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Modern Views of Gravitation
by Ron Kurtus (revised 15 September 2009)
Although Isaac Newton determined the classical laws of gravitation, he was never able to explain the properties of matter than caused gravitation except that it was a force that acted at a distance.
Albert Einstein reformulated the laws to fit his General Theory of Relativity, as a way to explain gravitation. He said that gravitation was similar to acceleration and that is it caused by a curvature of space.
Recent theories about gravitation state that it has wavelength and is a particle.
Questions you may have include:
- What is the classical explanation of gravitation?
- What is the relativistic view of gravitation?
- What are the latest explanations?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
Classical view
Scientists and philosophers from ancient times observed gravity on Earth. In 628, Indian astronomer Brahmagupta recognized gravity as a force of attraction. In the 1600s, Galileo Galilei, Robert Hooke and Johannes Kepler formulated laws of gravity near the Earth and gravitation among celestial objects.
Isaac Newton combined those concepts as his Universal Law of Gravitation in 1680. Although Newton is credited with "discovering gravity", there were many before him that studied the subject.
This classical view is that objects attract each other through some force that acts at a distance. It was uncertain what the mechanism was for that force and how it tied into other forces that acted at a distance.
(See Mysterious Force at a Distance for more information on that subject.)
Relativistic view
Physicist Albert Einstein examined gravitation in his study of the General Theory of Relativity.
Similar to acceleration
He noticed that if you are in an elevator that was going up, you felt heavier due to the acceleration of the elevator's motion.
Einstein concluded that since the force from acceleration had the same effect as the force caused by the Earth's gravity, there must be some mathematical relationship between the two. In fact, he said at first that gravity was actually caused by acceleration.
That idea is not too clear, since when the elevator is accelerating upward, it is directly pushing on you. On the other hand, gravity is a force that acts at a distance through some force field or perhaps unknown means. Perhaps gravity is similar to acceleration, but it is not caused but it.
This effect was the starting point in the development of an explanation of gravitation. Einstein considered the relationship of moving objects, their acceleration, and the apparent effects they had. This led him to the conclusion that space was curved.
Curvature of space
Einstein postulated that the presence of matter distorts the space around it.
This can be explained by picturing space as a grid of lines. Without matter, space would be a perfect grid of parallel lines. An object would move in a straight line through space.
The presence of another mass of matter would distort the lines, drawing some toward it. Thus a moving object would no longer travel in a straight line. Instead, it would curve toward the other object, appearing to be attracted to it. What this theory does is says that gravitation—the attraction of an object toward another—was not caused by the apparent force of gravitation between masses. Instead, it was simply a property of space.
This is a pretty abstract concept, but Einstein demonstrated it with highly complex mathematical equations. Many scientists accept this concept of the curvature of space as an explanation of gravitation.
Newer theories
One problem with the General Theory of Relativity's explanation of gravitation as being caused by the curvature of space, as opposed to being a force, is the question of why it is so different than other forces that act at a distance—such as magnetism.
Another problem is that it did not follow the rules of Quantum Mechanics or Quantum Physics—the study of matter at extremely shorts distances.
Gravitation as a waveform
Scientists then predicted that a gravitational field would exhibit wavelengths, similar to electromagnetic waves. Using highly sensitive instruments, experiments were made to verify that gravity is indeed a waveform of some sort.
Wave-particle duality
To follow the wave-particle duality in Quantum Physics, it was also predicted that gravity consists of particles called gravitons. This is similar to the theory that light is not only a waveform, but also consists of particles called photons. Electrons are also viewed as both particles and waves.
This view of gravity being a wave or particle goes back to the idea that matter exhibits gravitation and that there truly is a force of gravity. (Nobody said that Physics would be easy and that everything was known or explained.)
Quantum Mechanics
Recently there have been new theories that the force of gravity is caused by graviton particles or by gravity waves. These theories satisfy rules of Quantum Mechanics that Einstein's concepts didn't.
Dark matter
There is also a theory that there exists some sort of "dark matter" that repels instead of attracts, resulting in anti-gravitation.
Summary
Newton determined the classical laws of gravitation. Einstein stated in his General Theory of Relativity that gravitation was similar to acceleration and that is it caused by a curvature of space. Recent theories about gravitation state that it has wavelength and is a particle.
See the Side Menu for more Gravitation and Gravity topics
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Resources
The following resources provide information on this subject:
Websites
Books
Top-rated
books on Simple Gravity Science
Top-rated
books on Advanced Gravity Physics
Mini-quiz to check your understanding
If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.
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Modern Views of Gravitation