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joigus

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Everything posted by joigus

  1. This example is so abominable. I can't picture in my mind any English-speaking person in any situation saying it. "Once I make another cake, I will (possess, own, have) three cakes." This is much more natural IMO. Part of the reason is that verbs indicating ownership are generally stative verbs and don't allow you to do these things (use progressive tenses or other 'complicated' tenses. Example: I'm owning this car. I was owning this car. I will be possessing the house of my dreams. Let alone, I will have possessed 3 cakes. That's bad bad English IMO. Future perfect is used to project your mind to a time in the future with reference to a previous action or event (already in the future) which is necessary for the second action or event to happen. Example: Once I finish the exercise book, I will have mastered all that's necessary to become a practicing programmer. Pay attention to the verb. "own" or "possess" (stative) is not the same as "master" or "learn" (non-stative). Main uses of 'will': Prediction or wondering about an uncertain future, or expressing the will of a course of action, or asking someone for favour, help, etc: "Will you marry me?" "It won't rain tomorrow" "What will happen to him?" "If I study hard I will become a lawyer!" Also for promises (long term) or spontaneous offerings (now): "I will help you with your homework" "I'll answer the phone" "I will get back to you ASAP" On the contrary, "going to" future is for 1) Situations in which you predict the future in the presence of the evidence or a stong clue: "If you keep eating like this, you're going to die of a heart attack" "Stop monkeying around, you're going to break something!" "Look at those clouds, it's going to rain" I've + participle is present perfect, and it's for a completely different use: Recent past or past that's still relevant for some reason (news to the listener, even if it's happened in a remote past, etc.)
  2. Energy is only conserved in GR only when your metric doesn't depend on time or, more technically, when you have a timelike Killing field that's a symmetry of your metric. So no, energy is not conserved in general relativity. This is particularly notorious in cosmological models. Think about it, we only have a sensible conserved energy when the "physical recipes" for how systems evolve do not depend on time. The big bang is a notorious exception. Inflationary models are a parametrisation of this behaviour that we wouldn't expect in this day and age of the universe. I hope that helps.
  3. In the words of a conspicuous member of these forums: A big part of it was that I was under confinement at the time, and for some reason I still don't get, parks and open spaces with perfect ventilation and solar UV exposure (that I used to visit with my bike or just walking) became extremely dangerous for the authorities (I love to get lost and see a minimum amount of members of my own species). Serendipity.
  4. Quantum mechanics is puzzling in every which way you look at it when you approach it with a classical mind. Counterfactual definiteness is certainly one of the most bizarre ones. In order to clarify to anyone not totally familiar with the term, as well as check that we're talking about the same thing: Quantum systems have the ability to reveal their information and react accordingly (mostly by breaking their interference patterns) even when a detector that hasn't clicked is placed somewhere in the setup where the wave function takes significant values. The detector that hasn't clicked but was here, thus reveals that the other detector would have clicked, had we bothered to put it there. This happens even when no entanglement is involved (for just one particle: Elitzur-Vaidman bomb tester, etc.). It also happens, of course, for numbers of entangled particles. So yes, it happens when there's an observer (detector) even if it doesn't observe anything! And I agree that reductionism has a problem with entanglement.
  5. I know I'm not British, but I'm more of a Cambridge man, if I had to choose. To me it's doctor Marlettto, and nothing would please me more than see her idea come to fruition. Maybe it's just the great paradigm change we need. To me, it's up there with Kelvin's knots, Poincaré's tiny rigid electron, and other ideas. If anything, just much less naive than those of the great men. But the reason I think it won't work is because impossibility principles are formulated (finally) as logical obstructions. You need the logical framework in order to find the obstruction. Otherwise, what does it obstruct?
  6. There is no such thing as classical entanglement. Entanglement is a purely quantum phenomenon. There are several ways to talk about it. The one I prefer is the most general one. There is entanglement whenever you have two particles in a pure quantum state (maximally determined) and you cannot factor out the common state as a product of one state (for one particle) times another (for the other). The probabilities do not check with those of independent statistical collectivities. Some people call entanglement what really is maximal entanglement (maximum maximal confusion, or equal probabilities between the 1-2 and the 2-1 --exchanged-- states), which is peculiar in and of itself. I see no end to the confusion of terminologies. But as Swansont and Markus have stated before, it's not the hallmark of a distant interaction, but of a past one. Another way people like to characterise it is by saying that the state of both particles is more determined (or exhaustive) than the state of just one of them. It's It checks with what I know. This you cannot do with classical fields, because, eg., the electromagnetic field at one point is just one entity that's built up from the contributions of all the sources in the universe, making one big vector thing at that point. In QM, on the contrary, you have a phase space of "thingies" (1)x(2)x(3)... etc., so it's nothing like the classical case. You can have things like (1)x(2)+(1)'x(2)'. "Identity", so to speak, can be "scrambled". This is very peculiar. Some people talk about "classical entanglement" simply because they confuse the principle of superposition for classical fields with the principle of superposition for quantum states (that only when combined with composite states being so-called "tensor products" produces this situation. Entanglement is a consequence of the fact that the simplest physical systems are particles (the 1-thing, the 2-thing, the 3-thing,...) and fields (their values everywhere) at the same time. I'm not being very clear, and I know it, but I'm ready to be corrected/clarified/completed by other users, including you, of course. I apologise, @studiot, for my handwavy and cursory way to put it, but I find your topic fascinating and I hope to be able to contribute more significantly later --hopefully. One last thing before I say something stupid on account of being too tired today: There is no such thing as the quantum numbers. Quantum systems have incompatible sets of those. None is better than the other. That's why Pauli's definition: doesn't really cut it. Particularly severely for spin. Really looking forward to continuing this discussion.
  7. I'm sorry to join my voice to those that of the party poopers here, but I'm pessimistic about how you can make "negative principles" (principles of impossibility) the constructive groundwork for physics. They have immense heuristic value as a guide, but sooner rather than later you must assume plausible relations between the variables that implement those principles and make them "natural" or "obvious". So I think it's the other way: Impossibility principles by themselves don't allow you to build. I've been aware of this quantamagazine big anouncement for a while, but didn't make much of it, TBH. And I wish I were wrong for many reasons. Among others, it is very much in tune with my way of thinking of about 20[?] years ago --which would be a very nice revival of my youth years--, that I gave up on account of not really leading anywhere useful. "It is impossible to determine position and momentum at the same time" doesn't give you HUP all the way down by any means. Let alone the reason why it's true it works. But maybe there's a lot I ignore about this new idea. And I can give several more examples. Swansont has perfectly illustrated how it works with SR.
  8. Hi. Welcome to the forums. Please, take a look at Section 2 point 7 of the guidelines. https://www.scienceforums.net/guidelines/ A sphere is never "approximated by a point" when calculating gravitational forces outside the sphere. It's just that the field of both objects happens to be the same. That's called Newton's theorem, and in the case of General Relativity, Birkhoff's theorem. A different case would be if the matter distribution were not spherically symmetric. Molecular bonds are a completely different matter, and you really need some quantum mechanics to tackle them...
  9. Absence of chlorophyl for reasons Studiot explained highlights the carotenoids. I suppose carotenoids take longer to be chemically degraded, but I really don't know.
  10. Science today is vast, but interesting epistemological problems arise in all fronts. Ethical too, taking @swansont's cue. Philosophers today, willing to say anything significant --that scientist will pay attention to--, must learn at the very least the conceptual framework of scientific theories, their degree of success, as well as the point at which they fail, falter, or simply shrug their shoulders. Their limits, in short, and a working knowledge of how these limits appear. It takes a very special kind of person, and it requires a considerable degree of specialization. There are people like this, and sometimes they do a thankless job.
  11. I must confess I'm at a loss at defining what makes a good politician, in the sense that @MigL has used as a definition, which I think is quite appropriate for starters. But I suspect it's a lot more about wiles than it is about pure intelligence. I very seriously doubt that we will ever meet a successful politician that's a problem-solving whizz, or a paragon of creativity, or a master at engineering economic miracles. I also think there's an element of unpredictability. Enough people must like you --the hairdo, the way you speak or even smirk may play a part there--, and then you must manage to get some work done, so I suppose being able to spot the right people for the "real" job is a big part of it. I tend to see leading politicians as the final decision for the logo of your car make, TBH. Something like this, I suppose:
  12. It depends on what you mean by "information", and on what you mean by "the system". For example: If you mean accessible (macroscopic) information, and the system is the whole universe, it's never true. If you mean all information (the negative of so-called fine-grained entropy), and the system is the whole universe; it's also never true (fine-grained entropy is always constant for the whole system+environment). ... Only very rarely it's true (example: living organisms). Living organisms can organize (the information stored in them grows) at the expense of "disorganizing" the environment. So you see, you must be a lot more careful when making sweeping statements like that. I also agree with what you've been told by other users on numbers and the infinite.
  13. I couldn't agree more. I think the sooner we make this discussion less political and passionate, the better for the flow of ideas on a topic that interests us all. I don't want to commit an opinion yet. I want to consider more arguments. Very interesting topic BTW.
  14. I think @Peterkin has a point and should be given a fair hearing before anybody gives them another flurry of neg-reps. I would like to hear more arguments. After all, I don't know of any waiting list of well-to-do people in line for handling the LHC accelerator to produce QCD jets --wo. the assistance of a professional physicist. What about well-to-do people waiting in line to extract ice cores in Antarctica? --wo. the assistance of a professional field geologist? Aeronautics has an undeniable element of thrills for the rich that we should discuss dispassionately. Having said that, I totally understand @iNow's point: That element plays too. Mind you, amateur astronauts can fall on our heads. Perhaps irrelevant?
  15. You're welcome. I didn't know that form either. I did remember that the equation of an ellipse in polar coordinates is an ungodly mess if you try to express it in polar coordinates with the foci equidistant from the centre, but looks nice and simple with one focus sitting at the origin. I just assumed something similar happens for the catenary. The rest was a wikipedestrian approach.
  16. https://en.wikipedia.org/wiki/Whewell_equation Homework. No linear algebra or group theory here.
  17. I don't think MigL would have any problem with those. They're not of the insect variety.
  18. Naked mole rats are not really rats, and they're not just any mammals: (Wikipedia) Sharks are also very resistant to tumours. I don't know what this has to do with beauty, but it does have a lot to do with the unexpected. Nature is truly amazing.
  19. He's the only one who's objected to the beauty standards of this thread. But he didn't mention any wars...
  20. As always, we should ask the beholder. https://en.wikipedia.org/wiki/Naked_mole-rat I think they are. But I'm no expert on beauty. Let's ask @MigL.
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