I look around. I see the world. However I can do that in my dreams. In my dreams I can fly - sometimes.

Is there any way of using mathematics or logic to prove to myself that anything exists except me? (cogito ergo sum).

Has knowledge progressed in any way since Descartes made his famous remark, that can convince me there is a real world out there?


In response to comments that this is not a world building question, or more suited to philosophy I will say the following:

  1. Clearly this is the ultimate Worldbuilding question.

In lucid dreaming, it is possible to do miraculous things like flying or even destroying mountains. If I am dreaming the world, I should in theory be able to build or rebuild it any way I want. If someone can show that I am not dreaming it, then there is no point in my embarking on this endeavour.

  1. There is a philosophy tag in Worldbuilding. I might as well use it.


I am aware that the concept of solipsism is not new. I am asking the considerable brain-power of this site for a reason that solipsism is not valid.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Jul 19, 2020 at 5:52

3 Answers 3



What Descartes was describing is called "Solipsism", which basically touches on the "hard problem of consciousness". $\space$

And in fact, Descartes’ "Cogito, ergo sum" ("I think, therefore I am") didn't go far enough.

Philosophers Pierre Gassendi and Søren Kierkegaard point out some further constriants.

Recognition that one has a set of thoughts does not imply that one is a particular thinker or another. In fact, you cannot even know that something called "I" exists as an individual with an identity. The claim becomes 2 claims: "x thinks" and "I am that x". The first claim is self-evident, but the second claim may not be true.

The only claim that is indisputable here is the claim that consciousness of some form exists.

Further reading:

  • $\begingroup$ I think I can claim that consciousness exists in addition to cognition. $\endgroup$ Jul 17, 2020 at 23:43
  • $\begingroup$ I incorrectly used the 2 interchangeably here. I have edited the answer to be more accurate. $\endgroup$
    – cowlinator
    Jul 17, 2020 at 23:44
  • $\begingroup$ “panpsychism” – $\endgroup$ Jul 20, 2020 at 1:43

No, we cannot prove or disprove the dream.

Any discrepancy will be ignored, discounted, or twisted to support the original conjecture. Folks will believe what they want to believe regardless of facts, evidence, or logic.

  • See both the trial of Gallileo and conspiracy theories for examples of folks believing what they want to believe in the face of overwhelming evidence to the contrary.

  • See the Mpemba effect for an example of a documented, real-life discrepancy everybody (including you and me) ignores or discounts every day.

    (Interestingly, I've never seen any conspiracy theories about it.... Hmmm.)

Generally, I find it's easier to sway most folks with emotion. You can convince without proof; show up with donuts and nice hair...and folks will provide their own rationalizations.

  • $\begingroup$ There is no discrepancy for Solipsism. If Solipsism is true, then there are no known facts about the real world outside of the mind; therefore it is self-consistent. The trial of Gallileo, conspiracy theories, and the Mpemba effect are unrelated to Solipsism. $\endgroup$
    – cowlinator
    Jul 20, 2020 at 1:47
  • $\begingroup$ @cowlinator glad you agreed with the second paragraph. The veer into Solipsism was not yet part of the Question when this answer was written...which is why it's not mentioned in this Answer. This answered the original question: Can the OP's delusion be punctured using logic? $\endgroup$
    – user535733
    Jul 20, 2020 at 2:10
  • $\begingroup$ I see. In that case, the answer is still no, the delusion cannot be punctured using logic, because all logic must be founded on an assumed a priori axiom as the starting point. But this cannot be done. This is called the "problem of the criterion." en.wikipedia.org/wiki/Problem_of_the_criterion $\endgroup$
    – cowlinator
    Jul 20, 2020 at 6:46

It appears that we have not found an answer to this question as answered here. In this article they state that they have proved that a classical computer cannot simulate our galaxy. This, I assume, does not exclude a quantum computer. I like to think that even if I were virtual I would still be as even the characters in video games exist even if they are only electrons in a computer.

  • $\begingroup$ Thanks, interesting article - looks worth reading. However I'm wondering whether you exist or computers exist, or the galaxy exists, or anything exists other than me. $\endgroup$ Jul 17, 2020 at 23:37
  • 1
    $\begingroup$ There are very few things that a quantum computer can do all that much faster than a non-quantum computer. Simulating large systems is not one of them. $\endgroup$
    – AlexP
    Jul 18, 2020 at 21:28

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