Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Infinity and unique don’t mix. Theory

  1. Jun 24, 2010 #1
    Because space and time are infinite, doesn’t that make it impossible for anything to be truly unique. I propose there are an infinite number of this planet right now in this universe. The distance between each planet is probably unconceivable. Also there is an infinite number of this planet in the past and in the future. Not only is there an infinite number of earths exactly the same as this one, there are also an infinite number of this planet with slight differences and infinite number with extreme differences. This possibility is opened up because time and space are infinite. Nothing can ever be unique.
  2. jcsd
  3. Jun 24, 2010 #2


    User Avatar

    Staff: Mentor

    Neither space nor time are likely infinite.
  4. Jun 24, 2010 #3
    So your saying both have a start point and an end point? Well I believe otherwise. So humor me and pretend they are. Open your mind a little.
  5. Jun 24, 2010 #4
    I am far from an expert in these matters, but two fairly basic points come to mind.

    #1 - While infinities seem to have a functional place in mathematics, infinite quantities and values tend to have a rather dyspeptic relationship with physics.

    #2 - Just from the standpoint of mathematics, an infinite quantity of values does not imply all possible values for the class or variable in question. For example, if you imagine a number line, marked off in both directions with integer values, you have an infinite sequence of numbers, but you are hardly expressing _all possible_ numbers. Far from it, in fact. The same statement could be said for the rational numbers, the real numbers, etc... with each expressing an infinite sequence, yet containing 'more' numbers. Similarly, counting numbers and whole numbers are both infinite sequences, yet containing fewer numbers than the integers. FWIW, this has been a historical issue in mathematics of some controversy that involves some mind bending counter-intuitive thinking.

    An intersting popular/mid-level book on the subject and history of 'Infinity' is A Brief History of Infinity. Constable & Robinson. 2003. ISBN 1-84119-650-9


    By author Brian Clegg


    Last edited: Jun 24, 2010
  6. Jun 24, 2010 #5


    User Avatar
    Science Advisor

    Yes, these would all be logical consequences of a spatially infinite, infinitely old universe.
  7. Jun 24, 2010 #6
    Let's leave time aside, and focus on space. Spatial geometry of universe is flat as far as we can measure it. That implies that universe is either spatially infinite, or that it is really, really big (radius of curvature is so big that it simply can't be detected).

    So, you can take any arbitrary volume, and calculate all possible states and arrangement of matter in that volume, and then if physics is same everywhere, you can calculate how far is identical copy of that volume. Simple as that.

    Here is what famous multiverse guy Max Tegmark has to say about it. You can read whole paper at http://arxiv.org/abs/0905.1283" [Broken]:

    Is this your personal feeling, or is it based on some scientific argument?
    Last edited by a moderator: May 4, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook