Chinese Scholar Yang Jian liang Putting Wrongs to Rights in Astrophysics

Discussion in 'Astronomy, Exobiology, & Cosmology' started by heyuhua, Apr 22, 2018.

  1. NotEinstein Valued Senior Member

    Messages:
    1,234
    As the Wikipedia article says in the very sentence under the equations: if you are contracting over the wrong indices, you'll indeed pick up a minus sign. In that case, you are no longer using the Ricci tensor, because that's not the Ricci tensor anymore; in other words, you also draw the conclusion that Yang is wrong. (S)he mistakenly contracts over the wrong indices, and is thus a minus sign off.

    This is trivially proven false. G^uv=8paiGT^uv and G^uv=-8paiGT^uv can only both be true is G^uv=0, which obviously is not the case in general. You are wrong.
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. heyuhua Registered Senior Member

    Messages:
    171
    You are wrong, because the signs of the Ricci tensor defined in these two ways are the opposite, while the energy-stress tensor is defined in the same way, field equation must have two forms namely G^uv=8paiGT^uv and G^uv=-8paiGT^uv, which appear in different textbooks, obviously you read too few books
     
    Last edited: Jun 11, 2018
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. heyuhua Registered Senior Member

    Messages:
    171
    the definition of Ricci tensor used by Yang is being used in a lot of textbooks, it's completely correct. Obviously, Your knowledge is very incomplete, not systematic, not proficient, you know one and don't know the other.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. arfa brane call me arf Valued Senior Member

    Messages:
    5,586
    Unfortunately, because the Ricci tensor is the contracted Riemann tensor, the sign is defined by the latter.
    --https://en.wikipedia.org/wiki/Sign_convention

    As NotEinstein has been saying, Yang disagrees with Wikipedia. One version is wrong, and we're supposed to take your word for it it isn't Yang's?

    Here on sciforums? Because we're all dumbasses?
     
  8. NotEinstein Valued Senior Member

    Messages:
    1,234
    You can't define a term in two contradictory ways, and expect the results to make any sense.

    But let's say that Yang indeed uses that different definition, causing a sign-change in the EFE. That means that the sign-change Yang gets in the EFE is just notational: it's not a real difference. All the discussion in Yang's article that follows about how this sign-change means this-or-that is thus wrong.

    Let's try this trick elsewhere: say I define force to point in the opposite direction, so: \(F\rightarrow -F\)
    Then I get: \(F=-ma\)
    Look! Negative mass!
    No, obviously not. The minus-sign is needed to correct for the fact that the force \(F\) now points in the opposite direction. It's just a notational (or if you will, definitional) change. None of the physics have changed.

    Whether Yang does this or not, Yang is wrong. Either about the sign, or about its interpretation.

    Please provide even a single one of these textbooks.

    Then explain it to me. You've written more than 50 posts now after my initial pointing-out of the minus-sign, and you still haven't managed to explain anything at all. Why do I have to drag all the answers out of you? Why are you so unwilling to share this supreme knowledge? Why are you here, if that's not your goal?
     
  9. NotEinstein Valued Senior Member

    Messages:
    1,234
    (I have been extremely sloppy, and have been calling it the contracted Ricci tensor throughout this thread (I figured out my mess-up some posts ago; now I'm sticking with it to avoid confusing heyuhua). Really should brush up on my GR.

    Please Register or Log in to view the hidden image!

    )
     
  10. heyuhua Registered Senior Member

    Messages:
    171
    the Ricci tensor has indeed two ways to define, but they have no essential difference and do not bring new physics, for example in the book " introduction to general relativity" 俞允强, the definition is the same as Yang's article. see:
    http://www.doc88.com/p-0592619797194.html PP-50
     
  11. NotEinstein Valued Senior Member

    Messages:
    1,234
    I can't read Chinese (I think that's Chinese?) so I can't really comment in detail. I assume this is an (illegal?) copy of Yu Yun Qiang's 1997 work, correct? But, it seems you're right: there's a swapping of the terms in the Ricci tensor, on page 50, equation 3.6.8. This results in the EFE on page 52, first unnumbered equation in section 3.7. And based on that, I (re-?)discovered this:
    https://en.wikipedia.org/wiki/Einstein_field_equations#Sign_convention
    "Authors including Einstein have used a different sign in their definition for the Ricci tensor..."

    Which is discussed in a bit more detail here: https://www.physicsforums.com/threads/einstein-equation-quick-sign-question.794916/

    So there we have it. Yang is using this convention, which straightforwardly results in a minus-sign in the EFE. Then Yang incorrectly compares this result to the EFE that's using the other convention. This comparison is, of course, fundamentally invalid. In other words, Yang is misinterpreting his/her results based on his/her mix-up of minus-sign conventions. And thus, with yet another source considered (this time kindly provided by you, heyuhua), we have to once again draw the conclusion that Yang is wrong.

    Notice also how all sources in this thread (including the one just provided by you) state in no unclear terms that Yang is definitely wrong with his factor 2 difference in the EFE. In other words, even if this minus sign difference could be justified, Yang's result would still be wrong. And that's without considering all the other questions I brought up earlier, that you, wangchaoqing, and Yang have failed to address so far.
     
  12. heyuhua Registered Senior Member

    Messages:
    171
    you can't read Chinese, but the maths is common and you can see. In a lot of textbooks Ricci tensor is so defined like Yang's articles , not only the textbook I recommend to you above, it is impossible that all authors are wrong, in fact, the two definitions are completely equivalent and the two ways of definitions have the same effect
     
    Last edited: Jun 12, 2018
  13. heyuhua Registered Senior Member

    Messages:
    171
    I don't think it's necessary for us to continue to waste our time on this issue. If you can't calculate it yourself, your doubts will not really be eliminated, only through calculus can you really understand the beauty of this.
     
  14. heyuhua Registered Senior Member

    Messages:
    171
    The two ways to define Ricci tensors have the same effect and respectively correspond to the two methods to write the field equations, namely G^uv=8paiGT^uv and G^uv=-8paiGT^uv, corresponding to each of them. The two methods of field equations distribute in a large number of teaching books, you can find them yourself
     
    Last edited: Jun 13, 2018 at 12:24 AM
  15. arfa brane call me arf Valued Senior Member

    Messages:
    5,586
    This thread is based on a load of rubbish. The two forms of the Ricci tensor are an artefact of the sign convention (the metric signature). Obviously it's important to make sure you stay with the convention you use, and not compare your equations with those where a different signature is used.

    Otherwise you might as well say 1 = -1. Further, Yang's claim about cosmic expansion and the creation of matter just isn't supported by any evidence. This is definitely crank material and it's very likely I and everyone else is wasting their time here.

    Note the denials, the lack of evidence that heyuhua has any intention of engaging in any kind of discussion, the presentation hinting at "new and revolutionary" results . . .

    What a joke, it seems to be based on a mathematical error that the author isn't prepared to admit. It's the kind of error undergraduates make in GR courses and indicates a lack of understanding of the metric (distances are always positive, for instance; if you get a result based on negative distances you probably made a mistake somewhere).
     
    Last edited: Jun 13, 2018 at 1:57 AM
  16. heyuhua Registered Senior Member

    Messages:
    171
    The two sets of schemes to definn Ricci tensor are independent of each other, and if you use one, you can't use the other, there is no problem like 1=-1 at all. Besides, such the two sets of schemes are don't start from me, before, a lot of textbooks do so, if you feel incomprehensible, you can go to blame those experts
     
    Last edited: Jun 13, 2018 at 5:10 AM
  17. heyuhua Registered Senior Member

    Messages:
    171
    Random attacks are irrational. There have been a lot of facts about the continuous generation of matter, as described in Yang's article.
    You're ignoran
     
  18. arfa brane call me arf Valued Senior Member

    Messages:
    5,586
    It's interesting then, that Yang compares his version with another, "independent" version, as NotEinstein mentions.
    A lot of facts, huh? So where are the experiments confirming these "facts"? And why can't you spell the word "ignorant"?
    Never mind that last question, I know the answer.
     
  19. NotEinstein Valued Senior Member

    Messages:
    1,234
    Yes, and if you read my post again more carefully, you'll notice I did just that.

    You keep claiming things about "a lot of textbooks" this, but the first textbook you brought up didn't. The second one you (eventually, after 50+ posts) brought up did, but that's hardly "a lot".

    True, just as Carroll isn't wrong, and that Wikipedia-author isn't wrong either. Additionally, all authors of textbooks (and Wikipedia) mentioned in this thread so far agree about the \(8\) in the EFE. Everybody, except Yang. But, as you said, "it is impossible that all authors are wrong", so Yang must be by your own argument ad populum.

    Exactly. So when Yang compares the two directly, that's fundamentally nonsense, and a wrong thing to do. It appears you agree with me: Yang is wrong in claiming that this minus-sign has any physical meaning; it's just a minus-sign due to conventions, nothing more.

    Indeed. You have thoroughly helped prove that Yang is wrong.

    We now have four sources that do the calculations; I don't need to do it myself anymore.

    Why should I have doubts? We have four authors agreeing with each other, and as you said, "it is impossible that all authors are wrong". So I believe their derivations, which means Yang is wrong.

    I don't disagree there, but I don't see how that's relevant to the discussion at hand? Or are you saying that Yang can't understand the beauty of this, because (s)he can't go through the calculus properly?

    True, and I don't think I've claimed otherwise?

    Yes, and we've visited several of those in this thread. Well, eventually, after 50+ posts when you finally managed to find one source using the alternative definition. And from that source (you provided) we learned conclusively that Yang is wrong, even if we take this alternative convention into account.
     
  20. NotEinstein Valued Senior Member

    Messages:
    1,234
    Actually, I don't think that's the case. (I initially thought this as well.) There are two ways of defining the Ricci tensor; basically, you can contract the Riemann tensor over either the third or fourth index. It results in an overall minus-sign difference in the form of the Ricci tensor. This minus-sign difference then has to be 'compensated' in the EFE. This is unrelated (as far as I can tell) to the metric minus-sign convention.

    But of course, just as the metric minus-sign convention, it has no effect on the physical predictions made by the EFE.

    And the insults. Don't forget the insults!

    Funny thing is, heyuhua has already admitted Yang is wrong multiple times in this thread, just not explicitly. There's some massive cognitive dissonance at play here.

    I think the concept of minus-sign conventions is even explainable to and understandable by high school students...
     
  21. NotEinstein Valued Senior Member

    Messages:
    1,234
    Exactly, and since Yang does switch between the two when (s)he compares his/her EFE to the usual EFE, Yang is guilty of doing exactly that. So you once again agree with us that Yang is wrong.

    Can you rephrase that? I don't understand the point you're trying to make?

    Are you saying that you didn't come up with the two Ricci tensor definitions, so if they are confusing, we have to blame the experts for that? Nobody here is confused (anymore?) about this; only Yang is. If (s)he wants, Yang can go blame the experts for making him/her make simple mistakes; I have no need for it. (Although I will admit it would be nice if all these conventions were centrally documented somewhere, so it's much easier to find out about them, but I fully understand why this isn't the case, and that you can't blame the experts for this.)

    Are you referring to the insults you've been throwing at me in this thread?

    We didn't even get to that part of Yang's work, because we found a fundamental flaw much, much earlier on. I would suggest Yang fixes that first; most likely it changes the "facts" about the continuous generation of matter Yang describes in his article.

    Perhaps, but we're no longer ignorant about Yang being wrong.
     
  22. heyuhua Registered Senior Member

    Messages:
    171
    the earth is growing up, the sun is bright and bright, the moon is going away from the earth, the earth is going away from the sun, the earth's spin is slowing and slowing, and so on, such a series of phenomena an facts can uniformly and systematically explained based on continuous creation of matter
     
  23. NotEinstein Valued Senior Member

    Messages:
    1,234
    Perhaps, but what we do know is that Yang is wrong with his/her analysis of the EFE. Care to address that first?
     

Share This Page