The Universe has gravity as well. The biggest challenges to physicists are presented by this most common fundamental force.
Albert Einstein's theory of general relativity has been very successful in describing the gravity of stars and planets, but it doesn't apply to all scales.
The recent detection of ripples in the fabric of space and time is the culmination of many years of observational tests.
There are gaps in our understanding when we try to apply it to small distances or when we try to describe the whole universe.
Einstein's theory has been tested on the largest of scales.
The results suggest that the theory of general relativity may need to be changed on this scale, as we believe our approach may one day help resolve some of the biggest mysteries in the universe.
The vacuum is filled with energy. Our devices can only measure changes in energy, so we don't notice it.
The empty space is pushed apart by the vacuum energy. It was found in 1998 that the expansion of the Universe is speeding up.
The amount of dark energy needed to explain the acceleration is much smaller than what quantum theory predicts.
The big question is whether the vacuum energy exerts a gravitational force and changes the expansion of the universe.
Why is its gravity so weak? Why is the vacuum not moving?
We don't know what dark energy is, but we must assume it exists in order to explain the Universe's expansion.
We need to assume that there is a type of invisible matter presence called dark matter that explains how clusters evolved to be the way we see them today.
Scientists believe there is 70 percent dark energy, 25 percent dark matter, and 5 percent ordinary matter in the universe. The model has been able to fit all the data collected over the past two decades.
Physicists are wondering if Einstein's theory of gravity needs to be changed because most of the Universe is made up of dark forces and substances.
When it became apparent that different ways of measuring the rate of expansion were giving different answers, there was a new twist.
Two values of the Hubble constant are at odds.
The number predicted by the LCDM model is related to the light left over from the Big Bang.
The expansion rate is measured by observing the stars that explode.
There are many theories about how to explain the Hubble Tension. Alternative gravity theories are included in the list.
We can design tests to see if the universe obeys the rules.
General relativity describes gravity as bending the pathways along which light and matter travel. Light rays and matter should be bent by gravity.
The basic laws of general relativity were tested by a team of scientists. Modification of Einstein's theory could help resolve some of the open problems of the universe.
We are going to investigate three aspects of general relativity at the same time in order to find out if it's correct. The expansion of the Universe, the effects of gravity on light, and the effects of gravity on matter were some of the things that were mentioned.
The computer model we used to reconstruct the gravity of the Universe was based on three parameters.
The parameters can be estimated using the background data from the Planck satellite, as well as observations of the shapes and distribution of distant galaxies.
The reconstruction was compared to the prediction of the model.
There were some intriguing hints of a possible mismatch with Einstein's prediction.
It's possible that gravity works differently on large scales, and that general relativity may need to be changed.
The Hubble tension problem can only be solved by changing the theory of gravity.
A special form of dark matter, an early type of dark energy, or primordial magnetic fields are some of the things that could be used to make the full solution.
Maybe there is a systematic error in the data.
The validity of general relativity can be tested using observational data. We will have a lot more data from new probes in a few years.
We will be able to use these statistical methods to continue tweaking general relativity and explore the limits of modifications in order to resolve some of the open challenges.
Professor of physics at Simon Fraser University and Professor of astronomy at the University of Pompey.
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