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jtbell is offline
May10-05, 12:43 AM
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Quote Quote by Crosson
What if the energy is real, as in the case of electromagnetic waves? Such waves carry energy through a vaccum, and they are nothing more than oscillating electric and magnetic fields.
In what sense is energy "real?" In what sense are electric and magnetic fields "real?"

To the original poster ("myself"): You're venturing (probably without realizing it) into very deep philosophical matters here. Electric fields, magnetic fields, energy, and many other things, are all concepts that we use to explain the observed relationships involving physical objects and their motions. But "energy" is not a substance in and of itself; it exists only in the context of two or more objects. We cannot observe energy in isolation, or measure it directly. We can only infer the amount of energy involved in any process by measuring the positions and locations of objects before, during, and/or after that process, and performing some calculations.

Similarly for electric and magnetic fields. After all, we define the presence of electric and magnetic fields by the observation that certain objects placed in proximity to each other move in ways that cannot be explained by simple contact-type pushes or pulls.

I'm not trying to denigrate or belittle these concepts, or suggest that there's any useful replacement for them. They're amazingly useful, and I would not want to try to do physics without them. But we need to keep in mind the dangers of excessive reification of the concepts that we invent to explain what we actually observe. That is, we need to be careful not to associate "too much reality" to them.

Again to the original poster: don't worry too much about this stuff, except maybe when you have some free time. If you think energy in electric and magnetic fields is weird, just wait until you get to quantum mechanics, and you have to wrap your mind around the [itex]\psi[/itex] function!