Have you ever wondered if humans could one day spread across the entire Milky Way galaxy? Imagine moving beyond Earth to establish colonies among the countless star systems out there. It’s a fascinating idea, but also quite overwhelming. Our galaxy contains around 300 billion stars and stretches about 160,000 light-years across. Currently, we’ve only managed to send one spacecraft beyond our solar system, and it’s traveling at a mere 0.006% of the speed of light. At this pace, it would take over 2.5 billion years to traverse the galaxy from one end to the other.
One major challenge is human survival in space. The distances between stars are vast, and most planets aren’t suitable for sustaining human life. We need a lot of resources to survive. Despite these challenges, decades ago, scientists proposed that spreading human civilization across the galaxy could be possible without breaking any known laws of physics.
This idea is inspired by mathematician John von Neumann, who envisioned machines capable of self-replication—creating new generations of themselves. These are known as von Neumann machines. In space exploration, these machines could be built on Earth and launched into space. Once there, they would land on distant planets, mine resources, harvest energy, build replicas of themselves, and send those replicas to nearby planets, continuing the cycle. This would result in millions of probes spreading throughout the galaxy, much like a drop of ink dispersing in water.
Researchers calculated that a single von Neumann machine traveling at 5% of the speed of light could replicate throughout our galaxy in about 4 million years. While this might seem like a long time, on a cosmic scale, it’s incredibly fast—comparable to just 2.5 hours in an entire year. However, creating such machines would require advanced technologies we don’t yet possess, including sophisticated artificial intelligence, miniaturization, and improved propulsion systems. If we wanted to use them to spread humans across the galaxy, we’d also need the ability to artificially grow biological organisms using raw materials and genetic information.
If an alien civilization had created such machines and sent them our way in the last billion years, our galaxy would likely be teeming with them by now. So, where are they? Some astronomers, like Carl Sagan, suggest that intelligent aliens might avoid building self-replicating machines because they could become uncontrollable and exhaust planetary resources. Others believe the absence of these machines indicates that intelligent alien civilizations either don’t exist or go extinct before developing the necessary technologies.
Despite the mystery, people continue to imagine what it would be like if these machines were out there. Science fiction author David Brin envisions a universe filled with various von Neumann machines, each with different purposes. Some are designed to welcome young civilizations, while others seek out and eliminate potential threats. In Brin’s story “Lungfish,” some von Neumann machines are observing Earth, waiting for us to reach a certain level of advancement before making contact.
For now, all we have are curiosity and theories. The next time you gaze at the night sky, consider the possibility that billions of self-replicating machines could be traveling between stars in our galaxy. If they exist, one might eventually land on Earth, or maybe, just maybe, they’re already here.
Imagine you are an engineer tasked with designing a von Neumann machine for space exploration. Create a detailed blueprint of your machine, considering its self-replication capabilities, energy sources, and materials it would need to gather from planets. Present your design to the class and explain how it would help spread human civilization across the galaxy.
Participate in a class debate on the ethical implications of deploying self-replicating machines in space. Consider the potential risks and benefits, such as resource depletion and the possibility of encountering alien life. Prepare arguments for both sides and engage in a thoughtful discussion with your classmates.
Conduct research on the latest advancements in space propulsion technologies. Compare these technologies to the hypothetical requirements for von Neumann machines traveling at 5% of the speed of light. Present your findings in a report, highlighting the gaps and potential future developments needed to achieve such speeds.
Write a short story from the perspective of a human or von Neumann machine exploring the galaxy. Describe the challenges and wonders encountered during the journey. Share your story with the class, focusing on how it reflects the concepts discussed in the article.
Spend an evening observing the night sky. Reflect on the possibility of self-replicating machines traveling between stars. Write a journal entry about your thoughts and feelings, considering the vastness of the galaxy and the potential for human expansion. Share your reflections in a class discussion.
**Transcript:**
Translator: Jessica Ruby
Reviewer: Brian Greene
Could human civilization eventually spread across the whole Milky Way galaxy? Could we move beyond our small blue planet to establish colonies in the multitude of star systems out there? This question is quite daunting. There are around 300 billion stars in the galaxy, which is about 160,000 light-years across. So far, we’ve sent a single spacecraft outside our solar system, traveling at 0.006% of the speed of light. At that rate, it would take over 2.5 billion years just to get from one end of the galaxy to the other.
Then there’s the question of human survival. The distances between stars are enormous. We couldn’t live sustainably on most planets, and we require a lot of resources to stay alive. Yet, decades ago, scholars found that it’s theoretically possible to spread human civilization across the galaxy quite quickly, without breaking any known laws of physics.
Their idea is based on the work of mathematician John von Neumann, who designed machines that could self-replicate and create new generations of themselves. These are known as von Neumann machines. In the context of space exploration, von Neumann machines could be built on Earth and launched into space. There, the self-sufficient machines would land on distant planets, mine available resources, harvest energy, build replicas of themselves, launch those to the nearest planets, and continue the cycle. The result would be millions of probes spreading outwards into the universe like a drop of ink in a fishbowl.
Scholars calculated that a single von Neumann machine traveling at 5% of the speed of light could replicate throughout our galaxy in 4 million years or less. While that may sound like a long time, on a cosmic scale, it’s incredibly fast—equivalent to about 2.5 hours in an entire year. Creating von Neumann machines would require technologies we don’t have yet, including advanced artificial intelligence, miniaturization, and better propulsion systems. If we wanted to use them to spread actual humans throughout the galaxy, we would need the ability to artificially grow biological organisms and bodies using raw elements and genetic information.
Regardless, if an alien civilization created such a machine and set it multiplying its way toward us in the last billion years, our galaxy would be swarming with them by now. So then, where are all these machines? Some astronomers, like Carl Sagan, suggest that intelligent aliens might not build self-replicating machines at all, as they could become uncontrollable and deplete planets in their quest to replicate. Others interpret the absence of these machines as evidence that intelligent alien civilizations either don’t exist or go extinct before developing the necessary technologies.
However, this hasn’t stopped people from imagining what it would be like if they were out there. Science fiction author David Brin writes about a universe where many different von Neumann machines exist and proliferate simultaneously. Some are designed to greet young civilizations, while others aim to locate and eliminate potential threats. In Brin’s story “Lungfish,” some von Neumann machines are monitoring Earth, waiting for us to reach a certain level of sophistication before making their move.
For now, all we have is curiosity and theory. The next time you look at the night sky, consider that billions of self-replicating machines could be advancing between stars in our galaxy right now. If they exist, one of them may eventually land on Earth, or perhaps, just perhaps, they’re already here.
Human – A member of the species Homo sapiens, characterized by advanced cognitive abilities and the capacity for abstract reasoning, which allows them to explore and understand the universe. – In the quest to understand the cosmos, human curiosity has led to the development of powerful telescopes and space missions.
Galaxy – A massive, gravitationally bound system consisting of stars, stellar remnants, interstellar gas, dust, and dark matter. – The Milky Way is the galaxy that contains our solar system, and it is just one of billions in the universe.
Stars – Luminous celestial bodies made of plasma, held together by gravity, and undergoing nuclear fusion in their cores. – The life cycle of stars includes stages such as the main sequence, red giant, and supernova, depending on their initial mass.
Survival – The ability to continue living or existing, often despite challenging conditions, which can be applied to species, ecosystems, or civilizations. – The survival of a space mission depends on careful planning and the ability to adapt to unforeseen challenges in the harsh environment of space.
Machines – Devices or systems that use energy to perform tasks, often used in scientific exploration and experimentation. – Machines like the Mars Rover are essential for exploring the surface of other planets and gathering data for analysis.
Light – Electromagnetic radiation that is visible to the human eye, and is crucial for observing and understanding astronomical phenomena. – The speed of light is a fundamental constant in physics, playing a key role in theories of relativity and the measurement of astronomical distances.
Resources – Materials or assets that can be utilized to achieve a goal, often referring to natural or technological means in scientific contexts. – The search for extraterrestrial resources, such as water on Mars, is vital for the future of human space exploration.
Technology – The application of scientific knowledge for practical purposes, especially in industry and the development of tools and systems. – Advances in telescope technology have allowed astronomers to discover exoplanets orbiting distant stars.
Space – The vast, seemingly infinite expanse that exists beyond Earth’s atmosphere, where celestial bodies and cosmic phenomena occur. – Space exploration has expanded our understanding of the universe and our place within it.
Civilization – A complex society characterized by the development of cultural, technological, and scientific advancements. – The development of a space-faring civilization requires significant advancements in technology and international cooperation.
