How could you tell if you were a brain in a vat? If you were but a hunk of grey matter plugged into a souped-up mainframe of the future, running the latest version of ‘World In A Can’, say, would it be possible for you to know this for a fact? In modern terms, is there a way to discover if the world and its objects are but the wi-fi ‘smoke’ and fibre-optic mirrors of a super-cloud?
This question and its historical precursors have challenged the greatest of minds for generations. From the teasing shadows of Plato’s ancient cave to Rene Descartes’ seventeenth century grapple with his supernaturally ingenious deceiver. Descartes’ meditations led him to his unassailable truth – he thought, therefore he was. But where exactly was he?
The difficulty involved in answering brain-in-a-vat (BIV) type questions is that it is always possible to quibble and shift the goalposts. For example philosophers have since argued that Descartes’ logic is not as watertight as it first appears, as he takes the very concept of the ‘self’ for granted (self-evident, as it were!); it would be more prudent to rewrite his conclusion as: ‘There is doubt, therefore there must be a doubter.’
This certainly appears a stronger assertion but there is already the danger that what we have gained in abstraction we have lost in clarity, for the question now becomes: who is the doubter? Once we muddy the familiar integrity of the self this way we leave ourselves open to further concessions of identity that confuse the issue completely. Radical doubt has this tendency to unravel everything we take for granted. But could we catch Descartes’ demon, or Plato’s shadow caster, on an off day? And if so, could we outwit them? There is a slim chance.
Imagine we live in the year 3000. Neuroscience has advanced to the stage where it is possible for scientists to remove a sleeping subject’s brain, place it in a wired-up flotation tank, boot up a simulated universe, and trick the waking subject into believing that nothing is amiss. We can leave the plausibility of this technological timeline to futurologists to argue over – such is the infinite flexibility of the thought experiment.
In order for the simulation (or deception) to succeed it must manifest the same laws and principles which govern the physical world. This means it should be deterministic and predictable on macroscopic scales, but only as far as the limits of chaos and probability theory allow it to be in reality. In other words the flip of a bitcoin must be measurably random, and the flap of a binary butterfly’s wings in a northern winter should contribute to the formation or non-formation of a hurricane in a southern summer.
It follows that our subject – let’s call him Banks, considering the mass of data he is up against — must be granted freedom of thought and behaviour. For if the experiment determined and predicted his every move there would be nothing new to learn and the whole project could arguably be considered a colossal waste of funding. Banks’ challenge is to find a way to prove he has been placed inside the simulation and to record the details of his success or failure upon his return. With this is mind we can assume that the current social and economic state of the world has been funnelled into Banks’ virtual analogue so as to preserve continuity the moment he wakes up.
This is where things get tricky. Because our thought experiment incorporates the unpredictably chaotic dynamics of many real-world systems, the emergence of diverging events becomes unavoidable once the simulation is up and running. The principle of sensitivity to initial conditions, or the impossibility of computationally replicating the world with infinite precision, make this divergence inevitable.
On the morning of his transfer what Banks sees on TV when he wakes up will be near-identical to what we would see on our own screens at the same time. As his day progresses however, small variations will inevitably accumulate in complex systems such as the financial markets and the weather. His own freely chosen behaviour will also precipitate cascades of unpredictable consequences. Initially these differences would minimally affect the synchronous appearance of both worlds. But an alternate global history is already evolving to the point where, given enough time, the differences between them could in principle exceed their similarities. Not that Banks could know this unless he, quite literally, thinks outside of the box.
Ingenuity and luck are key to his challenge. We typically assume that scientists make progress solely through observing ready phenomena and then theorising about them. The better the agreement between theory and observation, the truer the model of reality which emerges (as with Newton’s laws of motion). It can also prove a fruitful exercise to construct a model that seems impossible to test immediately but can be confirmed or refuted at a later time when technology or circumstances allow it (as with Einstein’s general theory of relativity and its prediction of the bending of light rays by massive objects like the sun, proved after observing shifts in apparent positions of nearby stars during a total eclipse).
Pushing the speculative envelope further than this, though, leads theoreticians of all schools of thought (including theology), back to the realm of untestable metaphysics where turtles are just as likely to keep the earth afloat in space as the sun’s gravitational force. But this doesn’t mean there is nothing to be gained by chasing a sufficiently rational dream. The Oxford physicist David Deutsch has pioneered research into quantum computing after assuming the existence of multiple universes. In 1985 he wrote The Fabric Of Reality in which he describes how a working quantum computer could validate this extravagant notion. His theory runs along these lines: quantum computers are capable of distributing stupendously enormous calculations across a potentially infinite number of universes. Some of these calculations would be impossible to complete in ours alone, given its comparatively limited ‘memory’ resources. For example, factoring the enormous integers used to encrypt banking details online into their constituent primes would take longer than the age of the universe for any modern computer.
So if a quantum computer succeeds in solving a problem that requires more time, space, and energy than is available in the whole of our universe it must be getting it from somewhere else, hence we have the multiverse. To date quantum computing is still in its infancy: the highest number correctly factored into primes so far, using a method called Shor’s Algorithm, is 21 (3×7). It is important to note that Deutsch’s interpretation of quantum theory is just that – an interpretation, but it may one day be indirectly supported by new discoveries. If the Large Hadron Collider (LHC) in Cern detects extra dimensions as predicted by string theory then his theory will gain credence, not least because the conceptual distinction between a parallel universe and an extra dimension is an issue as knotty as string theory is ‘loopy’.
Returning to Banks’ mission it is fair to acknowledge, in this special case, that he has the advantage of already possessing a realistic estimation of the technological and theoretical limitations of the BIV project. This will enable him to formulate testable predictions, and he may not have to wait too long before the cracks in his reality begin to show. Before agreeing to take part in the experiment he was scheduled to accompany a crew of astronauts on an expedition to the star Vega, 26 light years away in the constellation of Lyra, to explore the possible planetary system discovered around it. Now he will have to take a synchronous virtual tour which will – indeed must – gather exactly the same data as its physical counterpart in order to keep his illusion consistent.
And though Banks will now not be visiting Vega fully bodied, as it were, the plan is for his brain to accompany the real mission, along with the BIV hardware; this way the crew can pre-emptively update the structure of his digital universe as they extend the known boundaries of their own. This should ensure Banks’ world does not run out of scenery much the same way cartoons portray characters racing too quickly from one frame to the next, only to find themselves floundering against an unfinished background.
The launch is scheduled a month to the day Banks goes into the vat, and for the first few weeks everything goes as planned: events in the two worlds coincide closely enough not to cause undue concern. However, come the morning of the actual launch an unforeseen storm forces the crew to delay it for another two weeks. On the face of it this hitch should not necessarily threaten the success of the BIV project, but you may already see where this is heading: in Banks’ inner world there has been no storm, in fact the weather couldn’t be better. On the day of his launch crisp blue skies and a gentle breeze greet him and the other astronauts as they step onto the launch pad.
Banks and his team are soon cruising in cyberspace towards the Vega system, two weeks ahead of the flesh-and-blood crew. As each day passes they enter uncharted interstellar territory which puts a heavier strain on the resources of the BIV database. An informational black hole is looming and, like a real one, once they cross its event horizon the laws of physics will beak down, in this case because the BIV media gallery has nothing to show them; not until the physical crew reach Vega and take the first real pictures of the extrasolar neighbourhood.
The decisive moment arrives when Banks peers through a porthole for his first glimpse of the outermost planet and sees…nothing! He has broken through the ‘information barrier’ and is faced with an inky blackness where there should be a vast crescent shimmering into view. It’s as if the BIV memory address reserved for the delayed images remains a string of empty zeros — the standard binary code for the colour black — and is being interpreted as an empty cosmos by the program as it runs in real time.
This confounding observation leads Banks to correctly surmise that he is now inhabiting an artificial universe; the evidence, or lack of it, speaks for itself (it is left as an additional exercise to work out if he can also convince his crew of their purely digital reality, and in fact whether he should convince them of it in light of his findings. But this is another can of philosophical wormholes). With the experiment over Banks’ brain is returned to his body and he jubilantly awakens with his success fresh in his mind.
Of course, the canny programmers at the BIV facility could have stymied his mission in advance by devising error-correction routines to prevent telling glitches surfacing in the virtual world (a case of deus ex machina codex?’). He could have had a problem opening the porthole screen during the whole of his expedition or, better still, a deliberately induced storm in his world could also have delayed his mission for two weeks, long enough to preserve consistent transfer of fresh data between the two worlds. Such mishaps may still give Banks cause to suspect higher level intervention, but his suspicion would be a poor substitute for certainty.
This raises an interesting question: could it be that error correction programmes are already regulating the progress of our own scientific discoveries? For instance, after the LHC in Cern was switched on in 2008 there were teething troubles – understandable given the unprecedented scale of engineering that went into its construction. But what if those hitches, which delayed the discovery of the now-confirmed Higgs particle, were due to similar delays in a ‘proper’ universe? Maybe our discoveries were deliberately held back until the correct data was collated in a world that was already simulating ours, one which had to deal with teething troubles and glitches with its own LHC. What if, like a mythical infinitude of turtles carrying the Earth, it is ‘virtual worlds all the way down’ (and all the way up too)?
As reasonable as this quibble sounds the scope of any BIV programmers’ anticipations would always be restricted by the unpredictability built into the simulation and subsequently manifested by it; in effect both sides would necessarily remain evenly matched. All we (and Banks) would need is vigilance and opportunity: sooner or later we would get lucky.
There is a substantial consolation to be had if a monstrous multiplicity of virtual worlds does indeed abound. And that is there need not be a great deceiver, or BIV team, keeping us entombed in a world without portholes or ‘Dodgsonian’ looking glasses. Deutsch’s vision of cross-cosmos computation implies that the observations we make in this world correlate positively and negatively with those occurring in others; so perhaps we are all unwitting geniuses blindly and reciprocally shaping each others’ perceptions in every possible universe, preventing any and all attempts at finding those special windows revealing unfinished moments in unfinished worlds. We ourselves, our thoughts and experiences, could be the rational glue holding reality together – and apart. So if we are not being fooled by quasi-divine intelligences better ‘in the know’ than we are, our reality is neither more nor less concrete than any other we could posit — no matter how radically we may doubt it.
If Banks were here he’d disagree of course, but as a character in a thought experiment he never had the choice to think otherwise. And if we are no more real or free in thought and behaviour than he is, then that would make us billion-dollar brains in billion-dollar vats in a world offering zero incentive to spend wisely!
First published as “Billion Dollar Brains: Billion Dollar Vats” on Academia.edu