h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

David Lewis has a very sensible response to the problem of paradoxes. Essentially, the problem of paradoxes is not as people have characterised it here. If you go back and kill your grandfather before your father is born, you would never live to do it, and this is the paradox. So we know you /can't/ do that. That's straightfoward. The problem that philosophers have with this is that it would seem to mean that there would have to be some weird force stopping you. You'd point the gun, but, weirdly, it just wouldn't fire.

Now David Lewis (with whom I ussually violently disagree, but not on this), says this is analagous to the way you say 'I can't speak Spanish' as well as 'A parrot can't speak Spanish' - just two different ways of using the word 'can't'. It is true that you can't kill your grandfather. Why not? Because he already lived to have your father. But that's no more than saying if fatalism is true, and you won't run 5 miles tomorrow, you can't. If it's a *fact* then obviously in some sense you can't avoid it, but that doesn't mean there has to be something that stops you.

Basically, you're saying that there is no free will. No matter how much you tried, you would be unable to kill your grandfather. I can understand that; it's a respectable theory.

PhysicsMan

No, not at all. Why should fatalism imply a lack of free will? Simply because there is a true that 'I will not go for a run tomorrow' does not mean that I have any less choice in the matter. All that fatalism implies is that there are always facts about the matter about questions of the future. I think it's obvious that fatalism holds, and can't really see what the problem is that people have with time travel if they don't hold that there are facts about other times. If you believe that there are truths about the past, it makes sense to believe in truths in the future.

I hope that this talk about fatalism isn't getting mixed up with the free-will/determinism debate.

To sumarise:

It is possible to have a deterministic universe in which we have free will. under those conditions, outside events constrain our options, which we then make a free choice between.

Often fatalism is about this, but often it is more about blind acceptance of what the universe throws at you.

People holding this later viewpoint often forget that refusing to make a choice is also a choice, and that when you refuse to choose, you just opt to let the universe continue restricting your options until you don't really have any options, and your actions are then forced.

This does not seem like a very clever way to live to me.

Erm, no, I think you're mistaken. If determinism holds, there can be no free will. The initial conditions of the universe and physical laws determine everything that will happen in the entire history of the universe, and therefore minds can have no place to affect what goes on.

However, with fatalism, you definitely *can* have free will. What fatalism says is that what will happen will happen, but only because there are already facts about what is going to happen. If you accept that when I say 'Tomorrow I shall eat an ice-cream' I am either saying something true or false, then you're a fatalist. Otherwise you have to deny truth to any statement about things that haven't happened yet. And basically that means being a presentist, i.e. believing that there are only facts about the present, and no past or future facts.

Let me see if I can figure out the determinism/fatalism/free will thing. According to fatalism (I think), you have limited free will; that is to say, you are free to act within a set of boundries set by fatalism. No free will means that you can make no decisions; the way the universe was initially set determines all that you can do. Personally, I don't like fatalism; I tend to have an all-or-nothing opinion towards free will: either you can make every decision, or you can make no decisions.

PhysicsMan

No. No no no. No no no no no.

Okay. You're mixing up multiple theses. Firstly, there is fatalism. That is the claim that there are truths about the past and future. Unless you're an intuitionist, and believe that the law of the excluded middle isn't always true (so that it isn't always the case that P or not-P for any statement), you should be a fatalist. Most people don't realise this. If you do, however, believe that when you say something like 'Tomorrow I will eat an ice cream' you are saying something that is either true or false, you are a fatalist.

Okay. Now there's a totally unrelated doctrine called 'determinism'. A determinist believes that the initial conditions of the universe, and the laws of nature determine everything that happens, ever. That is, there are no external influences (such as minds) or built in randomness.

Determinism, therefore, presumably prohibits free will, since minds can't have any effect. But unless you're a Cartesian dualist, you can't presumably believe in free will anyway.

Okay. Personally, I'm a fatalist. I believe there are truths about the past and future. I believe that if I say 'Tomorrow I'll eat an ice cream' there's a fact about the matter. I'm not, however, a determinist (because quantum theory introduces randomness).

For David Lewis to be correct, all we need is fatalism. Obviously you can't kill your grandfather, but that's the same sort of can't as saying 'You can't kill your grandfather and not kill your grandfather'. Likewise 'You can't both eat an ice cream and not eat an ice cream tomorrow'. Why on earth should that be paradoxical?

I agree that there are *some* truths about the future. If I say that the Earth will exist in 6 hours, I'm pretty sure that's a truth. However, I think there's a bit of difference between statements such as "No matter what I do, with or without time travel, I cannot destroy the Earth" and "No matter what I do, with or without time travel, I cannot kill my grandfather." The fact that the later is impossible hints at some sort of deterministic force guiding the universe, which I don't thin either of us believe in. If I try to go back, but all sorts of random things stop me from killing my grandfather, I would not say, "Oh, there are some things which are clearly impossible," but rather, say "Wow! My not killing my grandfather must have been determined in advance!" I'm sure this argument will bring me problems with matters of degree, but that's what I'm saying and I'm sticking to it.

PhysicsMan

The main problem it brings you, is that you can't say that there is a truth about things you did *yesterday*, or even five minutes ago. Some people are fatalists about the past, but not the future, but nobody's ever come up with a justification of this position.

That, and the fact you have to be an intuitionist - deny the law of the excluded middle, that nothing is both A and not-A. Which is a very extreme position to take...

And yes, my position (that I too am sticking with) is that fatalism has *nothing whatsoever to do with determinism*. As it is, since determinism aint so, it would be a ridiculous option.

What's wrong with saying the past is definite, but the future is indefinite? The past is done. Whatever quantum effects there would have been have already happened; nothing can change the past (except for time travel; if that's what you're alluding to, then so state it). The future is indefinite; there will still be new quantum effects which spin the universe into new possibilities; you cannot make definite statements in the future. You can say what's *likely* in the future; it is highly likely that the Earth will exist five minutes from now, but who knows? Weird stuff could happen, and destroy the Earth. Nothing about the future is set in stone.

Now, if time travel is involved, naturally we have problems. If you could go into the past and change whatever you wanted, problems would occur. You would say that the solution is that the past is set in stone, and therefore there would be certain things you *couldn't* do. I say, once you are in the past, the past becomes your present, and therefore, you can change it. If you *must* do certain things in the past, then you clearly do not have free will.

PhysicsMan

What wrong with saying the past is definite by the future not? Well ther are many, many problems (read the literature if you like - I'm in the middle of my finals, but I'll give you a pointer in about a week if you like). The main one is that we *presumably* want to construe claims about the past in the same way we do claims about the future. I.e. they're the same sort of claims as ones about the present, but with a time-difference. It is very unclear how you'll go about formalising your construal of sentence about the past or future if you deny this symmetry.

Also, what does it matter if you can't *know* stuff about the future. You can't /know/ what colour the moons of alpha centuri look, or whether Julius Caesar ate breakfast on the day he crossed the Rubicon. Presumably there's some /truth/ about the claim 'My eyes are green / brown' despite the fact you've never seen them.

So we're not going to limit truth just to that which you can know. even if you're a verificationist, you'll think the future is more verifiable than the past, and thus statements should be construed more truth-dependently...

OK. First of all, I can sorta see your point about knowing stuff about the past vs knowing stuff about the future. After all, why should *right now* be the watershed between known and unknown? The answer is, because *right now* is the present. What has happened has already happened; nothing will change this. We can change the future, possibly; if we actually have no free will, then this would change things, but I will discuss this presently. Besides, even with no free will, quantum effects will change the future and make it unknowable. And if we do have free will, then we can change the future -- but not the past. The future is indeterminate; the past is determinate.

Of course, if we have no free will, if what we *think* is free will is merely the *illusion* of free will, then I will concede that the future is as set in stone as the past (ignoring quantum effects).

Time travel complicates things. If we have time travel, but no free will (and no quantum effects), then there is no problem; since all your actions are set in stone, your visit to the past would be restricted to not changing anything, and there would be no problem. However, if you have both time travel *and* free will (even the fatalism you so like), there would be a problem. While you were in the past, you could change things, and make the present different from the present you came from. Maybe if time travel also allows you to travel across parallel universes, this won't be a problem, but if you change the present of your own universe, you would cause a paradox.

Oh, and about *knowing* things. I'm not talking so much as, what you can know based on historical records, etc. I'm talking more about whether something is set in stone and unchangable, or whether quantum or other forces could still change it.

PhysicsMan

1) Is there a yes / no answer to the question 'Does the first moon of Alpha Centuri look brown?'

2) Is there a yes / no answer to the question 'Are my eyes brown?'

3) Is there a yes / no answer to the question 'Did Julius Caesar eat breakfast the day he crossed the Rubicon?'

4) Do you know what colour the first moon of Alpha Centuri looks?

5) Do you know what colour my eyes are?

6) Do you know whether Julius Caesar ate breakfast the day he crossed the Rubicon?

7) Could you know what colour the first moon of Alpha Centuri looks?

8) Could you know what colour my eyes are?

9) Could you know whether Julius Caesar ate breakfast the day he crossed the Rubicon?

OK, it seems that we're having a problem defining the word "know." When I say that the past is knowable and the future is unknowable, I mean that the past is set and not likely to change, while the future is variable and can change. You mean that the future is more knowable than the past because if I want to, I can take a notebook and write down everything that happens in the future, while certain events in the past have been lost through the veils of time. Your definition of know is prolly more accurate; I'll use the word "certain" instead. I still argue that the past is more certain than the future; the past is done, and cannot be changed, while the future is uncertain, and can be changed by free will or quantum effects.

PhysicsMan

No no no. You misunderstand my point. I'd be genuinely interested to see your responses to those questions.

The point: I'm not talking about /knowing/ at all. What I'm interested in is what has a truth value, and that has nothing to do with what we know. Even if you're a verificationist, you hold that it is more likely the the future has truth values than the past.

The point is that whilst, because of quantum indeterminacies, we can't /know/ what will happen, we can still be right or wrong about it if we make a claim about the future. That is why you get paid money for making a correct bet - because, whilst you didn't know about the future, you 'said something correct about it'.

The point is, if I say 'India and Pakistan will descend into nuclear war', and you say 'India and Pakistan will not descend into nuclear war' one of us is right, and one is wrong. Sure, we can't know about that (yet) but so what? That doesn't stop one of us being right.

Otherwise you're committed to a really bizarre version of intuitionism, where you hold that some things that could be proved (by waiting) don't have truth value, whereas some things that never could do.

So the point of my questions: knowledge is not equal to truth value.

your example while good, has a problem.

it assumes absolutes in being true or false, and it isn't that simple.

for a start, there is the problem of classification. what qualifies for a nuclear war, 1 bomb each, 10, 20?

then there are conditional dependancies, which make it unlikely that you can make a clear prediction (as opposed to a vague "i think they will/won't").

It was proved over 100 years ago that the universe isn't black and white in it's parameters. A lot of paradoxes are because people try and force it into black and white pidgeon holes.

If your concept of "truth value" is whether a true statement can be made about something, than I have to agree with you that the future has a greater truth value than the past. I can say "The earth was destroyed yersteday," but that clearly has a truth value of zero, since it wasn't destroyed and my statement is false. However, if I say, "The earth will be destroyed tomorrow," than this would have a truth value of one (right?) because that *could* be a true statement.

However, that said, I really don't see the point of truth values. Arguably, that is the same thing that I'm saying, namely that the future can change but the past cannot.

One last thing: What is a "verificationist"? You seem to know more jargon than I (with the distinction between fatalism and determinism, and the "law of the excluded middle"), so could you clarify this, please?

PhysicsMan