You Are Immortal

I have become increasingly convinced that you, dear reader, will never actually die. What could I mean by this, you ask? In this essay, I’ll explain how our modern understanding of physics might give rise to immortality, and explore some practical and philosophical considerations of immortality.

Multiverse

In the history of science, we have often found that the world is not as it seems. Although the Earth appears flat to the senses, measurements tell us it is round. While the course charted by the sun and stars is plain to see, we know now that it is we who move as the heavens stand still. More recently, Einstein showed us that time and space are not the unchanging stage we intuit, but bend with the events of the universe. The case I’m about to present relies on the dissolution by science of one more illusion: that the universe follows only one true storyline.

Modern theories of physics, empirically tested and validated, suggest that we inhabit a multiverse, a collection of universes that share physical similarities but can’t interact with each other. Here I draw heavily from the works of Max Tegmark¹, which contain some interesting nuance about the multiverse Tegmark describes 4 levels of multiverse, each with a different mechanism. Either the first or third level alone is enough to make my case. The first level multiverse consists of finite-volume regions of infinite space, separated by the lightspeed limit. The third level consists of storylines happening in parallel in the same space, separated by quantum decoherence. It turns out that these theories make identical predictions of what we should observe, so I'll gloss over the ongoing debate among physicists of whether the level III multiverse exists, simply noting that I find it to be the most parsimonious explanation of experimental results. For more detail, refer to the footnotes. that isn’t central to my point. In the multiverse, there are infinite beings with the exact same history as yours, the exact same subjective experience, and the exact same sense of identity. An omniscient observer, looking at the multiverse from the outside, could pinpoint all of the copies, and describe every facet of each one’s subjective experience across all of time, but couldn’t say which is the “real” you; you all are.

Although the copies of you spread across the multiverse share the same observed pasts, your environments contain variation that you haven’t yet perceived. Therefore, the previously identical copies will experience different futures, splitting your story; everything that can happen, happens in some universe. In fact, because the collection being split is infinite, each outcome happens in infinite universes. Of course, any given instance of you will experience only a single past, which is what gives rise to the illusion that you have only a single future.

So, in every moment, your story splits into every possible future. Even an omniscient observer couldn’t tell you what will happen next in your particular universe, because no such universe is distinguishable; you ask the question identically in every universe you inhabit. How then should you think about prediction, of what to expect from the world? This is not a new problem, as humanity lived in the multiverse before we knew it as such. We call this phenomenon randomness, and model it with probability. We can talk about the chance of an occurence, a distribution of expected outcomes. Recognizing the multiverse, we can view probabilities as proportions of our collection of copies. Flip a coin, and half of you will see heads while the other half see tails, or in other words, the coin will come up heads with 50% probability. So far, while the concept of a multiverse might seem new and outlandish, it offers nothing new to your lived experience.

Identity

A common question at this point goes, “Ok, there are a bunch of copies of me out there. Why should I care?” To address this, we first need a clearer sense of what makes you “you.”

At the physical level, our usual notions of individuality begin to crumble. Particles, the building blocks of matter, lack any intrinsic identity. They are interchangeable and follow the same fundamental laws, with nothing that inherently distinguishes one particle from another. Similarly, there is no distinguished reference point from which to mark your unique location in space. This lack of a distinguished reference point applies to both 3D space and the Hilbert space underlying quantum mechanics.

Given that neither specific particles nor a location in the world provides a clear anchor for identity, consider defining “you” as a mostly-stable pattern of information – your memories, cognitive processes, and personality traits. This pattern endures across time, even as individual cells die and regenerate, as long as the overall structure of information remains intact.

Now, if the multiverse is real, then somewhere out there are other instances of this same pattern. Each copy is subjectively indistinguishable from you. From its own perspective, it has your memories, your thoughts, and your sense of self. Viewed this way, you are not confined to a single instance. Any observer with your subjective experience is you, just as you exist now. There’s no need to designate a “main” version. Your identity is that pattern, and if the pattern repeats infinitely, then all those occurrences count as you.

Anthropics

Now, imagine I flip 20 coins in front of you. What’s the probability that they all come up heads? $$ 2^{-20} $$, or roughly one in a million. Now, imagine that instead of simply flipping 20 coins, I assign millions of monkeys to each flip coins, recording each on a separate video. Now, despite those one-in-a-million odds, it is quite likely I will be able to show you a video of my monkey flipping 20 coins and getting 20 heads in a row. Make it infinite monkeys instead of millions, and it becomes a certainty that I can find one who flipped 20 heads, or 30 heads, or any sequence I care to show you, however unlikely.

This same principle applies directly to the consideration of immortality. All futures happen, but you only experience futures where you survive. Because the multiverse contains infinite copies of you, no matter how dangerous a situation is, some copies of you will always survive it, just as some of my monkeys kept flipping heads. Your subjective experience won’t be diminished by the deaths of your copies across the multiverse; you always perceive a single storyline, regardless of what happens in the other possibilities. In a deadly situation, anyone watching is likely to see you die, but multiverse theory implies that you will always find yourself in a world where you beat the odds and survived.

This logic applies to everyone, of course, but only applies subjectively. You will continue to observe that people die, just as you thought they would before you learned of the multiverse. Indeed, while physicists can test the models that suggest the existence of a multiverse, there is only one true test of my theory of immortality. Unfortunately, if the theory is wrong, testing it risks your death. However, every day you survive is another small piece of evidence against your mortality. I predict that you will outlive everyone you know. I hope, when you do, you think back to this essay and understand why. Take solace in the notion that your dearly departed survive in unlikely universes of their own, perhaps mourning you just as you mourn them.

Ramifications

If we are indeed immortal, how should that affect our decisions? Should we take high-variance, get-rich-or-die-trying gambles, secure in the knowledge that we won’t be around for the “die trying” side? I don’t jump to that approach, for a few reasons. First, while I do find this case for immortality to be fairly compelling, I’m not quite so confident that I’d bet my life on it. Even if we put aside that uncertainty and accept the premise of immortality, reasons remain to try to avoid death. For one, most risks of death carry associated risks of painful survival. You can’t experience being dead, but you can certainly experience being e.g. permanently injured. Also, if there are people who care about you, dying is a selfish act. The anthropic selection that keeps you alive doesn’t keep their futures connected to yours. If you die in 99% of worlds, you’ll hardly notice, but the vast majority of people you know throughout the multiverse must suffer your loss.

However, if one is willing to set aside the risks and the social harm, there are many opportunities to exploit immortality. For instance, consider the following setup: two strangers (or enemies!) pool their worldly possessions, then enter a machine that uses a quantum event to randomly select one for painless, instantaneous death. Each participant will find themselves to be the lucky survivor walking away with the other’s riches. I leave further examples as an exercise for the reader, but many courses of action become unlocked if death is not a concern.

In my case, there’s an additional wrinkle to immortality. I’m signed up for cryonics, with the goal that if I die, I will perhaps be revived in the future. However, if I always experience survival regardless, does this mean I’m simply shifting probability from worlds where I survive in my familiar life, A friend of mine argues that with multiverse immortality, I should expect to find myself in weirder and weirder worlds as I select for my increasingly unlikely survival, so that cryonics still steers me into preferable worlds. to worlds where I wake up in an unknown future where everyone I knew is long dead? How should I balance this concern against my uncertainty about whether this immortality theory holds?

Another philosophical consideration is that this theory of immortality only means you survive every moment. Survive long enough, however, and you will eventually be unrecognizable to your current self. The theory doesn’t preclude this long death by change, only the sudden kind. Is it immortality if no trace of you will ultimately remain? Even in a natural lifetime, we must address this consideration; how similar is an elder to the child who bore their name? In some sense, we already die and are reborn in every moment. While nothing in the world is permanent, every event is an immutable mathematical fact about the multiverse. Our decisions are indelibly written in the structure of spacetime, beyond the reach of change itself. However, I think expanding on that idea is best left for another post. Immortality of the sort I described here doesn’t change that fundamental truth, it just guarantees that there will always be a next moment of rebirth.

I’ve thought a fair bit about these considerations, yet I still don’t have good answers to all of the questions that arise. However, I remain convinced that the basic logic is sound: if the multiverse exists (as our best physics suggests), and if consciousness persists through our branching stories (as subjective experience suggests), then immortality follows as a conclusion. I’m publishing this essay partly in the hope that others will help clarify my thinking about the ramifications, so as always, please feel free to reach out!