As the fabric of the Universe expands, the wavelengths of any radiation present will get stretched as well. This applies just as well to gravitational waves as it does to electromagnetic waves; any form of radiation has its wavelength stretched (and loses energy) as the Universe expands.

From a cosmological perspective in 2026, the universe appears to be losing energy due to the expansion of space, a phenomenon most clearly seen in "cosmological redshift." As light travels through an expanding universe, its wavelength is stretched; because the energy of a photon is inversely proportional to its wavelength (E=λhc​), this stretching directly results in a loss of energy. While the First Law of Thermodynamics states that energy cannot be created or destroyed in a "closed system," General Relativity reveals that energy is not necessarily conserved on a global, cosmological scale because the geometry of spacetime is changing. Some physicists argue the energy is transferred into the "gravitational potential energy" of the expanding fabric of the universe, while others, following Noether's Theorem, suggest that because the universe lacks "time-translation symmetry" (it doesn't look the same from one moment to the next), a global conservation of energy simply does not apply.