Back in the 17th century, the great Italian physicist Galileo Galilei did a far-reaching experiment on the Leaning Tower of Pisa: two iron balls of unequal weights were allowed to fall freely from the same height, and the two balls landed at the same time.

Galileo concluded that any object, be it an iron ball or a feather, must have the same acceleration if it falls freely in a vacuum, and thus must land at the same time. This point of view, a direct impetus to the great physicist Newton summarized the three laws of motion on the force. And Einstein's theory of relativity was also based on this foundation. However, this unbreakable truth for more than 300 years has recently been seriously challenged. A team of American physicists, led by Feshbach, discovered that objects of different masses do not actually accelerate at the same rate in a vacuum.

Fischbach speculated that the reason for this is likely to be that in addition to gravitational forces, objects are subjected to an as-yet-unrecognized effect as they fall. Most scientists recognize that there are four kinds of forces in the universe: the first is the gravitational force, which is an object or a particle for another object or a particle of attraction, is the weakest of the four kinds of force; the second kind of force is called the electromagnetic force, due to its role, the formation of different atomic structure and the movement of light; the third is a strong interaction force, which is the nucleus of the individual particles are tightly attracted together; the fourth kind of force is a weak interaction force, which makes the object fall down, but also a weak interaction force, which makes the object fall down. is the weak interaction force, which causes objects to radiate in some way.