Specific allegation
The specific claim is that a “gravity hole” beneath Hudson Bay causes people or objects to weigh dramatically less, sometimes framed as a localized weakening of gravity hidden by official maps. Satellite gravimetry does show a negative gravity anomaly there. The claim exaggerates a real measurement; the test is its size, spatial extent, and consistency with geology and glacial history.
Scientific and historical chronology
Earth’s gravity field has long been mapped with satellite tracking and later missions such as GRACE. Hudson Bay emerged as a pronounced negative anomaly in global gravity maps. Geophysical models associate it with both mantle mass distribution and the ongoing viscoelastic response to the enormous Laurentide Ice Sheet, which depressed the crust and altered mantle flow.
Observations and records
GRACE measures gravity-field changes through tiny variations in the distance between two satellites; the anomaly is a spatial variation in gravitational acceleration, not a cavity. The signal is small—on the order of parts per million of surface gravity—and changes with glacial isostatic adjustment. There is no measured levitation, sudden loss of weight, or local failure of gravity.
Mainstream explanation and counterevidence
The anomaly reflects subsurface density and the lingering effects of ice-sheet loading and rebound. Numerical models combining mantle viscosity, ice history, and gravity measurements reproduce much of its pattern. This is an expected geophysical variation that geodesists measure, not a hole in Earth’s gravitational field.
Uncertainties and limits
The precise contribution of ancient ice history and mantle structure remains model-dependent, and regional gravity estimates are refined as satellite and terrestrial data improve. A small measurable change can matter scientifically without having a perceptible everyday effect. Uncertainty in model partitioning does not support a dramatic human-weight claim.
Evidence that could change the assessment
A calibrated gravimeter survey showing an unmodeled anomaly large enough to alter local weight substantially, independently replicated and inconsistent with mass and glacial-rebound models, would change the assessment. Direct weight measurements would need controls for latitude, elevation, tides, and instrument calibration.
Calibrated verdict
Hudson Bay’s gravity anomaly is real but tiny and explained by mass distribution and postglacial adjustment. It does not make people float or meaningfully lighter.
Annotated sources
- Tamisiea, Mitrovica & Davis, Science (2007)Uses GRACE observations to analyze gravity change and glacial isostatic adjustment.
- Peltier, Annual Review of Earth and Planetary Sciences (2004)Reviews postglacial rebound and its gravitational/geodetic signatures.
- NASA/JPL, GRACE missionExplains satellite gravity measurement and global mass redistribution.
- NASA Earth Observatory, gravity field mapsContext for interpreting GRACE gravity anomalies and their small physical scale.