The future of the universe is most likely flat.

This conclusion is supported by precise measurements of the cosmic microwave background radiation, which show that the universe has zero curvature or very close to it. A flat universe implies that its density is equal to the critical density, just enough to prevent collapse but not enough to curve space positively, as in a closed universe. In a flat universe, the expansion continues forever but gradually slows over time.

Additionally, the influence of dark energy suggests that expansion will keep accelerating, further supporting a flat model where the universe expands eternally but without a final collapse. If the universe is indeed flat, it will continue to expand indefinitely, with galaxies moving farther apart over time. This model aligns with both observed cosmic geometry and our current understanding of dark energy’s role in the cosmos.

However, to make a reliable prediction about the shape and future of the Universe, cosmologists need to know its density and to do this, they need to know what the Universe is made of.