Konstantin Tsiolkovsky's Theory of Cosmic Eras and What the Radiant Era Would Actually Require
Konstantin Tsiolkovsky divided the future of the universe into four eras and placed in the last of them a humanity that has stopped being made of ordinary matter. He is remembered for the rocket equation he published in 1903. The cosmic eras are the reason he wanted the rocket in the first place. The destination was never another planet. It was a form of existence that does not need one.
The scheme is worth stating precisely, because it is usually quoted loosely and because its source is weaker than its fame suggests.
The four eras, and where the account comes from
| Era | Stated duration | What it covers |
|---|---|---|
| Era of Birth | Several billion years | The period humanity enters within decades of the 1932 conversation |
| Era of Formation | Hundreds of billions of years | Settlement and reorganisation of matter across the cosmos |
| Era of Human Flourishing | Hundreds of billions of years | The long stable maximum |
| Terminal Era | Tens of billions of years | Matter converted from the corpuscular to the radiant form |
The archive of Tsiolkovsky’s cosmic philosophy gives the fourth era in his reported words. Humanity “will consider it a good thing to put into effect the second law of thermodynamics in the atom, i.e. it will turn from corpuscular matter into radiant matter”. Having made that transition, humanity “becomes immortal in time and infinite in space”.
Here is the part that most summaries leave out. This four era scheme is not something Tsiolkovsky published under his own name. It comes from Alexander Chizhevsky’s record of a conversation the two men had in 1932, when Tsiolkovsky was 75. Chizhevsky wrote the memoir down in the early 1960s, and it first appeared in the journal Chemistry and Life in 1977. The most cited statement of the theory is therefore a recollection set down roughly thirty years after the conversation and more than twenty five years after Tsiolkovsky’s death in 1935. Anyone building on it should say so.
The name “Radiant Era” follows from the content rather than from that table. The fourth era is the one in which humanity becomes radiant, and the phrase has attached itself to the era since.
The mechanism Tsiolkovsky actually proposed
Tsiolkovsky was explicit about how a bodiless humanity could still be a humanity, and his answer was panpsychism. In The Monism of the Universe, published in 1925, he held that sensation is a property of matter as such. His formulation was that all is alive, and that we count as living only what has the capacity to feel sufficiently. He returned to it in The Will of the Universe. Unknown Intelligent Forces in 1928, and in his writing on the wandering of atoms.
That commitment does real work in his system. If feeling belongs to atoms, then converting a person into radiant matter does not destroy the person, because the sensitivity was in the constituents the whole time. The Radiant Era needs no theory of how organisation produces experience. It needs only redistribution.
It is also the weakest joint in the argument, and it is the reason the theory reads as mysticism to most physicists.
What replaces the panpsychist step
Panpsychism buys continuity at the cost of explaining nothing about why a brain has a unified point of view and a bucket of atoms does not. That objection is not new, and it is the same combination problem that contemporary panpsychist positions still face. This site examines the current version of it in Philip Goff on cosmopsychism and the challenge to functionalist AI consciousness.
There is a different route to the same conclusion, and it did not exist in 1932. Nicolas Rouleau and Michael Levin mapped the major theories of consciousness against unconventional embodiments and found that none of them requires neural tissue as such, which is set out in why major consciousness theories do not require neural tissue. What the theories require is a pattern of causal organisation. Organisation can be realised in more than one material.
That claim does the job Tsiolkovsky needed panpsychism to do, and it does it without asserting that atoms feel. A mind is preserved across a change of substrate when the causal organisation is preserved. It is not preserved because the parts were already sentient.
The difference matters for what would count as evidence. Panpsychism makes no prediction that could fail. Substrate independence makes several. It predicts that the relevant organisation can be specified, that it can be measured in a system that is not a brain, and that a system lacking it will fail the same tests a brain passes. Those are the tests the field is currently arguing about, surveyed in the current scientific consensus on AI consciousness.
What the Radiant Era would require in practice
Read charitably, the fourth era is a claim about three separable things, and only the first is settled.
The first is that a mind does not have to be made of the material that minds have so far been made of. That is the substrate independence claim, and it is the one with a live research programme behind it.
The second is that the organisation can be carried by something with far better tolerances for radiation, vacuum, acceleration and elapsed time than a body has. This is an engineering question. Max Tegmark’s treatment of consciousness as a state of matter, covered in Max Tegmark and perceptronium as a state of matter, is the closest thing to a physical framing of it, and Tegmark treats the central quantities as uncomputable for real systems.
The third is that turning matter into radiation preserves anything at all. Tsiolkovsky asserted it. Nobody has shown it. Radiation carries energy and information, and a description of an organisation is not the same object as the organisation running. That gap is the whole of the uploading problem, and it is unresolved.
Tsiolkovsky is worth reading here for a narrow reason. He is the first person to pair a physical route out of the gravity well with a reason to want mind rather than bodies at the other end, and he derived the rocket equation while holding that view. The route he worked out is real. The passenger he imagined is still a hypothesis, and the argument he used to defend it has been replaced by a better one he would not have recognised.