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<h2 class="hd hd-2 unit-title">The Problem</h2>
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<h3><span style="font-family: 'book antiqua', palatino;">The Problem<br /></span></h3>
<p><span style="font-family: 'book antiqua', palatino;"></span></p>
<p><span style="font-family: 'book antiqua', palatino;">You are led into a room, and shown two boxes: a large one and a small one. You’re told that the small box contains a thousand dollars. You’re not sure what the large one contains, but you’re told that it either contains a million dollars or is completely empty. You are then offered two choices:</span></p>
<p style="padding-left: 30px;"><span style="font-family: 'book antiqua', palatino;"><strong>Two-Box</strong></span><br /><span style="font-family: 'book antiqua', palatino;">Keep the contents of both boxes.</span></p>
<p style="padding-left: 30px;"><span style="font-family: 'book antiqua', palatino;"><strong>One-Box</strong></span><br /><span style="font-family: 'book antiqua', palatino;">Keep the contents of the large box, but leave the contents of the small box behind.</span></p>
<p><span style="font-family: 'book antiqua', palatino;">The boxes were sealed before you entered the room, and your choice will not cause their contents to change.</span></p>
<p><span style="font-family: 'book antiqua', palatino;">How should you proceed? Should you one-box or should you two-box? The answer seems totally obvious. You should take both boxes! How could you possibly benefit from leaving a thousand dollars behind? Whether or not the large box contains a million dollars, you’ll end up with more money if you take the small box as well.</span></p>
<h3><span style="font-family: 'book antiqua', palatino;">A Twist</span></h3>
<p><span style="font-family: 'book antiqua', palatino;">Wait! There’s a twist. Let me tell you about what happened <em>before</em> you entered the room. A couple of weeks ago, a personality expert was summoned, and was handed as much information about you as could be gathered. The expert was then asked to predict, on the basis of that information, whether you would one-box or two-box. If the expert concluded that you would one-box, the large box was filled with a million dollars. If she concluded that you would two-box, the large box was left empty. In other words:</span></p>
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<tr class="header"><th align="left"><span style="font-family: 'book antiqua', palatino;">Expert’s Prediction</span></th><th align="left"><span style="font-family: 'book antiqua', palatino;">Contents of Large Box</span></th><th align="left"><span style="font-family: 'book antiqua', palatino;">Contents of Small Box</span></th></tr>
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<td align="left"><span style="font-family: 'book antiqua', palatino;">You One-Box</span></td>
<td align="left"><span style="font-family: 'book antiqua', palatino;">$1,000,000</span></td>
<td align="left"><span style="font-family: 'book antiqua', palatino;">$1,000</span></td>
</tr>
<tr class="even">
<td align="left"><span style="font-family: 'book antiqua', palatino;">You Two-Box</span></td>
<td align="left"><span style="font-family: 'book antiqua', palatino;">$0</span></td>
<td align="left"><span style="font-family: 'book antiqua', palatino;">$1,000</span></td>
</tr>
</tbody>
</table>
<p></p>
<p><span style="font-family: 'book antiqua', palatino;">The expert issued her prediction last night, and the boxes have been sealed since then. If the large box was filled with a million dollars last night, it will continue to hold a million dollars, regardless of what you decide. And if it was left empty last night, it will remain empty regardless of what you decide.</span></p>
<p></p>
<p><span style="font-family: 'book antiqua', palatino;">One final point: the predictor is known to be highly reliable. She has participated in many thousands of experiments of this kind, and has made accurate predictions 99% of the time. There is nothing special about your case, so you should think that the expert is 99% likely to correctly predict whether you will one-box or two-box.</span></p>
<p><span style="font-family: 'book antiqua', palatino;">How should you proceed now that you know about the procedure that was used to fill the boxes? Is it still obvious that you should two-box? (Keep in mind that the predictor knows that you’ll be told about how the experiment works, and about the method that was used to decide how to fill the boxes. So she knows that you’ll be engaging in just the kind of reasoning that you are engaging in right now!)</span></p>
<h3><span style="font-family: 'book antiqua', palatino;">The Predicament</span></h3>
<p><span style="font-family: 'book antiqua', palatino;">The fact that the predictor is 99% likely to predict whether you will one-box or two-box gives you the following two pieces of information:</span></p>
<ol>
<li>
<p><span style="font-family: 'book antiqua', palatino;">if you decide to take both boxes, it is almost certain (99%) that the large box will be empty; </span></p>
</li>
<li>
<p><span style="font-family: 'book antiqua', palatino;">if you decide to leave the small box behind, it is almost certain (99%) that the large box will contain a million dollars.</span></p>
</li>
</ol>
<p><span style="font-family: 'book antiqua', palatino;">Before learning about the expert, it seemed clear that two-boxing was the right thing to do. But now you know that if you one-box you are almost certain to end up with a million dollars, and that if you two-box you are almost certain to end up with just a thousand. Should you be a one-boxer after all? What to do?</span></p>
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<h3 class="hd hd-2">Video Review: The Newcomb Problem</h3>
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<h2 class="hd hd-2 unit-title">Could a Newcomb Predictor Really Exist?</h2>
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<p><span style="font-size: 12pt; font-family: 'book antiqua', palatino;"> When someone is first told about Newcomb’s Problem, they often worry about whether there could really be an expert of the kind the story requires. </span></p>
<p><span style="font-size: 12pt; font-family: 'book antiqua', palatino;">It is certainly <em>logically possible</em> for there to be such an expert. </span></p>
<p><span style="font-size: 12pt; font-family: 'book antiqua', palatino;">Consider, for example, a super-scientist who creates a molecule-by-molecule duplicate of your body, and makes her prediction by allowing your duplicate to experience a Newcomb case and observing the results. As long as you and your duplicate are subjected to identical stimuli, the two of you should carry out the same reasoning, and reach the same decision. Even taking quantum effects into account, there is no reason such a predictor couldn’t be 99% reliable, or more.</span></p>
<p><span style="font-family: 'book antiqua', palatino;">Of course, none of this shows that perfect (or near-perfect) predictions are possible in practice. But for our purposes it doesn’t matter if the Newcomb case could be carried out in practice or not. We will be using the Newcomb case as a <em>thought experiment</em> to help us understand what rational decision-making is all about. So all we really need is for Newcomb cases to be logically possible.</span></p>
<p><span style="font-family: 'book antiqua', palatino;">It is also worth keeping in mind that the discussion below won’t require perfect, or even near-perfect predictions. As you’ll be asked to show in the exercise below, anything better than chance will do. And it is certainly possible to imagine real-life predictors that do better than chance. Consider, for example, a predictor who works with identical twins. She starts by testing the Newcomb setup on one of the twins, and observing the results. She then predicts that the second twin will choose like the first. Even if such a predictor isn’t perfectly accurate, one might expect her to do better than chance.</span></p>
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<span style="font-family: 'book antiqua', palatino;">Earlier I suggested that it might be possible to generate better-than-chance Newcomb predictions using identical twins. Describe a different method for doing so.</span>
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