DanMP

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About DanMP

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  • Birthday 03/15/1968

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  • Location
    Cluj-Napoca, RO
  • Interests
    physics, cycling, mountains
  • College Major/Degree
    Babes-Bolyai Univ. - Physicist
  • Favorite Area of Science
    physics
  • Occupation
    Physicist (IR & Raman spectroscopy)

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  1. DanMP

    Special Relativity - SR - Time dilation

    Ok what you did wrong was not the actual swapping, but the fact that you didn't notice that the notations were different. In your LT calculation (not derivation, sorry) S' was moving to the right, while in the geometrical calculation, S was moving to the right, as you can understand from the picture and its caption: As I wrote above, in order to compare the results, you have to keep the same scenario/notations, because (unfortunately) the notations are not the same everywhere, as you may see also in other 2 examples/derivations: https://www.amnh.org/learn/pd/physical_science/week3/time_dilation.html https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/Map%3A_University_Physics_III_-_Optics_and_Modern_Physics_(OpenStax)/5%3A__Relativity/5.3%3A_Time_Dilation
  2. DanMP

    Special Relativity - SR - Time dilation

    The formula is the same. The problem is that you swapped the frames. Time dilation is usually calculated for a clock (it doesn't matter if it is a light clock as in your link or any other clock) and from a reference frame. In your LT derivation the clock was static in the origin of S' (the condition was x'=0), while in the geometric calculation the clock was static in S frame (the initial x' was different than the final x', while x was 0 all the time). So, in order to compare the results, you have to keep the same scenario/notations and to swap t' with t in one of the calculations.
  3. DanMP

    Special Relativity - SR - Time dilation

    The above shows (correctly) that for "SC1: x' = 0, x = vt", when the primed clock (consider it a light clock) is in the origin of the S' frame (x'=0), moving with the speed v away from the origin of the S frame (x=vt), Lorentz transformations yield: t'= t/γ (where t' and t are in fact Δt' and Δt, time intervals from the moment t1'=t1=0 when x1'=x1=0). On the other hand taken from: (more precisely https://en.wikipedia.org/wiki/Time_dilation#Velocity_time_dilation) is valid for x=0, not for x'=0 as in "SC1" (where x' and x are in fact Δx' and Δx), so t and t' are swapped ... This is the origin of the "error". In fact Lorentz transformations are correct, as we all know.
  4. Ok, thank you! I apologize for insisting with this question.
  5. I'm sorry but it was you who insisted to talk about that particular derivation : I referred to your source, so I'm not really off-topic. Sorry anyway, I just wanted to understand it better. When I wrote "you", I meant:
  6. The origin of the confusion(?) is not really Jan Slowak, as you can see in the pdf offered here. This is odd, because it is the second time I posted this question in this thread. First time was yesterday. So, again, why v'=v (in value, because in fact v'=-v)?
  7. It is also unbelievable that you don't have an answer to my question. I'm still waiting ...
  8. Yes, but when in S' we write x' and t' ... Why not also v'? The speeds are not seen/measured identical from different frames, so why this time v'=v? [This question is addressed to all the participants in this thread, not just to Jan Slowak.]
  9. After I wrote the above (something you may have considered redundant/obvious) I wondered why v is the same, I mean when x' = 0, x = vt but when x = 0, x' should be -v't'. Why v' = v ?
  10. In the above quote (with y = mx + b) you are right, those two problems have nothing in common, but in the first quote (with x' = Ax + Bt) the "problems" are not independent, they are about exactly the same thing seen from different perspectives (different frames). When x' = 0, x must be vt, because at t=0, x' = x = 0 and the "x' frame" moved with the speed v. In the "Special Case 2", where x = 0, x' must be -vt', for the same reason. This is not random as in your example (SC1: x = 0, y = 5 and SC2: y = 0, x = 0). [I'm not absolutely sure that all I wrote is correct, but I think it may help.]
  11. DanMP

    Global/Generalized Sagnac Effect Formula

    So I need to buy the above article in order to see how you(?) explain the Sagnac effect through optical fibers, where the speed of light is c/n?
  12. DanMP

    Global/Generalized Sagnac Effect Formula

    If it really is "global/generalized", you must also take into consideration (and deal with) the cases where n, the refractive index, is greater than 1 (e.g. when light is traveling through optical fibers, with the speed c/n). Did you? Maybe it is (as I wrote in this here forum), but it is very well explained using special relativity, as you can see here.
  13. Few indications towards my approach are mentioned in my Fizeau/Sagnac explanation. Maybe we should move & continue the discussion there, although I think it can wait. By the way, the F/S explanation is valid, no matter who (the electron in the atom or the atom/molecule as a whole) does the "absorption"+emission. Maybe I'll get back to this subject and answer your questions in a dedicated thread (my theory about the nature of light), but only when I'll finish with the main subject here. Regarding the above discussed proprieties/behavior of DM particles, take them as defined like that. If the theoretical tests I mentioned above will confirm my predictions, then I'll get back to the subject. Until then it would be a waste of time. As I said to Strange, let's wait for my new input (theoretical tests). Maybe they'll prove me wrong ...
  14. Why not? My Fizeau/Sagnac explanation is correct (see the math), consistent with the observations and useful in understanding how photons travel through matter. In the beginning it was included in this theory, but I decided to split them. You like it or not, dark matter will change many things/theories. The above is only the tip of the iceberg ... I have much more. And this is the way to do it, step by step, but interconnected, consistent with each other and with observations. I wrote in that conversation enough. Just read it. In short: the idea that the atom as a whole is absorbing the photon and then it transfers the energy to one electron in the cloud (in order to raise it to a higher orbital) implies that the energy can be shared to more than one electron, and this wasn't, in my opinion, really demonstrated. On the other hand, if you read my Fizeau/Sagnac explanation, you may see why I think that individual electrons in the electronic cloud are receiving the photons and then absorb them (together with the rest of the atom) in a trial and error process. When I say "together with the rest of the atom", I mean that momentum (and some energy?) may be transferred from the receiving electron to the rest of the atom by virtual photons, as you can read in Wikipedia: Absorption + re-emission is something different than electromagnetic interaction. It doesn't necessarily imply electromagnetic forces. In Compton scattering there are such forces, that's why a charge or a magnetic moment is needed. Remember "2. Scattering cross section" and the magnetic moment/field? In my opinion, the photon, with its electromagnetic field, can reject a charged particle (Compton scattering) OR it can attract it or just neither of two (the absorption). With a neutral DM particle it would be always absorption, promptly followed by re-emission, due to conservation laws. That's why DM is "dark" (invisible, perfectly transparent).
  15. Yes, technically the atom absorbs/emits the light, but, as you may see in this conversation, I think that the electron in the atom receives the photon and then absorbs its energy and momentum together with the rest of the atom. More about my reasons for this approach you may find in my other "speculation". I didn't know about "Neutron-photon scattering in the early universe" and I began to read the article you offered. Please read "2. Scattering cross section" and see that it is about magnetic moment/field ... Why should a DM particle have an magnetic moment? This wouldn't imply interactions with normal matter? I don't have time to read more, at least not now. Thank you anyway for the link. I found in wikipedia that: That's why, in my opinion, we can have Compton-like scattering off neutrons, like we have off electrons, but we can not have Compton-like scattering off DM particles.