Person B is standing in the room and is not moving relative to the room. Person A notices three things: a force that pulls all objects from the center, time travels slower farther away from the center and things become shorter farther away from the center. Person A does an experiment by measuring the radius r and circumference c of the disc using little rulers. Since the rulers become shorter when placed farther away from the center in the direction of the movement, he will find that . Then person B sends a light ray across the room. Person A will say that this ray of light went not straight but curved. From the last two experiments, person A will conclude that space is curved on the platform (Gamow 55).
If a rocket in outer space were accelerating, a person in this rocket would feel a force pulling him to the floor. In fact, this person would not notice any difference between this force and gravity. If this person sends a light ray across the rocket, the ray would curve in the same way the ray curved in the previous experiment. So, gravity can be interpreted as curvature of space in which time travels slower and things become contracted (Gamow 56).
This all reasoning is the subject of the theory of relativity, developed mostly by Einstein. This theory is saying the exact opposite of what physicists firmly believed from the times of Newton till the beginning of 20th century. They thought that space and time are independent. This is certainly not true because of the last experiment mentioned. But, as was shown by Einstein, the difference between classical and relativistic physics becomes noticeable only at speeds, which are close to the speed of light. So, the conclusion is that Newtonian physics is good in common life but fails at very extreme speeds.
Another extreme, where classical physics does not work is the case of very large distances, which is when we investigate the universe. Ukrainian physicist, George Gamow, proposed a theory in which he said that the universe started out as a small but very massive object and then exploded making stars, planets, and galaxies.