It is known that the universe is expanding at the present day, while its expansion rate is accelerating. As the universe consists of both dark energy and matter, they may have an influence on its expansion rate. There is a possible assumption that matter alone is enough for the universe to expand. However, it is the presence of dark energy that makes the expansion possible.
Dark energy is an energy component with negative pressure. It violates the strong energy condition and accelerates the universe (Aparicio Resco et al., 2020). It produces a gravitational repulsion because gravitational forces are influenced by the pressure they exert, and the dark energy’s pressure is negative (Popolo, 2021). In the past, the universe was not accelerated because dark energy was less, and it has increased since then.
Thus, it is not matter but the dark energy that makes the accelerated expansion possible. The reason for this is that its negative pressure produces gravitational repulsion, violating the strong energy condition and sufficiently influencing gravitational forces. Its increase has caused the accelerated expansion of the universe, which did not take place previously. Without it, therefore, the accelerated expansion cannot take place based on matter alone.
References
Aparicio Resco, M. A, Maroto, A. L., Alcaniz, J. S., Abramo, L. R., Hernández-Monteagudo, C., Benítez, N., Carneiro, S., Cenarro, A. J., Cristóbal-Hornillos, D., Dupke, R. A., Ederoclite, A., López-Sanjuan, C., Marín-Franch, A., Moles, M., Oliveira, C. M., Sodré Jr, L., Taylor, K., Varela, J., & Vázquez Ramió, H. (2020). J-PAS: forecasts on dark energy and modified gravity theories. Monthly Notices of the Royal Astronomical Society, 493(3), 3616–3631. Web.
Popolo, A. D. (2021). Invisible universe, the: Dark matter, dark energy, and the origin and end of the universe. WSPC.