exchemist

I'm still struggling to see what the "dimensions" of a photon, or even expectation values for a set of dimensions for an ensemble of them, can mean. According to my understanding, QM only describes how quantum objects are expected to interact (usually expressed in terms of probability distributions) and is deliberately silent on what they "do" in between. Do any of these authors suggest that the "shape" or "dimensions" of a photon predict how it will interact with other QM objects? If not, then it seems to me to be just building castles in the air.

My limited, chemist's understanding of QM is that you can't really speak of an "objective" EM field configuration for a single photon. If you could, it seems to me it would be a classical object rather than a QM one. But I think we probably now need a real physicist's input.

I'm sure you can say something about the distribution of probability of detecting the energy.

Ah, so the salt is used to generate chlorine by electrolysis - which I can see makes sense, if you don't mind swimming in salt water and the associated potential for corrosion, I suppose. I didn't know that. Thanks.

To be honest I have trouble seeing how asking what the "shape" of a photon is can possibly be a question with any meaning. One could only define a "shape" if one could find a way to interact with it in a way that did not disturb it, which does not seem possible to me. It also seems to me the uncertainty principle would suggest its extent in space would depend on the degree to which its momentum was defined. This seems to be merely an academic exercise in exploring, for fun, the ramifications of the Bohr model - which was abandoned as a model in the 1920s, due to its obvious inadequacies. I also note the paper is dated 2018, a decade after this George Hunter bloke, whoever he may have been, died. But I'm not a physicist. There are others that can comment more authoritatively, I'm sure.

In space travel, the numbers are awful. (Douglas Adams) These other civilisations may well have decided, quite coolly and rationally, that spending centuries flying through empty space is a pointless exercise. Oh, ninja-ed by @dimreepr, I see.

Those stains look like iron salts to me. You'll have to explain to me why you associate them with salt, as I'm a Brit and we don't have many outdoor swimming pools here. Do you use salt to treat the water in some way? Could it have iron as a contaminant, like the rock salt we put on the road in winter, which always looks a bit pink or brown? Chemically, I would expect ascorbic acid to form a "chelate" with iron Fe³⁺ ions, which is a sort of cage molecule enclosing it. This could serve to dissolve the iron salts off the sides of the pool, if that it what it is.

This looks like a question for someone with experience of the paint or allied industries. I can't answer this myself but I see from this: https://www.crayvalley.com/docs/technical-paper/dispersing-titanium-dioxide-with-sma-resins-(1).pdf that TiO2 is sometimes indeed given a surface coating, in this case involving Al2O3 and something organic. It may be that either Cray Valley or Millenium Inorganic Chemical could advise you further if you contact them.

It certainly looks as if it has pink feldspar, black mica and white quartz, so could be granite. It doesn't look porphyritic to me, in that there is no glassy or microcrystalline matrix. But I'm no mineralogist. It's rather a pretty rock, actually.

This looks like a case for early legislation, mandating that manufacturers take back expired batteries for recycling. From the article, the technology to do it does exist, so there is no need for it to be like nuclear waste that has to be just put in a hole in the ground. But it will be costly and nobody commercial will do it just out of the goodness of their hearts, so legislation must be the way to go, I think.

You're right, it's the empirical formula. Silica (quartz) is a covalent giant structure. As such, there is no molecular formula, since there are no discrete molecules in the structure. You could almost say that an entire crystal is in effect a single "molecule! So for giant structures, the empirical formula is what we use. Here is a picture, in which you can see the SiO4 tetrahedra sharing the O atoms at their vertices with their neighbours:

I don't know anything about this myself, but I did find this article by a wood panel manufacturer, who talks about the effect of pH of the wood on curing of adhesives:https://www.wbpionline.com/features/ph-and-why-you-need-to-know-it/ If you are interested in veneers, it occurs to me that you too may be concerned with adhesives.

I don't find this especially simple to grasp, actually. Though maybe it is if you stand in front of a class explaining it as you go. What I always used to do is consider what would happen if the angle went to zero. The Cos component is the one that goes to full value and the Sin component is the one that goes to zero.

Is this a trick question? I'd have thought the answer is "easily" - if you mean faster relative to some external observer.

I don't think it will. "Hardness", so far as I understand it, relates to the concentration of Ca²⁺ and Mg²⁺ ions in the water. This will not be affected by adding HCl. What you may do is reduce the amount of carbonate and bicarbonate in the water by lowering the pH and causing some of these to be converted to CO2, which is lost to the atmosphere. But you are introducing chloride Cl⁻ ions instead, so you are effectively replacing dissolved CaCO3 and Ca(HCO3)2 by CaCl2 - which I believe still counts as "hardness" according to most definitions. However, reducing the amount of carbonates and bicarbonates will reduce the tendency of these to precipitate out as scale deposits, so it may look like a reduction in hardness in practice. As least, I think that is how it works. Others more knowledgeable may correct me.

Haha, that's why I included the qualifier "mainly".😉 But as it happens, speaking as someone who had a Catholic upbringing, even if I have been semi-detached for many decades now, there is actually no testable claim made for transubstantiation either. See "essence" vs. "accidents", for the traditional (rather itchy-beard, to my mind) way of getting round this. I would treat the major established Western Christian denominations, including Catholicism, as among the "more reasonable manifestations", along with many branches of Judaism and educated Islam. I know less about other religions but would expect to be able include some of them too. All of these are mainly a guide for living one's life and do not try to offer an alternative narrative to science about the way the physical world works.

Shell: Anglo-Dutch, but with a large and semi-autonomous US arm. But I have in mind not only Shell itself but the companies we used to do business with, either as suppliers to us or as our customers, or as manufacturers whose machines used our products: I was exposed to all three in the course of my career, many of them American companies. There were some, usually smaller, who you could perhaps characterise as cynical and driven only by short term profit, but most of the larger ones took a much more nuanced approach to their business.

Speaking as someone who worked for an oil major for over thirty years, including a short spell in the US, I find this unduly cynical - or a bit naive. My experience is that while major corporations certainly are driven by the bottom line, as they should be for the sake of their shareholders, it is not that simple. A major issue for companies like mine was the long term reputation of the brand, which was seen as essential to secure a "license to operate" from society - and thus protect long term profitability. There was also considerable pride in the standards of the company, in such matters as product quality, engineering and above all safety. (The safety culture was extremely tough: people could be - and were - sacked for not switching off their mobile phones when driving, for example. Being at work in one of the oil refineries was, famously, considerably safer than being at home!) So it is a bit glib and superficial to claim that the profit motive drives towards unsafe products and working conditions. It may in some companies, but not in well-run ones. On taxation you are right, of course. No company will pay more tax than the law requires and multinationals do jump around to find the lowest tax rates. But this is driven by governments competing to offer the lowest rates, in order to attract business. This is an argument in favour of countries agreeing to stop this practice and start to harmonise corporate tax rates - as I gather Biden is now proposing, in a modest way.

This seems to be incorrect. So far as I am aware, antimony does not expand on freezing. You may be thinking of bismuth. And silicon and gallium also do this - along with water. Antimony was indeed used in typesetting, but alloyed with lead, not on its own, in order to reduce the degree of shrinkage on cooling, as well as to make a harder alloy to resist damage in the printing process. It did not cause expansion.

Glad it helped. By the way I see I made a typo in the formula for silica, which should be SiO2, not SiO4. (Although the units are SiO4 tetrahedra, by the time they share all their "O" vertices with neighbouring ones, the overall ratio of O:Si becomes 2:1.)

The first point is that all these elements are present in the form of compounds, in which their atoms are chemically bound to other atoms, whether by ionic or covalent bonding. The boiling point of oxygen (O2) is therefore not relevant, since free molecular oxygen is not what is being referred to. As @studiot says, oxygen is mostly present in magma as various kinds of silicate. The chemistry of silicates is very complex, but is all based around variants of the tetrahedral SiO4 unit, sometimes free but more often joined to others by shared vertices, to form chains, sheets or 3D arrays. These units are covalently bonded but tend to have a net -ve charge, thereby forming a family of silicate anions (SiO4⁴⁻, Si2O7⁶⁻, and so on) that can complement the metals you list, since they will be present in the form of cations. (You may be familiar with other complex anions such as carbonate CaCO3²⁻, sulphate SO4²⁻ etc, which also have covalent bonding internally but a net -ve charge overall. Silicates are like that.) However it is worth noting that pure silica itself, SiO4, in which SiO4 units form a 3D array, has no ions. When this melts, it requires some of the covalent bonds to break, temporarily, and reform, allowing the units to slide past one another. You get silica in most magmas, along with various silicates.

I had to look up what this is about. I assume you mean this: https://en.wikipedia.org/wiki/Optoelectric_nuclear_battery But there seem also to be non-luminescent nuclear battery devices that convert the energy of radiation directly to electric current: https://en.wikipedia.org/wiki/Betavoltaic_device These would not need to rely on a phosphor coating and a solar cell. I don't know how the efficiencies would compare. But since the mass of tritium would be proportional to the pressure in the tube, I'm sure you must be right that tripling the pressure would triple the power output, provided the energy conversion system was not saturated by it.

Oh, OK, that's a pity. But surely someone must give you feedback, or how do you know what needs attention? But if you have no feedback then, if I were you, I would choose a couple of topics where I know I am not very strong, and maybe a couple of topics that really interest me, where I can go further, perhaps beyond the course syllabus, out of interest. It's important to find things that interest you in school work, rather than just being a slave to the exam machine. It's one way to help decide you what to study at university.

Ask your teachers. They should know the topics on which you are strong and those on which you are weak. Also, with a mathematical subject like physics, it is worth getting some practice at solving problems. If you are like my son, you may understand the topics and know the equations but not be very good at answering problems involving unfamiliar scenarios, or requiring multiple steps. A bit of practice can give you more confidence. Avoid a scattergun approach. Decide on a small handful of things to work on and do those, until you feel you have made tangible progress. Good luck.

What you do is deploy what is known as critical thinking. This can include elements such as: - relying on a range of widely trusted sources for your information about the world, - cross-checking information from unknown or questionable sources against more reliable ones, - considering the likelihood of what is being claimed, compared to your previous information about the entities involved, - considering the quality of the evidence there is for what is claimed, - considering the motivation of the source: any known biases, agendas, affiliations, etc. This is not an exhaustive list, but it gives you an idea of how sensible people go about evaluating information they encounter. It is often worth taking the time to think for a bit about these issues before deciding what to information to accept. It is also a good idea to make a mental reservation about something new and surprising, in case it subsequently turns out to have been in error. Conspiracy theorists - as a rule- do not do any of this. They make improbable assertions, attributing malign motives and presuming illicit power of whoever their target happens to be. When you apply the above discipline to most conspiracy theories, you rapidly realise they are bunk. Just occasionally one of them may turn out to survive this scrutiny. Then, and only then, is the time to take it seriously.