Weblog
8 December 2024
J. M. Ezquiaga and M. Zumalacárregui (2018)
The usual principle of cosmology is predicated upon 4 issues: the construction of area and time, matter, darkish matter, and darkish vitality. Of those, darkish vitality is the one we presently perceive the least. Inside the usual mannequin, darkish vitality is a part of the construction of area and time as described by normal relativity. It’s uniform all through the cosmos and expressed as a parameter often called the cosmological fixed. However preliminary observations from the Darkish Power Spectroscopic Instrument (DESI) recommend the speed of comedian enlargement could range over time. If additional observations reinforce this, it might open up cosmological fashions to alternate options to normal relativity often called modified gravity.
In a latest paper on the arXiv, the authors have a look at one model of modified gravity often called Horndeski’s principle. The idea is predicated upon a generalization of normal relativity. Einstein’s authentic principle was primarily based upon the precept of equivalence, from which he derived a generalized description of spacetime via what is called a metric tensor. From this, you may derive the equations of movement for objects in a gravitation subject, simply as Newton’s legal guidelines result in equations of movement for objects underneath bodily and gravitational forces.
Basic relativity is the best mannequin with a metric tensor. Horndeski’s principle is probably the most normal mannequin with a metric tensor and permits for the presence of a uniform scalar subject. There are particular circumstances of Horndeski’s principle, such because the Brans-Dicke mannequin and the mannequin of quintessence. Each of those fashions have been used to explain darkish vitality in a extra normal means, in addition to darkish matter in some circumstances. Whereas observations of gravitational waves, galactic clustering and cosmic enlargement constrain these fashions to a point, they don’t totally rule them out. To date, our information on darkish vitality isn’t wealthy sufficient to tell apart between alternate options.
Chudaykin and Kunz
This newest work appears on the DESI leads to the context of Horndeski fashions, particularly the way it may deal with the time-evolution of cosmic enlargement advised by the DESI information. It discovered that if the time evolution is taken to be right, then a modified gravity is a greater match than the usual mannequin. The research goes on to indicate that Horndeski fashions solely work the place the time evolution of the scalar subject correlates to the proposed time evolution of darkish matter. This guidelines out some Horndeski fashions which have been used to clarify darkish matter.
General, the authors argue that the DESI observations make Horndeski’s principle a viable different to normal relativity. That’s, if the information holds up. The Darkish Power Spectroscopic Instrument is nonetheless in its early levels, and we don’t but know what the ultimate outcomes might be. However it’s clear that Einstein’s seat on the theoretical throne isn’t totally assured, and Horndeski’s principle may simply be the one to steal the crown.
