What is the origin of the 'Hollow Moon' theory? Is it scientifically valid to support this theory with the Apollo mission's 'moon rang like a bell for hours' observation?

Okay, no problem. Let's talk about this super cool "Hollow Moon" theory.

The "Hollow Moon": How a Sci-Fi Story "Collided" with the Apollo Program

Hello! That's a really interesting question you've asked. It perfectly blends science, history, and a touch of conspiracy theory, a topic that fascinates many people. I'll try to explain it clearly in plain language.

The Origin of the "Hollow Moon" Theory: From Sci-Fi to "Science"

This theory is actually older than you might think, with roots in science fiction. As early as 1901, H.G. Wells, the father of science fiction, depicted a hollow Moon inhabited by alien life in his novel The First Men in the Moon. This can be considered the earliest literary image of the "Hollow Moon."

However, what truly propelled this theory "out of the niche" and from sci-fi into "pseudoscience" were two Soviet scientists.

In 1970, two researchers from the Soviet Academy of Sciences – Mikhail Vasin and Alexander Shcherbakov – published an article titled Is the Moon the Creation of Alien Intelligence?

They proposed a startlingly bold hypothesis: The Moon is not a natural celestial body, but a gigantic, hollow spaceship modified by some kind of super-advanced alien civilization.

Their listed "evidence" included:

The Moon's orbit is too "perfect," always showing the same face to Earth.
The Moon's size and distance are also too "coincidental," perfectly covering the Sun to create total solar eclipses.
The Moon's craters are surprisingly shallow, suggesting an incredibly hard "shell" protecting the interior.

This article was more of a thought experiment or sci-fi story, filled with speculation. But during the Cold War, amidst the US-Soviet space race, Western media picked it up and spread it rapidly, cloaking the "Hollow Moon" theory in a veneer of "science."

The Apollo "Ring": What's the Truth?

Now, let's get to the key part you mentioned – the Apollo mission's "ringing." This is arguably the strongest "evidence" for the "Hollow Moon" theory and the most widely circulated piece.

Here's what happened:

During the Apollo 12 mission in 1969, after the astronauts returned to the command module, mission control remotely directed the spent lunar module ascent stage (the small part the astronauts used to leave the Moon) to crash into the lunar surface.

The scientific purpose was clear: This was an artificial "moonquake." Scientists wanted to test the sensitivity of the seismometers they had just placed on the Moon and observe how the Moon's internal structure responded to the vibrations.

The result surprised everyone: The seismometers showed that the Moon vibrated for nearly an hour! Later, during the Apollo 13 mission, an even larger rocket booster (S-IVB) was crashed into the Moon, and that vibration lasted over three hours.

A scientist involved in the project vividly described the phenomenon, saying: "The Moon was ringing like a bell."

Conspiracy theorists seized on this phrase as "irrefutable proof": See! Only something hollow rings like a bell for so long, so the Moon must be hollow!

So, does this claim hold up scientifically?

The answer is: No. "Ringing like a bell" was just a metaphor; the scientific explanation is far less mysterious.

The main reasons the Moon "rang" for so long are:

Extreme dryness, no water: Vibrations on Earth die down quickly because Earth's interior has vast amounts of water and molten magma. These fluids act like giant shock absorbers, rapidly dissipating seismic wave energy. The Moon, however, is an extremely dry planet with almost no water. Without water's "cushioning," the vibration energy has nowhere to go and simply reverberates.
Hard and intact structure: The Moon is a cooled planet with largely ceased geological activity. Its interior is like one big, dry, hard rock. Think about tapping a wet sponge versus a metal ball – which sound lasts longer? Definitely the metal ball. The Moon is more like that metal ball.
Surface "regolith" causes wave scattering: The Moon's surface is covered by a thick, powdery layer called "regolith," formed over billions of years by repeated meteorite impacts. When seismic waves generated by an impact propagate through the Moon's interior and encounter this loose layer, they scatter intensely. It's like light entering a room full of mirrors, bouncing back and forth, unable to settle quickly.

In simple terms: The Moon "rang" for a long time not because it's "hollow," but because it's dry, rigid, and fragmented (referring to the surface layer). This phenomenon is actually an important clue for scientists understanding the Moon's internal structure, proving it's a rigid, water-poor sphere fundamentally different from Earth.

Why is the "Hollow Moon" Absolutely Unscientific?

Beyond the explanation for the "ringing," several hard scientific facts directly refute the "Hollow Moon" theory:

The Density Problem: This is the most fatal flaw. Using the law of universal gravitation, we can calculate the Moon's mass very precisely. We can also precisely measure its volume. Mass divided by volume equals density. The calculated average density of the Moon is about 3.34 grams per cubic centimeter, which perfectly matches the density of a solid rocky planet. If the Moon were hollow, its mass would be much lower, its density absurdly low, making it impossible to maintain its current orbit; it would likely have disintegrated under gravitational forces long ago.
Moonquake Data: Scientists haven't just studied the Moon through artificial impacts; they've also recorded thousands of natural "moonquakes." The way seismic waves from these quakes propagate through the Moon's interior points to a solid sphere with a layered structure (core, mantle, crust), not an empty shell.
Formation Theory: The prevailing "Giant Impact" hypothesis states that the Moon formed from debris ejected after a Mars-sized body collided with the early Earth. This process simply cannot produce a hollow structure.

To Summarize

The "Hollow Moon" theory originated in science fiction and was later popularized after being packaged as a "scientific hypothesis" by two Soviet researchers.
"The Moon ringing like a bell" is a real scientific observation, but it's caused by the Moon's dry, rigid physical properties, not hollowness. This is actually an important scientific discovery, not a conspiracy.
From the perspectives of gravity, density, and moonquake data, the "Hollow Moon" theory is completely unscientific.

So, the next time you hear this story, you can appreciate it as a very interesting sci-fi concept. Its charm lies in how it cleverly blends humanity's romantic imagination about the cosmos with the real history of space exploration. But when it comes to scientific facts, our Moon is indeed a solid sphere.