Wikipedia:Reference desk/Archives/Science/2017 December 9

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December 9

Is there a way to know that NASA didn't know about an asteroid?

I just spotted a sensationalist news article ([1]) that an asteroid capable of "destroying New York City" went past the Earth at a third the distance to the Moon, and NASA didn't detect it until it was headed away. They accept the explanation that NASA simply missed spotting the asteroid before that -- they are supposed to have found most of them but of course never all of them.

But of course, I can think of another potential interpretation. Maybe NASA knew it was coming but couldn't be sure it was really going to miss Earth, and stayed mum about it. Possibly some senior politicians were given a chance to shelter, but the general proletariat needs to work, not panic, right?

So... is there a way to post mortem what happened? Can you look at the asteroid's trajectory, look up how NASA did its scan, and say oh, it went here before they looked thataway and after they looked thataway? I would imagine that some post mortem would be expected to come out in a case like this. Wnt (talk) 01:38, 9 December 2017 (UTC)

If NASA failed to tell us something, it will eventually come out. But how would widespread panic have served anyone's purpose? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:49, 9 December 2017 (UTC)

hehe, you remind me of the guy with the bullhorn at the World Trade Center who told the cubicle drones to get back to work. "نفديك بالروح وبالدم", American style, eh? Wnt (talk) 02:06, 9 December 2017 (UTC)

"We give you soul and blood"? What has that got to do with anything? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:47, 9 December 2017 (UTC)

There's a rather creepy tradition in the Middle East of people chanting that they sacrifice their blood and their souls to (some leader). In the WTC I guess it was the corporation. And here, well ... a lot of little people have to keep going about their lives if the big shots are going to catch their cab and their plane to the deep shelter, no? Wnt (talk) 18:11, 9 December 2017 (UTC)

All of NASAs data is public domain, and nearly all of it is regularly published on publicly available scientific repositories. In particular, the data of the various sky surveys is available. Space is big and asteroids are small, often dark, and fast - we cannot constantly scan all of the heavens all of the time. Any data will first be seen by some random NASA scientists, not by upper management. Just imagine how big a conspiracy you would need to keep such a thing secret. Then read On the Viability of Conspiratorial Beliefs. --Stephan Schulz (talk) 01:57, 9 December 2017 (UTC)

This is what I would hope. But is the data really being reviewed by random scientists like Lowell looking at glass plates, or do all these sky surveys go into a big computer program that spits out candidates ... and might omit some, leaving those who think they control it none the wiser? Wnt (talk) 02:08, 9 December 2017 (UTC)

At max brightness (c. 6:30a EST) it wasn't especially dim and not far from the anti-Sun, the Moon was 65% full and less than 90° away but not especially close, it was over 13 or 14°N latitude which isn't very inconvenient and near the plane of the solar system which is the most likely plane to look for asteroids. However it wasn't discovered till November 10th but it's designation is still only 2017 VL2. This means 2017 VA to VH and VJ to VZ were discovered some time time after October (by definition), then the second cycle (2017 Vx1), then half of the third. This has continued for a third of a thousand cycles in a dark V half-month which means very few minor planets were discovered before it this November. The 5 or 6 days before W half-month began saw 13 times more asteroids discovered than the other 9-10 days. This suggests that asteroid survey activity sharply drops off around Full Moon even when it's not close enough to full for avoidance of moonlight and twilight to be impossible (one of the best places to see it would've been Guam, it wouldn't have been that much harder to find (at a different time of November 9) for much of the big observatories outside Asia-Pacific though). If any amateur astronomers saw it they might've thought it'd already been discovered and didn't call it in. Amateur astronomers have a much harder time discovering asteroids and comets than say 2000 or 1995. There's lots of computer surveys now that I think automatically tag all moving objects based on whether they've discovered. It'd still require any amateur astronomer who saw it on the 9th to not be interested enough in a not that dim moving pretty fast (so near Earth) to look up what it is and then discover it's not discovered yet. They'd also have to not keep up with contemporary near-Earth asteroid flybys. If they did they'd probably wonder why they hadn't heard of a bright asteroid this fast and look it up and become the discoverer instead (emailing its coordinates to the Bureau of Astronomical Telegrams (is it still called that?) should make NASA know about it) Sagittarian Milky Way (talk) 05:17, 9 December 2017 (UTC)

CENTRAL BUREAU FOR ASTRONOMICAL TELEGRAMS STOP --47.157.122.192 (talk) 18:28, 9 December 2017 (UTC)

I stupidly radread the story when I saw it somewhere else before you linked to it. Well I mean I read the first few lines. It quickly became clear it was utter nonsense. As with all Daily Mail (edit: well I wasn't sure it was DM when I clicked but strongly suspect it was) stories it's sensationalistic, missing the point that this sort of thing isn't exactly a rare event. We're finding out all the time that something got slightly close to earth and we only just realised a few weeks or months later. (Edit: And those are the ones we know about!) Many people thingthink we need to get better at detecting these things sooner, although they often also acknowledge in some ways there's probably little pointactual advantage at thethis time since silly action movies aside, if we do find something headed here even in good time there's probably little we can do with outour current level of tech. Nil Einne (talk) 12:12, 9 December 2017 (UTC) edited at 06:48, 10 December 2017 (UTC)

It's worth noting that we could be doing a lot more to spot asteroids that might threaten Earth, like putting a telescope between Earth and Venus, but we don't because there's no political will to do so. Few people vote based on candidates' positions on asteroid defense. Of course, "conspiracy theories" are non-falsifiable, so maybe there is one there but the data is only made available to the Secret Conspiracy, and maybe they have plans to escape to their secret NASA child sex dungeons on Mars, and so on and so on. --47.157.122.192 (talk) 18:28, 9 December 2017 (UTC)

It's also worth noting that NASA's purpose is about space travel, space probes, airplane technology and things like that, not particularly about searching for asteroids. Here's a page of theirs about the sort of things they're working on currently. --69.159.60.147 (talk) 07:40, 10 December 2017 (UTC)

Big bang and size of the universe

At the Big Bang, the entire universe (as i understand) is thought to have been contained by a singularity. Does that imply that the universe as it now exists cannot be infinite? or could the singularity have contained an infinite universe within it? rossb (talk) 09:35, 9 December 2017 (UTC)

No, it doesn't imply it can't be infinite. There's a really simple "toy example" that shows this.

Suppose the universe at the current comoving time (let's normalize in such a way that the current comoving time is 1) is described by a standard Cartesian coordinate system — every point has (x, y, z) coordinates. And then suppose that, for particles moving along with the Hubble flow, at any time t before the present (that is, t<1), if the particle has coordinates (x, y, z) now, then it had coordinates (tx, ty, tz) at time t.

Then you can see that the universe is infinite, and was infinite at every time t>0. However, at time t=0 (that is, the exact instant of the Big Bang), all particles were at the same point.

It's a little hard to visualize the discontinuity, but luckily enough you don't have to. In practice cosmologists (almost) never talk about the exact moment of the Big Bang. They can talk about what happened 300k years after it, or a second after it, or 10⁻³⁵ seconds after it, but the Big Bang itself, no, they just don't touch that, usually. Could be it never happened at all; could be that time is an open interval that omits the instant of the Big Bang.

Of course there are all sorts of things wrong with the toy example in terms of relativity and known cosmology; it's not meant to be a serious proposal as to what happened. But it does show that the gross description of the Big Bang does not rule out an infinite universe. --Trovatore (talk) 10:28, 9 December 2017 (UTC)

I think this is the way to visualize the boundless universe. Let's say we live in a Universe of such a size that we cannot detect its boundary. Then all of a sudden a Big Bang happens here, right in the middle of our existence in such a way that every point of the space becomes a singularity. They all begin to expand and one of them will have all anthropomorphic parameters like our current Universe and eventually become populated by life forms. AboutFace 22 (talk) 16:11, 9 December 2017 (UTC)

No, I don't think that scenario (whatever it even means) is remotely responsive to the question. Mine, on the other hand, is. --Trovatore (talk) 20:03, 9 December 2017 (UTC)

• The notion of the universe emerging from a singularity was put forth by Hawking and Penrose in 1970, and they have since abandoned it as incompatible with quantum mechanics when the universe was the size of the Planck length. The question as posed is decades out of date. μηδείς (talk) 23:08, 9 December 2017 (UTC)

  Unless I've missed some spectacular development, no one knows how to reconcile general relativity and quantum mechanics. So it strikes me as speculative to say what the eventual reconciled theory would or would not say about the universe on the order of a Planck time after the Big Bang. But that just makes it even clearer that there's no direct or simple reason that the Big Bang should exclude an infinite universe. --Trovatore (talk) 21:04, 12 December 2017 (UTC)

The argument is that the notion of a Planck time after the singularity is meaningless, as quantum mechanics (the Heisenberg Uncertainty Principle) prevents a time or even smaller than the Planck time or length being physically defined. The matter is discussed at some length in The Fallacy of Fine Tuning whose first half deals with the Big Bang at length and in detailed math, with lots of meaty references. I just returned the book, so don't have the author's name at hand, but it was written in the last decade.

Hawking also discusses there not being a singularity in a more layman-friendly way in The Universe in a Nutshell. So, again, premising anything on a singularity pro-or-con infinity is dubious at best. The persistence of the idea of a singularity in the popular press and the confusion between an unbounded and a numerically infinite universe are two huge impediments to the discussion. μηδείς (talk) 21:58, 12 December 2017 (UTC)

The first work you refer to seems to be by Victor J. Stenger, and appears to be more an anti-theist polemic than a work of (or even exposition of) physics, which of course doesn't mean there isn't good physics in it.

The difficulty of dealing with spacetime either spatially or temporally below the Planck scale is well-known (this was I think the key issue in the earlier question about whether the universe "is" a manifold or just "is modeled by" a manifold). It doesn't follow that just because no one knows how to do it, it can't be done. Physicists are a bit prejudiced against singularities from the get-go, so while I haven't read Stenger or Hawking on this particular point, I'm not too impressed that they wiped their brows at the first reasonable excuse and said, whew, no singularities, go home, nothing to see here.

All that said, I completely agree with you that there's no basis for concluding anything about the finitude or infinitude of the universe from a presumed singularity at the Big Bang, whether or not such a singularity exists. And that in itself answers the original question. --Trovatore (talk) 00:58, 13 December 2017 (UTC)

Thanks; yes, it was Stenger. I found his intrusive anti-theist agenda distracting. All he needed to say was that even if there was a creation from a singularity it has nothing to do with the truth value of the claim that Jesus died for our sins. The scientific question of the strong anthropic principal (utter bollocks in my mind) was interesting enough that he need not have peppered the work with occasional potshots at young-earth fundamentalists and biblical literalists. In any case, if you can get through his turgid prose, the book is recent enough, and packed full of relevant scientific references. μηδείς (talk) 17:05, 15 December 2017 (UTC)

The idea of a singularity at the beginning of the universe seems a lot like the idea of a visual singularity at the horizon. I mean, the closer you look to the horizon the more stuff is packed into a confusing little space... then, eventually, some higher-order factor (the curvature of the earth) intervenes to conceal your view completely. Well, in the case of the early universe we're talking about unfathomable temperatures, particles with unfathomably relativistic speeds and/or high mass, according to unforeseen laws of unfathomably high energy physics. If a electron would need a thousand times the lifetime of the cosmos to complete one oscillation about a proton, and no atom can exist without being ripped apart a billion times over, is the time scale defined by our atomic clocks relevant? I tend to suspect that the length of time to cross the entire universe has always been a very long length of time in some more meaningful sense, especially when so many collisions would occur along the way... Wnt (talk) 22:52, 12 December 2017 (UTC)

The concept you want is an event horizon, User:Wnt. What's observable to us in our light cone is necessarily limited, anything beyond us for whatever reason; scale, time, entropy, distance; is beyond a horizon whether a singularity itself is involved or not. μηδείς (talk) 17:05, 15 December 2017 (UTC)

Cold-tolerant trees

How do woody plants survive the winter in cold climates? Consider taiga forests, which typically experience temperatures far below freezing. Xylem#Evolution (one of the longest non-table sections I've ever seen in an article) mentions how some plants are able to tolerate the effects of freeze-thaw cycles on their physical structures, but I'm more wondering about water and nutrient transport: when things are frozen, how does anything move? Ice can't be transported, in particular; I would imagine that a frozen tree would die for lack of water, but obviously that doesn't happen with your average healthy tree. Nothing else in xylem, and nothing at all in phloem, as far as I could see. Nyttend (talk) 17:04, 9 December 2017 (UTC)

How do Trees Survive Winter Cold? by Michael Snyder, Commissioner of the Vermont Department of Forests. Alansplodge (talk) 18:05, 9 December 2017 (UTC)

Alan's link is good, it's largely about antifreeze, and note that there just isn't much transport going on in the Taiga during winter. Our best general article is at Cold_hardening (And is understandably kind of hard to find if you don't know what they call it. Maybe you can link it from a relevant section of the other articles?). Hardiness_(plants)#mechanism is fairly useless. Antifreeze proteins are a big part of it, see e.g. here [2] for recent scholarly work. SemanticMantis (talk) 18:08, 9 December 2017 (UTC)

Critical is the part about water being relocated to storage organs; I wasn't aware that this was an issue. I guess I shouldn't be surprised by the lack of nutrient transport, since girdling doesn't kill a tree immediately (and deciduous trees survive temperate winters without leaves), but I was completely unaware of this stuff. Thanks a lot! Nyttend (talk) 22:21, 9 December 2017 (UTC)

Your original supposition "that a frozen tree would die for lack of water" was not too far wide of the mark though Nyttend; "Winter dessication or frost drought is assumed to be one of the main causes of the upper limit of tree growth in high mountains outside of the tropics..." Trees at their Upper Limit: Treelife Limitation at the Alpine Timberline (p. 5). Alansplodge (talk) 11:10, 10 December 2017 (UTC)

Exploding tree is relevant here. Wnt (talk) 22:45, 12 December 2017 (UTC)

Why isn't northern Vermont covered in ice?

New York City was covered in ice 20000 years ago. Since then, the Earth has warmed up 9°F.

At present, according to the cities' Wikipedia articles, New York City has a mean temperature of 55°F, and Burlington, VT has a mean temperature of 46°F, a 9°F difference.

This means that New York City 20000 years ago and Burlington, VT at present should have about the same climate with regard to temperature. Why isn't Burlington, VT (and southern Quebec) covered in ice like New York City was 20000 years ago? — Preceding unsigned comment added by HotdogPi (talk • contribs) 21:37, 9 December 2017 (UTC)

If temperatures warm, ice caps shrink and sea levels rise. Conversely, drop the worldwide temperature by 9°F, and increasing ice will lower sea levels, and oceanside cities like New York suddenly won't be on the ocean; the climate will be more continental because of the new inland location. Also, note that glaciers can exist where they can't form — since Arctic glaciers can spread southward, rising temperatures (and receding northern glaciers) mean that they have to travel a good deal farther to reach Burlington now than they did to reach New York before, even if the weather were similar. Glaciers won't always spread to adjacent places cold enough for them to tolerate (see #Ice-free northern Greenland), but they will in many situations. Nyttend (talk) 22:18, 9 December 2017 (UTC)

Also it seems hard for ice to survive for tens of millennia if the average annual air temperature was 46°F. Any precipitation in the summer would tend to be rain. These areas must've cooled more than the global average while the rainforests cooled less than the global average. Interestingly, global warming causes the poles to warm faster than the tropics. As a nitpick, only part of New York City was under ice at the last glacial maximum. Manhattan, the Bronx and the northernwestern halves of Brooklyn, Queens and Staten Island were under ice and the southeastern halves of those 3 boroughs weren't. There's no non-glacial ridge or something with this orientation and the ice limit parallels the 20000 BC coast so continentality may have something to do with the ice limit orientation. Sagittarian Milky Way (talk) 22:42, 9 December 2017 (UTC)

• Imagine a simple world-model in which the average yearly temperature is 40 degrees F. That could be consistent a mild climate with six months of 30 degree temperatures, where the snow never melts, and six months of 50 degree temperatures, where the snow melts slowly. Or it could be consistent with an extreme climate, where the 'winters' are 0 degrees F, and the 'summers' are 80 degrees F. Note that the average temperatures are the same: (30+50)/2 = (0 + 80)/2 = 40; but in the extreme climate all the snow melts quickly at the beginning of the warm period, while in the mild climate, even though the winters are warmer, the snow melts much more slowly over the summer, and some ice packs can last all year, building into glaciers.

This seeming paradox arises because although the average temperatures are the same on a year-round basis, snow doesn't care whether it is 0 degrees F or 30 degrees F. It won't melt in either case. The only thing that matters is the summertime temperature--the average temperature is irrelevant. Hence knowing only the average temperature difference between NYC and upstate Vermont tells you nothing. What matters is the summer temperatures in those places. μηδείς (talk) 22:59, 9 December 2017 (UTC)

The current annual temperature range of NYC is at least 43.9°F (more if you use daily averages instead of monthly and July avg highs instead of July avg means). Do you have evidence for your implied claim that the average annual temperature range of NYC when it had glaciers (and extra continentality) might've been only 20°F? Without seeing the evidence it seems possible but unlikely. Sagittarian Milky Way (talk) 23:35, 9 December 2017 (UTC)

Whom are you addressing, SMW? You have indented under me, ask "Do you have evidence..." and mention 20°F that I see nowhere else in this thread. μηδείς (talk) 01:20, 10 December 2017 (UTC)

50°F in summer and 30°F in winter is a 20° annual temperature range. Maybe glaciers formed that way somewhere near the West Coast but this doesn't seem to be the open and shut answer to the NYC/Vermont paradox (which it turns out is actually (at least partially) because the OP was mistaken and the NYC avg annual temperature was only ~33°F or less). Sagittarian Milky Way (talk) 22:20, 11 December 2017 (UTC)

Oh. That's a simple random coincidence based on my arbitrary choice of values with the same mean, and of no relevance to my point. I could have compared a year with constant 31 degree winters and constant 33 degree summers to one with 0 degree winters and 64 degree summers. The yearly snow accumulation would be vastly different (assuming the 0 degree winters didn't stop snow from falling due to lack of moisture in the air). You never mentioned "range" before my first post, although you did mention "average" four times, if I counted correctly. Range and avereage are totally different beasts. Hence my point that the average by itself is irrelevant. μηδείς (talk) 03:35, 12 December 2017 (UTC)

Temperature change is not uniform. Here is one estimate of the spatial pattern of change since the last glacial maximum: [3] Those temperature anomalies are in degrees C, so roughly double them if you want to think in degrees Fahrenheit. The biggest changes were associated with the melting of the Laurentide Ice Sheet over North America, where temperatures locally may have warmed >20 C (>36 F). For New York and Vermont, it looks like the estimated change is around 12-20 C (22-36 F), so much larger than the global mean change. Dragons flight (talk) 10:44, 10 December 2017 (UTC)

Warming continues to affect the poles more than anywhere else -- see https://data.giss.nasa.gov/gistemp/maps/ and make a map for say the latest five years vs. a reference period. (as I understand it, "the poles" are more or less land with high year-round albedo, water insulated by ice; melting that ice therefore increases surface temperature, which is averaged into a planet-wide temperature) Wnt (talk) 17:05, 10 December 2017 (UTC)

I think you are mistaken about the temperature change since the last glaciation. It probably was 9°C, not 9°F. See File:EPICA_temperature_plot.svg. Ruslik_Zero 19:58, 10 December 2017 (UTC)

@HotdogPi: In fact it may be lower than that: this paper indicates that the temperature anomaly may have been about −12°C or lower near present day New York. Ruslik_Zero 20:17, 10 December 2017 (UTC)

No, 9 F (5 C) is about right for the global mean change (plus or minus a few degrees of uncertainty). More at the poles (like EPICA), and less in the tropics. There was a good deal of spatial variability. See the map in my previous post. Dragons flight (talk) 22:33, 10 December 2017 (UTC)

There is some debate about the mean change. In addition all those anomalies are relative to the pre-industrial temperatures which are probably by ~1°C lower than the present day value. Ruslik_Zero 20:10, 11 December 2017 (UTC)

The way snow melts

I noticed that when the temperature rises above zero after a colder period, sometimes all that is left of a layer of snow, is where I walked through it, just a track of footprints made of snow.

Is it because compressed, denser snow is more resistant to the heat? Languagesare (talk) 21:50, 9 December 2017 (UTC)

Its mostly because normal "fresh" snow contains allot of air. Since air is a very good insulator it will slow down the complete melting. --Kharon (talk) 22:52, 9 December 2017 (UTC) Wrong. Much more complicated. --Kharon (talk) 06:05, 10 December 2017 (UTC)

Are you saying that the footprints "compress" the air as well as the snow? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:09, 9 December 2017 (UTC)

Kharon seems to have misinterpreted the question, since the OP says that the unpacked snow melts, and only his footprints are left, not that the footprints melt and only the fresh snow is left. μηδείς (talk) 02:41, 10 December 2017 (UTC)

It may be that Kharon is from a place that rarely sees snow. You and I both have had plenty of exposure to snow, and the OP's question describes a familiar phenomenon. And the OP's answer-in-the-form-of-a-question is what I would assume to be the explanation. Snow that's more densely packed will tend to take longer to melt. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:22, 10 December 2017 (UTC)

Yes, I was wrong and i misunderstood the question. It seems compacted snow takes longer to melt. I tried to read up about that but most of the literature on snow and melting is focused on Glaciers. However one major accelerating factor for the melting process seems to be that the melting water from a melting surface will flow down easier into uncompressed snow, that way transporting the heat from the surface down faster the less compact the snow crystals are baked together or even transformed into polycrystals. --Kharon (talk) 06:05, 10 December 2017 (UTC)

On mountains, uncompacted powder snow is often blown away leaving raised footprints, an important clue that a slope is not likely to be avalanche prone; however the loose snow is likely to have accumulated dangerously elsewhere, so they are both a good and a bad sign for winter mountaineers and off-piste skiers. [4] Alansplodge (talk) 11:02, 10 December 2017 (UTC)

No one has pointed out that snow has a greater crystalline surface areas than compacted ice by the order of several magnitudes. Back when ice was stored in ice houses, straw or saw dust was used to fill up all the gaps to stop the circulation of air. Air contains water vapor and water vapor transports heat. Water vapor has a high vapor pressure, and at the very moment the air temperature rises above 0 deg C, the dew point will suck heat carrying moisture out of the air. So of course, un-compacted air permeable snow is going to melt much quicker. Aspro (talk) 22:34, 12 December 2017 (UTC)

Thanks to everybody who answered!

Languagesare (talk) 22:06, 14 December 2017 (UTC)

United States map

Aaaarrrgh! Please help. I'm looking for a normal, high quality map of the US, like what you'd have on the wall. You know, a bit of topo, roads, cities, colours, that sort of thing. It is absurdly hard to find for me. Many thanks! Anna Frodesiak (talk) 22:18, 9 December 2017 (UTC)

Do you want to buy a physical map, or just have a machine readable one with a large size and a free license? You can also search google: https://www.google.com/search?q=united+states+map&dcr=0&tbs=sur:fmc,isz:lt,islt:4mp&tbm=isch&source=lnt&sa=X&biw=1280&bih=650&dpr=1.5 Graeme Bartlett (talk) 23:40, 9 December 2017 (UTC)

There's a company called WallPops selling through Walmart and Target that has National Geographic maps of the US for sale. They're about $15 dollars. Just Google it really. They're not hard to find.--Jayron32 03:28, 10 December 2017 (UTC)

Actually, I just want to view it on the computer. I just want that sort of map. Anna Frodesiak (talk) 05:17, 10 December 2017 (UTC)

Is this downloadable one any good? Or this screen view? Or did you want one you could use in a Wikipedia article? Alansplodge (talk) 10:49, 10 December 2017 (UTC)

Those are great! Thank you!

Now, I know commons has good maps, but how on Earth are people supposed to find them? Many people must go there for a normal map, as I described above, but just not be able to find one. Can anything be done? Maybe some sort of lead map at the top of the main cat? Anna Frodesiak (talk) 11:17, 10 December 2017 (UTC)

Anna Frodesiak, try to export OpenStreetMap. There are already several views. --Hans Haase (有问题吗) 11:41, 10 December 2017 (UTC)

Thanks Hans Haase. Actually, that's not a bad idea but the high res links above are best. Cheers and many thanks. Anna Frodesiak (talk) 02:24, 11 December 2017 (UTC)