Science fleeting thoughts

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Re: Science fleeting thoughts

Postby Eebster the Great » Mon Jan 28, 2019 5:51 am UTC

It would be almost immediate, even faster than cutting off oxygen to the brain.

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Re: Science fleeting thoughts

Postby Angua » Mon Jan 28, 2019 7:52 am UTC

Basically, imagine cyanide.
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Re: Science fleeting thoughts

Postby ijuin » Mon Jan 28, 2019 8:12 am UTC

Ok, most cells only keep enough ATP (the molecule used for on-the-spot energy delivery within cells) on hand to last for ten seconds at most. This can be supplemented by creatine phosphate stores, but that too will run out after another ten to thirty seconds. After that, cells turn to anaerobic fermentation for energy, but after another couple of minutes the lactic acid thus produced becomes itself toxic. Absolutely no aerobic metabolism can happen without functional mitochondria.

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Re: Science fleeting thoughts

Postby Eebster the Great » Mon Jan 28, 2019 2:57 pm UTC

I don't think your nerves can function at all anaerobically. Apparently they can use lactate to briefly maintain ion homeostasis, during which time you would arguably be "not dead" in the sense that if all your mitochondria magically reappeared, it''s just conceivable that you could be revived given instant medical attention, but you would have zero brain activity.

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Re: Science fleeting thoughts

Postby Ranbot » Wed Feb 06, 2019 6:34 pm UTC

InSight has deployed it's seismometer with an protective shroud. To counteract the weather and temperature variability on Mars, they built the seismometer out of different materials than are typically used on Earth. Details are in the linked article below. Of course this is in addition to the feat of even getting it to Mars.

https://www.nasa.gov/feature/jpl/insigh ... er-on-mars

Personally, I'm excited for this. Seismic data can tell you a lot of about geologic structures deep below the surface. I was growing tired of Mars rovers and orbiters just sending back lovely photos and "discovering" water/ice over and over and over again, but barely scratching the surface of the planet (literally).

Image

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Re: Science fleeting thoughts

Postby Link » Fri Feb 08, 2019 9:13 am UTC

Quizatzhaderac wrote:
I'm also seriously worried by the qoute provided by CERN's director: "But if you imagine the discovery of the electron by JJ Thomson in 1897, he didn't know what electronics was. But you can't imagine a world now without electronics." Plenty of electronics had been invented by then, because electronics isn't solely the manipulation of individual electrons.

Yeah, that's not exactly the kind of argument to support a €20 billion fundraiser. It does touch on something I've been thinking about recently, though: of the four fundamental forces, electromagnetism is the only one in which we have any appreciable finesse of manipulation; with the other forces, we're quite literally in the stage of just smashing stuff together and seeing what happens (or letting nature smash stuff together, in the case of gravity). That is of course to be expected, because biological length scales are exactly those where electromagnetism is most relevant, but to me it sounds quite plausible that there's as much "emergent" stuff that can be done with the other forces as we are doing with electromagnetism today, provided we somehow come up with a few "magic bullets" like the semiconductor. (Even in the vacuum tube era, it would have been hard to imagine connecting billions of them together like we do with transistors, let alone to predict the technology you could make with that!)

Even something as basic as a weak-force "radio" that efficiently emits and detects neutrinos has the potential to completely overhaul terrestrial communication by beaming straight through the Earth instead of having to rely on cables and satellites that follow the curvature. And imagine what we could learn about the universe if we could measure the cosmic neutrino (or even gravitational wave) power spectrum with WMAP-like resolution!

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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Feb 08, 2019 4:20 pm UTC

The electromagnetic interaction has unlimited range. The strong and weak interactions have very, very limited range. This makes them less than ideal for communication. That doesn't mean they can't be useful in other ways, though.

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Re: Science fleeting thoughts

Postby doogly » Fri Feb 08, 2019 4:56 pm UTC

Eebster the Great wrote:The electromagnetic interaction has unlimited range. The strong and weak interactions have very, very limited range. This makes them less than ideal for communication. That doesn't mean they can't be useful in other ways, though.

But they're really, really unlikely to be useful. If one of your main funding criteria is "potentially useful," you are going to fund research in solid state / condensed matter, atomic / optical, maybe some quantum computing / mesoscale qm.... basically anything but HEP.
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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Feb 08, 2019 6:52 pm UTC

I think none of these things are relevant to that fundraiser. The only way it would make sense to talk about high energy physics at a fundraiser would be to fund research into basic physics. (Physicists do after all like to use billion dollar pieces of equipment.) But I thought Link was just musing about the future, and it is at least conceivable that weak interactions could be relevant to some important device in the future in some way.

It is very difficult to imagine anything pervasive like electronics, because they are fundamentally different. But it could do, I don't know, something.

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Re: Science fleeting thoughts

Postby Nicias » Fri Feb 08, 2019 7:43 pm UTC

Neutrinos are useful for monitoring nuclear reactors from a distance:

https://www.aps.org/units/fps/newslette ... trinos.cfm

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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Feb 08, 2019 10:44 pm UTC

I was just thinking about this. The only way neutrinos are "used" in the status quo is in astronomy, so the most obvious extension would be to other observational technology, especially military surveillance. I was thinking that at a minimum, it could add another independent method for confirming the presence of a nuclear test. But if we extrapolate, we can also imagine that monitoring neutrino flux might be useful in a nuclear fission or fusion power plant. Outside of the realm of high energy physics, neutrinos are neither detectable nor very useful, but inside that realm, there are still some relevant technologies.

I should point out though that while the weak force is involved in the collision events of these neutrinos whose products we detect, we don't exactly "use the weak force" in the direct sense. We still use chemical and electronic detection methods.

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Re: Science fleeting thoughts

Postby Link » Sat Feb 09, 2019 9:15 pm UTC

Eebster the Great wrote:
I think none of these things are relevant to that fundraiser. The only way it would make sense to talk about high energy physics at a fundraiser would be to fund research into basic physics. (Physicists do after all like to use billion dollar pieces of equipment.) But I thought Link was just musing about the future, and it is at least conceivable that weak interactions could be relevant to some important device in the future in some way.

It is very difficult to imagine anything pervasive like electronics, because they are fundamentally different. But it could do, I don't know, something.

Pretty much, yeah. The thing is, it's pretty much been a recurring theme in history that totally unexpected uses of previously-known things start popping up once we get to the stage where we can start to "play" with those things. You're right in that the other interactions are very different to electromagnetism, and it's not unlikely that they'll never lead to any extremely pervasive technology. On the other hand, I don't think James Clerk Maxwell could ever have imagined his equations would lay the groundwork for handheld devices that provide near-instantaneous worldwide communication and access to the sum total of human knowledge, so you never know.

doogly wrote:
But they're really, really unlikely to be useful. If one of your main funding criteria is "potentially useful," you are going to fund research in solid state / condensed matter, atomic / optical, maybe some quantum computing / mesoscale qm.... basically anything but HEP.
Yeah, especially if you put it in terms of amount of useful stuff per unit time, HEP is a terrible investment. There's an incredible amount of stuff that we *know* can be immensely useful in condensed matter/QM/related fields, and it's at least as likely that those fields have a lot of hitherto-unimagined useful stuff as it is for HEP.

Still, I think there's a very real possibility that if we ever find a way to push HEP out of the regime of fuck-off-huge, insanely expensive, and outrageously inefficient experiments, and into something more manageable, we can discover potential applications that nobody alive today has ever even considered. It may very well take us centuries or millennia to reach that point, if we ever reach it at all, but doesn't seem unlikely to me that there are many potential uses of the other fundamental interactions.

--

Tangentially related fleeting thought: looking at the big picture, human science and technology are absolutely astounding, as is the pace at which they've advanced. It's incredible how much on this planet (and around it!) only exists because h. sapiens invented and built it, and the vast majority was done in the last few millennia. To the best of our knowledge, certainly nothing outside the genus homo has ever come remotely close in terms of abstract thinking and ingenuity. It's not hard to see why many people come up with ideas like souls or creationism, because we really are an anomaly in that sense. Basically our entire existence is just finding new ways to take whatever Mother Nature throws at us and make it our bitch. (And yet, at the same, it's often painfully obvious that we're really just glorified monkeys...)

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Re: Science fleeting thoughts

Postby Eebster the Great » Sat Feb 09, 2019 11:17 pm UTC

Well, in the specific example of Maxwell, he died shortly before electromagnetic waves were discovered, that's true. But the difference is that at that time, electromagnetism had only just begun to be understood. At the present, the weak interaction is very well understood, and the picture has not radically changed in fifty years. The electromagnetic interaction was known to be very long range, and the weak interaction is known to be very short range. The weak interaction is about five orders of magnitude weaker than the electromagnetic interaction even at the femtometer scale. And most of the time, when particles can interact weakly, they can also interact electromagnetically far more strongly. So we actually have very good reasons to believe that weak interactions will never be as useful to us as electromagnetism.

That said, that doesn't mean it won't have any application at all. I just wouldn't hold your breath for the neutrinic revolution.

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Re: Science fleeting thoughts

Postby Link » Sun Feb 10, 2019 12:08 am UTC

Fair enough; on the whole that's probably true. (Unless of course dark matter turns out to be something with rich dynamics, but I suspect we'd have more of a clue about its nature by now if that were the case.)

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Re: Science fleeting thoughts

Postby Angua » Sun Feb 10, 2019 7:21 pm UTC

Why I facepalm when anyone justifies anything by 'it stands to reason'

Public health interventions such as education and behaviour change programmes are not invasive and might be viewed as unlikely to cause any harm. However, there is evidence thatsome may do so. For example, training children in bicycle safety has been shown in some instances to have increased accident rates among children who cycle (probably because they or their parents became more confident after the training and they were then exposed to more risks). The ‘Bike ed’4programme in Australia, designed to reduce cycle injuries, actually increasedthe risk of injury overall, doubling it in boys. Furthermore, the most adverse effects were observed among younger children, children from families with lower parental education, and children who lacked other family members who cycled, hence increasing socio-economic and gender inequalities which are particularly marked in any case for childhood injuries. The implications of this observation are that well-intentioned and plausible interventions, even of a non-invasive kind involving only education, can do unanticipated harm. This suggests that there is a duty on those introducing such measures to monitor their actual impact over appropriate timeframes, rather than simply assuming they are beneficial.
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Re: Science fleeting thoughts

Postby Eebster the Great » Sun Feb 10, 2019 7:48 pm UTC

I agree with that principle in general, but I'm pretty unconvinced by this example in particular. I found the study referenced. It points out that "The only previous study of the effectiveness of Bike Ed as a teaching program was performed in Newcastle, Australia and showed that it appeared to be successful in producing an improvement in both bicycle riding knowledge and riding performance when compared with a control group." It points out difficulties classifying people by distance and time biking and by Bike Ed courses, the two most important classifiers. It points out that there could be confounding variables, in particular that Bike Ed courses could be most commonly offered in places that have high bike accident rates, something they did not check for (though they point out that in interviews, people said they were usually offered based on child interest... but children (and parents of children) that get hurt biking would tend to have the most interest, you would think). And the odds ratio was only 1.6 anyway. It seems like there may be a more plausible explanation behind these results than that the program which we know makes kids better at biking also makes them get in more accidents per kilometer.

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Re: Science fleeting thoughts

Postby Quizatzhaderac » Tue Feb 12, 2019 7:34 pm UTC

Link wrote:Still, I think there's a very real possibility that if we ever find a way to push HEP out of the regime of fuck-off-huge, insanely expensive, and outrageously inefficient experiments, and into something more manageable, we can discover potential applications that nobody alive today has ever even considered. It may very well take us centuries or millennia to reach that point, if we ever reach it at all, but doesn't seem unlikely to me that there are many potential uses of the other fundamental interactions.
Well that's the thing, even if we're able to figure out ways to manipulate the nuclear forces, we can't because of the crazy temperatures involved (in fact, several orders of magnitude too hot for a fusion reactor).

But if we were to somehow make HEF conductible efficiently that would be double awesome: 1) we could conduct the research much more efficiently. 2) we could efficiently apply results.
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Re: Science fleeting thoughts

Postby Soupspoon » Wed Feb 13, 2019 12:01 am UTC

Science(-Fiction) Fleeting Thought:
Martian colonisation is often(-enough) depicted with trains in 'glass' tubes linking various settlements.

Is this intended to be one (or any two?) of the following:
a) To maintain low(er than Martian) pressure for efficient fast-transit, maglev or otherwise,
b) To maintain transit through nominal Martian pressure (already better for the above than on Earth), but to exclude as much of the troublesome dust-storm particles as possible,
c) To allow a section of tube to be up-pressured* in the event of an emergency (not involving the integrity of the tube itself) for evacuation of the train occupants, letting them get to a strategic in-built refuge without having to suit up.

I think (c) is the more fantastical. So many things could go wrong, pressurising a section, and it would be so obviously impossible under many life-threatening circumstances that it probably negates its usefulness under the few circumstances it could be useful (as would having permanent 1 Earth-Atmosphere breathable contents of the tube, over-pressured against the pre-Douglas Quaid outside environment).

But (a) or (b) could have (c) as a backup option, even though stations might be best designed to keep the tube pressure as-is and let boarding/alighting commence through umbilical connections projected betwixt platform enclosure and train enclosure when the train is halted in the correct spot.

Maybe instead of traditional side doors, with the necessary thick 'airlock' proportions eating up train-space***, connections could be through the train roof and/or floor, with elevator/stair/escalator access projected through, as suits the practicalities of other needs to exit the train, such as directly into a conveniently provided sub-track refuge during a controlled emergency evacuation.


* - As also perhaps with (a), needs periodic irises or other kinds of closable doors ( taking into account the track itself**) to isolate track segments according to need.
** - Probably a maglev could have an 'iris gap' in its structure that allows closure and yet is smooth enough to "roll over" under normal operation.
*** - Though I originally pondered this issue regarding the case for a more Brunellian wide-gauge track, eight feet or even plenty more, train cabins not restricted to the traditional Earth cross-sections. Perhaps more a 747 fuselage (but with less cramming in of seats necessary?). Yet still a dorsal or ventral egress method (in the central parts of the tube cross-section with otherwise wasted head/foot-room) would seem a better engineering solution than reinforcing the sides into pinch-points to accommodate the necessary mechanics for passage to/from beyond the train interior.

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Re: Science fleeting thoughts

Postby ijuin » Wed Feb 13, 2019 6:42 am UTC

What the whole thing resembles to me is a Musk-style HyperLoop system, but with the tube being transparent rather than opaque. Aluminum oxide crystal would be a more than adequate material.

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Re: Science fleeting thoughts

Postby Soupspoon » Wed Feb 13, 2019 1:53 pm UTC

In the context of the fictional scene-setter (graphic designer, CGI modeller) it's perhaps as little as a "Woo! Futuretrain on Mars!" visual gimmick painted into the scene background/landscape-zoom, and easily CGIed/modeled from a distance. More visual than opaque tubes (which would be like hundred-mile tunnels and might as well be from a passenger's POV) and more 'likely' than open-'air' railroads (with dust problems). Networking via sending out TBMs (with extra 'void protection' abilities) would be time-consuming and paleoareologically disruptive if we're still carefully surveying for ancient life-signs, but potentially profitable in a more material world (plenty of tailings to pack around 'buried pod' settlements, and the rock cut through could additionally be surveyed for minerals of use and mining areas directly expanded around such points) if it's become more about resources than science.

Practically, with enough minor ribbing I could imagine it being a suitably-graded flexible polymer sheeting. Most especially for the ambient-pressure version, though it must now deal with the passing-train over-pressure. Maybe a down-pressure system could mostly have to withstand the evacuation more than the passage of the travelling pods (data from Hyperloop tubes/vehicles currently being tested).

Extruding a polymer (feedstock being atmospheric carbon left after split from oxygen, or via methane in a Zubrin-like synthesis, but would require hydrogen from somewhere, perhaps polar ice also farmed for oxygen, but to what balance of supply and demand?) might be useful, and easily replaceable in the event of micrometeorite damage or a stronger dust-storm that wouldn't damage most of a proper 'glass' of whatever oxide. (You could also use it in an over-pressured 'evacuation' situation, given it has to withstand a train passing, but I'd be nervous without making it multi-layered with intervening differential pressure(s) in the mid-layer and leak-sensors throughput the compartmemtalised skin.) The benefits are also evident in that when damaged (as all setups eventually will) the flapping shreddings themselves will be less damaging to any vehicle that can't avoid passing through them, compared with vitreous shards potentially littering its path.

With fluorine (noted as detected directly in Gale Crater, but not sure if it's easily extractable) you could go for something like ETFE polycells, bracketted between homegrown alloy supports with at least 1.5 unit depth (the outer one cell-pillow layer acts as the inner on the next layer, with offset nodes between the two for packing purposes and to try to limit structural failure) all cells boundaries having a slight positive pressure either inwards or outwards) to maintain a view-friendly dust-tunnel (with air-jet crawlers slowly traversing the network to gently de-dust the outer surface, and check for (perhaps repair) minor external damage) with mass-producable qualities.

Wouldn't necessarily look as Sci-Fi 'gleamy' as the "glass tube", and still I'm undecided which pressure differential would be the required one. But it was just a passing thought last night as I walked home (and I've no idea now why, though it might have happened about the time I overlooked the nearest railway track, across the valley, and saw an express pass; though only Om knows where the Mars element to the concept came from!), so don't expect this to be a fully-planned proposal, just a few mental building blocks linked together in a not obviously unstable combination. :D

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Re: Science fleeting thoughts

Postby Quizatzhaderac » Wed Feb 13, 2019 6:56 pm UTC

D negative (below vacuum) pressure.

I'd say the typical sci-fi scenario is depicting as a tunnel/tube is needed for dust and radiation, with other concerns being secondary.

D is the default in sci-fi because explosive decompression is awesome.
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Re: Science fleeting thoughts

Postby Eebster the Great » Thu Feb 14, 2019 2:20 am UTC

Dying in negative absolute pressure (that is, in tension) isn't so much "decompression" as being actively torn apart.

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Re: Science fleeting thoughts

Postby Pfhorrest » Thu Feb 14, 2019 4:53 am UTC

I saw someone once suggest that as the defining characteristics of dark energy are that it exerts a negative pressure uniformly through space, a better name for it might be "smooth tension".
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Re: Science fleeting thoughts

Postby Soupspoon » Thu Feb 14, 2019 12:52 pm UTC

Hmm, how to manipulate it for use in airships…

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Re: Science fleeting thoughts

Postby doogly » Thu Feb 14, 2019 1:53 pm UTC

You can't manipulate constants, that's sort of their deal.
cf why you can't build a time machine out of it.
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Re: Science fleeting thoughts

Postby Soupspoon » Thu Feb 14, 2019 2:12 pm UTC

Ah. It's a locked-down proprietary universe. Next time we should probably go Open Source.

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Re: Science fleeting thoughts

Postby Quizatzhaderac » Thu Feb 14, 2019 5:27 pm UTC

doogly wrote:You can't manipulate constants, that's sort of their deal.
cf why you can't build a time machine out of it.
Actually there pretty much has to be a non-constant negative pressure, because the universe's expansion doesn't match with a constant negative pressure.
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Re: Science fleeting thoughts

Postby doogly » Thu Feb 14, 2019 6:51 pm UTC

Quizatzhaderac wrote:
doogly wrote:You can't manipulate constants, that's sort of their deal.
cf why you can't build a time machine out of it.
Actually there pretty much has to be a non-constant negative pressure, because the universe's expansion doesn't match with a constant negative pressure.

It matches a constant extremely well, even better as Planck.
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Re: Science fleeting thoughts

Postby Eebster the Great » Thu Feb 14, 2019 7:36 pm UTC

Yeah, ΛCDM is by far the best model we have so far.

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Re: Science fleeting thoughts

Postby Quizatzhaderac » Thu Feb 14, 2019 9:59 pm UTC

It's constant for a relative to volume of space, but volume of space is not constant under either local or cosmological conditions.

In reality (and hard sci-fi) you are essentially correct, in that we can forget about manipulating it, or even seeing it change.

I was still thinking along silly sci-fi (see explosive decompression).
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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Feb 15, 2019 12:37 am UTC

The scale factor increases exponentially, which is what it means for the cosmological constant to be constant.

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Re: Science fleeting thoughts

Postby Xanthir » Fri Feb 15, 2019 4:30 pm UTC

Soupspoon wrote:
Science(-Fiction) Fleeting Thought:
Martian colonisation is often(-enough) depicted with trains in 'glass' tubes linking various settlements.

Is this intended to be one (or any two?) of the following:
a) To maintain low(er than Martian) pressure for efficient fast-transit, maglev or otherwise,
b) To maintain transit through nominal Martian pressure (already better for the above than on Earth), but to exclude as much of the troublesome dust-storm particles as possible,
c) To allow a section of tube to be up-pressured* in the event of an emergency (not involving the integrity of the tube itself) for evacuation of the train occupants, letting them get to a strategic in-built refuge without having to suit up.


Yeah, I'm assuming it would be (b), since Mars is *very* dusty. Maintaining above or below atmospheric pressure is a *maybe*, but seems unlikely to be useful enough to justify the expense on a colony. But keeping the train free from dust is really useful, and I could see it definitely being worth the cost.

Plus, as others mentioned, it looks cool and sci-fi.
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Re: Sea level

Postby Sableagle » Wed Apr 17, 2019 2:02 pm UTC

Follow-up surface gravity calculations can live here too, so I can find them again:
Sableagle wrote:
Spoiler:
Big G: 6.6719 * 10^-11 m^3 / s^2 kg
Earth: 5.972 * 10^24 kg
Product: 3.98445868 * 10^14 m^3 / s^2
Polar sea-level radius: 6356752 m
Equatorial sea-level radius: 6378137 m
Polar gravity: 9.860496668889 m / s^2 O!M!G! 666! The number people think is the number of the Beast because it sounds cooler than 616! FLEE!
Equatorial gravity: 9.794485788918 m / s^2 Clearly the South is closer to God than the North and we should bring back chattel slavery.
Siderial day: 86164.0905 seconds
Rate of rotation: 7.2921158579 * 10^-5 radians / s.
Centrifugal lightening at Equator: 0.033915713957 m / s^2.
Equatorial gravity minus centrifugal lightening at Equator: 9.76057007496 m / s^2.

(Text in bold is me taking the piss out of white supremacist religious fundamentalist conspiracy theorist flat-earthers.)

Gravitational potential energy being weight times height for small values of height, it's the area under the curve of effective weight plotted against radius for large heights.

Effective weight along the axis = 3.98445868 * 10^14 r^-2 N kg^-1.
Indefinite integral wrt r: -3.98445868 * 10^14 r^-1

Effective weight along an equatorial radius = 3.98445868 * 10^14 r^-2 - 7.2921158579 * 10^-5 r N kg^-1.
Indefinite integral wrt r: -3.98445868 * 10^14 r^-1 - 3.6460579590 * 10^-5 r N kg^-1.

Definite integral from 1 to 6356752 of effective weight along the polar axis:
-3.98445868 * 10^14 6356752^-1- -3.98445868 * 10^14 = 3.98445868 * 10^14 - 3.98445868 * 10^14 6356752^-1 = 398445805319268 Nm / kg.

Definite integral from 1 to 6378137 of effective weight along an equatorial radius:
(-3.98445868 * 10^14 6378137^-1 - 3.6460579590 * 10^-5 6378137 N kg^-1) - ( -3.98445868 * 10^14 - 3.6460579590 * 10^-5 N kg^-1 )
= 398445805529660 Nm / kg.

Considering I didn't have numbers accurate to that many significant figures, I should round that to at most 7 sig figs, so:
3.984458 * 10^14 at the pole;
3.984458 * 10^14 at the equator.

Cool! Figured it out.

Basketballs are max 29 inch circumference and ~20 ounces or max 30 inch circumference and ~22 ounces, depending whether they're women's balls or men's balls.
That gives a men's basketball a maximum radius of 121.2760666 mm. As that's a maximum radius, I'm going to call it a 120 mm radius.
22 ounces is 623.6895 grams, which I'll round to 624 g. It does say "about 22 ounces" after all.
Thus the surface gravity of the basketball is 6.67408 × 10^-11 m^3 kg^-1 s^-2 × 0.624 / 0.12^2 = 7.4275 × 10^-9 N/kg, which is about 1/1320760000 times that of the Earth.
To get the same actual and effective surface gravity at the equator of our basketball, assuming it doesn't go oblate on us when we rotate it,
9.794485788918 m / s^2 = 6.67408 × 10^-11 m^3 kg^-1 s^-2 × m / 0.12^2
0.1410406 = 6.67408 × 10^-11 kg^-1 × m
m = 0.1410406 / 6.67408 × 10^-11 kg^-1 = 2113258986.413396 kg, also known as 2.1 million tonnes.
0.033915713957 m / s^2 = w^2 r
w^2 = 0.033915713957 / 0.12 m m / s^2 = 0.28263 rad^2 / s^2
w = 0.53163 rad / s = 5.0766969691411033 rpm.
If they want to pour water on a spinning basketball and see whether it flies off, they should pour it onto a 2.1 megatonne basketball spinning at 5 rpm and see whether it flies off.

Don't worry about it pulling the entire ocean onto them when they try. Even 1 metre away, that thing's only got a gravity of 0.141 N/kg.
Still, it's probably best to try this well away from the sewers. How about on the roof of Trump tower?
Oh, Willie McBride, it was all done in vain.

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Re: Science fleeting thoughts

Postby poxic » Wed Apr 17, 2019 2:07 pm UTC

I was pondering dark energy and accelerating expansion while half-asleep the other day. I had a Sudden Insight that we might have it wrong - the universe's expansion only looks like it's accelerating because actually time is slowing down! And then I remembered how well most of my Sudden Insights go and decided the math probably would not work.

(Something something gravitational constant divided by average CMB temperature should not equal wombats plus apples. I do not advanced math well.)
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Re: Science fleeting thoughts

Postby Eebster the Great » Wed Apr 17, 2019 8:40 pm UTC

poxic wrote:I was pondering dark energy and accelerating expansion while half-asleep the other day. I had a Sudden Insight that we might have it wrong - the universe's expansion only looks like it's accelerating because actually time is slowing down! And then I remembered how well most of my Sudden Insights go and decided the math probably would not work.

But what does it mean for time to "slow down"?

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Re: Science fleeting thoughts

Postby poxic » Wed Apr 17, 2019 10:14 pm UTC

There you go, getting all technical on me ... I think I imagined that a unit of time is tied to something like a Plank constant, and that this constant would be getting bigger, so more stuff would happen per unit time, e.g. galaxies moving further per spacetime "tick".

If I ignore the fact that space is unlikely to be able to outpace spacetime, that is. This is why half-awake ponderings about the universe are not often fruitful, especially when untethered by any detailed understanding of physics.
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Re: Science fleeting thoughts

Postby Eebster the Great » Wed Apr 17, 2019 11:21 pm UTC

So it's not a crazy thought, but the difficulty is in how we can compare one time coordinate to another. I mean, if it makes sense for space to expand, it seems like it should make sense for time to expand too. Something analogous happens in special relativity, where each of two observers in relative motion sees the other as "time-dilated," i.e. everything goes slower for them. But of course it's a relative difference, and each person's clock is moving normally from their own reference frame.

In GR, over vast distances, space can expand. This means that objects separated by a large enough distance will appear to recede from each other, their proper distance increasing. We can measure this because the laws of physics are very much not scale-invariant, and they do not change. For instance, the Earth and everything on it cannot simply expand with the universe because the optimal lengths of molecular and intermolecular bonds and the like won't change. In particular, the speed of light doesn't change, so we can observe redshift. This is very different from what's going on in SR; in that case, from either observer's reference frame, the laws of physics for the other observer seem to change dramatically (except for the speed of light), including lengths of molecular bonds. And that is essentially what you are proposing: time is dilating, but we can't tell, because all the laws of physics are changing with it, so we don't notice, say, the length of the year or rates of chemical reactions change, because they all change along with it. In such a case, the dilation is inherently unobservable without someone "outside the universe" to compare to. It is not mathematically different from no time dilation at all.

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Re: Science fleeting thoughts

Postby p1t1o » Thu Apr 18, 2019 10:25 am UTC

Was it necessary to give the diameter of the basketballs to the nearest Angstrom lol!

And its two million ton mass to the nearest milligram? XD

But that rpm figure given to the nearest 10th of a femto-Hertz is a prize winner for sure!

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Re: Science fleeting thoughts

Postby gmalivuk » Thu Apr 18, 2019 11:52 am UTC

That level of precision is especially silly when we only know G to 4 or 5 significant figures.
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Re: Science fleeting thoughts

Postby Sableagle » Thu Apr 18, 2019 12:20 pm UTC

1) I wouldn't want to be accused of cutting the numbers short to conceal a "666" in there somewhere.
2) The rounding happens at the end. Rounding everything to 1 s.f. as you go is for figuring out which county you'll be in on Tuesday, not for building model aircraft.
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