The universe?

Discussion in 'Physics & Math' started by god-of-course, Sep 20, 2003.

  1. lethe Registered Senior Member

    Messages:
    2,008
    Mac:

    i am still waiting for that paper that shows MOND having anything to do with Dark Energy. are you having trouble finding it? do you remember the name of the author? perhaps i could check the arxiv.
     
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  3. MacM Registered Senior Member

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    10,104
    lethe,

    Still looking.

    Knowing to believe only half of
    what you hear is a sign of
    intelligence. Knowing which
    half to believe will make you a
    genius.
     
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  5. Mark Registered Senior Member

    Messages:
    150
    didnt catch the beginning
    Im curious to know too.

    I dont understand people being interested in MOND, it has never seemed too promising, and for example see this discussion of MOND and Dark Energy
    http://www.lns.cornell.edu/spr/2003-03/thrd4.html

    However lethe is asking for an article that relates MOND and Dark Energy and I did find one
    a quick googling googled-up an article by Peebles
    http://lanl.arxiv.org/abs/astro-ph/0207347
    from last year which discusses MOND vis a vis Dark Energy
    in paragraph 4 of the "cosmological tests" section.
    Article is called something like "The cosmological constant
    and dark energy" and certainly does relate it to MOND.

    here is the same paper HTML at a Caltech "level 5" site for immediate access without waiting for download
    http://nedwww.ipac.caltech.edu/level5/March02/Ratra/Ratra_contents.html

    if you can actually formulate a MOND hypothesis that allows discussing cosmology (BB etc) then there is an obvious connection between MOND and the predicted amount of Dark Energy (one feeds right into the other---I'll explain)

    but I dont expect anyone has written a paper about what I have to say about the MOND-dark energy connections

    the amount of dark energy (with usual assumptions, essentially a pos. cosm. const) is estimated by first estimating the Dark Matter needed to keep clusters and galaxies and such arrayed in proper order

    this Dark Matter together with the visible matter comes to around 0.2 joules per cubic kilometer, average, or equivalently 0.27 of rho crit----the critical density calculated using the Hubble parameter

    what they estimate for Dark Energy is just the balance! around 0.6 joules per cubic kilometer or about 0.73 rho crit. Because the U is seen to be very nearly flat.

    So MOND must have a strong effect on the estimated amount of Dark Energy.
    Personally I dont speculate about MOND. But if you do MOdify Newtonian Dynamics so that you can explain the stable clustering of galaxies without Dark Matter, and the rotation curve of individual spirals and all that without using Dark Matter

    then you will necessarily calculate a very different amount of Dark Energy, because it is the balance---what is needed beyond estimated matter to guarantee overall flatness.

    Other things equal, estimating less Dark Matter will make the model need more Dark Energy. But different MOND hypotheses will affect rho crit differently and influence rho crit as well, so saying "other things equal" is a bit of a simplification

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    maybe this what Ive been saying is obvious to everybody reading the thread and in particular to MacM and lethe. but it is sometimes hard to tell what is obvious so I'll just say it.

    I think a person could argue that you can exclude MOND simply because of its strong effect on the estimated density of Dark Energy! Postulating MOND would reduce the Dark Matter estimate and under reasonable assumptions would increase the Dark Energy estimate to much more, so it would have caused more acceleration than has been observed! I suspect that MOND is between rock and hard place and the possibilities for it have been narrowed down considerably in past 3 or 4 years.

    I will look too though, since lethe is obviously very interested in the question and pressing for a link to paper
     
    Last edited: Sep 28, 2003
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  7. 1100f Banned Registered Senior Member

    Messages:
    807
    What James did was to put a coordinate system on the line by labeling each point on the line by its distance from some arbitrary point P and saying that the points on the left will be labeled by a - sign and the points on the right of P will be labeled with a + sign. This has strictly nothing to do with the mathematical rules of + X + = + and - X - = +.

    If you take the segment consisting of the points on the right side of P, it will have an infinite length since for any point P' that you pick on the right side of the point P, there will allways be points that are at a larger distance from P than P'. A similar reasoning applies to the points that are at the left side of P. So the half line consisting of the point that are right to the point P has an infinite length, so is the left one.
     
  8. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    Re: RE:2inquisitive

    ==============================================
    ProCop, that is where my confusion comes from. If you are creating
    a circle from an (infinite?) line as you state, why does it have to be
    a ball? Definitions of Fractional Dimensions:
    A line has one dimension - length. It has no width and no height, but infinite length.
    <http://math.rice.edu/~lanius/images/line.gif>
     
  9. leeaus Registered Senior Member

    Messages:
    265
    Hello 1100F. You confuse a larger distance and infinite distance. Link = demonstration diagram. http://home.iprimus.com.au/siewk/inmis/

    Plain arithmetical sloppiness leaving distance out of infinite distance.

    Regards

    Leeaus
     
  10. leeaus Registered Senior Member

    Messages:
    265
    Hello 2inquisitive It should be noted that the line your link leads to has width. Can you demonstrate a line with zero width in reality?

    Regards
    leeaus
     
  11. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    ================================================
    Well, the definition of a line is that it is 1d. Can you demonstrate
    a line with infinite length in reality?
     
  12. 1100f Banned Registered Senior Member

    Messages:
    807
    Where is my confusion?
    Maybe it is because english is not my native tongue.
    I thought that when you said that: Therefore neither half is of infinite length, you meant that the two halves are not of infinite length.
    This is why I showed you that they are of infinite length.

    Sorry.
    My mistake.
     
  13. MacM Registered Senior Member

    Messages:
    10,104
    Mark,

    ANS: Thanks for your help. I have not found the statement I am looking for but you have hit the nail on the head. the above link you provided clearly shows the coupling affect MOND has between Dark Matter and Dark Energy.

    This is precisely what the article was saying and only makes good sense. I am at a bit of a loss for Lethe's instance that I produce the exact link but I will continue to look for it.

    Most make this general connection but the one I paraphrased was very explicit on that point.

    To say the least your point fits well with what they said.

    Knowing to believe only half of
    what you hear is a sign of
    intelligence. Knowing which
    half to believe will make you a
    genius.
     
  14. MacM Registered Senior Member

    Messages:
    10,104
    Lethe,

    Well I found it. But you aren't going to like it and I won't stand by it either except to say I like some of what he has to say.


    http://www.softcom.net/users/greebo/CVP.htm

    ... the Professor is the "Father of MOND" and MOND means "Modified Newtonian Dynamics". MOND is a theory which ... expansion of our universe (not dark energy - although the nether is the ...


    He further comments:

    Within the last couple of years, Einstein's theory of relativity has been conclusively disproved to anyone who is willing to take a good look at the facts.

    According to relativity, space is supposed to be curved. This has not proved to be true. In fact, space is not curved but "flat". Apparently, there is no space-time composed of some strange and exotic geometry.

    This fact, combined with others which have come to light in earlier times has shaken the faith in any form of relativity except relativity to the medium through which light travels.

    Of course, there are still those to whom facts are merely superfluous inconveniences.



    Since your bone has been challenging me to produce the link. I have done so. I have no interest in argueing the validity of his comments. Others can make up their own minds. We know yours.

    Knowing to believe only half of
    what you hear is a sign of
    intelligence. Knowing which
    half to believe will make you a
    genius.
     
    Last edited: Sep 28, 2003
  15. MacM Registered Senior Member

    Messages:
    10,104
    leeaus,

    ANS: Are you saying you reject "Strings Theory" outright. They are 1d vibrating stings (lines).

    \

    Knowing to believe only half of
    what you hear is a sign of
    intelligence. Knowing which
    half to believe will make you a
    genius.
     
  16. leeaus Registered Senior Member

    Messages:
    265
    Hello 1100f. Any length not containing all length is finite length. Is that what you are agreeing with? Apology accepted if so.

    If you take the segment consisting of the points on the right side of P, it will have an infinite length since for any point P' that you pick on the right side of the point P, there will allways be points that are at a larger distance from P than P'.(1100f)

    Your command of English seems fine. This was incorrect though as shown on the link. This post of yours says that that the distance to the right of P is greater than the distance to the right of P’. It does not say that the distance to the right of P is an infinite length.
    You were forgetting distance to the left of P when you made claim that the distance to the right of P was infinite.
    Many seem to make this mistake.
    Making the source of infinite distance a point or the gaze of the observer is the mistake.
    That is what JR was trying to do after originally recognizing that infinite distance must encompass all distance.
    Infinite distance can have no origin or source.
    You are trying to describe an infinite distance that has a precise beginning.
    The trouble is any chosen beginning of infinite distance leaves out the distance prior to the chosen beginning (or to the left as you are doing) and is thus sub infinite or finite distance on account of the left out distance.

    Think about it.

    Regards
    Leeaus
     
  17. 1100f Banned Registered Senior Member

    Messages:
    807
    What do you mean by "containing"?
     
  18. leeaus Registered Senior Member

    Messages:
    265
    Hello 1100f. Encompassing, all inclusive, none left out, is the answer to your question.

    regards Leeaus
     
  19. ProCop Valued Senior Member

    Messages:
    1,258
    Let's have a look at the infinity from the other side then:

    We start with an Endless Space ES

    What can be said about ES.
    P 1- there is nothing bigger then ES
    P 2- it cannot be divided (it wouldn't be endless if a piece of it
    was cut away from it.)
    P 3 - there can be 1 ES only

    an Endless Line (EL) is a cut from ES, by "creating" the EL the ES is destroyed and consequently ES and EL cannot (both) exist P1,P2,P3. (but I agree with you that you can imagine them apart - if that's what you meant).

    the ball
    you have EL turn it 180 degrees you get Endless Circle EC you turn EC 180 degrees (in right angle to the EL): you have the ball (not really a ball more the sort of "shapeless curved" something)
     
  20. 1100f Banned Registered Senior Member

    Messages:
    807
    And what is length?
     
  21. leeaus Registered Senior Member

    Messages:
    265
    Hello again 1100f Length is one of three spacial elements at right angles to each other.

    Regards
    Leeaus
     
  22. 1100f Banned Registered Senior Member

    Messages:
    807
    So you mean by length what is called in mathematical language one of the N dimensions in a N dimensional space (where you take N = 3).

    Then again, I don't understand when you speak about "length containing a length".

    Can you give me an example of a length containing a length?
     
  23. Persol I am the great and mighty Zo. Registered Senior Member

    Messages:
    5,946
    A line doesn't need to 'contain' all length. (I'm assuming that this means that the line passes each and every x coordinate; or whatever direction.)

    As James said, if you have a line that goes in 1 direction forever it is, by definition, inifinite. As long as atleast 1 end is missing, it is inifinite.

    Now the only place you could argue this is if space loops back on itself or something.
     

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