Interpretation of Quantum Mechanics with Indefinite Norm
Abstract
:1. Introduction
proposed by | T-parity | T-parity | norm | ||
Schroedinger | even | odd | , positive | ||
Dirac-Pauli | odd | even | , indefinite |
2. Quantum Mechanics Bypassing Probabilities
employs probability only if is a generic state. If instead is an eigenstate of the operator to be measured the probability is unity, which means certainty: The Born rule reduces to the following deterministic statement:“when an observable corresponding to a self-adjoint operator is measured in a state , the result is an eigenvalue of with probability ”
“when an observable corresponding to a self-adjoint operator is measured in an eigenstate of , the result is the eigenvalue ”.
2.1. Repeated States
2.2. Repeated Measurements
- (C)
- Coefficient convergence. Figure 1 shows that the height of the peak decreases with n, so both sequence of coefficients and tend to zero as . This would be exacerbated by choosing , while would make all coefficients divergent as . Given that we want to compute eigenvectors and eigenvalues, the normalization of states is irrelevant (as usual in quantum mechanics), so the right notion of convergence is projective:
- (N)
3. Interpreting Indefinite-Norm Quantum Mechanics
3.1. Observables That Commute with One Ghost Operator
- (N)
- Norm convergence. The indefinite-norm averages of projectors considered in Equation (15) are now given by
- (C)
- Coefficient convergence. The discussion in Section 2 about the algebraic properties of remains unaltered (in particular Equations (3), (9) and (11)), up to one new issue: The basis coefficients of can get big and diverge even when computing high powers of a unit-norm state such as . Since the overall normalization of states has no physical meaning, we renormalise the coefficients of , for example setting the biggest coefficient to unity (as already done in Equation (13) to deal with positive norm and ). Following this intuitive procedure one finds that for large n the coefficients of again projectively converge to a narrow bell peaked at the same as in Equation (8),
3.2. Observables That Don’t Commute with Any Ghost Operator
3.3. Observables that Commute with Many Ghost Operators
4. Examples
4.1. The Indefinite-Norm Two-State System
4.2. The Indefinite-Norm Free Harmonic Oscillator
4.3. The 4-Derivative Oscillator
5. Conclusions
- (1)
- If Equation (37) has a unique solution, allows to define a positive norm and a probabilistic interpretation of , which agrees with the interpretation suggested by repeated measurements. As discussed in Section 2, the solution is unique when the eigenvectors of define a unique basis: The eigenvectors must lie away from the null-cone of configuration space, and the eigenvalues must be non-degenerate.
- (2)
- If no ghost operator commutes with , we cannot associate any positive norm to and no interpretation. In Section 3.2 we show that this happens for operators with pairs of eigenvectors along the null-cone of configuration space. In such a case commutes with norm-preserving U(1,1) ‘boosts’ in the 2-dimensional subspace, given that ‘boosts’ act multiplicatively along the null-cone. Thereby such operators fail to define a basis in configuration space. In more physical terms, they correspond to measurement apparata that cannot split states into events. This is the case of the position operator in Pauli-Dirac coordinate representation.
- (3)
- If Equation (37) has multiple solutions, the interpretation of is ambiguous. This is the case of degenerate operators, which have the same eigenvalue for a positive-norm state and a negative-norm state . This describes measurements that do not discriminate from , as they manifest as the same macroscopic state. As discussed in Section 3.3, the Dirac-Pauli operator belongs to this category: it does not discriminate from . In such a case the ambiguity is removed by imposing that acts as translations, dictating the interpretation of .
Funding
Acknowledgments
Conflicts of Interest
References
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Strumia, A. Interpretation of Quantum Mechanics with Indefinite Norm. Physics 2019, 1, 17-32. https://doi.org/10.3390/physics1010003
Strumia A. Interpretation of Quantum Mechanics with Indefinite Norm. Physics. 2019; 1(1):17-32. https://doi.org/10.3390/physics1010003
Chicago/Turabian StyleStrumia, Alessandro. 2019. "Interpretation of Quantum Mechanics with Indefinite Norm" Physics 1, no. 1: 17-32. https://doi.org/10.3390/physics1010003
APA StyleStrumia, A. (2019). Interpretation of Quantum Mechanics with Indefinite Norm. Physics, 1(1), 17-32. https://doi.org/10.3390/physics1010003