5 Thought Experiments That Will Melt Your Brain
Some science is too big, dangerous, or weird to happen in a lab.
Albert Einstein famously made use of “thought experiments” (i.e. grand “what-if” scenarios that would be difficult — if not impossible — to conduct in a lab setting) to form his revolutionary theories.
These theories, of course, were more than mere fanciful navel gazing; they were backed up with a lot of peer-reviewed math. However, the role that thought experiments played in lighting the path shouldn’t be downplayed. In fact, many great scientific discoveries were foretold by imaginary scenarios that were posited decades (sometimes millennia, as you’ll see below) before science found ways to test them.
Thought experiments help scientists find which questions they should be asking, even if they don’t yet have the tools to answer them. Many thought experiments delve into things like advanced physics principals (Schrödinger’s famous cat, for example), but there are also several which don’t require a PhD.
Here are five mostly math-free thought experiments to melt your brain just a little (some of which science has caught up with, some of which still prompt debate). They may be fun to opine on, but keep in mind that these bits of rhetorical whimsy may have very real ramifications should science ever catch up.
1) Did Captain Kirk Die in Every Episode of Star Trek?
Did you know that you died last night? Well, you did. But you were replaced with an exact replica that has all the same physical qualities — even the same memories — of the “you” that died. Don’t believe me? Well, it would be really hard to prove wrong.
That’s the basic concept of the “Swampman” thought experiment posited by the philosopher Donald Davidson in the late-1980s. In this experiment a man is traveling through a swamp and killed by a bolt of lightning, but — by sheer chance — another bolt of lightning strikes a nearby swamp and rearranges all the organic particles to create an exact replica (including all the memories and such) of the man who was killed. The new Swampman wakes up and lives the rest of the deceased man’s life.
Is this new Swampman the same man if the replica (not to mention the rest of the world) can’t tell the difference? That depends on what you consider to be the “self.” (This particular experiment also prompts many interpretations related to various many-worlds theories — there’s lots of navel gazing to be had all around.)
The whole Swampman scenario seems like an unnecessarily convoluted way to put forth this question. Especially when we have a far more approachable metaphor regarding replicas from science fiction: The transporter from Star Trek.
So, think of it this way — every time Captain Kirk went through the transporter, did he actually die? And was a replica of himself rebuilt on the planet below? As far as the rest of the universe is concerned (including the “new Captain Kirk”) nothing changes. The only person for whom anything is awry is Kirk 1.0, who was just unceremoniously killed.
This may all sound like interesting — if ultimately useless — pondering, but that may not always be the case. In the not-too-distant future, we may very well find a way to 1) teleport matter a la Star Trek or 2) upload our minds into digital form all Kurzweil-style. And it might be in our best interest to get a handle on these sorts of questions first — wouldn’t you want to know if you were committing suicide every time someone “beamed you up”?
2) All Head Starts Are Insurmountable
Some of the most famous and enduring thought experiments are the handiwork of an ancient Greek philosopher, Zeno of Elea (there is some debate as to whether modern science and mathematics has finally answered “Zeno’s Paradoxes,” but more on that below). Apparently Zeno had crazy spare time on his hands, which allowed him to come up with unnecessarily intriguing quandaries such as the famous “Achilles and the Tortoise”:
Achilles was the great hero of Greek lore who, according to Zeno’s experiment, decided to challenge a tortoise to a foot race. According to Zeno, Achilles was so confident in his turtle-racing abilities that he gave his opponent a sizeable head start. Of course, even with this handicap, the great Achilles — not to mention any able-bodied adult human — should easily overtake the tortoise and once again cement mankind’s dominance over the testudines, right?
Well, as it turns out, not so much. When seen through a particular logic filter, it is actually impossible for poor Achilles to ever win this race. Something sound funky here? First let us hear the problem as described by Aristotle from Physics: Book VI:
In a race, the quickest runner can never overtake the slowest, since the pursuer must first reach the point whence the pursued started, so that the slower must always hold a lead.
Let me attempt to explain. In this thought experiment, we assume that Achilles and the tortoise are racing at constant speeds: Very fast and very slow, respectively. At some point in the race, Achilles reaches the tortoise’s original starting point. But in the time it took Achilles to get there, the tortoise has moved forward. So, then Achilles’s next task would be to make up the new gap between himself and the tortoise, however by the time he did that, the tortoise would have again moved forward by some smaller amount. The process then repeats itself again and again. Achilles is always faced with a new (if smaller) gap to overcome. The takeaway: The great Achilles loses a race to a big dumb lumbering tortoise and no deficit is ever surmountable.
Of course, this isn’t reality. Any able-bodied human (let alone a top athlete) could easily overtake a slowpoke tortoise even with a (reasonably surmountable) lead. But although its conclusion is incorrect, you can’t simply negate the logic that got you there. You can read a fairly detailed rebuttal of the situation here that pins the apparent paradox to a misinterpretation of infinity. Meanwhile, adherents of quantum mechanics would say the solution is our inability to know where any object is for sure. But this shows how a thought experiment can help spur deeper investigation.
3) We Shouldn’t Actually Be Able to Do Anything
Here’s another one from our old pal Zeno, and it’s a thinker about the nature of motion (and, once again, there is some debate as to whether contemporary science has satisfactorily answered it).
First, imagine someone firing an arrow into a target a few dozen feet away. “Here’s another lovely example of elementary Newtonian physics working as it should,” you might think. However, when viewed through a very particular logical filter, this should be absolutely impossible.
Now, let’s say you just froze time at some point along the arrow’s trajectory (all Langoliers style, if you want to go super obscure). At that particular instant, the arrow is suspended in space in a single location. In any one instant of time, no motion is occurring. The arrow can only be in one place or the other and never in-between. So, how does it get from one instant to another if there is never a moment when it is in between the two places? Nothing should actually be able to change its position from one instant to the next.
Of course this isn’t really a problem. Things are moving willy-nilly all over the place all the time, despite a sound millennium-old logical argument about why they shouldn’t be able to. There are some top-shelf physics explanations about why movement actually is possible. But there remains some debate over whether Zeno’s paradoxes have truly been satisfactorily answered.
4) Reality Doesn’t Really Exist
We are all observing the world in the same exact way, right? Well, it’s becoming more and more obvious that that’s not actually the case. And the nature of observation and understanding is at the center of a problem posited by the 17th-century philosopher, William Molyneux.
Here’s how he articulated the problem in a letter to fellow professional ponderer, John Locke:
“Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt one and the other, which is the cube, which is the sphere. Suppose then the cube and the sphere placed on a table, and the blind man made to see: query, Whether by his sight, before he touched them, he could now distinguish and tell which is the globe, which the cube? To which the acute and judicious proposer answers: ‘Not. For though he has obtained the experience of how a globe, and how a cube, affects his touch; yet he has not yet attained the experience, that what affects his touch so or so, must affect his sight so or so…”
In brief, the question at hand is would a blind person who learned to distinguish basic shapes by touch be able to distinguish those objects when he suddenly received the power of sight? In other words, does information from one sensation translate to another, or do we associate them only in our minds? We actually know the answer to this one, so make your guesses now.
This question has prompted much debate since it was first posited centuries ago. But as it turns out, in the very recent history, medical science has progressed to the point where we can return vision to some people and therefore answer this question—and the answer is no, people are not able to translate tactile feel into visual information.
But here we see the value of thought experiments: The contemporary experimenter would probably have never thought to even attempt this real-world experiment had philosophers not wrestled with it over the previous centuries.
5) If a Google Car Has to Kill Someone, Who Should It Be?
Imagine this: You are on a bridge overlooking a set of trolley tracks and you notice that five people have been tied down to the tracks by a devious (and presumably moustache-twirling) villain. Then you see an out-of-control trolley barreling down the tracks that will certainly kill the unfortunate people unless someone intervenes. Oh no!
In this scenario, you are too skinny to stop the trolley. But you realize that you are sharing your bridge with a gigantic fat man, who — if you were to push him in front of the trolley — would have enough girth to stop the trolley and save the five bound people, though he will certainly be killed.
You are now faced with the following options: 1) Do nothing and the five people will die, or 2) Push the fat man in front of the trolley and sacrifice him for the five people. In either scenario, are you at all culpable in these innocent people’s deaths? Should the law make any distinction?
This quandary has been adapted a number of ways, including versions in which the five people (or the fat man) have been replaced with a reprehensible villain. The story prompts a lot of navel gazing about culpability and hierarchy of values with little practical implications . . . until recently.
This question is of very immediate concern as we share roads and highways with an increasing number of driverless vehicles. And, to be sure, these vehicles (or rather, their software developers) will face similar scenarios, but ones in which the outcomes will be far from as certain as they are in the original problem.
Should a driverless car lunge into another lane in order to avoid a small child who just ran into the street? Should it make a full stop to avoid hitting a galloping deer, knowing there is a speeding car right behind it? Do these decisions change if the driverless vehicle happens to be a prison bus transporting convicted murderers, or perhaps an ambulance with a pregnant woman heading to the hospital to give birth to twins? If someone is killed or injured in these scenarios, who should be held accountable?
This is one of those times when problems descend from the clouds to the ground. Even if the technology isn’t here quite yet, it couldn’t hurt to start talking about it.
Read more: The Dilemma of Teaching Ethics to Self-Driving Cars.
Originally published at www.pcmag.com.
