The Accelerating Universe

Plate 73 speaks for itself: “The farthest lights were dimmer than they should have been.”

The Physics

Distant type Ia supernovae looked fainter than a decelerating universe allows. The extra distance means the expansion is speeding up, driven by dark energy.

d_L = (1 + z) c ∫₀ᶻ dz′ / H(z′)

• d_L: luminosity distance, m
• z: redshift, dimensionless
• c: speed of light, m s⁻¹
• H: Hubble parameter, s⁻¹

Riess et al. 1998 and Perlmutter et al. 1999. Planck 2018: Ω_Λ ≈ 0.68, Ω_m ≈ 0.32.

Honest caveat: The integral form assumes a spatially flat universe.

Sources

• A. G. Riess et al., Astron. J. 116, 1009 (1998).
• S. Perlmutter et al., Astrophys. J. 517, 565 (1999).
• Planck Collaboration, A&A 641, A6 (2020).

On the poster

Plate 073, “The Accelerating Universe”: the pixel-art plate with its slogan “The farthest lights were dimmer than they should have been.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.