Predestination (idea)

Definitions:
1. Choice
"Choice" in this description indicates one's ability to take arbitrary courses of action. It follows that, when the ability to choose ("free will") is present, no being with this ability is 100% predictable.
2. Free-will (or, "agency")
The ability to select from a number of alternatives arbitrarily, i.e., to choose.
3. Destiny
In Christian religions, there exists a concept of "salvation", wherein those who make "good" choices will go to a better place after death, and those who do not will not. Variations are commonplace.

"Proof":

Since human beings exist on Earth on a finite timeline, we can represent a person's life in terms of all of their actions taken (however minute). No notion of dependence is assumed by the following, i.e. all actions are looked at as separate from all other actions. We can define a person at any given moment as the sum of all of their actions. "Sum" in this usage does not indicate a numeric sum, but the notion that actions are cumulative. We will refer to the meaningless value of S_n as a person's "state", and that since a person's Earthly life eventually comes to an end, there exists a "final" state S_end, after which no further actions are taken. Let S_n = &Sigma A_n, where A_n denotes the nth action taken by the individual in question. n is assumed to be a member of the positive integers.

Let P(n) be the proposition that "Person p's state after taking action A_n is known to god".
We argue by induction on n:

Basis step: Show P(1) to be true.
By Assumption 2, god knows the first action a person will take, and thus its outcome.

Induction Step: Show P(k) = P(k+1), i.e., show that if god knows a person's state at any given time, he knows their next state as well.
Consider a person in state k (having just taken action A_k). Since "actions" are defined to be as minute as possible, then at every possible time t, the person takes an action A_t. Since life on Earth can be represented as a sequence of actions, A_t becomes synonymous with A_k. By Assumption 2 above, god knows the person's state at S_k. God also knows the person's following action, A_k+1. It follows that god knows the person's state at S_k+1 (at time t+1). This holds whether or not times t and t+1 have already occurred.

By this logic, god knows the person's final state, S_end, and by that the person's destiny.

We have shown, in a cumbersome and somewhat pedantic manner, that if god knows everything, then he knows what you are going to do at all possible moments, and it follows that he knows your final destiny as well. Before your advent on Earth, all of the actions you would take were known to god. Therefore, your life could be safely aborted and you could be filed in your proper place immediately.

A possible objection is that "choice" is a matter of perspective. This is not the case. For example, if mind control were possible, and I could force a person to take actions determined by myself, the person would still believe they were acting with free will. However, since I can predict all of their actions, I know that they do not have free will. The fact that he or she believes that he or she is making arbitrary choices (determined by himself or herself) has no bearing on what actions are taken. Conversely, if I am observing another person who I do not control, I cannot predict with 100% accuracy what actions they will take, and thus must assume that they are acting arbitrarily. The key concept is that once an event is known, it occurs with a probability of 1, regardless of perspective.

Since god knows all the actions you will ever take, god could write out a program for you, before you are born, and you would act out that program. However, a stipulation of the program is that you believe that you take arbitrary actions. Effectively, you are blinded to your own robotic state. Thanks to Reason, the veil has been lifted. Your destiny is foreordained, say the Priests of Reason, if you presume the existence of an omniscient god. Furthermore -- and this should be obvious -- the notion that one person's actions depend on the actions of another is irrelevant if all persons are considered to be acting according to a script.

The concept that everything we do is already planned out is disturbing to most people, because we enjoy making choices and prefer to think that all that we accomplish is the result of our own intelligence. However, we prefer to think that our mistakes and shortcomings are the result of some inevitable circumstance. We would be happy if all our mistakes were foreordained -- then we would not be responsible for them.

But this predestination crap doesn't allow one to escape accountability on Earth. All your actions are known in advance to god, but not to you or to the rest of us. Therefore, as far as the rest of us are concerned, you take arbitrary actions. The concepts of "responsibility" and "blame" are only relevant in the human perspective, but are still relevant. Since your "program", so to speak, is hidden from us and from yourself, the concept of free will springs into existence.

When we finally crack god's password and are able to freely distribute the source code for all the people in the universe, you will no longer be held accountable for your actions -- they're right there in the code. But the notion of accountability will disappear, and although your "mistakes" will no longer be upbraided, your "accomplishments" will likewise go unnoticed.

In terms of religion and salvation, if your religion assumes that god is omniscient, then you can rest easier and ignore religion altogether. God already knows where you are going to end up. You are powerless to affect this, as shown above. This is neither good nor evil, it just is.

However, most modern Christian religions appear NOT to assume that god is omniscient. If they did, they would fall victim to the traps above. What they apparently assume is that god is aware of all information at the present and in the past, but is not aware of the future. This means that he knows everything you have done and why you did it, and can always read your mind, but that your future is stil determined by you. This tenet results in the following:

1. You need to "be good", because if you don't, you will be punished.
Punishment is nonsensical unless there is accountability. If all is foreordained, there can be no accountability. God promises punishment for wrongdoings in the Christian scriptures (all of them), so by this definition, God himself admits that he cannot see into the future and cannot affect it.

2. You cannot deceive god.
Since god is always aware of all details of the past and present, he would know you were lying to him. This is also mentioned explicitly in the Christian scriptures.

3. The purpose of life on Earth is to determine whether you will be eligible for a particular post-death destiny.
It makes no sense for god to "test" people if he already knew what they were going to do. If he doesn't know what they are going to do, then a test is required. Some religions hold that the entire point of human existence is to determine your later divine status. In that case, god definitely cannot see into the future.

Since the tenets listed above seem to be espoused by Christianity at present, we can assume that they do not actually espouse total omniscience for God, but a limited omniscience, where he knows more than you do, but not everything. In this case, if you are Christian, you should go to Church, donate the proper amounts of money, and follow all other instructions. An eternity of pain and torment may be your only alternative.