Proof for Problem 1.1.1 of Shankars Prin of QM

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SUMMARY

The discussion focuses on proving the equation |-V> = -|V> as part of Problem 1.1.1 from Shankar's Principles of Quantum Mechanics. Participants emphasize the importance of rigorous justification in mathematical proofs, particularly in quantum mechanics. The proof involves recognizing that |W> can be defined as -|V>, leading to the conclusion that V + (-1)V = 0, confirming that (-1)V is indeed the unique vector -V. The discussion also references the eighth axiom for linear spaces, which states that 1V = V.

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  • Understanding of quantum mechanics concepts, specifically vector notation.
  • Familiarity with linear algebra, particularly vector spaces and axioms.
  • Knowledge of mathematical proof techniques and justification methods.
  • Experience with Shankar's Principles of Quantum Mechanics, particularly the relevant sections.
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  • Study the axioms of vector spaces in detail, focusing on the eighth axiom regarding scalar multiplication.
  • Review linear algebra proofs involving vector addition and scalar multiplication.
  • Examine additional problems in Shankar's Principles of Quantum Mechanics to reinforce understanding of vector notation.
  • Explore mathematical justification techniques in quantum mechanics to enhance proof-writing skills.
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Students of quantum mechanics, particularly those studying Shankar's text, as well as educators and anyone interested in mastering mathematical proofs in the context of quantum theory.

Mindstein
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I think I may be over-thinking this as I have had one formal course in QM and an independent study course in QM, but any help is MORE THAN GREATLY APPRECIATED!

Homework Statement



Prove that |-V> = -|V>


Homework Equations



He instructs us to begin with |V> + (-|V>) = 0|V> = |0>


The Attempt at a Solution



Let -|V> = |W>

Then

|V> + |W> = 0|V> = |0>

which implies that

|W> = |-V> ?

I'm really confused.
 
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Okay, first I think you mean problem 1.1.2, unless you have a different edition.
This is the kind of proof where you have to doubt everything. Act as if you are in a mathematical minefield. Only do the things you can completely justify.

I find myself wanting to say that 1V = V, but that actually isn't an axiom...

Assuming that for the moment,
V + (-1)V = 1V + (-1)V = (1 + -1)V = 0V = 0 (by part 1 of the same problem)
And thus (-1)V is the unique vector -V such that V + -V = 0

Looking up in other books, 1V = V is listed as an eighth axiom for linear spaces. Shankar described it by interpretation in a paragraph, but didn't actually state it overtly as an axiom.
 

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