I want to remind myself how and when the polarity of the Neutron flow is reversed... in Star Trek :-)

That is, I'm asking in which episodes of Star Trek someone does someone suggest they "reverse the polarity of the neutron flow", or some sentence close enough to that one.

(I'm guessing this only happens in TNG but not sure even about that.)

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    – Valorum
    Commented Oct 8, 2014 at 21:46
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    You? I'd say you cannot :P But seriously, since Neutrons are electrically neutral, this is indeed a, shall we say, curious endeavour...
    – Zommuter
    Commented Oct 9, 2014 at 9:18
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    You can certainly reverse the polarity of the flow. Commented Oct 9, 2014 at 19:57
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    @FrancisDavey: You're thinking about reversing the direction of the flow. Calling it the polarity is stretching the semantics too much, I think.
    – einpoklum
    Commented Oct 9, 2014 at 20:40
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    @einpoklum When I first saw The Three Doctors I parsed it as "reverse the polarity of the (neutron) flow". Certainly works in my dialect of English. Polarity of a flow seems to be a concept fairly widely used in the sciences, see eg geology.gsapubs.org/content/33/1/e87.full (used of water flow). Commented Oct 9, 2014 at 21:37

3 Answers 3


I think you may be confusing Star Trek for Doctor Who. The phrase "reverse the polarity of the Neutron flow" is something of a catchphrase of the Third Doctor...

To the best of my knowledge, a whole lot of things get their polarities reversed in Star Trek (including shields, magnetic constrictors, magnetic probes, etc) but never a neutron flow.


If you're sure it's Star Trek, there is one case of all the "reverse the polarity"s that contains all the pieces, and yet never uses the phrase. The scene it occurs in also popped into my mind upon reading the question, but because the phrase is never used it took a while to find.

In TOS 3x14, That Which Survives the magnetic seal on the fuel flow is ruptured. (A few minutes later, Scotty also refers to it as a "magnetic flow". However, we know from later series that the "fuel" is actually antimatter, which could be neutrons (and yes, antineutrons exist!))

Scotty goes into the "service crawlway" (also known as a Jefferies tube) in order to seal the rupture, during which time Spock performs an analysis on the ship to try and figure out why the ship felt different to Scotty.

The results are that the Enterprise was reassembled by a molecular transporter slightly out-of-phase, and Spock tells Scotty that "reverse polarity should seal the incision".

The specific image that came to mind upon reading the question was this scene:

Scotty sealing the magnetic rupture with a reverse-polarity tool

So yes, Scotty reversed the polarity of that tool in order to seal the rupture on the fuel/antimatter/possibly antineutron flow.

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    I'd +2 you if I could...
    – einpoklum
    Commented Oct 9, 2014 at 5:15
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    This is a bit of a reach. You can have a +1 for effort :-)
    – Valorum
    Commented Oct 9, 2014 at 11:35

There is another case of "reversing the polarity" in TOS: Who Mourns for Adonais. Said before Pertwee ever did!

SPOCK: Ready to reverse polarity, Mister Sulu?

SULU: Computed and standing by to generate, sir.

SPOCK: Activate all units.

  • Weclome to SFF.SE! Great find!
    – Skooba
    Commented Oct 18, 2016 at 15:08

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