The tree. The apple tree that inspired Isaac Newton to work on law of universal gravitation is still alive after over 400 years, attended by gardeners, secured with a fence, and cared for by National Trust for Places of Historic Interest or Natural Beauty.

Isaac Newton changed the way we understand the Universe. Revered in his own lifetime, he discovered the laws of gravity and motion and invented calculus. He helped to shape our rational world view. But Newton’s story is also one of a monstrous ego who believed that he alone was able to understand God’s creation.

“Aha!” he shouts, or perhaps, “Eureka!” In a flash he understands that the very same force that brought the apple crashing toward the ground also keeps the moon falling toward the Earth and the Earth falling toward the sun: gravity.

Newton, however, was suspicious of Descartes’s theory, and continued to calculate the interaction of the heavenly bodies: in 1666 he calculated the force of attraction that held planets in their orbits, and the Moon in its orbit around Earth, as varying inversely with the square of their distance from the sun.

Newton’s theory of gravity states that two objects attract each other with a force of gravitational attraction that’s proportional to their masses and inversely proportional to the square of the distance between their centers.

In the 20th century, Newton’s model was replaced by general relativity where gravity is not a force but the result of the geometry of spacetime. Under general relativity, anti-gravity is impossible except under contrived circumstances.

Contrary to popular belief, NASA does not have “anti-gravity chambers” where people can float around like astronauts on the space station. It is NASA’s premier facility for conducting ground-based microgravity research.

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Gravitational waves are invisible. However, they are incredibly fast. They travel at the speed of light (186,000 miles per second). Gravitational waves squeeze and stretch anything in their path as they pass by.

Kopeikin and Fomalont concluded that the speed of gravity is between 0.8 and 1.2 times the speed of light, which would be fully consistent with the theoretical prediction of general relativity that the speed of gravity is exactly the same as the speed of light.

To detect a graviton with high probability, a particle detector would have to be so huge and massive that it would collapse into a black hole. This weakness is why it takes an astronomical accumulation of mass to gravitationally influence other massive bodies, and why we only see gravity writ large.

By rapidly projecting gravitons in a cohesive beam, he could generate a force blast with a maximum concussive force equivalent to the primary shockwave of an explosion of 20,000 pounds of TNT.

The Standard Model includes the electromagnetic, strong and weak forces and all their carrier particles, and explains well how these forces act on all of the matter particles. But luckily for particle physics, when it comes to the minuscule scale of particles, the effect of gravity is so weak as to be negligible.

The speed of gravity has been measured for the first time. The landmark experiment shows that it travels at the speed of light, meaning that Einstein’s general theory of relativity has passed another test with flying colours.