The Ultimate Science: 5 Shocking Truths About Senku's Time Machine In Dr. Stone

The question of whether Senku Ishigami, the genius scientist of the Stone World, ever achieves his final, most ambitious goal—building a time machine—is one of the most hotly debated topics following the conclusion of the Dr. Stone manga. As of December 2025, the definitive answer lies not in a completed invention, but in the ultimate, long-term vision for the newly revived human race. The final chapters and the special epilogue reveal that while Senku’s hands-on work on the device is in progress, the true "4D Science" project is a commitment that extends far beyond his own lifetime, setting up a mind-bending future for the Kingdom of Science.

The pursuit of a time machine represents the pinnacle of Senku's scientific ambition, moving past the immediate need for survival and restoration to tackle the root cause of the 3,700-year petrification. This ultimate invention is the only way to truly undo the catastrophe and prevent the whole Stone Age from ever happening, a challenge so monumental it requires the combined knowledge of all humanity and the very technology that caused the disaster: the mysterious Medusa device.

Senku Ishigami: The Ultimate Inventor's Biography and Final Goal

Senku Ishigami is the undisputed protagonist of Dr. Stone, a hyper-rational, science-obsessed teenager whose sheer intellect and relentless curiosity drive the plot. His life’s mission, even before the petrification, was the advancement of science, a goal he embodies with his catchphrase, "Ten Billion Percent."

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• Full Name: Senku Ishigami (石神 千空)
• Age: 16 (Pre-Petrification); Over 3,700 (Chronological); 18-20 (Post-Revival/Manga Epilogue)
• Family: Byakuya Ishigami (Adoptive Father, deceased astronaut)
• Affiliation: Founder and Leader of the Kingdom of Science
• Key Inventions: Revival Fluid, Electricity, Cell Phone, Penicillin, Steam Engine, Telescope, and ultimately, the Time Machine (in progress).
• Manga Status: The main conflict with Why-Man is resolved, and his final goal is the creation of a time machine.
• Seiyuu (Voice Actor): Yūsuke Kobayashi

After defeating the sentient petrification devices known as Why-Man, Senku’s objective shifts from "reviving all of humanity" to "preventing the petrification from ever happening." This is the catalyst for the time machine project, an invention that elevates the Kingdom of Science from a Stone Age civilization to a futuristic powerhouse.

1. The Time Machine is Senku's "In-Progress" Ultimate Invention

Contrary to some fan speculation and hopes, the Dr. Stone manga does not end with Senku successfully traveling back in time. The final chapters, including the *Dr. Stone: 4D Science* epilogue, firmly establish the time machine as the Kingdom of Science's ultimate, long-term project.

The Final Chapter's Mind-Bending Reveal

In the manga's conclusion, after the conflict with Why-Man is resolved, a significant time skip occurs. The Kingdom of Science has made incredible strides, having built a working space shuttle, a nuclear reactor, and even fusion power. However, the one invention that remains unfinished is the time machine.

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Senku acknowledges the monumental nature of the task, stating that it will take "years or decades" for the team—including the brilliant mind of Dr. Xeno, the crafting skills of Kaseki, and the raw power of Taiju—to complete the device. This ending is a testament to the series' core theme: science is an endless, cumulative journey, not a single, instantaneous achievement. Senku passes the torch, ensuring the next generation will inherit the goal.

The very concept of the time machine is what ultimately convinced Why-Man to stop the petrification ray. The Medusa devices, which are highly advanced artificial intelligences, calculated the extreme improbability of a stone-age human like Senku not only surviving but also reaching a technological level high enough to attempt time travel. This proposal—to prevent the petrification and thus ensure the Medusa's survival—was deemed a viable "future" by the AI.

2. The Science of the "4D" Time Machine: Medusa and Fusion Power

The time machine in Dr. Stone is not based on typical science-fiction tropes like wormholes or black holes; it is rooted in the very technology that created the Stone World: the Medusa device. The time machine is an exercise in what Senku calls "4D Science," the application of science to time itself.

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The Medusa Device: The Key to Time Manipulation

The Medusa is a small, trefoil-knot-shaped device that can emit a petrification ray. Crucially, the Medusa also possesses the ability to reverse the petrification process, effectively halting and then restarting the biological clock of a person. This power is the cornerstone of the time machine concept.

Senku's hypothesis is that the Medusa's ability to manipulate the "time" of a human body (stopping and reversing cellular decay) can be scaled up to manipulate spacetime itself. The petrification ray, in a sense, is already a form of localized time suspension. The time machine would be the ultimate evolution of this technology, requiring a massive, unprecedented amount of energy.

The Helium-3 Power Problem

The main bottleneck for the time machine is power. The energy required to manipulate spacetime on a large scale is astronomical. The Kingdom of Science determines that the only viable power source is a sustainable fusion reactor, fueled by Helium-3.

This is why the final arc involves a journey to the Moon: to gather the necessary Helium-3 from the lunar surface. While Senku's team successfully retrieves the resource and begins the process of building the fusion reactor, the full-scale power plant needed to charge the time machine is a multi-decade project. The machine is essentially a Medusa device scaled up to a colossal degree, powered by the cleanest, most potent energy source available.

3. The Time Travel Paradox and the John Connor Parallel

The time machine project introduces a classic science-fiction problem: the paradox. If Senku succeeds in building the machine and prevents the petrification, he would erase the 3,700 years of the Stone World, the Kingdom of Science, and all the friends he made, including Chrome, Kohaku, and Gen Asagiri.

The "John Connor" Analogy

CBR drew a direct parallel between Senku's final mission and the plot of the *Terminator* franchise, labeling Senku as a "John Connor." John Connor is the future leader who is sent back in time to prevent a catastrophe. Senku's goal is exactly that: to travel back and prevent the petrification from ever occurring.

However, the manga avoids a definitive answer to the paradox. By ending with the time machine still under construction, the story leaves the philosophical implications open-ended. It suggests that the true value was not in the destination (time travel) but in the journey: the revival of science, the collaboration of humanity, and the relentless pursuit of knowledge that made the impossible goal even remotely plausible.

4. The Legacy: A Multi-Generational Scientific Commitment

The most unique aspect of the Dr. Stone ending is how it reframes the time machine as a legacy project. Senku, the man of science, understands that some achievements are too big for one person or one generation.

The final scene of the manga shows the next generation, including the children of the Kingdom of Science, continuing the work. They are taught the fundamentals of science, from the stone-melting solution to the complex principles of fusion, all with the ultimate goal of completing the time machine. The story concludes with a message of hope and faith in the future of science, trusting that their successors will eventually complete the "4D Science" project.

The time machine is therefore not an invention of Senku Ishigami alone, but the combined, multi-generational ultimate invention of the entire Kingdom of Science.