In the episode The Sound of Drums. when Martha, Jack and The Doctor find the TARDIS, after Martha comments that the TARDIS sounds like it was sick.

The Doctor: It can't be. No no no no no. It can't be.
Martha: Doctor, what is it?
The Doctor: He's cannibalized the TARDIS.
Jack: Is this what I think it is?
The Doctor: It's a paradox machine.

It sounds like Jack had encountered a Paradox Machine before as he is about to identify it. I am wondering if it's a part of a Time Agent's Basic Training to know what a Paradox Machine is and how to identify one, or has he encountered one before? (I haven't seen a lot of Torchwood).

  • The real clue about what Captain Jack thinks would be in his next line of dialogue. The Doctor has realized it's a paradox machine, but Jack might have thought of something else. This is just as possible as him believing it's a paradox machine. Though it would be nifty if he did know it was a Paradox Machine.
    – a4android
    Aug 2, 2019 at 2:36

1 Answer 1


There is no post 2005 tv canon episodes that expand on paradox machines, or on the technical aspects of Jack's time as a Time Agent. Much of Jacks past is shrouded in mystery. The shows both play this up to show Jack as a Doctor Lite.

Additionally, there is nothing to suggest that a paradox machine is unique to TARDI instead of being a possibility of any time machine.

  • 3
    Being a former Time Agent, he must have been trained in what a paradox machine does or at least might be capable of. He's not certain, which implies that he hasn't actually encountered one before.
    – Chahk
    Mar 3, 2015 at 16:42
  • Also, in the First Season Jack seemed to know how to fly the TARDIS and how to repair it and add stuff, like Machro Kinetic Extrapolator
    – Kmi
    Mar 11, 2015 at 16:22

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