this is from his website:(adsbygoogle = window.adsbygoogle || []).push({});

"In what class of 4-dimensional spacetimes does there exist a real, non-constant scalar field φ with the following properties:

It obeys the wave equation: ◻φ=0

Its gradient is everywhere null: ∇φ.∇φ=0"

somehow i think it is concerned with his work, but what is its siginificance?

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# A teaser from deustch

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