Different forms of physical energy

[Der_Trihs]

Wrong thread

[Absolute]

@Chronos

So, you can’t measure any sort of energy directly, but you can directly measure the rest energy of a car?

No, you can’t, really. You can measure the mass, and then calculate how much of this abstract quantity called “energy” that corresponds to.

@WoodenTaco

Really? What about gauge bosons? Do you think photons don’t exist?
What does exist to you?

Photons are something discrete that we can detect and observe, that do things to the world. Energy is not. Can you build an “energy” detector? Can energy exist independently of objects that we describe as having it? Of course not. It’s purely a mathematical tool, and an abstraction that helps us understand how things behave.

Let me steal a more eloquent quote from elsewhere:

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.

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.

[Chronos]

No, you can’t, really. You can measure the mass, and then calculate how much of this abstract quantity called “energy” that corresponds to.

OK, I measure that the car has a mass of 700 kg. I then calculate that that corresponds to 700 kg of energy.

If we’re going to be calling something that trivial a “calculation”, then what doesn’t require calculation?

[Absolute]

@Chronos

OK, I measure that the car has a mass of 700 kg. I then calculate that that corresponds to 700 kg of energy.

If we’re going to be calling something that trivial a “calculation”, then what doesn’t require calculation?

In a consistent system of units, you need the c^2 factor to translate whatever your unit of mass is, into whatever your unit of energy is.

[Chronos]

And in a really consistent system of units, c = 1, so your unit of mass can be the same as your unit of energy.

[WoodenTaco]

@Absolute

Photons are something discrete that we can detect and observe, that do things to the world. Energy is not.

This is quickly devolving into endless semantics, but photons are energy. All the force carriers are, essentially, what we conceive of as energy.

Can you build an “energy” detector?

Not generically since energy exists in the form of lots of different gauge bosons, but a thermometer is absolutely an energy detector. So is a spectrometer.

Can energy exist independently of objects that we describe as having it? Of course not.

Yes, it can. Force carriers are the transmitters of energy; in a very real sense, they are energy.