exchemist

Aren't you forgetting the strongest interaction by far, in both cases: hydrogen bonding?

I'm not so sure. This is an ion, HeH⁺, that is isoelectronic with H₂, i.e. with 2 electrons in a σ-bond formed by overlap of the 2 1s atomic orbitals. Though it will be strongly polar, due to the higher charge on the He nucleus (i.e. the 1s on He will be pulled in and won't overlap so well). I'm sure it is highly reactive: as a cation it will tend to pull electrons off whatever it comes into contact with, and it can easily form He by donating the proton to something. What strikes me about it is that as, unlike H₂ it is polar, it will have a vibrational and rotational spectrum, so presumably can be detected in the IR and microwave regions of the spectrum. P.S. I see there is a Wiki article on it: https://en.wikipedia.org/wiki/Helium_hydride_ion#cite_note-Epa-23 according to which the bond strength is 178kJ/mol, about 40% that of H₂ so quite respectable. Also I notice they think it was a constituent of the primordial plasma, 280,000 yrs before the universe became transparent. So presumably it is not expected to fall apart thermally so easily.

Also, it is now common practice for plumbers to freeze the water in a radiator pipe when disconnecting the radiator, thereby avoiding the need to drain the system. (I've had a guy do this to two radiators in my house recently.) So clearly it can be done without cracking the pipe. Copper is ductile so can take a certain amount of stretching before it cracks. From what I have managed to look up quickly, it retains this ductility down to very low temperatures. So my best guess would be it is unlikely to split - provided there are no joints in the vicinity.

Not on the basis of this and other similar poor reviews I've read.

No, it just seems to be a terrible film, that's all: https://www.theguardian.com/film/2021/dec/27/look-away-why-star-studded-comet-satire-dont-look-up-is-a-disaster. According to the review it is worthy, cynical, smug and condescending. And who is it for? According to this review, it seems to be made for people who inhabit the same bubble as the film maker, encouraging them to point fingers at everyone else.

Then you need to put forward a mechanism by which a photon can somehow transfer a part of its quantum of energy to another entity, without being deflected from its trajectory. As I and others have pointed out, the known scattering processes are no good because these deflect the light in all directions, so that it would no longer seem to be coming from the source in question. In other words they would just attenuate the signal rather than reddening it. So you must have some new process in mind, unknown to physics so far. What is it and how does it work?

I don't see why a satellite can't just sit at L2, albeit with occasional nudges to keep it there and stop it starting to slide either in towards, or out away from, earth, which is what would otherwise happen, given that L1, 2 and 3 are only metastable locations. There was some information posted earlier in the thread explaining that the the telescope will be put into an orbit so as to keep it out of the shadows of the earth and the moon. I'm not sure why this is necessary, but evidently it is.

Now now, don't be greengrocerist.....😊

Well to be fair there are some inelastic scattering processes involving photons (see: https://en.wikipedia.org/wiki/Raman_scattering ), but as these involve scattering, they change the direction of the photon as well, so they cannot be responsible for the red shifts we observe.

And Happy New Year to you as well. Yes my error was to consider everything as happening in the plane of the ecliptic. In that plane you see a saddle, but that is because it is a cross-section through a doughnut.

Impossible to determine just from reading one co-authored paper. But one can get an idea of how Tozzi is seen by people working in the field, by the quality of the collaborators willing to be associated with him and by the quality of the institutions that recognise him, and them. From that point of view I don't see any danger signals.

Well done, you've found it! The stack exchange correspondence explains it. What I was missing is that this is of course a 3D problem. In the plane of the Earth's orbit around the sun, it is a saddle, with the flanks of the saddle extending radially towards and away from Earth. So an object that is not exactly at L2 will tend to slide in or out along the radius of the Earth's orbit around the sun. BUT, perpendicular to that radius, it is a gravity well, so an object can indeed orbit L2 if it does so in a plane perpendicular to the radius. The only correction needed is to stop its tendency , driven by the saddle effect described earlier, to drift in or out along the radius, i.e. to stop movement out of its orbital plane around L2. I think that must be it. But let's see if @Januscan be tempted away from his mince pies and port to confirm.

Now and then? If it's a saddle, there is no orbit at all, surely? Any object not perfectly at L2 will tend to oscillate between the "upward" slopes to either side of the saddle, while at the same time "falling down" one or other flank, never to return. That's never an "orbit" with occasional tweaks. It seems to me that making the telescope describe a closed loop around L2 has to be a totally artificial exercise, requiring continual interventions to force it into such a path. Why do that, considering the expenditure of rocket fuel when, if it just sat at L2 itself, it would require only tiny corrections as it started very slowly to drift off-station? I realise I must be missing something here but the responses to date don't seem to be addressing my difficulty.

Yes you have a point. 300MW is the output of a decent sized power station.

These videos do not answer my question. Later note: To explain myself a bit more: according to my understanding, there is no centripetal force acting towards L2, to keep an object in orbit around it. On the contrary, as soon as an object drifts away from L2 by even a minuscule amount, the net forces cause it to move even further away. There is thus a kind of net repulsion from L2, rather than an attraction towards it (if I understand the situation correctly). I do not understand how an object can orbit L2 on this basis. If what they are doing is artificially keeping the telescope in a circular path around L2 by means of rocket thrust, that is not an orbit - and why are they doing it?

I see that it is said the telescope will not just sit at L2 but will be in orbit around it. I don't understand how this works, as I gather that L2 is at a "peak", rather than a"hollow", in the gravitational field due to the Sun/Earth system, with the result that objects at L2 will drift away from it (rolling down the slope, as it were), unless artificially returned to it at intervals. If this is right, how can the telescope orbit L2? Can someone explain?

No. True and false conclusions derive from testing a proposition against given information. There is nothing necessarily +ve or -ve about that. As for fuzzy computing, I know essentially nothing about this but my very limited understanding is that it is designed for situations in which the information supplied is not definitive, or is expressed in terms of a range, e.g. of probability, and returns an answer that is similarly expressed as a range e.g of probability, rather than a "black or white", true or false result. Quantum computing is something else entirely. I gather it is to do with faster speeds and miniaturisation (hence greater computing "power"), rather than any different logic.

I thought logic mainly returned values of "true" or "false" rather than +ve or -ve. But then there is fuzzy logic.............

Yes I get an ad strip at the bottom of the window (I'm on Apple Mac Safari). Irritatingly, many of the ads have a prominent rectangular button to click, at the right hand side, the same size and shape as the button you click to post a reply on the forum and positioned quite close to it. Obviously the hope is that you will accidentally click on their poxy ad by mistake. To add insult to injury, there is even one for essay writing (i.e, academic cheating) that comes round regularly! I've got used to it though and manage to ignore it. And at least the bloody things don't flash or move.

Freudian slip? 😊

What “universal field”?

I hope my explanation, which crossed with your post, does a bit better........

Indeed. Seems they've found anomalous Helium isotope ratios in hot springs in Panama that are consistent with the material coming up from the mantle at the Galapagos hotspot, even though these Panama locations are hundreds of km away and, moreover, on the far side of the subducting slab of the Cocos plate that lies in between. So a hole or break in the subducting plate is to be presumed. But, er, not "a hole in Earth's centre", whatever that might be supposed to mean! Here is the abstract of the PNAS paper: It is well established that mantle plumes are the main conduits for upwelling geochemically enriched material from Earth's deep interior. The fashion and extent to which lateral flow processes at shallow depths may disperse enriched mantle material far (>1,000 km) from vertical plume conduits, however, remain poorly constrained. Here, we report He and C isotope data from 65 hydrothermal fluids from the southern Central America Margin (CAM) which reveal strikingly high 3He/4He (up to 8.9RA) in low-temperature (≤50 °C) geothermal springs of central Panama that are not associated with active volcanism. Following radiogenic correction, these data imply a mantle source 3He/4He >10.3RA (and potentially up to 26RA, similar to Galápagos hotspot lavas) markedly greater than the upper mantle range (8 ± 1RA). Lava geochemistry (Pb isotopes, Nb/U, and Ce/Pb) and geophysical constraints show that high 3He/4He values in central Panama are likely derived from the infiltration of a Galápagos plume–like mantle through a slab window that opened ∼8 Mya. Two potential transport mechanisms can explain the connection between the Galápagos plume and the slab window: 1) sublithospheric transport of Galápagos plume material channeled by lithosphere thinning along the Panama Fracture Zone or 2) active upwelling of Galápagos plume material blown by a “mantle wind” toward the CAM. We present a model of global mantle flow that supports the second mechanism, whereby most of the eastward transport of Galápagos plume material occurs in the shallow asthenosphere. These findings underscore the potential for lateral mantle flow to transport mantle geochemical heterogeneities thousands of kilometers away from plume conduits.

What is curious about this news is that the wrong information that is was done by Russians seems to come from a Russian (dis)information news site: https://www.altusintel.com/public-yy752j/ But anyway, what is more interesting is why formaldehyde is thought so significant. This seems to be for two reasons. One is that it has a clear rotational spectrum, which astronomers can use for a number of purposes, e.g determining temperatures and velocities (via Doppler shift) of clouds of dust and gas. The other is that it can react with ammonia to produce amines and ultimately amino acids.

Russian scientists? This paper is a collaboration between the Universities of Stuttgart, in Germany, and Leiden, in the Netherlands. But indeed a new, low-barrier i.e. potentially fast, mechanism for formaldehyde synthesis, on ice-coated dust grains, at the low temperatures of interstellar space. I note they comment that the James Webb telescope may carry out observations to confirm the abundance of formaldehyde in interstellar ice. And a neat mechanism it is, too.