The void in the universe: the key to solving the Hubble problem and an alternative to dark matter

The universe is expanding. This fact was discovered by American astronomer Edwin Hubble in 1929. He discovered that galaxies are moving away from each other at a constant speed that is proportional to their distance. This speed is called the Hubble constant, and it is one of the important parameters in cosmology.

However, in recent years, the Hubble constant has become the subject of intense debate among scientists. Different methods for measuring this quantity produce different results that are inconsistent with each other and with theoretical expectations. This leads to one of the biggest mysteries in modern cosmology: the so-called Hubble tension. A possible explanation for this discrepancy has been proposed by a group of British and Israeli scientists. They argue that we live in a vast void in the universe, a region where the density of matter is below average. This can distort local measurements of the universe’s expansion rate and cause discrepancies with global predictions.

The Standard Model of Cosmology To understand what Hubble’s problem is, we first need to understand the basics of the Standard Model of cosmology. This model, also known as the Lambda Cold Dark Matter (ΛCDM) model, describes the evolution and structure of the Universe based on Einstein’s theory of general relativity and a number of assumptions and parameters. One of these parameters is the Hubble constant, which characterizes the current expansion rate of the universe. By definition, it is equal to the speed at which a galaxy is moving away from us divided by its distance.

The Hubble constant is measured in kilometers per second, or megaparsecs (an astronomical unit of length equivalent to about 3.26 million light-years). According to the standard model, it is about 70 km/s/Mpc. This value can be predicted using another important source of information about the Universe: the Cosmic Microwave Background Radiation (CMB). This radiation left over from the Big Bang fills the entire universe, carving out traces of conditions from the earliest times in the universe’s history. By examining the CMI, you can reconstruct the standard model parameters and check their consistency with observations.

Hubble Voltage However, measuring the Hubble constant using other methods based on closer objects such as galaxies or supernovae gives different values ​​- about 74 km/s/Mpc. This is 10% more than the standard CMI-based model predicts. This contradiction is called the Hubble tension, and it challenges our understanding of the universe.

There are many possible explanations for this discrepancy, none of which are satisfactory. Some scientists believe that this is just a statistical error that will disappear as measurements become more accurate. Some believe this indicates that adjustments need to be made to the Standard Model, such as adding new types of matter or energy or changing the laws of gravity. The Void of the Universe One of the most radical and original proposals is the idea that we live in a vast void of space. A void is a region where the density of matter is below average, resulting from uneven distribution of matter in the universe.

The void occupies most of the volume of the universe and is surrounded by dense regions of galaxies and galaxy clusters. Suppose we are at the center of such a cavity. The radius of its cavity is about 1 billion light years, and its density is 20% lower than average. We then observe that the galaxies around us are moving away faster than expected. This is because cavities are susceptible to material outflow. The dense regions attract material from the cavity and tear it apart. This effect increases with distance as the density of the cavity decreases towards its edges.

Alternative theories of gravity But for this idea to work, we need to make other assumptions. We assume that the standard model of cosmology is not valid, and instead we must use an alternative theory of gravity called Modified Newtonian Mechanics (MOND). MOND has been proposed as an alternative explanation for anomalies in galactic rotational speeds, apart from assumptions about the existence of invisible matter called “dark matter.” Instead, MOND argues 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 scientists who proposed this model conducted a series of tests and compared it with a variety of cosmological data, including CMR, galaxy distribution, and galactic currents. They found that the model agreed fairly well with observations, assuming we are at the center of a deep, vast cavity.