Rodney Brooks

Robots, AI, and other stuff

How Much Things Can Change

This post is about how much things can change in the world over a lifetime. I’m going to restrict my attention to science, though there are many parallels in technology, human rights, and social justice.

I was born in late 1954 so I am 65 years old. I figure I have another 30 years, with some luck, of active intellectual life. But if I look backward and forward within my family, I knew as an adult some of my grandparents who were born late in the nineteenth century, and I expect that both I will know some of my own grandchildren when they are adults, and that they will certainly live into the twenty second century. My adult to adult interactions with members of my own direct genetic line will span five generations and well over two hundred years from the beginning to the end of their collective lives, from the nineteenth to the twenty second century.

I’m going to show how shocking the changes have been in science throughout just my lifetime, how even more shocking the changes have been since my grandparents were born, and by induction speculate on how much more shock there will be during my grandchildren’s lifetimes. All people who I have known.

Not everything will change, but certainly some things that we treat as truth and obvious today will no longer seem that way by early next century. We can’t know exactly which of them will be discarded, but I will put up quite a few candidates. I would be shocked if at least some of them have not fallen by the wayside a century from now.

How Has Science Changed Since Relatives I knew were born?

My oldest grandparent was born before the Michelson-Morley experiment of 1887 that established that the universe was not filled with aether, but rather with vacuum.

Even when all four of my grandparents were first alive neither relativity nor quantum mechanics had been thought of.  Atoms with a nucleus of protons and neutrons, surrounded by a cloud of electrons were unknown. X rays and other radiation had not been detected.

The Earth was thought to be just 20 to 40 million years old, and it wasn’t until after I was born that the current estimates were first published.

It was two months after my father was born that Edwin Hubble described galaxies and declared that we lived in one of many, in our case the Milky Way. While my father was young the possibility that some elements might be fissile was discovered, along with the idea that some might be fusible. He was an adult back from the war when the big bang theory of the universe was first proposed, and it is only in the last 30 years that alternatives were largely shouted down.

In my lifetime we started out with nine planets, went down to eight, and now have observed thousands of them in nearby star systems. Plate tectonics, which first revealed that continents were not historically statically in place and explained both earthquakes and volcanoes were first hypothesized after I was born.

Crick and Watson determined the structure of DNA just the year before I was born. I was a toddler when Crick hypothesized the DNA to RNA translation and transcription mechanism, in school when the first experimental results showing how it might work came in, and in college before it was mostly figured out. Then it was realized that most animal and plant DNA does not code for proteins, and so it was labeled as junk DNA. Gradually over time other functions for that DNA have been discovered and it is now called  non-coding DNA. All its functions have still not been worked out.

I was in graduate school when it was figured out that the split of all life on Earth into prokaryotes (cells without a nucleus) and eukaryotes (cells with a nucleus) was inadequate. All animals, plants, and fungi, belong to the latter class. But in fact there are two very distinct sorts of prokaryotes, both single celled, the bacteria and the archaea. The latter were completely unknown until the first ones were found in 1977. Now the tree of life has archaea and eukaryotes branching off from a common point on a different branch than the bacteria. We are more closely related to the unknown archaea than we are to bacteria. We had completely missed a major type of living organism; the archaea on Earth have a combined mass of more than three times that of all animals. We were just plain unaware of them–they are predominantly located in deep subsurface environments, so admittedly they were not hiding in plain sight.

In just the last few years we have realized that human bodies contain ten times more cells that are bacteria, than they contain cells that have our DNA in them, though the bacterial mass is only about 3% of our body weight. Before that we thought we were mostly us.

The physical structure of neurons and the way they connect with each other was first discovered when my grandparents were already teenagers and young adults. The rough way that neurons operate was elucidated in the decade before my birth, but the first paper that laid out a functional explanation of how neurons could operate in an ensemble did not occur until I was already in kindergarten (in the “What the Frog’s Eye Tells the Frog’s Brain paper”). Half the cells in brains, the glia, were long thought to be physical support and suppliers of nutrients to the neurons, playing no direct role in what neural systems did. In the second half of the twentieth century we have come to understand that they play a role in neurotransmission, and modulate all sorts of behavior of the neurons. There is still much to be learned. More recently the role of small molecules diffusing locally in the brain have been shown to also affect how neurons operate.

What is known in science about cosmology, physics, the mechanisms of life, and neuroscience had changed drastically since my grand parents were born, and has continued to change right up until today. Our scientific beliefs have not been static, and have constantly evolved.

Will science continue to change?

It seems entirely unlikely to me that my grandchildren will one day be able to say that up until they were born scientific ideas came and went with accepted truth regularly changing, but since they were born science has been very stable in its set of accepted truths.

Things will continue to change. Below I have put a few things that I think could change from now into the beginning of the next century. I am not saying that any particular one of these will be what changes. And I would be very surprised if more than half of these will be adopted. But I have selected the ideas that currently gnaw at me and do not feel as solid as some other ideas in science. Some will no doubt become more solid. But it will not surprise me so much if any individual one of these turns into accepted wisdom.


  • There is no dark matter.
  • The Universe is not expanding.
  • The big bang was wrong.


  • There is a big additional part of quantum mechanics to be understood.
  • String theory is bogus.
  • The many worlds interpretation is decided to be confused and discarded.


  • We discover that there is a common ancestor to archaea, bacteria, and eukarya, a fourth domain of life, that still exists in some places on Earth–and it is clearly a predecessor to the three that we know about now in that it does not have the full modern DNA version of genetics, but instead is a mixture of DNA and RNA based genetics, or purely RNA, or perhaps purely PNA, and has a simplified ancestral coding scheme.
  • We discover life elsewhere in the solar system and it is clearly not related to life on Earth. It is different, with different components and mechanisms, and its abiogenesis was clearly independent of the one on Earth.
  • We detect life on a planet that we can observe in a nearby solar system.
  • We detect an unambiguously artificial signal from much further away.


  • We discover the principles of a rich control system in plants that is not based on neurons, but nevertheless explains the complex behaviors of plants that we can observe when we speed up videos of them operating in the world. So much for electro-centrism!
  • We move away from computational neuroscience with a new set of metaphors that turn out to have both better explanatory power and provide tools that explain otherwise obtuse aspects of neural systems.
  • We find not just a different metaphor, but actual new mechanisms in neural systems of which we have not previously been aware, and they become dominant in our understanding of the brain.
How to have impact in the world

If you want to be a famous scientist then figure one of these out. You will redirect major intellectual pursuits of mankind. But, it will be a long lonely road.


One comment on “How Much Things Can Change”

  1. I am a few years older than you and often think along these lines but it seems to me that the pace of basic scientific discovery has slowed down. The 50 years before we landed on the moon seem so rich in paradigm explosions compared with the 50 years after. I am gobsmacked that SpaceX gets kudos for recapitulating engineering that was commonplace in the 60’s. The greatest medical advance in my lifetime was getting people to stop smoking. But I hope you’re right.

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