1. ## exchemist

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2. ## studiot

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3. ## John Cuthber

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4. ## StringJunky

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## Popular Content

Showing content with the highest reputation on 07/18/21 in all areas

1. ## If I move a box with nothing in it, does the nothing move with it?

When I first saw the OP I thought it was a deep question. On second thought I realise that it is actually much deeper than I first thought. TheVat made a worthwhile distinction between concrete and abstract nouns This is one of the advantages English has over Mathematics. So to discuss your question, let us consider two well defined sets. 1) The set of people born on or after 1950. 2) The set of people born on or after 2050. The first set has a specific finite number of members. This number is given (measured) by the natural or counting numbers, otherwise known as the positive integers. Note these does not include zero. We show these in set notation by listing between curly brackets (braces) thus {1,2,3,...}. The three dots at the end (ellipsis) denotes indefinite continuation. The second set has no members and is called the empty set or the null set. Thus we denote the empty set {}. This is very important to show that there are no members. Note also that it is not the number zero. Create as many copies of the null set as we need. Then collect them together, grouped in sets within a larger container set. { {{}}, {{},{}}, {{},{},{}},...} Which corresponds to our set of natural numbers {1,2,3,...} So we have constructed as many counting numbers as we wsih for nothing ! That is almost enough set theory for our purposes but there are two theorems we need that I will state but not prove. 1) There is only one empty set. 2) The empty set is an (honorary) member of all sets. The first theorems comes into play with the issue of moving the box. Suppose I form my box from the curly braces with nothing inside and send it to you over the net. I have moved an empty abstract box and, so long as there is no data corruption along the way, it is still empty at your end. Mathematically the question of what is in your box is answered by theorem 1 which says that it must be the same nothing as there is only one empty set. In case you think this is rather arbitrary, smart ass even, there is a definite application in Engineering and Physics in Fluid Mechanics and other places. In Fluid Mechanics there are two formulations of the equations of fluid motion depending upon your viewpoint. An abstract box with abstact walls is constructed in the imagination and suprimposed within the flow. View 1 considers the flow flowing through the box, which is fixed in position, size and shape, in and out through the walls. It is known as an Eulerian analysis. The flow into / out of the box brings with it physical variables such as momentum, energy, mass, force on the walls and so on. This causes changes in other properties such as density etc. https://alldifferences.net/difference-between-lagrangian-and-eulerian-approach/ View 2 considers the box to move with the flow and is called a 'with the flow analysis', or Lagrangian analysis In some flow patterns the flow can actually be at a standstill ie there is no flow. These are called stagnation points. They appear directly in front of obstructions to the flow and other places. If the box is located at such a stagnation point it enclose zero momentum since there is zero motion. Don't forget that the spark plug gap can actully be zero (nothing) if the electrodes are touching. This is a different nothing from the what is in the space between them, since there is not even space between them. Time is not the same as space and considering the quantity of space within the box must involve a relativistic calculation, due to the problem of defining simultaneity.
2 points
2. ## Would it be possible to capture an atmosphere fully, comprising all the chemical compounds?

Yes, presumably GC-MS.
2 points
3. ## Would it be possible to capture an atmosphere fully, comprising all the chemical compounds?

The smell of petrichor is largely this. https://en.wikipedia.org/wiki/Geosmin The first big problem is that there are something like a billion known chemicals, and we can't look for all of them in one sample. If we did then the analysis report would be rather unmanageable; a billion lines most of which said "not detected". I think that's something like a thousand big thick books (and it wouldn't be cheap) The other big problem is that, for some materials, you can smell them at concentrations which are below the limit of detection by GC/MS (or most other techniques). Cloning would be a perfectly acceptable term if I was, for example, seeking to copy a trademarked perfume. It's also a term commonly used for copying a computer. https://en.wikipedia.org/wiki/Clone_(computing) And the word is used for credit card fraud involving a copied card.
1 point
4. ## Would it be possible to capture an atmosphere fully, comprising all the chemical compounds?

If you are a fine art student at a university, perhaps you can get in touch with someone in the chemistry department to help you further. Most things that the human nose reacts to are organic compounds that are not themselves gases but whose vapour, at low concentration, is detected by the olfactory system. But it's a very complex business. One of the chemists I studied with at university went into the wine trade and tried to analyse what gives wines their individual flavour. It's just about a lifetime project. The smell of roast chicken probably involves hundreds of compounds. Or, if you are interested in something more poetic, like the smell of a wet city street after rain, I have no idea what you would be looking for or at what concentration levels. But it sounds rather fun to try.
1 point
5. ## Would it be possible to capture an atmosphere fully, comprising all the chemical compounds?

Isn't it a mass spectrometer what's needed?
1 point
6. ## Would it be possible to capture an atmosphere fully, comprising all the chemical compounds?

I’m not quite sure what you mean by capturing. Do you mean a complete chemical analysis of a sample of air? The issue with that will be down to what threshold of detection, because there will be traces of all sorts of things at very low concentrations. The other issue is you need to have some idea of what molecules you are looking for in order to pick the best analytical method to use. If this is a smell project I imagine you won’t be interested in the major gases, but more in organic compounds , and possibly at the ppm level. Is that right, or are you thinking of inorganic components that the human nose detects, e.g SO2, H2S, etc?
1 point