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Gravitation as a Fundamental Force

by Ron Kurtus (revised 22 January 2011)

Several theories state that there are four Fundamental Forces or Interactions that affect the way that objects or particles of matter interact with each other at a distance or separation. These forces are considered fundamental because they cannot be described in terms of other interactions.

Originally, the Standard Model Theory gave the fundamental forces as strong weak nuclear forces and electromagnetic force. However, the model did not address general relativity or gravitation. The more recent String Theory and Theory of Everything added gravitation as a fundamental force.

The theories provide an explanation of how gravitation fits in the scheme of things and seem to resolve the disconnect between General Relativity and Quantum Mechanics. They explain forces as an exchange of fundamental particles.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Nuclear forces

Nuclear forces are divided into what they call Strong and Weak forces.

Strong force

The strong force is the attraction that holds the nucleus of an atom together, overcoming the repulsive electrical force of the positive (+) charged protons.

Strong force holds nucleus together

Strong force holds nucleus together

The relative strength of the strong force is designated as 1. The range of this force is small, approximately the diameter of a medium-sized nucleus (10−15 m). Apparently, this force does not decrease by the inverse square as do the gravitational and electromagnetic forces. Instead, it just stops at its given separation.

The Theory of Exchange Forces designates the gluon as the "glue" that holds the nucleus together, through some sort of exchange between nuclear particles.

Weak force

The weak force in a nucleus involves an exchange of W and Z vector boson particles. The strength of the weak force is 10−6 that of the strong force. Its range is only 10−18 m, which is about 0.1% of the diameter of a proton.

The apparent purpose of the weak nuclear force is to allow deuterium fusion to take place. This is necessary for our Sun and the stars to burn. Deuterium is a hydrogen isotope. The force is also necessary for the creation of heavy nuclei and causes phenomena such as beta decay.

Electromagnetic force

Electromagnetic force consists of the attraction and repulsion of materials consisting of electric charges, as well as magnetic materials.

Strength and range

The relative strength of the electromagnetic force is 1/137 of the strong nuclear force. Its force drops off as the square of the separation between charged particles or magnetic poles, although the range is infinite.

Electric force

Electric charges can be positive (+) or negative (−), where like charges repel and unlike charges attract. Protons have a positive (+) charge and electrons have a negative (−) charge. Electric forces are what hold atoms and molecules together.

(See Basics of Electricity for more information.)

Magnetic force

Magnetic poles can be north (or north-seeking) and south (or south-seeking). Like poles repel and unlike poles attract. Moving and spinning electrical charges create a magnetic field, depending on their direction of motion.

(See Magnetism for more information.)

Cause

At one time electromagnetic forces were explained as a property of space that consisted material called aether. The present theories explanation is that the force is caused by the exchange of photon particles.

Gravitational force

Gravitational force is the attraction between objects. It can be compared with the other three interactions or forces.

Range and strength

Gravitation has at reach or range to infinity. However, it is the weakest of the fundamental forces. The gravitational strength is only 6*10−39 of the strength of the strongest nuclear force.

Note: 10−39 equals 1/1039, where 1039 is 1 followed by 39 zeros. That is a very small number.

The strength of the gravitational force decreases as the square of the separation between two objects, as does the electromagnetic force. The nuclear forces do not have that feature.

Although the gravitational force is much smaller than the other fundamental forces, it's impact concerns objects of large mass, such as planets and stars. Gravitation is what keeps the Earth and other planets in orbit around the Sun, as well as the Universe in order.

Explanations of gravitation

The Theory of General Relativity explains the force due to gravitation as a result of the curvature of space caused by matter.

(See General Relativity Theory of Gravitation for more information.)

The Theory of Quantum Mechanics explains gravitation as caused by the exchange of graviton particles between the masses. Graviton particles travel at the speed of light. Also, the wave-particle duality of Quantum Mechanics means that gravitation waves are possible.

(See Quantum Theory of Gravitation for more information.)

Effect of dark energy

Although gravitation is only an attractive force, some scientists speculate that there may be a sort of anti-gravitation that causes objects to repel away from each other. This has been measured in the rate of expansion of the Universe, which is increasing, as opposed to decreasing due to gravitation. The force causing the increase in expansion is called dark energy.

(See Effect of Dark Matter and Dark Energy on Gravitation for more information.)

Summary

The four Fundamental Forces that affect the way that objects or particles of matter interact with each other at a separation are strong nuclear, weak nuclear, electromagnetic and gravitational forces. They are part of the Theory of Everything that is an effort to resolve the differences in relativity and quantum mechanics.

Gravitation is the weakest of the fundamental forces, has an infinite range and is apparently implemented by an exchange of graviton particles.


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Resources and references

Ron Kurtus' Credentials

Websites

Does Gravity Travel at the Speed of Light? - by Steve Carlip et al at Deutsches Elektronen-Synchrotron

Speed of Gravity - Wikipedia

Measuring the Speed of Gravity - MathPages.com

Basic tutorial on Gravitational Waves - California Institute of Technology

Gravitational Wave - Wikipedia

Gravitation Resources

Books

Top-rated books on Gravity

Top-rated books on Gravitation


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


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