Quote by Albert Einstein
We shall therefore assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system.
Summary
This quote expresses the principle of equivalence put forward by Albert Einstein in his theory of general relativity. It states that a gravitational field is indistinguishable from an accelerated frame of reference. In other words, the effects of gravity can be viewed as the result of being in a reference system undergoing acceleration rather than being in an actual gravitational field. This principle was a fundamental component in Einstein's understanding of gravity and its effects on space, time, and matter.