最新研究显示，弦理论首次构建出一个包含暗能量的宇宙模型。Bento 和 Montero 选择了类似环面的六维“黎曼平坦”流形来压缩额外维度，使计算显著简化，并成功得到正的暗能量解。与此同时，另一组研究者利用不同但互补的方法，也在类似的几何设定下通过卡西米尔效应得到了暗能量结果，两种独立路径在结论上一致，增强了该思路的可信度。
该模型的关键限制在于其暗能量并非恒定，而是随时间衰减的“不稳定”解。在物理学语境中，这意味着暗能量保持近似恒定的时间尺度不应超过一个哈勃时间，即约140亿年。过去的大多数观测支持暗能量为常数，但2024年暗能量光谱仪的初步结果，以及一年后的进一步分析，暗示暗能量可能正在减弱，这为这种动力学暗能量模型提供了潜在的观测动机。
为简化问题，Bento 和 Montero 从 M 理论入手，该理论要求11个维度，而非弦理论常见的10个。将其中6个维度压缩后，模型仍然留下一个五维宇宙，而现实宇宙仅有四个宏观维度。研究者承认这是一个根本性问题：若无法从5D进一步降至4D，该方案就无法成为最终解答。鉴于弦理论在过去数十年中屡遭技术与概念障碍，这一进展虽重要，但仍可能面临新的挑战。
Recent work shows that string theory can, for the first time, describe a universe with dark energy. Bento and Montero chose simple six-dimensional Riemann-flat manifolds, resembling tori, to compactify extra dimensions, greatly easing calculations and yielding a solution with positive dark energy. Independently, another team used complementary methods in a similar geometric setup to derive dark energy via the Casimir effect, with both approaches arriving at consistent results, strengthening confidence in the framework.
A central limitation is that the resulting dark energy is not constant but unstable and decays over time. In physical terms, “unstable” means the period over which dark energy remains roughly constant should not exceed a Hubble time, about 14 billion years. While most past observations favored a constant cosmological constant, results presented in 2024 by the Dark Energy Spectroscopic Instrument, reinforced a year later, suggest dark energy may be weakening, lending potential observational support to such dynamical models.
To simplify their construction, Bento and Montero worked within M-theory, which has 11 dimensions rather than the 10 of standard string theory. After compactifying six dimensions, their solution still describes a five-dimensional universe, one dimension more than observed. Resolving this mismatch is critical: without a viable four-dimensional outcome, the model cannot be final. Given decades of unresolved difficulties in string theory, this advance is significant but likely not the last obstacle on the path.