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Given the Universe is expanding. Therefore everything within the U is expanding, in all dimensions, subatomic to cosmic. Then all metre sticks are expanding. The question: How can we measure U expansion with metre sticks that are also expanding? Alice only knew she had grown ten feet tall by comparing herself to her surroundings.

Qmechanic
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mbailey
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1 Answers1

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Space is expanding. However, nearby atoms (e.g. those in a metre stick) are not moving away from each other because the inter-atomic forces restore them to their original positions.

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Similarly, as the space between the earth and the sun increases (at an insignificant rate), the gravitational force restores the earth and sun back to their equilibrium distance.

lemon
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  • Great visual explanation for this common (and reasonable) question. – BMS Sep 05 '14 at 23:44
  • This is true, but only for a constant rate of expansion. In an increasingly accelerating universe the newly created space does have a non-trivial effect, hence the possibility for a "big rip" event. – CuriousOne Sep 06 '14 at 00:42
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    Also we should note that the current expansion rate is about $2\times 10^{-18}/\mathrm{second}$. This tiny expansion is completely swamped by thermal vibrations that are many orders of magnitude greater. – Mark Adler Sep 06 '14 at 04:21