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The speculation that gravity is the key to solving the quantum measurement problem has been alive for decades, without any convincing demonstration of a solution. One necessary factor in the relevant proposals is that the gravitational energy of mutual interaction, which scales quadratically with the mass, facilitates the spontaneous collapse of the wavefunctions in spatially separated superpositions. Relying on a simple physical input from electrodynamics, supported by robust first principle calculations, we show that the speculations connecting gravity and the hypothetical spontaneous collapse of the wavefunction are inconsistent and not tenable. The result suggests that the gravitational solution to the problem of the collapse of the wavefunction be put to rest., Comment: 6 pages, 1 figure, Honorable mention in Gravity Research Foundation 2021 awards

The Strong Equivalence Principle (SEP) holds the full essence and meaning of the General Theory of Relativity as the nonlinear relativistic theory of gravitation. It asserts the universal coupling of gravity to all matter and its interactions including the gravitational interaction and the gravitational self energy. We point out that confirming the gravitational coupling to gravitons, and hence to the gravitational waves, is the direct test of the SEP. We show that the near simultaneous detection of gravitational waves and gamma rays from the merger of binary neutron stars provides a unique and the most precise test of the SEP, better than a part in $10^{9}$, which is also the only test of the SEP in the radiation sector., Comment: RevTeX, 8 pages, 1 figure

Gravitational waves propagate at the speed of light in general relativity, because of its special relativistic basis. However, light propagation is linked to the electromagnetic phenomena, with the permittivity and permeability constants as the determining factors. Is there a deeper reason why waves in a geometric theory of gravity propagate at a speed determined by electromagnetic constants? What is the relation between gravity's own constants and the speed of gravitational waves? Our attempt to answer these fundamental questions takes us far and deep into the universe., Comment: 7 pages. Honorable mention in 2018 Gravity Research Foundation essay competition

The assumed universality of the equivalence principle suggests that a particle in a gravitational field has identical physics to one in an accelerated frame. Yet, energy considerations prohibit radiation from a static particle in a gravitational field while the accelerating counterpart emits. Solutions to the fundamental problems of radiation from charges in a gravitational field and consequences to the equivalence principle usually contrast the far-field and global nature of radiation with the local validity of the equivalence principle. Here, we suggest reliable physical solutions that recognizes the essential need for motional currents and the magnetic component for radiation to occur. Our discussion reiterates the need for a fresh careful look at universality of free fall for charged particles in a gravitational field., Comment: 7 pages, honorable mention in GRF essay awards 2014

Quantum gravity remains an elusive theory, in spite of our thorough understanding of the quantum theory and the general theory of relativity separately, presumably due to the lack of any observational clues. We argue that the theory of quantum gravity has a strong constraining anchor in the sector of gravitational radiation ensuring reliable physical clues, albeit in a limited observable form. In particular, all types of gravitational waves expected to be observable in LIGO-like advanced detectors are fully quantum mechanical states of radiation. Exact equivalence of the full quantum gravity theory with the familiar semiclassical theory is ensured in the radiation sector, in most real situations where the relevant quantum operator functions are normal ordered, by the analogue of the optical equivalence theorem in quantum optics. We show that this is indeed the case for detection of the waves from a massive binary system, a single gravitational atom, that emits coherent radiation. The idea of quantum-gravitational optics can assist in guiding along the fuzzy roads to quantum gravity., Comment: 10 pages. Based on seed ideas in our Gravity Research Foundation Essay 2013

We present a gravitationally rigorous and clear answer, in the negative, to the question whether gravimetry with atom interferometers is equivalent to the the measurement of the relative gravitational time dilation of two clocks separated in space. Though matter and light waves, quantum states and oscillator clocks are quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle, there are crucial differences in the context of tests of gravitation theories., Comment: 10 pages, 1 figure

There are discernible and fundamental differences between clocks, waves and physical states in classical physics. These fundamental concepts find a common expression in the context of quantum physics in gravitational fields; matter and light waves, quantum states and oscillator clocks become quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle. With this insight, gravitational effects on quantum systems can be simply and accurately analyzed. Apart from providing a transparent framework for conceptual and quantitative thinking on matter waves and quantum states in a gravitational field, we address and resolve with clarity the recent controversial discussions on the important issue of the relation and the crucial difference between gravimetery using atom interferometers and the measurement of gravitational time dilation., Comment: Gravity Research Foundation honorable mention, 2011

We provide an overview of the fundamental units of physical quantities determined naturally by the values of fundamental constants of nature. We discuss a comparison between the 'Planck units', now widely used in theoretical physics and the pre-quantum 'Stoney units' in which, instead of the Planck constant, the charge of the electron is used with very similar quantitative results. We discuss some of the physical motivation for these special units, attributed much after they were introduced, and also put forth a summary of the arguments supporting various cases for making specific physical interpretations of the meanings of some of these units. The new aspects we discuss are a possible physical basis for the Stoney units, their link to the Planck units, and also the importance of Planck units for thermodynamical quantities in the context of quantum gravity., Comment: 22 pages, 1 table

The objective of a SEE mission is to support development of unification theory by carrying out sensitive gravitational tests capable of determining whether various alternative theories are compatible with nature. Gravitation is a key "missing link" in unification theory. Nearly all unification theories incorporate gravity at a fundamental level, and therefore precise measurements of gravitational forces will place important constraints on unification theories. Ground-based gravitational measurements to the accuracy required are impossible due to the many sources of noise present in the terrestrial environment. The proposed space-based Satellite Energy Exchange (SEE) mission will measure several important parameters to an accuracy between 100 and 10,000 times better than current or planned measurement capabilities. It will test for time variation of the gravitational "constant" G and for violations of the weak equivalence principle (WEP) and the inverse-square-law (ISL), and it will determine G. It is well-known that the discovery of breakdowns in WEP or ISL and the possible determination of a time-varying G would have significant consequences on virtually all aspects of unification theory., Comment: Presented at the 2004 Pescara Meeting on Tests of the Equivalence Principle

A substantial improvement in the accuracy of G-dot tests (The dot denotes the time derivative.) would make it realistic to speak in terms of a measurement of G-dot, rather than merely a smaller upper bound on |G-dot|. We show that the accuracy delta|G-dot/G| \approx 10^-14 yr^-1 may be sufficient, given the accuracy of other cosmological parameters, to observe effects predicted by higher dimensions theories and, hence, to discriminate among different models. The \.G design goal for the SEE (Satellite Energy Exchange) mission is delta(G-dot/G) \approx 10^-14 yr^-1., Comment: 17 pages, 3 figures Version 2 is revised as per editorial/referee comments