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  1. fresh_42

    "Fatal" mistake for flat earther

    Hagar or Eratosthenes, that is here the question. It's tempting to feel a kind of joy, but on the other hand: some human being died completely without any sense. Guess the Darwin award this year will be his. What's really sad is, that Thales of Milet said it 2,600 years ago, and...
  2. fresh_42

    About the protein shape of covid-19

    Italy is in the news, but the other European countries are affected, too. And they said it's now on all continents. (I guess they have forgotten to mention antarctica as exception, but who knows.) On Teneriffa is an entire hotel with 1,000 people under quarantine. Hardly. covid-19 basically...
  3. fresh_42

    Challenge Math Challenge - February 2020

    I guess it's time to give both of you - @suremarc and @Antarres - the credit for solving the problem, since you both have had a correct strategy. Since this problem - Lemma of Babuška-Lax-Milgram - is a bit confusing, I'll add my proof. There was nothing wrong with either of yours, but for all...
  4. fresh_42

    Challenge Math Challenge - February 2020

    I'm a bit skeptical about your use of duality. E.g. why is ##\operatorname{im}B_1 =\mathcal{H}\,?## Didn't you use ##\mathcal{H}=\left(\mathcal{H}^*\right)^*## with ##\beta## instead of the inner product? In other words: why does ##B_1## land in the space you claim it does? You have only added...
  5. fresh_42

    Random Thoughts part 6

    But that's an order, not a question. The question would be: "Would you consider to give me your lunch money or shall I beat you up?" in which case yes or no is still the only solution, depending on the fitness of whom has been asked.
  6. fresh_42

    Random Thoughts part 6

    Í like questions with an OR. They are usually so easy to answer.
  7. fresh_42

    Today I learned

    I'm not totally sure, but isn't there a massive lack of Lithium in the universe?
  8. fresh_42

    Today I learned

    You should have bought a couch instead of a smell on fibers attached. :wink: Maybe someone thought people would expect this, as they do in new cars. Btw. new airplanes have this smell of new like cars, too.
  9. fresh_42

    Random Thoughts part 6

    ##3 \nmid 28## Blame the Babylonians and the Semitics. But there is a solution for you. Since you cannot return to the days when moon orbited earth faster, maybe you can wait until it is far enough that it takes ##30## days. Then you can introduce a week of ##6## days.
  10. fresh_42

    I Group Theory sub algebra of unitary group of U(6) group.

    I already told you in post #2.
  11. fresh_42

    Learning physics from scratch

    So have a look at the books on the RICE university site. You can download them as pdf and look into it! Just try and find out whether they are o.k. for you, too difficult or too easy. Whatever, it's for free.
  12. fresh_42

    I Group Theory sub algebra of unitary group of U(6) group.

    Sorry, I do not download what I don't trust. If you want to type it instead, see https://www.physicsforums.com/help/latexhelp/ And I bet there are more than three subgroups in ##U(6)##.
  13. fresh_42

    Learning physics from scratch

    I don't know books in English at this level. I often cite https://openstax.org/subjects because they are free and can help to get started, and to find out what has to be learnt. However, there are better ones. Have you looked into our...
  14. fresh_42

    I Group Theory sub algebra of unitary group of U(6) group.

    Sub groups, not sub algebras. Of course we need to specify each inclusion separately. And it is not really an inclusion in the sense of subsets, they are embeddings in the sense of monomorphisms, injective group homomorphisms. E.g. ##O(n) \hookrightarrow O(n+1)## can be done by ##A\longmapsto...
  15. fresh_42

    Learning physics from scratch

    Yes, there is a little disappointment built in here. It is the math. It will work to look up mathematical concepts, like e.g. a gradient. But only for a while. You won't miss both, physics and mathematics, if you jump back and forth. So before physics takes place, you will need a basis in...
  16. fresh_42

    Today I learned

    By the way: What do we have about the Lithium puzzle? Do we have an insight?
  17. fresh_42

    Today I learned

    Oh, that easy. I was looking for some message behind atoms with three valence electrons, or Lithium.
  18. fresh_42

    Studying Good research areas in pure math

    Well, the algebraic part of Lie algebra theory is linear algebra, as they are subalgebras of the general linear algebra. I don't know enough about functional analysis, so I cannot answer this part. To me it is a giant mess of pits, traps and slings: several concepts of convergence, theorems...
  19. fresh_42

    I Convergence of a sequence of sets

    Sure, but what makes you confident, that ##f## doesn't destroy that behavior? If ##f## is continuous, o.k., but is it?
  20. fresh_42

    Today I learned

    ... and I still don't see what you mean. Could you enlighten me?
  21. fresh_42

    About the protein shape of covid-19

    I just came around an interesting assessment: https://www.theatlantic.com/health/archive/2020/02/covid-vaccine/607000/ Unfortunately I couldn't find any peer reviewed papers related to Lipsitch's opinion. The closest I got was https://jamanetwork.com/journals/jama/fullarticle/2762028...
  22. fresh_42

    Studying Good research areas in pure math

    I have a rather simple, but as far as I know, new idea. However, I don't know what it's worth. It's about Lie algebras. I once hoped to shine some light into the classification of non semisimple Lie algebras but I haven't found a good key. Only many, but none of which opened actually some...
  23. fresh_42

    Studying Good research areas in pure math

    Define "good"! This is a personal assessment, so how can we know what you consider good or bad?
  24. fresh_42

    How is this graph Hamiltonian and Eulerian?

    It is a Hamilton graph, but it is not an Euler graph, since there are 4 knots with an odd degree. https://en.wikipedia.org/wiki/Eulerian_path
  25. fresh_42

    I E=mc^2 before Einstein

    Einstein only used Maxwell as far as I can see on a quick glimpse: http://users.physik.fu-berlin.de/~kleinert/files/1905_17_891-921.pdf of which ##E =mc^2 ## https://www.zbp.univie.ac.at/dokumente/einstein4.pdf is just a corollary: Is a body's inertia depended on his energy content? I assume...
  26. fresh_42

    I E=mc^2 before Einstein

    Neither do we. So? Without clear references which stand a rigorous historical and therewith scientific test, each of those statements is worthless, just propaganda. Yes, there have been similar formulas found before, a fact which nobody objects. Wrong. This is simply not true. Einstein only...
  27. fresh_42

    For animal lovers

  28. fresh_42

    Need help on how they got these numbers -- solution to a trig equation

    Do you know how to solve ##ax^2+bx+c=0##? ... and it does belong into our homework forums, whether it is or not.
  29. fresh_42

    Challenge Math Challenge - February 2020

    It does no harm to give an elementary proof.
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