02 Jun 2026

The subsurface: Earth’s largest unmapped environment

Read our London Tech Week blog from Delta G.

Gravity is the same everywhere on Earth, right?

No, it’s not.

In high school physics, we are taught that gravity is a constant 9.8 m/s^2. In reality, Earth is a "restless planet" with a gravitational field that is constantly shifting. It might not be noticeable to us in our daily lives, but these shifts are vital for understanding the planet's composition and structure.

The non-uniform nature of gravity is caused by a few key factors:

The composition of the Earth's crust. Gravity is essentially a measure of mass; therefore, the "pull" you feel changes based on the density of the material directly beneath you. Gravity is slightly stronger over dense rock types, like gabbro. These “heavier” (i.e denser) rocks create slightly stronger local gravitational anomalies, or put it another way, a stronger gravitational pull. Less dense rock, like limestone, have lower densities and lower gravitational pull.
Distance from the Earth’s Centre: gravity follows an inverse-square law, meaning it weakens as you move further from the source of mass. For example, gravity is slightly stronger in valleys than on hilltops because the valley floor is closer to the Earth's centre
Gravity is not just varied by location; it also changes over time due to the movement of mass within the Earth system, for example, melting glaciers, groundwater depletion, and aquifer recharge redistribute mass and subtly alter the local gravitational field.

The variations in gravity are all so tiny that they can only be detected using special equipment. There are classical tools for measuring gravity, like gravimeters. These sensors measure this “pull” at a single point. If you imagine gravity as a hill, this tells you how high you are at that specific point. This is useful, but it can be difficult to distinguish small underground features from the much larger background signal created by the Earth itself.

Gravity gradiometers work differently. Instead of measuring the total gravitational pull at one point, they measure how gravity changes between two points. In the hill analogy, they measure the “slope” rather than the “height.” This matters because nearby underground structures, like tunnels, salt domes or ore bodies, create small local changes in the gravitational field. Measuring the gradient makes these local variations stand out more clearly against the broader background. Rather than seeing a vague gravitational “blob,” they can help resolve the shape, edges, and structure of what lies beneath the surface.

However, traditional gravity gradiometers struggle outside of highly controlled environments because they are extremely sensitive to vibration, motion, and environmental noise. Even small disturbances from vehicles, machinery, waves, or changing terrain can overwhelm the tiny gravitational signals they are trying to detect.

So why haven’t we mapped every city or countryside before now?

Einstein’s equivalence principle creates one of the biggest challenges in gravity sensing: a sensor cannot easily tell the difference between gravity and motion. To the sensor, the gravitational pull from something underground, like a tunnel, salt dome, or ore body, looks almost identical to the vibration caused by the environment, such as passing traffic, wind, waves, or even distant seismic activity. This means environmental noise becomes mixed into the gravity measurement and creates major limitations for traditional gravity sensors:

Small underground signals are often buried beneath environmental noise
Making a sensor more sensitive does not automatically solve the problem because it may just detect more noise
Traditional systems often need to remain stationary for long periods to average out environmental disturbances and produce a usable reading

This gap in our understanding of the subsurface (underground and underwater) is a massive economic drain. Just think about it, every time a shovel hits a pipe that wasn't on a map, or a sinkhole opens under our feet, the clock starts ticking on a very expensive disaster. In the UK alone, our inability to accurately "see" the subsurface costs the economy billions annually just from accidental utility strikes. The UK sees 1.5 million street works annually. While the direct economic impact is £1.5 billion, the secondary costs, traffic congestion, pollution, and lost business, reaches an estimated £5.5 billion.

This problem is multiplied across almost every single sector. Any industry that relies on understanding the subsurface (underground and underwater), is losing billions.

The Delta.g Quantum Solution

Our Quantum gravity gradiometry solves the noise problem through atom interferometry. Our patented approach uses clouds of atoms, cooled to near absolute zero, as "test masses". The breakthrough in noise rejection comes from vertically stacking two of these sensors and "sharing" a single laser reference between them. Because the laser hits both clouds simultaneously, any environmental vibration is imprinted identically on both. When we subtract the readings, the vibration, the "common mode" noise, is cancelled out, leaving only the tiny difference in gravity between the two heights. Think of our sensor like the ‘noise-cancelling headphones’ for the subsurface.

By eliminating the noise that has masked the subsurface for centuries, we are finally gaining the spatial intelligence required to build safely and navigate surely. Because the utility of this "Invisible Map" also extends into navigation.

We have mapped the topography of the Moon and Mars, yet we remain remarkably blind to the complex structures just a few meters beneath our feet. The map has always been there; we are just finally building the light to read it.

To learn more about Delta G, click below:

Our team:

Alex Smith

Head of Channel Strategy and Brand, techUK

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The subsurface: Earth’s largest unmapped environment

So why haven’t we mapped every city or countryside before now?

The Delta.g Quantum Solution

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Our team:

Alex Smith

techUK Annual Dinner 2026