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Latest comment: 11 hours ago by Modocc in topic flocking and threshold
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August 13
editHow to start making cellular automata
editWhat's the way to get into cellular automata? What's a good book to read with interesting "case studies?" I'm interested in things like varied fields with rules diversified within that create conditions for filtering and longevity of items. Neural automata within classical fields. User manipulation to make attractor conditions or simple destruction of items. Fun stuff like that. A glossary of terms would be a help too. Thank you. Gongula Spring (talk) 19:00, 13 August 2025 (UTC)
- Are you talking about Cellular automaton? ←Baseball Bugs What's up, Doc? carrots→ 20:58, 13 August 2025 (UTC)
- We can give you better direction if you tell us a little about where you're starting from. Do you know any programming already, and if so, what languages?
- On balance, Netlogo is a good system for cellular automata and other similar types of simulation and modeling. See eg [here](https://ccl.northwestern.edu/netlogo/models/CA1DElementary) SemanticMantis (talk) 00:13, 14 August 2025 (UTC)
- I can't say I haven't tried programming before, but I can confidently deny any proficiency. Gongula Spring (talk) 00:47, 14 August 2025 (UTC)
- Rather a deep dive, Wolfram's A New Kind of Science can be read for free as an e-book. Linear (one-dimensional) cellular automata, which include the Turing machines, are introduced on page 24, while two-dimensional cellular automata make their first appearance on page 170. ‑‑Lambiam 02:07, 14 August 2025 (UTC)
- Our article on Conway's Game of Life gives a good overview of one of the first such programs. I remember coding that up in machine code on a ZX81, which was how I first became interested in computing. Mike Turnbull (talk) 19:11, 15 August 2025 (UTC)
- Thanks! And wow, Wolfram writes interesting, doesn't he? I can stand the arrogance, but not the repetition. I found this recent paper on longevity: https://arxiv.org/abs/2507.12306
- Gongula Spring (talk) 19:20, 15 August 2025 (UTC)
- Rather a deep dive, Wolfram's A New Kind of Science can be read for free as an e-book. Linear (one-dimensional) cellular automata, which include the Turing machines, are introduced on page 24, while two-dimensional cellular automata make their first appearance on page 170. ‑‑Lambiam 02:07, 14 August 2025 (UTC)
- I can't say I haven't tried programming before, but I can confidently deny any proficiency. Gongula Spring (talk) 00:47, 14 August 2025 (UTC)
August 14
editWhy wasn't snow always visible on analogue TV?
editIf you tuned an analogue TV to any channel which didn't have a station transmitting on it, you would see snow and hear white noise. This was because you were picking up the omnipresent background noise, from such sources as dying stars.
All very well, but why weren't the pattern and the noise imposed over every broadcast channel? If it's just that the signal from the transmitter was louder than the background noise, why wasn't the background noise grey? Marnanel (talk) 13:38, 14 August 2025 (UTC)
- Automatic gain control turned the gain to maximum in the absence of a signal catslash (talk) 13:48, 14 August 2025 (UTC)
- The signal to noise ratio is massive in a properly tuned TV or radio. That background noise is multiple orders of magnitude lower in amplitude than the broadcast signal being beamed at high power from nearby.
- Edit: Btw, TV snow is the exact same phenomenon as static on a radio that's not tuned to a station or is moving out of range. That gain that that catslash mentions is a technique used to ensure the radio doesn't change in volume as you receive more or less of the signal due to distance. If you've ever heard a radio station gradually growing staticky as you drive out of range, that's what's going on -- it's amplifying the signal, and the noise with it, until all you can hear is the noise. We just don't tend to gradually move out of range of TV stations. -- Avocado (talk) 13:51, 14 August 2025 (UTC)
- Noise radiation from star sources and the CMB (Cosmic Background Noise) are detectable by sensitive radioastronomy antennas with ultra-low noise amplifiers. Domestic analog TVs are quite incapable of displaying such noise. Describing the off-program "snow" display as interstellar in origin is a common "lie to children". What one is actually seeing is thermal noise generated in the TVs own input circuit that greatly exceeds any supposed signal from space. — Preceding unsigned comment added by 2A02:FE1:4088:5E00:454:9CE8:B297:115F (talk) 08:40, 16 August 2025 (UTC)
- Over here tv stations kept transmitters off during the day and if TV was turned on it was Cosmic Noise audible with dots very fine small dancing dots and TV technicians used to asses the quality of TV reception to be after few hours , it was always correct .Tv sets were CRT, B & W . Dr chifti (talk) 05:25, 26 August 2025 (UTC)
- Noise radiation from star sources and the CMB (Cosmic Background Noise) are detectable by sensitive radioastronomy antennas with ultra-low noise amplifiers. Domestic analog TVs are quite incapable of displaying such noise. Describing the off-program "snow" display as interstellar in origin is a common "lie to children". What one is actually seeing is thermal noise generated in the TVs own input circuit that greatly exceeds any supposed signal from space. — Preceding unsigned comment added by 2A02:FE1:4088:5E00:454:9CE8:B297:115F (talk) 08:40, 16 August 2025 (UTC)
August 15
editpregnancies
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which appropriate discussion website can i talk about pregnancies because i am a student ashley researching pregnancies?(117.202.165.2 (talk) 18:45, 15 August 2025 (UTC)
So...normally I would respect the close box and the call of a regular colleague make a troll call, but in this case I think it is worth asking: are we sure this is not someone very young and/or from a culture where discussion of reliable facts about reproductive health is taboo or restricted enough that they felt awkward asking these questions without a cover story? what exactly was asked, last time? SnowRise let's rap 09:27, 16 August 2025 (UTC)
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August 17
editflocking and threshold
editBoids provokes a question:
Each boid adjusts its position and velocity to those of (I guess) its N nearest neighbors; and/or those within a distance R. Does varying N or R make the behavior resemble that of different real bird species? —Tamfang (talk) 03:04, 17 August 2025 (UTC)
- With the AI's assistance, I found this article Statistical Mechanics for Natural Flocks of Birds that states, based on field data, "...interactions are ruled by topological rather than metric distance." Boid models must account for these and other factors. Modocc (talk) 19:12, 17 August 2025 (UTC)
- This is a great paper, do you have any more like it? Gongula Spring (talk) 18:03, 26 August 2025 (UTC)
- No, I do not. Modocc (talk) 20:45, 26 August 2025 (UTC)
- This is a great paper, do you have any more like it? Gongula Spring (talk) 18:03, 26 August 2025 (UTC)
- The Introduction section of the paper describing the boid model[2] contains this passage:
- "The success and validity of these simulations is difficult to measure objectively. They do seem to agree well with certain criteria and some statistical properties of natural flocks and schools which have been reported by the zoological and behavioral sciences. Perhaps more significantly, many people who view these animated flocks immediately recognize them as a representation of a natural flock, and find them similarly delightful to watch."
- In the Conclusion section, the author writes:
- "The animations showing simulated flocks built from this model seem to correspond to the observer's intuitive notion of what constitutes 'flock-like motion.' However it is difficult to objectively measure how valid these simulations are."
- Furthermore, in the description of the model, we read:
- "The flock model presented here is actually a better model of a school or a herd than a flock [of birds]."
- In particular, it appears that natural birds look further ahead than artificial boids, perceiving the approach of a 'manoeuvre wave' and anticipating its arrival.[3] So there is no claim, express or implied, that this is a valid model for flocking behaviour, but merely that it looks convincingly similar. It is not a scientific article about animal behaviour but a technological article about a difficult aspect of CGI.
- While there have been a few studies on the properties of actual biological flocks, these seem to have been with respect, each time, to a single species, reporting the observations in a non-standardized way that makes comparisons of different species almost impossible. How well turning the N and R knobs make the boid-model simulation resemble the natural flocking behaviour of different flocking bird species will depend on the subjective judgement of observers familiar with these specific behaviours. ‑‑Lambiam 09:47, 18 August 2025 (UTC)
Thanks both! —Tamfang (talk) 23:43, 21 August 2025 (UTC)
August 19
editIs the speed of light constant, when measured by a remote inertial observer, who non-locally measures a photon traveling a long way in a curved vacuum?
editI'm asking, because our article speed of light states confusingly: "In non-inertial frames of reference (gravitationally curved spacetime or accelerated reference frames)...the speed of light can differ from c when measured from a remote frame of reference".
This sentence seems to ignore the situation I'm asking about, when the remote observer's frame of reference is inertial, but the spacetime the light travels through is curved. HOTmag (talk) 08:32, 19 August 2025 (UTC)
- The length traveled by a photo should be the path length as measured along its curved trajectory, a geodesic of the manifold that is spacetime. I am not sure how you propose the stationary observer is going to measure this. It is in fact not even clear how to define the path length (in the mathematical model of curved spacetime, a Lorentzian manifold) with respect to a given, fixed frame of reference. Inertial frames of reference are useful in special relativity, when objects not acted upon by a force travel in straight lines. Space curvature means that there are no "straight lines", so the inertial model for establishing a reference frame breaks down. ‑‑Lambiam 14:07, 19 August 2025 (UTC)
- Let's assume we (as inertial observers) see a photon travel near the sun in a curved trajectory. Do you claim we can't use any tool (e.g. a telescope or whatever) for measuring the length of this photon's curved trajectory? HOTmag (talk) 15:59, 19 August 2025 (UTC)
- We can detect only photons that arrive at our ___location. If a remote photon interacts with something else in such a way as to cause emission of another photon in our direction, we can detect the resulting photon but we're not directly observing the trajectory of the initial one.
- Saying "what if as remote observers we see a photon travel near the sun" is like saying "what if as fans watching a soccer match from 10 miles away, we get hit by the ball on its way from the players foot to the goal". A remote observer can't observe a photon's trajectory. -- Avocado (talk) 17:49, 19 August 2025 (UTC)
- So what does the quote (from Wikipedia) in my original post mean, about when c is "measured from a remote frame of reference"? Doesn't the measurement of c made by a remote observer, mean measuring the ratio between, the photon's trajectory measured by that remote observer, and the time it takes the photon to travel this trajectory - when this time is measured by that remote observer? HOTmag (talk) 18:29, 19 August 2025 (UTC)
- I'm not a physicist nor the person who wrote the article. I would assume that we can know the time of the photon's origin based on whatever caused it to be emitted also having other effects (gravitational waves, other photons, etc) that reach us directly. And that we can measure the time of the photon's arrival at another point based on the effects of its arrival (reflected or re-emitted light, for instance) that reach us directly. And that we can thus measure the time elapsed between departure and arrival and deduce its speed. But we can't observe its trajectory, only infer it. -- Avocado (talk) 20:15, 19 August 2025 (UTC)
- Please note that the condition of "local measurement" (as opposed to "non-local" one) is a well known requirement for the speed of light to be constant. I've asked whether the requirement of locallity of measurement is also needed when the observer's frame of referenece is inertial. HOTmag (talk) 06:47, 20 August 2025 (UTC)
- I'm not a physicist nor the person who wrote the article. I would assume that we can know the time of the photon's origin based on whatever caused it to be emitted also having other effects (gravitational waves, other photons, etc) that reach us directly. And that we can measure the time of the photon's arrival at another point based on the effects of its arrival (reflected or re-emitted light, for instance) that reach us directly. And that we can thus measure the time elapsed between departure and arrival and deduce its speed. But we can't observe its trajectory, only infer it. -- Avocado (talk) 20:15, 19 August 2025 (UTC)
- So what does the quote (from Wikipedia) in my original post mean, about when c is "measured from a remote frame of reference"? Doesn't the measurement of c made by a remote observer, mean measuring the ratio between, the photon's trajectory measured by that remote observer, and the time it takes the photon to travel this trajectory - when this time is measured by that remote observer? HOTmag (talk) 18:29, 19 August 2025 (UTC)
- Let's assume we (as inertial observers) see a photon travel near the sun in a curved trajectory. Do you claim we can't use any tool (e.g. a telescope or whatever) for measuring the length of this photon's curved trajectory? HOTmag (talk) 15:59, 19 August 2025 (UTC)
- You can imagine that you have a torch in your hand and point it towards a remote black hole. The light from the torch will travel in the direction of the event horizons but will never cross it (from the point of view of an external inertial observer). This effectively means that the speed of light becomes zero in the vicinity of the horizon. However the proper speed of light will remain c of course. Ruslik_Zero 20:33, 19 August 2025 (UTC)
- When a photon is approaching a black hole, both the distance traveled by the photon, and the time it takes the photon to travel that distance, approach infinity (from the inertial observer's viewpoint), so the "effective" velocity becomes meaningless rather than "zero". HOTmag (talk) 06:47, 20 August 2025 (UTC)
- Sorry, but the distance cannot become infinite because it is a known quantity. Indeed, you can measure the distance to the black hole and its mass and then calculate the distance to the horizon from the observer.
- Actually there is no need to use black holes at all. You can put a mirror on the Earth's surface and direct the laser beam at it from a remote ___location in space. Then since you know the distance and can measure the time when the reflected signal comes back you can calculate the speed by dividing the first quantity by the second. The result will be that the (apparent) speed of light is less than c. Ruslik_Zero 10:39, 20 August 2025 (UTC)
- I can see some practical issues with measuring the distance to a black hole. And also some theoretical issues. ‑‑Lambiam 16:53, 20 August 2025 (UTC)
- Any black hole is just a mass. You need only to measure the orbital parameters of test particles moving around it. Ruslik_Zero 17:34, 20 August 2025 (UTC)
- I can see some practical issues with measuring the distance to a black hole. And also some theoretical issues. ‑‑Lambiam 16:53, 20 August 2025 (UTC)
- Actually there is no need to use black holes at all. You can put a mirror on the Earth's surface and direct the laser beam at it from a remote ___location in space. Then since you know the distance and can measure the time when the reflected signal comes back you can calculate the speed by dividing the first quantity by the second. The result will be that the (apparent) speed of light is less than c. Ruslik_Zero 10:39, 20 August 2025 (UTC)
- This is far from the first time I have been exposed to these facts, but this concept still breaks my brain a little. I think it's on account of how we utilize the notion of an observer from an outside frame of reference as an abstraction. Obviously, in terms actual empirical observation at this point, the photon is completely red-shifted and has no chance of ever escaping. So it can't ever be directly observed. And yet we regard it as being unable to ever being able to be observed to have crossed the event horizon. Can someone help me with the structural distinction here? Because obviously if we had a photon's trajectory bent around the gravity well of a black hole (or any mass), we could observe it only by directly interacting with it by intercepting it somewhere along its path. So what do we mean when we talk about observation in an instance that is not in any scenario actually physically possible? SnowRise let's rap 06:44, 24 August 2025 (UTC)
- Just a small remark: "red-shifted" (as you say), only when it tries to escape a black hole, but here we are talking about a photon approaching a black hole, so it's blue-shifted. 2A06:C701:745A:B800:B559:3320:A4F4:C460 (talk) 10:22, 24 August 2025 (UTC)
- Regardless of their colour (frequency), photons can only be directly observed when they hit the observer. This was already pointed out above by Avocado. They can only be observed, directly or indirectly, when they are detected by some detector, which means in quantum terminology that they are "measured". Measurement of a photon means a change in a macroscopic system (a photoreceptor cell in the observer's eye, a photographic plate or film, a photodetector, ...) as the result of an interaction with that system. Unless the measuring system is close to where the photon is, the probability of an interaction taking place is vanishingly small. ‑‑Lambiam 12:05, 24 August 2025 (UTC)
- Do you claim, any measurement (e.g. by a telescope or whatever) of the length of a photon's curved trajectory - whether near the sun - or in any phenomenon of gravitational lensing, is a local measurement? HOTmag (talk) 13:11, 24 August 2025 (UTC)
- Does Principle of locality help? {The poster formerly known as 87.81.230.195} 90.210.150.115 (talk) 18:03, 24 August 2025 (UTC)
- I think you've mis-interpeted my inquiry here, Lambiam. As it happens, I'm a bit of an expert in visual cognition, and so very familiar with the physics/biophysics of photoreceptive media. That's not the part I am struggling to fix in my mind here. My epistemological confusion about the terminology is this: since a photon trapped at the event horizon never escapes to interact with such a medium, what do we mean when we talk about "observation" when, for example Ruslik0 says
The light from the torch will travel in the direction of the event horizons but will never cross it (from the point of view of an external inertial observer).
? Is it a conceptual conceit/misnomer for describing the relation of the frames of reference? If so, can you think of a thought experiment that would explain those interactions in such a way that accounts for the fact that, as a strictly empirical and ontological matter, no observation at a distance can be made? Maybe Ruslik0 just mixed their metaphors and terminology a bit? If not, I'm super confused as to what the act of observation means in that description. SnowRise let's rap 22:10, 24 August 2025 (UTC)- You are right, I misunderstood the essence of your post. My reaction was triggered by the statement connecting our inability to observe the photon to its colour, which is I think essentially correct – in the model its wavelength tends to zero as it approaches the event horizon – but irrelevant. Scenario's of a photon traveling to an event horizon can be described that conform to a mathematical model of GR, such as Schwarzschild's exact solution to Einstein's equations. Such descriptions need a frame of reference, preferably one that in the limit, away from the mass, is an inertial frame. I too think the wording of these scenario's is sometimes confused. The scenario may include an observer for which this frame is stationary who can observe phenomena as predicted by the model, which in real life would validate the model. But such observation can only be through information that reaches them from afar, such as transmitted by electromagnetic waves. An astronaut approaching the event horizon might broadcast a livestream witness report that reaches the observer, but a photon can do no such thing. The models do not allow an observer to observe the unfolding of the scenario with regard to the traveling photon, so describing the scenario in terms of observations is confused. ‑‑Lambiam 23:58, 24 August 2025 (UTC)
- What I actually meant is shapiro time delay, which can be interpreted as slowing of light in presence of a gravitational field. Ruslik_Zero 20:33, 25 August 2025 (UTC)
- Do you claim, any measurement (e.g. by a telescope or whatever) of the length of a photon's curved trajectory - whether near the sun - or in any phenomenon of gravitational lensing, is a local measurement? HOTmag (talk) 13:11, 24 August 2025 (UTC)
August 26
editPharmacology
editA friend once mentioned a book similar to an Encyclopedia, describing background events behind the development of many well known medicines . Please inform if a similar book can be found and how to "custom search" at any of the sites of WIKI for such a book . Thnx Dr chifti (talk) 05:05, 26 August 2025 (UTC)
- You might find such a work used as one of the many references for the article History of medicine, athough what you describe would be a Tertiary source (like Wikipedia itself) rather than a Secondary source which Wikipedia prefers for article sources.
- Searching Wikipedia for the term "Encyclopedia of pharmacology" led me to the article Pharmacology Research & Perspectives whch uses as its reference 4 The Sage Encyclopedia of Pharmacology and Society – see that article for its bibilographical details. {The poster formerly known as 87.81.230.195} 90.210.150.115 (talk) 08:04, 26 August 2025 (UTC)
- Searching Archive.org for history of medicines turns up many candidates, including Our Modern Medicines (F Bandelin, 1986) which seems to match your description. -- Verbarson talkedits 15:04, 26 August 2025 (UTC)