%0 Journal Article %T The Gravitational Constant G May Decrease between Millimetre-Sized Masses %A Qinghua Cui %J Journal of Modern Physics %P 133-139 %@ 2153-120X %D 2025 %I Scientific Research Publishing %R 10.4236/jmp.2025.161005 %X The Newtonian gravitational constant G is one of the most important fundamental constants of nature, but still remains resistant to the standard model of physics and disconnected from quantum theory. During the past >100 years, hundreds of G values have been measured to be ranging around 6.66 to 6.7559 × 10⁻¹¹ m³·kg⁻¹·s⁻² using macroscopic masses. More recently, however, a G value ((6.04 ± 0.06) × 10⁻¹¹ m³·kg⁻¹·s⁻²) measured using millimetre-sized masses shows significant deviation (by ~9%) from the reference G value, which the authors explained is resulted from “the known systematic uncertainties”. However, based on the observation of historical G values and the protocol of the millimetre-sized masses based experiment, here we proposed a theory that this deviation is not from “systematic uncertainties” but actually G will rapidly decrease when masses sphere diameter is less than 0.02 metres. Moreover, this theory predicted the G value will be 5.96 × 10⁻¹¹ m³·kg⁻¹·s⁻² between masses whose diameter are 2 millimetres (0.002 metres), which matches the measured G value very well. %K Gravity %K Gravitational Constant %K Cosmic Microwave Background %K Diffraction %U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=140091