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Size of the Universe

  1. Apr 19, 2007 #1
    I'm writing a speech for tommorow for my pre-university physics class. I can find basic facts for some basic theories on estimating the size of the universe, i just wondered if any of u guys have any easily understandable thoughts of your own that i could include. Or maybe you know some kind of not well known theory which could be useful explaining. Bear in mind this isnt advanced astronomy or anything :tongue2:

    the speech is only 5 minutes long and i think i'm going to finish with this very intriuging video: http://www.youtube.com/watch?v=EDNEV9EW06g&NR=1

  2. jcsd
  3. Apr 19, 2007 #2


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    You might get some inspiration from


    which goes through visual representations of some 40-odd orders of magnitude, from 10^25 meters (where the Virgo supercluster of galaxies is barely visible as a dot), through 10^0 meters (a man at a picnic), down to 10^-18 meters.

    There's a well-known film by the same name, but I couldn't get the website to display it.
    Last edited by a moderator: Apr 22, 2017
  4. Apr 20, 2007 #3
    thanks, i used it and it went well
  5. Apr 23, 2007 #4
    The SIZE of the universe is equivalent to the COLOR of space.
    It is infinite. Undefined. Size is a definition and it has no 'size'.
  6. Apr 25, 2007 #5


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    Few modern cosmologists believe the universe is infinitely large, at least not the portion that is, or ever will be observable to us. The universe may be a subset of a 'metaverse' that is larger, perhaps even infinitely larger than the portion detectable by us, but that is the realm of metaphysics, not science. The universe might be turtles all the way down, or it might be a single turtle standing on pixie dust.
  7. Apr 25, 2007 #6
    The Universe is all which exists. At least it was when I was a kid. If you are going to use a subset, use 'the known universe' or 'the universe of idiots' - don't change the original meaning of the word and then coin a higher degree of something already omnific. You cannot have more than 'all'.

    The simple proof you find in basic number theory which disproves the existence of a highest number is the same proof which precludes a greatest distance. At any given instant, three independent values (coordinates) are all that is necessary to uniquely specify any point of existence within the Universe - hence there are said to be three 'dimensions' (more accurately, three axes). And if someone wants me to believe the universe is finite, then all they have to do is simply convince me that at least one of those three independent variables has a limit. Good luck.

    When they begin manufacturing extra dimensions and particles which travel back and forth in time, academics are obviously playing fast and loose with the most basic, observable and self evident principles of logic. If anyone wishes me to believe there are more than three dimensions, then prove to me that there are locations in the cosmos which cannot be specified within the three aforementioned coordinates. (Hint: you will probably have to ply me with alcohol well in advance)

    The scholarly sleight of hand to which contemporary theorists occasionally descend in order to achieve publication is, indeed, amazing. How sad that supposedly intelligent individuals are reduced to spouting and defending that which is obviously ridiculous. The kings have no clothes - no matter how much alphabet soup follows their names.
    Last edited: Apr 25, 2007
  8. Apr 25, 2007 #7


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    My first astro teacher, who instilled in me a sense of how professional astro/cosmo people talk, was always very careful to say "observable universe" when he meant observable universe.

    When he simply said "universe" he meant the whole thing as inferred by fitting a model to the part we can see, based on the key assumption that the rest was uniformly similar. He made clear that he was assuming this kind of large-scale average uniformity ("homogeneity and isotropy" also called the "cosmological principle").

    Without explicitly invoking this SAMENESS assumption, he would not make statements about the universe at large.

    BTW this was not a boring guy. His lectures were exciting. But he was careful in his use of words in certain maitters. when he said observable universe that was different from what he called universe.

    I think that is fairly typical although I can't actually speak about ALL cosmologists, only those I have observed.

    Also he didn't talk about "extra dimensions" and "multiverse" or anything especially speculative. He could get published plenty with straightforward research based solidly on observation. (String theorists are a different kind of animal, in general, from astronomers---conditions in their community are different and what they consider legitimate research to publish about is different.)

    My teacher often explained that the SCALE FACTOR which for lack of a better word is sometimes (in casual informal talk) called "the size of the universe" by astronomers was not, in fact, to be confused with the size of the observable universe. It is also called "the average distance between galaxies".
    The scale factor is a number that changes with time and tracks the expansion and is usually set equal to 1 at present, by convention. You need it to construct a model that will fit the data. It is written a(t) or sometimes R(t) and it depends on time. Unfortunately astronomers have a careless habit of calling it "the size of the universe" when talking to laymen or journalists, but the correct term is the scale factor.

    He was always careful to point out that the universe could be spatially finite or spatially infinite. Either way the model, where you have the scale factor, works. Finite and infinite are just two different versions of the same model.
    The scale factor, this "average distance between galaxies" number a(t) that is growing with time can be approximately the same in either version.

    The scalefactor is a well-defined number even if the universe is spatially infinite. Indeed it is convenient to assume that it is spatially infinite and that is commonly assumed when you do number-crunching. But I never heard an astronomer claim to KNOW whether it was spatially infinite or finite.

    either way, as I said, the same a(t) or R(t) scalefactor, increasing with time, works.

    what I get from this is that, on this issue, you Thor are not so different in your thinking from the PhD people I happen to have encountered and whose stuff I read, and who are basically pretty sensible and clear-headed.

    In your TONE you sound provoked, and as if you don't like Academics and suspect them of abusing words and spouting B**S***.
    But in what you say you are not so different (on this issue) from Academic folk I've encountered.

    So you could calm your tone down and we could talk about these things, if you want.:smile:
    Last edited: Apr 25, 2007
  9. Apr 26, 2007 #8
    Marcus -

    Sounds like you went to college in the 60's/70's when at least some common sense still prevailed in academia. I don't know if it was the 'new math' or the psychedelic drugs, but scholars today seem eager to disregard accepted, self evident basic precepts and ply their respective disciplines with fantasies and conjecture which is commonly picked up by the media and distributed to the dumb masses as gospel. (yeah...a tone-down might seem appropriate :surprised )

    Yes, string theorists are particularly pernicious, but even stodgy old cosmologists continue to refer to the 'Beginning' of the universe when it is so easily shown that the phenomenon of existence is not the result of cause and effect. (actually Newton discovered the principle which explains existence - he just didn't take it far enough)

    "Spatially finite" does not jibe with the fact that none of the three independent variables which determine relative distance and position within the universe seems to have a limit. Why would 'spatially finite' even be given serious consideration. But, of course, if you take the universe into a fourth dimension, then you can bend it, twist it, tie it in a knot and it still keeps on ticking. (still looking for that 4th spatial axis)

    Particle physicists are still seeking the holy grail of a simple set of homogeneous and structureless 'fundamental particles'. Why on earth would they think the most basic elements of the cosmos would be structureless? WECIB? (What Else Could It Be?) I was weaned off of WECIB in 9th grade geometry. Quantum 'mechanics' are looking for something which doesn't exist...AND SOME ARE CLAIMING TO HAVE FOUND IT.

    It is frustrating to watch all that wasted effort seeking answers that don't exist to questions that are falsely premised...i.e. the 'size' of the universe
    Last edited: Apr 26, 2007
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