| MadSci Network: Physics |
Greetings: The answer to your question is related to the definition of matter, a definition which has been modified several times during the past century. --------------------------------------------------------------------------- Reference: Webster’s New World Dictionary, Second College Edition Matter – 1. What a thing is made of; constituent substance or material 2. what all (material) things are made of; what ever occupies space and is perceptible to the senses in some way: in modern physics , matter and energy are regarded as equivalents, mutually convertible according to Einstein’s formula E=mc^2 (energy equals mass multiplied by the square of the velocity of light). --------------------------------------------------------------------------- These definitions begin by saying that matter occupies space and is perceptible to the senses. Our eyes can detect photons of light, yet more than one photon can occupy the same space at the same time. By this definition photons are not matter. This was the definition of matter before Albert Einstein’s work during the first decades of the 20th Century . However, after Einstein equated matter (mass) and energy, the modern physics definition of matter was extended to include photon energy. A photon has no mass but it does have energy, and given the right conditions, such as inside a star, photons can be converted to mass. It does not require a star to convert mass to photons. By the modern physics definition photons are included in matter! It bothers you that the modern physics definition of mass includes photons, packets of energy that do not have mass. The answer to this problem is related to the concept of momentum. Momentum is important in physics because forces are required to increase or decrease momentum. For a particle of conventional matter that has mass and occupies space, momentum equals the particle's mass multiplied by its velocity. For example the force required to stop a ten ton truck moving at 100 km per hour (60 miles per hour) is ten times greater than the force required to stop a one ton automobile moving at the same velocity. Thus, even though the two vehicles are moving at the same velocity, stopping the truck requires a ten times greater force because the truck has ten times the momentum of the automobile. Photons have a strange characteristic, they do require a force to stop them, even though they have no mass. The reason is that photons do have momentum! However, the momentum is called electromagnetic momentum, not mass related momentum. Einstein received his Nobel Prize for work in this area. It turns out that momentum, and the forces required to increase or decrease momentum, are at the heart of the laws of physics and also Einstein’s theory of Relativity. Relativity also teaches us that mass increases as it approaches the velocity of light and that the mass of a hunk of matter would become infinite if it could reach the speed of light. However, it would require an infinite force to propel matter to the speed of light. Because you and I are composed of conventional matter we cannot travel at the speed of light, yet photons without mass must always travel at the speed of light, they cannot stop. Recently scientists have been able to reduce the speed of light (photons) from 300 million meters per second (186,000 miles per second) in a vacuum to a few feet per second within a special state of matter called Bose-Einstein condensate (BEC), a state of matter that exists at temperatures very close to absolute zero. Perhaps by slowing photons down in BEC, we can learn more about their strange behavior from these studies. BEC is a very complex subject and you can read a little bit about it on the American Physical Society’s web pages at: http://focus.aps.org/v2/st22.html Best regards, Your Mad Scientist Adrian Popa
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