- The Chicago Astronomer -
Copyright 2004-2014 All rights reserved by Joseph Guzman Administrator/Founder/Chief Astronomer.
All text and images are the property of the original authors/artists and shall
not be used without permission.
Albert Einstein used Isaac Newton's weak equivalence principle by extending special relativity to include gravity. This modification of Einstein's says that in a sealed room, the observer would be unable to perform any experiment to discern a difference between the acceleration of gravity, and an engine constantly accelerating the room.
The insight was instrumental in developing the well-tested concepts of general relativity and curved space. Although he missed one refinement, it does not change the outcome of these modern concepts.
One test will indeed distinguish between the two. The observer inside a room constantly accelerated by an engine will experience the same acceleration in all places in the room. The observer in a room in a gravity field such as on Earth will experience more gravity on the floor than on a tabletop.
This gravity gradient is a consequence of Newton's inverse square law. Round figures for the radius of the Earth gives 6 million meters, and it gives 10 meters per second per second for the acceleration of gravity at the floor. Because the tabletop is 6,000,001 meters from the center of the Earth, the gravity there reduces to only 9.999 997 meters per second per second, which our technology is well able measure.
If the universe is a ball the size of America, then the solar system is almost as large as the smallest cell in the human body.