At the time of writing, the oldest person ever to have lived was Jeanne Calment, who died at age 122 years, 164 days in 1997.
It is my belief that you, the person reading this book, will far outlive Jeanne. In fact, you will simply not die, ever.
And you won’t have to take up a special diet, or join a religious order – it’s just a consequence of how reality works.
This is an outrageous claim, so I need to explain how it works.
How does Quantum Immortality work?
Quantum Mechanics (QM) is one of the most accurately tested theories of how the universe works. QM is hard to understand, but its predictions have been tested and retested for a century, and have held up.  
QM says that every time anything happens, every single possible version of the event happens, and one is “chosen” to become real (to “cohere”). This is described as “collapsing the wave”, or “quantum coherence”.
There is a very interesting interpretation of QM that leaves out the collapse, and simply says that all versions of the event happen, and each can be said to be separate versions of reality; each of which is as real as the one you are in right this moment. This is known as the “many-worlds interpretation”. 
A consequence of the many-worlds interpretation is something called “quantum immortality” . It’s also known as quantum suicide, but that’s a rather negative name for something so extraordinary and life-changing.
The idea is basically this:
- Let’s say you are lying in a hospital bed dying, and the doctors say you have a 50/50 chance of living to see another day.
- The next day arrives.
- Because there was a 50/50 chance of living or dying, the many-worlds interpretation says that you are dead in half of the newly branched universes, and alive in the other half.
- You cannot experience being dead, so you wake up that morning and dare the doctors to come up with another prediction.
This works, whether the prediction was 50/50, ¼, 1 in a million, whatever! If there is even the slightest chance that you will survive, then you will survive.
Do other people die?
You have probably attended funerals, or lost friends to accidents, disease, old age.
Your question at this time is: if quantum immortality is true, then why are those people dead?
Well, let’s consider the case of cousin Bob, who died after his car brakes failed and he slammed into a car. You are at his funeral, wondering why Quantum Immortality doesn’t mean that he’s alive.
There are many ways that this could have played out – the car brakes don’t fail, the brakes fail and the car misses the tree and slides to a halt in a muddy field, the brakes fail and the car hits the tree and Bob is thrown clear through the window and survives with a broken leg, or the brakes fail and there is a funeral held a few days later, where you wonder what happened to Quantum Immortality.
The fact that you are attending a funeral means that you are conscious of a reality where Bob did not survive. Bob is not conscious of this reality, so for Bob, this reality is not real. But for you, it certainly is.
Bob could have survived the accident in many ways, and because Quantum Immortality says that Bob can only be aware of versions of reality where he can be aware, this funeral simply did not happen. The Many-Worlds interpretation says that every possibility is its own reality, so Bob actually survived his accident and this is all a non-issue for him.
Unfortunately for you, you will never speak to Bob again – he’s dead in your reality. But, you can take heart in knowing that he’s alive and well in his own reality.
This, by the way, has huge “spiritual” implications. It means that everyone lives forever, even if you see them die. All you saw was one possible version of that person dying, but you need to keep in mind that every possible version of that person exists, and at this moment, the versions which could possibly be alive somewhere are alive.
This means that there is no true death. You may see people die, but they actually experience something different. You might see someone breathe their last on a deathbed, but in their own experience, they took that one last breath, and followed it with another and yet another, until they finally got over their ailment and got out of bed.
But what about when the odds are against you?
Naysayers may say that in some cases, it’s just too unlikely that survival could happen.
Let’s say, for example, that you fall from a tall building, and there is a one in a million chance that you land on a car roof (like in so many films), and a further one in a million chance that you survive this and get off the car roof and go about your business.
Well, that’s a one in a trillion chance that you survive the fall. That couldn’t possibly happen, right?
QM says that every single possible event has a probability, and the many worlds interpretation says that they all have their own realities.
So, in most realities, you might slam into the ground and you are dead, full-stop.
Then there are the realities where you fall a little to the left or right of that spot, closer to the parked cars, but still die. And then there are further realities where a car is driving along the road below and you just miss it and slam into the road behind it.
Each of those realities are real. But you are not aware of them.
You are only aware of the realities where either a gust of wind blew you enough that you landed on a parked car, or you landed on the moving car below.
Even then, there’s a million to one chance that impact with the car roof kills you.
Well, guess what? Million to one chances are a dime a dozen to QM. In Quantum Mechanics there are practically an infinity of possible results, so there are an infinite number of worlds in which you are a survivor.
Sounds great, right? Want to go jump off a building now to test it? Don’t.
You see, even though Quantum Immortality says that you will survive, it does not say that you’ll be all in one piece…
You will survive the fall, but you will very likely break most of your important bones, and be in hospital for months or years before you can hobble out. It’s survival, but it’s not nice.
So, let’s summarise then with this:
You will live forever.
You will see people die over the years, but should be happy that they are living forever in their own realities.
Even though you are essentially immortal, you can still be hurt badly, so don’t do stupidly dangerous things.