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Showing content with the highest reputation since 09/26/22 in Posts

  1. The mathematical "engineer" (I prefer that to "father") of GR was Bernhard Riemann. And the mathematical "engineer" of QM is David Hilbert. By that I mean the people who introduced the "mathematical scaffolding" that later accomodated the physical theory. But I don't think either one of them would have come up with the respective physical theories without experimental or theoretical physics input. In fact, when the essential ideas of both theories were formulated, the physicists that did it couldn't imagine the mathematical tools were there already. That realisation, as always, came later. I think there's always a cycle that goes something like --example: electromagnetism--, 1) Induction: Observation of patterns, or "crude" observation: Lenz, Biot-Savart, etc. 2) Inference of a mathematical or pre-mathematical simple relations: Faraday. 3) The big picture in mathematical terms: Maxwell 4) Experimental confirmation of further predictions: Hertz Something like that. The history of the development of electromagnetism is a great example of how this works. But, of course, it's more complicated than just that. The different "branches" feed each other in a complicated way. Once we get the mathematically-closed form of the laws, the great generalisation, it's a matter of pushing and pushing the mathematical model until we find where it contradicts the experiments. It's also a matter of doing more and more refined experiments to check everything's OK. In the case of quantum mechanics: 1) Wien, Stefan, the spectroscopists (Lymann...), etc. 2) Planck, Bohr, Einstein 3) Heisenberg, Schrödinger, Dirac, etc. find out about a previously-existing mathematical scaffolding -> matrix algebra, Hilbert spaces, Poisson's formulation of mechanics... 4) Anderson finding positrons, which is a prediction of the relativistic version... Etc. Sometimes it goes the other way. We find a puzzling experimental discovery, and the theorists must rack their brains, within the mathematical scheme we already trust, in order to understand the unexpected result. If it doesn't, the mathematical scheme must be generalised minimally, ie, in such a way that the treasure of previous results is preserved. Example: discovery of the neutrino. So it's complicated. We may differ a little bit in what stage is what, but I think we agree in general terms.
    3 points
  2. @MigL I second your call to be careful with words, name-calling, and labelling, but, examine this: as a reply to Phi for All's critique. Does that set a tone of respect, or an inkling of an axe to grind? If points are to go unaddressed, leave them unaddressed, or, what is the purpose of the disparagement? The responses, assertions, and argumentation style used here deserved to be lampooned and harshly characterized. Again, I second your point to be careful and address the arguments, but there is a flavor of irrational disrespect coming through that perhaps cannot be well met with measured and reasoning counter-argument. Note "zero effort to quantify" a qualitative property: historical context. And in both prior responses PfA had couched things being in historical context! Irrational responses! I do think bigot is maybe too strong a word for what was a poorly formulated overgeneralization, but, TheVat artfully used it to illustrate a point, and zapatos drew an easy parallel to what was effectively name-calling/labelling by Dr Derp. I do think it makes sense to police bad-faith behavior if that starts to come through in our verbal arguments. There is an absence of malice in either TheVat or zapatos's posts where they use the term; they are indirect, it should not bully down discussion such a usage.
    2 points
  3. If you heard me make a statement about some other social group, ethnicity, or creed beginning with "the problem with [members of this group]..." and continue on with a blanket statement that betrayed ignorance of said group, you might well conclude that I was a flaming bigot. No need to waste any more time with your ill-informed prattle.
    2 points
  4. That’s not true. General Relativity - which is the best model of gravity we currently have - is a purely local constraint on the metric of spacetime. The influence of distant sources enters only via boundary conditions. In order to capture all real-world degrees of freedom of gravity, you need at least a rank-2 tensor field. Scalar and vector fields aren’t enough. The div, grad and curl operators are only defined in three dimensions, but our universe is manifestly 4-dimensional. These equations are also not covariant, so you need to specify what frame you are working in. It is possible to formulate gravity in the way you suggest (this is called gravitoelectromagnetism), but this only works as an approximation in the weak field limit. A full description of gravity requires GR.
    2 points
  5. On what level do you want an answer? Because on one level, it was a bunch of wars and abolition movements. But that doesn't answer how all those wars and abolition movements came together. On another, it was a bunch of philosophical movements that led to ideas of liberty. But that doesn't answer why those movements came to the forefront. On another, it was a result of economic forces giving rise to systems that outcompeted slavery. But that doesn't answer why they hadn't happened earlier. And so on and so forth.
    2 points
  6. The electron that’s captured is an “inner” electron (1S) and bonding is via “outer” electron(s), so the effect on the decay is likely minimal. That Be sees an effect makes sense to me, since it only has the four electrons, so you would have the most possible effect on the 1S orbital depending on what bonds are formed.
    2 points
  7. At one time, back in the 60's, I learned to program computers in machine language, and I delighted in the fact that I could actually know, step by step, how the computer was performing its operations. Since then we have reached the stage in technology where the actual operations performed by the computer are complete buried in layers of code-- and the performance is vastly enhanced. Sure-- someone who knows a lot about the esoteric details might conclude that IEEE 754 was not the best approach. BUT its the one that things are built on. What you have in in the linked article is someone who sees the inefficiencies in the "wheel of choice" and wants to re-invent the wheel. The question is, can they demonstrate a financial and sociological benefit to the user of computation devices to make the change. "This is better" doesn't cut it.
    1 point
  8. If they are going to paint an entire group of people with such a broad brush, I'm not against making them feel a little unsafe. Especially when it's unbidden as it was here. One person - and AFAICT not among those DD was responding to - had identified themselves as atheist. It was an assumption, consistent with "if you are questioning my religious stance you must be an atheist" as if one can't cite the Bible and point out inconsistencies if one is a follower. I think we can do without that.
    1 point
  9. I read the following comment on a Telegraph article about Hydrogen power, and the conversation swayed on to Global Warming, and wanted to know if what was written was factually true: The most abundant greenhouse gases in Earth's atmosphere in decreasing order are water vapor, carbon dioxide, methane, nitrous oxide, ozone, Chlorofluorocarbons, Hydrofluorocarbons and Perfluorocarbons. Some points that may be of interest: • Without any greenhouse gases, the average temperature of Earth's surface would be about −18 °C, rather than the current average of 15 °C. • The atmospheric concentration of carbon dioxide has increased by almost 50%, from 280 ppm in 1750 to 419 ppm in 2021. The last time the atmospheric concentration of carbon dioxide was this high was over 3 million years ago. • Carbon Dioxide is only 0.04%, and the other greenhouse gases only make up 0.1% of the Earth’s atmosphere. • Water vapour is the main greenhouse gas element, but it would be hard to live without clouds and rain. It contributes between 36% to 72% to the greenhouse gas effect. Carbon dioxide contributes between 9% to 26%. Methane contributes between 4% to 9% and Ozone 3% to 7%. • Water vapour only has a ‘residency’ of about 9 days. The other gases stay in the atmosphere for much longer. Thus, the other gases have a much greater impact. This is the reason why carbon dioxide, methane and nitrous oxide are targeted as they have greater concentrations than the fluorocarbons and stay much longer in the atmosphere than water vapour. • Some gases have a cooling effect, such as sulphur dioxide. Unfortunately, sulphur dioxide (along with nitrogen dioxide) caused acid rain and has been removed from emissions to reduce the impact of acid rain since the 1970s. perhaps the reduction in sulphur dioxide is part of the global warming problem. But putting sulphur dioxide back into the atmosphere is not a good idea. It's not the political position that I am interested in, just the science. Also, if anybody can reference to a primary source on these points that would save me the trouble
    1 point
  10. It's good form when someone polices your responses by saying "We aren't the thought police".
    1 point
  11. joigus....I agree that communication via entanglement is impossible now, only that a technical solution might change that in the future, and speculate that if the sub structure of everything is math, that is the key to achieve a technical solution.
    1 point
  12. Scientists who found a new unknown element in the Sun's spectrum did not yet know about fusion. The name was given only because it was found on the Sun (its spectral lines).
    1 point
  13. The problem with bigots is that they assign negative traits to individuals based simply on their membership in a group.
    1 point
  14. Generally speaking, animal welfare is related to the ability of an animal to suffer in some form. Depending on country, the laws will vary, but typically we assume that animals that are closer to us are more likely able to suffer. So generally, warm-blooded animals are most protected, and this also often extended to animals with a spinal cord (e.g. fish). Local regulations can be stricter than that and some also include e.g. certain cephalopods. Beyond that, most animal use is exempt from animal welfare considerations as folks assume that they have limited ability for suffering. This is why no one gets charged with animal cruelty if they squish flies or put out ant killers.
    1 point
  15. 1 point
  16. I think the last major effort to deviate from von neumann architecture was the cell processor which was co developed by sony, toshiba and IBM sometime before 2010. There's nothing sinister or particularly remarkable about VNA. Its simply the easiest and most expedient method to connect standard computer components we have on hand. Its a basic BUS networking architecture.
    1 point
  17. Well the essay is to be on how things actually are, not an imagined scenario.
    1 point
  18. You need to share the science of how you think you could do this. "Enwrapped with a lot of energy" is not a good start. Energy isn't a thing; it's a property of things.
    1 point
  19. The 'model' facilitates calculations and predictions. Don't confuse the 'model' with 'reality'.
    1 point
  20. The ability to utilise Infrared would be a big step forward - and not primarily for achieving higher conversion efficiency in sunlight but by making it possible to use low grade heat, including back radiation from nighttime sky or heat from the ground, or waste heat. It would open up the potential for 24/7 energy from a wide variety of sources, either to avoid storage requirements or by opening new possibilities for thermal energy storage. Besides thermo-electric generators there are Optical Rectennas that might manage this as well some other possibilities arising out of graphene research - but none are standing out as viable. Yet.
    1 point
  21. Ah yes, mixtures of states. That doesn't fit the idea of clean separate dimensions, indeed. Well I hope @geordief gets something out this at least. It seems to me important to stress that Hilbert space is an abstract mathematical concept and one should not think of these "dimensions" in the loose way that the word is often employed in sci-fi, denoting a series of alternative universes to ours or anything like that.
    1 point
  22. But what is space without matter? Isn't it just distance, and specifically distance between things? Isn't the vacuum itself observer-dependent? Space isn't made of some "stuff" that is measurable independent of other things, I think. Anyway I think scientific answers don't depend on those questions, because science deals with definitions and measurements. If expansion is defined as "expansion of the metric", and not of "space", then it doesn't matter what space is. If expansion is defined only for gravitationally unbound objects, and defined as their increasing separation, then I think there's no expansion without that separation, and no way to apply it to gravitationally bound masses. But yes, it doesn't make sense that matter would "stop" expansion. For example, consider 2 comoving distant galaxies that are separating due to expansion. Then say there are 2 gravitationally bound small masses somewhere between them. There is metric expansion between the 2 galaxies. It seems fine to say that space is expanding everywhere throughout the distance between them. What is happening between the 2 small masses? The definitions can answer that! In comoving coordinates, the galaxies have fixed coordinates, and the measure of distance itself is increasing. In these coordinates, for the 2 smaller masses to remain a fixed distance from each other in their local coordinates, one or both must be changing location in comoving coordinates. That gives the answer, that space is expanding between the gravitationally bound masses and they're moving through that space (at the very least mathematically!). But then, we can also consider the local coordinates of the gravitationally bound masses, where in this example they're stationary. You really can say that the masses aren't moving through space (which means nothing more than that they're not changing location in these coordinates). The metric is covariant but I'm still not sure if expansion would be something that is an absolute part of the metric, or dependent on the coordinates. I think it's reasonable to say "space is still expanding here" but with the implication that it's referring to space generally, or in other coordinates, not space in local coordinates. Interesting, I hadn't thought of the physics of the model beyond being an example. I think that even a bunch of photons scattered in all directions would start separation because of decreased mass density.
    1 point
  23. Nothing fancy about Hilbert spaces. They are just ordinary cartesian x,y,z... 'spaces' that have an infinite count of dimensions. So the space is not ordinary physical space - it is phase space, which is a fancy way of saying that it has as many dimensions as necessary to draw a 'graph' in.
    1 point
  24. Thanks, but it does not my question. What physical process happens when gravity shrinks particles? Ok. Earth (and other celestial bodies) is full of old particles that have spent long time in different gravitation so you comment implies that now there is a mix of particles with various size? Protons for instance should, as a result of your explanation, vary in size depending on their history of exposure to gravity. To the best of my knowledge no such differences are observed. Why? Accelerated particles does not shrink*. Ok. But: There should be great differences since gravity differs within the galaxy and in the solar system? For instance Jupiter should shrink faster than mercury or astroids do, over billions of year, due to the different strength of gravity. Note that rocks on the moon have been in lower gravity for long time vs old rock on earth. Why do samples of moon rock not deviate physically? Then old stars should emit light in shorter wavelength than your ones. And stars evolving in weaker gravitational fields should have different spectrum than ones evolving in stronger gravitational fields. It should be easy to see when observing a massive vs. a less massive galaxy; the star light should differ? Are there any supporting observations? *) Note: Length contraction (and time dilation) in special relativity is not particles shrinking
    1 point
  25. Have always liked economist David Graeber's view that debt, and the concept that people have "worth," always tends to lead to slavery in some form. The labor movement has always struggled with this. As the guy says in the folk song Sixteen Ton, "I owe my soul to the company store." Capitalism wants labor to be cheap. Which means somewhat trapped. And it's indebtedness that helps maintain that state. The first slaves shipped to the Americas were debtors. They were held by tribal chieftains to whom they were indebted, or their families were indebted, and their bodies were payments. The chieftain could either work them or sell them to European slave traders. The latter was often the simplest option, with a quick return. Fastest way to end all slavery might be a MBI and cancelling of all debt. But that's another thread perhaps.
    1 point
  26. There were many breakthrough moments and much infilling in between. QM has always also been intimately bound up with particle physics. Quantum theory started in 1900 when Max Planck announced a mathematical solution to the mathematical problem of the 'ultraviolet catastrophe'. Einsten came next using this quantum idea to mathematically describe the photoelectric effect, in 1904. 1913 brought the Bohr atom which tried to describe electron orbits in terms of classical electro-mechanics, whilst introducing a quantisation of the energy levels. This is called the old quantum theory. Quietly Max Planck was busy during this time and introduced 'zero point energy' in 1911. This led to the old quantum theory being modified to include this phenomenon. At this point quantum theory quantum theory provided specific energy levels using 3 'quantum numbers' to describe transitions between them. This was enough for the develoipment of orbit(al) mechanics a la Schrodinger and Heisenberg. In turn this provided chemists and spectroscopists with mathematically based formulae describing their observations. However there was blurring of the spectral lines, originally observed by Zeeman in 1896, and this phenomenon was re-examined. This led to the introduction of a fourth quantum number the spin quantum number which is non classical in its physical manifestation. Pauli introduced his exclusion principle (1925) and spin matrices (1927. By this time researchers were beginning to uncover a whole new catalogue of particles. The rest of the 20th century saw the relationship between QM and particle physics develop symbiotically as one feed on and influenced the other. So we had Quantum Field Theory (QFT) in 1927 and Quantum Chromodynamics (QCD) in 1973. and so on. I suggest you look at this book in your local library or even buy a S/H copy. https://books.google.co.uk/books/about/Q_is_for_Quantum_Particle_Physics_from_A.html?id=rS_8BUE7eN8C&source=kp_book_description&redir_esc=y
    1 point
  27. Gamma photon(s) can be emitted by the nucleus, and X-rays and UV photon(s) can be emitted by electrons transitioning to the ground state of the daughter isotope. The 1s orbital is vacant, so further electrons will have to decay via photon emission to reach their final states.
    1 point
  28. Chart of the nuclides give decays for the known isotopes. There are a few software packages out there, and websites.
    1 point
  29. Now that we have gone through it for a while, what we have seen in practice is that online teaching is even less effective as in-Person. The latter kind of forces at least a minimum level of student engagement, whereas online it is just very difficult to achieve, even if you throw in all the gimmicks there are at them (polls, questions, exercises etc.). Folks just check out mentally much faster in front of a screen as opposed to have someone right in front of them (and scowling at them).
    1 point
  30. we2 has been banned for sharing everything except science discussion.
    1 point
  31. One of the things about quoting Einstein is that he often wrote several versions of his papers as time went on. For instance compare the 1920s, 30 40s and 50s versions of sundry papers about Space, Time, Ether, and Geometry.
    1 point
  32. Came here to say the same thing. Just finished rereading it again a few weeks ago.
    1 point
  33. Not if the Hadley cell has dropped dry air on the ocean. As I mentioned earlier in this thread. You can buy a humidifier for a building. They don't have to use heat. There are many different types. Two of them are spray humidifiers, and impellers. The impeller type has a rotating disk which flings the water against a diffuser, breaking it up into tiny droplets. So your above statement is wrong. Nobody said pumping was free. How much is astronomical? That's just stating the obvious. If there was no significant onshore wind, you wouldn't embark on a project in the first place. My suggestion was for siting an installation where there WAS a reliable onshore wind. If there was an onshore wind for a significant period, then an installation would be turned off whenever there was no wind. That's obvious. You would only be using energy when the wind was significant and onshore.
    1 point
  34. When I was in high school, English ( literature ) was mandatory. Memorable books that come to mind Merchant of Venice Macbeth Animal Farm 1984 Lord of the Flies The Great Gatsby Of Mice and Men Catcher in the Rye Outside of school, I read mostly Science Fiction.
    1 point
  35. Mulberry tree are very fast and easy to propagate. If you just cut a 2 foot tip from the tree branch and pop it into a pot of soil, keep watered it will sprout roots very quickly and should bear fruit within its 1st year. They grow fast and are quite hardy. No rooting hormone or fancy magic needed for them. I have 8 started from before winter and every one has buds and roots come spring. Might help to keep the cutting out of very hot dry conditions for a few weeks. I've never tried such a huge branch, not needed, but you could try reducing that by half and giving it a try as well as the tips as an experiment. Younger, new wood should work better though and the speed of growth is very good. It helps if you strip all leaves except the those on the top tips of your cutting.
    1 point
  36. I read The Godfather in 7th grade.
    1 point
  37. I can see this from a few angles , I lost my Stepdad to suicide nearly 12 years ago I have tried Ending my life a few times And have multiple mental health conditions I now wish to live And try to deal with my mental health issues every day And also help others people being negative towards people who try to end their lives will only make matters worse will make them feel why are they here , no one loves me , etc Being Neutral and being informing to people who are trying to end their lives , what every condition tell them things that can help like CBT . Or therapy , how to deal with triggers and upset , tools to help them ground themselves etc giving them the tools to keep going and to deal with what is going on in their heads like therapy, Medication , Things to avoid feeling so bad and keeping as busy as you can and call a helpline or asking for help get a support worker etc now because i have the tools to deal with how i feel i can use the tools But you have to want to use the tools to help yourself if you dont use the tools things will go backwards and i see my Psych every Three months just to check in , i still have a long way to go * i cant go out the house on my own due to my anxiety and OCD at the moment or even go on a bus for very long but i am working on it with my support workers and be on my own is very upsetting for me *
    1 point
  38. I would say that it's 100% the usb power connector. USB plugs are a nightmare for working/not working. Sometimes you just move them a tiny amount, and they connect. If the blue light doesn't come on, then the power connection is not being made. It's usually the sockets, not the plugs, but in this case it sounds like the plug that's iffey. If you can get at it, try a few strokes of a very fine wirebrush. If you can't it sounds like it needs to be binned, unless you can swap the USB plug for a good one. Does the blue light come on with the laptop that it doesn't work with? That would tell you that it's not connecting up the power, either to the wall plug or the laptop, so it points to the usb plug.
    1 point
  39. I am working on a platform that does not have z buffering hardware support. I am trying to sort polygons in a scene according to z distance so I can implement the painter's algorithm, but I am having no luck. Currently I divide the game into regions and sort the polygons manually in each region according to what looks right. But I would like to know the mathematical solution. I don't have any cyclical overlaps and I don't have any intersecting objects but I do have polygons that touch. Thank you for your help.
    1 point
  40. The blue flame sounds to me like sulphur burning. I think if you heat pyrite (FeS2) you will drive off sulphur and form FeS and then in the presence of air probably you will get iron oxides. If you add HCl you will get chlorides, which can look pale green. I suspect your first picture, after addition of acid, could be a mixture of oxides and/or hydroxides of iron plus chlorides, hence the red/brown and greenish crystals. The later pictures seem to show crystal growth - rather nice dendritic growth in some of the pics. Would that make sense of what you saw?
    1 point
  41. The extra plastic waste is certainly a concern. Not just from the protective gear, but from all sources. Fewer people going to work downtown, while bad for the coffee and street food vendors, also reduces the garbage from takeout food. At the same time, however, people are ordering takeout food at home, and ordering groceries and prepackaged foods online. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8166460/ In the first few months, our supermarkets gave out plastic shopping bags instead of letting reusable into the store. When it became widely known that the risk of transmission on surfaces is minimal, they went back to encouraging customers to bring their bags and pack their own groceries (a great improvement, to my mind; both safer and less wasteful). Other changes, like air quality, have already been mentioned. Here is a good overview What we don't know, and won't for a long time, is how the pattern of work, transport, industry, domestic arrangements and social activity will be affected in the long term. ATM, rents are out of control in North America https://www.bloomberg.com/news/articles/2021-10-05/tenants-struggle-with-red-hot-u-s-rental-market and property prices are still increasing as well https://blog.remax.ca/canadian-housing-market-outlook/ So there will almost certainly be a building boom, with all its pollution and waste products. There will also be a major shift in the patterns of industry and transport. I'm hoping for more local production and small independent operations - especially in food and building material, but it's very far from clear how politics and disease will affect our decisions over the next couple of years.
    1 point
  42. That is certainly true. Most students do not realize that a lecture is supposed to be a general guidance to the material, and is not the material itself.
    1 point
  43. What does "relative to the other" mean? What "other"? [math]tan(\alpha- \beta)= \frac{tan(\alpha)- tan(\beta)}{1+ tan(\alpha)tan(\beta)}[/math] so [math]tan(2X- \phi_0)= \frac{tan(2X)- tan(\phi_0)}{1+ tan(2X)tan(\phi_0)}[/math]. By the same formula [math]tan(2X)= tan(X- (-X))= \frac{2tan(X)}{1- tan^2(X)}[/math]
    1 point
  44. Bit can contains value 0 or 1. If we group 8 bits it is byte. The all other data types have resolution in multiple of byte: 16 bits, 32 bits, 64 bits etc. From computer point of view they are always binary. If typical computer application must print number to user, it has to convert binary to decimal (for non-programmers). It is just on screen. Internally it is is still binary. Conversion takes CPU time and memory. In older times sometimes was used BCD. Now I think it is obsolete. https://en.m.wikipedia.org/wiki/Binary-coded_decimal It could be found in e.g. embedded systems. Display and basic maths are easier and takes less time than full binary to decimal conversion (because they need multiplication, division and/or modulo.. which maybe are not implemented in cheaper weaker chips e.g. Atari/C-64 CPU Motorola 6502/6510 don't have built-in multiplication, division and modulo instructions). CPU has flags: zero, overflow, carry, nagative and others. Some CPU instructions modify some of these flags. Usually arithmetic instructions. If you subtract e.g. variable x0 from x1 (register from register/memory) and you get zero result there is set zero flag in CPU. What does it mean? That x0 was equal to x1. Therefore instructions to perform jumps are called je, jne, beq and bne. Shortcuts from Jump if Equal. Jump if Not Equal. Branch if EQual and Branch if Not Equal. They test state of zero flag in CPU. It is what is used by higher level languages if()/for()/while() etc. functions. And by Boolean to check its state and perform jump. What you see on the screen is just bunch of pixels with shape of digit.
    1 point
  45. You're right. My post was definitely off-topic, Apologies for derailing the thread.
    1 point
  46. You would likely find many more of these on the beach at the base of a basaltic cliff. The white veins are quartz that have permeated the basic fine grained black rock after it was formed, but before pieces broke off to form the beach pebbles. The shape will have resulted from water action 'tumbling' pieces eg on a pebble beach. Cornwall is a good place to look for such pebbles. A scale is a good idea to add to a photo such as yours.
    1 point
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