To account for the representation of gravity in quantum mechanics\u2014an atomic and subatomic scale\u2014the field equations of general relativity need to be modified by correction factors. The first and key numerical amendment is a parameter called alpha (\u03b1), the exact value of which has not yet been determined. One of the purposes of alpha is to influence the interaction between gravitons (hypothetical quantum particles with no mass), which theoretically carry gravitational force and transmit it to other particles.<\/p>\n
An article by three theoretical physicists has now calculated the minimum value alpha would have to be for the theory of relativity proposed by Albert Einstein (1879\u20131955) to be able to describe gravitational interactions in the microscopic universe of particle physics. According to the paper, published in the scientific journal Physical Review Letters <\/em>(PRL<\/em>) in August 2021, alpha would have to be equal to or greater than 0.14. The result reached by the researchers was almost equal to the lowest known value of alpha, which was identified by defenders of string theory in the 1990s: 0.1389.<\/p>\n Obtaining a numerical expression for this correction factor is an essential step towards the formulation of quantum gravity\u2014like an embryo of the theory of everything, capable of unifying the ideas of general relativity and quantum mechanics. Until now, the only mathematical model to successfully attempt to calculate a minimum value for alpha was string theory.<\/p>\n According to the theory, instead of being point objects, the elementary particles of matter are one-dimensional microscopic filaments (strings) that vibrate across 10 dimensions of space-time. \u201cWe were surprised with the result of our work. It may or may not have been a coincidence,\u201d says Portuguese scientist Pedro Vieira, one of the authors of the article, whose research is partially funded by FAPESP’s S\u00e3o Paulo Excellence Chair (SPEC) program. \u201cIt\u2019s still too soon to say that string theory is right or that it\u2019s the only possible way of uniting general relativity and quantum mechanics. In addition to alpha, there are other correction factors that need to be calculated, such as beta and gamma.\u201d<\/p>\n Vieira divides his working time between teaching and research at the Perimeter Institute in Canada and at the International Center for Theoretical Physics (ICTP) of the South American Institute for Fundamental Research (SAIFR), which operates from the Institute for Theoretical Physics (IFT) at S\u00e3o Paulo State University (UNESP). Andrea Guerrieri, an Italian physicist from Tel Aviv University, Israel, and Jo\u00e3o Penedones, a Portuguese physicist from the Swiss Federal Institute of Technology Lausanne (EPFL), Switzerland, also contributed to the PRL<\/em> article.<\/p>\n Newly calculated correction value was almost equal to the value proposed by string theory<\/p><\/blockquote>\n The three scientists used a new approach to calculate the minimum value of the primary correction factor for relativity equations, making use of a mathematical method called the S-matrix bootstrap, <\/em>which they previously used to study the properties of pions (a class of very light subatomic particles), described in another article they published in 2021. \u201cThe bootstrap technique began being used in the 1960s, when it became popular in quantum physics, but later lost ground to other approaches,\u201d explains Guerrieri, who did a three-year postdoctorate at ICTP, SAIFR, between 2017 and 2020.<\/p>\n The method is based on general principles or postulates\u2014such as causality, Lorentz invariance (the laws of physics are the same regardless of the location of the observer), and the fact that a probability cannot be greater than 1\u2014to calculate certain properties arising from interactions between subatomic particles in the quantum world. In this instance, it was used to predict the lowest possible value of the alpha correction factor. Because the S-matrix bootstrap<\/em> method demands such a high computational capacity to perform a series of operations, Vieira, Guerrieri, and Penedones had to adopt a simplified model of reality in their research, based on a dominant version of string theory.<\/p>\n In the world idealized by this theory, there are 10 dimensions of time and space (six more than currently known) and the manifestation of a property called supersymmetry. According to this property, every particle in the Standard Model of Particle Physics\u2014the dominant theory that has explained the interactions between known forces other than gravity and the constituents of matter for the last half a century\u2014must be accompanied by another particle, called a superpartner. \u201cIn future studies, we will try to calculate alpha in environments with fewer dimensions,\u201d says Vieira.<\/p>\n Not everyone has interpreted the newly calculated minimum possible value for the alpha correction factor as a new impetus for string theory, which for now, lacks experimental evidence. \u201cAll the observational data indicate that the Universe has four dimensions, with no supersymmetry,\u201d says Andr\u00e9 Landulfo, a physicist from the Center for Natural and Human Sciences (CCNH) at the Federal University of ABC (UFABC) who was not involved in the study. \u201cTo me, the scope of this study doesn\u2019t seem broad enough to be used in theories of quantum gravity based on physical reality. It is thus difficult to use the results as support for string theory as a viable alternative, let alone the only viable alternative, in formulating a theory of quantum gravity.\u201d<\/p>\n Project<\/strong>
\nApplications of quantum field theory (n\u00ba 19\/24277-8<\/a>); Grant Mechanism <\/strong>Regular Research Grant; S\u00e3o Paulo Excellence Chair Program (SPEC); Principal Investigator<\/strong> Pedro Vieira (UNESP); Investment<\/strong> R$888,746.51.<\/p>\n