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  1. I

    I Largest sphere in the space between dense packed spheres

    I didn't know where to start, whether drawing a tetrahedron and 2D circles is relevant.
  2. I

    I Largest sphere in the space between dense packed spheres

    If I consider a tetrahedron of four densely packed spheres of unit radius, what it the radius of the largest sized sphere that can fit in the space in between?
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    B Electrical version of Faraday effect?

    Thanks for that. So the Kerr Effect induces birefringence in the direction of the field, and the Pockels Effect induces birefringence perpendicular the field. I wonder whether either effect is used in an astrophysics context? I note that there is "A novel technique for remote sensing of...
  4. I

    B Electrical version of Faraday effect?

    The Faraday effect is a magneto-optical phenomenon caused by the interaction between light and a magnetic field. Is there a corresponding electrical-optical phenomenon, caused by the interaction between light and an electric field?
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    B Electromagnetic waves/radiation properties?

    As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other. Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to...
  6. I

    Redshift, Earth's orbital speed, and the speed of light

    The Earth is moving around the Sun at around 30km/s, a change of 60km/s over the course of the year. Presumably, measurements of the speed of light would show a redshift up to ±30km/s? Are redshift measurements this accurate? Likewise, the speed of the Solar System around the Milky Way, is...
  7. I

    Laws, principles and facts

    Although scientists once thought that radioactivity violated the law of conservation of energy, then new understanding of nuclear decay helped demonstrate that the law was fact. So why do we continue to call the Conservation of Energy a law, and not a fact. Why not a principle? Is there a...
  8. I

    Is fire a plasma?

    I think that most people would describe a lightning bolt as a plasma because of the ionised air it produces. There are several parameters that may define a plasma. Interestingly, a gas may be ionized to only a fraction of a percent, and fulful the requirements that define it as a plasma:
  9. I

    Is fire a plasma?

    It is not as clear cut as that. Fire may be a plasma. See https://www.physicsforums.com/showthread.php?t=203289#10"
  10. I

    Plasma types

    Plasmas are usually "typed", or classified, in other ways. For example: Cold, warm and hot plasmas Fully/partially ionized plasma Collisional/Non-collisional plasma Neutral/Non-neutral plasma High/medium/low density plasma Magnetic /Non-magnetic plasma Dusty/grain plasmas...
  11. I

    Plasma types

    A plasma is generally described as a collection of charged particles, but the species of ions does make for different kinds of plasma. More usually, the (positive) ions are mixed with equal numbers of negative ions: electrons. Ionizing any element will produce its corresponding plasma. So yes, a...
  12. I

    Is fire a plasma?

    Have a look at some of the links at the beginning of this thread. In summary, fire is sometimes a plasma, and sometimes not. It all depends on your definitions, and how you define a plasma.
  13. I

    Quick Plasma Question

    It depends on the plasma. A candle flame, a very weak plasma, requires nothing to "contain it". A bolt of lightning is self-contained by its own electromagnetic pinch. The plasma in a neon sign is contained by glass (though it forms a sheath parallel to the glass surface). And the plasma in...
  14. I

    Is Dark Matter a solid, gas or liquid?

    I don't think that's quite right, because "cold plasma" and "hot plasma" have special meanings in plasma physics. For example, the plasma created in a fluorescent light tube is defined as a cold plasma, yet it emits light.(Ref) Conversely, the Solar Wind is classed as a hot plasma, but as far...
  15. I

    Plasma cosmology

    I would argue that the approach is irrelevant, a citation stands by itself. As an example, Ivan Seeking has noted that "Wiki is not a credible scientific reference. However, it is allowed within a context that is already well understood"(post). Two examples: So if there is a general...
  16. I

    Plasma cosmology

    Are you saying it's not a reliable source because it is not peer reviewed? I thought academic books were adequate, and the one cited is published by Springer, relatively recently in 2005, and its editor Dr ames Lequeux has been Editor–in–Chief of Astronomy and...
  17. I

    Plasma cosmology

    I would appreciate a couple of examples that highlight why you consider this. I'm not being argumentative, but constructive criticism is always useful.
  18. I

    Plasma cosmology

    (a) Can you just remind me in which post I suggested this, and how I assess my degree of expertise? (b) Would it be fair to say that some scientific journal editors are not experts in all the fields they include articles on?
  19. I

    Plasma cosmology

    I assume that this would rule out linking to Wikipedia (as per post #2 here) and (post #1 here). And also a link to a mentor's personal web site (post #4) who describes himself as "an intermediate-level amateur astrophotographer"?
  20. I

    Plasma cosmology

    I asked a fair question for clarification, so I think your reply is somewhat heavy-handed (no disrespect intended). But thanks you for the first explicit answer to my question on this matter, whereas other PF Mentors have said that "the problem is not your site", you can see why perhaps I...
  21. I

    Plasma cosmology

    Do you think that where I have used links to my own site, that I have done so responsibly and can continue to do so, or should I still PM someone each time I wish to do so.
  22. I

    Plasma cosmology

    Forgive me for not replying to each of you previous posts, I think they were more summing up. I generally agree with this post. My personal view, is that there should not be a blanket ban on YouTube and Web sites, as a link may depend very much on context and presentation. Likewise, I would...
  23. I

    Plasma cosmology

    Criticism is not necessarily a refutation. Recall that Chapman criticised Birkeland's model of the aurora for 50 years before in situ satellite observations decided the matter. Agreed.
  24. I

    Plasma cosmology

    I would expect something published in peer reviewed journals. Some sources suggest that interstellar medium includes ionized interstellar gas (ie. plasma) at temperatures up to 5 x 105K (ref), whose magnetic fields are generated by electric currents (ref), and that it may form its own...
  25. I

    Plasma cosmology

    Thanks for the clarification, I wasn't sure. Sounds like a good example of where being more specific with the claims and observation would be scientifically useful. I am aware that the Electric Universe makes lots of claims, some of which are standard astrophysics.
  26. I

    Plasma cosmology

    Same reason as before. It's difficult to write about a subject with giving prominence to it. In writing about Birkeland's work, I'm most interested in adding information about it, again, because a lot of this information, or collection of references, is not generally available elsewhere. If I...
  27. I

    Plasma cosmology

    I think that is indeed part of it, but also perhaps the perception that the "Plasma Universe" model is bogus, and hasn't been investigated via peer review.
  28. I

    Plasma cosmology

    I'm in a no-win no-win situation. I can disagree with Nereid, but my status is unknown, and "my word" effectively worthless. Or I can let people judge for themselves by providing a peer reviewed citation which necessarily includes the publishing details. Since it has been hammered home that the...
  29. I

    Plasma cosmology

    I agree with you that Birkeland currents more commonly refer to auroral field-aligned currnets, but perhaps this is because it is a more common area of research. As Hannes Alfvén wrote (my emphasis): ".. it was [Alex] Dessler who discovered the electric currents that Birkeland had predicted...
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    Plasma cosmology

    Do I really have "Electric Universe" as a synonym for "Plasma Universe" on my Web site? I have tried very hard not to imply this, as I am aware of differences. Can you give me a link to the page? And likewise, "the Sun and stars were formed by z-pinches" is language I would hopefully not use on...
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