The Scientific Indian

Matter Displacement Detector, ahoy!

A few days back, I happened to watch a few scenes of an old Star Trek episode. There was the usual fare of beam-me-ups, tea materializer, mother levitator, etc. And then there was the Matter Displacement Detector. That piqued my interest. This device allows the Star Trek crew to check if there was someone at a place in the past. Presumably, the said person left eddies in the spacetime continuum that can be detected to ascertain the presence of the person in question. Naturally, I started wondering if the physics behind it is plausible in some way. It was not explained in the episode, so we can only speculate picking our clues from the almost childlike imagination of Star Trek creators (I say childlike in both the good and the bad sense: good when it pushes the envelope on what we think is possible, bad when it exhibits astonishing level of scientific ignorance).

So, what could possibly be a Matter Displacement Detector. Linguistic analysis tells us that it is a device with which we can detect if the cheese was moved by analyzing molecular movement (don’t they have this at hotel room fridges already?). It is clear that detection in Star Trek’s case is not by way of chemical analysis of leftovers, but by detecting the displacement of matter. That, to put it charitably, is bollocks. Unless – oh, dare I say -, unless, Star Trek crew was using a whole new kind of scientific knowledge, whereby they can routinely solve many-body problems for small masses like molecules. A many-body what?

A many-body problem. This is an appropriate name in physics for the problem where you try to figure out the past (or future) location of, say, the red ball on the snooker table by working out all the collisions it had (will have) with other balls. This is essentially an impossible problem to solve as time goes by (think Butterfly effect, Statistical methods were invented precisely for this reason when physicists realized one cannot figure out stuff about gases by working out what individual molecules do).

If we suspend disbelief and accept that Star Trek crew do indeed have little gadgets that solve such apparently intractable problems – given all that Star Trek crew do, this is a small thing to ask -, then, hey, Matter Displacement Detector is a fine thing. I don’t want to give an impression that I am put off by Star Trek, quite the contrary. Evidently, I find it engaging. Star Trek has helped nudge many, especially kids, to take interest in science. This is a good thing (except, when it is not).

That said, if modern crime scene investigation is any indication, we have got pretty good at detecting traces of someone at a place. We are made of watery goo and much of it leaks from us all the time leaving our slimy traces everywhere we go. If the Star Trek crew had opted for straightforward forensic analysis, I suppose they would have more success in their investigation (obviously, the producers of the show may not have succeeded in their investment, which lies at the heart of why Star Trek crew do things the way they do).

Enough. Here’s a fine story from COSMOS magazine I ran into while researching (heh) for this blog post.

I hope to see the new Star Trek movie this weekend. Hear good things about it.


  1. #1 Ian
    May 19, 2009

    If you ever see the new Star Trek movie, please blog on it!

  2. #2 CqnuckRob
    May 19, 2009

    Perhaps the Federation had developed homeopathy into a science and were just detecting the memory of the formerly there matter in the “water” of spacetime. Was there ever an episode where Bones said “Dammit Jim, I’m a homeopath, not a doctor!”

    On the other hand, your answer of bollocks seems totally adequate.

  3. #3 rpsms
    May 19, 2009

    In my mind, if they have working teleporters, and something that can make tea which you can drink out of some lint and string, then they have solved the problem.

    Then again, if they can make tea you can drink, why can’t things escape the holodeck?

  4. #4 James Sweet
    May 21, 2009

    Wait, so is the many-body problem provably unsolvable, or is it just thought to be unsolvable? Sorry for my ignorance here…

    Heh, on a side note, I had flashes of the final novel in David Brin’s second Uplift trilogy… they talk about how Galactic society had long ago given up on actually solving any equations, because their computers were so fast/had so much storage that it was easier to just do very fine linear approximations of everything. Of course, Brin himself characterized the Uplift and Uplift Storm trilogies as “an unapologetic space opera”… but it made me think of that. Given unlimited computing power (yes, I know, just run with me here for a second) it’s relatively easy to approximate a solution to the many-bodies problem to within a certain amount of precision, right? You just compute the instantaneous forces on all the bodies at a particular time, apply that as if it were a constant force for a miniscule amount of time, lather, rinse, repeat… So, maybe the MD detector has to compute more data points than there are particles in the universe in order to get a reasonably precise result… but hey, it’s Star Trek!

    Or is all of that nonsense to begin with?

  5. #5 Ian
    May 21, 2009

    “Then again, if they can make tea you can drink, why can’t things escape the holodeck?”

    That’s the difference between tea and tease….

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