Leslie's Firing Squad Can't Save The Fine-Tuning Argument

post by dadadarren · 2020-09-09T15:21:19.084Z · LW · GW · 6 comments

This is a link post for https://www.sleepingbeautyproblem.com/7-1-leslies-firing-squad/


  The Firing Squad
  The Rebuttal To WAP
  Analysis of the Firing Squad
  The Disanlogy
  Think As An Alien
  Begging the Question

This post argues against fine-tuning, especially the fine-tuning argument for design. It again shows the importance of perspectives in reasoning as discussed in a previous post [LW · GW].

I previously argued [LW · GW] why fine-tuning is a misconception. Reasoning from a first-person perspective, I endorse the Weak Anthropic Principle (WAP) response. Leslie’s Firing Squad is perhaps the most famous argument against this response. I think it would be interesting to examine it in detail.

It should be pointed out my objection to fine-tuning differs from most, if not all, anthropic objections since perspective-based argument (PBA) rejects the notion of observation selection effect (OSE). The WAP should only be regarded as a logical truth, not as selection bias. Nonetheless, the firing squad argument can still be used to counter PBA. Therefore it deserves an explanation.

The Firing Squad

Suppose you are a prisoner facing the death penalty. You are blindfolded and placed against a wall. A firing squad consist of a dozen expert marksmen stands just a few meters away to carry out the deed. The order is given. The shots ring out. Yet somehow you find yourself alive after the whole ordeal. Every single bullet has missed.

Considering you are still alive you should be vastly more confident that the marksmen intentionally spared you, i.e. by design. After all, the probability of all 12 marksmen missing by chance is immeasurably small.

The Rebuttal To WAP

The firing squad scenario may seem analogous to the fine-tuning argument. WAP suggests all fundamental constants being compatible with our existence is a logical truth, i.e. to be expected. Therefore it is no evidence supporting a designed universe. Then by the same logic, after surviving the firing-squad I should also conclude that is to be expected. Because being alive is the only observation I can make, a logical truth. Consequently, it is not evidence suggesting the marksmen intentionally missed either. That is obviously irrational.

I suggest the analogy drawn between the firing squad and the fine-tuned universe is flawed. There is a critical difference between the two cases. Based on my research, this rebuttal has not been published before.

Analysis of the Firing Squad

The core of my argument (PBA) is to reason from one consistent perspective. So I am going to be explicit about it in the analysis.

Let’s take the prisoner’s first-person perspective. After hearing the shots and realizing I am still alive, I shall reason as follows: The world ought to be compatible with my existence. Whereas the scenario of the marksmen successfully hit thus killing me is incompatible. Therefore it is precluded as a possibility. All there remains is either they intentionally spared me or the immensely improbable case that they all missed by random chance. This would greatly increase the probability that they missed on purpose.

Now let’s take the perspective of some random bystander. Here I would make the exact same probability update as the prisoner. Though there are some differences in the reasoning. This update is not based on the logical truth of WAP. All execution outcomes are compatible with my existence. Instead, I would use the prisoner’s survival as new evidence, since I am not guaranteed to find him alive. The end result is the same: a major increase in the probability that the marksmen missed intentionally.

The Disanlogy

Both the prisoner and the bystander analyze the problem by focusing on the prisoner. This may seem like an obvious thing to do. Trivial, even. However, this perspective asymmetry is based on our background knowledge of what a firing squad is. A firing squad is designed to execute prisoners. We know its purpose. That’s why no matter which perspective we choose to take, the attention is always on the prisoner. Because knowing the firing squad’s purpose, the prisoner’s life-or-death is logically significant to the problem.

That is distinctively different from the fine-tuning argument. The purpose of the universe is unknown. Nothing is logically inherently significant. The fine-tuning argument is formulated to focus on the perspective center. I would ask why is the universe compatible with “my” existence. The fine-tuning argument chooses to use more generalized categories of “my kind” (such as humans, life, sentient observers, or complex physical system) instead of using “me” specifically, to appear less egocentric. It is only a trick to make more allies. Yet the fact remains fine-tuning is rooted in the first-person perspective.

Think As An Alien

Let’s use our imagination, picture some intelligent alien in a far corner of the universe whose physical structure is radically different from us such that our usual definition of “life” doesn’t describe it. Now let’s think from its perspective. When pondering upon the fundamental constants of the universe, it won’t ask “why is the universe compatible with “life” as defined by some bipedal carbon-based creatures light-years away?”. There is no reason for this attention. In the spirit of the fine-tuning argument, it would only ask “why is the universe compatible with me? (or my kind)”.

Now suppose we introduce Leslie’s Firing Squad to the alien. As long as it understands the concept of execution, it would analyze the problem basing on the prisoner’s life-or-death, not its own. This is where the analogy breaks down. The fine-tuning argument depends on one’s own existence. Whereas Leslie’s Firing Squad, with the knowledge of its purpose, depends on the prisoner’s. Supporters of fine-tuning argument deliberately picked the prisoner’s perspective in their rebuttal to make the two cases superficially similar.

That is why the WAP is indeed the correct response to the perspective based fine-tuning problem. Because to myself, my existence, and the world being compatible with it, is a logical truth. Period. For the firing squad, from the prisoner’s perspective, finding myself alive is not in itself surprising. But the fact that I am analyzing the outcome of my own execution is. This surprise hinges on my background knowledge of the firing squad’s purpose. That is what motivates the probability update.

Begging the Question

The fine-tuning argument for design is basically asking a perspective-dependent question while demanding a perspective-independent answer. They formulated a first-person specific problem yet insist on an objective explanation. It is a paradox caused by not reasoning from a consistent perspective.

In my opinion, using Leslie’s Firing Squad as a rebuttal achieves the opposite effect. It highlights the issue of the fine-tuning argument for design. The argument analyzes the fundamental constants by their compatibility with life as an obvious thing to do. Yet, as the firing squad case shows, that would require a prior assumption of the universe’s purpose being life-related. Instead of arguing for life’s significance, it subtlely builds that conclusion into the premises. Begging the question, essentially.


Comments sorted by top scores.

comment by shminux · 2020-09-10T00:52:23.326Z · LW(p) · GW(p)

Note that speaking of probabilities only makes sense if you start with a probability distribution over outcomes.

In the firing squad setup we have an a priori probability distribution is something like 99% dead vs 1% alive without a collusion to miss, and probably the opposite with the collusion to miss. So the Bayesian update gives you high probability of collusion to miss. This matches the argument you presented here.

In the fine tuning argument we have no reliable way to create an a priori probability distribution. We don't know enough physics to even guess reliably. Maybe it's the uniform distribution of some "fundamental" constants. Maybe it's normal or log-normal. Maybe it's not even a distribution of the constants, but something completely different. Maybe it's Knightean. Maybe it's the intelligent designer/simulator. There is no hint from quantum mechanics, relativity, string theory, loop quantum gravity or any other source. There is only this one universe we observe, that's it. Thus we cannot use Bayesian updating to make any useful conclusions, whether about fine tuning or anything else. Whether this matches your argument, I am not clear.

comment by Jayson_Virissimo · 2020-09-10T06:55:09.868Z · LW(p) · GW(p)

A similar "measure function is non-normalizable" argument is made at length in McGrew, T., McGrew, L., & Vestrup, E. (2001). Probabilities and the Fine-Tuning Argument: A Sceptical View. Mind, 110(440), 1027-1037.

comment by dadadarren · 2020-09-10T20:23:55.006Z · LW(p) · GW(p)

Very interesting...

I think proponents of the fine-tuning arguments for design are saying there doesn't need to be a reliable way to assign a prior. You can assign any prior you deem reasonable. Nonetheless, after considering our seemingly unlikely existence, the probability would greatly shift towards a teleological conclusion that the universe is designed for life.

So unless you are willing to commit that not only there is no reliable way to assign a prior, but also assigning a probability in this situation is invalid in itself, it doesn't counter their argument per se. It would be just pointing out even with the probability shift we should still be skeptical that the universe is designed due to the unknowns (but less skeptical than before considering fine-tuning). Are you saying what I think you are saying?

Just to be clear, I am not against the invalidity of probability in this situation. In fact, I probably support it more than you would like. I just choose to counter the proposed probability update because that is more direct.

comment by shminux · 2020-09-11T05:49:39.881Z · LW(p) · GW(p)
So unless you are willing to commit that not only there is no reliable way to assign a prior, but also assigning a probability in this situation is invalid in itself

Indeed. If you have no way to assign a prior, probability is meaningless. And if you try, you end up with something as ridiculous as the Doomsday argument.

comment by dadadarren · 2020-09-11T14:34:27.605Z · LW(p) · GW(p)

Well, in that case, our arguments actually have a lot in common. My position regarding anthropics is that perspectives are axiomatic in reasoning. So a valid argument/notion must be formulated from one single perspective. This postulate refutes the probability shift in fine-tuning. It also invalidates the notion of self-locating probabilities like in the case of the doomsday argument.

comment by Ian Roberts (ian-roberts) · 2020-09-21T07:49:57.082Z · LW(p) · GW(p)

In this Firing Squad analogy there is another possibility that could be considered.

We have -
1. The firing squad missed by design.
2. The firing squad missed due to poor marks-person-ship.

3. God intervened to deflect the bullets.

Lest anybody scoff at this, remember the attempt to kill pope JP II - by John Paul II's assessment, "It was a mother's hand that guided the bullet's path,"