"Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it."

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I am beginning to believe that nothing can ever be proved. These are honest hypotheses which take the facts into account: but I sense so definitely that they come from me, and that they are simply a way of unifying my own knowledge. Not a glimmer comes from Rollebon's side. Slow, lazy, sulky, the facts adapt themselves to the rigour of the order I wish to give them; but it remains outside of them. I have the feeling of doing a work of pure imagination.

— Jean-Paul Sartre