## How can you prove Newton's laws?

• 9
I would like to know how can you prove these laws, but not using devices that use the the same laws.
• 797
Launch yourself into deep space and see if you keep on going?
• 3.6k
how can you prove
Given what you're asking about, I'm guessing you've got more on your mind. Maybe this will help: what exactly do mean by "prove"? What do you understand "prove" to mean?
• 9
Thank you guys for your answers. Tim, by "prove" I mean how can you show they are true. I hope this can help.
• 4.6k
You can show they are true by running the experiments. You need the equipment. You can't prove them by thought alone.
• 9
But what if the equipment need the laws to be true?
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What does that even mean?
• 9
Lets say you use a chronometer. The chronometer uses f=ma to perform calculations.
• 4.7k
I would like to know how can you prove these laws, but not using devices that use the the same laws.

Every white swan you see is evidence that swans are white. However, this doesn't mean ALL swans are white. If the chornometer is following the Newton's laws then it must be white swan. Newton never saw a black swan.
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Don't use a chronometer. Use a ruler, a sand timer, a spring, and a weight. Kids do this in early high school.
• 4.7k

Don't use a chronometer. Use a ruler, a watch, a spring, and a weight. Kids do this in early high school.

I think what he's trying to say is that argument is circular. Newton's laws proving Newton's laws.

If the instruments obey Newton then Newton would be one happy dude wouldn't he? I guess the OP wants to compare the situation to a court case where Newton is the client, the lawyer, the judge and the jury. Happy happy Newton!
• 4.6k
This is meaningless.
• 4.7k

If the instruments didn't follow Newton's laws then they would disprove Newton.

It's necessary that the instruments too must obey the laws.
• 1.1k
I would like to know how can you prove these laws, but not using devices that use the the same laws.

You could never prove them. For one thing they're not "true," if by true you mean that the universe actually works that way. We know that for objects moving at very high speeds and/or objects with extremely large mass, Newton's laws are superseded by Einstein's; and that even for everyday object like bowling balls, Newton's laws are only an approximation.

Secondly, NO law of physics can ever be proved; because every law of physics is a historically contingent approximation, good to a few decimal places, to the results of the experiments we're capable of doing at any given level of technology. Our very best physical theory, quantum electrodynamics, gives the magnetic moment of the electron to "a few parts in $10^{13}$. That's great by physics standards but there are a lot more decimal places out there and a lot of physics we still don't know.

https://physics.stackexchange.com/questions/497087/what-is-the-most-precise-physical-measurement-ever-performed

No physical theory is true. Or rather, "true" is defined in physics as our best physical theory! So Newton's laws were true in 1687 with the publication of the Principia, and became false in 1915 with Einstein's publication of general relativity.

Pick your definition of true. The ultimate truth of the universe -- if there even is any such thing? Or just the latest widely agreed on theory from the physicists?
• 4.7k

Let's not get too technical. The problem for the OP is how an instrument that is Newtonian can ever prove that some other event is NOT Newtonian in nature. If I only have red paint, whatever I paint will surely be red.

A better analogy is the biased judge adjudicating a case. The trial wouldn't be fair.
• 1.1k
Let's not get too technical. The problem for the OP is how an instrument that is Newtonian can ever prove that some other event is NOT Newtonian in nature. If I only have red paint, whatever I paint will surely be red.

A better analogy is the biased judge adjudicating a case. The trial wouldn't be fair.

I responded primarily to the title of the OP without reading much of the post, and without reading the other responses in the thread. If I misconstrued the question, so be it. It's kind of a reflex on my part to point out that the laws of physics are historically contingent approximations; and that whether there are laws of the universe at all, let alone ones accessible to humans, is an open question. But if that wasn't the question, then ... well, what was the question. I didn't understand the bit about how Newtonian instruments could prove an event is not Newtonian. In fact perfectly conventional Newtonian telescopes were used to observe the solar eclipse in 1919 that confirmed Einstein's theory of relativity.

https://en.wikipedia.org/wiki/Solar_eclipse_of_May_29,_1919

Note that by Newtonian telescope, I meant not only the OP's sense of a telescope operating by Newtonian physics; but also that the Newton invented the reflecting telescope! So there's a double meaning there.
• 4.6k
an instrument that is Newtonian

There are no 'instruments which are Newtonian'.
• 4.7k
Your post was great but I don't think it would've satisfied the OP who said:
I would like to know how can you prove these laws, but not using devices that use the the same laws

Actually I think your answer was the best by saying scientific claims are contingent.
• 4.7k
There are no 'instruments which are Newtonian'.

I meant which follow Newton's laws
• 1.1k
Your post was great but I don't think it would've satisfied the OP who said:

I have already confessed to not reading the post and only lazily making one of my standard hobby horse points. Did you want me to confess again? Is there a particular punishment you have in mind? I watched the entire Democratic debate tonight, that was punishment enough!
• 4.6k
As distinct from what? Instruments which don't follow Newtons laws? Like you have a choice? What are you talking about?
• 4.7k

As distinct from what? Instruments which don't follow Newtons laws? Like you have a choice? What are you talking about?

There's an even bigger point here which the OP is hinting at - that the theory of relativity which has supplanted Newton's was proven by instruments that had to follow Newton's laws.

Kindly take one step back to the OP's question.
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Trash, again, as usual.
• 4.7k
Trash, again

I wish you'd clarify our doubts because they probably reveal more ignorance than knowledge/understanding.
• 4.6k
You don't have 'doubts', you can't even get the grammar right, let alone the logic.
• 4.7k
:up: :ok: :broken:
• 4.7k
I would like to know how can you prove these laws, but not using devices that use the the same laws.

If you've read my other posts then you know that the Theory of Relativity was derived from measurements from instruments that followed Newtonian laws. What do you have to say about that?
• 3.6k
1) Every object in a state of uniform motion will remain in that state of motion unless an external force acts on it.
2) Force equals mass times acceleration .
3) For every action there is an equal and opposite reaction.

These are the laws in question. "Proof" requires a definition. But meanwhile I'll offer one method: reductio ad absurdum.

And what Fishfry said.
• 4.7k
:chin:

Every instance of the laws being verified is part of the proof isn't it?

The OP is not as concerned with the meaning of "proof" as he is concerned about the circularity of the proof. By "proof" he probably means the derivation process of the laws. It must have been that measurements were taken of mass, acceleration, and force to get to the equation F = ma, right? If each such measurement followed Newtonian mechanics then it, to the OP, looks like the laws proving themselves. This is what appears problematic to the OP (unfortunately he isn't here to confirm this) - that Newton's laws were/are used to prove Newton's laws.

Personally, I think if the instruments didn't follow Newtonian laws then that would be a problem because they would be the disconfirming exception, invalidating Newton's laws.

I mentioned the theory of relativity being proved by instruments that followed Newton's laws but what I forgot was that the theory of relativity is applicable at non-relativistic speeds too. The same can't be said of Newton's laws which are now like Aristotle's belief that objects naturally come to rest and that heavier objects fall faster than lighter ones.

Can you kindly clarify on the circularity which I mentioned above?

Is it a real/interesting question or is it a question borne out of ignorance? Or is it both?

Which areas of logic, science and math does such a question touch upon?
• 3.1k
Can you prove they describe the world somehow without checking? No.

Can you prove they are consequences of other math? Yes. I think you can get all the basic laws from Hamiltonian/Lagrangian mechanics.
• 4.7k
Can you prove they are consequences of other math? Yes. I think you can get all the basic laws from Hamiltonian/Lagrangian mechanics.

What do you mean by that? Mathematical models proves that Newton's laws must be true?

How so?
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