In a recent post that I've missed until now, Eric Lippert describes a simple mental experiment: why a mirror reverses left and right, but not top and bottom. This weird property (called chirality) has a fascinating history, and deep implications everywhere: in physics, biology, chemistry, etc. (Chirality is still an interesting research domain today. For more details see this link)
One example: many chemical compounds, especially the organic ones (including sugar, for example) are tridimensional structures that are not identical with their image. These compounds are called enantiomers:
As a direct consequence, there are two different types of sugar which are almost identical (even in taste), but not quite. Actually, it's more complicated: a sugar molecule is based on a glucose-fructose pair, and each of these molecules have their own variations. For example, there are two forms of glucose: D-glucose and L-glucose, and so on. An intriguing fact is that only the D-glucose is present in living organisms, which makes the L-form interesting. This hides a much deeper problem: there is a high degree of chiral assymetry in the biological world. The helix-form of the DNA or example, is strongly assimetrical:
By the way, did you notice that no matter how you rotate a spring, the helix always goes the same direction? No matter how you look, the helix looks the same. In the case of DNA helix, if you look from the top to the succession of aminoacids, they always go in clockwise-direction!
Bringing on Sci-Fi experiments
Enough with reality... let's walk on the wild side. Let's just assume that there is an "invertion machine" that would invert any physical object and produce its mirror form. Even more, let's assume that I succeeded to build some sort of "tunnel" which you can walk in on one end, and come up completely inverted on the other end!
This experiment would have all sorts of weird consequences. For example, let's assume that I am going to be inverted. After this experiment everything around me looks completely the other way around. First, I would observe that the cardinal directions are now interchanged. Sun is going the "other way around" - the sunrise it's happening now at my definition of West (but everyone would insist that this is East, in fact). Any text will look like in the mirror", cars would be driven on the right side, etc. You can "peek" this reality by just looking through a mirror, of course.
A side note: some people went even further - a scientist (I forgot his name) built a special set of glasses that inverted the light, and wore them for several days. At first, he had a terrible headache, because everything was the "other way around". But after a while he got used to the new world pretty quickly. And of course he had a similar lag when we gave up in using the special glasses...
But much more severe consequences might happen because now our biological world will enter in contact with living things from "beyond the mirror". Take bacterias, for example: their inverted DNA will make them immune to the current antibiotics!
So if I go through an invertion machine, I will be exposed, first of all, to various forms of the "inverted" forms of life (which can cause me unknown types of diseases). Not only that but, as a host of all sorts of organisms, I will be the one that brings the inverted forms on earth for the first time! Remember that normal microorganisms in the word will appear inverted for me, and microorganisms that I host (and which appear normal to me) will appear inverted to the world. Who knows if some species of bacteria (like Escherichia coli) will cause a disaster if present in inverted form.
So, this little experiment can have disastruous consequences. Or maybe no consequences at all; who knows... Nobody tried to "mix" natural life with inverted life.