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Eise

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Eise last won the day on November 27 2019

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About Eise

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    the old world
  • Favorite Area of Science
    Physics, Astronomy
  • Biography
    University degree philosophy, subsidary subject physics
  • Occupation
    Database administrator, a bit of Linux too

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  1. It is at least difficult to imagine... But this brings me to another point. If it is correct what Kip Thorne says (which I strongly assume, knowing what kind of expert he is), then we have 2 completely different 'pictures' based on which interpretation we choose: gravity curves spacetime, and all free moving objects follow geodesics in spacetime gravity is a force, which affects paths of free moving objects, durations and distances But especially my use of 'force' seems to completely contradict the way GR is usually presented: that gravity is not a force. How could one formulate the second interpretation in a better way? Maybe I should stick to Mordred's view: it seems to have the least metaphysical baggage of all descriptions of GR. Word of the day... So glad that Wikipedia exists... OK, now I play for a moment devil's advocate (in this case as a Kantian philosopher): the concept of curvature only makes sense when there is a higher dimension. A line is said to be curved because there is one dimension more, namely the second (wow, that sounds stupid. And as I think to understand, for a 1-D organism there is no chance, not even with differential geometry, to discover that his universe is curved.); a surface is said to be curved, because there is one dimension more in which it is curved. But a 2-D organism can at least discover that, by measuring angles and distances. But how can he conclude that this 3rd dimension does not exist, and that the curvature of his world is intrinsic only? And of course the same questions for 3-D organisms, that discover that their world can best be described as if it is curved? Shouldn't they conclude that there is one dimension more? Or locally diffeomorphic?
  2. Yes, it was in Thorne. He says that one can formulate GR in flat spacetime, where gravitation deforms lengths and durations, whereas the standard interpretation is that lengths and durations stay the same, but spacetime is deformed by the presence of matter/energy. The results are the same, but it seems the math is not completely, and so, dependent on the kind of problem, one can use the interpretation that makes the calculations easiest. And he explicitly says that the question if spacetime is really curved is a philosophical question that does not bother physicists.
  3. I understand, but with some hesitation. Maybe it is because of my (stupid?) idea that intrinsic curvature is the way out for 'n-D' organisms to discover that they live in a curved space, because they cannot access the n+1th dimension to actually see it. But you are saying they cannot discover that they are living in a cylindrical universe based on its intrinsic curvature: the metrics of a flat universe and a cylinder universe are the same. Wow! And I thought one extra dimension would suffice... Obviously that is when one, like me, only has a very superficial understanding of differential geometry, and has to do with analogy arguments. (I am not @scuddyx, who talks about 'tensor force' as if he is understanding what he is talking about...). Gasho, Eise
  4. Isn't that an example of a 2-D object with intrinsic curvature? (And for which we can make a 3-D model.) My idea (hopefully), was even simpler, say the curvature of the surface of a ball (the ball is 3-D, but the surface is 2-D). Isn't it true that one can use both descriptions? In that case we see the 3-D space in which the 2-D surface of the ball is curved, so we can describe it extrinsically. The most important lesson about this in GR, that I thought I learned, is that one can describe curvature intrinsically, and therefore, because we cannot observe 4 dimensions, the question in what the 3-D universe is curved is a metaphysical question (and therefore physics can do without it). Therefore also my 'as if' in my previous posting:
  5. scuddyx, see this video. Much closer to what GR says than the rubber sheet analogy. Are these two types of curvature, or are these different ways to describe curvature? E.g. one can describe the curvature of the surface of a 3 dimensional object in 3 dimensional space in both ways, no? And my understanding of the 'curvature' of the universe is that it is as if it is curved. If I remember well, Mordred said that GR only says how worldlines of free moving objects in the universe look like. In some book I read that one can formulate GR without the use of curved spacetime, which for some kind of problems seems to make the calculations easier (I think this was in the book about black holes of Kip Thorne).
  6. In line with the answers already given: if 2 particles are entangled, then they: were entangled themselves, which means at least they were interacting directly in such a way that we only can know the wave function of the two particles together, not for the particles individually ('normal' entanglement) or they share a history in which the quantum state of the particles is determined by two particles that were entangled (that would be 'quantum-teleportation') See the second point above. If they 'incidentally' share a history based on an entangled pair, then yes. And thereby it does not matter how they got entangled, by human intervention, or just some 'blind physical process'. Otherwise no. But do not forget: locally, an observer can never find out that the particle he measures is entangled with another. The entanglement only shows up when two observers compare their measurements of the entangled particles. Then it shows that their measurements are correlated.
  7. Then stop posting meaningless mathematical looking symbols. LOL. Everything is wrong with your physics.
  8. Strange, do not feed the troll... 'Complexity' has shown not to understand any physics and math at all. And he doesn't want to learn, so what is the use?
  9. Search answers yourself first. Google. Wikipedia. Whatever. https://en.wikipedia.org/wiki/Electric_battery#Self-discharge
  10. That is only half of the story: the current is flowing from one pole of the battery to the other, through the fan. So the answer is: none. The only force is that coming from the potential difference between the two poles of the battery. I saw your postings in some other threads. Your understanding of physics is so bad, that you cannot even ask the correct questions. Please, read some introductory physics books, get a course in physics, but stop asking stupid questions. I would propose that nobody here answers your questions anymore, unless they are questions that arise from you reading a physics book, or following a physics course. But questions that arise out of the conflict between your world view, and not accepting the answers because these do not fit your world view, is simply a waste of time for us all, including yourself.
  11. Eise

    Travelling light...

    @koti: Did you see3 this? Nobody objected.
  12. That is a good point. Of course a system where nothing happens is impossible, but I think my example shows that one can only speak of time when there are changes; and also the other way round. However, we cannot observe time, but we can observe changes (especially hands of a clock), which for me makes 'change' the more primitive concept. As in a thread a long time ago (i.e. many changes happened since then...), about the same topic, you said 'time' is an abstraction, to which I only added "yes, to be specific, an abstraction of change". I find this an unfair comparison. Take such a 4D manifold, and compare it for T = 0 and T = 1. If everything else is the same, then there was no change; if not there was. I do think that time exists, but it exists in another way than physical objects, that exist in time (and space, of course). It is similar to the question if the laws of nature exist. There I also say they exist, but again in a different way than physical objects. When one does not account for this different ontological status of physical objects, time and space, and laws of nature, it can lead to all kind of stupid philosophical questions (as we had here several times) like 'how do the laws of nature govern the universe'.
  13. But it isn't caused by time either. Causality is a relationship between events. One event can cause another, and the cause precedes the effect. That means we need the concept of time to describe causal relationships. But time itself causes nothing: it is a concept we need to describe our observations.
  14. So one has a period where there are changes, and periods there are not. So say we have a clock perfectly measuring time during the changes. But then, when there is no change, the clock does not change either. Say it says 13:03h at the end of a change period. Then, at the beginning of the 'new change period' it will still saying 13:03h. So there is no way of telling there was a gap. The clock itself introduces the change. No change, no clock.
  15. How could one decide that there are gaps?
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