Technically, every single object in the universe with mass or energy emits a gravitational field, and scientists have been able to measure the gravitational field of objects far smaller than a human. General Relativity Einstein revolutionized our understanding of gravity with his magnum opus, the general theory of relativity. The theory transformed our perspective of gravity from a simple property of objects relating to their mass, to a view of the cosmos where space and time can bend, flex and warp in the presence of massive objects. According to general relativity, just about everything is capable of bending spacetime: anything with mass, energy, and tension. Naturally, more massive and energetic objects bend spacetime more than less massive or energetic objects. Also, the more compact objects are, the more strongly they can bend spacetime. For example, a typical black hole that isn’t much more massive than the Sun, but it’s compressed into such a small volume – only a few miles across – that it can create an event horizon, where nothing can escape from. Read More: How Many Ways Can the Sun Kill Us? A Small Gravitational Field But overall, gravity is exceedingly weak. It is, by far, the weakest of the four fundamental forces of nature. Even if gravity were a billion, billion, billion times stronger than it is, it would still be the weakest force of nature. Gravity is so bizarrely weak that there’s even a major program of active physics research devoted to understanding why. It takes a lot of mass to make a decent gravitational field. The Earth weighs a whopping 6*10^24 kilograms, but you can overcome its entire gravitational pull simply by lifting up your arm. To completely escape the pull of the Earth permanently, however, does take a little bit of work: you have to reach escape velocity, which is a speed of 25,000 miles per hour. To give a sense of the smallness of a human’s gravitational field, we can scale down that escape velocity to less massive objects. Asteroid Ryugu, a near-Earth asteroid and target of the Japanese Hayabusa2 mission, weighs about 5*10^11 kilograms and has a radius of around 1476 feet. Its escape velocity is less than one mile per hour: You could jump hard enough from the surface of Ryugu and never return. If we take the average human weight to be 154 pounds and a radius of 3.36 feet (let’s pretend people are perfectly spherical, just to make the calculations easier), our own escape velocity is around 100 micrometers per second. In other words, literally nothing is gravitationally bound to us in any way, shape or form. Even the air molecules floating around the room you’re in right now have more than enough velocity to bounce off us without a second thought. Measuring Human Gravitational Fields But even with that incredibly small gravitational field, scientists have devised clever experiments to measure it. In 2021, a team of scientists at the University of Vienna in Austria took two gold spheres weighing only 90 milligrams each – about the size of a sesame seed. They hung one from a pendulum and vibrated the other in a specific pattern. Isolating all the sources of noise in the experiment was an incredible feat, but they could use lasers to measure the position of the free-swinging gold sphere. When they found the vibration pattern copied in the free-swinging sphere, they knew they were measuring the gravitational pull of the sphere they controlled. It was the tiniest gravitational field ever detected. Their experiment was so sensitive that the researchers claimed that they could detect the first finisher of the Vienna marathon, which finished over 1.2 miles from their laboratory. So, even though humans have incredibly feeble gravitational fields, the sensitivity of our experiments is more than capable of measuring it.
