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joigus last won the day on July 28

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About joigus

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  • Birthday 05/04/1965

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    Biology, Chemistry, Physics
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    Theoretical Physics
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    I was born, then I started learning. I'm still learning.
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  1. Panta rhei That's in the nature of things. Changes require adaptations, which bring about further changes, which require further adaptations. Were it football, I would be worried, if I cared about football at all. Education is different. It was there millenia before football, and it will be there long after football becomes a hazy memory.
  2. I don't even have a mirror to show me where I left my glasses 20 minutes ago. So... LOL
  3. If I could only tell you how many times. I have no answer for why is that. But the fact that once you solve the equations of evolution for one simple system, you can perform this miracle on a small scale, of seeing the whole histories, that's what's kept me wondering for decades. And still does. I have this nagging feeling that most of us here share this intuition that what appears as time and slices (exterior of cones, rather) of present space is a characteristic of whatever makes some systems (us, conscious beings, other organisms, maybe some machines), and not something particularly intrinsic to the universe. Saying that is one thing; trying to picture a mathematical structure that embeds this illusion, if you will; is quite another. I remember that trend in the 70's[?] when the director showed you what was going on at different places by splitting the different courses of action in simultaneous squares. Airport (1970) was a good representative of that trend. Needless to say it didn't last. @MigL always has a metaphor for physics from movies. I wonder what he thinks of that. That's a very slippery slope. Edit: On second thought... That's very interesting. +1. Silly me. If your coordinates in your self-reference are (0,0,0,0) at any moment, what direction is any direction? In particular, what direction is your time direction? The mathematics of vector spaces suggest, if anything, that that's just a choice.
  4. I'd go with option 2 as the most demographically significant. But I agree with Strange that 1 would probably be very popular among conspiracy nuts. If I were allowed, I'd pick something like a 40 % 60 %, fifty-fifty or the other way. The reason is that people tend to look at the past with the strangest mixture of incredulity and gullibility. Example: It is impossible that an ancient society like the Egyptians 5000 y.a. were able to build the pyramids (incredulity), therefore some alien civilization must have made it (weird, weird gullibility). When things are happening before your eyes, so to speak, I think it's more difficult to be gullible against the facts.
  5. Don't be. If Plato was right and all knowledge is remembering, let me remind you of what you already know. Try to picture your whole life as a chain of "congruences" of events, so to speak (relativity of simultaneity aside). Everything you live from birth to death is there placed in some database. Let's imagine that you can consult this database. Let's go to the day of my graduation. Bzzzz... There it is. You can also see the news of that day, the weather, everything! Someone yelling "taxi!!" 10 meters away, a fly landing on the window, your thoughts at a particular moment. Everything. Because the equations of physics don't allow dynamical states of the whole system to repeat, except for very-long-time recurrences in closed systems, you could use your timeless concatenation of dynamical states to answer any question about what goes on in your life without ever having to use time. Your space of occurrences would have to include positions and momenta, of course. This database describes the whole physics, but time is out of the picture. One last thing: You could use a parameter. You could re-wind the whole movie at any speed you want. Slow it down or speed it up. That would represent the re-parametrizations of an instrumental parameter that moves you back (rewind class of parameters) and forth (forward class of parameters). But that parameter would not be part of the physics. If you think about it, when you solve the equations of motion you're kind of doing the same thing on a small scale. You get access to a small part of that database.
  6. Very good question. +1 A quick scan of, https://books.google.es/books/about/The_Global_Approach_to_Quantum_Field_The.html?id=-LtutgAACAAJ&redir_esc=y (The Global Approach to Quantum Field Theory, Volume 1 By Bryce Seligman DeWitt) Allows you to find only a couple of paragraphs where space and time inversions are introduced on a coordinate-patch basis. Nothing like the predictive power and generality of CPT in flat space-time is suggested. For all I can remember, the context where CPT is really powerful is the S-matrix approach. And defining assymptotic states in a curved space time is problematic, to say the least. Searches on other more modern books, or on Quantum Field Theory in Curved Space-Times, also by Brice DeWitt, haven't produced anything that remotely resembles "CPT". Not even mentioned AFAIK. I do not think there is anything like CPT valid for curved ST that is remotely as robust as it is in flat ST. But I would be very thankful if anybody knows. This is very interesting, because it connects with my question following up on a suggestion by you on the thread about "What is time?" Would you have some licence to consider signature-preserving continuous transformations that re-shuffled the space-time coordinates, of which our T, P transformations were a discrete version?
  7. You mean C and H. Take a look: Not very significant difference in electronegativities, is it? 2.5/2.1 That's why.
  8. OK. Not that it's interesting to anybody, but I was raised in a Catholic country, and had to do away with a lot of cultural/religious/mythical/ceremonial baggage. I tend to mistrust my own opinions very often; let alone other's. I did that at a very high price. The brain can be a crook. It likes to show to you pleasing landscapes. It likes to prove you right. It also tends to have you accept propositions just because they will make you fit in socially, or stand out. I don't trust the brain's inertial forces. I suppose I'm just a runaway from belief towards degrees of certainty.
  9. That's not what I said. Here's what I said: Can you read it now? Take some time. Read it twice, three times, if necessary.
  10. You believe too much with too little evidence. AAMOF, you believe I believe something. Not only that; you go on to assert it, as if you were privy to my mental states. You couldn't be farther from knowing how I form my opinions. Which goes to prove that you give too much value to your beliefs. I don't to mine. Neither I do to yours.
  11. Thanks a lot for your drawings and explanations, @studiot. +1 The only reason why I would wait a little bit before totally endorsing your picture would be that, if anything, QFT has shown us that whatever it is that we perceive as space and time must be very deeply connected with the space of charge. After all, it's the composition of the 3 inversions (CPT) that produces a very robust discrete symmetry of Nature. But I see no a priori reason why the "internal" dimension of charge could not be added to your picture. Very interesting your rescuing Eddington's observation. It is so interesting that I will re-type it here: (my emphasis). I couldn't agree more. But, in fact, it amounts to something both you and I (at least) have already (at least) implied: IOW: describing relations between points in space as intrinsic, with no oriented parameter. And, AAMOF, I have implied it too. Here it is: Maybe I didn't say it explicitly, but my point was that it is the first, the implicit picture, that is more objective. The oriented parameter t in this picture would be, let's say, just psychological, instrumental, etc., what have you, and have nothing to do** with what goes on in the physical world at large. That objective reality would be described by the intrinsic interdependence of states. The parameter would be just an artifact you need to introduce if you want to account for your experiencing the world as an ordered sequence of configurations. Nothing more. I wouldn't dare to call it emergent, but maybe immersive (more related to how the observer experiences the world). Now, using the arc-length on the curve gives you a natural parametrization, defined except for its sign and a family of infinitely many re-parametrizations. I think most of us here would be closer to common ground for agreement if we made it as clear as possible what we mean.*** ------------------------------------------------------------- * I shouldn't have said "clear-cut" here. After all it's an infinite family. ** Well, not "nothing to do", but a lot more to do with what goes on in the observer's mind, measuring instruments, etc. *** (Edit): This is rather meant as self-criticism, as I don't think I've been as clear as I could have, going back to my previous posts.
  12. Universe did a pretty nifty job of looking as if it had existed long before any intelligent observers were around. That's all I can say.
  13. +1. Very interesting, meaningful and inspiring conversation going on here. I only wish to emphasize observation by @Duda Jarek that charge symmetry can indeed be formulated either locally or globally.
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