SelfAwarePatterns<p><strong>Is quantum immortality a real thing?</strong></p><p>In discussions about <a href="https://en.wikipedia.org/w/index.php?title=Many-worlds_interpretation&oldid=1293306075" rel="nofollow noopener" target="_blank">the Everett interpretation of quantum mechanics</a>, one of the concerns I often see expressed is for the perverse low probability outcomes that would exist in the quantum multiverse. For example, if every quantum outcome is reality, then in some branches of the wave function, entropy has never increased. In some branches, quantum computing doesn’t work because every attempt at it has produced the wrong result and people have concluded it doesn’t work. In other branches, you as a macroscopic object might quantum tunnel through a wall.</p><p>Of course, for enthusiasts, this comes with a hopeful aspect. Because in some branches, you would go on living indefinitely, no matter how improbable it might be. Hugh Everett himself was reportedly a believer in <a href="https://en.wikipedia.org/w/index.php?title=Quantum_suicide_and_immortality&oldid=1292097023" rel="nofollow noopener" target="_blank">quantum immortality</a> and so had little concern about the unhealthy lifestyle that led to his early demise in this branch. The idea is that if every outcome happens, then there are versions of you reading this that will live until the heat death of the universe.</p><p>This is vividly illustrated in the infamous quantum suicide thought experiment. One version described by Max Tegmark involves rigging up a gun to fire if a certain quantum event happens. Say the quantum event has a 50% chance of happening in any one second. You then put your head in front of the gun and begin the experiment. In half of all worlds where you begin the experiment, you die in the first second, but you go on living in the other half. In half of that remaining half you die in the next second, but go on living in the other half. </p><p>For you as the experimenter this goes on indefinitely with increasingly improbable outcomes leading to your survival. Of course, in virtually all worlds you leave behind grieving friends and family who are less convinced. But for you subjectively, if many-worlds is reality, you continue living until the experiment ends.</p><p>(Before getting too comforted by the possibility of quantum immortality, it’s important to remember that this is more of a side-life than an afterlife. Most of the versions of you will still experience an approaching death. It’s also worth noting that a you a million years from now would likely have evolved into something utterly strangle and unrecognizable to the you of today. And there’s no guarantee this ongoing existence would be pleasant. Indeed, under many-worlds, some would inevitably be hellish.)</p><p>One question that often comes up in discussions about this is whether reality allows for these infinitesimally low probability outcomes, or whether there is some inherent minimal discreteness at the base of reality that prevents it. There’s nothing in the math to indicate it, but of course the math, at least the math we have today, is a description of reality that is likely only an approximation.</p><p> However in a recent interview with Curt Jaimungal, David Wallace, a proponent of the many-worlds interpretation, may have provided another reason to doubt these outcomes: quantum interference. (Note: if the embed doesn’t work right, the relevant remarks are at around the 1:21 mark. Also you don’t have to watch the interview to understand this post, but it is an interesting discussion.)</p><p><a href="https://www.youtube.com/watch?v=4MjNuJK5RzM&t=4901s" rel="nofollow noopener" target="_blank">https://www.youtube.com/watch?v=4MjNuJK5RzM&t=4901s</a></p><p>To understand Wallace’s point, it helps to realize some important points about how quantum decoherence works. Decoherence is the process of the quantum particle losing its wave like nature and becoming more particle like. This happens because as it interacts with the environment, the phase relations which keep the wave coherent become disrupted. The wave becomes fragmented. We call the fragments “particles”. This leads to the famous (infamous?) quantum interference effects disappearing. (As shown by <a href="https://www.youtube.com/watch?v=A9tKncAdlHQ" rel="nofollow noopener" target="_blank">the double slit experiment</a>.)</p><p>But the word “disappearing” here in reference to the interference effects should be understood to mean “become undetectable”, not that they cease to exist entirely. Under decoherence the interference never goes away entirely. Like the wave overall, it becomes fragmented, and settles into an underlying “noise”. (Note: this is actually a difference in predictions between collapse and non-collapse interpretations that should, in principle, be testable. Of course, figuring out a way to do the test is another matter.)</p><p>Wallace’s point is that infinitesimally low probability outcomes should be swamped out by this remnant interference from higher probability outcomes, meaning that they should be prevented from existing. If so the branches where entropy never increased, where quantum computing never works, or to use his example, where he as a macroscopic object quantum tunnels through a wall, shouldn’t exist.</p><p>What does this mean for quantum immortality? I don’t know that it wipes it out entirely. Many of the initial survival scenarios may be very low probability, but not <em>profoundly</em> low ones, and so may not be swamped by interference from the other branches. But it does seem like it shortens the duration and overall makes it less certain, even once someone accepts the existence of the other worlds. So there may be versions of you reading this that live for decades or centuries beyond the normal lifespan, maybe even millenia, but probably not until the end of the universe.</p><p>Still, the implications are interesting and fun to speculate about. If there is a version of me alive in the far future, I wonder if he (it?) will remember these speculations. </p><p>What do you think of Wallace’s point? If we assume many-worlds is reality, does the idea of quantum immortality seem plausible? Or are there other reasons to doubt it?</p><p><a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://selfawarepatterns.com/tag/interpretations-of-quantum-mechanics/" target="_blank">#InterpretationsOfQuantumMechanics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://selfawarepatterns.com/tag/many-worlds-interpretation/" target="_blank">#ManyWorldsInterpretation</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://selfawarepatterns.com/tag/philosophy/" target="_blank">#Philosophy</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://selfawarepatterns.com/tag/quantum-immortality/" target="_blank">#QuantumImmortality</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://selfawarepatterns.com/tag/quantum-mechanics/" target="_blank">#QuantumMechanics</a></p>