Voynich Manuscript (pictured at left) is currently one of the bigger linguistic mysteries out there . It is a set of some 240 hand-illuminated pages, bound in codex form, making what appears to be a reference work on such topics as herbalism, biology, and astronomy. Many of the illustrations are of plants and flowers that do not actually exist or cannot be precisely identified. Most puzzling is the text, which is written in an unknown and undecipherable script that bears no relation to any known language or script. You can see high-quality scans of the book here, courtesy of the Yale Library.
It is believed that the manuscript is a pharmacopoiea, as it bears some similarities to other such works. However, much of it is puzzling, and incomprehensible. Some scholars have proposed the manuscript to be a fake, one of a number of herbals made in the Middle Ages by alchemists and charlatans to impress simple people with the possessor's supposed knowledge. The text is gibberish, mere squiggles on a page, meant to look like writing and yet containing no message. That's one proposal.
Yet, the script looks intentional. The same letters are repeated, and even specific ligatures are discernible. The letters are repeated in such a way that shows consistency, as though the author were writing in an actual script, and not merely scribbling.
There are all kinds of hypothesis about how and why the manuscript was authored. The most plausible is probably that the text is an invented script meant to write an East Asian tonal language. Other theories are that it is a secret script or language invented by the author to hide his writing, or that the script is a code, containing information in some secondary feature of the words.
Those are the best theories.
But I want to propose a crazy theory, and a way to test it.
Suppose the Voynich manuscript were written by a time traveler from the future. Suppose the language in the manuscript is a language that has not yet come to exist, but that will exist at some time in the future, when time machines are built. Suppose the author were an explorer, who went to the Middle Ages, and either brought the Voynich manuscript with him, or wrote it in the past, in his own language, to record knowledge he had brought from the future to help him survive in the Middle Ages.
Supposing the manuscript were written by someone from the future writing in a future language and script, then this hypothesis let's us figure out what that language and script is right now.
We need a team of linguists. People unfamiliar with the Voynich manuscript, its history, proposed theories of it, yet proficient in the patterns of human language and writing. We will introduce this team to the symbols, and how they occur in words, but absolutely not to actual passages in the actual book. We ask them to assign meaning to the symbols. They assign them in a way based on human language, but not on supposed translations of the text, but otherwise arbitrary. Whatever meaning they want, so long as it is consistent with what they know about other languages. This task is similar to the construction of Dothraki, Klingon, or Quenya; we're not asking them to decipher, but to invent. It is important that their decision of meaning is by no means influenced by hypotheses about the words as they occur in the manuscript.
Then, whatever language they come up with using those symbols, we declare those symbols to be the Voynich language. We publish books listing all of the rules of the Voynich language, and start popularizing the language, maybe through fictional universe tie-ins.
Assuming that our construction of the Voynich language begins seeing use, then, if the original Voynich manuscript were indeed written by a time traveler from the future, we would expect the author's use of the Voynich language to, at worst, be a naturally evolved version of our published Voynich language.
We have now reduced the problem of deciphering a bizarre and alien script with no clues as to content, to a matter of translating one version of a language to a later version of the same language. This is much easier to work with.
If it turns out that our published Voynich language sheds absolutely no knowledge on what the original Voynich manuscript says, then I think we can fairly safely rule out the possibility of time travelers from the future. If, using our invented language, we are able to clearly read the Voynich manuscript, then that is pretty strong evidence for the existence of future time travel.
Is the Voynich manuscript written by a time traveler from the future? I really, seriously doubt it. But if it is, then now we know a way to test it, and more interestingly, a way to read it.