Method · Ground survey
Electrical resistivity tomography, and why a second instrument matters more than a better one
Pass a current between electrodes, measure the voltage, and invert for the distribution of resistance underneath. Air resists enormously and damp limestone does not, so a void stands out. In 2025 it was applied inside the Great Pyramid and found the same corridor the muons found. It reached about 2 metres in, not nine.
Pugacheva 2025, Scientific Reports, CC BY 4.0. Corridor confirmed to at least 2 m, not 9
The answer to "how do we know that void is real and not an artefact of the processing" is never another detector of the same kind. It is a different physical process, with different failure modes, aimed at the same target.
Electrical resistivity tomography is about as different from cosmic-ray counting as you can get. Place electrodes in contact with the surface. Inject a current between two of them, measure the potential difference at others, repeat across many electrode combinations, and invert the whole set for the distribution of electrical resistance in the volume below.
Air is an extremely poor conductor. Limestone carrying trace moisture is a much better one. A void therefore appears as a region of high resistance, provided your inversion knows the real geometry of the surface it is sitting on.
What the 2025 survey did
P. Pugacheva and colleagues published the first application of the method inside the Great Pyramid. Ten measurement lines with mesh electrodes on the Chevron itself, and a 3D model of the Chevron area built from a laser point cloud so that the inversion worked against the real surface rather than a flat approximation. That second part is the hard engineering: the Chevron is a set of huge gabled beams, not a plane.
The corridor is there. Average cross-section of roughly 2.5 metres by 2.5 metres, starting about 1 metre behind the face, extending at least 2 metres into the pyramid. The paper also reports that the resistivity result, a simultaneous ground-penetrating radar survey and an ultrasound tomography survey put the corridor within about half a metre of each other.
Pugacheva, P. et al. (2025), Scientific Reports 15. DOI 10.1038/s41598-025-29081-4. CC BY 4.0.
Read the second number, not the first
At least 2 metres. Not nine.
Resistivity does not reach nine metres into a pyramid and the paper does not claim it does. What it confirms is that a void of that cross-section starts where the muon work says it starts. The 9.1 metre length is still carried by one method, unconfirmed by anything else, and it is the number everybody quotes.
This is the shape of most genuine cross-checks and it is almost always reported as if it were total. Two instruments agreeing on existence, position and section is a strong result. It is not the same as two instruments agreeing on the headline figure.
How independent is independent
Why the agreement counts
Three physical processes with unrelated failure modes: particle absorption, electrical conduction, acoustic reflection.
They converge to within about half a metre on position and size.
A processing artefact in muon data has no reason to reappear in a resistivity inversion.
Why it is worth less than three cold results
All three were deployed on the same face at the same time by overlapping teams.
Everyone involved knew where the corridor was supposed to be, which affects electrode placement and the reading of a marginal signal.
None of them is a blind replication, and none was preregistered.
Both columns are true at once. The discount is real and the result survives it comfortably, which is more than can be said for most of what this series examines.
The measurement that would settle it
Run the resistivity lines along a stretch of the north face where no corridor is supposed to be, and report how often the inversion produces a void anyway. That is the false-positive rate, it is entirely achievable with equipment already on site, and as far as we can trace nobody has published it.
The four questions, applied
The same four we put to every result on this site, turned on this method.
- How much of the corpus?
- The Chevron area of one face of one pyramid. Ten measurement lines.
- What was recovered?
- A void of roughly 2.5 by 2.5 metres beginning about 1 metre behind the face and extending at least 2 metres in, agreeing with radar and ultrasound to within about half a metre.
- What did they say about what they could not do?
- The depth limit is stated plainly as "at least 2 metres" rather than dressed up as confirmation of the full corridor. That is the paper being careful.
- Did anybody check it independently?
- Three methods at once, which is genuinely good, and all three deployed by overlapping teams on the same campaign with knowledge of the expected answer. Strong, and not blind.
Sources
- Investigation of the North Face Corridor in the Great Pyramid of Giza using Electrical Resistivity Tomography. Pugacheva, P. et al., Scientific Reports 15, 2025.
- Precise characterization of a corridor-shaped structure in Khufu's Pyramid by observation of cosmic-ray muons. Procureur, S. et al., Nature Communications 14, 1144, 2023.
Related
Where this is written up in full
Lost Under the Sand
A Nobel laureate pointed muons at a pyramid in 1970 and found nothing. That null result is why the 2017 discovery is worth believing.
All four are written and none is on sale. Advance readers can read them first, in exchange for an honest review.