Everything in the universe has gravity—and feels it, too. However, it is the most common of all the fundamental forces, presenting the greatest challenges to physicists.
Albert Einstein’s general theory of relativity has been very successful in describing the gravitational forces of stars and planets, but it does not fit well on all scales.
General relativity went through years of observational testing, the Eddington Scale, the sun’s deviation from starlight in 1919, the last detection of gravitational waves.
However, when we try to apply it at much smaller distances, gaps in our understanding begin to appear when the laws of quantum mechanics come into play, or when we try to describe the entire universe.
Our new study, published in natural astronomyNow Einstein’s theory has been tested extensively.
We believe our approach will one day help solve some of the biggest mysteries in cosmology, and the results suggest that general relativity must be adjusted on this scale.
wrong model?
Quantum theory predicts that empty space, emptiness, is full of energy. We don’t notice their presence because our devices can only measure changes in energy rather than their total amount.
However, according to Einstein, vacuum energy has a repulsive gravitational force – it pushes empty space. Interestingly, in 1998 it was discovered that the expansion of the universe is indeed accelerating (the result given the 2011 Nobel Prize in Physics)
However, the amount of vacuum energy, or dark energy, is necessary to explain that the acceleration is several times smaller than what quantum theory predicts.
So the big question, the so-called “old cosmological constant problem”, is whether vacuum energy is really what’s moving gravity — it’s pushing gravity and changing the expansion of the universe.
If yes, why is its attraction so much weaker than expected? If a vacuum has no gravity, what causes the cosmic acceleration?
We don’t know what dark energy is, but we must assume that it exists to explain the expansion of the universe.
Likewise, we must assume that there is some kind of invisible physical presence of dark matter, to explain how galaxies and clusters evolved into what we observe today.
These assumptions are built into scientists’ standard cosmological theory, called the Lambda Gold Dark Matter Model (LCDM) – which says the universe is made up of 70 percent dark energy, 25 percent dark matter, and 5 percent ordinary matter. The model has been remarkably successful in fitting all the data that cosmologists have collected over the past 20 years.
But the vast majority of the universe is made up of dark forces and matter, which take on strange, meaningless values, which has led many physicists to wonder if they should adapt Einstein’s theory of gravity to describe the entire universe.
A few years ago, a new development appeared, the so-called various methods for measuring the rate of cosmic expansion. Hubble’s constant Give different answers – known as the Hubble tension problem.
There is disagreement or tension between two values of the Hubble constant.
The first is the number predicted by the LCDM cosmological model, according to which the residual light from the Big Bang (the cosmic microwave background radiation) is generated.
Another is the expansion rate, which is measured by observing exploding stars called supernovae in distant galaxies.
Several theoretical ideas for LCDM modulation methods have been proposed to explain the Hubble tension. Among them are alternative theories of gravity.
Searching for answers
We can design experiments to verify that the universe obeys the laws of Einstein’s theory.
General relativity describes gravity as the curvature or distortion of space and time, bending the paths traveled by light and matter. It essentially predicts that the paths of light and matter rays should be bent the same way by gravity.
Together with a team of cosmologists, we put the fundamental laws of general relativity to the test. We also investigated whether modifying Einstein’s theory could help solve some open problems in cosmology, such as the Hubble tension.
To find out if general relativity is true on a large scale, we set out for the first time to examine three aspects of it simultaneously. These are the expansion of the universe, the effects of gravity on light, and the effects of gravity on matter.
Using a statistical method called Bayesian inference, we reconstructed the gravitational force of the universe through cosmic history in a computer model based on these three parameters.
Parameters can be estimated using cosmic microwave background data from the Planck satellite, supernova catalogs, and observations of the shapes and distribution of distant galaxies. SDSS and DES telescopes.
We compare the reconstruction with the prediction of the LCDM model (mainly Einstein model).
We found interesting hints about the inconsistency with Einstein’s predictions, although the statistical significance is low.
However, there is a possibility that gravity on large scales will work differently, and general relativity may need to be adjusted.
Our study also found that it is very difficult to solve the Hubble tension problem by modifying the gravitational theory alone.
A complete solution would require a new component of the cosmological model, which would be before the time protons and electrons first combine to form hydrogen. The Big Bang is a special form of dark matter, such as the first type of dark energy or primordial magnetic fields.
Or perhaps there is an as yet unknown systematic error in the data.
Our study demonstrated that the validity of general relativity can be tested at cosmic distances using observational data. Although we haven’t solved the Hubble problem yet, we’ll have a lot of data from the new probes in a few years.
This means we can use these statistical methods to continue to tweak general relativity, explore the limits of mods, and pave the way for solving some of the most glaring challenges in cosmology.
Kazuya Koyama is Professor of Astronomy at the University of Portsmouth and Eleven Bogosian Professor of Physics at Simon Fraser University
This Conversation article has been republished under a Creative Commons license. Continue reading the original article.