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The cosmological principle in simple models of the universe

  1. Jul 11, 2006 #1
    NOTE: Taken from another thread on a similar subject: https://www.physicsforums.com/showthread.php?t=125698

    "An infinite amount of space with matter uniformly distributed throughout", is not a claim of infinite matter – at least it shouldn't be.

    If matter is assumed to be inside of a greater space that is infinite – then matter is necessarily less than infinite.

    I would hope his point, is simply about the uniformity of distribution at the infinitesimal. This is quite possible.

    Otherwise, it's just a short-sighted rehash of a relative ad infinitum.

    One way of looking at an open and closed model is this:

    A closed model has an edge – because matter is outside of space.
    An open model has no edge – because space is outside of matter.

    Another way of looking at them is this:

    A closed model – has both matter and space as finite.
    An open model – ha both matter and space as infinite.

    A closed model – has a big bang and crunch.
    An open model – has no big bang and crunch.

    Finite – has a beginning and end.
    Infinite – has no beginning or end.

    Finite – means the universe began, is, and will stop "actually" happening.
    Infinte – means the universe is always in the state of potential of "will happen".

    Either way, however – we can't tell unless we know what is outside the universe. Any description of the universe as "all" – begs the same question. What is outside of it? Space and matter are only capable of being a relative ad infinitum. Without an absolute there is no answer.

    Is the Absolute inside or outside the universe? It can't be both.
    Last edited by a moderator: Jul 12, 2006
  2. jcsd
  3. Jul 11, 2006 #2


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    Eric England, if you are interested in Cosmology this is a nice forum to hang around! But please, do not try to answer questions about stuff you don't have a good grasp of. It may be confusing for the OP.
  4. Jul 12, 2006 #3
    Excuse me! Who died and made you the God of cosmology?

    First of all, to state the big bang is this or that, without also stating that science doesn't even know if there was one, is as misleading as it gets.

    Secondly, what do you mean by "grasp"? Grasp of physics, mathematics, philosophy, religion, logic – what?

    Thirdly, is your blanket dismisal out of insecure ignorance, or would you actually like to have a civil arguement?

    Actually, I challenge you to one. You have given me every right to do so, and you have taken on a responsibility. Pick any point I made and tell the OPs exactly why it is wrong. And please, no bs about them not being arguable.

    I will be entirely civil in my response.
  5. Jul 12, 2006 #4


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    Eric England, my comment to your post was mainly written since I didn't want the OP to get confused. I didn't mean to offend you. However, to me it's clear you lack some improtant bits of understanding about cosmology and Big Bang theory, but no big deal about that, this is a nice place to be in if you want to learn more (speaking out of my own experience).

    No no, that is SpaceTiger...

    Science can never tell any "truths" if that's what you're looking for. However, there are a large amount of observational evidence in favour of Big Bang theory, and I think most cosmologists would agree the theory is well established.
    Anyway I'm pretty sure the OP's question was about BB.


    To take one of your points:
    A closed model does not have an edge, matter is inside of the space.
  6. Jul 12, 2006 #5


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    Eric England, EL is quite right, please don't attempt to answer questions on things you're not knowledgable about.

    The same rule applies to anyone answering questions. If you're not an expert, but would like to attempt to answer a question, please be humble and ask about things you're unsure of. We would really like to avoid confusing the questioner.
    Last edited: Jul 12, 2006
  7. Jul 12, 2006 #6
    Dear El and SpaceTiger,

    A thank you to EL for your graciousness. A "?" to SpacTiger for making assumptions.

    Cosmology includes all disciplines, until one or more are found to be capable of a complete theory. It is quite possible that thinking outside the box of science will be required.

    A closed model is spatially finite. Traveling in a "straight" line will have one arriving where one began. That is putting "matter" outside of "space"... is it not?

    An open model is spatially infinite. Traveling in a "straight" line will not result in arrirving at where one started. This puts "space" outside of "matter". This leads one to believe that matter is finite. Matter distributed (uniformly or not) throughout space, means matter is less than infinite.

    I realize that in science it is common to believe that space is always outside matter, but this belief is a logical short-sightedness. I think it is fair to say this short-sightedness is a possibility.

    I would add one other thing. Matter and space are both infinite. They intermingle. One does not ultimately contain the other. I will however, not digress with an explantion, although an explanation is readily available.

    As far as me not being an expert and having misconceptions – I would remind SpaceTiger that we are in cosmology. Physical cosmology is just a subset of cosmology, is it not? What "expertise" are you refering to?

    Not to drop a name, but Hawking says that the "why" of the universe is not answerable by science. He also says that the "what" is only answerable by first knowing the why.
  8. Jul 12, 2006 #7
    Just as a refresher – this is the original question.

    I spoke directly to it, although I did go on to make statements beyond the question. If you'll notice in the question, there are two statements:

    1. There is both an infinite amount of space and matter in the universe.
    2. There is an infinite amount of space with matter uniformly distributed thoughout.

    What I spoke to, is the disparity between the two statements.

    One has matter and space infinitely intermingling – with neither one ultiamately containing the other. Wouldn't this be the case?

    The other has an infinite amount of space containing a finite amount of matter. If matter is always inside of infinite space, then matter is less than infinite. Wouldn't this be so?

    This is a very important question that loseyourname is asking. Maybe we could zero in on it and discuss our perceptions of it.
  9. Jul 12, 2006 #8


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    No, it's not. Perhaps you're stuck on the balloon analogy and are taking the inside of the balloon to be "space". In this analogy, it's only the surface of the balloon that is meant to be "space".

    The classic "open" model of the universe is homogeneous and isotropic. Since space is infinite in extent, there is also an infinite amount of matter in this universe. Again, the "space outside matter" doesn't make any sense.

    I think it's fair to say that you don't know enough to be accusing astronomers of short-sightedness.

    Obviously, expertise on the concepts referred to in the question.
  10. Jul 12, 2006 #9


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    SpaceTiger gave you an (as always) clear answer, and I'll just fill in some comments.

    Science is done by doing science. Period.

    Incorrect. The matter in the universe is of course in the universe. I can't see how you could say something is "outside space"?

    Again, the matter in our universe is in our universe. I still cannot see why you are using such strange phrases as saying that "space and matter are inside or outside each other?
    Less in what sense?
    This might be a good analogy for you to think of:
    Imagine an infinitely long ruler. At each centimeter marking now place a cent. How many cents are there now along the ruler?
    In the same way a spatially infinte universe with matter uniformly distributed in it, contains an infinite amount of matter.

    Cosmology is science. Period. Nothing else.
    Last edited: Jul 12, 2006
  11. Jul 13, 2006 #10
    Well, I don't know why you moved this discussion or why you titled it what you did, but I suppose it is self-evident to the forum – that it is not my thread nor my wording.

    Since you guys seem to be on the same page, I'm going to lump you together as one – I hope you don't mind.

    First of all, you are either misinformed or uninformed on the the scope of cosmology. Physical cosmology (science) is not the only cosmology. It is a subset. Do your homework.

    Secondly, don't believe Hawking or others, if you like – but science is not the be all end all. Again, do your homework.

    When I said – "It is quite possible that thinking outside the box of science will be required." – and you said "Science is done by doing science. Period." – your response indicates you know little about the limits of the box you are in. This is fine if you intend to work in the applied sciences, but you will not have success in theoretical science, if you don't recognize the limits of the box.

    When I said – "that is putting 'matter' outside of 'space'... is it not?" – and you said – "Incorrect. The matter in the universe is of course in the universe. I can't see how you could say something is 'outside space'? – my response to this, is that you must think that space only exists outside the universe.

    Your analogy of the infinitely long ruler is also inaccurate. Matter (cent) distributed throughout space (infinite ruler) is always at least two cents short of the ruler. One cent on the infinitesmal end and one cent on the other end. As long as space is considered to be ultimately outside of matter and not also vice versa, matter will always be finite.

    This is why I said that for them both to be infinite, requires matter to be distributed throught space and space to be distributed throughout matter. One does not ultimately contain the other. They infinitely intermingle inside & outside of each other.

    What is outside this intermingling is another story. This is ouside the box of science, however, so I'll do us all a favor and pass on it.

    In closing, I'm wondering if you guys think that the big bang happened inside of space?
    Last edited: Jul 13, 2006
  12. Jul 13, 2006 #11


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    You seem to have been misinformed about (or are oblivious to) the purpose of this forum. This is a forum for science (physical cosmology). That this is not plainly obvious from the content of the other posts is a mystery to me.

    I'm not sure if the rest of what you're saying should be called genuine philosophy, but either way, this is not the place for it.
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