The Prediction Paradox

The prediction paradox is a thought experiment which may demonstrate that a deterministic universe is inherently impossible.  It attempts to show that under some circumstances, a deterministic chain of events may lead to two mutually exclusive outcomes, both of which must happen.  The impossibility of that is what produces the paradox.

The thought experiment begins with the stipulation, already accepted by many (if not most) physicists that the universe is in principle predictable in every detail, and has been since it began.  The chain of cause and effect, in principle, is immutable and inalterable.

A familiar way of simplifying that concept is to cite a row of dominoes, wherein the tipping of one domino produces a chain reaction that leads to the tipping of all the dominos.  In this example there is no paradox.

Let’s use another example.  Suppose that one has planned a picnic on a certain date.  One then forecasts the weather, and sees that there will be inclement weather that day.  This forecast causes one to change the plans for the picnic, either to cancel it or to reschedule it.

This is still not the paradox, but it sets the stage for it.

Now, let us examine the paradox.  It begins with the question of whether the predictability (in principle) of the universe can produce a correct prediction (in actual fact) by a human (or other agent).   

If the answer to that question us no, that in itself poses a philosophical dilemma which bears careful investigation—what principle prevents accurate prediction in a theoretically predictable universe?

On the other hand, if the answer yes—if practical inerrant predictability is possible—then can such a prediction be the cause of altering subsequent events, thereby rendering the inerrant prediction to become false?

At this point, the paradox becomes a bit more convoluted, as do the rebuttals.  Those rebuttals perhaps are made plausible because there may be a flaw in the way the paradox is expressed, but there is a persistent underpinning that seems to remain despite all the rebuttals.

The most convenient way out of the paradox is to reject the idea that the universe is, whether in principle or not, inherently predictable.

If predictions are made by human agents whose thinking is not dictated by inexorable cause and effect, but rather, by people who can think as truly independent agents through their free will—if this is the case, then the chain of cause and effect in the universe is alterable by such free-thinking agents.

Since most physicalists seem to reject even the possibility of such volition, it remains their duty (imposed by me) to answer the following questions:

1. Can the predictability (in principle) of the universe produce a correct prediction (in actual fact) by a human (or other agent)?   
2. If not, then what principle prevents accurate prediction in a theoretically predictable universe? 
3. What would be the consequences of practical unpredictability in a deterministic universe?
4. On the other hand, if the answer yes—if practical inerrant predictability is possible—then can such a prediction be the cause of altering subsequent events, thereby rendering the inerrant prediction to become false?
5. Is there a way out of the paradox other than the existence of free will?

= = = = = =

Other recipients:

Thanks for a well-stated post, Adur. As you say, there are so many problems with determinism and multi-verse theory that the proponents bear a heavy burden of proof. For example, the theory that says, "anything that can happen, must happen, and

A reader responded on another discussion board.

My reply:

As you say, there are so many problems with determinism and multi-verse theory

that the proponents bear a heavy burden of proof.

For example, the theory that says, "anything that can happen, must happen, and must happen an infinite number of times," is in my view, another way of saying that "nothing ever happens."

i.e., if you flip a coin, and it lands both heads and tails, then in effect, the outcome is neutral.The two cancel each other out.  Things may happen locally, but on the whole, nature would be a non-event.

My proposal takes a short-cut, by attempting to prove that determinism cannot rule the universe,

and that, therefore, free will must come into play.  Since free will is a force external to physics, it
strongly implies that there is a nature above nature, a super-nature, a spiritual reality that underpins
physical reality.
 
But that's jumping ahead.  Let's back up.
 
In the past, when I have proposed the paradox, the response has been something like this:
 
In a deterministic universe, any possible prediction would already have been "foreseen" (so to speak)
by the chain of events, by cause-and-effect.  Not only would the chain of events have predicted that the
prediction would be made, but also, any consequences of that prediction are also predetermined.
Therefore, there can be no paradox.
 
While this initially sounds like it disqualifies the paradox, a deeper dive is required.

That is why I ask the five questions at the end of the OP.

 

1.       Can the predictability (in principle) of the universe produce a correct prediction (in actual fact) by a human (or other agent)?   

2.       If not, then what principle prevents accurate prediction in a theoretically predictable universe? 

3.       What would be the consequences of practical unpredictability in a deterministic universe?

4.       On the other hand, if the answer yes—if practical inerrant predictability is possible—then can such a prediction be the cause of altering subsequent events, thereby rendering the inerrant prediction to become false?

5.       Is there a way out of the paradox other than the existence of free will?

I have not seen these questions asked or answered in any other forum.

Perhaps there are really good answers to them that disqualify the prediction paradox,
and perhaps any answers are beyond my limited intellectual abilities.
 
Even a blind squirrel can find a nut now and then, and I smell a nut in here somewhere.

= = = = =
It would seem absurd that in a predictable, deterministic universe,

a predictor could be forced to make a prediction which is accurate,

and then be forced to predict that his accurate prediction will now alter the original prediction,

rendering it inaccurate, in which case, he would no longer have to alter the prediction,

making it accurate once again, in an eternally oscillating series of conflicting predictions.

= = = = =
 

Previously poorly worded post:

Here is a puzzle.  Can you solve it?

In a deterministic universe, it should be possible, in principle, to predict the future course of events.  Furthermore, if such a prediction were made, it would itself be made because deterministic cause-and-effect forced it to be made.  Moreover, the prediction might be correct, insofar as it was based on the inevitable outcome of the past chain of cause-and-effect.  Herein, a paradox could arise.  The very act of making the prediction could itself cause the prediction to not occur, even though based on determinism, it was correct and inevitable. 

However, if the prediction were accurate, it would have to predict that the prediction itself would render the prediction inaccurate.

Therefore, because of this possible paradox, it must be concluded that a predictable determinism cannot exist.

Can a correct prediction, based in determinism, predict that the prediction itself will alter what it predicted, making it incorrect?