Some Thought Experiments

Its an utterly beautiful concept. And it provides so much insight into the nature of knowledge.

Suppose you are sitting in a car and the car is accelerating forward. What do you feel ? Well, a push backwards. Suppose the car is accelerating up. Now what do you feel ? A push downward. Now suppose that you cannot look out of the window of the car. Can you tell whether you are accelerating ? Yes, ofcourse by the push. But suppose you are out in the space with no gravity and you are accelerating at precisely 9.8 m/s^2 (the acceleration with which you fall on Earth). Now the big question. Can you differentiate between two possible situations ? Are you in an accelerating spaceship or are you just sitting on the surface of the Earth ? Well, the answer is no ! So how do you really differentiate between gravity and any other acceleration ?

Consider another situation. Suppose you are in a lift in a very tall building and the lift rope snaps. You start falling down. Will you be able to differentiate this situation compared to one where you are out in the gravity free space ? Well the answer is, to a high experimental degree, no. But everything is not lost and it is this small thing which is left, that defines gravity. Consider the lift example again and also consider that as soon as the rope snaps, you let go of two rocks which you were holding in each of your hands. What happens to the rocks as they fall down along with you and the lift. First of all, they will be stationary to your eyes since you are also falling down as fast as them. But wait ! Everything is falling towards a common center i.e. the center of the earth. So the rocks are not exactly following a parallel path but their paths are going to intersect if the lift somehow reaches the center of the Earth. Hence, if you could measure closely enough, you would notice the rocks coming towards each other extremely slowly. And herein lies the clue which gives the secret presence of gravity away ! Its funny in a certain way. To put it down in a fancy way, Gravity does not manifest itself uniquely by the act of the falling down of an object but by the act of apparent mutual attraction between two objects ! Would the situation be any different, if instead of rocks you had used gold blocks or wood or even electrons? Absolutely not. So in essence, everything irrespective of its material will follow the same curved path which is being followed by the rocks. Here is where Einstein took a big leap in imagination. Is the path of the rocks a property of space itself ? Is there no gravity ? Is it just the curved space which decides the path of the rocks and not some mysterious gravitation force ? In essence, is it just GEOMETRY ! And sure it was. The thought experiment which upstaged more than 200 years of the notion of Gravity.

So I am led to ask. All the knowledge is surely out there. Is it just begging a more insightful eye and a more daring imagination ?