According to our current understanding of physics, the curvature of spacetime is intimately connected to the presence of mass and energy. The more mass or energy an object possesses, the stronger its gravitational field, and thus the greater the curvature of spacetime around it.
In Einstein's theory of general relativity, which describes gravity as the curvature of spacetime, mass and energy act as sources of gravity. This means that without mass or energy, there would be no gravitational effects, and therefore no bending or curvature of spacetime.
However, it is important to note that there are other phenomena that can affect the curvature of spacetime indirectly, even in the absence of mass. For example, in the context of general relativity, the presence of momentum and pressure, which are related to energy, can also contribute to the curvature of spacetime. This is often referred to as the stress-energy tensor, which encompasses mass, energy, momentum, and pressure.
Additionally, in certain theoretical scenarios, such as in the context of quantum field theory, it is suggested that virtual particles and quantum fluctuations can temporarily arise from the vacuum and have an impact on the curvature of spacetime. These fluctuations involve the exchange of energy, and therefore can contribute to the bending of spacetime.
In summary, while mass and energy are the primary sources of spacetime curvature, other factors such as momentum, pressure, and quantum effects can also influence the curvature of spacetime even in the absence of mass alone.