Given a big enough computer, is it possible to predict the course of a
person's life exactly?

Stephen Wolfram treats this subject in 'A New Kind of Science'. He
establishes the concept of 'computational irreducibility', explaining
that while some physical phenomena can be simulated by simple programs
by 'shortcutting' the computations that the phenomena are performing,
other phenomena are 'computationally irreducible'. Wolfram explains
that simulating these systems requires doing exactly as much
computation as the real systems are doing. This seems possible with a
big enough computer. But, he further implies that part of the
computation in some systems is the passage of time itself, so it may
not be possible.

The topic is fully treated in Chapter 12, Section 7. You can get the
full text of this book for free at wolframscience.com.

Searching the forums on that site for 'free will' does not yield a
treasure-trove, but may still be helpful.

Tim Silverman

Thanks for your comment supertim... very helpful. Does anybody else
have anything to add?

Hm, interesting idea. In order to predict the total outcome of a
persons life, you would have to have a knowledge of every variable
that would ever affect the person. Therefore, it seems the challenge
is not to build a computer big enough, but rather, to gain enough
knowledge to be able to program that computer to know what variable to
calculate and account for. For example, let's say that the person dies
from cancer. Well, what caused the cancer? Perhaps it was a faulty
gene that the person inherited. Or perhaps it was cause by a burst of
radiation that caused a chemical change in one of the nucleotides of
DNA one day from a solar flare. And which gene did that affect. That
would affect the type of cancer. Anyway, you can quickly see that the
micro- and macro-cosmos quickly come into play in one's normal life.
So I think that if you were capable of predicting one person's life,
you would have to be able to predict EVERY person's life. Interesting.

I also want to point out that being able to predict one's life is not
the same as predestination. Predestination is where you have no choice
on the outcomes. Agency is the ability to choose the outcome, but
because of universal laws, we can still predict the outcome (i.e., if
you are God, you can know someone's personality, neural connections,
genetics, life experiences, etc. and know how that will all act with
physical laws...). Also, I'm not sure that there is actually such a
thing as "free will" or "free agency," because when you put the word
"free" with those terms, it implies that there are no consequences,
i.e., that I have the free agency to commit a crime. Well, yes, I can
certainly commit a crime, but there will always be consequences. Or
yes, I can choose to let go of a jar in my hand, but because of laws,
it will fall to the ground and break. Is this making any sense? But I
guess I'm just playing a sort of word game-- as long as you mean
"agency" by "free will," that's what I'm getting at. Anyway, these are
some of my random thoughts.

"So I think that if you were capable of predicting one person's life,
you would have to be able to predict EVERY person's life."  

great comment.  However let me extend your idea to the next level.  If
you had the ability to predict every person's life exactly then you
could also predict every possible event in all time of the entire
Universe.

Hypothesis - Every event in the Universe effects every other event.
(this is in stark contradiction to Einstein - who thinks we are
insignificant)

The bottom line (my view) - for the computer to make the prediction it
would need the position, velocity, etc of EVERY particle in the
universe at a single moment of time.  Which is impossible due to the
uncertainty principle. :)

However it might be able to make SHORT term predictions if you could
get all the input data in.  After all it takes a finite time for
external events to reach the human in question.

If the computer which rai130 describes could do this - it would also
have the ability to predict its own answer.

My view - There is no free will - we are but made of subatomic particles.

:) wouldn't it be easier (or even a good use) to use this computer to
know what really happened in the past? If it can guess the future, it
should have almost shudderingly perfect hindsight. In fact, I'd hazard
a guess that the computer will have to know what's happened in the
past in order to make a good guess on the future. I say "guess"
because of the "Psychic out of business" sign... One would think she'd
have known...

The answer is "42"!  I swear!