Galileo began investigating the tides. It had been noted for centuries that the tides coincided with the phases of the Moon, but Galileo was convinced the tides were caused by the rotational movement of the Earth. He didn’t think there was a connection to the movements of the Moon. His theory on tides was wrong and he never did find the proof he was looking for.

    Galileo did lay the foundations for modern physics. His methods for conducting experiments and recording all the results are still used today. He proved that all objects fall at the same speed no matter what their mass. His studies on rates of descent and motion, along with Kepler’s laws of planetary motion, are what led Isaac Newton to formulate the laws of motion and the laws of gravity.

     Sir Isaac Newton was born in England in 1642. He is considered one of the most important scientists of all time. His universal laws of gravitation and motion helped explain how objects move on Earth as well as in space. He invented calculus and established the modern study of optics. He built the first reflecting telescope.

     Newton theorized that the force that causes an apple to fall from a tree was the same force that held the Moon in its orbit around the Earth. He noticed that a top would spin indefinitely if not for the friction of air slowing it down. The Moon he reasoned, had much less air friction to deal with, therefor would continue spinning around the Earth like a top for a much longer period of time.

     All moving objects tend to move in straight lines at a constant velocity. To cause a change in velocity or direction, an outside force must act on the moving object. Newton saw gravity as an attractive force between all particles of matter. The Moon’s direction of travel was being changed to a curve by the Earth’s gravitational pull. The Moon’s horizontal momentum kept it moving at a constant velocity, just as an object such as a ball thrown through the air maintains a constant horizontal velocity throughout its trajectory.

     Newton’s theory of gravitation was not perfect, but it did work very well for planetary motions and was accepted for the most part by the entire scientific community.

     In 1905, Albert Einstein published his first paper on his new theory of relativity and gravity. It was completely ignored. Eleven years later, in 1916 he tried again, and this time he changed the world of physics completely. Einstein did not see gravitation as an attractive force. He saw it as a field emanating from matter, that caused space to warp. The Moon thinks its traveling in a straight line, but the space it is traveling through is warped by the presence of the Earth’s mass, thus causing a straight line to be curved. Einstein predicted that gravity would bend light because of this warp in space, and his prediction has been verified several times since then with experiments involving total eclipses of the Sun.

     The cornerstone of Einstein’s theory is the fact that gravitation and acceleration are mathematically equivalent. Acceleration feels just like gravity. In fact you can’t tell the difference without experimentation.