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We tested Einstein's theory of gravity on the scale of the universe - here's what we found

Researchers who have examined whether Einstein's theory of gravity works on the largest possible scale claim that there are deviations that need to be checked and corrected similar to those at small distances that can be answered using quantum theory

By Kazuya Koyama, Professor of Cosmology, University of Portsmouth and Levon Foghossian, Professor of Physics, Simon Fraser University

The cosmic background radiation in the microwave field. Photo: NASA
The cosmic background radiation in the microwave field. Photo: NASA

Every object in the universe has gravity - and it feels it too. However, the most common of all the fundamental forces is also the one that poses the greatest challenges to physicists. Albert Einstein's theory of general relativity was remarkably successful in describing the gravitational pull of stars and planets, but it doesn't seem to apply perfectly on every scale.

General relativity has undergone many years of observations and measurements, from the measurement of the deflection of starlight by the sun discovered by Eddington in 1919 to the recent discovery of gravitational waves. However, gaps in our understanding begin to appear when we try to apply it to extremely small distances, where the laws of quantum mechanics operate, or when we try to describe the entire universe.

Our new study, published in the journal Nature Astronomy, tested Einstein's theory on the largest orders of magnitude. We believe our approach may one day help solve some of the biggest mysteries in cosmology, and the results suggest that general relativity may need to be revised on this scale.

Defective model?

Quantum theory predicts that seemingly empty space is actually packed with energy. We do not notice its presence because our instruments can only measure changes in energy and not its total amount.

However, according to Einstein, the vacuum energy has an opposite attraction or repulsion force - it pushes the empty space apart. It is interesting to note that in 1998 it was discovered that the expansion of the universe is indeed accelerating (a discovery that won the 2011 Nobel Prize in Physics). However, the amount of void energy, or dark energy as it was called, needed to explain the acceleration is orders of magnitude smaller than what quantum theory predicts.

Hence the big question, known as the "old cosmological constant problem", is does the vacuum energy act on the force of gravity and change the expansion rate of the universe?

If so, then why is its gravity so much weaker than predicted? If the void does not extend at all, what causes the cosmic acceleration?

We don't know what dark energy is, but we have to assume it exists to explain the expansion of the universe. Similarly, we must also assume the presence of some form of invisible matter, known as dark matter, to explain how galaxies and clusters evolved to be the way we observe them today.

These assumptions are embedded in scientists' standard cosmological theory, called the Lambda Cold Dark Matter Model (LCDM) - which suggests that the cosmos has 70% dark energy, 25% dark matter and 5% normal matter. And this model has amazingly succeeded in fitting all the data collected by cosmologists over the past 20 years.

But the fact that most of the universe is made up of dark matter and matter, which take on strange values ​​that don't make sense, has made many physicists wonder if Einstein's theory of gravity needs modification to describe the entire universe.

A new direction change was discovered a few years ago when it became clear that different ways of measuring the rate of cosmic expansion, known as the Hubble constant, give different answers - a problem known as the Hubble voltage.

The dispute, or tension, is between two values ​​of Hubble's constant. One is the number predicted by the LCDM cosmological model, which was developed to match light left over from the Big Bang (the cosmic microwave background radiation). The second is the rate of expansion measured by observing exploding stars called supernovae in distant galaxies.

Many theoretical ideas have been proposed for ways to modify LCDM to explain grief stress. Among them are alternative theories of gravity.

Looking for answers

We can design tests to test whether the universe obeys the laws of Einstein's theory. General relativity describes gravity as a curvature or curvature of space and time, bending the paths along which light and matter travel. More importantly, it predicts that the paths of light rays and matter should be bent by gravity in the same way.

Together with a team of cosmologists, we put the basic laws of general relativity to the test. We also looked at whether changing Einstein's theory could help solve some of the open problems of cosmology, such as the Hubble stress.

To find out if general relativity is correct on a large scale, we set out, for the first time, to simultaneously investigate three aspects of it: the expansion of the universe, the effects of gravity on light, and the effects of gravity on matter.

Using a statistical method known as Bayesian inference, and using cosmic history, we reconstructed the gravity of the universe in a computer model based on these three parameters. We can estimate the parameters using the cosmic microwave background data from the Planck satellite, catalogs of supernovae as well as observations of the shapes and distribution of distant galaxies by the SDSS and DES telescopes. We then compared our reconstruction to the prediction of the LCDM model (actually Einstein's model).

We found interesting hints of possible inconsistency with Einstein's prediction, although they are of rather low statistical significance. This means that there is still a possibility that gravity works differently on a large scale, and that general relativity may need to be modified.

Our research also found that it is very difficult to solve the Hubble tension problem just by changing the theory of gravity. The complete solution will likely require a new component of the cosmological model that existed before the time when protons and electrons first combined to form hydrogen immediately after the Big Bang, such as a special form of dark matter, an early form of dark energy, or primordial magnetic fields. Or, perhaps, there is an as-yet-unknown systematic error in the data.

However, our research has shown that the validity of general relativity can be tested over cosmological distances using observational data. While we haven't solved the Hubble problem yet, we will have a lot more data from new probes in a few years.

This means that we can use these statistical methods to continue to modify general relativity, to explore the limits of the changes, to pave the way to solving some of the open challenges in cosmology.

For an article in The Conversation

More of the topic in Hayadan:

7 תגובות

  1. Claim: Gravity does not slow down time
    I recently read online about gravity and how it distorts space and time (see space-time).
    Scientists say that time progresses more slowly the closer you get to Earth and found this to be true, for example, in measuring time by GPS satellites compared to measuring time on Earth.
    I want to make a different argument. Gravity does not slow down time but simply makes it difficult for any matter to move or change energy. Like it will be much easier for us to run and jump for example on the moon. Our clocks are all made up of matter or measure a change in energy and therefore we are wrong to think that the progress of time itself is changing. But the problem is with the tools we have to measure time. Our most accurate clocks, such as an atomic clock that measures the frequency of movement of electrons, are limited to measuring the movement of matter or a change in energy. I claim that electrons and all types of matter slow down due to gravity. For example, gravity can bend even a ray of light in its path (see gravitational lens).

    And going a little further, I want to suggest that time is not a real thing. If there is no change of energy or movement of matter at all then there is no progress of time.

    I will be happy to respond

    Eli Isaac - academic private tutor for computer science and mathematics and senior software engineer

  2. This means that there are mass concentrations in the universe with a gravitational effect.

    For example, our galaxy and others in the local cluster are moving towards a point a few hundred million light years away, called 'The Great Attractor'. Nothing can be seen at this point to suggest that there is anything there.
    If it were a black hole, it would have to have a mass of a trillion suns...

    So there are attraction factors in the universe that are not yet known to us.

  3. Everything is done in reverse. Nothingness is existence and existence is nothingness. It is the force of compression and not the force of gravity

  4. very interesting. Thanks for the article.
    In my understanding, the theory of general relativity is incredibly accurate and has stood up to this day in every experiment in which it has been tested (with the exception of the controversy with quantum mechanics).

  5. I read a saying according to which: the way to stop believing in God has not yet been found.
    My answer: You will never find the reason: Einstein himself did not find it, every scientist tries and fails, as much as the person, of course, with the help of his mind tries to grasp with understanding enormous and unimaginable phenomena, he will think he succeeded, others not at all, the word think is not yet a proof necessary to establish knowledge, to stop believing It won't be, the majority of humanity fails in their maximum understanding to perceive, to think, to appreciate the enormous and unimaginable phenomena - from a distance the size of the universe is a massive black hole - huge.
    For example, I can't grasp the fact that 2 neutron stars come to orbit each other in less than an hour, amazing, right? Or what is the gravity of a black hole on a massive one - in human language its weight is trillions of tons - it is not enough and there is no number for a human mind to grasp it, suggest a ton times a trillion times a trillion a ton is a gram and multiply the gram by a trillion times a trillion to the power of a trillion maybe someone will understand.
    It is too late for me to continue due to health reasons and fatigue of the whole body including the brain.
    Good night.

  6. The model is incorrect, the range in which the light propagates is not empty, there is a three-dimensional matrix that is not taken into account

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