What a doubt ! It's true that - as far as I am concerned - I only heard a tree fall once in my life. A quite interesting experience in the radically auditive aspect it had. I never saw this tree fall and to be honest, I had never seen any tree fall and I had never heard any tree fall before this one. And yet, I recognized the specific noise without tye slightest hesitation. Where could such an amout of science come from ? And so quickly ? Was it sure science at least ? Caught by a doubt, I ran towards the direction where the noise came from in order to confirm my intuition and who knows... To see the end of the fall. I found the tree without any problem and in such a state that no questions were left regarding its recent fall. This at least proves that trees do fall, even when no one is there to see them fall :-).
However, let's stick to the philosophical approach of existence... One may first think that the above question is actually so old and so respectable that people go on with asking it, although a quite important number of sound recording means and media have been invented since the age of philosophers. :-) and lots of people - not only spies - use these sound recording means to collect sounds that are produced while they are away. In other terms, one may think that it is not very tricky to build an experiment that would prove that trees make noise when they fall even when no one listens. For instance, one could select a good tape recorder of the type that starts only when a certain level of noise is produced close by, set it up under a shelter near a fragile tree and wait until ne next storm.
An astrophysicist friend of mine told me that many scientists theorize that there are actually many other universes besides the one in which we live.
Have they not been recently caught to pretend that no event could possibly happen in the absence of some measure instrument to record the effects of this event ? And a tape recorder is a measure instrument, in a way...
Even non-specialists will have recognized the famous explanation related to "the collapse of the wave function", which is usually illustrated by the non-less famous paradox of "Schrödinger's cat", a cat that remains in a sort of mixed state - half alive and half dead - until a human being opens the box and puts an end to this awful quantic undetermination.
In other terms, it has been possible to find a good number of physicists to believe that not only "the viewer makes the painting", but even further, that the observer makes the world exist - happen !
These other universes would be very different from ours, with completely different laws of Physics. They are virtually undetectable by us. My question is then : if there is a universe in which there is no life or anything to be aware of this universe, nor can it be detected from any other universe, does such a universe exist?
Even without inviting parallel universes to the feasts of the Being, if it was possible that our universe only existed by the perception of the viewer, then the viewer's perception would have to create - to build out of emptiness - an entire past, and what is a bit more tricky, a consistent past. In other terms, stating that human perception make the world exist, lead to question the existence of any past that would have occurred prior to the human species. This because per definition, for such a past to exist, some sort of human being would have had to make it exist through its perception.
This incidently leads to some consistency problems as regards what is know of the beginning of the human species, and more generally with classical darwinian statements, leading quantum physicists to place themselves on the side of creationists. Because... What happens to the limit between animal and man if man's perception or consciousness makes the world happen ?
What happens is that the tale of Schrödinger's cat apparently tells much more about the hatred for cats among physicists than about Physics itself : just replace the cat by a human being and ponder the value of the whole story... If the man who replace the cat is conscious, then is he still like the cat is supposed to be, that is half dead and half alive until another man makes a measure ? In the case he is actually half alive and half dead, what sort of story shall he tell when the wave function has finally collapsed and he comes back? Or is he alive because he, himself as a measurement instrument makes the wave function collapse ? Or is he alive because he is conscious and his consciousness makes the wave function collapse ? And if this is the case, what happens if he falls asleep during the experiement ? What happens if he faints and loses consciousness ? Using a cat as the basis for the story works well because cats do not speak, and hence they can't contradict a physicist statement about them or whatever else. But a man can speak and contradict whoever goes against his own experience... So why not use a man in this Schrödinger's cat mind-experiment instead of a cat. Why not have taken the risk ?
Now if the human consciousness as such was to make the universe happen, another problem would arise as regards determining when this human consciousness itself started to exist. If you stick to the - somewhat proven - belief that man has common ancestors with apes, then when did the ancestors of man start to be conscious ? If you do not stick with the darwinian story, then you are on the creationists side, and... What are all these skulls and skeletons doing there ?
Things go slightly better if you carefully state that the world is made to happen by the perception of any living being. Although this seems excessive at first, it is a fact that any living being can be said to shows some minimal form of perception, simply based on the fact that anyone can tell whether it is dead or alive, that is, able of self reproduction or not.
And, if we admit that the universe pre-exists to the human perception, then we can also accept that complex chemical elements such as iron, oxygen and carbon have been built by nuclear reactions in the core of stars fromthis extremely simple element called hydrogen, a chemical element which anyway remains by far the most frequent element in the universe.
Now, if I summarize the above "proof" I find that the following 3 principles are at work:
1 - our experience - the human experience is valid. This is a prerequisite for any discussion.
2 - logic is valid. One is not allowed to contradict one's own statements. This is another prerequisite for any discussion.
3 - Evolution flows one way. One may obtain something new by organizing pre-existing elements, but an assembly does not create - does not make its components exist.
Strictly speaking point 3 is false, because we do know examples of chemical components that only exist because a certain assembly of these components pre-exists. A good quantity of organic molecules fulfill this property and exist within a living cell and nowhere else. Yet "the law of composition" I suggest above is not really violated because these organic molecules are made of chemical elements that are found to exist independently of living cells.
What I essentially said is that Life could not be anything primary because Life is organisation - something that was well known to D.A.F de Sade although it is yet so poorly understood by lots of modern authors.
Further, it seems to me that underneath points 1 et 2 lies a kind of hypothesis related to stability or continuity, an hypothesis that states that things are in some way "linked together", along the time dimension of the universe, so that - for instance - we implicitly expect that the vision we currenly have of the world should not too different from the vision we shall have of it one 1/10 th of second later.
A universe that would not obey such basic stability requirements as I attempt to identify above may possibly exist. For instance a universe may be that would exist right now, then cease to exist for 10 seconds (or a year just as well in a random way) and later on start to exist again under entirely different form, based on entirely different laws of physics - or not. But... Assuming that we may exist in such a "violent" and "chaotic" universe we would not have the time to invent the words to speak of it and describe it.
Now of course, if we assume that our perception makes the world happen, then we may also assume that our minds are built in such a way that they can't accept any description of the world that would not rely on such things as "the arrow of time" and "the laws of Physics". In such a perspective, Physics would appear as a part of pyschology.
This is really the fundamental hypothesis Einstein makes when building his relativity theory:
if it is allowed to speak of the world in a consistent way (i.e. if the laws of Physics are the same everywhere, then the world has this characteristic (space may contract or expand under specific circumstances) or this other characteristic (time may slow down of accelerate under specific circumstances).
All well considered, the condition and proof that the universe existed before life is that we do not encounter any noticeable inconsistency when making such an hypothesis, even when we use this hypothesis to make verifiable predictions. Ultimately, a proof that the world did exist in the past long before living beings appeared is that when we use this hypothesis for making predictions about the future, it works ! That is to say not only that we do not die when relying on such an hypothesis, but moreover, we can tell a consistent story that links past and present together.
And, that's exactly what good doctor Schrödinger used to say (in "Ma conception du monde") : the heart of the problem, the really surprising thing, is that individual consciousnesses understand eachother when discussing their respective experiences. The astonishing thing is that all these isolated and separated consciousnesses prove to be able in some way to build and tell a common history - where we meet again with the universe as community and/or a communication network. Even if the universe did not exist outside of our consciousness it would still have this essential property : to be what we all have in common. (And hence the very opposite of private property. :-) )
And even if nothing existed, but me. And if you were to be nothing else than a creation of my mind, the hypothesis I make when assuming that you exist independantly of myself does not create any noticeable inconsistency. We are safe : I can still love you.
And to go even further, exchanging doubt for doubt - and there stopped the western philosophers (before me :-) ) - I can (and even I must if I am consistent) also assume that my own existence itself is a creation of my "consciousness", so that my consciousness would be the only thing left there, with the strange power of making us exist, you and me, as well as all the rest.
The simple addition of one single abstraction level - into which (as anyone can see) I was forced by the most elementatry move of love and justice - reveals the soft emptiness of this so said unbreakable atom : the individual. Because from the point where I am now, I may drastically simplify everything and cleaning up the initial statement, I can remove the "my" from the expression "my conciousness", since this engine, the/a consciousness, produces "me" as well as "you" and not less than "all the rest".
As one may see, what is highly specious in Berkeley - as Marx rightfully sensed - as well as in René Descartes with his "Je pense donc je suis", is to designate the primary entity, the active entity as being the ego. In order to reach this point - which obviously has something to do with christianity - they have to cheat. They have to slow down the movement of the lottery wheel in such a way that it stops each time nicely on "ego" and so that they may proudly say : "look I won again...".
But what is that ? Just a low level treachery, a basic trick, just a way of abusing the syntax. It is, actually and quite precisely a quiproquo.
Because... What happens if - as a good mathematician and as I suggest above - I replace the "I" or the "ego" by a "that" ?
Well nothing happens actually. Nothing at all. The part of truth Berkely and Descartes actually say remains there proudly standing alone : the world remains intact ; the world remains a permanent creation of the/a "that", "that thinks hence that is" (as would gracefully have said Spinoza) and as far as we are concerned, you and me, "that loves!"
What kind of proof, what kind of authority do Berkely and Descartes use to state that the/a "that" is an ego, considering the step of the inquiry they stand from ? None !
They would certainly be allowed to speak of an "I" or an "ego" if - at the level of primitivity where they pretend to be - they had the slightest element at hand to oppose an "ego" to whatever else, or just to distinguish (etymologically "sting in between") this ego from some sort of background... But that's not the case, that cannot be the case, as casually and almost automatically corrects Hegel when speaking of the "this" instead
What is hence left of the arguments and paradoxes developed by Berkeley and Descartes ? What is left of this individual that they pretend be the root of all things, what is left of it but this pure decision, this simple choice they cast without the slightest hint of evidence on their mental experience. A decision they make with a complete grammatical and logical inconsistency, that what actually exists is an ego, that is, a kind of bourgeois false dignity that unduly comes to haunt what otherwise would not be anything else than an immemorial and logically clean buddhist "self"?
But then... Then we are back to the starting point : a being or more rightly a process, the universe or just the tail of Schrödinger's cat, in a word "something" that makes you and me exist, and the world and all the friends... And we can go on speaking about it among ourselves in the café or under a tree, as all men do since there are men.