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  1. 5 points
    We can all agree that violence on either side is wrong and should be avoided. What we seemingly cannot agree upon is why so many feel the need to engage in whataboutism and mention a protest in favor of following our laws done in Portland with an insurrection on our democracy itself trying to dismantle our laws in Washington DC. Whether intentionally or not, this suggests an equivalence between the events which is false and which only distracts us from dealing with each separately, appropriately, and in accordance with our laws. Person A: Climate change is a major problem. Person B: What about covid?! That’s a problem, too. Me: Both are. They’re not equivalent. They’re not mutually exclusive. We must deal with both at once. Walk and chew bubble gum. Simply replace climate and covid with DC and Portland. This isn’t exactly rocket science.
  2. 4 points
    If you expose frozen chips to air, more moisture will condense on the chips from it. Every ml of water condensed from the air adds 1g to the chips.. The chips, after baking, lose moisture, which concentrates the calories, so if you now weigh 100g of baked chips there are more calories.
  3. 3 points
  4. 3 points
    Hasn't the OP just proved (in a rather long-winded way) that the inner product of four acceleration and four velocity is zero and, hence, that if the four velocity is \( V^t=c \), \( V^x=V^y=V^z=0 \) then the four acceleration has \( A^t=0 \) (and that the four acceleration is spacelike if it isn't zero)? They just appear not to have noticed that in general \( \frac{dA^t}{d\tau} \neq 0 \), so the conclusion that \( \gamma=\mathrm{const} \) does not follow. The fact that a function is instantaneously zero does not mean that either its integral or its derivative need be zero. To me, the argument looks similar to saying that in circular motion in the x,y plane there comes a point where \( (v_x,v_y)=(v,0) \), and at that point \( a_x=0 \), and hence \( v_x \) can never change and circular motion is impossible. Obviously that's nonsense, and realising that \( \frac{da_x}{dt}\neq 0 \) is a part of understanding why it's nonsense.
  5. 2 points
    @MigL Hope you don't mind, but I'm gonna take our PM exchange into the thread here (keeping your point unquoted, will share my reply here instead). We're still talking passed each other. While I said I can understand the underlying motivations, I have NOT made excuses for violence perpetrated in the name of BLM. There is violence happening as part of the movement. I don't agree with it. I'm not making excuses for it. I'm not pretending it doesn't exist. My primary point has been that the violence is the extreme outlier in BLM. It's marginal. It's super rare. It's uncommon. It's been inflated as a rightwing talking point. There has been violence. Some of it came from BLM protestors unprovoked. Some was provoked by police being too heavy handed and hitting peaceful protestors with clubs and firing tear gas into the faces of unarmed grandmothers. Some of it was rightwing extremists engaged in false flag operations. My primary point has been that it's a mistake to focus so much energy there... another example of of our white privilege. In these threads, people keep saying "it's horrible that another innocent black man was killed by another cop in another city, but destroying property has to stop." Yeah, okay... but try saying instead, "It's horrible that property is being destroyed, but these continued killings of innocent black men by police has to stop." See the difference? The pushback is saying you're prioritizing the wrong part... not that the violence is acceptable because it was done by "my team." Focusing so much on the tiny amounts of violence happening at the extreme margins of the movement distracts us from dealing with the issues motivating the movement itself. I'm not making excuses for the violence. I'm saying it's so rare that bringing up so often suggests an agenda, whether you're conscious of it or not. Please stop saying I support the violence. Please stop suggesting I'm making excuses for it. I'm simply not.
  6. 2 points
    Two weeks is more accurate. Because of libration (a wobbling motion) of the moon we can, over time, see about 59% of the lunar surface. Ice is confirmed in craters at the lunar south pole. The presence of this water is the primary reason this is targeted for visits and base contruction in NASA's Artemis human landing program.
  7. 2 points
    There is no constantly dark or light side
  8. 2 points
    This claim is not meaningless it is just plain wrong and arises from a basic misunderstanding of celestial navigation with a sextant, where the term 'arc of the sun or arc of other celestial body arises' It is not the altitude (which is the arc measured in degrees) but the plane from which is it is reckoned that changes with altitude and with altitude and other factors which have to be corrected for. This plane is called the true horizon and is not directly available to the observer so various 'observable horizons' are employed - marine navigators use the water horizon, aerial navigators use an 'artificial horizon' (yes aircraft still carry sextants for emergency navigation when the more modern electronic systems are broken). Clearly these calculations are correct since navigators do arrive at their destinations using them. The calculations and sight corrections can be quite complicated, here is a simple explanation. https://knowledgeofsea.com/correction-to-sextant-altitudes/
  9. 2 points
  10. 2 points
    Since that is merely a disguised form of your (4), all you are saying is that a tensor that is antisymmetric is antisymmetric. Taking six equations to get to a tautology seems excessive, but isn't wrong. (7) still does not follow from (6). I already gave an example of a non-zero Riemann tensor that satisfies (6). All you've done is shown that a zero tensor is not inconsistent with some of the properties of the Riemann. I have no idea which comment you are referring to.
  11. 2 points
    Oh, but that's not because it's much worse than I pointed out. It's because it's bound to get worse if you make a notational blunder of that magnitude. If you want to discuss anything in terms of a 2-index tensor being diagonal in a certain point --o perhaps everywhere?, the OP didn't tell us--, you could arrange to distinguish this by using Latin capital letters, e.g., \[A^{BB}=\frac{\partial x^{B}}{\partial\bar{x}^{\mu}}\frac{\partial x^{B}}{\partial\bar{x}^{\nu}}\bar{A}^{\mu\nu}\] Meaning, \[A^{00}=\frac{\partial x^{0}}{\partial\bar{x}^{\mu}}\frac{\partial x^{0}}{\partial\bar{x}^{\nu}}\bar{A}^{\mu\nu}\] \[A^{11}=\frac{\partial x^{1}}{\partial\bar{x}^{\mu}}\frac{\partial x^{1}}{\partial\bar{x}^{\nu}}\bar{A}^{\mu\nu}\] etc. So it can be done, but not the way the OP is doing it. Not that it's very useful to consider tensors as objects that are or aren't diagonal in any invariant geometrical sense, as they are objects referred to two different bases. Absolutely. When I'm doing maths and I get to such surprising results as "the whole of tensor algebra/calculus is bonkers, because all tensors are null" --or something like that, I'm not completely sure if that's the point--, I try to retrace my steps and, sure enough, I can spot a silly mistake. The last thing that would cross my mind is to highlight the "result" and announce to the world, "hey, I've found an enigma".
  12. 2 points
    Again, this essentially comes down to the difference between topology and geometry. When we say the universe is spatially infinite, what we actually mean by this are three things: 1. Spacetime has no boundary 2. For any arbitrary pair of (spatial) points {A,B}, there exists another pair of points {C,D} the spatial separation of which is greater than that of {A,B}. 3. Spacetime is singly connected Herein, (2) actually implies (1), but I’m listing them separately for added clarity. These three conditions are true at all times t>0, including immediately after the BB, and at the present time; so this does not change, and it - roughly - represents an aspect of the global topology of the universe. On the other hand, when we say that the universe was singular at the BB, what we mean is that as t -> 0, the separation between any pair of arbitrarily chosen spatial points will tend towards zero; and it means that no geodesics can be extended beyond the hyperslice t=0, without them extending into the future again (so this is a bit like a “pole” in spacetime). It does not really mean - at the danger of straying into the disciplines of metaphysics and philosophy here - that only a single point existed; the spacetime manifold was already there in some sense, but there was no notion of “separation between events” yet. So it’s the geometry that was singular, but not necessarily the topology. Of course, this is the purely classical picture, it does not account for any quantum effects (which will likely change the story quite radically).
  13. 2 points
    That's not what MigL claimed though. He was suggesting that iNow was unfairly dismissing valid claims of Democratic/Progressive mis-steps. You'll need to show not that iNow said "false equivalency" but that he did it simply as a dismissal of a valid criticism. @MigL - I know you did not mention me specifically as someone who was dismissive of comments regarding poor 'Progressive' behavior but if you think I am guilty I'd honestly like to hear so. I don't think I am but of course it is sometimes difficult see ones own flaws.
  14. 2 points
    Having taught math successfully in Junior High and High school I though I would have a lot of great examples for you-- but on further reflection realized my best ones were not something that could be generalized. I had the greatest success when I could connect the math lesson to the students' experiences. For example, in my rural area the vast majority of the students have experience with guns and many also have reloaders in their families (people who make their own ammunition). When I first tried to teach statistics I got blank looks from many students, So that weekend I took my test equipment out to the rifle range and measured velocities of 10 rounds of ammo I had built. On Monday I put the data up on the screen and asked the students if the load I had developed was consistent enough for hunting. This lead to a successful lengthy discussion and the development of the idea of mean and standard deviation. The lesson I learned and applied from then on is this: The goal is not so much to make the students think differently, but rather to create a use for the math knowledge in a way that connects to their experiences. I can think back to lots of examples of good teaching tricks, but realize they are were specific to a certain student or group of students. Not much help to what you want.
  15. 2 points
    OK so I will try to discuss communication of Mathematics, rather than principle of Mathematics. I can't see where you have mentioned any basic Maths, computer code is hardly basic if it is indeed Maths at all. However I beg to disagree with your outright rejection of History. Perhaps your experience of History at school was of the sort "History is a list of dates of battles, deaths and treaties to be learned by heart and regurgitated for the examiner". History actually offers many lessons for those that care to peer into them. Not the least being concerning computer code. Coding languages have a very short lifetime; I have seen them come and go and stopped bothering to learn the new fashion decades ago now so I have little idea of the meaning of your example. The last serious program I wrote was PFortran TRIP (Trigonometric Intersection Program). British schools went through a phase of demanding that every child learn 'programming'. This mean resources were wasted on teaching first, different versions of BASIC, then PASCAL, then some early scripting. None of which are current today. History also tells us that the basic mathematical operation of counting is at least as old as writing, probably much older. Now schools used to teach using the old fashioned balance scales. Good schools would actually get the pupils to set up pretend shops acting as customers and shoperkeeps. They would weigh out amounts of materials, say potatoes or sand and also practice with pretend money. This allowed a method of counting by the custemr presenting say a half crown coin and the shopkeeper saying That's one and fivepence and then making up the one and fivepence to half a crown with coins to provide the change. Instant communication of arithmetic and fractions. For those who were a dunce at school arithmetic there was the joke, you say you can't do maths but you can still instantly recognise that you need a treble eighteen, double top and single nineteen to finish in a darts match when you are on 113! Would these be the sorts of examples you are looking for ?
  16. 2 points
    The improvement comes from spin squeezing; one partner of the entanglement has much less uncertainty in a particular state than the other, and this gets them below the standard quantum limit. They tout the improvement in the measurement but not the actual stability, which is more than an order of magnitude worse than the better optical frequency standards. That’s not to say that they won’t get there, though. https://arxiv.org/pdf/2006.07501.pdf I’d put my money on the latter being closer to the truth
  17. 2 points
    Entanglement conveys no information. The sources of this pop article seem not to know that. Saplakoglu writes: It just doesn't work like this. A pair of particles unmeasured are not meaningfully in any state at all. If measured, they're not entangled. Some logical fails follow: No, it is not at all like placing 100 coins with 50/50 mix. That implies a measurement already taken. It's more like having 100 unknown coins and measuring 99 of them gives zero clue as to what the last one will be. Entanglement is like slicing 100 coins in half and sending the 100 halves to Pluto. Now if you count the halves here on Earth, you know what the Pluto guy will count if he ever looks at them. Nevertheless, the Pluto guy will have no idea what the last one will be if he hasn't received a message from Earth about the expected totals. I'm saying that either this 'Vuletić and his team' are complete fools, or their suggestions are being completely misrepresented by this Saplakoglu pop-science article writer. What I suspect is going on is having 50 coins split in half and all put on the table. Then, without measuring any of them, you know ahead of time that it's a 50/50 split. Nobody is carrying any of the coins elsewhere, and somehow having them entangled in pairs like that makes some kind of measurement more stable on average, thus allowing construction of a better clock. I'm guessing. The author of the article doesn't seem to comprehend the concepts involved.
  18. 2 points
    (7) does not follow from (6). The term in square brackets in (6) is symmetric in \( \alpha \) and \( \beta \), so (6) is satisfied by any arbitrary four-index tensor \( R_{\alpha\beta\gamma\delta} \) (not just the Riemann tensor) as long as it is antisymmetric in \( \alpha \) and \( \beta \). This is not surprising, since (6) is nothing more than a restatement of (4), which itself is nothing more than a statement that \( R \) is antisymmetric in its first two indices (true of the Riemann, but also of a great many other tensors). It certainly does not follow that all components of the Riemann tensor (or any other arbitrary four index tensor antisymmetric in its first two indices) are zero, as can be verified by (for example) calculating the Riemann tensor for the Schwarzschild metric and confirming that (6) is satisfied for at least one choice of \( \gamma \) and \( \delta \) for which at least some of the \( R_{\alpha\beta\gamma\delta} \) are non-zero. E.g: pick \( \gamma=r, \delta=t \). The non-zero \( R_{\alpha\beta r t} \) in (+---) signature Schwarzschild coordinates are \( R_{trrt}=2m/r^3 \) and \(R_{rtrt}=-2m/r^3 \). Thus (6) expands to \[ R_{trrt}(g^{t\mu}g^{r\nu}+g^{r\mu}g^{t\nu})+R_{rtrt}(g^{r\mu}g^{t\nu}+g^{t\mu}g^{r\nu})=\frac{2m}{r^3}(g^{t\mu}g^{r\nu}+g^{r\mu}g^{t\nu}-g^{r\mu}g^{t\nu}-g^{t\mu}g^{r\nu}) \]The term in brackets on the right hand side is clearly zero, so (6) is satisfied even though the Riemann tensor is clearly not zero.
  19. 2 points
  20. 2 points
    Sounds like a stroboscopic effect. Have you tried it in natural or incandescent light? A spinning ring/disk will not reverse direction, but the spin goes anti-clockwise and the precession of the primary axis turns clockwise and the latter becomes more noticeable as the spin flattens.
  21. 2 points
    Lest we forget https://twitter.com/i/status/1324078979775684608
  22. 1 point
    Haven't seen this type of behavior since ( video clips of ) the late 60s. Seems violent protest is the new normal for American society. This past year has seen an insurrection on the elected Government of the Country, as well as a Summer of violent protests against authority/Judicial system, while cities were taken over, and held, by unlawful protesters. D Trump just lit the fuse ( or recognized the flaw ), it can't all be blamed on him; this is uncharacteristic behavior for the American people, on both sides of the political spectrum. Does the end justify the means now? Is violence and destruction warranted when you think your cause is just ? Whatever happened to reasoning and discourse ? Has it been replaced by emotional response ? You guys better tone it down, before you actually tear your country apart ( remember 1861 ? )
  23. 1 point
    This is where my head was UNTIL I read that previous post of yours. “Nah, they were just there like at a rally... sure, they doubt the election results, but whatever. They’re just regular old Tom, Dick, and Sally’s out holding signs and taking photos.” But you made a point that gave me pause... that made me view things differently. Majority of them DID want to overturn a free and fair election, to throw away votes they didn’t like, and circumvent the process. That in itself is a type of sedition. It’s a desire to overthrow our democratic principles and our republic. Sure, everyone exists along a spectrum and some were more aggressive/extreme than others who were meek and mild, but NONE of them were there supporting our legal processes or allowing the justice system to sort through the claims of fraud. The sincerity of their beliefs isn’t relevant. They felt they knew better than those in charge and were acting like vigilantes who desired to replace the actual election results with their own personally preferred winner. In short, they were trying to overthrow our government. That’s a well made point I can’t simply ignore or dismiss. Dude, I’m an experienced wood worker now. I wear safety glasses. No splinters in these eyes. Matthew 13:13 Therefore I speak to them in parables: because they seeing see not; and hearing they hear not, neither do they understand
  24. 1 point
    Interesting but somewhat confusing. You want a differentiation between the mathematical description, and actual, physical space. You have stated we have the mathematical description, but haven't yet tackled what we mean by actual, physical space. IOW, we have the model, but what is the actual reality ? ( and Dad says we don't know, which you agree is valid ) I would assume, as a scientist, you know how science works. We build models ( mathematical models, not toys ) and test them against reality to find their limited areas of applicability. The only model that is 100% applicable is the reality itself. I have to ask, how else would you model actual, physical space, if not mathematically ??
  25. 1 point
    actually I have exactly 15 questions. I've done 10 of them, but I couldn't understand them and that's why I found this place. Maybe I expected the people here to understand them and show me a solution. You may have scolded or humiliated in your own way, but there was no need to humiliate that much because I uploaded it with an incomplete explanation. I'm sure more well-intentioned people will come across. have a nice day. actually I have exactly 15 questions. I've done 10 of them, but I couldn't understand them and that's why I found this place. Maybe I expected the people here to understand them and show me a solution. You may have scolded or humiliated in your own way, but there was no need to humiliate that much because I uploaded it with an incomplete explanation. I'm sure more well-intentioned people will come across. have a nice day.
  26. 1 point
    As a lay person with an interest in science and the scientific methodology, my perhaps simplistic view is as follows....Space is what exists between you and me, or between the planets and their stars. Time is what stops everything from happening together and the means by which the intervals between sequential events are measured. Spacetime is the four dimensional framework against which we locate and calculate events. The concept of spacetime follows from fact that the speed of light, "c," is constant and does not vary with the motion of the emitter or the observer. It is essentially a description of reality common for all observers, while at the same time, the measured Intervals of space and time when considered separately will vary between observers and different frames of references. Gravity of course as GR tells us, is the geometry of spacetime in the presence of mass/energy. All are essentially real: Space is expanding and the source of what we know as Dark Energy. Time is essentially interchangeable with space and is a variable quantity. Spacetime can be bent, warped, curved, lensed in the presence of mass. Any errors, alterations or corrections? Please be gentle with me. 😜
  27. 1 point
    I'm no expert either, so be my guest. And of course it would be nice that some of the local experts can give us a hand. Yes, DNA does get old. That's at the basis of cellular aging, and thereby the organism's aging itself, AFAIK. The replication mechanism is some kind of bi-directional zip assembly, so it's always imprecise at the ends. In one direction the replication process is very smooth, because the initial fragment (RNA primer) and the DNA polymerase work in the 5' to 3' direction, but in the opposite strand, primer and polymerase are forced to work against the uncoiling of the double strand, so it must interrupt and restart the copying work over and over again --the so-called Okazaki fragments. That's why there's always a mismatch at the end. Eukaryotes use a meaningless[?] chunk of DNA at the end --telomere-- which is partially replenished with every replication process, to kind of delay this ongoing degrading of the information. Also, as you point out, different cells down the line of cellular development, have different adjustments to their particular function. Red blood cells being the perfect examples of cells that will never go back to be able to produce anything in the way of stem-cells or higher-potent cells, because they've completely lost their DNA. Other extremes are neurons and cells from the digestive lining. The average life of the latter is, if I remember correctly, 48 to 72 hours. And neurons, because they never get replenished by sister cells mitotically splitting. Although new neurons do appear directly from stem cells, especially in the hippocampus*. Also, they retain some ability to reconnect, or change connections. That's about the summary of what I know. * Google search: "newborn neurons in hippocampus and olfactory bulb"
  28. 1 point
    Dr. Yamagishi and his team came to this conclusion by placing dried Deinococcus colonies on display panels outside the ISS. Samples of various thicknesses were exposed to the space environment for one, two, or three years, and then tested for their survival. Three years later, the researchers found that all colonies larger than 0.5 mm had partially survived in space. Observations show that although the bacteria on the surface of the aggregate died, it created a protective layer for the bacteria underneath, ensuring the survival of the colony. Using survival data after one, two, and three years of exposure, the researchers calculated that a granule greater than 0.5 mm thick could live 15 to 45 years on the ISS, thus proving the possibility of natural interplanetary transfer of microbial life that would otherwise called panspermia.
  29. 1 point
    Cyanoacrylate adhesive ( superglue ) is often used to 'seal' open wounds, where stitches might be too obtrusive. Doctors don't seem to be worried about absorption and toxicity. And superglue might keep your hairpiece on for months at a time. Better yet, shave your head and grow a beard.
  30. 1 point
    But the sister cells are just as old. Excepting cells that are manufactured (*), all bad (damaged, stressed) cells are replaced by mitosis of the remaining ones, all of which are essentially as old as you are. Maybe I'm wrong about that. Hardly an expert here. The DNA is also replicated this way, not manufactured from scratch, so all the DNA is effectively as old as you are,. Neurons can't just split since their connections cannot be reproduced, so they're intended to exist without replacement after their initial allotment is complete some months after birth. * Blood is a nice example of manufactured cells. Red blood contains no DNA and cannot reproduce by mitosis. They're short lived (1/3 year?) and manufactured continuously by non-blood cells.
  31. 1 point
    Anyone wish to own up ? https://www.bbc.co.uk/news/business-55738540
  32. 1 point
    New User here. Hi everyone. Please advise me where to go and what is appropriate, my apologies in advance for getting it wrong so far. 1. Thanks for pinning this post to the top of the board, it seems like a good one for newbies to start with. 2. It would help if the original creator(s) posted an update, so that we could see what the article looks like after 4 years of comments and editing. I've only had a scan through all the comments and that took a whole day. 3. Are you sure people often ask "What is space made of"? Have you got any surveys or other evidence for that? In my limited experience, most are happy to assume it's an empty vaccum. However, I do agree that people are quicky and frequently mis-lead into thinking that space is a stretchy fabric. I also agree with many of the later comments about quantum foam and vaccum energy that you could try to incorporate into your definition of space. If you are determined to incorporate QFT then I suppose spacetime does have to have fields in it. The problem is being certain that you have covered everything in your attempt to say what space is made of or even what mathematical objects must be supported and exist in space. There is almost no way of future-proofing the idea. Early General Relativity only really considered simple particle theories. It's unlikely anyone knew that anything like QFT, dark energy or vaccum energy could be added later. It's amazing that GR still seems to hold so well given that we have incorporated so much more into it than it was originally designed to model and we would be extremely optimistic to assume that nothing more will ever be added. As a consequence, I suspect the original creator would be better off not trying to tell people what space is actually made of - but instead focuses on what is the least amount of structure required for GR. Therefore, his/her definitions of spacetime as a (pseudo) metric space seem the better way to go. It is an ambitious target to try and describe all the (intangible) objects, like fields, that may be inferred or required to exist in space.
  33. 1 point
    If I may comment on just this bit, our moon is tidal locked meaning that one side of the moon always faces Earth and the other side always faces away from Earth. Both sides do receive sun exposure amid this locked rotation. The "dark side" of our moon is not a reference to its level of luminosity but rather to its unobservable position relative Earth.
  34. 1 point
    I've mentioned this before in another Flat Earther thread, but in Junior High in the early seventies I had a history prof that was a "flat earther". He never admitted he didn't believe it, but seemed to be using it as a teaching tool to be skeptical about accepted facts. The class had fun with it. The reason he gave that a boat disappeared over the horizon was that the light was affected by gravity so the hull of the ship disappeared first then superstructure due to distance. We came up with our own reasons that "proved" the Earth was flat and argued both sides. I'm not sure why anyone takes them seriously outside of the entertainment value.
  35. 1 point
    An alternative proof from direct Taylor expansion in the metric coefficients and counting how many parameters are left that I cannot set to zero by changing the coordinate system: https://www.youtube.com/watch?v=gf-G4QiAHLY&list=PLaNkJORnlhZnwjIXnOHrX50FEyoyiTh4o&index=5 Those must coincide with the number of independent components of the Riemann. \( \frac{1}{12}n^2\left(n^2-1\right) \) Uses Young tableaux, which allows you to count free parameters very easily.
  36. 1 point
    This doesn’t make any sense. The apparent motion of the sun through the sky in the course of a day is due to Earth’s rotation, not due to relative motion between Sun and Earth. So the Sun-Earth distance does not come into this at all. The issue of course is that Flat Earth rejects the notion of a rotating planet, so pointing this out will just result in hand-waving dismissal. My advice: don’t bother. I’ve been there too, and all it ever resulted in was unnecessary grief. That particular community rejects not only basic scientific observations (such as gravity e.g.), but even the very scientific method itself; there simply isn’t any common ground to base a meaningful debate on.
  37. 1 point
    All you have done is repeat what you had already stated, you did not actually address any of the points raised.
  38. 1 point
    Is there any case where you would consider employing violence against the State justified? You have blacks being killed for no reason in their own homes by the 'lawful authorities' on the one hand and a group wanting to overturn a democratic election and hang a fellow conservative on the other.
  39. 1 point
    If you had stopped there, I would have given you a +1 also. Unfortunately you misguidedly went on about 'whataboutism', when some of you guys are the biggest offenders. Anytime JC or I ( and a few others ) mention mis-steps by American progressives/Democrats, your first answer ( as well as Swansont, Phi, and a few others ) is always "But the Republicans do much much worse; they can't even be compared. So why are you even bringing it up ?" If you can't think of the times you've done this, I can post numerous examples/quotes. If that is your attitude, it is going to be a boring 4 years in the Politics Forum. Everytime someone criticized the new Government, your first response will be "But D Trump did much worse during his Presidency." And then I'm told I have biases
  40. 1 point
    Neutrinos take away ~10MeV from a typical fission of U-235
  41. 1 point
  42. 1 point
    It depends on the nuclei. Uranium 235 will undergo fission from a thermal (slow) neutron but Uranium 238 will undergo fission from a fast neutron.
  43. 1 point
    The answer for your initial question is:
  44. 1 point
    Quite possibly so! To be honest, I am still struggling to understand what it is the OP is actually trying to do. It also seems he has abandoned this thread, just like all the other ones he opened before this. Indeed - very well summarised! +1
  45. 1 point
    Well, they are useful to represent the perspective of a stationary observer at infinity. The crucial point to realise is that that is the only situation where measurements of space and time made in Schwarzschild coordinates actually coincide with what physically happens, since such measurements are always purely local in curved spacetimes. Anywhere else other than for a stationary observer at infinity, Schwarzschild coordinates are only a bookkeeping device, but they do not necessarily reflect what actually happens there, locally speaking. They also don’t cover the entirety of the spacetime. Many students of GR either do not understand this, or refuse to acknowledge it, since it goes against Newtonian intuition. The unfortunate result is all manner of misconceptions and misunderstandings. So you have good reason to mistrust Schwarzschild coordinates - they can be useful in certain circumstances, but they are also dangerous if not understood correctly. I think the only reason why pretty much every GR text uses them is because they are algebraically simple.
  46. 1 point
  47. 1 point
    Many people, who have little or no experience in science, look at a book or paper on science and see what looks, to them, like gibberish. Unfortunately, a few people conclude from that, that if they write gibberish, they are writing science.
  48. 1 point
  49. 1 point
    I demonstrated the concept of subtraction to my children by eating their French fries. It worked quite well, and served the parallel purpose of being an education in social interaction with people more powerful,than you... that life isn’t always fair. Sorry... yours is a weird OP
  50. 1 point
    I guess the answer is science doesn't know. Why guess?
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