Are There Problems That Computers Can't Solve?

13 906 Áhorf 1,4 m.

All about Hilbert's Decision Problem, Turing's solution, and a machine that vanishes in a puff of logic. MORE BASICS:
Written with Sean Elliott SeanMElliott/
Graphics by William Marler
Audio mix by Graham Haerther
I'm at
on Twitter at tomscott
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and on Instagram as tomscottgo


  1. Tom Scott
    Tom Scott
    4 mánuðum síðan

    Both my co-author Sean and I are worried that we're oversimplifying here -- but then, this series is called The Basics!

    1. MammutBerlin
      5 dögum síðan

      But what if a machine could develop a way to decide for itself that "this loop causes my system to crash. It is a paradox and therefore gets discarded"? Wouldn't that be a kind of solution to this problem? To discard it because its not solveable?

    2. TheSpaceChicken
      19 dögum síðan

      Yes yes

    3. kostas melissourgos
      kostas melissourgos
      2 mánuðum síðan

      My 6month series of lectures in 6minutes 😂😂

    4. Alyn Sterner
      Alyn Sterner
      2 mánuðum síðan

      Mr Scott, that program will halt because eventually it will run out of possibilities (the head machine) since you can put (theoretically) any program into the Turing machine, then it would halt because the machine would run out of available questions unanswered

    5. Claudia
      3 mánuðum síðan

      For me, a complete computer science noob, but still a little interested, you didnt oversimplify at all! You did break it down into something I understand and I thank you for it! It's very interesting to hear you explain these things.

  2. Mohamad Kaddoura
    Mohamad Kaddoura
    4 klukkustundum síðan

    I never understood this paradox. The program that you call "opposite" reads it self to check if it ever loops. But we know that at some point the program opposite loops whether the input allows it to do so or not. What I am trying to say is the "opposite" program has the ability to loop therefore putting it in itself will halt.

  3. Rory LeBlanc
    Rory LeBlanc
    17 klukkustundum síðan

    could i run skyrim on a turing machine?

  4. Sharkycat109
    2 dögum síðan

    Tom Scott: Everything can run on a Turing Machine! Me: *But can it run Crysis*

  5. davida1hiwaaynet
    2 dögum síðan

    "It halts in a puff of logic!" I love this and will start using it in my industrial control software work. :)

  6. Sam Hew
    Sam Hew
    2 dögum síðan

    Maybe this is completely idiotic, but why add the opposing module? If machine can determine yes or no, is that not the goal here?

  7. NonStopYousef
    3 dögum síðan

    1:11 i thought my tablet was freezing

  8. dontcheckmychannel
    3 dögum síðan

    But people are just computers. Different computers, sure. But computers all the same. And I can look at Opposite and tell it will keep contradicting its own answer. So I'm not sure that actually works.

    3 dögum síðan

    Why does a piece of buttered toast, always land buttered side down. And if you tape it to a cat, whould it still land butter side down ?

  10. Austin goodwyn
    Austin goodwyn
    4 dögum síðan

    Ent shy doong

  11. Spectr3x
    4 dögum síðan

    Yes. My life.

  12. ATA1289
    5 dögum síðan

    Yes, Is this a cat?

  13. Patrick Hector
    Patrick Hector
    7 dögum síðan

    I mean at the end of the day, all you're proving with the last example is that it's sometimes impossible to have a "perfect" solution to every problem. In the same way that you can divide any number by 0 except itself, you could probably feed Opposite any code except it's own. How is an imperfect solution the same as having no solution, and even if it is the case why is anyone surprised that you can't, say, materialise a 1 kilo dodomeat sandwich made on Saturn in yiur hands just by closing your eyes and wishing for it? You can phrase that circumstance as a "problem", and of course it cannot be solved- that's demonstrable by simply closing your eyes, wishing for an impossibly exotic sandwich and opening your eyes to discover it never apparated.

  14. Troy Lewis
    Troy Lewis
    8 dögum síðan

    Romantic human compatibility.. fact!

  15. Zach Ovftjrdchdc
    Zach Ovftjrdchdc
    8 dögum síðan

    Just dont make it do the opposite. No paradox computers have been saved... Thank you... thank you

  16. Mr. Mquaider
    Mr. Mquaider
    8 dögum síðan

    Tom loves dunking on technology.

  17. Alexander Van Den Hoogen
    Alexander Van Den Hoogen
    9 dögum síðan

    the answer to this question is 42 though

  18. karateswords
    9 dögum síðan

    Simplifying equations

  19. MR. UNKNOWN Gamer
    MR. UNKNOWN Gamer
    10 dögum síðan

    After watching this video i think i know nothing about computers. I cant understand a single word 😭.

  20. vector 7
    vector 7
    10 dögum síðan

    Try asking my pc why a windows xp pc can render things it can't

  21. MySerpentine
    10 dögum síðan

    Was that an H2G2 reference?

  22. Cryosen
    10 dögum síðan

    "there are no systems that can tell u if a code halts or not" *angry compilernoises*

  23. Gurjinder Singh
    Gurjinder Singh
    11 dögum síðan

    "Alexa, What is Donald Trump going to Tweet tomorrow?" *Infinite Loop*

  24. ZombieDasher
    11 dögum síðan

    yes, my parents divorce

  25. Ragnar Þór Guðmundsson
    Ragnar Þór Guðmundsson
    11 dögum síðan

    Ah yes, the oñosecond

  26. Vítek Špirek
    Vítek Špirek
    11 dögum síðan

    Though logically speaking we are talking about something that has the output either as 01 or 10, as in loop+no loop, or no loop+loop. So the opposite would be the same thing just the other way around?

  27. Julian Danzer
    Julian Danzer
    11 dögum síðan

    that is just conservation of complexity - no computer will ever be capable of running a complete physics simulation of itself detailed enough for the simulation to run either

  28. Julian Danzer
    Julian Danzer
    11 dögum síðan

    computers can't solve problems that cannot be solved that's mathematically insightful I just wish people would stop trying ot use that as an argumetn for why computers are limited which is a realyl complicated question because well, if something is literally unsolvable then not being able to solve it isn't really a drawback it's just obeying hte baisc laws of logic

  29. Jay Paans
    Jay Paans
    12 dögum síðan

    I'm not buying this ONE BIT. Don't agree? BYTE me.

  30. Terrain
    13 dögum síðan

    In my opinion this is solvable though, opposite will go into an infinite loop if halts says it’ll halt, therefore there’s a point in opposite when it won’t halt, therefore halts should say no, it doesn’t halt - In this input, opposite will halt, but it won’t *always* halt

  31. JavaJumper
    13 dögum síðan

    int main() { while(1) { } return 0; }

  32. Im On Da Web
    Im On Da Web
    14 dögum síðan

    i just did something like that code on a calculator from guess and check like an hour before i watched this

  33. Colin
    14 dögum síðan

    6:50 I mean that’s assuming you give opposite the output. It would normally finish thinking about it and ... well halt.

  34. Fredtheunicorn3
    14 dögum síðan

    7 minutes and 58 seconds of Tom saying words I understand in sentences that mean nothing to me. Cool, I’ll watch the whole thing

  35. Mule The Donkey
    Mule The Donkey
    14 dögum síðan

    but the computer can't make an *instant change.* So it WOULD halt, then start again. *It'd just be a bumper-to-bumper program. So there isn't a paradox* Laws of *physics*

  36. Pleb James
    Pleb James
    15 dögum síðan

    Have you seen the final episode of "The Prisoner"? The protagonist causes a supercomputer to self destruct by asking it "Why?" But that always got on my nerves because surely the rational answer is "because"

  37. klawypl
    15 dögum síðan

    can someone tell me how the hell that paradox works cuz when i think of it it just works, if you run "opposite" in "opposite" then you just get opposite ancer, like if "halt" can halt at some point it cannot be looping on its own so... opposite will be alvays looping so that mean output will be that it halts (sinxe it is oposite) :|, so... where is paradox? [edit:] typed that other way around

  38. Jonathan Clark
    Jonathan Clark
    15 dögum síðan

    Also computers can’t generate random numbers

  39. eNBee
    15 dögum síðan

    When you said paradox the only thing I could think of is GLADoS from Portal

  40. Adrian Khorany
    Adrian Khorany
    16 dögum síðan

    1 divided by 0.... NEVER SOLVED