[deleted]
Tom / Rob
We are arguing in circles! So let me try to 'square the circle'. I will again take it one idea at a time, listed and numbered, and you can pick and choose and agree or disagree (True / False). With well reasoned arguments of course!
1)Physical laws are different from mathematical identities.
2)Physical laws depend on certain physical assumptions for their derivation, or on empirical evidence for their validation. They are simply assumed to always be true as long as their premises are true. In this sense, they could be thought as "identities" but that's NOT what I do. A "postulate" for me is NOT an "identity". A=A is logically very different from assuming F=ma is always true when m is constant.
3)Mathematical identities do not depend on any physical assumptions, unlike physical laws.
4)Both physical laws and mathematical identities can only be applied to situations where all their premises are known to be true.
5)Newton's Laws are considered to be physical laws. I do not call these mathematical identities "true by definition". That's sophistic play on words. They are not! Since these depend on empirical validity.
6)Planck's Law for blackbody radiation is also considered to be a physical law, since in its derivation the physical assumption of "energy quanta" is used.
7)I have shown (through my derivation of it) Planck's Formula to be a mathematical identity and not a physical law per se. This mathematical identity is a functional relationship between the incremental change of a quantity E(t) over an interval of t, the average of the quantity E over the same interval and the value of E(t) at the beginning (or end, if we reverse t) of that interval. When E(t) is a simple exponential of t, then this relationship is exact. For any other integrable E(t), this relationship is a limit. (See my chapter, The Thermodynamics in Planck's Law).
8)All physical laws contain physical assumptions. All physical assumptions presuppose a physical view. All physical views are descriptions of "what is" the Universe (Nature). Any description of "what is" is metaphysical in essence. Basing Physics on mathematical identities instead of physical laws (assumed to be true) keeps physics from 'morphing into metaphysics'. I argue we can have Physics without assuming 'physical laws'.
Tom you write:
"Your claim that physical laws are mathematical tautologies is either falsified ... or trivial"
Physical laws are different from mathematical identities. What I am arguing is that we can and should formulate Physics in such a way that what otherwise would have been physical laws are instead derived as mathematical identities without any physical assumptions.
"There are any number of mathematical tautologies that have nothing to do with physics." True! But so what!
"you neglect that Planck's law applies only in the case of blackbody radiation. To take this special case -- (albeit an important case, since it is the limiting case of a body's heat content, which is why it is a "law") -- and declare that it is general, ignores, e.g., radiation effects in out of equilibrium conditions, such as LASER, which do depend on the quantization hypothesis."
Nothing changes about Planck's Law but its derivation using no physical assumptions. Planck's law as was derived by Planck applies only to ideal blackbody conditions. But the same result can be obtained as a mathematical identity and without the "quantization of energy hypothesis". If E(t) is a simple exponential of time, than Planck's Formula is exact. For any other integrable E(t), Planck's Formula is a limit. There are no other premises to my derivation. Just a very simple mathematical identity I am using. I fail to see how you conclude I "declare that it [Planck's Law] is general". Unless you mean this Formula generally applies whenever we want to express the quantity E(t) knowing its incremental change and average value over a duration of t. Which it does! And this is pure math with no physical assumptions made.
"If you are just saying that the mathematics describes a limiting case in every instance of physical law, how is that nontrivial?"
I am not saying or doing anything of the sort! I am only suggesting Physics can be so formulated that Basic Law of Physics can equivalently be derived as mathematical identities. The advantage would be that no physical assumptions are made which could ultimately lead to metaphysics.
Rob, you write:
"force is the first derivative of linear momentum, with respect to time."
That is also how I am considering force. No problem here!
Constantinos