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Explanation of Quantum Theory of Gravitation - Succeed in Understanding Physics. Also refer to gravity, atomic, subatomic, General Relativity, quantum mechanics, universal gravitation, wave-particle duality, fundamental forces, graviton, String Theory, Loop Theory, physical science, Ron Kurtus, School for Champions. Copyright © Restrictions
Quantum Theory of Gravitation
by Ron Kurtus (6 February 2010)
Quantum Gravitation (or Quantum Gravity) is an effort to explain gravitation on the atomic and subatomic levels. While the Theory of General Relativity explains gravitation for large scale events and the Law of Universal Gravitation provides an equation for ordinary situations, neither are able to explain gravitation for extremely small sizes and masses where quantum effects take place.
This is based on Quantum Mechanics, which provides a different view of matter, energy and space at very small distances. There are several theories that attempt to resolve how gravitation works at the quantum level, as well as to fit with the General Relativity concepts. However, there are also problems concerning quantum gravitation. This is due to the wide range of quantum theories and difficulties proving them for gravitation.
- What is Quantum Mechanics?
- What are the Quantum Gravitation theories?
- What are are some problems with those theories?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
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Quantum Mechanics
At the atomic and subatomic levels, classical or Newtonian physics loses its validity and Quantum Mechanics (or Quantum Physics) takes over. There are several main concepts that provide changes.
Energy is discrete
Quantum theory states that physical interactions and exchange of energy cannot be made arbitrarily small. Energy comes in tiny packets called quanta (plural of quantum). This helps to explain the properties of electrons in atoms and the relationship of energy to matter.
Fundamental forces
Another Quantum Mechanics concept is that there are three fundamental forces or interactions between particles of mass. The forces occur through the exchange of virtual or particles without mass. Each interaction consists of a quantum packet.
Strong nuclear force comes from the exchange of gluon particles between nuclear particles, creating the force of attraction. Weak nuclear force comes from the exchange of vector bosons. Electromagnetic force is caused by the exchange of virtual photon particles.
Wave-Particle duality
A third concept that relate to quantum gravitation is that both light and matter exhibit wave and particle behaviors.
Subatomic particles can appear as waves. For example, an electron can have properties of a waveform. Likewise, waves can appear as particles. An electromagnetic wave can be a photon or light particle.
Theories of quantum gravitation
Extending the Quantum Mechanics theories to gravitation is an effort to explain the force at the quantum level. Some concepts try to reconcile quantum gravitation with general relativity.
Gravitation as fourth fundamental force
One aspect of the Quantum Theory of Gravitation is that gravitation is the fourth fundamental force. This would unify all the forces or interactions between particles of matter under one concept.
Gravitation is the weakest of the fundamental forces, with a strength of only 6*10−39 of the strength of the strong nuclear force at a sub-nuclear distance.
Note: 10−39 equals 1/1039, where 1039 is 1 followed by 39 zeros. It is a very small number.
However, at distances beyond the sub-nuclear range, the strength of gravitation is much larger than the nuclear forces, which are essentially zero at those distances. But still, gravitation is only 4*10−37 of the electromagnetic force at the same distances.
This theory also says that gravitation is caused by an exchange of graviton particles or quanta between objects. Also, due to the wave-particle duality, this would mean that gravitation waves are possible.
Transfer of gravitons between two molecules
String Theory
String Theory is an effort to reconcile Quantum Mechanics and General Relativity into a Quantum Theory of Gravitation.
The theory states that particles of matter are one-dimensional oscillating lines or strings. The mathematics of String Theory describes the fundamental forces into a complete system.
One aspect of String Theory is that up to 12 dimensions are required to describe matter and its interactions.
Loop Quantum Gravity Theory
Loop Quantum Gravity also attempts to reconcile the theories of Quantum Mechanics and General Relativity by quantizing the gravitational field. The theory suggests that space consists of moveable tiny loops that can be viewed as an extremely fine fabric.
However, the theory keeps gravitation separate from other fundamental force fields. It also incorporates General Relativity without requiring String Theory's higher dimensions.
Problems with Quantum Gravitation
There are several problems concerning theories of Quantum Gravitation.
Not universally accepted
One problem is that there are so many theories of Quantum Mechanics that none are universally accepted. This, of course, affects the Quantum Theory of Gravitation.
Does not correspond with General Relativity
Another problem is that Quantum Gravitation does not correspond very well with General Relativity. String Theory and Loop Quantum Gravity Theory make an attempt to find a common ground with General Relativity. However, a major problem with String Theory is that it may be impossible to prove or even disprove. The same may be true of Loop Quantum Gravity Theory.
Verification extremely difficult
Experimental verification of Quantum Gravitation is extremely difficult, primarily due to the small sizes and weak interactions. Thus far, the existence of gravitons or gravitational waves has never been verified.
Summary
The Quantum Theory of Gravitation is an effort to explain gravitation on the atomic and subatomic levels. It is based on Quantum Mechanics, which provides a different view of matter, energy and space at very small distances. There are several theories that attempt to resolve how gravitation works at the quantum level, as well as to fit with the General Relativity concepts. However, there are problems in verifying quantum gravitation due to the small forces involved.
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Resources
The following resources provide information on this subject:
Websites
Acceleration due to Gravity Calculations - from Western Washington University
Gravity and Gravitation Resources
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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