Dark Energy, Gravitational Waves and the Future of Cosmology: New Scientist Interview

Short Summary

In this New Scientist interview, a leading cosmologist explains dark energy as the dominant component of the universe, making up about 70 percent of its energy, and distinguishes it from dark matter. The conversation covers how observations of distant supernovae revealed the accelerating expansion of the universe, and why the standard cosmological model relies on a cosmological constant that is both puzzling and tiny. Desi results hint at evolving dark energy, a potential game changer for gravity and cosmology. The interview then explores ideas beyond a constant, including extra dimensions, new fields, and a thermodynamic view of gravity, before turning to gravitational waves as a powerful probe. The discussion ends with look-ahead to future surveys and detectors like LIGO, LISA, Euclid, and the Vera Rubin Observatory.

Medium Summary

The video centers on the nature of dark energy and its role in the expanding universe. The guest explains that while dark energy is the largest energy component of the cosmos, making up roughly 70 percent, it is distinct from dark matter, which attracts matter via gravity. The standard explanation uses a cosmological constant, a fixed energy density of space, but its tiny observed value is physically puzzling. The host traces the discovery to observations of distant supernovae showing that the expansion rate is accelerating, which cannot be explained by matter alone, hence the dark energy label. Over the last two decades, multiple probes, including galaxy clustering, the cosmic microwave background, and gravitational waves, have supported the cosmological constant model, though DESI has reported hints of evolving dark energy. This potential shift would imply a changing equation of state for dark energy, offering a new handle on its nature and on gravity itself.

The dialogue surveys proposed explanations for a dynamic dark energy component. One route is changing gravity itself, potentially through extra spatial dimensions, additional fields, or even a thermodynamic interpretation of general relativity. The idea of extra dimensions posits gravity as the only force that propagates into a higher-dimensional bulk, altering the Friedmann equation that governs cosmic expansion. Alternative routes add scalar fields coupled to gravity, which can drive acceleration and cause the effective strength of gravity to vary in space and time, including environments far from Earth where screening might hide new forces. A thermodynamic view of spacetime, drawing on parallels with black hole thermodynamics, is another provocative but not yet mature direction for explaining dark energy. Each of these ideas strives to be both elegant and predictive, but none has yet emerged as the definitive solution.

The discussion then shifts to gravitational waves as a clean, independent probe of gravity and cosmology. Detectors such as LIGO, Virgo, and upcoming projects like KAGRA and the space-based LISA will test how gravitational waves propagate and how their amplitude scales with distance, offering constraints on modified gravity and dark energy models. A landmark event, GW 170817, involved a neutron-star merger with electromagnetic counterparts, providing a stringent test of the speed of gravitational waves and the physics of dense matter. The video also previews the dramatic growth of gravitational-wave astronomy, with plans to detect tens of thousands of events per year in the coming decades, enabling precise mapping of dark energy, structure formation, and the large-scale geometry of the universe.

In addition to gravitational waves, the speakers discuss grand future facilities: the Euclid satellite, the Vera Rubin Observatory, and the DESI galaxy survey, all aimed at tightening constraints on dark energy and cosmic expansion. The conversation culminates in a forward-looking view of how upcoming instruments, including LISA, will extend gravity tests to new frequency ranges and cosmic epochs, potentially revealing new physics beyond the current models. The guest emphasizes that while the data are becoming more precise, the quest for a compelling, fully explained theory of dark energy remains a central challenge for fundamental physics and cosmology.