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Is The Definition Of A Singularity Incorrect?

  1. Jul 25, 2008 #1
    Hi, i'm no expert at physics, so please forgive any blatant errors my following statement may contain. I've been discussing with others that the definition of a singularity is wrong and needs to be redefined. The reasons are as follows.

    By definition the singularity was of zero volume, had zero mass but infinite gravity. The arguements for this so far have been due to gravitational calculations.

    1) gravity = weight / mass

    2) Fg = G x mA x mB / r x r

    Fg = gravitational force between 2 objects
    G = gravitational constant
    mA + mB = mass of object A + mass of object B
    r = distance between the 2 objects in metres.

    Now so far i am told infinite gravity can occur when there is no distance between matter, as essentially anything / 0 = infinity.

    I have argued that gravitational formulae cannot be used for zero values, as that would imply wherever nothing is, by calculation, there is infinite gravity. this cannot be as it would not allow the gravity fields of our space - time to exist, and matter would be evenly distributed across infinity, as infinite gravity would be constant across infinity.

    I have suggested that a singularity had mass and volume and existed in space - time(perhaps somewhat distorted due to it's incredible gravity field, but space - time of a kind).

    I have also suggested that an external force not an internal one caused it to seperate, or a combination of internal / external forces were the cause.

    I have only been told i am wrong to all of this, so i thought i'd ask the experts, so please someone, please agree with me, or explain in terms i will understand ie; if you use equations explain each part. I feel i've missed something fundamental as i've been looking into singularities and most attempted explanations break down because the usual laws of physics did not apply, but what if they did??
     
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  3. Jul 25, 2008 #2

    cristo

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    What is the definition of a singularity that you are using?

    Note that most professionals do not suggest that a singularity exists in nature. It is merely a mathematical warning which tells us that our theory is not defined in the region it is being applied to.
     
  4. Jul 25, 2008 #3
    The definition is a point in space -time at which gravitational forces cause matter to have infinite density and infintessimal volume, and space and time to become infinitelt distorted.

    I was questioning this definition and have been told it was theoretically possibly by derivations of calculating gravity.

    I personally can't see how, but my logic is not as good as many on this site, i am hoping to know

    1) is the definition of a singularity correct??

    2) if so how is it possible, and why would infinite gravity not evenly distribute matter across infinity?

    3) what forces could cause a 'big bang' from a singularity of the above definition?
     
  5. Jul 25, 2008 #4

    marcus

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    Astronomers don't say that a singularity actually existed in nature. that is only in newspaper popularizations and books intended for wide audience.
    Like Cristo says, a singularity is just a breakdown in a manmade theory. In the past we have gotten rid of singularities in other theories by improving the theory so it doesn't break down.

    This is now happening in cosmology. Researchers are working on ways to improve the theory so it will work better and not break down.

    So it will compute sensible numbers instead of nonsense like infinite density.

    1) your definition is OK, it is just a way of saying that a singularity is where a manmade theory blows up and says crap like infinite density

    2) you ask how is it possible. It isnt possible. Theorists are working on improving the theory so it doesnt predict infinities. A lot of progress in the past couple of years by people at Penn State.

    3) no forces I know of, the singularity idea is unphysical, so there is no reason to worry about it. You just improve the theory so it doesnt break down. In the Penn State work there ARE forces that expand from a state of high density----but it is not infinite. they run both computer models and equation models and consistently go back in time before the beginning of expansion without a singularity (breakdown---infinities etc.) occurring.

    it's really a separate topic

    anyway the answer to your 2) and 3) are that it's not possible, and no forces.

    Your questions are pretty good because they point out why scientists don't think that singularities exist in nature (you get that misconception more in popular books meant to sell to general readership)
     
  6. Jul 25, 2008 #5
    How do you conclude a singularity is a point in spacetime?

    Note also that there are different kind of singularities.
     
  7. Jul 26, 2008 #6
    I was quoting the official definition from a google search. you have confused me now though, as the prior post to yours seems to totally disagree with your statement, as it says they are impossible, which is what i thought but was unsure as i'm no expert, but i am definately thinking of taking up physics as i am more and more interested the more i learn.
     
  8. Jul 26, 2008 #7

    marcus

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    I wrote the prior post to Jennifer's. I believe she said that in General Relativity, a manmade theory, there are several different kinds of singularities. Indeed there are for a fact!
    Some people have spent a good part of their lives studying all the different ways that theory can break down.

    It doesn't necessarily break down at an isolated point, the region where it blows up and doesn't calculate can be larger.

    Pathological behavior of a manmade theory does not imply that Nature breaks down or stops. In the past other manmade theories have had singularities and it has been fixed by finding an improved version. Major advances in science can come from fixing singularities!

    We may all three (you, me, Jennifer) be basically in agreement on some things. If there is confusion it may be mainly verbal.

    One thing you could do, if you use google and find definitions and stuff online, is give LINKS to your sources. That makes it efficient for us, because we can immediately follow back to the source and see where you are coming from.

    Incidentally in the English language as you probably realize the word singularity has several different meanings. In the context of cosmology it means the breakdown of a theoretical model (blowing up, computing infinities or other nonsense, breaking down altogether etc...).

    In other contexts the word can mean other things, so for all I know for geologists or biologists there may be natural singularities (according to their technical jargon) which do exist in nature. That does not concern us here.

    But it does show why it is important to give sources---so that if there is an apparent contradiction it will be easy to trace back and see the original context.

    Are you content, Azzkika? Or do you have further questions? Welcome, by the way. I see you are new. You asked a very reasonable question (there is widespread confusion in the public mind about that concept.)
     
  9. Jul 26, 2008 #8
    i am now only confused as to which definition you refer when saying singularities occur. i hope that it is the 'breakdown of theoretical model' definition, otherwise i'd be very curious as to what these singularities' physical properties consisted of and what laws, if any, can applied to them.

    as you have noticed, i am new and not very adept at physics whatsoever, but i am very fascinated by alot of science.
     
  10. Jul 26, 2008 #9

    marcus

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    As far as I know, in Cosmology (what we talk about in this forum) the ONLY meaning of singularity is a breakdown in a manmade scientific theory.

    I don't know if biologists or geologists or others use the word differently. Maybe they do and maybe they don't. Maybe there is a real layer in a real piece of rock which geologists call the "Ordovican Pseudo-Permian Singularity". probably there isn't :smile:
    it would sound pretty silly. But technical jargon is unpredictable.

    Just remember that HERE in this forum, the Cosmology part of PF, a singularity is not something real occurring in Nature. It is something researchers are trying to get rid of by improving their models.

    since you seem to have a voracious curiosity, I will offer you a link to a lot of more or less illegible technical articles by people who are developing improved singularity-free cosmology.
    http://www.slac.stanford.edu/spires...+DATE+>+2005&FORMAT=www&SEQUENCE=citecount(d)

    the point is that even technical research papers sometimes have something comprehensible in the summary, or the introduction, or the conclusions section at the end---so you can see for yourself some of what is going on in current research and not depend entirely on secondhand info.

    the search I linked to here is an academic data base called Spires, and the search parameters are to list all the papers published since 2005 which have keywords QUANTUM COSMOLOGY and to list these papers in order of citation count. The most highly cited papers are listed first. These are the ones that are usually most representative of what is going on in a research field, because they are the ones that the other researchers cite as references in their own work. You can play around with the search tool and change the parameters if you want.

    quantum cosmology is the name of the research area where they are working on new cosmology models which get rid of the singularity. the classical GR and Friedmann equations break down, so they are developing quantum versions of GR and the Friedmann model which do not break down. And that is called quantum cosmology research. That is why I used that keyword.

    the field is changing fast. lots of new results. so it pays to restrict attention to recent papers. that's why I said "date > 2005" in the search.

    Have fun :biggrin:
     
    Last edited: Jul 26, 2008
  11. Aug 20, 2008 #10
    I am also not an expert, so I also want to ask you guys a question about this same topic. In quantum theory it says that a particle can be at more then one spot at a time right? The particle is at ever place that is possible. Well then in result with a singularity the size of it would only be the size of the probability. So the volume would just be the probability of the place of each particle, and since there all at the same place, then it would all be the same. Hence there is a point where quantum theory doesn't allow for it to get smaller. Please point out what is wrong with this, because I am sure if it was true it would have already been pointed out by other top physicist's. So please help me learn.
     
  12. Aug 20, 2008 #11

    marcus

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    You are on the right track. You are trying to think thru what happens when you introduce quantum mechanics into the picture----into a situation where the classical non-quantum model of General Relativity experiences a failure.

    What can happen is with the quantum version of GR you don't get a breakdown (i.e. a singularity) you get a bounce.

    As you suggest, the gravitational collapse can only continue up to a certain point, where quantum-geometric effects become important (think of it as analogous to the uncertainty principle in ordinary quantum mechanics, which prevents ever pinning a particle down completely) which actually make gravity repellent. So when it reaches very high density the collapse bounces.

    this is an example of a mathematical model (a type of quantum GR theory called loop quantum cosmology) doing what your intuitive description says it ought to do. It never reaches the infinite density of a classical non-quantum singularity.
     
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