Abstract:
The most pressing questions in cosmology fundamentally boil down to measuring distances. Particularly the "Hubble Tension" between early- and late-universe measurements. Current standard candles rely on the traditional cosmic distance ladder, which suffers from compounding calibration errors and struggles to extend to high redshifts. To address this, we present "The Quasar Distance Elevator," a methodology utilizing Active Galactic Nuclei (AGN) as independent "standard rulers" to measure cosmological distances in a "single rung". Our approach is based on the "Standard Speed-Gun" formalism, which relies on the speed of light to calibrate a standard ruler. Assuming AGN radio variability is constrained by the speed of light, we estimate the linear size of an emitting region using the relation $R=c\Delta t$. Combined with apparent sizes measured via Very Long Baseline Interferometry (VLBI), this yields distances. Making these measurements is a huge undertaking and includes huge data volumes, supercomputers and advanced Fourier analysis. I will present early results from our global VLBI observing program thaat has produced the first-ever "single-rung" joint cosmological fit.