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Imagine that two people who have the ability to read anyone's mind confront each other. Each one of them knows that the other is able to read minds and so they try to read each other's mind.

Let's call the two subjects Subject A and Subject B:

Subject A starts reading Subject B's mind, but simultaneously, Subject B starts reading Subject A's mind. Assuming that the process of thinking is finite, eventually the thoughts of Subject A or Subject B should lead to something concrete, but apparently, both of them would be reading each other's mind in a endless process that would require an infinite time to get it done. So the question is the following:

Would either of them be able to think something concrete after a finite amount of time?

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I agree with bowlturner. If you want a better answer than that you'll need to define your terms better. – MackTuesday Jan 29 at 18:24
"Gosh Subject A/B is an idiot..." – Jerenda Jan 29 at 19:06
You'll get the classic playground argument- "Did not!" "Did so!" "Did not!" "Did so!" ........ – cobaltduck Jan 29 at 20:01
Clearly this would result in a ... (wait for it).. stack overflow. – Jamie Hanrahan Jan 30 at 2:59
This isn't any different from reading your own thoughts. – djechlin Jan 30 at 3:15

11 Answers 11

Have you ever looked into a pair of mirrors that are facing each other? It looks like an infinite tunnel of mirrors, but because the mirrors aren't perfect the farther down the tunnel you look the more blurry it gets.

You could think of mind reading as looking into a window. While you are reading someone else's mind, your window becomes a one-way mirror. So two people reading each other's minds would mostly see the infinite tunnel. Of course, one-way mirrors aren't perfect, so you would still be able to see glimpses of what's hiding behind it, but it does make for an excellent defense against someone who is trying to read your mind.

This also provides for an interesting mechanic - the better you are at reading minds, the more perfect your mirror is, making it harder for your opponent to catch glimpses of what's behind it.

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It really depends on how telepathy is working. When you 'read' someone's mind, are you just reading the surface thoughts that they are concentrating on? Is that all you can read?

I expect mind reading to be a bit more than that. I also expect that if you are reading a mind, you also have your own thoughts and feelings floating around in there. So if two people are reading each others mind, they would see what the other person is thinking and feeling about different things as well as their reactions to what they might be finding in their own brain. There might be some 'mirror' qualities, but both of you would be standing between the two mirrors and able to see all of both of you.

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It depends on what "reading one's mind" means.

Are you interpreting what they're thinking at the same time? Because that's how what we do when we're reading a book. It's such a peculiar situation and it hurts my brain to just imagine it, but if the "thoughts" are read in the way we recall things by emulating our sensory input, then the interpretation of that data would be the first instance of an individual thought.

I feel like mind-reading wouldn't necessarily preclude the ability to have one's own individual thoughts aside, such as sensing, feeling, interpreting, etc, simultaneously.


  • Person A: Thinks of a banana.
  • Person B: Reads mind, sees banana, interprets data.
  • Person A: Reads mind, sees interpretation, interprets it.
  • Person B: Reads mind, sees interpretation of interpretation, interprets it.
  • Infinite loop, based off of Rob Watt's answer.


  • They enter a sort of "lock," one that doesn't loop. I wish I could put it into words but I seem to be unable to at the moment. I may revisit this later.

You can imagine them breaking out of the loop - all they have to do is be able to stop reading.

Your question is

Would anyone of them be able to think something concrete after a finite amount of time?

And I believe the answer to that is a) when the first interpretation occurs prior to the infinite loop, b) each individual's unique thoughts aside from the mind-reading, or c) the first thoughts and senses they exercise upon ceasing their mind-reading. One of those three.

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If one is reading the other's mind, meaning they are hearing the thoughts of the other person, then this seems like it would create an ever-increasing feedback the same way a microphone placed next to its speaker creates infinite feedback.

The two people would probably die.

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Or, maybe, pass out and stop reading each other's minds before their minds are overloaded so much that they die. – wizzwizz4 Jan 30 at 11:25

There is actually a mathematical proof that this cannot occur in a universe governed by statistics. (I'm trying to dig up the paper, but I can't seem to find it). You cannot have two beings that know about each other perfectly and simultaneously have freewill. If I remember the paper, this even holds true when the knowledge sought is statistical.

Accordingly, the only way for both subjects to read eachother's mind successfully is for one or both of them to give up perfect free will. They must be willing to accept that there are some things they cannot think about during the mind read.

As a trivial example, if both agree to think about a purple balloon, and then read eachother's mind, its easy for both to see a purple balloon. However, as one pushes with more and more pointed attempts to force a paradox (such as trying not to think about what the other is thinking), it gets more difficult to achieve an easy resolution.

Freewill may also be limited by imperfections. All it takes is one grumbly stomach and the process may collapse into a concrete image of a doughnut (thanks, Homer!) A light breeze might even be enough to create a slight decrease in freewill from Person A because they could not think of some particular thing while a light breeze was passing by. This might be enough to create a slight decrease in freewill from person B, because whatever person A was thinking about limited them. This could go back and forth until it collapses to both of them thinking of a concrete thing.

Of course it doesn't always collapse. There is a story of two warriors, with none their equal, meeting to settle their differences on the battlefield. Both warriors strode up, looked eachother in the eye, and then stood there for what must have been hours. Finally, both warriors smiled, and went their separate ways.

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Without being able to read the paper you're referring to, this seems off. For example, being unable to not think about what the other is thinking doesn't limit your free will any more than gravity making it impossible for you to fly does. – Rob Watts Jan 30 at 1:44
@RobWatts The paper (which I still cannot find) went into a statistical proof, but the basic idea is that if you have two entities, A and B, and each is omniscient (or in this case, able to read the key parts of the opposing entity's mind), and B wants to know what A is thinking, A is incapable of thinking of something except that which B observes them thinking. But if A wants to think of "everything B is not thinking of," the wording creates a logic paradox, which cannot be resolved if A has the freedom to think of "everything B is not thinking of." The paper demonstrated that this is true. – Cort Ammon Jan 30 at 1:51
in a statistical scenario as well, where B only has to know what A is thinking some probability of the time. There is a series of thoughts that A can have which cannot be known perfectly by B. The issue arises from the use of omniscience (or in this case, the ability to know the one thing that matters) and simultaneity with more than one omniscient entity. Its a slightly more mathematical formulation of the classic questions regarding God and omniscience. – Cort Ammon Jan 30 at 1:52
+1 for the general idea. -0.1 for the confusing and badly explained bit about free will. I rounded up because I was feeling generous. – wizzwizz4 Jan 30 at 11:28
@CortAmmon That totally depends on what "freedom of will" means. If you hold that two omniscient beings are still governed by the laws of logic, then of course, one being cannot hide something from the other being. In fact what if A wants to think of something he's never thought of before? That creates an identical paradox (as if he was truly omniscient, he's thought of everything). Point is, "perfect free will" (the ability to do anything, ungoverned by logic) is never possible. – Nathan Merrill Jan 30 at 13:29

this is a standard inducer/capacitor circuit. a thinks of A and b thinks of B. even assuming instantaneous interpretation, a now has B and b now has A. and of course, in the next 'pulse', we'll have a back at A (from b) and b back at B. you can modulate the frequency at which thought exchange happens by increasing the complexity of A or B. same as the circuit, a larger inducer makes the overall circuit an inducer and vice versa. so if a is much smarter or faster at reading b, the overall exchange is a reading b.

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This is quite a novel interpretation (I never would have thought to look at it that way myself), however, I don't really see how it answers the question of whether or not the subjects would continue to generate concrete thoughts. Perhaps if you could mention something about what happens when such a circuit is overloaded by feedback. – Chef Cyanide Jan 29 at 22:27

Well, I don't have much mind-reading experience, but I think I can relate to the subject through some basic object-oriented thinking.

Let's suppose that we have our 2 mind readers (Subject A & Subject B), and they each have a set of thoughts that are "active" in their minds (we'll ignore the exact content of the thoughts for the sake of the simulation).
In addition, we'll assume that since they have opened an active channel between their thoughts, that they have synchronized their mental clocks such that over the course of 1 unit of an arbitrary time scale (we'll call it "mind-time") they both refresh their own thought-base, as well as retrieve data from the thought-base of the other. In other words, it takes 1 unit of time ("mind-time") for each of them to first think some new thoughts, and then peek at the other's thoughts.

Assuming that this is the initial setup of the situation, there are two possible ways in which the scenario could proceed, depending on how the telepathic stream is set up:

The obtained thoughts are externally processed:
In other words: reading the other subject's mind allows each subject to access the other's thoughts, but they do not copy them over into their own mind. If this were the case, then the result of this bi-directional mind reading would effectively be a Vulcan mind-meld (insert Start Trek reference here), where each of them has access to all of the thoughts flowing between them in exactly 1 iteration (there are no redundant copies of each thought).

The obtained thoughts are internally processed:
In other words, in order to see the other's thoughts, each must first transfer them over to their own mind. If this were the case, the mind-melded state would be the same as stated above, except that each thought would exist in (T + 1) iterations, with T being the time in "mind-time" since the thought was first created. Consequently, the number of thoughts passing between them would grow exponentially with time, and unless each of them has a mind capable of processing an infinite number of thoughts, they will both eventually end up with splitting head-aches, as well as possibly some neuron-damage.

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As stated, it would really help if you were more specific about what is entailed in "mind-reading". But let's compare it to some real-world scenarios.

In normal speech, or when I'm typing like right now, I can be simultaneously thinking about the concepts I'm trying to convey, the speech/text synthesis, that Star Trek episode where Data rattles off a list of mental processes he was considering while kissing his girlfriend, how I should probably be in bed but am instead on Stack Exchange, the fact that I'd really like to get in an hour or so of Fallout 4 so I should type this quickly, and a number of other things that take less precedence like how my right foot has been resting on my left leg for quite a while and the pain in my left leg is increasing but isn't yet bad enough to necessitate moving my foot.

I would expect that reading someone's mind would be similarly non-linear, so A) you're not somehow reading every single little process in their head at once (it would be impossible for you to process that much data anyways unless you completely stopped processing any data in your own brain which would be a rather fatal way to read minds) and B) even if the entire mind-reading process turned into garbled nonsense, the rest of your brain would still be wondering whether that rumbling in your stomach is from the nachos you had at lunch or the giant soda you bought on the way home even though you know you're supposed to be cutting back. Like watching a camera that's watching the screen ad infinitum doesn't somehow cause your brain to hardlock. You just say "whoa, trippy!" then go back to finishing your soda because you'll cut back tomorrow.

I'm not sure how typical this is, but I commonly experience dissociated cognitive functionality, where one aspect of my thoughts appears as another entity in my head. At its simplest, it's just a bunch of voices screaming different things (or sometimes the same thing), with the most pressing urges being perceived as the loudest voices.

In a more interesting case, I often tell myself I need to accomplish some task. At that moment, my mind splits into three pieces. There's my self, then there's the responsible guy, then the lazy guy. In a heartbeat, all three of us know exactly how the conversation is going to play out. I tell the responsible guy I know he's right, but I agree with the lazy guy (who is at that moment telling me he already knows I'm going to slack off so stop bothering to play out the conversation that I'm currently having with the responsible guy who obviously is actually just a facet of me) and remark that it's stupid that I'm having a conversation with myself when I already know the lazy guy is going to remark that I'm going to remark that I agree with the lazy guy and am in fact going to just be lazy.

And then sometimes I'm lazy, sometimes I'm responsible, and sometimes I realize it's not even the right day and I don't actually have anything I need to do. Turns out that my own mind isn't capable of figuring out what it's going to do thirty seconds into the future with very good certainty, despite the fact that there are three voices in one head in complete agreement.

(FYI, the pain in my left leg just got to the point where it necessitated moving my right foot.)

Similarly, I would expect that the act of reading someone's mind which is reading yours would create instabilities because the two minds can't perfectly predict the actions of the other. So the other mind tells you a lie about your own thoughts which you believe as the other mind realizes it made a mistake, then the paradox is perceived differently by each mind, which amplifies the discrepancy. This forces the two minds to act with agency despite seemingly having no choice at all.

(And I just realized I spent more than 20 minutes writing this and won't get an hour to play Fallout 4 and am debating whether I should just go to bed or bother playing a little and risk going to bed even later and being really tired tomorrow which will make me less likely to finish my homework when I get back from work. These thoughts occur to me as I proofread once before hitting submit in another example of non-linear processing.)

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I would generally equate telepathy akin to one of the other senses. None of our senses "lock" our ability to think or process other information, listening to music doesn't block out thinking about dinner or what you're also seeing.

In the same way I imagine telepathy would be similar to a sense, you can "focus" on it for better detail, like actively listening and not letting yourself get distracted by other senses; but the telepathy itself would still be on it's own "channel" in the brain and as such you can shift your focus to other senses again.

If telepathy copied a brain state then I suppose a infinite loop could result as you suggest, but that would imply that "reading" a mind was literally placing all of the subjects thoughts in place of yours, sort of like a screwed up reverse mind control.

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Since our brain can concentrate on only one thing at a given time voluntarily, telepathy would be done voluntarily as well and in an attempt to read other person's mind when he/she's reading your, I believe you will be indirectly reading your own mind. As Rob Watts stated the example of 2 mirrors facing each other, it will be a mirror looking at it's own reflection in the other mirror facing it.

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Maybe it would be based on distance?

*The psychics sufficiently far apart wouldn't notice each other,

*psychics closer together would be able to make out a few levels of feedback before the signal blurs out,

*but psychics would have to get very close to each other before the feedback got strong enough to give one/both of them seizures

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