Researchers say that as China builds a huge hydroelectric dam on one of its biggest rivers, it also changes the way the Earth spins, making the day a little longer by a fraction of a microsecond Earth spins microsecond.
China’s huge dam that changes time by a little bit
The Three Gorges Dam is the main project in this story. It is a huge hydroelectric dam on the Yangtze River in Hubei province, central China. It took almost 18 years to build, and it has been fully operational since the early 2010s. It is widely considered to be the largest hydroelectric dam in the world in terms of installed capacity and reservoir volume largest hydroelectric dam.
The Chinese government built the dam to do a lot of things, including controlling floods on a notoriously dangerous river, generating a lot of electricity for an economy that needs it, and making a strong political statement about the country’s power and engineering skills strong political statement.
The Three Gorges Dam holds so much water that it changes the way the Earth spins on its axis a little bit Earth spins axis.
The National Center for Space Studies (CNES) in France says that the reservoir can hold about 40 cubic kilometres of water. In other words, we’re talking about moving about 10 trillion gallons of water from a river that flows quickly into a large lake that is higher up. That’s when NASA comes into the picture because of the redistribution of mass redistribution of mass.
NASA says that megastructures can change the rotation of the Earth.
NASA scientists looked into how big events and big engineering projects can change the way the Earth spins in 2005. The 2004 Sumatra-Andaman earthquake and tsunami, which literally shook the whole world, was not the beginning big engineering projects.
That earthquake moved big chunks of rock around in the Earth’s crust. The way the planet spins changes when its internal mass moves, just like a spinning top wobbles when its weight moves. NASA scientists figured out that the 2004 event made the day about 2.68 microseconds shorter 2.68 microseconds shorter.
Dr. Benjamin Fong Chao of NASA’s Goddard Space Flight Center said, “Any global event that involves the movement of mass affects Earth’s rotation movement of mass.”
The same physical law applies to things that people make. You can change the planet’s moment of inertia by moving a lot of mass up or down, closer to or farther from the axis of rotation. That tells you how easily something can spin. A higher moment of inertia means that something will turn more slowly moment of inertia.
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You can picture all of this by thinking of a figure skater. When skaters pull their arms in toward their bodies, they spin faster. They slow down when they stretch their arms out. The total spin energy stays about the same, but the way it is spread out changes figure skater spin.
The Earth acts in the same way. The moment of inertia goes up when mass is concentrated near the equator or at higher elevations. This makes the daily rotation a little slower. It speeds up when mass is pulled toward the center or the poles daily rotation slower.
When the Three Gorges reservoir is full, a lot of water is higher above sea level than it was before. NASA’s math shows that this change makes Earth’s moment of inertia go up a little bit. The effect on time is very small, but modern tools can measure it modern tools measure.
How much does the Three Gorges Dam slow down the rotation of the Earth?
NASA’s team thought that a full Three Gorges reservoir would add about 0.06 microseconds to the length of the day. The earthquake that caused the 2004 tsunami changed the day by about 2.68 microseconds 0.06 microseconds.
Event: Change in the length of the day length of day
Three Gorges Dam filled up in 0.06 microseconds.
Sumatra earthquake in 2004: -2.68 microseconds
A microsecond is one millionth of a second, which means that 0.06 microseconds is 0.00000006 seconds. There would never be a difference on any clock in your house. An atomic clock needs a long time to keep track of changes that small atomic clock track.
The Three Gorges effect on time is real, but it’s too small to have any effect on technology or daily life technology or daily life.
NASA’s study also found a small change in shape. The dam makes the Earth a little rounder in the middle and a little flatter at the poles by moving water around. That effect is also very small and can only be seen with very accurate geophysical measurements accurate geophysical measurements.
Why scientists still care about these small changes
Why bother if no one can feel a 0.06 microsecond stretch to the day? These small changes are like a diagnostic tool for geophysicists. They help scientists figure out how mass moves around the world over time and how these changes affect our rotation diagnostic tool geophysicists.
Earth’s spin is always being pulled on by a number of forces and processes Earth’s spin forces:
- Big earthquakes that move rocks around in the mantle and crust
- Melting ice sheets move water from the poles to the oceans.
- Weather patterns that change with the seasons and move air and water around the world
- Large-scale groundwater extraction and building dams are examples of human engineering projects.
Every factor changes the length of the day by a few microseconds. When you add them all up, they change the way the Earth rotates over time, causing small changes called length-of-day fluctuations length-of-day fluctuations.
Changes in the climate, dams, and moving water masses
Climate change is already changing where water is on Earth. Water flows into the oceans as ice sheets in Greenland and Antarctica melt. This changes the rotation of the Earth and even the tilt of its axis. Researchers have found that the axis has already moved several centimetres per year because of the loss of mass from ice and glaciers tilt of axis.
Big reservoirs add another layer. They usually hold water in the middle of the country, and often at higher elevations than the ocean. When countries build a lot of big dams, the effect on the shape and rotation of the Earth becomes more complicated and needs to be carefully tracked carefully tracked rotation.
However, recent studies indicate that natural processes, particularly ice melt and mantle dynamics beneath the crust, predominantly influence the long-term scenario. The Three Gorges Dam is a striking example because of its size, not because it changes the laws of physics on Earth natural processes influence.
What “slower days” really mean
The Earth’s rotation isn’t always perfectly steady. Over millions of years, tidal forces between the Earth and the Moon transfer energy, which makes it slow down. Scientists sometimes add “leap seconds” to Coordinated Universal Time because of this long-term braking leap seconds added.
Changes caused by dams and earthquakes are on top of that slow trend. In practice, this means that timing agencies keep a close eye on how fast the Earth spins using radio telescopes and satellites. When the difference between atomic time and the Earth’s rotation gets big enough, they change the official time by one second official time change.
The Three Gorges Dam’s effect is so small that it doesn’t directly cause leap seconds. Instead, it’s just one small part of the equations that keep the world’s time in sync with the planet’s spin world’s time sync.
The main ideas behind the headlines
In this discussion, two technical terms that come up a lot are moment of inertia and length of day technical terms moment.
The moment of inertia tells you how mass is spread out around an axis of rotation. A dumbbell with weights at the ends has a high moment of inertia, which means it spins more slowly for the same amount of energy than one with weights near the center. The Three Gorges reservoir moves water away from the center of the Earth, which makes that moment bigger axis of rotation.
The length of day (LOD) is the exact amount of time it takes for the planet to make one full rotation. It says 24 hours on paper, but in real life it changes every few milliseconds and microseconds. Geophysicists keep an eye on changes in LOD to learn more about what is happening inside and on the surface of Earth planet full rotation.
What if we built a lot more “Three Gorges” in the future?
Many people wonder what would happen if there were dozens of dams around the world that were as big as the Three Gorges. According to current physics, even a huge global program of megadams would only add a few microseconds to the length of a day huge global program.
That amount of change would still be much less than what would affect daily life, the seasons, GPS systems, or satellite operations. The main worries about these kinds of dams are still social and environmental: people who have to leave their homes, river ecosystems, sediment build-up, and the risk of earthquakes caused by the weight of the reservoir on faults social and environmental.
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What the NASA work shows is not a new threat to life, but a clear example of how engineering, climate, and basic behaviour of the planet are all connected. A single infrastructure project on one river in one country now has effects that can be traced all the way to the length of the day itself with enough accuracy engineering climate connected.
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