On Feb 2, 2013, at 7:14 PM, Ludwik Kowalski wrote:
The short essay below was inspired by recent philosophical conversations. Comments will be appreciated.
Our material world is made of physical objects; anything that has a certain mass, and occupies a certain volume in space, is an object. Some objects, such a stars and galaxies are very large, others, like electrons and molecules, are very small. Collections of objects, such as airplanes, cell phones and molecules, are also objects. The same is true for a certain amount of water, or air, and for living creatures. To avoid confusion, objects are named. Existence of objects is recognized by using our senses, directly or indirectly, for example, with eye glasses, telescopes, microscopes, Geiger counters, antennas, etc.
But not all names used by physicists refer to objects; some concepts, such as force and acceleration, were invented to promote thinking. Does kinetic energy exist in the same way as a moving car? I do not think so. Energy, like force and acceleration, is a physical quantity invented to describe and understand objects. Such theoretical quantities exist in our mind; they do not exist objectively, like physical objects in our material world.
Theoretical reality is subjective; physical reality is objective. It is not difficult to imagine a planet on which material world phenomena have been successfully described, and understood, in terms of theoretical concepts that are different from ours. Many misunderstandings would be avoided if the verb 'to exist' were always qualified. To "exist subjectively" is not the same thing as to "exist objectively." Do you agree?
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Bill Nettles responded:
"Hmmm...
So p + p + 2 GeV of subjective CM kinetic energy --> p + p + 2 more objective masses (p + p_bar) ? What is the subjective/objective mediator?"
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1) What do you mean by the word "mediator," in this context?
2) Let us start discussing philosophical topics at the level of an introductory physics course. Topics related to creation of new particles, according to the m=E / (m*c^2), is worth addressing later.
3) Referring to the concept of energy, Feynman reminds us (Vol 1, Chapter 4) that it "has a large number of different forms, and there is a formula for each one. These are: gravitational energy, kinetic energy, heat energy, elastic energy, electrical energy, chemical energy, radiant energy, nuclear energy, mass energy. If we total up the formulas for each of these contributions, it will not change except for energy going in and out.
It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity, and when we add it all together it [always] gives ... the same number. It is an abstract thing in that it does not tell us the mechanism or the reasons for the various formulas."
Why do I say that energy is a subjective quantity? Because it exists in our minds only. Verbally I often describe energy (in class) as if it were an object (existing objectively). But I know that this is not literally correct. Existence of energy is not the same as existence of a real object, such as our moon, or my body. That does not mean that subjective entities are not very useful.