Does Quantum Immortality Save Schrödinger's Cat?

**SPEAKER_1** (0:00)
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**SPEAKER_3** (0:58)
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**Matt O'Dowd** (1:00)
To quote eminent scientist Tyler Durden, On a long enough timeline, the survival rate for everyone drops to zero.
Actually, not necessarily. If the quantum multiverse is real, there may be a version of you that lives forever.
In the last couple of episodes we've been delving into a key mystery of quantum mechanics.
Why don't we have quantum magical powers?
Or more scientifically, what causes the divide between the weird behavior of the quantum world and our large-scale macroscopic world? In particular, what causes quantum systems to transition from simultaneously existing in many states at the same time to having only one clear observable state at the moment of measurement? This is the measurement problem. We've been exploring decoherence as a mechanism for this quantum classical transition. And we're not done yet, but today I want to take a step back to think about and acknowledge something very important. By itself, decoherence does not solve the measurement problem. It only explains why separate branches of the wavefunction, separate alternate histories, stop being able to interact with each other. In order to understand what happens to those different branches, and to understand why we find ourselves in one of them, we need to embrace one of the interpretations of quantum mechanics. For example, the Copenhagen interpretation, which says that the wavefunction branches that we don't observe somehow vanish at the moment of measurement. Or the many worlds interpretation, which states that those other branches are just as valid as ours, implying that reality may split and multiply in all possible ways. In that case, we only see one branch because we live in that branch, and the others are rendered inaccessible by decoherence. The problem with these interpretations is that on the surface they seem untestable. We can't ever peer into those other realities, so how do we know they exist? Today I'm going to offer a test. Admittedly not a very useful test, but one that is very fun to think about. We'll call this test quantum immortality. It's based on the famous Schrödinger's cat thought experiment. As a refresher, a cat is in an opaque box with a vial of deadly poison, which is released on the radioactive decay of an atom. There's a totally random 50-50 chance of the radioactive decay over a certain period of time. That means the quantum wavefunction of the atom splits equally. The atom is simultaneously decayed and not decayed until we observe it. So then surely the cat's wavefunction splits too, into dead and alive. According to Copenhagen, one of these results becomes real when the physicist opens...

**SPEAKER_1** (4:00)
This episode is brought to you by Accenture. When you're advertising operations fall out of sync, everything else follows. Spotify and Accenture are working together to reinvent the rhythm of ad sales. Using automation, analytics, and smarter workflows to simplify campaign delivery and access better data across the business. The result? Less time spent on operations, more time connecting brands with the moments and fandoms that matter most. Learn more at accenture.com/spotify.

**SPEAKER_2** (4:32)
Back to school is busy enough. The last thing you need is shopping that makes it harder. Whether you're moving into a dorm, your first apartment, or just getting organized for the semester, Wayfair makes it easy to get everything you need in one place. Furniture, bedding, storage, decor, study essentials, all at prices you'll love with fast shipping before move-in day.
Get everything you need for back to school season. Shop wayfair.com today.

**SPEAKER_1** (4:58)
Wayfair, every style, every home.

**Matt O'Dowd** (5:00)
The box, while the other branch of the wavefunction vanishes. But in many worlds, both branches continue forever, and the physicist's wavefunction also splits in two. I guess into guilty and relieved?
Neither version of the physicist knows about the other, and it seems like there's no way for them to confirm the existence of the other branch of the wavefunction. But there is one test, a rather morbid one. The physicist could crawl into the box instead of the cat. And instead of a vial of poison attached to one radioactive atom, connect the vial to many atoms, so the poison is released if any of them decay.