Talk:3254: Detector

The deluxe edition of the machine probably has "Detected/Not detected" lights for each of those items. I would guess its cost would be significantly higher. 47.248.235.170 21:39, 3 June 2026 (UTC)Pat

To whoever wrote the initial transcript: the title text should not be included. Barmar (talk) 21:57, 3 June 2026 (UTC)

It doesn't even detect a vacuum? Useless thing, showing not even a vacuous truth. 2A02:590:1402:2E01:102F:245D:DD57:1937 22:15, 3 June 2026 (UTC)

It also has zero false positive Rtanenbaum (talk) 23:17, 3 June 2026 (UTC)

Not necessarily. We are told that it never says "No" when it should be saying "Yes", which suggests that there will be no false negatives. If were trust that assertion.

But we aren't given any assurance at all (even a simple nodding statement with no provability behind it) that the machine will not continue to say "Detected" even if it somehow really shouldn't. Should it do so, it would be be a false positive. Even though various other existential problems might be more important to anyone around who might care about it, at that point. 81.179.199.253 23:45, 3 June 2026 (UTC)

My point is that there is no circumstance that the machine would exist where all of the items it detects are no longer present i.e. the case of a false positive just cannot happen. Rtanenbaum (talk) 03:03, 4 June 2026 (UTC)

Failing to detect states would be a particularly worrying prospect for people in the USA. --2A10:D586:3E93:0:CC7B:253E:A0AA:2FA9 08:00, 4 June 2026 (UTC)

I would claim the assertion about false negatives is incorrect. It's impossible for a true negative to be displayed by the machine, so it's enough for a single malfunction that ever makes the machine display a negative to get a 100% false negative rate. 2A00:79E0:2820:8:9966:10CC:BAF3:62E 09:13, 4 June 2026 (UTC)

Not necessarily true. If the machine is set up to scan a volume of space that includes its own green lamp, then it should be recording the matter, light, etc of that green lamp, so no question that it would (self-reinforcingly) be detecting the thing that says it is detecting things, and never .

But if it's monitoring a distinct space a few feet away, and (because of handwavy occurances that I'll leave to your imagination) that whole area of space gets changed/replaced/displaced by some utter shielded void of some kind, that could result in there now being a true negative result to report, whether or not the machine can or will do.

Which is moot if there's no way for the Not Detected lamp to light (there's no way for the circuitry to light it... there is no circuitry attached to it... it doesn't even have a bulb... there's an ED209 standing nearby to aggressively shoot anyone who ever looks like they're trying to install the necessary bits to overcome any or all the deliberately omitted ways for the lamp to even apparently be lit up...) the instances of it being negative/"Not" might be ruled out by even the weirdest quantum effects (there just is no solution to the universe's wavefunction that results in the other light being lit), even in the apparent philosolhy of "if anything is possible, it must happen in an infinite universe".

What it comes down to is whether the possibility of the light ever lighting is (unlike the unspoken possibility of a bubble of non-existence spontaneously forming or passing over the right spot) sufficiently unlikely within the xkcd-verse to make it less unreliable (for negative reporting) than all the other detectors. Like how many times have neutrinos passed through the neutrino detector without being detected (very high false-negative; false-positives may also happen when someone cannonballs into the pool during the pool-party), but less so for more reliable experimental detectors. 82.132.239.222 12:26, 4 June 2026 (UTC)

If the Not Detected light were to turn on, it would be detected, and would thus turn off, providing opportunity for oscillation. But at what frequency? 173.188.194.118 12:56, 4 June 2026 (UTC)

Perhals (Planck time)^-1 if it was immediate (and no silly 'speed of light' delay within itself, or other processing delays like collating/multiplexing the various inputs for all the different sub-detectors prior to choosing which light to light) plus could detect an intensity of light as low as the NDL emits. (Imagine that it only triggers when a supernova-level of light is detected? It may be a very insensitive detector, by what degree of detectable-stuff it can measure, even though it is also sensitive to a wide variety' of different detectable-stuffs, at least once they get beyond some arbitrary individual thresholds for their respective quality of detectability.)

Though the Detected-light would already be detected (as light and mass and electrical fields and everything else), by the same assumption of its light-sensitivity (assuming the NDL isn't purposefully dimmer than the DL, exactly enough to prevent this NDL-detection), so if the lighting of the light is relevent to a Detection event, then Detection events are assured regardless of whether one starts from a Non-Detection Event baseline (immediately flips to being a Detection, then stays there). 82.132.239.222 15:15, 4 June 2026 (UTC)