One great unsolved question in physics is why gravity is so weak compared to the other three forces of nature? This fact is not intuitive at all to many of my students whose experience gravity is that it is ever present, unforgiving, and at times brutal.
The Earth is huge, and acts unrelentlessly to pull us towards its center. This lack of an ability to jump even 3 feet in the air, or for the best athlete in the world to jump 8 feet in the air (Mr. Javier Sotomayor), makes us respect this downward-pulling force.
What we perhaps take for granted is that we also do not actually sink towards the center of the Earth, as the Earth would have it. Instead, the electrons in our skin, or in the soles of our shoes, repulse the electrons in the ground. We triumphantly stand firmly on the surface of the Earth.
In this same vein, we can also take a magnet and use it to lift up a paper clip. What power we have to combat the gravitational pull of the entire Earth by employing the humble refrigerator magnet! In both examples, we see evidence that the force of electricity and magnetism is significantly stronger than that of gravity. So why is gravity so weak?
One proposed model states that gravity is actually not weak, but is merely mostly drawn out into “extra dimensions.” The model, however “science fictiony,” purports that there are not just the four dimensions we are accustomed to of length, width, height, and time, but also other dimensions. These “extra” dimensions are very small and as yet unseen, yet large enough to “absorb” most of the gravitational force.
If true, then there is the prediction that the gravitational pull between two objects, Newton’s inverse square law for gravity, should break down on small scales. Experiments are underway now to search for such differences in Newton’s supposed “universal” law of gravity, ranging from the mighty Large Hadron Collider at CERN to tabletop experiments in physics labs.
