What is truth?
By Serge Kreutz
Actually, it isn’t much. Not the truth, anyway.
The emphasis is on “the”. Not on “truth”.
Because, as far as truth goes, it may be true. And the opposite of truth is what?
Of course, the opposite is also true.
It’s a counter-intuitive idea that may need some time to get used to.
But the idea that the earth is a ball rotating around the sun and itself is also counter-intuitive, or at least it was when first presented.
But it could be measured. Galileo Galilei did.
Difficult to imagine, but again, measurable. It’s knowledge born out of an observation in quantum mechanics whereby, for an example, an atom’s electrons, even though they have a mass, do not have a location that could precisely be determined (Heisenberg’s uncertainty principle)(youtube video see here) .
For another aspect of the topic, we have to go back to the German philosopher Immanuel Kant.
In his Critique of Pure Reason, he distinguished between things-in-itself as they exist independent from an observer, and the perceptions we have of them. These perceptions depend on the apparatus used in their observation (for humans their senses and brains).   
To give a simple example. Feces itself does not stink. It just radiates gases. The idea that it stinks rests entirely with the observer. For flies, it just smells sweet.
But it’s not just beauty in the eye, and bad smell in the nose of the observer.
Immanuel Kant’s philosophy prepared the ground for Albert Einstein’s theories in which he correlated the speed of light with time, reasoning that if we were to move faster than the speed of light, we would travel back in time.   
We have learned time and again that intuitions and perceptions are a poor indicator of truth.
So, I guess the multiverse is just fine.
The surest, an observer can feel about is himself. Therefore, Descartes famously stated: “I think, therefore I am.”
And the philosophical school of solipsism is based on the recognition of the fact that the only thing a mind can truly be sure of is its own existence. Everything else which is experienced as reality may just as well be imagination.   
In fact this may just be it. Anyway, if there is an indefinite number of universes, there are enough of them for each of us to occupy his or her own.
We can already recognize the pattern that the truest truths are those that are closest to the biological observer. This is why I don’t doubt the reality of my sensations: pain, hunger, sexual desires, pleasure.
These observer-focused realities are so true that we do not even need language to be aware of them.
But the more complicated our perceptions become, the more difficult to think of them in categories other than language.   Intuitions like “democracies are the political system best suited to safeguard human rights” could not be expressed, and would be hard to think of as true, in any way other than through the application of words.
And thereafter, it 20th century philosopher Ludwig Wittgenstein emphasized that the ideas we entertain, including those considered philosophical, are a function (in the mathematical sense) of the language used to express them. And that “whereof one cannot speak, thereof one must pass over in silence”. Knowledge on most everything depends on the absence oflexicographic voids.
Just a difference of language already can make for different truths, not even multiverse awareness is needed for that.
A lot of complex European philosophy is very hard to express in analytic (as opposed to inflectional) languages where more meaning is carried in single words, rather than deductive statements.   That’s why the work of Martin Heidegger is so difficult to translate into Chinese where the concept of “being” often is included in nouns and adjectives, and verb forms do not differentiate tenses.
For the co-existence of divergent truths, the preservation of the world’s linguistic diversity is important, indeed.
Because some truths can only enter and exit the human mind if there is a language adequate for it.
And because complex truths all so often are just a question of the language used, and because what is false in one language may just as well be true in another one, and because the potential number of languages is just as indefinite as the number of universes in the multiverse, the ideas of a German Marxist, an Arabic Islamist, and a Papuan Animist are equally acceptable to me. Even though they contradict each other, they may be true in themselves, in their own languages, in their own universes.
On the other hand, for me personally, and for other humans (if they exist outside of my imagination), concepts that express themselves only in languages are less relevant than primary realities that do not need languages, such as pain, hunger, sexual desires, pleasure.  
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