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Ever since its conception in the early 20th century, quantum mechanics has continued to puzzle physicists and scholars about what it all means. Among many interpretations that attempt to explain the weird world of the quantum, the orthodoxy, Copenhagen interpretation (CI), and the Many-worlds interpretation (MWI) are the most controversial ones and the latter is taking prominence among physicists and pop culture lately. Quantum immortality stands as a potential way to find out which is true of the two.
In quantum mechanics, particles exist in multiple states - superposition of states - at once before being measured. Measurement of a particle’s state yields a single result. According to CI, the particle randomly collapses to one of those states during measurement. In MWI, all of those possibilities become real, yielding multiple independent and individual results. This translated from the quantum world to the macro where we live in, is the single reality vs multiple realities debate.
In a nutshell, the CI vs MWI argument asks this: Did the particle randomly collapse to one of the possible states, or are there multiple realities out there that individually possess all the possibilities? An attempt at answering this question gave life to the idea of Quantum Immortality.
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The origin of quantum immortality dates back to 1956 when Hugh Everett published his paper on the “Theory of Universal Wavefunction,” which postulates the MWI of quantum mechanics. And as it is the case with most interpretations of quantum mechanics, the challenges with Everett's hypothesis came from its untestability.
Max Tegmark on "How to get empowered, not overpowered, by AI" at TED conference in 2018.
Later in 1997, MIT physicist Max Tegmark published a paper proposing an experiment to prove the Many Worlds interpretation of quantum mechanics. The test has received a lot of scrutiny over the years, but it stands as a fun thought experiment that anyone can conduct, even you, as you are reading this article right now.
To begin, we need to revisit the core ideas of the famous Schrodinger’s cat in a box thought experiment, as the quantum suicide test itself is an extension of that.
Illustration of Quantum superposition
Instead of observing what happens to the cat, the observer gets inside the box and becomes a test subject themselves. This is the idea of the quantum suicide thought experiment, but how does that settle the measurement problem?
Max Tegmark explains it via a game of Quantum Russian Roulette. To play Quantum Russian Roulette, one essentially needs a quantum gun that acts as a trigger, a machine gun that fires or skips firing based on the trigger, and the test subject who also needs to be the observer. The difference between a typical or classical Russian roulette and the quantum one is the quantum gun that functions on qubits - quantum bits that can be in the superposition of states.
Say, the quantum gun triggers the machine gun to skip firing for bit 0 and fires a bullet for bit 1. Since the quantum gun is in a superposition, it randomly triggers the machine gun to skip or fire. And the observer is unaware of the triggering and the firing mechanism - observing the outcome will make it a classical event - making this whole set-up a quantum event.
Now imagine that the observer enters the quantum suicide experiment. The brave observer places their head on the barrel and is waiting for the gun to go off, which can either skip or fire shots.
In CI, the probability of the observer surviving this test is incredibly low, and therefore should be expected to be dead after the 2nd or 3rd firing if not the very first. This is because there is only one reality in CI and to obtain the possibility of the observer surviving this experiment takes about a million trials, before which you can guarantee with a maximum probability that the observer will be dead. But MWI promises survival with 100% certainty since all possible realities are equally real as the other.
When the gun goes off, It’s not that the bullet hits the observer and they continue to live immortally. But the bullet never fires in the first place, at least in one reality of the many worlds. Repeating the experiment multiple times will drastically decrease the chances of survival and thus surviving all of it makes a strong case to safely conclude that the MWI is real. Because all the other interpretations of quantum mechanics simply do not support this possibility. This is quantum immortality in action.
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So if quantum immortality is real in this sense, what happens to senescence?
According to experts that either means external torture or advanced tech that allows us to defeat aging, and make use of the quantum suicide experiment separately to achieve immortality.
Can we ever truly agree with the test result even if it were conducted perfectly in an ideal case?
Even if the test is carried out with much caution and efficacy, it's highly likely that only the observer can ever confirm that quantum immortality works, and everyone else will probably conclude that the result is a fluke or that the apparatus is broken.
1. One of the common misconceptions of quantum immortality, or MWI is that it is the conscious observer that makes realities happen, resulting in a constant branching of many worlds. This is wrong because we are either a branch of possibility (MWI) - wavefunction - or we ARE the possibility (CI), and we don’t exist beyond or apart from it. It is simply a matter of interpretations.
Tegmark himself put this well in his paper:
“What Everett does NOT postulate:
At certain magic instances, the world undergoes some sort of metaphysical “split” into two branches that subsequently never interact….According to the MWI, there is, was and always will be only one wavefunction“
2. Another preconceived notion about quantum immortality is that it also proves the multiverse. On the contrary, many worlds (quantum multiverse) and multiverse are fundamentally two different concepts. Where one is an interpretation of quantum mechanics while the other is simply a distant region in space that is unobservable to us because it is so far away. So the quantum suicide experiment only proves the MWI.
Quantum immortality is considered a controversial subject even within the scientific community but it sure is an amusing thought experiment to execute. In case if it has left you with more questions than it has answered and a wobbly head induced by existential dread, remember this comforting quote that’s famously attributed to Richard Feynman,
“I think it's safe to say that nobody understands quantum mechanics.”
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