I have a question related to the philosophy of time. If something happened, but all memory traces and records of it has been wiped out, with not even indirect records left for forensic experts to uncover, did it exist?

If a tree fell in a forest millions of years ago but no one was there to hear it, and the tree rotted away, did it make a sound? Did that sound exist?

How much of the past actually existed?

  • Welcome! While maybe fun to talk about, your question seems to boil down to "if a tree falls in the forest..." which doesn't really strike me as a particularly urgent or critical philosophical concern. Is there any chance I might persuade you to tell us a little bit more about your motivations and context here? What might you be reading or studying that makes this problem an interesting or important one for you? What exactly are you looking for in an answer -- what do you need someone here to explain to you about this? And what have you found out already? – Joseph Weissman Dec 2 '11 at 18:41
  • Do you remember all your ancestors? Are you there? They must have existed! – Samuel Duclos Dec 13 '11 at 6:06

I think we can refine the terminology a bit; we generally speak of entities existing, and events occurring.

Now, existing usually implies persistence through a duration of time; occurring, on the other hand, is often momentary.

If a tree fell in a forest a million years ago, that event (the falling of the tree) occurred, by definition. The fact that the tree no longer exists, and there are no recoverable traces of the occurrence (or the entities involved in the occurrence) is completely irrelevant. How do we know the tree fell in the forest? Because we just stated that the tree fell in the forest.

Taken from the other side: if we refuse to stipulate that the tree fell, we are left asking "What events occurred in the past that we have no means of knowing about?" to which the only possible answer is "We have no way of knowing, by definition."

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  • +1 Exactly. Put another way, there's a big difference between what really occurred and our memory of what really occurred. – stoicfury Dec 13 '11 at 6:26

Because I like to think in a scientific way, the short answer is yes.

The long answer is that, regardless of anyone remembering something existing, or even discovering evidence of its existence without knowing what this evidence means, it existed purely because it did. Let me explain with an example.

No one might remember, or have heard, the tree falling in the woods, millions of years ago, and all evidence of its existence might have been eradicated, but as sound is the propagation of sound waves across the air, as soon as those sound waves were generated, the sound existed.

Now, you will have to take a third person perspective to answer like this, because on some level you need to have knowledge of whether something did exist at one point to answer the question "did it ever exist?". If such knowledge doesn't exist, we can only theorise. It's the whole Schrodinger's cat theory in effect.

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When a tree falls, the crash causes ripples in the air. These ripples can be detected by a nearby creature having ears and a brain. It takes ears and a brain to make a sound out of ripples in the air. The ripples occur in the air; a sound occurs in the brain.

So, in your "millions of years ago" scenario, it is true to say the tree caused ripples in the air. If there were a hearing creature nearby, it is also true to say that the tree made a sound.

But let's address your primary question, which is, did the event occur at all, given that there is no record of it today.

In the world as we perceive it, it turns out that the situation at this moment determines the situation at the next moment. If I drop my coffee mug, it will fall, and the next moment there will be a mess. This seems to be a basic law of the universe, the law of cause and effect.

From this we can also say that the world as we perceive it was determined by the world as it was at the previous moment. That world was determined by the moment previous to it, and so on into the far past. There is a very definite chain of events.

Now we can begin to see that every event in the past is meticulously recorded in the moment that comes immediately after it. Everything at a given moment is not only a consequence of, but also a record of, what just happened. That moment in turn is meticulously recorded in the next moment, and so on into the far future. It does not matter that we are unable to comprehend the present clearly enough to be able to read the record of the past in it. The record is there.

We are able to comprehend some of this record. Your tree rotted away, but another fell in a bog and was preserved as a fossil imprint. But even your tree which rotted after it fell, so that we do not have the ability to reconstruct its falling as an event, is still linked in an unbroken chain to events afterward, such as decomposition, reuse in other creatures, burial in the silts of time, and metamorphosis into rock strata. It still happened. This moment contains within it the meticulous record of the tree falling.

Nothing is ever forgotten.

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