Wikipedia:Reference desk/Archives/Science/2021 March 8

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March 8

chemistry

heating ammonia on a bunson burner makes what poison? — Preceding unsigned comment added by 173.49.56.54 (talk) 13:31, 8 March 2021 (UTC)

Ammonia can be used as a fuel (see Ammonia#Uses) and when oxidised will give the oxides of nitrogen, mainly nitric oxide or nitrogen dioxide as well as water, depending on how much oxygen was available. However, assuming that you had an aqueous solution of ammonia (which is the form most readily available), the main result of heating it would be to generate gaseous ammonia and give you a nasty, choking smell and eye irritation. So, overall, don't try this at home! Mike Turnbull (talk) 17:01, 8 March 2021 (UTC)

Speaking as someone who used to work with ammonia on an industrial scale, I couldn't agree more with your last point. On one occasion, workers on the plant got severe headaches and nosebleeds from having the wrong filters in their respirators (for dust rather than vapours) while they were handling multiple kilograms of ammonia. Rhythdybiau (talk) 19:24, 8 March 2021 (UTC)

I #3 this -- I experienced it the hard way by accidentally inhaling ammonia vapor, and although it was only a small amount I burned the inside of my nose quite severely and lost all sense of smell for several weeks! 2601:646:8A01:B180:C98E:59B1:C877:CE68 (talk) 06:27, 9 March 2021 (UTC)

Back in 2009, a natural gas line at a ConAgra plant making Slim Jims exploded about 2 miles from my house. The explosion ruptured an ammonia gas pipe; compressed ammonia is a common refrigerant. It was a Big Deal. Several tons of ammonia gas were leaked in a short period of time. read about it here. Ammonia is all kinds of useful, but also all kinds of dangerous. IIRC, it wasn't the natural gas explosion that caused most of the injuries from the accident, it was the ammonia leak. --Jayron32 13:03, 9 March 2021 (UTC)

In standard model of particle physics, what needed to be discovered?

From thorough research, I find Graviton still needed to be discovered. So anything else needed to be discovered in standard model table? Rizosome (talk) 13:36, 8 March 2021 (UTC)

The graviton is not part of the standard model. The Standard Model does not include gravity as among its forces. The most recent, and arguably last necessary, discovery to complete the Standard Model was the Higgs boson, discovered in 2012. Which is not to say that the Standard Model is a "theory of everything". It is not; it is only complete over its own domain with regard to particle physics, and then only in the sense that the fundamental particles it predicts have essentially all been discovered. It doesn't include gravity because it wasn't ever really designed to include gravity. It is self-consistent in the sense that it has no internal holes (i.e. nothing that it actually predicts is wanting or undiscovered or contradictory), but it is not, nor does it try, to account for all physical phenomena. There are a LARGE number of unsolved physics problems that the Standard Model does not address, and which are still largely unsolved. You can read more about this in several places. First of all, in the Standard Model article, in the lead section, the entire second paragraph deals with various aspects of physics the Standard Model leaves unanswered. Secondly, in the same article, if you go down to the "Challenges" section, you'll find some elaboration the same topic. Thirdly, there are several other Wikipedia articles you can read to learn more, including Physics beyond the Standard Model, and List of unsolved problems in physics. --Jayron32 19:21, 8 March 2021 (UTC)

Backwards time travel during black holes merger

In this video Neil deGrasse Tyson claims that before the event horizons overlap there's a trajectory that results in backwards time travel. Is there any serious, cite-able source for this? אילן שמעוני (talk) 19:56, 8 March 2021 (UTC)

Timestamp? --Amble (talk) 21:12, 8 March 2021 (UTC)

What? אילן שמעוני (talk) 08:41, 9 March 2021 (UTC)

"Timestamp" presuambly means at what point in that 17 minute video? Context is everything, but we don't want to have to watch the whole thing.--Shantavira|^{feed me} 09:01, 9 March 2021 (UTC)

The link was wrong somehow. Here's the right one that already contains timestamp: https://www.youtube.com/watch?v=iLKTZr00xBg&t=139s

אילן שמעוני (talk) 09:30, 9 March 2021 (UTC)

Sounds like bunkum to me. When I wrote the binary black hole article I consulted around 100 academic papers on the topic, and I cannot recall any such mention. If backwards time travel was in there I would certainly have noticed and written about it. Even more surprising than what NdGT mentioned was masses of black holes in a merger 1+1≠2 instead 1+1≈1.9 as mass is lost due to gravitational waves. Also when the gravitational waves pass, space is permanently deformed. And since gravitational waves carry momentum as well as energy, the merged black hole can shoot off at high velocity. Graeme Bartlett (talk) 11:00, 9 March 2021 (UTC)

Velocity at the expanse of mass? אילן שמעוני (talk) 12:49, 9 March 2021 (UTC)

Such things don't even require two black holes. Just one rotating black hole is required. See Penrose process. --Jayron32 15:36, 9 March 2021 (UTC)

• It sounds like he's oversimplifying the concept of a Closed timelike curve, but this is a well-trodden area of theoretical physics and General relativity. For most standard solutions, the spacetime path of a closed timelike curve ends up inside the event horizon of a black hole, or some other thing which makes them essentially useless for practical time travel; indeed one of the axioms of physics is causality, insofar as even if in some way time travel were possible, it wouldn't be possible to violate causality; this is called the Chronology protection conjecture, and basically says that once you actually work out any spacetime path that would result in actual time travel (except in the case of virtual particles and things like that where information can't actually be transmitted backwards in time, even if the particles themselves can travel that way) ends up not working because some other aspect of physics gets in the way. What NdGT is talking about, from my understanding, is that in the rare case of a pair of colliding black holes, there is a spacetime path that does not cross the event horizon of either black hole and thus would be theoretically possible. These kinds of bizarre solutions have been known about for some time, indeed Hawking proposed the chronology protection conjecture to deal with them; IIRC his solution was that something we haven't yet discovered about quantum gravity would turn out to fix the problem that NdGT is depending on to make his statement. --Jayron32 12:52, 9 March 2021 (UTC)

Sounds plausible enough. Whatever this specific solution is - he can't be the source for it - he himself states that GR math is not his field. Question is where he got this from. אילן שמעוני (talk) 15:22, 9 March 2021 (UTC)

The answer is likely "from something he vaguely remembered about closed timelike curves". It's "right enough" for the discussion he's having with the child in question, but of course lacks nuance. I couldn't find a specific example, but I didn't look too hard. If you google "closed timelike curve merging black holes" or something like that, you may find the specific scenario in question. --Jayron32 15:33, 9 March 2021 (UTC)

I did this search of course, found nothing relevant. אילן שמעוני (talk) 22:43, 9 March 2021 (UTC)

Thanks for the corrected link. As Jayron points out, Tyson is describing a closed timelike curve (CTC). There are many papers that include a review of spacetimes in GR that contain CTCs: [1], [2], [3]. If someone had shown that mergers (or near-miss encounters) of black holes gave rise to CTCs that don't cross an event horizon, that would be an essential result that would answer some of the open questions raised by that literature -- definitely important enough to be mentioned in these reviews (so that Graeme Bartlett would have read about it hundreds of times by now). So what is Tyson talking about here? Here are two possibilities that I think are reasonable:

1. He's talking about the Gott solution [4], which is one of the standard examples listed in the review articles and involves two objects passing by each other in a way very similar to what Tyson describes. However, it requires the objects to be infinitely long cosmic strings, not black holes. It sounds to me like this is what Tyson has in mind, and he's giving it as an example of the kind of thing that could happen with strongly curved spacetime, while leaving out the caveats (or else misremembering them).
2. He's talking about wormholes in the Kerr metric. This does relate to black holes, although it doesn't need two black holes; one is enough. This is another standard example listed in the review papers. It contains CTCs, but none that are entirely outside the event horizon, as Tyson seems to imply, but doesn't quite say. When he says "go around", he might be referring to paths that go through the middle of a ring-shaped singularity.

My best guess is that he's really talking about these types of scenarios in general, especially the Gott and Kerr solutions which are well known, and not trying to describe a specific solution (which might not be remembered in detail off the top of one's head). I don't think there's a known solution where encounters of two black holes produce CTCs that don't cross the horizons, since this would be an important result that would be mentioned in all the review articles, but we don't find it there. --Amble (talk) 18:07, 9 March 2021 (UTC)