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Comment by hristov | Hacker News Reader

So where does it get the energy? Suppose you get a rope made out of this meta material and tie one end to a nail in a wall, and tie a weight to the other end. The material should contract and lift the weight up. Thus, by lifting the weight, the magic material would be doing work, and expending energy. But where does it get the energy from?

Seems very dubious to me. To quote Homer Simpson "In this house we follow the laws of thermodynamics!"

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Sounds like the energy is bound into the material during its formation: "there is an internal latent strain between the building blocks that constrains the overall shape".

Does that imply that it wouldn't automatically revert to its original state?

> Thus, by lifting the weight, the magic material would be doing work, and expending energy. But where does it get the energy from?

From the pull of gravity on the weight.

"The pull of gravity" is not a source of energy. When the weight rises in the Earth's gravitational field energy must be supplied.

Thinking about it more, yea, fair point. When water loses energy and freezes, it expands, that expansion could lift a weight. Is this not a similar change in molecular structure doing a similar thing? Where is the input of energy lifting this weight.

No. When you apply pressure on ice it becomes liquid. In other words: water doesn't lift things by freezing if that requires an amount of energy larger than what is needed to change state.

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