The Von Neumann Problem - Where Are All The Aliens?

It was in 1948 when John von Neumann wrote his paper "The general and logical theory of automata," in Cerebral Mechanisms in Behavior: that his interest in self-replicating machines first became apparent. Von Neumann was a mathematics genius and contributed to the fields of quantum mechanics, mathematics and applied mathematics, writing 150 papers during his lifetime.

However it is his theories surrounding self-replicating computers that are the most widely known and have been at the centre of many debates over the years.

Perhaps what is most remarkable about von Neumann's early work, is that he began it before the discovery of DNA and therefore was not fully aware of how living planetary organisms replicated.

Von Neumann theorised many types of self replicating probe, however it was his work on kinematic self-replicating machines that really caught the imagination.

The theory was that a machine would be able to replicate itself with just four elements, that is to say:

• A constructor that can build a machine, when fed explicit blueprints of that machine.

• A blueprint copier,

• A controller that controls the actions of the constructor and the copier.

• A set of blueprints, explicitly describing how to build a constructor, a controller, and a copier.

As you'd imagine this simple theory has captured the imagination of science fiction writers and cosmologists alike. In fact we could say; it has put the proverbial cat among the pigeons.

Fermi's Paradox - The First Set Of Pigeons

The Italian physicist Enrico Fermi postulated the argument that seeing as there are around 200-400 billion stars in the Milky Way alone, and that several tens of millions of those stars are similar to our own sun. Plus many of those stars are billions of years older than us, the argument for intelligent extra-terrestrial life is extremely strong.

Yet with all of those stars, and all of those planets circulating those stars we have had no concrete evidence of alien life, this came to be known as Fermi's Paradox.

Stirring The Paradox

In 1981 American physicist Frank J. Tipler claimed to have solved Fermi's Paradox. Tipler used the von Neumann probes to do so, the argument is explained like so:

If indeed life is replicated throughout the galaxy, and suns that are billions of years older than ours have intelligent life orbiting them.

Then the chances of us being the first civilisation to think about creating von Neumann probes is slim to none. In fact the galaxy would be crawling with these machines by now, making them impossible to miss.

Ergo . . .

There are no aliens.

This argument is pretty hard to shake, because indeed we may launch (within the next 5-15 years) our own version of (non-replicating) von Neumann probes.

Project Dragonfly was a competition launched by the Initiative for Interstellar Studies and was attended by teams from four qualifying universities. The winning results showed that we are not far off being able to accelerate a small probe to around 10% light speed (10% c) using an earth bound laser and a solar sail.

So if we are close to doing it after evolving on a circa 4.5 billion year old planet, surely we can't be the first?

Sagan's Response

The renowned astrophysicist Carl Sagan, along with his colleague William Newman, responded to Tipler's argument by saying that he had vastly underestimated the replicating powers of such machines.

That in fact von Neumann probes would be so destructive in their self replicating abilities, that any intelligent species would not make them, and would destroy any they found on sight.

Further arguments supporting Sagan's response are that such machines could be built in with a kind of Bladerunneresque limited lifespan, whereby they would self destruct after a certain amount of time.

Other arguments say that with simple radio transmissions, machines could monitor each other and not self-replicate if they were in a certain amount of cubic parsecs of each other.

Touching The Void

For me there is a final argument which hasn't really been explored, and that is that such probes do exist, but they do not self-replicate. Or at least if they do, do not pass on their self-replicating abilities.

Which means that their progress across the galaxy would be a lot slower than the original half a million year estimation by Tipler, and they are on their way here and at some point we will see one.

If one has been sent from say 51 Pegasi, a star located about 50.1 light-years from earth, then a probe travelling at 10 percent the speed of light would take 500 years to get here, and that's if they were lucky enough to point it exactly in our direction.

That's a big if, because at that distance just a fraction of a degree this way or that, could mean the probe misses us by trillions of miles.

I for one believe that interstellar travel is very difficult, not just for us, but for everyone, for the simple reason that the laws of physics that we have discovered are universal. Add to that that we are very small, and the universe is very big, then it is quite easy for alien civilisations to live within (astronomically) close distances and still not bump into each other.

Hopefully we'll launch our own von Neumann probe soon and point it at Proxima Centurai, where we have discovered a possible rocky planet orbiting close to the dwarf star. At four light years distance it is the closest one to us, however at the proposed speeds it will take over 40 years for the probe to reach its destination, and then a further 4 years for the signals it sends back to be received on earth.

So hopefully I will live well into my nineties to see the results! Either that or I'm hoping we discover someone else's von Neumann machine pretty soon!

We are not alone, of that I am (almost definitely) sure!

WHAT ABOUT YOU; WHAT'S YOUR TAKE ON FERMI'S PARADOX AND VON NEUMANN PROBES? WHY HAVEN'T WE SEEN ALIENS YET? DO YOU BELIEVE THEIR EXISTENCE IS INEVITABLE, IF SO, IS OUR BUMPING INTO EACH OTHER EQUALLY INEVITABLE?

AS EVER, LET ME KNOW BELOW!

Sources

Kinematic Self-Replicating Machines - MolecularAssembler.com

Self-replicating spacecraft - Wiki

John von Neumann - Wiki

Fermi paradox - Wiki

Frank J. Tipler

The Artificial Self Replication Page - Mosheshipper.com

Project Dragonfly - Initiative For Interstellar Studies

51 Pegasi - Solstation.com

Title image: Greg Rakozy on Unsplash

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