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==Explanation== | ==Explanation== | ||
{{incomplete|This page was detected recently. Don't remove this notice too soon.}} | {{incomplete|This page was detected recently. Don't remove this notice too soon.}} | ||
| − | [[Ponytail]] and [[Hairy]] are showing [[Cueball]] | + | [[Ponytail]] and [[Hairy]] are showing [[Cueball]] various detectors in this room, which include an {{w|electron microscope}} (which showers a target with electrons and images their reflections), an XRF scanner (i.e. "{{w|X-ray fluorescence}}", which hits a target with high-energy X-rays and measures the spectrum of the fluorescence they emit) and a {{w|mass spectrometer}} (which measures the mass-to-charge ratio of ions to determine the proportions of particular isotopes present in a sample). |
| − | + | These are all out of frame, from any comic panel, but the piece of equipment that we see is a machine of indeterminate purpose, simply labeled "Detector" and with the most prominent feature being the words "Detected" and "Not Detected" written in seperate lines next to two lights, one above the other, the first of which is glowing green. This, they claim, is their most sensitive detector, with nothing in the subsequent conversation indicating that it is anything other than a reasonably reliable (though also esoteric) piece of scientific equipment. | |
| − | + | Normally, detectors have a designated detecting job, such as the aforementioned off-panel devices which can provide complex imagery or a profile of a sample's composition. Some, such as smoke detectors, merely detect the presence or absence of smoke and (usually as a safety device, rather than a piece of scientific equipment) only needs to alert the user if there is smoke identified. | |
| − | One possible explanation for a scenario that might cause a "Not Detected" result could be a {{w|false vacuum}} decay event which, depending on the particular details of the true vacuum, could alter or overwrite the fundamental laws of physics as we know them. This would indeed be "bad" for, among other things, the persistence of life on Earth. | + | The sensitivity of a detector can vary. [[3249: Neutrino Project|Neutrino detectors]] try to detect neurinos, but neutrinos are very hard to measure so can only give data for a very low number of the actual neutrinos that could possibly have been measured. Devices being more sensitive means that they can detect (and perhaps quantify) far lower quantities/magnitudes of the targeted phenomena, and/or more of those that might otherwise have been missed. |
| + | |||
| + | For the device in this comic, however, "more sensitive" seems instead to mean that it is sensitive to more ''different'' things. To quote Ponytail, it detects "gas, dust, particles, light, radio waves, gamma rays, protons, neutrons, electrons, fields, forces, events, potentials, or states", which runs almost the entire gamut of things that ''might'' be detectable, and leaves little room for there being any situation in which none of the aforementioned items are there to be detected. The constituent particles of the machine itself would be present for detection, and exist in "states" and have "potentials" relative to each other, assuming that the machine is sensitive enough (in the traditional sense) to detect them, and the detection area that it observes includes at least some parts of itself. | ||
| + | |||
| + | Regardless of that, some or all of the wide range of the detectable things are also going to be present, in detectable quantities, in practically ''any'' location that they might feasibly be monitoring, and even if it was capable of discerning nuances (such as relative quantities, differing proportions or even which detectable thing is the most significant presence in any given set of measurements) its output boils down to merely whether it has (or has not) detected ''something'' from its extensive list of detectables. Which, by any reasonable assumption, would seemingly mean that it is only ever going to need to indicate that it has "Detected" things, leaving the possibility that it has "Not Detected" things as an unlikely result to display instead. | ||
| + | |||
| + | Cueball points this out, and Hairy admits that it ''has'' been continuously lit this way ever since they turned it on. Ponytail is audibly shocked in response to Cueball asking what would happen if the light labeled "Not Detected" were to shine. Hairy explains that such a thing would be pretty bad. The presumption being that, if that were to happen, there would have to be no matter, light, forces, etc. within the detector's established range of detection. (Though it could be interpreted as the dectector not working properly, the contextual reactions of those most familiar with it seem to show a faith that the detector is still likely to be faithfully summarising the true status.) | ||
| + | |||
| + | One possible explanation for a scenario that might cause a "Not Detected" result could be a {{w|false vacuum}} decay event which, depending on the particular details of the true vacuum, could alter or overwrite the fundamental laws of physics as we know them. This would indeed be "bad" for, among other things, the persistence of life on Earth. However, in such a scenario the detector itself would presumably also be rendered at least inoperable, and possibly non-existent, with a similar fate befalling any observer who might have been around to witness the changing output. | ||
| − | + | There might still be an unavoidably built-in uncertainty. [[1132: Frequentists vs. Bayesians]] was a previous comic featuring a more specific detector that tells whether the Sun has gone nova (also a very bad scenario, even if less cosmically extreme), but incorporates some risk of conveying an inaccurate output. (But, again, these people familiar with this device do not seem to feel the need to consider it as potentially inaccurate, like that.) | |
| − | The title text states that the machine has the lowest {{w|false | + | The title text states that the machine has the lowest {{w|false negative}} rate out of any other machine. If it never has stated a negative (i.e. explicit non-detection, being a different scenario from a power-outage or indicator failure that just causes the Detected light to stop being lit) then it can never have been ''wrong'' about it being negative. There is also the potentially independent notion that the "Not Detected" light is just set up ''never'' to be lit, [[2236: Is it Christmas?|playing the odds]]. |
| − | + | It is not made clear to us under what circumstances would legitimately result in a negative state being indicated. Nor, apart from the concerned expectations of Hairy and Ponytail, whether the detector will then necessarily correctly state that. It might still fail to properly respond to the new situation, just continuing to provide an incorrect indication that all is 'normal' (on the assumption that the device both still exists ''and'' functions, under such extraordinary circumstances), and result in a {{w|false positive}} instead. But, for many possible reasons, the chances and consequences of any displayed false positive may easily bear no relation to that of a false negative. i.e, the "Not Detected" light could always be 100% accurate (leading to Hairy's "bad" scenario), yet any given cessation of detections often fails to stop "Detection" from being indicated (being just as "bad" but, as the icing on an already possibly unpalletable cake, also with the Detector being functionally wrong). | |
==Transcript== | ==Transcript== | ||
Latest revision as of 05:16, 5 June 2026
| Detector |
 Title text: No other experiment has a lower false negative rate. |
Explanation[edit]
|
This is one of 44 incomplete explanations: This page was detected recently. Don't remove this notice too soon. If you can fix this issue, edit the page! |
Ponytail and Hairy are showing Cueball various detectors in this room, which include an electron microscope (which showers a target with electrons and images their reflections), an XRF scanner (i.e. "X-ray fluorescence", which hits a target with high-energy X-rays and measures the spectrum of the fluorescence they emit) and a mass spectrometer (which measures the mass-to-charge ratio of ions to determine the proportions of particular isotopes present in a sample).
These are all out of frame, from any comic panel, but the piece of equipment that we see is a machine of indeterminate purpose, simply labeled "Detector" and with the most prominent feature being the words "Detected" and "Not Detected" written in seperate lines next to two lights, one above the other, the first of which is glowing green. This, they claim, is their most sensitive detector, with nothing in the subsequent conversation indicating that it is anything other than a reasonably reliable (though also esoteric) piece of scientific equipment.
Normally, detectors have a designated detecting job, such as the aforementioned off-panel devices which can provide complex imagery or a profile of a sample's composition. Some, such as smoke detectors, merely detect the presence or absence of smoke and (usually as a safety device, rather than a piece of scientific equipment) only needs to alert the user if there is smoke identified.
The sensitivity of a detector can vary. Neutrino detectors try to detect neurinos, but neutrinos are very hard to measure so can only give data for a very low number of the actual neutrinos that could possibly have been measured. Devices being more sensitive means that they can detect (and perhaps quantify) far lower quantities/magnitudes of the targeted phenomena, and/or more of those that might otherwise have been missed.
For the device in this comic, however, "more sensitive" seems instead to mean that it is sensitive to more different things. To quote Ponytail, it detects "gas, dust, particles, light, radio waves, gamma rays, protons, neutrons, electrons, fields, forces, events, potentials, or states", which runs almost the entire gamut of things that might be detectable, and leaves little room for there being any situation in which none of the aforementioned items are there to be detected. The constituent particles of the machine itself would be present for detection, and exist in "states" and have "potentials" relative to each other, assuming that the machine is sensitive enough (in the traditional sense) to detect them, and the detection area that it observes includes at least some parts of itself.
Regardless of that, some or all of the wide range of the detectable things are also going to be present, in detectable quantities, in practically any location that they might feasibly be monitoring, and even if it was capable of discerning nuances (such as relative quantities, differing proportions or even which detectable thing is the most significant presence in any given set of measurements) its output boils down to merely whether it has (or has not) detected something from its extensive list of detectables. Which, by any reasonable assumption, would seemingly mean that it is only ever going to need to indicate that it has "Detected" things, leaving the possibility that it has "Not Detected" things as an unlikely result to display instead.
Cueball points this out, and Hairy admits that it has been continuously lit this way ever since they turned it on. Ponytail is audibly shocked in response to Cueball asking what would happen if the light labeled "Not Detected" were to shine. Hairy explains that such a thing would be pretty bad. The presumption being that, if that were to happen, there would have to be no matter, light, forces, etc. within the detector's established range of detection. (Though it could be interpreted as the dectector not working properly, the contextual reactions of those most familiar with it seem to show a faith that the detector is still likely to be faithfully summarising the true status.)
One possible explanation for a scenario that might cause a "Not Detected" result could be a false vacuum decay event which, depending on the particular details of the true vacuum, could alter or overwrite the fundamental laws of physics as we know them. This would indeed be "bad" for, among other things, the persistence of life on Earth. However, in such a scenario the detector itself would presumably also be rendered at least inoperable, and possibly non-existent, with a similar fate befalling any observer who might have been around to witness the changing output.
There might still be an unavoidably built-in uncertainty. 1132: Frequentists vs. Bayesians was a previous comic featuring a more specific detector that tells whether the Sun has gone nova (also a very bad scenario, even if less cosmically extreme), but incorporates some risk of conveying an inaccurate output. (But, again, these people familiar with this device do not seem to feel the need to consider it as potentially inaccurate, like that.)
The title text states that the machine has the lowest false negative rate out of any other machine. If it never has stated a negative (i.e. explicit non-detection, being a different scenario from a power-outage or indicator failure that just causes the Detected light to stop being lit) then it can never have been wrong about it being negative. There is also the potentially independent notion that the "Not Detected" light is just set up never to be lit, playing the odds.
It is not made clear to us under what circumstances would legitimately result in a negative state being indicated. Nor, apart from the concerned expectations of Hairy and Ponytail, whether the detector will then necessarily correctly state that. It might still fail to properly respond to the new situation, just continuing to provide an incorrect indication that all is 'normal' (on the assumption that the device both still exists and functions, under such extraordinary circumstances), and result in a false positive instead. But, for many possible reasons, the chances and consequences of any displayed false positive may easily bear no relation to that of a false negative. i.e, the "Not Detected" light could always be 100% accurate (leading to Hairy's "bad" scenario), yet any given cessation of detections often fails to stop "Detection" from being indicated (being just as "bad" but, as the icing on an already possibly unpalletable cake, also with the Detector being functionally wrong).
Transcript[edit]
- [Hairy is standing to the right of a large machine labeled "Detector". The front of the machine has two lights, labeled "Detected" and "Not detected". The "detected" light is lit up in green. Ponytail and Cueball walk towards the machine from the left.]
- Ponytail: Over there are our electron microscope, XRF scanner, and mass spectrometer.
- Ponytail: And this is our most sensitive detector.
- Cueball: What does it detect?
- [The next panel zooms in on the detector. Ponytail's voice comes from the left of the panel.]
- Ponytail (off-panel): Lots of stuff.
- Ponytail (off-panel): Gas, dust, particles, light, radio waves, gamma rays, protons, neutrons, electrons, fields, forces, events, potentials, or states.
- [The next panel zooms out. Cueball and Ponytail are standing to the left of the machine, and Hairy on the right.]
- Cueball: I don't understand. Aren't most of those always present?
- Hairy: Yeah, it's been saying "detected" continuously since we turned it on.
- [Cueball and Ponytail still standing to the left of the machine, and Hairy on the right. Ponytail has her hand on her chin.]
- Cueball: What happens if it says "not detected"?
- Ponytail: Oh gosh.
- Hairy: That would be pretty bad, I think.
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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)
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