The quality or state of being doubtful; uncertainty or lack of confidence.
Formed from 'doubtful' plus the abstract noun suffix '-ness' (from Old English 'ness,' expressing state or condition). This follows productive patterns seen in words like 'happiness,' 'sadness,' and 'darkness.'
The doubtfulness of quantum mechanics—where particles exist in multiple states until observed—is one of the deepest paradoxes in physics, which is why even Einstein himself expressed 'doubtfulness' about whether quantum mechanics was complete.
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