D9 Dark Energy

Topic

The central element of this model is the wide-field space telescope, which maps the geometry and structure of the universe across a vast expanse of the sky by combining two instruments: one for ultra-high-resolution visual imaging—to measure weak gravitational lensing in billions of background galaxies—and an infrared spectrograph—to measure galaxy redshifts for the study of baryon acoustic oscillations.

Combining the weak lensing measurements from this telescope—sensitive to both the universe's geometry and the growth of its structures—with those same acoustic oscillations—sensitive only to geometry—will make it possible to measure the dark energy equation of state with one-percent precision.

The most remarkable feature of this satellite is the stability of its point spread function in space; measuring weak lensing requires knowing the shape of each galaxy with a level of precision far beyond what Earth's atmosphere—with its constant fluctuations—would ever allow from the ground. The fact that this spread function remains stable and predictable over years is what enables such precision, making it possible to determine whether the dark energy equation of state is truly constant or if, instead, it varies over cosmic time. Thus, from the wide-field space telescope that opens this document to the determination regarding dark energy's constancy that concludes it—encompassing weak gravitational lensing and baryon acoustic oscillations along the way—dark energy drives a process where two complementary techniques, combined on a single satellite, ultimately answer the very question that currently divides the early universe from the late universe.

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