# The Feynman way of explaining Symmetry in Physical laws

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• mark2142
In summary, Feynman discusses the idea that the laws of physics are symmetrical for translational displacements, meaning that they do not change when we make a translation of our coordinates. He explains that this is an assumption that we make in order to do physics, as we cannot test the laws of physics in every point in the universe. He also mentions that if the laws of physics do vary, then it means that our understanding of them is not fundamental and can be improved upon.
I, for one, do not understand the distinction you are trying to create. Perhaps you could succinctly restate your question.

hutchphd said:
I, for one, do not understand the distinction you are trying to create. Perhaps you could succinctly restate your question.
Ok! I am simply asking how is “right everywhere” is same as “right from everywhere”?
mark2142 said:
This does not happen. We can write the correct laws using the new coordinates. There is no absolute space and origin from which the laws are right. So it’s right everywhere or from everywhere ?
You can see in the logic I had put a question mark. The math says only “right from everywhere” not “right everywhere”.

PeroK
mark2142 said:
Ok! I am simply asking how is “right everywhere” is same as “right from everywhere”?
Take a piece of equipment and study it. Move it somewhere and study it again from a distance. Is it working the same? Repeat and repeat until you are convinced that the laws you have that describe the instrument are "right everywhere".

Bring the equipment back to you. Now you move somewhere and study it again from a distance. The laws governing your function don't change (we just established that) and the equipment hasn't moved. Thus the results will be the same and the laws are "right from everywhere".

Ibix said:
Take a piece of equipment and study it. Move it somewhere and study it again from a distance. Is it working the same? Repeat and repeat until you are convinced that the laws you have that describe the instrument are "right everywhere".

Bring the equipment back to you. Now you move somewhere and study it again from a distance. The laws governing your function don't change (we just established that) and the equipment hasn't moved. Thus the results will be the same and the laws are "right from everywhere".
It’s already been explained before in many posts and I already know the laws don’t change upon displacement. I want to understand the proof that Feynman gave. I am unable to follow from math that laws don’t change upon displacement. The math is proving the law is same for different observers.

I'm not aware that Feynman anywhere proved Noether's theorem in his textbooks. Do you have the source. I'm sure, it's a masterpiece. Otherwise you'll find this proof in any modern textbook on classical analytical mechanics, e.g.,

F. Scheck, Mechanics (5th ed.), Springer (2007)

Is the OP aware of the Messenger Lecture on symmetry? He does some fun hand waving on Noether.

vanhees71
mark2142 said:
It’s already been explained before in many posts and I already know the laws don’t change upon displacement. I want to understand the proof that Feynman gave. I am unable to follow from math that laws don’t change upon displacement. The math is proving the law is same for different observers.

I think @Ibix has answered this question, essentially, "Feynman has not proved that the 'real' laws don’t change upon displacement"

Ibix said:
... So Feynman is proving that his model of the laws of physics are translation invariant and hence his equipment is predicted to be translation invariant. He does not prove (and you cannot prove) that this is a correct model of reality, but it's been an accurate model every time so far.

"his model" in this case is Newton's ##\vec F = m \vec a##

vanhees71 and Ibix
mark2142 said:
The math is proving the law is same for different observers.
I think the only difference is how you interpret the offset, ##a##. Is it the distance between two coordinate system origins, or is it the negative of the x displacement between two pieces of identical equipment measured in the same coordinate system? (I may have incorrectly assigned the negative sign there, so beware.) Depending which way you interpret it you are proving either.

mark2142
Ibix said:
Depending which way you interpret it you are proving either.
(Now this means that there exists a way to measure x, y, and z on three perpendicular axes, and the forces along those directions, such that these laws are true.)
Do we measure x by scale and F by some machine?
Can you tell how do we measure and write newtons law?

mark2142 said:
Can you tell how do we measure and write newtons law?
By doing physics theory in the classroom and experiments in the lab.

So if we assume right most vertical line as origin and the body move to middle vertical line y’ then we can write a law which we call newtons law for the displacement. Then body moves to left most line y and again we can write the same law with different coordinates. So if we see we can realise that the law doesn’t change from middle line y’ to left most line y. Law is translational invariant. That’s what I think of. Yes?

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