Challenges of Interstellar Expansion

We rightfully focus on near term innovations which will make the world better, but today I want to zoom out and look at what problems have to be solved for humanity1 to survive and expand into space. I propose a broad plan for how this might be done, examine the steps needed to get there, and sort the existing challenges into those I consider mostly solved (or trending towards solved) and those I consider unsolved.

Note that by focusing on interstellar expansion in the long term, I am ignoring many near-term, critical problems. This is not because I am dismissive of these problem’s importance! However, when thinking on the scale of millennia, the priorities change significantly.

How did I categorize things? I decided to group different challenges as “mostly solved” versus “mostly unsolved”. I did this by asking the question: “If no special effort is made, does this problem seem like it will be solved ‘by default’ as part of a larger effort to explore the solar system?”. For example, though the cost to launch objects into space is pretty high right now, recent competition in space launch has made prices much more reasonable, and suggests that this problem is trending towards being solved on its own. This distinction seemed natural to me, since it is important to know which fields might limit interstellar expansion in the long term if nothing is done to accelerate them.

Determining if a challenge seemed solvable also depended on whether the task required fundamentally new technology, or simply a scaled up, sophisticated version of existing technology. In this framing, building (say) large information processing systems looks tractable since this task only requires scaled up versions of the supercomputers we use today. This is not to say that it will be easy to create these systems, but rather, that humanity already has completed important milestones and is on the path to reaching these goals.

These are not objective categorizations, and I encourage others to complete a similar analysis. Determining where there has been inadequate progress can help better direct efforts towards expanding into space.

The Challenges

It seems to me that humanity will need to complete the following challenges in order to expand beyond our solar system (they are approximately chronological):

  1. Manage existential risks
  2. Develop affordable transport into space
  3. Develop industry and communications in space
  4. Build self-sustaining colonies within our solar system
  5. Capture a large percentage of the sun’s energy
  6. Store large amounts of energy
  7. Build massive information processing systems
  8. Invent efficient means of interstellar travel
  9. Create self-sustaining spaceships for interstellar travel
  10. Develop general purpose techniques to adapt to new solar systems
  11. Agree on a unified system of ethics and apply it to our situation (this should happen sooner rather than later, but could, in theory, come at the end)

Some other things which would be nice to have but are not strictly necessary:

  • Highly sophisticated science and engineering
  • Effective coordination and governance
  • Cryonics
  • Brain Emulations (Em’s)
  • Controlled fusion

For the remainder of this post, I divide the listed problems into challenges we are moving towards solving and those which are not close to being solved.

Mostly Solved Problems

I label these problems “mostly solved” because the path to success is pretty clear, there are not too many unknowns, and there are no fundamental limitations in our way. Despite this, I am aware that an extraordinary amount of work still needs to go into these areas! In fact, we may not see some of these problems solved in our lifetimes. But these challenges look tractable given that we will have centuries to work on them.

Manage Most Existential Risks

See my post on existential risks. The overall conclusion I draw is that only AI risk and the risk of global totalitarianism seem like major, unsolved risks. More on these later. The other existential risks seem unlikely, solvable, or both.

Develop Affordable Transport into Space

Space transport has become much, much cheaper. As the technology continues to develop over centuries, space tethers, renewable fuels, and manufacturing in space will drastically reduce launch costs.

Develop Industry and Communications in Space

Satellites already support a substantial amount of communications in space, but these will need to expand throughout the solar system. Developing general purpose industry in space is a much larger step. This would require advances in robotics and the creation of space colonies. There will be a lot of new challenges to doing this in space, but the problems seem tractable with enough trial and error. Casey Handmer’s blog has more qualified, technical discussion about how this might be done than I could possibly provide.

Build Self-Sustaining Colonies Within Our Solar System

Space manufacture might already require colonies in space, but taking the extra step of developing resource independence from earth is crucial. This is because self-sufficient colonies can serve as a trial run for interstellar ships. Developing this capability will require solar energy, space mining, space manufacture, fuel-from-air, and yeast bioreactors to eliminate reliance on terrestrial support. Like with space manufacture, I do not see any major reason this can’t be achieved given enough time.

Capture a Large Percentage of the Sun’s Energy

To reach the next level on the Kardashev scale, we need to harvest much more of the suns energy. To do this, we can simply repurpose solar panel technology to create a Dyson swarm. Controlling the flight of the swarm or inventing better systems for energy capture are hard, but not infeasible.

Build Massive Information Processing Systems

Computers on Earth already have a large information processing capacity. Simply scaling up existing systems on Earth is fine for now, but in the very long term there may need to be a way to compute on more common substrates such as hydrogen or black holes. This was hard to categorize, since scaling up existing computer systems for space will be viable for a long time, while creating something which can compute using a black hole is much harder. I ended up deciding to put it in the mostly solved category since it is possible that scaling existing approaches to computation might provide all the capacity we need.

Create Self-Sustaining Spaceships for Interstellar Travel

Projects like the ISS are a good start but ships will need more protection from radiation and flying objects during interstellar travel. Lessons learned from developing self-sufficient colonies in our solar system will be essential to this project. However, this challenge is significantly harder than making independent colonies, since interstellar ships will need to protect against impacts and radiation while functioning for centuries. Regardless, this still feels like a solvable problem.

Highly Sophisticated Science and Engineering

I expect than science and engineering will keep progressing and I am confident that with centuries of work and solutions to the other problems on this list, this will not become a major binding constraint.

Effective Coordination and Governance

Yes, I know, lots of people have complaints about modern governance (often for opposing reasons). But some places actually can govern well. Centuries of building better institutions and testing out different forms of governance will produce superior systems of cooperation than today.

Problems Still to Solve

Here are the problems which I put into a distinct category from the solved problems. These seem much harder, either because there is not currently a clear path to success, or because we have so little direct experience to learn from at the moment.


There are many important questions in ethics which we haven’t even begun to answer, let alone come to consensus on. A few examples:

  • What moral value should be assigned to animals, AI’s, and Em’s?
  • How should we make decisions regarding population ethics?
  • Is it moral for society to continue and grow?
  • Should we seed new life elsewhere?
  • If we discover alien life, should we leave it alone?

These questions are more slippery than the engineering problems of the previous section. It is hard to determine which sub-problems need to be solved or if any progress has been (or will be) made, putting this problem into the unsolved category.


Here I am considering the difficulty of developing a system which can preserve a person and successfully reanimate them. This is different from the modern practice of cryonics, which focuses on preserving people while relying on future medical technology in order to revive preserved patients.

Cryonics has strong compliments with the development of Em’s. New scanning techniques, better understanding of the brain, and experimentation on different fixing techniques are all needed. Designing better legal infrastructures to support cryonics seems important too. The fact that there are so many unknowns in cryonics and the fact that ethical experimentation is extremely hard (who wants to be the first trial run for resurrection?) suggests that progress on this area could take much longer than the “mostly solved” challenges.

Brain Emulations (Em’s)

Brain emulations would be a huge innovation, allowing us to create many happy lives with fewer resources and provide something akin to artificial intelligence. Unfortunately, it seems like Em’s are very far off; there are many research questions which need to be answered before they become a reality. We know so little about how the brain works, and it is uncertain what degree of detail is required for an accurate simulation.

Even if they are built, they raise several important questions. First, how do Em’s change our systems of governance and ethics? Second, how can we prevent massive amounts of suffering from occurring once brain emulations exist?

The technical, legal, and ethical challenges brain emulations present indicate that progress towards creating Em’s will be very hard, and their invention will present new challenges.

Store Large Amounts of Energy

Though Dyson swarms can quickly generate lots of energy from a star, it might be hard to utilize all of it immediately. Instead, there should be a system to store the captured energy so that it can be used later, like a massive battery. It may be possible to store energy as chemical fuel, but this approach is limited by the total mass of chemicals we have access to. Rotating celestial bodies could potentially store large amounts of energy, but once again, this approach has scale limitations. The ultimate battery might be a black hole, but we have no way of determining if this is viable until we get near a black hole that we can experiment with.

Invent Efficient Means of Interstellar Travel

Relativistic time dilation means that passengers can reach the edges of the galaxy in only a few years of experienced time, but the fuel requirements and collision dangers are enormous. Methods of propulsion need to become more efficient at converting energy into thrust. Additionally, complicated route planning will need to be used to hasten the colonization of new worlds. Is it better to fly straight to a destination with a large amount of fuel? Or is it better to stop at many intermediate stars and refuel along the way? Is there an efficient way to slingshot around different stars to reduce fuel requirements?

Additionally, the longevity of the passengers is an important constraint, which is why the development of cryonics and Em’s would be very useful for interstellar travel.

At this stage, there are too many unknowns for us to make much progress on the logistics problem and many existing propulsion methods are too inefficient for interstellar travel.

Develop General Purpose Techniques to Adapt to New Solar Systems

It is hard to prepare for living in new solar systems when we haven’t fully adapted to our own solar system. Given our inability to prepare, progress on this challenge will have to wait on the solutions to many other problems.

AI Risk

The difficulty of mitigating AI risk has been thoroughly detailed in other places so I won’t reiterate here. My impression is that we do not have a good handle on what needs to be done or what success looks like (though there has been a lot of amazing work in this field). This is a particularly tricky problem because we must get it right the first time without complete knowledge of what an artificial general intelligence looks like.

Risk of Global Totalitarianism

In a previous post on existential risk, I noted that some form of global totalitarianism could prevent humanity from going into space and thus curtailing society’s potential. How do we prevent this sort of thing from happening? Like AI risk, we have little direct experience with this problem and cannot afford even a single failure. Adding to the complexity, certain forms of global governance and coordination seem essential. But how do we prevent global systems of governance from becoming too powerful? What does a transition to global totalitarianism even look like? Similar to other hard problems, the number of unknowns make this a distinctly difficult problem.

Controlled Fusion

Controlled fusion is nice because it might provide cheaper energy and better rockets. But more interesting is the possibility of using fusion for nucleosynthesis (e.g. making metals from hydrogen) since we probably will need heavier elements than hydrogen and helium to build anything interesting in the universe. Unfortunately, we don’t have any way of experimenting with the conditions needed to make heavy elements in the near term (which are much higher than the conditions required for simply producing energy), so this idea will remain on the back burner for quite a while.

Bonus: Unknown-unknowns

This analysis assumes certain basic facts about reality. But what if we discover something fundamentally new? For example, what if we really are in a simulation? Or figure out how to travel between multiple universes? Or travel into the past? Or harvest dark energy? Though these results are unlikely, they would entirely change the set of problems which need to be solved. We should be on the lookout for these kinds of paradigm shifts and be ready to change plans. Determining where and how to search for these revelations is quite hard.


Having identified some key challenges, which ones (if any) are the most important to work on right now?

Work on many of these problems are not possible in the present. For example, we can’t figure out how to store energy in a black hole until we can actually experiment on one (the nearest known black hole is approximately 1000 light-years away). However, these hard problems seem like they could benefit from more contemporary effort2:

  • AI risk
  • Global totalitarianism risk
  • Ethics

All of the problems I place in the “mostly solved” category would also benefit from further study and are very important to work on. But I find this categorization interesting because it suggests that some problems might be solved on their own as humanity works to explore the solar system, while others may need an additional push.

But let’s step back from the details for now, since I am sure that others will have different opinions on which problems present the largest challenge.

The most important takeaway from this post is that others should identify concrete challenges facing civilization in the long term. Having people consider and debate which problems are truly difficult (as opposed to problems which “merely” require massive engineering effort) will better direct our collective efforts.


1. Though I use the word “humanity”, I don’t imagine this process involving only modern humans. I think it is likely that AI’s and Em’s will be part of this project as well.

2. In addition, the other hard problems might benefit from more theoretical work.

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