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What is the smallest existing thing in theory and law?

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Possible duplicates: physics.stackexchange.com/q/28720/2451 and links therein. –  Qmechanic May 10 '13 at 21:51
    
It's string (of String Theory). If you expand an atom to the full size of observable universe, the String would be a tree. Think how much smaller it is. –  Sachin Shekhar Mar 27 at 1:01
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2 Answers

The short answer to this question is that there is no answer because the question makes invalid (classical) assumptions. "Things" start to get blurry. They stop having a definite position, size, and boundary.

Take an electron for example. The electric field extends to infinity and the mass appears, to the best we can measure, to be a point in the center.

Theoretically, the Planck Length may be the smallest length that has any sort of physical meaning.

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If by 'thing' you refer to a physical thing, not a distance (as opposed to what Brandon was thinking of when he mentioned the Planck Length), then I guess the answer is the Preon, which is believed to be the particle that Quarks/Leptons are made of.

But of course, maybe tomorrow some physicist discovers a smaller particle (back when I was in high school, the proton was still considered the smallest)...

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I think Brandon's point regarding the Planck Length is that nothing could be smaller than an object with a measure equal to the Planck Length (ie. no ball with a smaller diameter). –  tpg2114 Sep 26 '13 at 22:10
    
So, you're saying that a Preon measures 1 Planck? –  knocte Sep 27 '13 at 0:07
    
I'm not saying anything -- particle physics is not my thing. I was just offering what I interpreted as the meaning. –  tpg2114 Sep 27 '13 at 0:24
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And, of course, there is as yet no evidence at all for the existence of preons. –  hdhondt Mar 26 at 22:56
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