1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can two objects ever be exactly the same?

  1. Nov 28, 2014 #1
    Hi! I will say outright that I know almost nothing about physics or the sciences. However, I'm pretty inquisitive and try to watch docos and read. This often leads me to questions, which are probably silly to you guys, but I'd still like to know what the answers are, if any.

    So, I was lying on the grass and looking at the sky and I thought, wow, everything in the world is completely different. No two things are the same. Then I thought, am I sure? Can two objects ever be exactly the same? You could come close if you tried. I mean you could get pin-point manufactured, say, bricks. They're both exactly the same in size, shape, colour. But even then, they would have been built at different times, maybe by different machines. Their appearance is identical, but their history is not.

    So is there any circumstance or evidence that two objects can be EXACTLY the same. I don't know what I mean by object really either. But some way that two… things… could occupy the exact same space and history? Even so, could they even be observed, as wouldn't merely viewing them make them different?

    Anyhow, it's late. I don't know if any of that made sense. In the scheme of things, I guess it doesn't really matter if two things can be perfectly identical, but thought you guys might know. If you do have any ideas, could you please try and reply in layman terms? I am smart, but I'm not quantum physics smart haha… :p
  2. jcsd
  3. Nov 28, 2014 #2

    Doug Huffman

    User Avatar
    Gold Member

  4. Nov 28, 2014 #3
    But what in all likelihood, are the actual chances of there being another me in a parrallel universe somewhere? I mean it'd be possible sure, but come on, surely the chances are very slim...

    To add a thought onto my original question... so what about Schroedinger's cat? Technically while in the box, the cat is not either alive or dead, but both simultaneously alive AND dead. So the two outcomes are identical, as they share the same history, provided no one observes them. Does this count towards two things being identical? Or have they merged into one "thing" and no longer count as two separate entitites? (Sorry if I haven't explained that well).
  5. Nov 28, 2014 #4

    Doug Huffman

    User Avatar
    Gold Member

    If there is one "parallel universe" then why not two and then a multiplicity that may be uncountable?

    Open at my side is Karl Poppers Quantum Physics and the Schism in Physics of his Postscript to Logic of Scientific Discovery, in which he agonizes over the interpretations of QM, more of which have been conceived since his writing. His stuff is hard, tedious, but enlightening!
  6. Nov 28, 2014 #5

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    I can't see how this conversation is going to go anywhere - at least not anywhere scientific - unless one defines one's terms. What is an object? What does it mean to be identical?
  7. Nov 28, 2014 #6


    User Avatar

    Staff: Mentor

    Vanadium 50 hits the nail on the head... as usual.
    This thread is closed because it's heading in a direction that is off-topic for this forum. Some of the links and references will be of interest to readers who wish to follow up on their own, but PF is not the place for this discussion.

    That's a common misunderstanding, and illustrates the pitfalls of discussing the philosophical implications of QM without first understanding QM. Schrodinger proposed the thought experiment not because he or any one else seriously thought that the cat was both dead and alive, but to point out a flaw in the then-current understanding of QM - it didn't say whether the cat was alive or dead. This flaw has been largely corrected during the 75+ years since then.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook