Norton's Dome

[studiot]

 

I'm not going to get into an argument over whether a physics law from the early 1700s is better than the version accepted today. It doesn't matter, the link in #1 is using a modern version of the law.

 

 

With the greatest respect if you are going to make an assertion, you need to be prepared for it to be subject to considered scrutiny and to back up your assertion if that scrutiny reveals chinks.

 

 

Use of the word 'unless' asserts that there is no other cause or concurrent agent possible. However it does not assert that just because the agent is present the effect will occur either.

 

 

The word compelled asserts that if such an agent is present it will act to create a stated effect. However it says nothing about the relationship in time between the two. In particular it does not preclude them being simultaneous and continuous. Nor does it preclude other (un-named) agents also being able to effect the same cause.

 

So the discussion should not be

 

Which definition is better ?

but

Why do they demonstrably not mean the same thing ?

[md65536]

The word compelled asserts that if such an agent is present it will act to create a stated effect. However it says nothing about the relationship in time between the two. In particular it does not preclude them being simultaneous and continuous. Nor does it preclude other (un-named) agents also being able to effect the same cause.

I disagree with your interpretation of "compelled" (to change by something), but it suits me better for me to be wrong about it.

 

If you're correct, then I retract the argument that the original version implies causality, and I cannot demonstrate any difference in the meaning of the versions (other than re. inertial frames which isn't an issue here), and your interpretation allows even Newton's originally stated 1st law to remain unviolated by Norton's dome.

What makes the mass move if it's in equilibrium? The only way I can see it, is that it takes some unknown time to move because there is some physical disequilibrium within the mass, when it sits on the top for some indeterminate duration, which has not yet manifested as movement. Although it is measurably still, it is not settled; in a sense, it's momentum may temporarily be equally distributed in all directions. Is that scientifically sensible?

Does "what makes it happen" need to be answered?

What makes the mass stay at rest if there is no force? This doesn't have to be answered, it suffices to have a law that describes what is observed (or "what happens", if you wish), which is that it indeed stays at rest if there is no force.

 

I think we all agree, if the mass is not at rest it must be acted on by a force.

If the mass is not at r=0, there is a force acting on the mass.

So if the mass is not at r=0, there is no need for a reason that the mass should be at rest.

 

Why must there be an additional reason that the mass is moving, if there is already no longer a reason why the mass must remain at rest? AND if you insist that there is such a necessary additional reason, is it demanded by Newton's 1st law?

 

The answer to the "why" question is, I think, "Because there must be a cause for everything". Even if that were true (I doubt it), that's not a part of Newton's first law.

Edited June 13, 2015 by md65536

[overtone]

 

But the gravitational force and normal force cancel. There is no net force on the object. It is at rest, and must remain at rest, without some other force on i

- - -

What makes the mass move if it's in equilibrium?

 

The entire point of the article linked is that there are no forces, and nothing "causes" it to move from its equilibrium if it does. All that language is what the author calls "folk science" - a less rigorous but very useful shorthand or metaphorical or analogical approach to keeping track of what some theory implies in the way of observable pattern.

 

Newton's theory is usually handled in terms of forces and causes, but this folk description is not exhaustive - as we see in the example, "spontaneous" motion without an initial cause or initial force does in some circumstances satisfy Newton's equations of motion. So the folk description - even if we got it from Newton himself - is incomplete.

 

If forced to handle this thing theoretically, my first guess approach would be to try showing that the solution space of spontaneous motions was of measure zero in some relevant sense, and then define "exists" to mean "of finite non-zero measure".

Edited June 13, 2015 by overtone

[studiot]

 

I disagree with your interpretation of "compelled" (to change by something), but it suits me better for me to be wrong about it.

 

I am puzzled where this definition comes from?

 

The English verb to compel comes directly from the Latin com and pellare (= to drive as in forced direction) which Newton actually used and means pretty much the same thing. It does not include the change, since compulsion can be preventative as well as causative.

Perhaps you meant a(p) and pellare which use is closer to your translation?

Edited June 13, 2015 by studiot

[md65536]

The English verb to compel comes directly from the Latin com and pellare (= to drive as in forced direction) which Newton actually used and means pretty much the same thing. It does not include the change, since compulsion can be preventative as well as causative.

A translation of Newton's first law as originally stated is "Law I: Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." (emphasis mine) So whether "compelled" doesn't imply change doesn't matter, I'm not looking at the meaning of single words in isolation, the law includes the meaning 'change' verbatim, why am I even arguing this it only detracts from my point, perhaps you're right.

 

The entire point of the article linked is that there are no forces, and nothing "causes" it to move from its equilibrium if it does. All that language is what the author calls "folk science" - a less rigorous but very useful shorthand or metaphorical or analogical approach to keeping track of what some theory implies in the way of observable pattern.

 

Newton's theory is usually handled in terms of forces and causes, but this folk description is not exhaustive - as we see in the example, "spontaneous" motion without an initial cause or initial force does in some circumstances satisfy Newton's equations of motion. So the folk description - even if we got it from Newton himself - is incomplete.

 

If forced to handle this thing theoretically, my first guess approach would be to try showing that the solution space of spontaneous motions was of measure zero in some relevant sense, and then define "exists" to mean "of finite non-zero measure".

You would define "exists" so that theory would conform to what you expect to happen, ignoring what is observed to happen?

 

 

 

I think this quote applies to all physical laws:

"If you want to know the way nature works, we looked at it, carefully, (look at it, see) that's the way it looks! You don't like it..., go somewhere else! To another universe! Where the rules are simpler, philosophically more pleasing, more psychologically easy. I can't help it! OK! If I'm going to tell you honestly what the world looks like to the... human beings who have struggled as hard as they can to understand it, I can only tell you what it looks like." -- Richard Feynman

 

Consider it all in this light:

Physical laws are not rules that define a set of behaviors that nature is forced to follow.

Physical laws are rules that nature is observed to always follow.

 

If you look at a set of laws in isolation, as we're doing here with Newton's first law, if you take the laws and say anything along the lines of "these are the only rules that nature is allowed to use and everything nature does must use these rules as an instruction manual of what to do", then you're doing it wrong!

If you take the laws and say "does this observed behavior follow the rules?" then you're doing it right. If observations don't follow the rules, you make new rules. If thought experiments don't follow the rules, you find the flaw, devise physical experiments to test the prediction, etc.

 

If thought experiments follow the rules, as in Norton's dome, and you don't like it... too bad! Go learn more, go devise experiments to prove wrong all the other "human beings who have struggled as hard as they can to understand it".

 

Edit: of course this all needs a huge grain of salt and it's unfair of me to falsely suggest that using a law to make predictions is in any way wrong, only that a prediction shouldn't be treated as evidence against another valid prediction, or something like that.

 

 

 

What I don't understand in this thread, with so many people here who understand science more deeply and broadly than I do, is that we all learn to accept this, that the universe does not have to conform to our expectations of how it should behave. We accept it and we learn to make sense of what the science says. But then as soon as something clashes with what we still believe must be, it's like we're back at the beginning! It's like we've only adjusted our common sense to accept some of the science we understand, and still resist thinking scientifically about some things.

 

Apologies if I'm wrong, to those actually being scientific here whom I'm failing to understand.

Edited June 13, 2015 by md65536

[overtone]

You would define "exists" so that theory would conform to what you expect to happen, ignoring what is observed to happen?

No, I would define "exists" so that I could continue to use my folk science lingo in the circumstances in which it is useful to the point of being invaluable.

 

It's just a definition of convenience for the range in which I am trying to get something done, like roof a barn. I find "cause and effect" description, with its associated meanings of words such as "exists" and "real" and "force", to be very useful.

 

Edit in: I want to "recover", in the article's sense, my folk science from the rigorous theory - in the same sense that Newtonian "forces" and so forth are recovered from modern relativity theory.

Edited June 13, 2015 by overtone

[studiot]

 

Consider it all in this light:

Physical laws are not rules that define a set of behaviors that nature is forced to follow.

Physical laws are rules that nature is observed to always follow.

 

If you look at a set of laws in isolation, as we're doing here with Newton's first law, if you take the laws and say anything along the lines of "these are the only rules that nature is allowed to use and everything nature does must use these rules as an instruction manual of what to do", then you're doing it wrong!

If you take the laws and say "does this observed behavior follow the rules?" then you're doing it right. If observations don't follow the rules, you make new rules. If thought experiments don't follow the rules, you find the flaw, devise physical experiments to test the prediction, etc.

 

 

I like this +1

 

 

 

A translation of Newton's first law as originally stated is "Law I: Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." (emphasis mine) So whether "compelled" doesn't imply change doesn't matter, I'm not looking at the meaning of single words in isolation, the law includes the meaning 'change' verbatim, why am I even arguing this it only detracts from my point, perhaps you're right

 

I'm having more trouble with this since, as I understand it, Newton didn't mention straight lines either.

Again straight is one modern interpretation of "in its right line", there are others which suggest Newton was leading into geodesics.

 

Interestingly I was looking at modules 3 and 4 (mechanics) of the London University modular A level mathematics and physics and what do you think they were analysing at high school level?

 

You got it in one

 

The Norton Dome, although they did not call it that.

[Harold Squared]

Citations are very important for those of us unable to make our own arguments.

 

So droll and yet so true! Touché!