In any experiment, specifying a physical quantity of interest always relies on a reference frame. For example, identifying the time at which an event happens only makes sense relative to a clock.
The original version of this story appeared in Quanta Magazine. Imagine standing on a railway platform watching a trolley go past. A girl on the trolley drops a bright red ball. To her, the ball falls ...
The Nature Index 2025 Research Leaders — previously known as Annual Tables — reveal the leading institutions and countries/territories in the natural and health sciences, according to their output in ...
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