One Lifetime Cannot Do It: Exponential Dissolution of a Large Vacuum Density Fails Nucleosynthesis and Today Simultaneously

If a once-large vacuum density dissolved exponentially with a single lifetime, that lifetime would be fixed by today's observed density and bounded above by nucleosynthesis. This paper computes both for initial densities at the Planck, electroweak, and QCD zero-point estimates. Matching today's 2.52 x 10^-47 GeV^4 from the Planck estimate requires a lifetime of 0.05 billion years, while nucleosynthesis permits at most 5.07 x 10^-3 seconds, a conflict by a factor of 3.09 x 10^17. The same conflict, at factors of 1.52 x 10^17 and 6.76 x 10^16, applies at the electroweak and QCD initial densities. Single-exponential dissolution is thereby excluded as a complete history. The paper computes from stated assumptions and reports no measurement.