A while ago I read Max Tegmark‘s “Our Mathematical Universe” (Amazon link) – which introduced me to the concept of “Quantum Suicide” and the idea that if the “many worlds” interpretation of quantum physics is correct then, if death is a result of quantum processes (e.g., does this particular atomic nucleus decay, releasing radiation, causing a mutation, leading to cancer and so on), then, actually, we can expect to live forever – in the sense that our consciousness would continue on in that universe where all the quantum randomness was for the best.
It’s a powerful, if quite mind-bending idea, and it had quite a profound effect on me.
Until, that is, at the end of January, when I slipped on a London street, smashed my face on the pavement and swallowed the broken piece of tooth. Three months later the pain in my upper left arm – with which I tried to break my fall, is a constant reminder that maybe Niels Bohr and the Copenhagen Interpretation was right after all.
There is a fascinating article in this week’s New Scientist about the idea that quantum mechanics and general relatively could be linked via the idea of the “wormhole” – a fold in spacetime that links what appears to be two very distant parts of the universe.
The article – as is generally the case in a popular science magazine – is more hand wavy than scientific, but the concepts involved don’t seem to be difficult to grasp and they might answer some of the more mysterious aspects of quantum mechanics – especially the problem “spooky action at a distance“: quantum entanglement.
Quantum entanglement is the seeming evidence that two particles separated by distance appear to exchange information instantaneously: for when one particle changes state (or rather when its state is observed), the other does too. The suggestion is that, actually, these two particles are not separated by distance by are linked by a wormhole.
Sounds like a piece of Hollywood science, for sure, but it is an idea based on our understanding of black holes – a prediction of Einstein’s general relativity that we have lots of (indirect) evidence for: these would seem to be surrounded by entangled particles – the so-called quantum firewall.
This another one of those bizarre thoughts that cosmology throws up which manages to be both simple and profound.
Imagine the wave function for the whole universe.
By its nature the universe cannot change its quantum state: it’s the ultimate closed system. Of course there is a probabilistic distribution of energy inside the system but the total energy of the system does not change and therefore its quantum state cannot change either.
So, in quantum terms the universe is unchanging over time.
So, let us conduct a thought experiment that might suggest “you” can live forever.
In this world we assume that you don’t do anything dangerous – such as commute to work. The only factors that could kill you are the normal processes of human ageing (and related factors such as cancer): your fate is completely determined by chemical processes in your body.
And we accept the “many worlds” view of quantum mechanics – in other words all the possible quantum states exist and so “the universe” is constantly multiplying as more and more of these worlds are created.
Now, if we accept that the chemical processes are, in the end, driven by what appears to us as stochastic (random) quantum effects – in other words chemicals react because atoms/electrons/molecules are in a particular range of energies governed by the quantum wave equation – then it must surely be the case that in one of the many worlds the nasty (to our health) reactions never happen because “randomly” it transpires that the would-be reactants are never in the right energy state at the right time.
To us in the everyday world our experience is that chemical reactions “just happen”, but in the end that is a statistically driven thing: there are billions of carbon atoms in the piece of wood we set fire to and their state is changing all the time so eventually they have the energy needed to “catch fire”. But what if, in just one quantum world of many trillions, the wood refuses to light?
So, too for us humans: in one world, the bad genetic mutations that cause ageing or cancer just don’t happen and so “you” (one of many trillions of “you”s) stays young for ever.
The obvious counter argument is: where are these forever-young people? The 300 year olds, the 3000 year olds? Leaving aside Biblical literalism, there is no evidence that such people have ever lived.
But that is surely just because this is so very, very rare that you could not possible expect to meet such a person. After all, around 70 – 100 billion humans have ever been born and each of them has around 37 trillion cells, which live for an average of a few days (probably) – so in a year perhaps 37 billion trillion cell division events – each of which could spawn a new quantum universe – take place. That means the chances of you being in the same universe as one of the immortals is pretty slim.
Yet, on the other hand, we all know someone who seems to never age as quickly as we do…
…I’d be really interested in hearing arguments against the hypothesis from within the many worlds view of quantum physics.
The fundamental difficulty with quantum mechanics is that it says we cannot know, with total accuracy, the position and momentum of a particle. This “uncertainty” is what creates the “spooky interaction at a distance” – because if we measure the momentum of one paired particle then uncertainty and energy conservation laws “appear” to make the other particle assume a certain state instantaneously.
In the “Copenhagen interpretation” we are essentially asked to accept that this is due to an instantaneous “collapse” of the physical laws we have been using to this point. It’s as if our quantum rules are just a window on to a “real” physical world and that our poking shakes up what is going on behind the scenes in ways we cannot hope to understand.
That’s not very convincing, though (even if it “works”).
So, what are the alternatives?
Valentini is reviving an idea of Louis DeBroglie that was rejected in favour of the “Copenhagen interpretation”: namely that our paired particles remain linked by a “pilot wave” that communicates the state change instantly.
That, though, appears to offend against the physics of the world of general relativity – we are conditioned to think such instant communication is impossible because our physics tells us that we need infinite energy to move a massive body at the speed of light: hence making that an unbreakable speed limit.
And then there is the “many worlds” interpretation – namely that all that might happen does happen and so there are an infinite number of those paired particles and “our universe” is just one of an infinite number.
None of them really seem that satisfactory an explanation.
Well, the answer is pretty plain: Einstein‘s theory of general relativity – which even in the last month has added to it’s already impressive list of predictive successes – tells us that to travel at the speed of light a massive body would require an infinite amount of propulsive energy. In other words, things are too far away and travel too slow for us to ever hope to meet aliens.
But what if – and it’s a very big if – we could communicate with them, instantaneously? GR tells us massive bodies cannot travel fast, or rather along a null time line – which is what really matters if you want to be alive when you arrive at your destination – but information has no mass as such.
Intriguingly, an article in the current edition of the New Scientist looks at ways in which quantum entanglement could be used to pass information – instantaneously – across any distance at all. Quantum entanglement is one of the stranger things we can see and measure today – Einstein dismissed it as “spooky interaction at a distance” – and essentially means that we can take two similar paired particles and by measuring the state of one can instantaneously see the other part of the pair fall into a particular state (e.g., if the paired particles are electrons and we measure one’s quantum spin, the other instantly is seen to have the other spin – no matter how far away it is at the time).
Entanglement does not allow us to transmit information though, because of what the cosmologist Antony Valentini calls, in an analogy with thermodynamic “heat death”, the “quantum death” of the universe – in essence, he says that in the instants following the Big Bang physical particles dropped into a state in which – say – all electron spins were completely evenly distributed, meaning that we cannot find electrons with which to send information – just random noise.
But – he also suggests – inflation – the super-rapid expansion of the very early universe may also have left us with a very small proportion of particles that escaped “quantum death” – just as inflation meant that the universe is not completely smooth because it pushed things apart at such a rate that random quantum fluctuations were left as a permanent imprint.
If we could find such particles we could use them to send messages across the universe at infinite speed.
Perhaps we are already surrounded by such “messages”: those who theorise about intelligent life elsewhere in the universe are puzzled that we have not yet detected any signs of it, despite now knowing that planets are extremely common. That might suggest either intelligent life is very rare, or very short-lived or that – by looking at the electromagnetic spectrum – we are simply barking up the wrong tree.
Before we get too excited I have to add a few caveats:
While Valentini is a serious and credible scientist and has published papers which show, he says, the predictive power of his theory (NB he’s not the one speculating about alien communication – that’s just me) – such as the observed characteristics of the cosmic microwave background (an “echo” of the big bang) – his views are far from the scientific consensus.
To test the theories we would have to either be incredibly lucky or detect the decay products of a particle – the gravitino – we have little evidence for beyond a pleasing theoretical symmetry between what we know about “standard” particle physics and theories of quantum gravity.
Even if we did detect and capture such particles they alone would not allow us to escape the confines of general relativity – as they are massive and so while they could allow two parties to theoretically communicate instantly, the parties themselves would still be confined by GR’s spacetime – communicating with aliens would require us and them in someway to use such particles that were already out there, and perhaps have been whizzing about since the big bang itself.
But we can dream!
Update; You may want to read Andy Lutomirski’s comment which, I think it’s fair to say, is a one paragraph statement of the consensus physics. I am not qualified to say he’s wrong and I’m not trying to – merely looking at an interesting theory. And I have tracked down Anthony Valentini’s 2001 paper on this too.
Feynman argues that there is no radiation without absorption: in other words a tree that falls in an empty forest does indeed make no sound (if we imagine the sound is transmitted by photons, that is).
This sounds like a gross violation of all common sense – how could a photon know when it leaves a radiating body that it is to be absorbed?
But how can a body that exists for no time at all, exist at all?
Then again my assumption in asking this question is that time is in some sense privileged as a dimension of spacetime. This is a pretty deep controversy in theoretical physics these days and I am not qualified to shed much light on it – but let us assume that a body can exist with a zero dimension in time but real dimensions in space, can we then have bodies which have zero dimensions in space but a real dimension in time? If so, what are they?