Cutlery
Why does the fork have four tines? The Evolution of Useful Things has an explanation of how the fork came to be, but not a coherent explanation as to why the number stopped at four. More tines would clearly be better, because it would require less force to skewer food and hold it in place better. It appears to be an engineering limitation - tines are very thin, and you don't want them to bend excessively.

Can modern materials do better? The strength of a tine is proportional to the fourth power of its width, so the strength of a tine on a fork with five tines instead of four needs to be about (5/4)^4 ~~ 2.5 times as strong as a regular tine. My rather sketchy research indicates that titanium ought to be able to handle that, and in fact the tines on a titanium fork I got are about the right width for five to fit. To get to six tines, they need to be about 5 times as strong as with four, which might be a bit much, although a material such as tungsten, corundum, or tungsten carbide might do the trick.

I decided, given the above calculations, to try other materials of cutlery. My other reason for trying other materials is that I find metallic tastes overwhelming, and wanted to see if any of them don't interfere with my enjoyment of food.

The two types of cutlery I tried are titanium and lexan. Both of these seem to be intended primarily for camping, and so are designed to emphasize their light weight than their other desirable properties.

Titanium I found unfortunately to have a slight metallic taste. Less than stainless steel, and much less than aluminum, but still there. Also, titanium cutlery being designed for light weight while camping tends to be rather small. It does have the nice small tines, which could be used to give it five tines but isn't. I think if there were titanium cutlery which was made to the size and appearance of regular table cutlery, but with five tines instead of four, it would be quite nice.

Lexan I'm rather fond of. After having it in my kitchen for a while I find I always instinctively reach for a spoon or fork made of lexan, particularly the spoons, because of the amount of contact between one's tongue and the spoon when eating soup or cereal. In fact, I've noticed that when using metal cutlery I always hold my tongue back while biting in a weird and awkward way to try to avoid the taste of metal, but I don't do that using lexan, which makes the food eating process much more enjoyable. It also has very low thermal conductivity, which is very nice when eating soup or ice cream, although it is possible to heat lexan enough to melt it, so you can't use it like a spatula. The lexan knife is somewhat pointless though - it isn't very strong, and knives don't generally come in contact with your mouth anyway, so there isn't much of a taste issue. There's unfortunately an aesthetic limitation of lexan cutlery as well. It looks plastic and disposable, which it most certainly is not. I don't know if that's a result of the strength and production engineering needs of making lexan cutlery, or simply poor design.

With currently used materials, I think what I'd really like is a cutlery where the forks and spoons had lexan ends, for taste and low thermal conductivity, and metal handles, for strength, and the knife was an ordinary metal knife.

Possible new materials, and I'm completely speculating here, are tungsten, corundum, and tungsten carbide. Tungsten would probably be a lot like titanium only more so, and rather heavy. Corundum and tungsten carbide would probably score very well in terms of both flavor and strength, and it would be amusing to have cutlery made of sapphire, although cost might be an issue. Or not. The cost of both of those materials has plummeted recently, and cutlery used to be something which held a significant fraction of peoples's savings, while these days a set is considered expensive if it costs much more than dinner at a fancy restaurant. For items used every day for decades, a budget of several thousand dollars seems not unreasonable. People certainly are willing to spend bizarrely large amounts of money on wedding and engagement rings.

When I bring up the subject of cutlery and my observations it has an odd effect on people. They seem to get a desperate need to find some other subject to talk about, or go feed their cat. Very strange considering how fascinating the subject matter is.