The preceding BCA (Stamper-Kurn et. al., arXiv:1607.01454) asserts that our observation of interference contrast in a half-metre-scale atom interferometer (Kovachy et. al., Nature 528, 530-3 (2015)) does not prove the existence of macroscopic quantum superpositions and hence does not test quantum mechanics at long length scales. Moreover, the BCA implies that intrinsic atomic interactions or technical imperfections could prevent the application of our work to future differential measurements. On the contrary, we argue the following: i) in standard quantum mechanics, there is no known mechanism in our system that prohibits its use in future differential measurement applications; ii) our experiment tests quantum mechanics in that it constrains any modifications that would reduce contrast in an interferometer with arms that propagate over widely separated trajectories; and iii) using a standard definition of superposition, our observation of interference results from quantum superposition at the half-metre scale. In particular, quantum superposition is a more general concept than first-order coherence.
The preceding BCA (Stamper-Kurn et. al., arXiv:1607.01454) asserts that our observation of interference contrast in a half-metre-scale atom interferometer (Kovachy et. al., Nature 528, 530-3 (2015)) does not prove the existence of macroscopic quantum superpositions and hence does not test quantum mechanics at long length scales. Moreover, the BCA implies that intrinsic atomic interactions or technical imperfections could prevent the application of our work to future differential measurements. On the contrary, we argue the following: i) in standard quantum mechanics, there is no known mechanism in our system that prohibits its use in future differential measurement applications; ii) our experiment tests quantum mechanics in that it constrains any modifications that would reduce contrast in an interferometer with arms that propagate over widely separated trajectories; and iii) using a standard definition of superposition, our observation of interference results from quantum superposition at the half-metre scale. In particular, quantum superposition is a more general concept than first-order coherence.
I show in this paper why the universality of quantum mechanics at all scales, which implies the possibility of Schrodinger's Cat and Wigner's Friend thought experiments, cannot be experimentally confirmed, and why macroscopic superpositions in general cannot be observed or measured, even in principle. Through the relativity of quantum superposition and the transitivity of correlation, it is shown that from the perspective of an object that is in quantum superposition relative to a macroscopic measuring device and observer, the observer is already sufficiently well correlated to the measuring device that once the object correlates to the measuring device, there is no time period in which the observer can perform an appropriate interference experiment to show that the measuring device is in a superposition.
Hypothetical models have been proposed in which explicit collapse mechanisms prevent the superposition principle from holding at large scales. In particular, the model introduced by Ellis et al. [J. Ellis et al., Phys. Lett. B 221, 113 (1989)] suggests that quantum gravity might be responsible for the collapse of the wave function of massive objects in spatial superpositions. We consider here a recent experiment reporting on interferometry with atoms delocalized over half a meter for a time scale of 1 s [T. Kovachy et al., Nature (London) 528, 530 (2015)] and show that the corresponding data strongly bound quantum-gravity-induced decoherence and rule it out in the parameter regime considered originally.
Recent experimental advances in matter-wave interferometry have demonstrated quantum interference in increasingly large and massive composite objects, including nanoparticles composed of thousands of atoms. These results are often interpreted as evidence that quantum superposition can, in principle, scale arbitrarily with mass and size, with practical limitations arising primarily from environmental decoherence. This technical note argues that mass and size alone are insufficient criteria for assessing the applicability of global quantum superposition descriptions. It introduces a minimal, non-biological architectural distinction between systems that admit an effective global quantum description and systems whose internal organization renders such descriptions operationally ambiguous or illegitimate, even in the absence of significant external decoherence. The analysis does not propose any fundamental limitation on quantum mechanics, nor does it claim that global quantum states cease to exist. Instead, it focuses on the conditions under which global quantum descriptions remain meaningful and useful as effective representations. In architecturally composite systems, internal degrees of freedom may function as endogenous sources of decoherence, limiting the descriptive legitimacy of a single global quantum state. The contribution is diagnostic in nature and aims to clarify common ambiguities in discussions of the quantum–classical transition, the interpretation of large-scale interference experiments, and claims concerning the scalability of quantum superposition. No new physical principles or theoretical modifications are introduced.
Recent Quantum Galileo Interferometer experiments compare two coherent wave packets of the same atom: one following a ballistic free-fall trajectory and the other magnetically held in the laboratory frame. Their measured relative phase agrees with the standard prediction, whose idealized leading dependence is cubic in the free-fall time (T³). This paper develops a structure-first interpretation of that result within Harmonic Physics. On this reading, intrinsic phase relations constrain the paths that can be jointly resolved, observer-level geometry describes their organization, and recombination makes the differential phase accessible without creating the underlying distinction. The experiment supports a reproducible path-dependent phase relation and the consistency of quantum evolution with the equivalence principle in the tested regime. It does not uniquely confirm Harmonic Physics, establish that gravity is non-dynamical, or directly test objective-collapse mechanisms. A distinct empirical test would require an independently defined phase-relational quantity and a reproducible residual beyond the complete standard interferometer model and its known systematics. The paper therefore presents the experiment as a clear interpretive case for structure-first ordering and as a platform for future discriminating tests.
Lying at the heart of quantum mechanics, the notion of quantum superposition causes enormous difficulty in understanding the problem of quantum measurement, which concerns the Einstein-Bohr debate on the conceptual foundations of the quantum theory. According to Bell’s theorem, Einstein’s viewpoint in his debate with Bohr seems to be wrong. In the present paper, a new principle (referred to as the general principle of measurements) is introduced and proved as a mathematical theorem. Based on this principle, various forms of quantum superposition (including quantum entanglement) and the corresponding experiments are scrutinized. The main findings are as follows. (a) Einstein’s viewpoint is correct and Bell’s theorem is problematic. (b) Measurement outcomes of any actual experiment with individual microscopic objects described in a form of quantum superposition, in particular, the experimental results of testing Bell inequalities, are all erroneously explained. (c) Bell inequalities failed to capture the essence of the Einstein-Bohr debate, i.e., whether quantum superposition is legitimate for describing individual microscopic objects. (d) All kinds of quantum superposition violate the general principle of measurements and hence are illegitimate. (e) Quantum mechanics can be completed by using disjunction (“or”) as the logical relation between the orthonormal vectors that span an arbitrarily given Hilbert space for describing a single microscopic object, and the mathematical setting will remain essentially unchanged; hidden-variable theories are irrelevant to the real world. (f) After completing quantum mechanics as above, the difficulty in understanding the problem of quantum measurement disappears naturally. Implications of the findings are also discussed.
At present, there are two possible, and equally plausible, explanations for the physics of quantum measurement. The first explanation, known as the many-worlds interpretation, does not require any modification of quantum mechanics, and asserts that at the time of measurement the Universe splits into many branches, one branch for every possible alternative. The various branches do not interfere with each other because of decoherence, thus providing a picture broadly consistent with the observed Universe. The second explanation, which requires quantum mechanics to be modified from its presently known form, is that at the time of measurement the wavefunction collapses into one of the possible alternatives. The two explanations are mutually exclusive, and up until now, no theoretical reasoning has been put forward to choose one explanation over the other. In this article, we provide an argument which implies that the collapse interpretation is favored over the many-worlds interpretation. Our starting point is the assertion (which we justify) that there ought to exist a reformulation of quantum mechanics which does not refer to a classical spacetime manifold. The need for such a reformulation implies that quantum theory becomes nonlinear on the Planck mass/energy scale. Standard linear quantum mechanics is an approximation to this nonlinear theory, valid at energy scales much smaller than the Planck scale. Using ideas based on noncommutative differential geometry, we develop such a reformulation and derive a nonlinear Schrödinger equation, which can explain collapse of the wavefunction. We also obtain an expression for the lifetime of a quantum superposition. We suggest ideas for an experimental test of this model.