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An excerpt from the book "The Order of Time," by Carlo Rovelli is presented which focuses on the aspects of time, citing the theory on the association between time and space according to physicist Albert Einstein, the speed and time, and duration of time to travel the discovered planet Proxima b.

Nothing truly exists – except in relation to other things. If we can get our heads around that one idea, we can begin to grasp the quantum realm, says Carlo Rovelli

Lawrence et al. have presented an argument purporting to show that “relative facts do not exist” and, consequently, “Relational Quantum Mechanics is incompatible with quantum mechanics”. The argument is based on a GHZ-like contradiction between constraints satisfied by measurement outcomes in an extended Wigner’s friend scenario. Here we present a strengthened version of the argument, and show why, contrary to the claim by Lawrence et al., these arguments do not contradict the consistency of a theory of relative facts. Rather, considering this argument helps clarify how one should notthink about a theory of relative facts, like RQM.

If there is a ‘platonic world’ ℳ $\mathcal {M}$of mathematical facts, what does ℳ $\mathcal {M}$contain precisely? I observe that if ℳ $\mathcal {M}$is too large, it is uninteresting, because the value is in the selection, not in the totality; if it is smaller and interesting, it is not independent of us. Both alternatives challenge mathematical platonism. I suggest that the universality of ourmathematics may be a prejudice and illustrate contingent aspects of classical geometry, arithmetic and linear algebra, making the case that what we call “mathematics” is always contingent.

ABSTRACT:I show that Aristotelian physics is a correct and nonintuitive approximation of Newtonian physics in the suitable domain (motion in fluids) in the same technical sense in which Newton's theory is an approximation of Einstein's theory. Aristotelian physics lasted long not because it became dogma, but because it is a very good, empirically grounded theory. This observation suggests some general considerations on intertheoretical relationships.

The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime, is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i) The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii) A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler’s “spacetime foam” intuition. (iii) Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv) A derivation of the Bekenstein-Hawking black-hole entropy. (v) Low-energy calculations, yielding n-point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.

In this extract from his latest book, Carlo Rovellisuggests that black holes sucking in all matter that strays too close may be only half the story

We compute some components of the graviton propagator in loop quantum gravity, using the spinfoam formalism, up to some second-order terms in the expansion parameter.

We construct a macroscopic semiclassical state for a quantum tetrahedron. The expectation values of the geometrical operators representing the volume, areas and dihedral angles are peaked around assigned classical values, with vanishing relative uncertainties.

We study how physical information can be extracted from a background-independent quantum system. We use an extremely simple 'minimalist' system that models a finite region of 3D Euclidean quantum spacetime with a single equilateral tetrahedron. We show that the physical information can be expressed as a boundary amplitude. We illustrate how the notions of 'evolution' in a boundary proper time and 'vacuum' can be extracted from the background-independent dynamics.

In four dimensions (4D), general relativity (GR) can be formulated as a constrained BF theory; we show that the same is true in 2D. We describe a spinfoam quantization of this constrained BF formulation of 2D Riemannian GR, obtained using the Barrett-Crane technique of imposing the constraint as a restriction on the representations summed over. We obtain the expected partition function, thus providing support for the viability of the technique. The result requires the nontrivial topology of the bundle where the gravitational connection is defined to be taken into account. For this purpose, we study the definition of a principal bundle over a simplicial base space. The model also sheds light on several other features of spinfoam quantum gravity: the reality of the partition function, the geometrical interpretation of the Newton constant and the issue of possible finiteness of the partition function of quantum GR.

The problem of finding the quantum theory of the gravitational field, and thus understanding what is quantum spacetime, is still open. One of the most active of the current approaches is loop quantum gravity. Loop quantum gravity is a mathematically well-defined, non-perturbative and background independent quantization of general relativity, with its conventional matter couplings. Research in loop quantum gravity today forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained are: (i)The computation of the physical spectra of geometrical quantities such as area and volume, which yields quantitative predictions on Planck-scale physics.(ii)A derivation of the Bekenstein-Hawking black hole entropy formula.(iii)An intriguing physical picture of the microstructure of quantum physical space, characterized by a polymer-like Planck scale discreteness. This discreteness emerges naturally from the quantum theory and provides a mathematically well-defined realization of Wheeler’s intuition of a spacetime “foam”. Long standing open problems within the approach (lack of a scalar product, over-completeness of the loop basis, implementation of reality conditions) have been fully solved. The weak part of the approach is the treatment of the dynamics: at present there exist several proposals, which are intensely debated. Here, I provide a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.

Abstract: I suggest that the common unease with taking quantum mechanics as a fundamental description of nature (the “measurement problem”) could derive from the use of an incorrect notion, as the unease with the Lorentz transformations before Einstein derived from the notion of observer-independent time. I suggest that this incorrect notion that generates the unease with quantum mechanics is the notion of “observer-independent state” of a system, or “observer-independent values of physical quantities.” I reformulate the problem of the “interpretation of quantum mechanics” as the problem of deriving the formalism from a set of simple physical postulates. I consider a reformulation of quantum mechanics in terms of information theory. All systems are assumed to be equivalent, there is no observer-observed distinction, and the theory describes only the information that systems have about each other; nevertheless, the theory is complete.

In building intelligent network agents, computer scientists may employ a variety of different design strategies, and their design decisions can have a significant effect on the ultimate nature of network interactions. Some agent designs are “co-operative”, and populations of agents based on them would be able to interact smoothly, effectively utilizing network resources. In contrast, other agent designs can lead to ineffective and wasteful competition for network resources, resulting in massive bottlenecks and unacceptable access delays. We focus here on a particular design question, themultiple-access problem: if an agent seeking a piece of information knows of several sites that have, or might have, that information, how many queries should it issue, and when? We provide a formal analysis that demonstrates the viability of cooperative responses to this question under certain assumptions. We then discuss the limitations of this analysis and present the results of experiments done using a genetic-algorithms approach in which simulated network agents “evolve” co-operative strategies, under less restrictive assumptions than those made in the formal analysis.

Weaves are eigenstates of geometrical operators in nonperturbative quantum gravity, which approximate flat space (or other smooth geometries) at large scales. We describe two such states, which diagonalize the area as well as the volume operators. The existence of such states shows that some earlier worries about the difficulty of realizing kinematical states with non-vanishing volume can be overcome. We also show that the Q operator used in earlier work for extracting geometrical information from quantum states does not capture more information than the area and volume operators.

Without addressing the measurement problem (i. e., what causes the wave function to “collapse,” or to ”branch,” or a history to become realized, or a property to actualize), I discuss the problem of the timing of the quantum measurement: Assuming that in an appropriate sense a measurement happens, when precisely does it happen? This question can be posed within most interpretations of quantum mechanics. By introducing the operator M, which measures whether or not the quantum measurement has happened, I suggest that, contrary to what is often claimed, quantum mechanics does provide a precise answer to this question, although a somewhat surprising one.

We study quantum gravitational effects on black hole radiation, using loop quantum gravity. Bekenstein and Mukhanov have recently considered the modifications caused by quantum gravity on Hawking's thermal black-hole radiation. Using a simple ansatz for the eigenstates of the area, they have obtained the intriguing result that the quantum properties of geometry affect the radiation considerably, yielding a discrete spectrum, definitely non-thermal. Here, we replace the simple ansatz employed by Bekenstein and Mukhanov with the actual eigenstates of the area computed using loop quantum gravity. We derive the emission spectra, using a classic result in number theory by Hardy and Ramanujan. Disappointingly, we do not recover the Bekenstein-Mukhanov discrete spectrum, but — effectively — a continuum spectrum, consistent with Hawking's result. The Bekenstein-Mukhanov argument for the discreteness of the specrum is therefore likely to be an artifact of the ansatz, rather than a robust result (at least in its present kinematical version). The result is an example of concrete (although somewhat disappointing) application of nonperturbative quantum gravity.

Scientists can provide governments with essential knowledge to take informed decisions, but cannot decide on their behalf, according to Carlo Rovelli.

The author discusses how if he had chance to be ruler, he would abolish schools, armies and documents such as passports as everyone should respect one another as human and mentions how one's society builds on basic primate instinct compete for higher position of hierarchies.