For more than two centuries, scientists have tried to determine one of the most important numbers in physics: the universal gravitational constant, known as "big G." It defines the strength of gravity throughout the universe, influencing everything from falling objects on Earth to the motion of galaxies. Yet despite its importance, researchers still cannot agree on its exact value.
That uncertainty weighed heavily on Stephan Schlamminger, a physicist at the National Institute of Standards and Technology (NIST), as he prepared to open a sealed envelope containing a crucial secret number. For nearly 10 years, Schlamminger had devoted much of his career to measuring big G with extraordinary precision. The hidden number inside the envelope would finally allow him to decode his team's results.
Why Measuring Gravity Is So Difficult
Gravity may shape the cosmos, but it is surprisingly weak compared to the other fundamental forces of nature. Electromagnetism, for example, is far stronger. Even a tiny magnet can lift a paper clip against the pull of Earth's entire gravitational field.
That weakness becomes an enormous challenge in the lab. Scientists must measure the gravitational attraction between relatively small objects, and those forces are incredibly faint. The masses used in experiments are roughly 500 billion trillion times smaller than Earth, making the gravitational pull between them extremely difficult to detect accurately.
