The value of Theory overstated
In the recent Chemistry World, we read the heading "Technetium carbide refuted; proof that the compound cannot exist after all". The article then goes on to show that a team of computational chemists made calculations and showed that the carbide cannot exist, and what experiment had shown was there is a new phase of the metal.
Sorry, but that is just plain wrong. Not the calculations, necessarily, which may or may not be correct. The point is, you cannot prove anything by theory. One of the most successful theories of all time, in my opinion, was Newtonian mechanics, and when used to calculate the orbit of Uranus, observation failed to match the calculations. Either the theory was wrong or it was not, but whatever, nobody argued that the theory was right and observation wrong. The only way out was to postulate a new planet and Neptune was discovered. That was a triumph for theory. It put observable facts into the theory to predict something new, and there it was. However, when Newtonian mechanics was used to calculate the orbit of Mercury, observation failed to match the calculations. Again, either the theory was wrong or it was not, but whatever, nobody argued that the theory was right and observation wrong, and worse, no new planet could fix this problem. In the end, it was found that Newtonian mechanics is merely a good approximation to Einsteinian relativity.
As far as I am concerned, I have no idea whether technetium carbide exists. I know manganese carbide exists, and I know it is not especially resistant to certain reagents, so it is easy to make it and then lose it. Because of the nuclear instability, I doubt anyone really worries too much about technetium carbide, because it is extremely unlikely to be of significant use, but that does not matter. Further, the failure to make something in a synthesis does not prove the compound does not exist, but merely that is not the way to make it. There are an awful lot of unstable compounds that can be made, if you know how to go about it. As an aside, from my experience with manganese carbide, you may be better off not starting with the metal, as then that new metallic phase is far less likely to form.
As for the calculations, the best theory can do is make predictions. Only Nature can tell us whether they are correct. For me, calculations help us know we understand nature, but you cannot use calculations to prove something. All you can say is, if my theory is correct, then this is what you should expect.
Posted by
Ian Miller on May 23, 2016 5:08 AM Europe/London
