The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), combined with data from the cosmic microwave background (CMB), has placed an upper limit on the sum of neutrino masses, ∑m_ν < 70 meV (95%). This result excludes the minimum sum associated with the inverted hierarchy and peaks at ∑m_ν = 0, close to excluding even the minimum sum of 58 meV at 2σ. The paper explores the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined from the suppression of clustering in the late universe. Allowing clustering to be enhanced, the DESI analysis was extended to ∑m_ν < 0, finding ∑m_ν = -160 ± 90 meV (68%) and excluding the minimum sum at 99% confidence. This preference for negative masses challenges explanations via shifts in cosmic parameters. The paper discusses models where ∑m_ν = 0 could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics accessible in experiments. The paper also discusses how a negative neutrino mass signal could arise from new long-range forces in the dark sector or a primordial trispectrum resembling CMB lensing. The paper concludes with a summary of the implications of these findings for cosmology and particle physics.The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), combined with data from the cosmic microwave background (CMB), has placed an upper limit on the sum of neutrino masses, ∑m_ν < 70 meV (95%). This result excludes the minimum sum associated with the inverted hierarchy and peaks at ∑m_ν = 0, close to excluding even the minimum sum of 58 meV at 2σ. The paper explores the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined from the suppression of clustering in the late universe. Allowing clustering to be enhanced, the DESI analysis was extended to ∑m_ν < 0, finding ∑m_ν = -160 ± 90 meV (68%) and excluding the minimum sum at 99% confidence. This preference for negative masses challenges explanations via shifts in cosmic parameters. The paper discusses models where ∑m_ν = 0 could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics accessible in experiments. The paper also discusses how a negative neutrino mass signal could arise from new long-range forces in the dark sector or a primordial trispectrum resembling CMB lensing. The paper concludes with a summary of the implications of these findings for cosmology and particle physics.