Deep Thoughts: The Stomach in a Jar Problem

Many throughout history have wondered about the relationship between mind and stomach. Imagine, if you will, that your body had been almost completely destroyed. Imagine still, that whatever destroyed your body left your stomach remarkably unscathed, and that we put your stomach in a vat. But this vat is a very special kind of vat: It can give you stomach all the physical and chemical signals it would have had if the stomach had stayed in your body, and when your stomach does something, the vat reacts just as your body would. Your stomach could be kept alive like that for quite a long time, perhaps indefinitely. 

Imagine still that we could build a robot that functioned in all the ways your old body functioned, but that it did not have a stomach. In place of your stomach, there was a complex interface that took whatever signals the robot-body would give a stomach and transferred those signals to the vat. The vat would translate everything to your stomach, and anything your stomach did that affected the vat was in turn transmitted back to the interface in your fake body. The interface was so advanced that if your robot body ate food, it would travel down the esophagus, merge with the interface, and eventually the semi-digested result would go into your robot small intestines.

Here is the question, one that has baffled philosophers for decades:

1. How do you know that “imaginary” scenario isn’t the case right now? How do you know you are not just a stomach in a vat, and what you think is your body is just a robotic shell with some advanced interface of the type described? 

True story! This really has baffled them for decades. For millennia, if you consider the problem as a variant of the famous shadow-food problem in Plato’s cave (highlighted, in something similar to its classic form during this scene, from The Matrix). There are many related questions that are also interesting to entertain. For example: 

1. How does this possibility affect our understanding of knowledge claims? Can you be sure that you ate protein, just because your stomach is producing the digestive juices it would produce if you had actually eaten protein? The response of the organ would be the same whether you had eaten protein or robot-you had eaten protein, or, worse, computer-simulated-you. It seems like you should be able to save knowledge claims by reducing them to “confidence” claims, but that won’t work, because there is no basis upon which to be confident, as your experiences would all be the same in the real-world or the jar-and-robot world.
2. Given the possibility that you are just a stomach in a jar, how does that affect ethical decision making? Many people, for example, do not eat meat for ethical reasons. However, if there is no good reason not to think that your entire conception of meat is simulated, and not real, then there is no good reason to think that your eating “meat” causes anything to die