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Can we say that we are crystals because just like crystals we are made up of very small unit (cell) making up almost the same shape (our body) everywhere.

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Crystals are solids. But "we" are solid and liquid and gas. So no. There are many repeating patterns in Nature however. –  Roy Simpson Mar 11 '11 at 14:09
    
@Roy given the recent advances in material science, it wouldn't come as much of a surprise to discover a crystalline material which nevertheless behaves as a fluid. @LifeH2O one could say that a human body is a "crystal", if one were to stretch the conventional definition of a crystalline object to cover semi-regular objects such as organic tissue. But even then, it would be pushing it. Perhaps you have a more specific question in mind? –  user346 Mar 11 '11 at 14:58
    
@Deepak ""it wouldn't come as much of a surprise to discover a crystalline material which nevertheless behaves as a fluid. "" This non-surprise experience was made by a certain Prof Lehmann about 150 years ago. Since then liquid crystals are well-known, since the late 1960ties a lot of use is made of them for displays. Maybe You look at a liquid crystal display right now. –  Georg Mar 11 '11 at 15:46
    
@Georg, well, yes. In my defense, I was thinking of something a little more macroscopic. But, good point. –  user346 Mar 11 '11 at 16:00
    
@Deepak Vaid : Actually I wonder if any Stack users are bots (c.f. Jeopardy). In that case the "we" of a question like this refers to the crystalline silicon of said bots. –  Roy Simpson Mar 11 '11 at 16:04
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3 Answers

up vote 5 down vote accepted

No.

Of course, to argue if a definition applies, we must first agree on a definition. Wikipedia gives this one:

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions.

Humans are certainly solid-ish, and our constituent molecules are arranged in a somewhat orderly pattern in all three dimensions. However, I think we fail the 'repeating' portion of this definition. If you want to use a more broad definition of a crystal, link to it.

Finally, supposing the answer was 'yes'. What are the practical predictions which follow from this assertion? We certainly don't diffract x-rays into a regular grid, for example.

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The interesting question is that can life exist in the form of crystals? –  Anna Mar 11 '11 at 16:00
    
@Anna, the only way to act "lifelike" for a crystal is to act as a seed crystal when growing new ones. Al other essentials to life (eg metabolism) I can't imagine with crystals –  Georg Mar 11 '11 at 18:21
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Certainly not. Crystals by definition have some translation invariant lattice structure and humans do not.

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The answer is No, we are not crystals by any definition of crystal.

What I think you are asking though can be answered in a larger set of definitions, which includes crystals. " A quantum mechanical state function exists and in principle could be found which mathematically describes crystals and can predict their appearance and interactions" .

In this sense, one can aim at finding a quantum mechanical state function describing parts of the living body, neurons for example, or cells in general. In principle it should exist, in practice I do not think anybody has reached that point. People are working with chemical potentials etc, which are a meta level to the underlying quantum mechanical state functions which are there.

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