Einstein’s happiest thought (1907): “For an observer falling freely from

the roof of a house, the gravitational field does not exist” (left).

Conversely (right), an observer in a closed box — such as an elevator or

spaceship — cannot tell whether his weight is due to gravity or acceleration (einstein.stanford.edu)

the roof of a house, the gravitational field does not exist” (left).

Conversely (right), an observer in a closed box — such as an elevator or

spaceship — cannot tell whether his weight is due to gravity or acceleration (einstein.stanford.edu)

Equivalence Principle

Equivalence Principle is a basic postulate of general relativity, stating that at any point of space-time the effects of a gravitational field cannot be experimentally distinguished from those due to an accelerated frame of reference. Einstein online explains on this principle in the following.

Imagine you are in an elevator or, more precisely, in what looks like an elevator cabin from the inside, and that you are isolated from the outside world. If you pick up an object and let it drop, it falls down to the floor, in exactly the way you would expecte given your experiences here on Earth. Does that mean the elevator is indeed situated in a gravitational field like that of the Earth — as shown in the following illustration?

It ain’t necessarily so. Theoretically, you could be in deep space, far away from all significant mass concentrations and their gravitational influence. The room you are in could be a cabin aboard a rocket — as long as the rocket engines work at exactly the right rate to accelerate the rocket at 9.81 meters per square second. This is sketched in the following illustration:

**Inside a rocket, Tom cannot decide whether or not in a gravitational field or not**

Thus, inside an elevator, we cannot decide whether or not we are in a gravitational field or not. Whether or not objects accelerate towards the floor is a matter of reference frame: Even in a gravity-free region of space, objects fall towards the floor if the room we are in is being accelerated. Conversely, even in a gravitational field, objects drift weightlessly through space, as long as the elevator is in free fall.

Einstein became convinced that this inability to distinguish a region with a gravitational field from one without was not just restricted to observations of falling bodies. He postulated that it holds true for any physical measurements at all: No experiment, no clever exploitation of the laws of physics, he claimed, can tell us whether we are in free space or in a gravitational field. This statement is called the equivalence principle.

Einstein’s ‘happiest thought’

Einstein’s happiest thought led to the Equivalence Principle 108 years ago.

While pondering the nature of gravity, Einstein had a sudden revelation, which he would later dub his “happiest thought.”

*Imagine a workman standing on the roof of a house and losing his footing. As he plummeted in free fall, everything within his grasp (a toolbox, for example) would plunge with him. Therefore, from his local perspective gravity wouldn’t seem to exist.*

The Equivalence Principle allows us to make calculations involving gravity by considering instead reference frames undergoing acceleration. By applying the Equivalence Principle, the answer equally applies to a reference frame with the same gravitational acceleration. Let’s see how …(phys.ufl.edu-lectures)

For more than 100 years there are many physicists and astrophysicists believe in equivalence principle without a doubt; that is something astonishing facts and surprising. Equivalence principle explains the condition of object falling looks very well, but actually are not well enough. Because the effects of gravity have a quantity; the effects are not merely a falling object on the surface of the Earth.

All objects on Earth are affected by the force of Earth’s gravity. The strength of Earth’s gravity varies depending on location. The strength of Earth’s gravity on the poles of the Earth and on the equator region is not the same. Experience shows that the force of Earth’s gravitational force in the sea area near the equator is not the same. This experience is known in the case of increasing or decreasing the speed of the ship; and it is not caused by wind and current factors. This is all unknown in the time when Einstein’s ‘happiest thought’!

Variation in gravity and apparent gravity. Effective gravity on the Earth’s surface varies by around 0.7%, from 9.7639 m/s2 on the Nevado Huascarán mountain in Peru to 9.8337 m/s2 at the surface of the Arctic Ocean. In large cities, it ranges from 9.766 in Kuala Lumpur, Mexico City, and Singapore to 9.825 in Oslo and Helsinki.

Therefore, Einstein’s happiest thought was the “ancient time thinking”. Moreover, if associated with a new discovery of Gravity wave (not ripples in spacetime/gravitational waves); equivalence principle of Einstein is useless.

In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium.(Image from Pinterest)

Einstein’s explanation on his original idea of the equivalence principle, as we can read in the book ‘The Universe and Dr.Einstein’, by Lincoln Barnett, are incomplete. It is very clear there has been a mistake in logic: Logical fallacies of Einstein’s theory’.

*That is fallacy of composition, assuming that something true of part of a whole must also be true of the whole.*

*With Newton’s Law of Gravitation I can say Tornadoes, Earthquakes, and Tsunamis are driven by Earth’s gravity (Gravity waves); Not Ripples in Spacetime or Gravitational Waves that are useless.(Image from USA Today)*

Einstein’s general relativity (Einstein’s Field Equation of Gravitation) nothing more than the model which contain ideas about equivalence principle in spacetime that do away or eliminate the existing of atmospheric medium around the massive bodies like the Sun, Stars, and Planets.

*“In every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted.” (Rene Descartes).*

*Read on: medium.com*