The recent “Hubble tension” in cosmology is characterized by contradictory expansion rate measurements, raising questions about standard cosmological models. A new theory postulates that huge, low-density cavities could explain these discrepancies, casting doubt on traditional views about the distribution of matter in the universe and raising the possibility of a revision of Einstein’s theory of gravity. suggests.
Cosmologists have proposed a giant void in the universe as a solution to the “Hubble tension”, questioning traditional models and suggesting modifications to Einstein’s theory of gravity.
One of the biggest mysteries in cosmology is the rate of expansion of the universe. This can be predicted using the Standard Model of Cosmology (aka. Lambda cold dark matter (ΛCDM). This model is based on detailed observations of the light left over from Earth. big bang – The so-called cosmic microwave background radiation (CMB).
As the universe expands, galaxies move away from each other. The further away they are from us, the faster they move. The relationship between a galaxy’s speed and its distance is determined by the “Hubble constant,” which is about 43 miles (70 km) per megaparsec (a unit of length in astronomy) per second.this means galaxy Approximately 50,000 miles per hour increase It moves away from us every million light years.
But unfortunately, for the standard model, this value has recently been debated, and scientists have “Hubble tension” Measuring the expansion rate using nearby galaxies or supernovae (exploding stars) yields a 10% larger expansion rate than predicted based on the CMB.
![huge void](https://scitechdaily.com/images/Giant-Void-777x731.jpg)
The artist’s concept of a huge cavity and surrounding filaments and walls.Credit: Pablo Carlos Budassi
among us new paper, we offer one possible explanation. That means we live in a giant void of space (a region with below average density). This indicates that the local measurements can be inflated through the outflow of material from the voids. Outflow occurs when dense areas surrounding the void pull it apart. The outflow will exert a greater gravitational force than the less dense material within the void.
In this scenario, we would need to be near the center of a cavity with a radius of about 1 billion light-years and a density about 20% lower than the average for the entire universe, but not completely empty.
Such large and deep voids are controversial because they are unexpected in standard models. The CMB provides a snapshot of the structure of the early Universe, suggesting that today’s matter must be fairly evenly spread out. However, if we directly count the number of galaxies in different regions, certainly suggests We are in a local vacuum.
Tweak the laws of gravity
We wanted to further test this idea by reconciling many different cosmological observations, assuming that we live inside a large void that has grown from small initial density fluctuations. Ta.
To do this, our model ΛCDM was not included, but modified Newtonian mechanics (Mondo).
MOND was originally proposed to explain anomalies in the rotational speeds of galaxies, which led to suggestions of the existence of an invisible substance called “dark matter.” Instead, MOND suggests that the anomaly can be explained by a breakdown of Newton’s law of gravity when gravity is very weak, as is the case in the outer regions of galaxies.
The overall expansion history of the universe in MOND is similar to the standard model, but structures (such as galaxy clusters) grow faster in MOND. Our model captures what the local universe looks like in the MOND universe. And this shows that today’s local measurements of expansion rates can vary depending on location.
![Heat map of cosmic microwave background radiation (CMB) temperature fluctuations](https://scitechdaily.com/images/Heat-Map-Temperature-Fluctuations-Cosmic-Microwave-Background-CMB-777x389.jpg)
CMB temperature fluctuation: Detailed all-sky images of the early universe created from nine years of WMAP data reveal temperature fluctuations (shown as different colors) over 13.77 billion years ago.Credit: NASA / WMAP Science Team
Recent observations of galaxies have enabled important new tests of the model based on predicted velocities at different locations. This can be done by measuring something called bulk flow, which is the average velocity of matter within a given sphere, with or without density. This depends on the radius of the sphere. recent observations showing it continues Up to 1 billion light years.
Interestingly, the bulk flow in galaxies of this size is four times faster than expected by the standard model. It also appears to increase with the size of the region considered, contrary to what the standard model predicts. The chance of this matching the standard model is less than 1 in a million.
This allowed us to see how the bulk flow is predicted in the study.I found that it gave pretty good results match For observation. That requires us to be fairly close to the center of the void, and that the center of the void is the most empty.
Has the case been resolved?
Our results come at a time when general solutions to the Hubble strain are running into difficulties. Some think we just need more precise measurements. Some believe that the problem can be solved by assuming a high expansion rate measured in the field. is actually the correct one. But that requires making slight adjustments to the expansion history of the early universe so that the CMB looks correct.
Unfortunately, an influential review pointed out seven problems. problem With this approach. If the universe expanded 10% faster over most of its history, the universe would become about 10% younger. This contradicts the history of the universe. age Among the oldest stars.
The presence of deeply extended local voids in the galaxy count and the observed fast bulk flow suggest that structures grow faster than expected in ΛCDM on scales of tens of millions to hundreds of millions of light years. strongly suggested.
![Galaxy cluster “El Gordo” and mass map](https://scitechdaily.com/images/Galaxy-Cluster-El-Gordo-With-Mass-Map-777x471.jpg)
This is a Hubble Space Telescope image of the most massive galaxy cluster ever known to exist, when the universe was just half its current age of 13.8 billion years. This cluster contains hundreds of galaxies that swarm together under collective gravity. New Hubble measurements refine the cluster’s total mass, which is estimated to be equal to 30 billion Sun-like stars (about 3,000 times the mass of the Milky Way), but much of the mass remains hidden. . as dark matter. The location of dark matter is mapped with a blue overlay. Dark matter doesn’t emit radiation, so Hubble astronomers instead measure precisely how its gravity distorts images of distant background galaxies, like a funhouse mirror. This allowed us to derive cluster mass estimates. In 2012, X-ray observations and kinematic studies first suggested that this star cluster was unusually large for the era in which it existed in the early universe, giving it the name El Gordo (Spanish for “fat one”). It was given the nickname “meaning”. Hubble data confirmed that this cluster is undergoing a violent merger between her two smaller clusters. Credit: NASA, ESA, and J. Jee (University of California, Davis)
Interestingly, a large galaxy cluster, El Gordo (see image above), has been found to have formed. too fast The most important model in the history of the universe, its mass and collision velocity are too high to be compatible with the standard model. This is further evidence that structure formation is too slow in this model.
Since gravity is the dominant force on such large scales, perhaps Einstein’s theory of gravity, general relativity, needs to be extended, but only on scale. greater than 1 million light years.
But there’s no good way to measure how gravity behaves on much larger scales. No object exists that is bound by such a huge force of gravity. We can assume that general relativity is still valid and compare it with observations, but it is precisely this approach that exposes us to the very severe strain that our best cosmological models currently face. is connected to.
Einstein is thought to have said that you cannot solve problems with the same thinking that created them in the first place. There’s a good chance we’ll see the first reliable evidence in over a century that our theory of gravity needs to change, even if the changes needed aren’t radical.
Written by Indranil Banik, Postdoctoral Researcher in Astrophysics, University of St Andrews.
Adapted from an article originally published in conversation.