A friend of mine asked me a few days about something that he had heard in a quantum physics lecture, feeling that he had surely misunderstood the lecturer's comments. And being quantum mechanics, which is bizarre at the best of times, that is always a possibility. However the comment in question is in fact an interesting aspect of quantum physics which is still hotly debated by the experts.

According to quantum mechanics, you are immortal and will never die.

Now that the quantum physicists have stopped laughing, and the remainder of my readers are wondering if I have finally gone mad, I will explain. First I must add the qualifier that this is only true in certain interpretations of quantum mechanics.

As I have written in past articles, the equations of quantum mechanics were developed roughly ninety years ago but are still unexplained. Every physics student knows how to apply the laws of quantum mechanics to make predictions, with a wave function evolving over time according to Schrodinger's equation or Dirac's equation, and then something happens and you get a result. The 'something happens' part is usually quickly glossed over as 'an observation is made, and the wavefunction changes' but no one gives much detail. The reason is that the process of measuring the wavefunction and collapsing it has never been understood or explained. We just don't know what happens at that moment.

One interpretation which is reasonably popular is the many-worlds model of quantum mechanics. This interpretation, originally developed by Everett while a graduate student at Princeton in the 1950s, posits that whenever there are multiple possible outcomes of an experiment, multiple copies of the world are generated with each containing a different outcome. Then the supposed collapse of the wavefunction is nothing more than checking which world this copy of you happens to be in. In terms of the infamous Schrodinger's cat, this model claims that two identical worlds are created - one with a live cat and one with a dead cat, but both are equally real.

But now suppose you do the following rather extreme quantum mechanical experiment. Instead of a cat, suppose you were to build a device that could kill you. A quantum mechanical event occurs in the machine, with a random chance of firing a bullet into you that is instantly fatal. Because this is a truly random event, you are likely to die after several runs of the experiment.

Except you don't die. You run the experiment the first time, and two copies of you are made - one that survives and one that dies. But the dead copy is unaware of the results, and so only the live copy continues. On the second run the same thing happens - a dead copy of you is unaware they are dead, and the live copy thinks they have been lucky to survive twice. You test the machine by standing back and running it, and the gun fires half the time without fail. Then you get in front of it again, and once again every random event in the machine keeps you alive. 

Now extend this thought experiment to life in general. You have a random chance of getting in a fatal car crash, but following this same principle you never do. There is a chance you get a fatal disease, but this principle says that you never will. Every potentially fatal event can be dismissed with this same odd thought experiment, making you immortal.

Of course those around you are not. A world can be created in which you live and they die, and that is perfectly acceptable. This principle of quantum immortality will only protect you. As far as you can tell, in your own world, you never die.

It is a very bizarre prediction of the many world interpretation of quantum mechanics, and one that is not accepted by all (or perhaps even most) specialists in quantum theory. But it also cannot be proven to be false, and no serious flaws in it have been found. 

So just maybe, quantum mechanics can makes us each immortal, at least in our own minds.