Wikipedia:Reference desk/Archives/Science/2019 October 9

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October 9

Black hole center

People assume density at black hole center is infinite, Infinity does not exist, so where does the stuff go?--213.205.192.210 (talk) 01:22, 9 October 2019 (UTC)

Who says that infinity doesn't exist ? It certainly exists in a mathematical sense, and may well in a physical sense, too. See singularity. There is a theory that mass can come back out of a white hole, but most are skeptical that they exist in reality. SinisterLefty (talk) 01:44, 9 October 2019 (UTC)

About infinity, it depends on what you mean by "exist". It exists as a concept of boundlessness. But it is not a number. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:11, 9 October 2019 (UTC)

mathematics of intervals are such that there is no difference between (−∞, +∞) interval and (0,1). That is, the former is just as infinite as the latter, you can switch between with a simple variable change; for instance, u=log(t), where t is time starting at big bang, will throw big bang back to infinite as measured in u units of log-time. Not saying this is relevant, just meant to illustrate that if you think there exist some beginning you cannot actually reach, you just imagined infinity actually exist in another set of unit. Gem fr (talk) 10:17, 9 October 2019 (UTC)

No. The former set is clopen, the latter is not, and the image under the logarithm of (0, 1) is (-∞, 0), not the whole real line. And this is a bad analogy too because we don't live in "log time". "Infinite" densities can be well-modeled using a Dirac delta function, but we cannot say how physical that really is. The OP is correct to surmise something fishy, but "infinity" is not as unimaginable as they might think.--Jasper Deng (talk) 10:28, 9 October 2019 (UTC)

Both (0, 1) and (-∞, -∞) ARE open. I did not meant to imply that logarithm was the relevant function to map the former into the latter, just that it could be done (log(x)-log(1-x) would do). Nor that we live in log-time (although if we were, I am not sure we could find out). It is easier to imagine time going on forever, or space never ending, than to imagine some sort of bottomless gravitational pit; I think this is because infinite calls "boundless" to mind, it is harder to imagine some sort of horizon around a well we can easily make a turn around. Gem fr (talk) 12:41, 9 October 2019 (UTC)

Nobody knows where the stuff goes, or what happens to it. We call the centre of a black hole a "singularity" (in both the mathematical and gravitational senses) because the mathematics we currently have seem to indicate that it becomes infinitely small and dense, but we don't necessarily think that's literally true, and accept that we don't (yet) have the theory or mathematics to understand what is really going on. The people who eventually figure it out will undoubtably win Nobel and other prizes. {The poster formerly known as 87.81.230.195} 2.121.161.82 (talk) 06:28, 9 October 2019 (UTC)

Specifically, we don't know without an accepted theory of quantum gravity.--Jasper Deng (talk) 06:39, 9 October 2019 (UTC)

or any other theory, for that matter. So we don't know, period. Gem fr (talk) 10:17, 9 October 2019 (UTC)

Stephen Hawking knew a little about it too.--Jasper Deng (talk) 10:29, 9 October 2019 (UTC)

And I will add that stuff falling into a black hole will never be seen to cross the event horizon. It will appear to approach the speed of light and be red shifted to invisibility. If Hawking radiation is real, then the infalling material will never get to the balck hole event horizon before it evaporates. So there is no reason to worry about the interior of a black hole, as there is nothing there yet. Graeme Bartlett (talk) 11:34, 9 October 2019 (UTC)

That's is not the case to an observer the fall seem to take infinite time. From the falling matter perspective, the time is finite. אילן שמעוני (talk) 19:22, 13 October 2019 (UTC)

Longest time alone in Space.

Who holds the record for the longest time in space without another human being in the spaceship? Is it one of the Mercury or Early Russian flights, one of the CM Pilots while the LM was down on the moon or someone else. (I was watching the first episode of the original Twilight Zone and I'm not sure in reality we've ever had someone alone for that long in space (in the episode, I think it was several weeks).Naraht (talk) 03:32, 9 October 2019 (UTC)

According to List_of_spaceflight_records#Longest_solo_flight, Valery Bykovsky hold that record at almost five days. WegianWarrior (talk) 04:07, 9 October 2019 (UTC)

Thx.Naraht (talk) 14:10, 9 October 2019 (UTC)

Notably, Steve Fossett conducted a solo balloon flight around the Earth, in the capsule for 13 days - alone in a flight vessel, traveling around the Earth for a longer duration than any astronaut on an orbital mission. Although he didn't reach the fairly-arbitrary altitude that many organizations claim as the "boundary" of outer space, his craft and his missions were historic and record-setting. Nimur (talk) 14:44, 9 October 2019 (UTC)

The figure used as the boundary of outer space may be arbitrary, but any altitude where travel by balloon is possible is clearly not in space. --04:28, 10 October 2019 (UTC) — Preceding unsigned comment added by 76.69.116.4 (talk)

That would depend on how you define space. If it's by an absence of a detectable atmosphere, then I agree. But there could be other measures, like the percentage of UV light that's blocked, where virtually none would be blocked at that height. SinisterLefty (talk) 05:12, 10 October 2019 (UTC)

If you think someone defines space that way, I say "". --76.69.116.4 (talk) 07:15, 10 October 2019 (UTC)

It's where the sky turns black and a jet engine won't work anymore. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:36, 10 October 2019 (UTC)

See Kármán line for sourced definitions. PrimeHunter (talk) 12:29, 10 October 2019 (UTC)

Global radiation budget - the numbers don't add up?

I'm referring to a diagram in Outgoing longwave radiation. According to the nice diagram, Earth receives 235 W/m^2 from the sun, and emits back (195+40)=235W/m^2. Thanos would say "Perfectly balanced... as all things should be." Evidently this can not be true since the warming already occurs and is easily measured. What gives? אילן שמעוני (talk) 06:30, 9 October 2019 (UTC)

The surface of Earth is constantly being warmed by the hot interior. Dbfirs 06:35, 9 October 2019 (UTC)

In that case it should have been warming forever. I mean even if all there was no sun to warm Earth up, it would have been (452-235)W/m^2 balance. That doesn't work either. אילן שמעוני (talk) 07:53, 9 October 2019 (UTC)

Geothermal heat only accounts for about 0.09 W/m², according to Earth's internal heat budget. Heating the top 200 meters of the oceans by 0.02 K per year takes about 0.4 W/m², which is much more than the geothermal heat, but still low enough to disappear in the rounding of that 235 W/m² ingoing and outgoing radiation. PiusImpavidus (talk) 09:00, 9 October 2019 (UTC)

The warming is on average about 1 Watt per square meter. It's small enough to get lost in rounding errors on a simplified diagram. Someguy1221 (talk) 09:59, 9 October 2019 (UTC)

OK, makes sense. I suggest, though, that because of the importance of the issue, the diagram must present this 1 W/m^2, either substructing from the output or increasing the input. אילן שמעוני (talk) 11:18, 9 October 2019 (UTC)

I copy this question+answers to Talk:Outgoing_longwave_radiation#Global_radiation_budget_-_the_numbers_don't_add_up?. I suggest we'll discuss modifying the diagram there. I do not know the rules here about transferring discussions so I will not delete it from here. אילן שמעוני (talk) 11:21, 9 October 2019 (UTC)

The question has been answered. See bullet points #2 and #5 of Wikipedia:Reference_desk/Guidelines#What_the_reference_desk_is_not. TigraanClick here to contact me 11:23, 10 October 2019 (UTC)

1)warming is not easily measured. Humans just started studying the stuff less that half a century ago, argo floats started less than 20 years ago, satellites started not long before, etc. Lots of this stuff is still just estimates, produced by models (that is, NOT data). You'll find in Earth's energy budget another estimates, were the values are actually close to 240 W/m², and a 0.6 W/m² imbalance. Both lacks accuracy and precision, if these were given, there would be surprises... 2)Actually, there is just no reason why the thing would perfectly balance. Each point of the Earth is always out of balance, gaining energy by day/summer, losing it by night/winter. There are, for sure, some balancing mechanisms, but not some perfect control. 3)even if it were a perfectly balanced energy budget, some "warming" or cooling can be experienced. This just require some energy moving from a reservoir to another with a different Heat capacity. For that matter, and for instance, heat capacity of water (ocean) is 4,184 J/K/kg, while Nitrogen's (atmosphere) is only 736 J/K/kg (that is, air temperature will rise >5x more than ocean temperature will fall, if energy is transferred from the latter to the former; and vice versa). Also, water turning to ice will release heat with no local change of temperature, but the released heat could find its way elsewhere where it will rise temperature. 4)you can have the same budget with very different average temperatures, because radiated power is ~T4. For the same budget, the average temperature will rise if the range of temperatures gets smaller, and lower if the range broaden. (Bottom line: temperature is an awful metrics of warming, and average temperature an even worse, if possible. This is one of the very first thing you learn in thermodynamics). 5)the balance numbers say absolutely nothing about the temperature. For instance, Venus as so great an albedo that the energy that enter the Venus thermal system is less than 235 W/m² -- and so is the energy getting out -- (not sure of the value, can be calculated from relative solar constant and albedo of Earth and Venus), but it still has far greater surface temperature all in all, you do need a positive imbalance to increase the energy inside the system, but whether this will result in a temperature rise is quite different. And, symmetrically, you can very well experience temperature rise while energy is balanced. Foehn wind is an interesting example of air actually losing energy, but increasing temperature. Gem fr (talk) 12:02, 9 October 2019 (UTC) The source for that diagram, which is originally a NASA science summary poster, further cites Earth's Global Energy Budget (2008), which gives detailed analysis and summarizes the NASA CERES project to aggregate source-data from ground- and satellite- measurements. Readers who are concerned with the data beyond the decimal-places probably need to go a little further than the summary-poster, which is essentially just an informative and educational cartoon for consumption by children. The really authoritative data and analysis of Earth's energy balance will be found published in scientific literature; and while there is room for a little bit of scientific disagreement and/or uncertainty, the numbers in most analyses do actually add up to a net warming effect - otherwise, responsible scientists wouldn't be so confident in their statements that our planet is presently experiencing a warming trend. The exact details are complicated - where the energy comes from and where it goes - but when we reduce it to a single net incident power figure, that value is positive - and while the value superficially appears to be quite small, it is still larger than the uncertainty, and also larger than a negligible quantity - so it is manifesting as as a true effect on our climate. Nimur (talk) 14:59, 9 October 2019 (UTC) In science when you have 2 legit measurement of something, say 235 and 240, then the uncertainty cannot be less than their difference, that is, 5, no matter what each source claim. And, uncertainty add up even when you subtract to get a net. That is, the uncertainty on net incident power is no less that 10. Which is far more than the claimed 0.6 (meaning, this could actually be anywhere between -9.4 and +10.6. Since it is highly implausible that the real value is so far off 0, it just mean we don't know, and just should tell that). Now if the 235 figure is NOT legit anymore, which could very well be, it should just be erased from wikipedia. I would also be very concerned if the claimed uncertainty for the 235 figure was lower than 5: unless some drastic improvement in uncertainty estimates is documented, there is no reason why the new figure is as accurate as it claims to be. Gem fr (talk) 15:30, 9 October 2019 (UTC) I'm not really here to quibble over which digit is correct. My point is pretty simple: interested readers who care about scientific accuracy should be consulting the published literature. Wikipedia, as an encyclopedia, is not a good place for this level of detail - especially not when it comes to very precise and accurate quantitative factual data. What we can and should be doing here is to point our readers to good resources - references - like the specific scientific source for the diagram at issue in our OP's question, or to recent publications Bulletin of the American Meteorological Society or Geophysical Research Letters. Those sources are updated frequently - e.g., if you care about the most accurate numbers known to the scientific community and vetted by the peer-reviewed professional staff, as of this week, then pop over to one of those publications. They literally have the latest energy-budget numbers, and they cover the academic debate over the details - as of this week. There are just too many complicated details for the volunteer editors of our articles to curate, nor even to perfectly remove all the stale or outright-wrong data. We do our best, but this kind of work is a full-time endeavor, and that's why professional publications exist. Our volunteers can't reasonably sift through volumes of detailed data or cull the stale data from millions of articles or fact-check a million changes a day. We are volunteers. We keep the egregious errors out, and we try to make sure the information is accessible to a wide audience. What we have is a bunch of mostly-good articles that provide broad-brush-strokes summary information. If you're the kind of person who needs to know numbers, this encyclopedia isn't the right format. Those who cannot be bothered to expend the effort (or cost) to find and use the professional publications are just going to have to settle for "free"-quality facts. Categorically, that is going to mean less clarity, less quality, and less timeliness in the delivery of the current state of knowledge. As a case in point, the reader who stumbles through our article won't know if the net energy flux is -9.4 watts, +10.6 watts, or negative a-thousand wibbly-watts because it has been recently-vandalized. There isn't a full-time professional editorial staff to provide peer review here. That's just how it is. So use your brain, be paranoid about the sources of your information, and be prepared to justify any data that you present. Take my advice on this point: it's waaaaaaay not useful to quote ten significant digits when we talk about climate. It is useful to quote a methodology and a reliable source. Observe: "NASA scientists accurately computed the global energy budget by analyzing satellite data, and here is some of their work: the CERES instrument on the Terra satellite mission. These scientists have rigorously studied the data in detail, and they concluded - along with most other scientists - that Earth is warming and humans are causing this climate change, and we need to get our pollution under control." The decimal digits don't really even matter. Nimur (talk) 15:48, 9 October 2019 (UTC) Actually, there is noting to curate about this series of article, just like pretty much all politically touchy stuff, it is completely overrun by activists claiming to be scientists holding the truth: "we need to get our pollution under control", while pretty obvious, is just NOT science (see, I am paranoid enough ;-) ). Now, here is not the place to make or complain about science, we take things as they are, no matter how full of crap, so Wikipedia will be fine in, like, 3 decades, when some science will actually have been done (it just began). Gem fr (talk) 17:28, 9 October 2019 (UTC) I'll just pop in here to note that you make a flawed assumption to begin with - that the uncertainty in the difference between two values even has to bear a relation to the uncertainty in the values themselves. You ignore the possibility that there is an entirely separate method of measuring the difference itself.[1] Someguy1221 (talk) 19:05, 9 October 2019 (UTC) Ye, this is the kind of stuff that is highly damaging to climate science. Earth albedo is about 0.30; 1 is worth ~340 W/m², so 0.001 albedo 0.34 W/m². If albedo were just the only thing with uncertainty (and is it not, among the hundreds of parameters of Hansen's model), you would need to know it precisely at ~0.0004 precision to get to the claimed O.15 W/m². Just check yourself NASA data (as good as possible, but still not without uncertainty data): [2] ... And that, even with disregarding the fact that climate is chaotic, that is, uncertainty exponentially increases with iterations (that is, a 0.001 W/m² uncertainty grows not to 0.002 then 0.003, but to 0.01 then 0.1 W/m², and keep growing until it all turn to nonsense. aka butterfly effect). You have to have good pal reviewer to get away with this, and he does. And of course, you did not even noticed the prediction of the paper failed, despite being quite weak. And somehow the line of reasoning "A=>B, B, so A" doesn't seem strange to you. You probably forgot Feynman's warning "Science is the belief in the ignorance of experts". Gem fr (talk) 21:35, 9 October 2019 (UTC) Are the world's glaciers melting? ←Baseball Bugs What's up, Doc? carrots→ 21:47, 9 October 2019 (UTC) Has the climate experienced flat zero natural change in half a century for the first time in history? Have a bunch of geniuses discovered a magic statistical bullet to assess this and to predict the future of a chaotic system, shitting on Edward Lorenz legacy and pretending he did not warned them, with no one applying in all other trades this sure recipe for so fabulous wealth it would make Larry Ellison's ridiculous, without getting three Nobel prize (chemistry, physics, Medicine) and a Fields medal in the process?Gem fr (talk) 09:42, 10 October 2019 (UTC) I don't see anything in the Ed Norton article about glaciers. ←Baseball Bugs What's up, Doc? carrots→ 10:20, 10 October 2019 (UTC)