# TeVeS (Tensor-Vector-Scalar Gravity) – Definition & Detailed Explanation – Cosmology Glossary

## I. What is TeVeS (Tensor-Vector-Scalar Gravity)?

TeVeS, short for Tensor-Vector-Scalar Gravity, is a modified theory of gravity proposed by Jacob Bekenstein in 2004. It is an alternative to General Relativity, the prevailing theory of gravity put forth by Albert Einstein in 1915. TeVeS aims to address some of the shortcomings of General Relativity, particularly in explaining the phenomena observed in the universe at both large and small scales.

In TeVeS, gravity is described by three fields: a tensor field, a vector field, and a scalar field. These fields interact with each other to produce the gravitational effects we observe. The tensor field is responsible for the gravitational attraction between masses, while the vector field mediates a long-range repulsive force. The scalar field, on the other hand, controls the strength of gravity and plays a crucial role in modifying the theory to match observational data.

## II. How does TeVeS differ from General Relativity?

One of the key differences between TeVeS and General Relativity lies in the additional fields present in TeVeS. While General Relativity describes gravity as the curvature of spacetime caused by mass and energy, TeVeS introduces new fields to account for the observed discrepancies in the behavior of galaxies and galaxy clusters.

Another significant difference is in the predictions made by the two theories. General Relativity accurately describes the motion of planets in the solar system and the bending of light around massive objects. However, at larger scales, such as the rotation curves of galaxies, General Relativity falls short and requires the existence of dark matter to explain the observed velocities of stars in galaxies. TeVeS, on the other hand, aims to explain these phenomena without the need for dark matter by modifying the gravitational force law.

## III. What are the key components of TeVeS?

As mentioned earlier, TeVeS consists of three fields: a tensor field, a vector field, and a scalar field. These fields interact with each other through a set of equations that govern the behavior of gravity in TeVeS. The tensor field is responsible for the attractive gravitational force between masses, similar to the role of the metric tensor in General Relativity.

The vector field in TeVeS introduces a long-range repulsive force that helps explain the observed flat rotation curves of galaxies without the need for dark matter. This field also plays a role in mediating the gravitational interactions between masses at large distances.

The scalar field in TeVeS is perhaps the most crucial component of the theory. It modifies the strength of gravity in a way that matches the observed behavior of galaxies and galaxy clusters. By adjusting the scalar field, TeVeS can reproduce the gravitational effects attributed to dark matter in General Relativity, providing an alternative explanation for the observed phenomena.

## IV. How does TeVeS explain the phenomena observed in the universe?

TeVeS offers a new perspective on the gravitational interactions in the universe, particularly at the scale of galaxies and galaxy clusters. One of the key phenomena that TeVeS aims to explain is the flat rotation curves of galaxies. In General Relativity, the predicted velocities of stars in galaxies decrease with distance from the center, leading to the need for dark matter to explain the observed velocities. TeVeS, however, introduces a long-range repulsive force through the vector field that counteracts the attractive force of gravity, resulting in flat rotation curves without the need for dark matter.

Another phenomenon that TeVeS addresses is the gravitational lensing of light around massive objects. General Relativity predicts the bending of light rays near massive objects, such as galaxies and galaxy clusters. TeVeS modifies this prediction by incorporating the effects of the scalar field, which alters the gravitational force law and changes the way light is bent. By adjusting the scalar field, TeVeS can reproduce the observed gravitational lensing effects without the need for dark matter.

## V. What are the strengths and weaknesses of TeVeS as a theory of gravity?

One of the strengths of TeVeS is its ability to explain the observed phenomena in the universe without the need for dark matter. By introducing additional fields and modifying the gravitational force law, TeVeS can reproduce the flat rotation curves of galaxies and the gravitational lensing effects seen in General Relativity. This makes TeVeS an attractive alternative to General Relativity for explaining the behavior of gravity at large scales.

However, TeVeS also has its weaknesses. One of the main criticisms of TeVeS is its complexity compared to General Relativity. The additional fields and equations in TeVeS make it more challenging to work with and test against observational data. Additionally, TeVeS has not yet been able to fully explain all the observed phenomena in the universe, such as the dynamics of galaxy clusters and the large-scale structure of the cosmos.

## VI. How is TeVeS being tested and validated in the field of cosmology?

Despite its challenges, TeVeS is actively being tested and validated in the field of cosmology. One of the ways researchers are testing TeVeS is through simulations of galaxy formation and evolution. By inputting the equations of TeVeS into computer models of the universe, scientists can compare the predicted behavior of galaxies and galaxy clusters with observational data. This allows them to assess the accuracy of TeVeS in reproducing the large-scale structure of the cosmos.

Another method of testing TeVeS is through gravitational lensing studies. By observing the bending of light around massive objects, astronomers can test the predictions of TeVeS against the observed gravitational lensing effects. If TeVeS can accurately reproduce these effects without the need for dark matter, it would provide strong evidence in support of the theory.

In conclusion, TeVeS offers a unique perspective on gravity that aims to address some of the shortcomings of General Relativity. By introducing additional fields and modifying the gravitational force law, TeVeS can explain the observed phenomena in the universe without the need for dark matter. While TeVeS has its strengths and weaknesses, ongoing research and testing in the field of cosmology are helping to validate the theory and shed light on the nature of gravity at large scales.