people lose sponsors, advertisers, and even jobs after making racist comments. It is not acceptable. I don't see why we should be an exception.
  6. 3 points
    ! Moderator Note No, you're racist because you espouse racist beliefs, the expression of which on this forum (besides being wrong) is also against the rules. Consider yourself banned.
  7. 3 points
    Just to add info. The oxygen in photosynthesis comes from the breaking up of water molecules. The possibility that it came from CO2 has been ruled out experimentally by using isotopic tracers. https://www.amazon.com/Life-Science-William-K-Purves/dp/0716798565 (chapter 8: Identifying Photosynthetic Reactants and Products) Water was very abundant in the atmosphere after the late heavy bombardment.
  8. 3 points
    Your advocacy for police brutality suggest your statement here is unequivocally disingenuous. You've touted your belief in police brutality and, thereby, confirm you do believe it exist. It's hardly convincing that a person who holds such beliefs is in anyway sincerely or slightly interested in humans rights protection whatsoever. As decent human beings raised with a modicum of morals, they should have innately known to weigh "following training/orders" against the loss of common decency. "I was just following training/orders" is not an excuse for crimes committed while doing so.
  9. 2 points
    With the exceptions of occasional crackpots, the selfish, the unkind, and the uncouth; and on rare occasions, the sheer lunatics that come and go, most of the members of this community are giving me an enormously valuable environment to exchange ideas. Teaching has been a great pleasure for me for many years. Now, for the first time, I'm tutoring a boy that suffers from Asperger's syndrome. After a month now, I must say that it's been one of the most gratifying teaching experiences I've had so far. Things are going pretty well, good results keep coming, and everyone involved seems to be happy. We've started with maths. Every time he shouts “now I understand it!” is priceless. But he's emotionally vulnerable, and also gets quite anxious when he misunderstands something and gets embroiled in the wrong calculation. The verbal feedback is somewhat wanting, because he stumbles over words and speaks too quickly for me. So sometimes it takes me a while to realise what he really means. Any experience that any of you may have to share with me, any tips and directions, will be greatly appreciated. Especially heads-up when it comes to physics, which I'm kind of dreading.
  10. 2 points
    Sound we regularly experience carries very little energy. 80 dB is ~ 1 milliwatt, so assuming 100% efficiency: “to heat up a quarter liter of coffee 50 C it would take: 1 year, 7 months, 26 days, 20 hours, 26 minutes and 40 seconds” https://www.physicscentral.com/explore/poster-coffee.cfm 130 dB is just 10 watts, though it is logarithmic https://en.wikipedia.org/wiki/Sound_power
  11. 2 points
    My very short answer: A value of a random variable. Let's say you receive a symbol "1". If this is the only possible symbol the fact that you received it does not give you information. But if this symbol is one of two possible, "0" and "1", then the reception of symbol "1" may contain information. So having more that one symbol is a requirement, but not sufficient. Lets say you receive the pattern "111111...". The probability of the symbol "1" is 1. Again there is no information. But if random sequences are allowed, for example "00", "01", "10", "11" then we may use these sequences to represent information. So conceptually information can be seen as a value form of a random variable. The above is an attempt at an extremely short introduction to information theory, which is tied to discrete probability theory. Most important early contributor was Claude E. Shannon and his paper “A Mathematical Theory of Communication”, dealing quantitatively with the concept of “information”. Shannons concepts and the mathematics he used to describe information and to measure information content is a remarkable contribution. I believe it's tricky to find any areas of IT where his work does not contribute. Wikipedia* has links to some concepts related to your question. Feel free to ask additional questions. *) https://en.wikipedia.org/wiki/A_Mathematical_Theory_of_Communication For an early predecessor of Shannon, working on sinus signals and frequencies, see Hartley: https://en.wikipedia.org/wiki/Ralph_Hartley
  12. 2 points
    No. They are purely about the "completeness" of formal systems. In other words, can a formal system (e.g. mathematics) prove that anything that can be written down using that formal system is either true of false. And the answer to that is no. You can write something using mathematics that you cannot use the same mathematics to prove or disprove. You can extend your formal system to make it more complete and allow you to prove that statement. But then there will be other statements that this extended system cannot prove. And so ad infinitum. Physics uses mathematics but it is not limited by that mathematics in the same way. (And some mathematicians complain that physicists are a bit "ad hoc" and don't really stick to absolutely formal derivations.)
  13. 2 points
    That is out of my knowledge. The only thing I can say is that trying to change the elements (river, sea, land) in a specific way most of the times drive to unexpected results. I have the experience where a hotel constructed a small dock in the sea for his single inflated boat sportcraft had the result to erase completely its sandy beach.
  14. 2 points
    If you have scientific evidence for a non-mainstream topic, and you think you can defend it reasonably, put it in Speculations. If it pertains to a field of personality studies you can defend using science, post in Psychiatry/Psychology. If it's something you feel might pertain to a specific philosophy or ethical approach, post in Philosophy. If it's just New Age mysticism that works because you say so and wave your hands a LOT, please don't post anything at all.
  15. 2 points
    There are things the Bible doesn't say and almost everybody believes it does. There was no apple. It could have been a quince, or maybe a fig, as there were no apples back then in the Middle East. The Bible doesn't say it was an apple, actually. The Bible doesn't say Jonah was eaten by a whale either. The Bible doesn't say there was an angel at the Garden of Eden, but a cherub, which was a mythical animal represented very frequently in the gardens of palaces throughout the Middle East. The Hebrew Bible doesn't say that Mary was a virgin, but a "young woman." ------------------------------------------------ There are things the Bible says and few people know it does. The Bible talks about a pantheon of gods that are subservient to Yahweh. And names God both as Yahweh and El. Is it the same god? I'm not sure. Asherah, the wife of Yahweh, is also mentioned, but the interpretation was presumably changed, as it's mentioned as a synonym for "a stick" in very obscure passages, when she is known to have been a goddess, as archaeology has shown. The stick was one of the symbols of the goddess. Back to Adam and Eve: There's at least one thing the Bible says twice in different (incompatible) ways: Ezechiel 28. Two prophecies, one of them against the king of Tyre. There you can see that the king of Tyre is expelled from the Garden of Eden, on account of his sins. The cherub also appears. Very similar legend; two different narrative uses. Who was expelled from the Garden of Eden, Adam and Eve or the king of Tyre? I'm not so sure. The authors of the Bible seem not to be either. Some scholars believe the Oracles against the king in Ezechiel 28 predate the Adam and Eve story in Genesis. ------------------------------------------------ There are things the Bible says that are taken from somewhere else: The Bible takes the story of Noah from The Epic of Gilgamesh, Utnapishtim , and adapts it to its own narrative needs. ------------------------------------------------ There are blatantly obvious things the Bible is silent about: Omri, big king of Samaria, was a very relevant character of the Assyrian domination period, but the Bible only mentions him in passing, as a baddie. The Bible also plays down the role of many other kings, like Manasseh, although he made Israel into an important olive oil factory and brought a period of peace, contrary to what Hezekiah, his father, did. ------------------------------------------------ And lastly, there are many things the Bible says that cannot be true. Josuah didn't conquer Jericho, as Kathleen Kenyon has proved. Jericho was uninhabited at the time. Plus the Egyptians were in control of Canaan and had the country strongly policed from Beit She'an. I don't believe God gave the law of gravity a suspension for some hours for the benefit of his people to the detriment of the Canaanites either. Plus the Canaanites and the Israelites were the same people: No difference in material culture or belief system, as Israel Finkelstein has shown. Abraham could not have possibly used camels. Camels were domesticated about 1000 years later.
  16. 2 points
    Hello Francis and welcome. The short answer is no Godel is not about statements we can prove, like yours, but statements we will miss out because we cannot derive them from our axioms. There is a really good introductory book by Raymond Smullyan about this called Forever Undecided Which is fun to read. I think a pdf may be available. Meanwhile here, what do you know about axiomatic structures in Mathematics?
  17. 2 points
    One of the best little pieces of comic theatre of all time was based on this. Here is wikipedia, you may be able to find a ytube of it. https://en.wikipedia.org/wiki/Class_sketch Yes indeed it is quite long, so I do not find it suprising there are some contentious points. The author is rather dismissive of the use of auxiliary verbs in general and the verb to be in particular. He claims that the verb to be is unneccessary and has almost withered away. Not so. Consider the travels of Marco Polo to China, a jourrney that took several years. Had he been English, Marco might have said, "I'm going to go to China next week." As he left Italy he might have said "I'm going to China". Two years later he was still "going to China", he had not by then arrived. One thing he would not have said would be "I go to China". The action was "imperfect" as it occupied an extended length of time and was still in progress during other events that might be spoken about. Imperfect here means that it is not complete at the time of utterance. A perfect action is complete from start to finish. An imperfect one may never be completed for some reason. Two other gripes with the article. Firstly no mention is made of the difference between spoken and written language when comparing English to other languages. It is my belief that this difference is one of the key factors as most languages are largely phonetic, English being the glaring exception. So it is emminently possible to learn and know many words and the associated grammar in English but not to be able to say or recognise them when spoken. Even English speakers sometimes have this trouble. Take the letter a as in car or cat. The big difference in the pronunciation of the 'a' leads to two difference pronunciations of the word castle, which confuses many. Secondly the thesis that it was the influence of the Vikings who did away with the manyfold word endings. One wonders why they did also do this with old French. Or why the endings were still there in middle English a couple of centuries after the end of the Viking era.
  18. 2 points
    When people say "Well, the dictionary says..." they obviously don't realize that a modern dictionary is a contemporary record of usage and not an authority. The people at large determine the usage in any given period.
  19. 2 points
    That is a really good question, because I still don't know what your position actually is. You seem to be saying that the concept of an evaporating Schwarzschild black hole is self-contradictory - which is trivially true, because Schwarzschild black holes are of course stationary by definition. But evaporating black holes aren't of the Schwarzschild kind, so where exactly is the issue? Then so you also seem to be saying that even ordinary Schwarzschild black holes are self-contradictory, because somehow event horizons can't exist? But I don't understand why you think this, because the reasons you give don't make any sense.
  20. 2 points
    I think it makes no sense to say that the vedas were twisted or not. They have grown organically. There are so many reasons for a text to change, especially when it originally was an oral tradition. Without having the 'original' how would you see that the texts changed? There are methods to find out which of the present versions we have are probably the oldest, but of course we can have no idea what the first written down version of the vedas were. And then there are many reasons why texts change over time, just to name a few: errors when copying the texts corrections of (language) errors authors putting in their ideas into the texts, in good or ill faith I only know a little about the history of Christian texts, which are of course not so old as the vedas, and also here already the problem exists that we do not know exactly what the original texts were. But we know copyists made errors, corrected errors, put in sentences or even complete stories, often because these copyists had a theological agenda to promote their version of Christianity. From some texts we know that there must have been more original texts, but they did not survive. With the vedas this will be worse, because they were orally passed to others for a much longer time. In Christianity, especially the new testament, there are at most only about 100 years between the oral tradition and the first written down versions we have (often less: the gospels were written till about 100 years, the earliest one probably only 30 years, after Jesus' death). With the vedas it is several millennia before they were written down.
  21. 2 points
    This is what I got from your posts: 1) A black hole and all the events in its interior can be described in the coordinates of an observer at infinity. 2) A Penrose diagram of an evaporating black hole shows that the formation and disappearance of a black hole have the same time coordinate. 3) If an event A has a coordinate time that is less than the coordinate time of an event B, then A happened before B (maybe even in B's past?). Problems with this: (1) The interior events do not have meaningful time coordinates for this observer. (2) If that's what the diagram really shows, then the coordinates used in that diagram can't be the same as for the observer in (1). (3) You're comparing coordinate times of events that have no causal connections, and their ordering is irrelevant, but you see "logic problems" by treating it as something physical.
  22. 2 points
    Really ? Cosmic rays enter the atmosphere billions of times, yet not a single micro BH has ever been detected. Maybe you can produce a citation of a detected micro BH. I can certainly post numerous citations of cosmic ray detections.
  23. 2 points
    Stu the cockatoo is new at the zoo...
  24. 2 points
    The issue that I see with this thread is that I'm proposing actual implementable changes. To the Police Unions and Hiring/training practices, for example. Then we start to work on the DAs who bring up unfair charges on minorities. Saying the problem is systemic ( your meaning CY ) means the whole justice system ( and more ) needs to change, from cops, all the way to the Supreme Court. And we both know that's not going to happen; so nothing will change. The higher up you go in the justice system, the more political it is. And with your polarized two party system, who would even propose such a change, and hope to get re-elected ? Myself, I don't see the point of self-flagellation, and saying "It's all whitey's or the system's fault, and not trying to do something about it. People are dying needlessly, and all I'm hearing is blaming, but no solutions.
  25. 2 points
    Where did this red herring come from? We’re not talking about all criminal activity, we’re talking about police, who are supposed to protect and serve the public, and who should be held to a higher standard. We’re also talking about violent behavior. That’s not an instance of excessive force. I was short of straw before but now I have a lifetime supply. Sure. But you had only proposed screening for white supremacy Yes. If they had not tolerated such behavior, you might say...
  26. 2 points
    They are NOT the exact same things. You are confusing the word "special" with the word "preferred". We don't laugh at the the idea of the Earth being in a special place, we laugh at the idea that the Earth might be in a preferred place. When you were but a wee child and your mother said you were "her special boy", she simply meant you held some significance for her. You were 'neat', or 'cool'. She wasn't implying that the universe was centered on you. Similarly, we live in a special time and place. We witnessed the first time humans detected gravity waves and the invention of the autostereogram. If we weren't at this location (on Earth) at this time, we could not have seen that with our own eyes. Unfortunately we did not exist at that special time when the four fundamental forces were combined, but we are lucky to live at the special time when all these superclusters can be detected. And that is really neat.
  27. 2 points
    Yes it helped and I got my answer.
  28. 2 points
    That's what I think. Art and/or symbolism certainly imply intelligence. But I would make the further qualification that first hints only too reasonably come later than the real thing. The excavations of Homo naledi (335,000–236,000 years ago) at the Rising Star cave in South Africa have shown that, very likely, a stray cousin of ours that looked very much like an upright ape and didn't use tools or made any kind of art, seemed to go to the trouble of carefully placing their dead in an almost inaccessible dead end of a cave where no other fossils of animals have been found. My suspicion is that some "human" attributes go farther back than we dare to postulate. Cautiousness is mandatory, of course.
  29. 2 points
    My earlier comments related specifically to Schwarzschild black holes - which are stationary, hence they don’t evaporate. Generalising this to the case of an evaporating black hole is not straightforward or trivial. Such black holes are called Vaidya black holes, and this represents an entirely different solution to the field equations, and thus a spacetime with a different geometry. While Schwarzschild is a vacuum solution, Vaidya is not, because now all of spacetime is filled with radiation, so we are no longer in a vacuum. Adding relative motion between observer and a Vaidya black hole does of course not yield the aforementioned Aichlburg-Sexl ultraboost, but some different metric, which I have not encountered in my studies. Like in the Schwarzschild case, that new metric would be related to the Vaidya metric by some coordinate transformation, but I suspect the transformation will be a lot more complex than in Schwarzschild spacetime, mostly due to the presence of off-diagonal terms in the metric tensor. I’m sure it can be done though, and probably has been, though a quick search does not immediately turn up anything. But the answer to your question will be “no” regardless, because in both cases we are in a curved spacetime, so you can’t naively use the transformation rules of SR. The total time dilation here has a kinetic component from relative motion, and a gravitational component from spacetime curvature. So the lifetime a specific observer calculates for the black hole will be subject not only to his relative speed, but also to the particulars of the geodesic he traces out (i.e. to the initial and boundary conditions of his motion), and where on this geodesic he is when he performs the calculation; so it will be some (probably quite complicated) function of his trajectory and the surface area of the horizon (which will itself be some complicated function, since the horizon is no longer spherical for such an observer). This is a common misunderstanding based on the fundamental error of using the wrong solution to the field equations for the scenario at hand. I know that countless papers have been published showing this calculation, but ultimately these results are not physically meaningful. If you naively go and consider free-fall observers in Schwarzschild spacetime, then yes, the maths will show you that they can’t detect Hawking radiation. However, evaporating black holes are by definition not Schwarzschild, so this point is moot. When done correctly using Vaidya spacetime, the free fall observer will definitely detect radiation (it is a non-vacuum spacetime after all!), just at a different temperature relative to other observers. The type of physical spacetime one is in is characterised by curvature invariants, which is something all observers always agree on, even if they use different coordinate charts to map that spacetime. Like I said, one must use the correct spacetime to model this scenario. How in-fall time is related to evaporation time of a black hole in Vaidya spacetime is a question I can’t answer off hand. It would likely depend on the initial mass of the black hole, its age (as calculated by the in-falling observer), and the in-fall geodesic. For solar-mass (at the time of in-fall) black holes though the lifetime of the black hole will be much longer than the length of most in-fall geodesics, by many orders of magnitude.
  30. 2 points
    Generally speaking, I am on your side. In this specific case, they made a comment where it is difficult to interpret it in any way that isn't racist: The first part of this comment implies that the people that Hitler deliberately committed genocide against don't get to count as "people". The second part is so facially false in its misrepresentation of basic history that it indicates the writer is either a troll or such a committed racist that they don't even care about the genocide itself. Either way, a forum setting is not going to convince them to change their ways. Part of the difference is that they did more than express distaste. They used that distaste to make derogatory claims about black culture as a whole, and to dismiss the protests without even engaging with the basic claims of the protests, with a strong implication that black people don't deserve to protest. On a side note: I strongly disagree with the implication that "disrespect for authority" is necessarily a problem. To a large extent, the protests are about the claim that that authority is being abused - and authority being abused should not be respected.
  31. 2 points
    Racism isn't about labels, it's about hate. Hate is an issue of emotion not intellect. As emotion, the afflicted may only be solved or remedied by therapy rather than by reasoned discussion as we may find in open forums like this. In this forum, we can intellectualize the causes and cures for hate but we can no more treat that condition via our online debates with racist than we can remotely remove a tumor. There's a reason why this science forum discourages visitors seeking medical advice. Similarly, there are reasons why hate filled sufferers are equally discouraged in this forum. They need help we can't render here.
  32. 2 points
    essereio has been permanently banned for repeated violations of rule 2.1.
  33. 2 points
    I assume you aren't making the final decision so don't take that responsibility. You should create a PowerPoint presentation referencing the various options that are available and present that to the other members of your team so an informed decision can be made. If you are uncomfortable doing so yourself I'm sure you can recruit a consultant on a temporary basis to do so.
  34. 2 points
    With the limited information available my answer will be very general. I would be cautious if someone provides detailed answers based on limited information. 10s of thousands can be a tiny or huge depending on the amount of data, how the traffic is clustered, response time requirements, processing required to create an answer, what standard services that are already available as services, API, micro services etc.
  35. 2 points
    Not sure what you mean by time being reactive. And I don't understand why that would mean it travels. I don't even understand what it would mean for time to "travel". 🤷‍♂️ No. Photons are massless. It has nothing to do with terminal velocity. Light always travels at the same speed. No. Photons do not have mass. And even if they did, it would not imply that space has drag. Nothing with mass can travel at the speed of light. No. Photons always travel at the speed of light. Which is why it takes them 8 minutes to get to Earth from the Sun. No.
  36. 2 points
    In mathematics the problem is the 'almost'. So no it makes no sense. In Physical Science then yes phrase may have value, for instance an 'almost infinite thermal reservoir' in Thermodynamics or 'almost infinite dilution' in Chemistry. In each physical case the phrase measn that the quantity concerned is so large compared to the change considered that the quantity is constant or unaffected by the change. This is just making use of one mathematical property of infinity that infinity plus or minus x is still infinity.
  37. 2 points
    Well, I'm not too sure what 'mild' in this context really means, but I'm certainly high functioning, and require no intervention or assistance to live a normal life. This is mostly because I have learned since childhood to mask my autistic traits to such a degree that most people won't be able to tell at first glance that I'm neurodivergent. In my case, I find it easy to express myself in written form; however, if we were in the same room, and I was asked to explain some GR concept verbally, then that would be much harder for me, especially if I didn't have time to prepare beforehand. And the subtleties and complexities of casual social situations will forever remain a mystery to me, even though I can outwardly play certain roles if necessary. This is a difficult subject, because the spectrum is so wide. Personally, I never thought of myself as having a disorder of any kind - I think of myself as neurodivergent. As being differently abled, rather than disabled. I consider it a gift, and if I was being reincarnated, and somehow given the choice, I would without a shadow of a doubt choose to be on the spectrum again, since for me the positives greatly outweigh the (nonetheless very real) challenges. I do recognise though that many others on the spectrum would disagree, since their autistic traits are more challenging for them, and they suffer from various comorbidities, such as ADHD and SPDs.
  38. 2 points
    At maximum height \[\boldsymbol{v}=0\] but \[\boldsymbol{a}\neq0\] Is that what's confusing you?
  39. 2 points
    Nice post +1, I'll just add, in my work with differently abled humans, a good way to think of the differences; if a bus runs into a group of people, one extreme is, OMG how many people were hurt, while the other is, what colour is the bus. The OMG's will never really understand the what colour's, and vice versa; all we can really hope is, we understand that there's a difference in all of us...
  40. 2 points
    If you get really good at setting expectations, you'll find it helps with everybody on the spectrum (which I suspect is broader than we think and may include a lot more of us). It may simply work on everyone. It's the equivalent of someone like Elizabeth Warren always having a plan. It allows people to make their own plans based on yours, and it's very comforting and satisfying, and makes folks feel great about following your lead. I recommend watching Hannah Gadsby's new Netflix comedy special Douglas if you can. She's been diagnosed with high-functioning autism, and she has this brilliant convention where she tells you EXACTLY how her standup show is going to unfold before she starts, in order to set your expectations as an audience member (I hope she continues this format in future shows). Then she does the show, and it's amazing how much funnier it is because you know what's coming. She also touches on several spectrum-related behaviors you should be aware of (beware the Puffer Fish). Thank you for taking the extra time, and also for recognizing that the way these beautiful minds work is just different, not abnormal. Your student appreciates it more than they're probably telling you.
  41. 2 points
    You're both welcome. A couple of things more. First, I just wanted to add that Fermi was no idiot, of course. But the assumptions he made date back to 1950. We know much more about planets now. Something we know now, for example, is that the Earth-Moon system is far from typical. The Moon is an unusually large satellite and has a rather bigger than normal stabilizing effect on the Earth's tilt. To the point that astronomers are starting to look upon the Earth-Moon system as a binary planetary system, rather than a standard planet and its small satellite or group of satellites. The huge tidal effect that the Moon has on the Earth is believed to have played a major part in the origin of life at least during the first billion years, stirring the chemicals dissolved in water and thus triggering volume reactions (much quicker and efficient) rather than surface effects. https://www.space.com/12464-earth-moon-unique-solar-system-universe.html Another factor is the presence of outer giants like Jupiter and Saturn, for billions of years playing the role of shuttles for asteroids from the Kuiper belt, etc. Water and amino acids in the asteroids are also thought to have been very important. In case any of these factors were found to be essential to the appearance of life, it could be a basis to estimate the number of solar systems in the Milky Way that satisfy similar conditions. Would other different sets of conditions be just as good, or maybe even better? I don't know. I don't know if anybody knows. Drake's equation came later than Fermi's argument (in 1961). Actually, I think Drake's equation is a more promising ground for estimating the chance of there being intelligent life forms, among other things, precisely because, although ambitious, it's a much less assuming parametrization of the probability, rather than an equation or a "closed" calculation. There is room for re-estimating the factors as we learn more about the phenomenology of galactic (or extra-galactic) solar systems. Plus the last factor is, if I'm not mistaken, the probability that a civilization will be able to send signals, rather than travel to Earth, which significantly increases the odds. Fermi was concerned with interstellar travel, AFAIK. The detection of signals with a message in them will probably be the first evidence, if there ever is one, of some form of intelligent life besides us in the universe, rather than the flight of UFOs. But here's the bad news, IMO: Take a look at this table with time gaps separating the appearance of new levels of organization: First prokaryotes (from Earth's formation): 1 billion years First eukaryotes (from prokaryotes): 800 million years First multicellular eukaryotic organisms (from single-celled eukaryotes): 2 billion years First intelligent life (from multicellular eukaryotes): 700 million years Average for the appearance of a new level of organization: 1.125 billion years Now suppose there's a planet out there with something like eukaryotes (cells with a nucleus). You're going to have to sit there waiting for 1.1 billion years for you to see anything interesting to happen if the above table is anything to go by. That's the problem.
  42. 2 points
    Perimeter is a one dimensional attribute, while area is two dimensional. IOW, you need one piece of information for one and two for the other. That allows for considerable ( infinite ) variation.
  43. 2 points
    Other people will give you much better answers (or provide more information). Have you looked at https://www.w3schools.com/php/php_arrays_multidimensional.asp (first link that came up, the language (PHP) does not matter to understand multi dimensional arrays)? An array contains a collection of elements, such as integers, strings and booleans. Let's say we have: Array = [1,2,3,4] Then Array[0] = 1 and Array[2] = 3 A multidimensional array contains arrays as its elements. MultiDimensionalArray = [ [1,2,3,4], [5,6,7,8], [9,10] ] (this array has 2 dimensions) Then the first position of this MultiDimensionalArray will be MultiDimensionalArray[0] = [1,2,3,4] if we want to access one of the numbers in this array, we would specify a second dimension: MultiDimensionalArray[0][1] = 2. Does this help? Other people will be able to help you further, but I highly recommend reading/searching about these things yourself first and explain the parts that you do not understand, that way people can help you more and you will learn faster. Good luck!
  44. 2 points
    Issac Asimov wrote an article about this called The Relativity of Wrong We once thought the world was round, and then we corrected that to it being a sphere. That was further corrected to being an oblate spheroid, and later, further refinements were made. The point is that this represents a series of refinements, each step being a smaller adjustment to the previous. When it comes to the Earth's shape, we will never again see such a large shift as between flat Earth and round Earth. Just because we once thought it was flat and now believe it to be round doesn't mean that some day we will conclude that is is shaped like a tetrahedron. Likewise, any correction to Relativity would still need to fit our present observations of the universe, which do indicate that c is a natural speed limit built into the universe. While we can never absolutely be sure that there might not be a way around this, there is no reason to believe that this will ever be the case. It is entirely possible( maybe even likely) that c is an insurmountable barrier. It is important not to let what you would prefer to be true to influence what you believe to the be true. As pleased as I would be if it turned out that the universe was populated with advanced civilizations and that FTL travel between star systems was practical, I can't bring myself to believe it to be true given the lack of any credible evidence for it.
  45. 2 points
    Can we please acknowledge that increased availability of guns in the US does add risk to officers during every police interaction, but that being black also adds risk to ones life during every police interaction, and that neither of these things justify the way police are treating suspects after they’re already in custody or the way they’re marching on and being violent with peaceful protesters exercising their constitutionally protected rights? Surely, we can move on now... Please don’t make me write another horrible run-on sentence one that
  46. 2 points
    OK so studying Thermodynamics is like watching a good play, film or reading a good book. The actors are introduced and a lttle bit of information is given about them. Enough to know who they are some of their relationship to the other actors and why the audience should be interested in them. As the play unfolds more information is revealed. In the same way, in Thermodynamics we first learn about the main quantities, their relationship to the other main quantities and why we might be interested in them. Now sonmeone who is just starting Thermodynamics is at the beginning of the play. He has learned about Boyle's Law P1V1 = P2 V2 (1662) Charles Law V1T2 =V2T1 (1780) Avogadros Gas Law PV = nRT (1812) Something about energy (Young 1802) Something about 'work' as the force times distance Something about 'heat' being mass times specific heat So he is in the same position of scientists in the first half of the 19th century that is 50 years before the first version of the First Law of Thermodynamics. So to get to the First Law some study needs to be carried out filling in the gaps and strengthening the definitions of these variables. Additionally he will need to learn some of the structure of Thermodynamics. In particular what is a system and what is a process and what is a state and a state variable. Once these ideas have been absorbed (they are all important) additional details can be studied and understood. Such the meaning of isolated, open, closed and flow systems. The difference between reversible and irreversible processes The difference between intensive and extensive variables and so on. So our student learns about different types of energy, including something called internal energy (symbol here U) and arrives at the First Law This connects the State Variable: Internal Energy to two variables heat and work. These are not system properties but variables that connect the system to its surroundings. U2 - U1 = q + w But he notices that whilst q and w can easily be measured or directly calculated from measurable variables , U cannot be directly measured. Furthermore the other state variables already mentioned P, V and T can also be easily measured and the equations stated allow calculation of w. So Internal Energy is the first quantity he has come across that he cannot directly measure. However he realises that it is a very important quantity since it is like a bank balance which = money in - money out. This was so important to early engineers in the development of steam engines that they invented a special diagram called an indicator diagram to show the work part - w. This work is the area under a P - V graph or plot And they even invented a mechanism to fix to steam engines called an 'indicator', which is where the name came from. Now you will have noticed by now that there are three measurable connected variables, P, V and T and that we have only used one of them. So guess what? Someone said, "Wouldn't it be nice if we had another variable we could plot against temperature (the unused variable) to calculate q in the same way ?" Bingo there you have it Entropy as Clausius named it. I have drawn the indicator diagram for Temperature v Entropy side by side with the one for Pressure v Volume so you it can be seen that they have the same format. Entropy is not some mystical property. It is simply the thing we need to multiply temperature by to get a particular energy in this case the heat exchanged across the system boundary. Again we cannot directly measure entropy, but simple equations exist to calculate it from easily measurable ones. Now that we are not frightened of it we can study more details and proceed to the next level of the development of Thermodynamics. Also if there are any details in the foregoing that are unclear please ask.
  47. 2 points
    Some good comments triggered ideas for a new post! True.I guess that if any single one name on your list had not been around it would maybe have slowed down development but modern IT would still emerge. And the other way around, no single individual could have created everything needed to have modern IT. Teams, collaborations and/or building on previous work is required. Exelent! Had forgotten about Shannon. I guess a comparison of Turing & Shannon and their contribution to computer & Internet could be done by looking at a pair of their important papers (emphasis mine) Turing - "On Computable Numbers, with an Application to the Entscheidungsproblem" Shannon - "A Mathematical Theory of Communication" Would it be too bold to claim that once the concept for computing machines was created it was inevitable that some scientists or engineer will try to connect them? It seems there are similar cases for other historical inventions. Here are analogies (slightly of topic) to illustrate why I think @Strange's comment seemed good an applicable for a more general case computer - networks, Internet car - network of roads with gas stations Ship - harbours and support Plane - airports within reach Are there innovations that fits on the left side where there are no concepts matching the right side? Maybe we close to that point for space flight. There are working rockets but yet no established way of maintaining space travel between earth and other celestial bodies. I do not know the full story but I've had to consider converting to and from EBCDIC in recent projects (at least two after 2012). AFAIK there's EBCDIC in use in contemporary IBM System z. *) Not writing this to try to remove any credit from Turing (or other great contributors), it was after all Turing who wrote "On Computable Numbers, with an Application to the Entscheidungsproblem". It just means to say that the groundwork done was available so others (one or many in collaboration) could possibly have taken the same steps.
  48. 2 points
    You know what? It's pretty clear that you're here to push ugly as an agenda. I'm perfectly OK with your shitty personal outlook, and it's not my business why you disparage so many people, but we're not the place for your hate. You don't listen to the science, you ignore any detractors, and you attract other shitty people to the site. I don't say this a lot, but I just don't want you hear anymore. I've been defending your right to an opposing stance because it's good for others to practice standing up to bigotry and racism, but now I'm going to recommend you be banned. You're not healthy for a reasoning person to deal with, and if you aren't getting paid to be a shit-stirrer, you should probably look into that.
  49. 2 points
    A question about a sign convention that leads to a lot of confusion. This is not the only instance multiple sign conventions in Science. In this case it is a result of History. Thermodynamics was originally developed by physical scientists and engineers. They were concerned with making machines (steam engines) for the industrial revolution. Steam engines are heat engines. That is they thought in terms of input (heat in the form of fuel) and output (work). Both of these were thought of as 'naturally being' positive quantities. So they wrote their version of the Law of Conservation of Energy (The First Law of Thermodynamics) as ΔU = q - w. Chemists came to the scene from a different point of view. They wanted all forms of energy to have the same sign, whichever side of the conservation appearance they appeared so they could present the equation as a sum on both sides of the equation. So they wrote their equation as ΔU = q + w. By then it was also realised that, although all the terms are energies, there is a difference between ΔU , which is a state variable of the system, and q and w which are exchange variables of the energies crossing the system boundary. So they tidied up by stating that all energies crossing the boundary from the system to the surroundings are negative and all energies passing from the surroundings to the system are positive. Now they could add them up, move them about in equations and between equations in other parts of Science in a consistent manner. It is an improved system But it shows the importance of knowing the sign convention in use and the equations that go with it. This last remark also applies to other such instances of multiple conventions such as those in Electricity, Elasticity and elsewhere.
  50. 2 points
    You beat me to it. I was going to post this under the title "Good things can come in small packages". The annual death toll from malaria runs just under half a million. Great to see a potential solution. Some more information on malaria in general here. (It's from the WHO, so Trump supporters should look away now.)
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