Eise

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About Eise

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    the old world
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    Physics, Astronomy
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    University degree philosophy, subsidary subject physics
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    Database administrator, a bit of Linux too

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  1. Just found this in the Wikipedia entry of 'Spacetime':
  2. It seems to me that you see spacetime space as a fluid, as something in itself, that has influence on objects in it. Many physicists here already explained that this view on space is wrong. It it were true that galaxies are accelerating one would be able to measure the fictitious force caused by the acceleration. But we don't. Now you could think that therefore our galaxy is exactly in the middle of the universe, every other galaxy (except maybe the galaxies that belong to our cluster) recedes from us, so these would be able to measure acceleration. But that is against the idea of the cosmological principle, that we have no preferred place or orientation in the universe. Spacetime is an abstraction of measuring of distances and periods, it is not a physical substance. So saying 'space expands' says nothing more than that distances become bigger. General Relativity can describe this without the idea that galaxies recede from each other due to some local forces. So spacetime does not exert any force on galaxies. Your understanding of space expansion is flawed.
  3. I've lived one year long in Ireland. The risk there seems very real to me... Markus, I would like to (mis)use this opportunity to thank you for your very clear postings everywhere on these fora, bringing in your deep expertise, and in name of some others, for your patience explaining the nearly impossible. @Quantum321: I have two analogies. The first is the balloon again. But look from this side: the balloon is inflating because of the pressure from the inside, so there is a force in the outward direction. But there is no force between the dots drawn on the surface. The second is two people on the north pole of the earth: say they walk to the south, but under a slight angle. Given their experience that the earth is locally flat, they expect that their distance increase with time uniformly: if they have walked two kilometer, their distance will be twice as much as when they had walked for one kilometer. But to their astonishment, they measure that the distance between them increases less and less the farther they walk. So they conclude there is some force that tries to push them to each other. But we know there is no such force: it is a consequence of the curvature of the earth. (So in this example, their universe accelerates less and less. The curvature of the earth is positive, but if you imagine a negative curvature (the form of a saddle) they will get away from each other faster and faster, without any force.) Just imagine that the direction they are walking, is the time dimension.
  4. What is this fallacy?

    Ha! Very good! That was what my physics teacher used to say when he called somebody for the blackboard, and he/she stood there hopelessly how to solve the problem: 'Think loud, please!'. Most of the times absolute silence was the result...
  5. What is this fallacy?

    I don't think you have to refer to mental illness: in many organisations finger-pointing is a normal practice, meaning 'I am not responsible, (s)he is!'. I do not see this as the essence of your examples. Or you have given not the kind of examples of what you really have in mind.
  6. What is this fallacy?

    I am not sure if this is a fallacy. The only thing that comes close I know of is bad faith. At least it is lying about who really is responsible for the situation, denying one's own responsibility.
  7. Hi geordief, I think in Why does E=mc2 (Brian Cox and Jeff Forshaw) does a very good job in explaining this. It first argues that because of causality only a Minkowski-space works, i.e. there is an 'absolute universal speed-limit'. Only afterwards it identifies that this speed limit is the same as the speed of light, with two arguments: the formula for time dilation previously derived with the 'light clock' is the same as the formula derived from the Minkowski-space, which means that c must be the light speed. After showing that E=mc2, it shows that massless particles must move at exactly this speed limit. It is a good read for lay people, with Pythagoras as one of the most advanced mathematics you need. I made a quick reread of the book specially to be able to react on your thread, so better read it!
  8. Maybe this helps. This is the Windows color-Applet: As you see, red/green/blue are at their maximum, which produces white (see the arrow). As several people here have said, blue and red light are absorbed by a green leaf, maybe not totally, I don't know but you can see the result by decreasing the red and blue components. Then you get this: And please confirm that you understand that - the Bohr model only applies to hydrogen - it only explains the main transitions, so it is a out-of-date model - Atoms in molecules form totally different electron orbitals then the atoms a molecule is build off (so the colours of molecules is not just a mix of the colours of the atoms on their own). If you do not acknowledge this, further discussion seems useless.
  9. Clouds changing color inside rainbow arch

    The inside of a rainbow is always lighter than the outside. But these pictures were made when the sun was low above the horizon, so it was shining red. Therefore also the rainbow itself is mainly red. See this picture, that was obviously made when the sun was still higher above the horizon: I just looked it up: the raindrops reflect both from the backside as from the frontside. The light that reflects from the backside of the raindrops makes the rainbow itself, the light that reflects from the frontside are just reflected, and therefore has the same colour as the incoming light, mainly red in your case. See here.
  10. Hijack from God and science

    Sounds like Cyclosophy... The original article is in Dutch: Velosofie. Maybe you can use some Webtranslator to read it. What he derives from his bicycle: distance sun - earth vacuum velocity of light constant of gravity fine structure constant age of the earth age of the universe (which was estimated at 18 billion years those days. The article is from 1990. But it surely is possible to get at 13.8 billion years) Praise the holy bicycle!
  11. You are right. It was Edwin Hubble, who discovered in 1923 that those spiral nebulae were much farther away than one previously thought. The Hubble telescope is named after him.
  12. Position Grounds

    Not true. I've read a few books of Ehrman, and where he shows that the most rational standpoint, based on the sources we have, that Jesus existed, he definitely does not believe that the empty tomb and postmortem appearances are historical. Just to set that straight.
  13. what is quantum theory?

    You could also start here.
  14. It does represent reality. Just not precisely. But there is no reason for house builders to account for the earth's real form. Every representation of reality leaves something out. But I already said that frames of reference do not exist at all in reality. A frame of reference is like a coordinate system you use to make calculations. There are no coordinate systems in nature. But if the calculations are correct (e.g. you can predict the outcome of experiments with it), then you are methodologically justified to use them. And there is a very simple definition of what inertial frames are: all objects that stand still in relation to each other and no force works on any of these objects are said to belong to the same frame of reference. But there is no 'natural inertial frame', let alone one that is absolutely at rest. And as told you by several others here, light always moves with the same speed in any inertial frame, so it is no substitute for any 'preferred state of rest'. Further you underestimate how fundamental special relativity is. Any theory in physics that claims to be universal, must be consistent with special relativity, i.e. its laws of nature must be Lorentz-invariant. To give an example: the first formulations of quantum mechanics were not Lorentz-invariant. Dirac however did the job of formulating QM in a Lorentz-invariant way. But two predictions rolled out of it: that electrons have spin, and that they have anti-particles. Both were confirmed empirically. So in summary: you can derive special relativity without referring to inertial frames (relative velocities between objects suffice); and special relativity belongs to the bones of all physics, and is also tested to the bones. So what is the 'cul de sac' you are talking about??
  15. You are very precise in your expression: you use the word 'called'. I think the real question would be: did we observe nature and discovered 'natural frames', or did we create the concept, because we find that the laws of nature have their simplest form in such a frame? (I assume you mean with 'self referential frame' the frame of reference in which the object of interest is at rest.) I am inclined to say that when a concept only has a clear meaning in the context of a scientific theory, then it is an 'invented' concept. And with 'inertial frames' I would even go farther: they do not exist at all. They are (very) useful abstractions: they make talking about relativistic effects much simpler. But I assume one could explain relativity and do not use that concept at all. So what I am saying to Simplicio is: yes it is an invented concept, and it has turned out that this concept helps an awfully lot to understand relativity. To use the formulation I used elsewhere: Simplicio's argument is true, but it is irrelevant. He obviously doesn't see that in science it is essential to invent new concepts.