# What Einstein meant when he termed something a 'mollusc'

In summary, Einstein uses the term "mollusc" to refer to a non-rigid reference-body in his theories. These reference-bodies are used to define time and are equivalent to Gaussian four-dimensional co-ordinate systems. The term "mollusc" may be used to suggest a curvy shape, similar to that of an octopus or a slug. For more information on this concept, refer to the idea of "diffeomorphism invariance" and the animated diagrams on the webpage provided.
I have been reading over the two theories, and cannot figure out what Einstein meant when he termed something a 'mollusc'. Can someone please explain?

For this reason non-rigid reference-bodies are used which are as a whole not only moving in any way whatsoever, but which also suffer alterations in form ad lib. during their motion. Clocks, for which the law of motion is any kind, however irregular, serve for the definition of time. We have to imagine each of these clocks fixed at a point on the non-rigid reference-body. These clocks satisfy only the one condition, that the “readings” which are observed simultaneously on adjacent clocks (in space) differ from each other by an indefinitely small amount. This non-rigid reference-body, which might appropriately be termed a “reference-mollusk,” is in the main equivalent to a Gaussian four-dimensional co-ordinate system chosen arbitrarily.
He's just talking about arbitrary noninertial coordinate systems, maybe he used the word "mollusk" to suggest a curvy shape like the body of an octopus or a slug. Take a look at http://www.aei.mpg.de/einsteinOnline/en/spotlights/background_independence/index.html , particularly the part where they talk about "diffeomorphism invariance", for more on the idea that the equations of GR work in arbitrary coordinate systems...the last animated diagram on the page shows some rather "mollusk-like" curvilinear coordinate systems.

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thanks for the help :)

## 1. What did Einstein mean when he termed something a 'mollusc'?

Einstein used the term 'mollusc' as a metaphor to refer to a slow and sluggish person or thing. He often used this term to describe individuals who lacked motivation or ambition.

## 2. Was Einstein referring to an actual mollusc when he used this term?

No, Einstein was not referring to an actual mollusc. He used this term as a figure of speech to convey a certain characteristic or behavior.

## 3. Why did Einstein choose to use this term specifically?

Einstein was known for his creativity and love for metaphors. He likely chose to use 'mollusc' as it represents a slow and unassuming creature, which aligns with his intended meaning.

## 4. Did Einstein use this term frequently in his work?

Yes, Einstein used this term quite frequently in his writing and conversations. It was one of his go-to metaphors to describe certain concepts or individuals.

## 5. Is the use of this term considered offensive?

No, the use of this term is not considered offensive. It was used by Einstein in a playful and lighthearted manner and is not intended to be derogatory towards any individual or group.

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