Newton’s Gravitational Constant Big G is not a Constant

Newton's gravitational constant Big G, appearing in both Newton's law of gravity and Einstein's general relativity, is essential for our todays understanding of gravity. Thus far, despite of the very long history of measurements of Newton's gravitational constant Big G, a definite value is still not in sight. Surprisingly, the results of different experiments have varied by much more than would be expected due to systematic or random errors. Why do measurements of Newton's gravitational constant Big G vary so much? It is the purpose of this publication is to provide a logically and mathematically self-consistent theoretical proof that Newton's gravitational constant Big G is not a constant.