Afterlife in quantum gravity might be a natural topic for this year's Christmas Eve, a blog post that follows one on the elixir of youth. ;-)
Even though the combination of the quantum gravity and afterlife keywords returns over 350,000 Google hits, it's a topic that hasn't been discussed on the part of the blogosphere we know, not even by the "most audacious" commenters.
This guy (just another Jew, as I was taught by my PhD adviser) was or wasn't resurrected 1980 or 1983 years ago. Just to be sure, he was born during Christmas – exactly 2014-2019 years ago – and died during Easter.
Perhaps, I decided to partially legitimize these topics under the influence of various fiction movies I saw on TV in recent days – including Inception (2010) where Leonardo DiCaprio (the same actor who starred as myself in The String Kings) has to do some job in a dream within a dream within a dream within a dream to get rid of the attachment of his wife who is dead in the level-0 but who wants to drag him back from level-minus-two to level-minus three.
(Time goes 20 times faster at each level than at the parent level; two days spent at level-0 give you 50 years of fun at level-minus-three. I didn't quite follow the storylines at each level; you must be a Milner Prize winner to follow them.)
Don't get me wrong. My basic attitude – at least when it comes to the science I would call substantiated and working – is as materialist and atheist that you can get. There is a "real spacetime" with some phenomena whose events we essentially share and all our dreams and perceptions that disagree with the "objective" events within this spacetime are artifacts of our brains' not preserving their full contact with the reality. Quantum mechanics forces us to formulate the fundamental laws of physics in a subjective way but this subjectivity seems like a "temporary fluke" whose final purpose is to make predictions about facts that may be treated as objective or classical facts.
However, I am sometimes worried – or tempted to think (depending on one's mood and emotional attitude) – that the subjectivity in quantum mechanics could be able to run deeper and it could legitimize some of the themes that sound decidedly spiritual or religious to a scientifically trained ear.
In particular, I can imagine that the properly understood fundamental laws of physics give the "full reality status" to various kinds of dreams – and near-death experiences. In other words, it's plausible that according to the fundamental laws, it is not possible to prove that the "real lives" we are experiencing are fundamentally more real than some of our dreams and related perceptions and signs of consciousness. Their being "real" could be just a quantitative issue or a convention.
Again, I am surely not saying that I have a proof. I don't have a proof by contradiction, either. Of course that I am sane so I appreciate that the general picture with one reality and "dreams as signs of malfunctioning or relaxing brains" is perfectly consistent with all the empirical facts we know about Nature and with the general physical principles we've been able to induce by looking at patterns in our empirical observations.
However, it's also plausible that the fundamental rules are different. And I am not talking about some old uninformed debates between science and religion. I am talking about some of the newest technical developments in theoretical physics.
In January 2009, I would provoke the dear readers by a text about the reincarnation of the infalling observer. The basic claim was that the usual "objective" sorting of the facts (outcomes of measurements) applies to the regions outside black holes. But the infalling observer who is going to die may require a much more subjective framework, one in which his or her soul gets reincarnated as the information is being nonlocally transferred from the black hole interior.
The wording – and especially the title – was deliberately provocative and spiritual from a writer like myself (be sure that over 99% of the people on Earth would count me as a stronger atheist than themselves) – but I would claim that
the basic idea of reincarnation of the infalling observer was quantitatively expressed by Maldacena's and Susskind's ER-EPR correspondence.According to the usual picture of the spacetime, the life of an infalling observer has to end in the black hole interior where the existence of the singularity (a region where the curvature invariants diverge or approach the huge Planckian values) is unavoidable. However, the information carried by the infalling observer doesn't get lost at the singularity. No information is ever lost so we may imagine that there are nonlocal processes that transfer the information from the black hole interior to the exterior. And this nonlocal transfer of the information may be interpreted as a sign of a "soul travelling somewhere".
The point of my provoking title in 2009 was that the abrupt end of the spacetime in the middle of the black hole depends on a particular reconstruction of the spacetime geometry. In the usual diagram (the Penrose diagram above), the region near the singularity seems to be disconnected from the regions outside the black hole. They are very far. But if the information gets transferred from one place to another, there must be a sense in which these two places are very close – an alternative picture of the spacetime geometry where the region near the singularity (where the infalling observer is going to die) is connected to some regions outside the black hole by a thin connection. Well, that's what Maldacena and Susskind concluded; they are connected by the Einstein-Rosen bridge, a non-traversable wormhole.
The existence of entangled degrees of freedom may be interpreted as a geometric bridge of a sort.
The ER-EPR correspondence leads us to a "less dogmatic" picture of the spacetime geometry, its topology, and especially its connectivity. The existence or non-existence of such a bridge is no longer a good observable in quantum gravity. Instead, the reconstruction of connections and wormholes between two places in the spacetime (or spacetimes) is determined at an information-theoretic basis: the bridges are there [and/or they are thick and smooth] if the degree of entanglement between these two places is nonzero [and/or high].
As I wrote previously, the ER-EPR correspondence makes the choice of the spacetime background (even its topology) dynamical or convention-dependent and some topologies are just more convenient for certain purposes (but not more fundamental) than others.
In the basic pictures of Maldacena and Susskind, it's being assumed that the entangled objects are spacelike-separated objects in the same spacetime. But in fact, one may think about the possibility that they are timelike-separated; and they may live in different spacetimes, too.
For example, the ER-EPR picture offers a new possible perspective on the Poincaré recurrences (for example in a de Sitter space). After an exponentially long time, the events in any physical system with finitely many degrees of freedom (finite maximum entropy) inevitably start to repeat themselves. I think that because the periodicity obeys the mathematical definition of an entanglement, the ER-EPR paradigm allows us to say that the time is literally periodic in such a situation. This conclusion about the "literal periodicity" is consistent with an old lore that there are no global symmetries in quantum gravity. The discrete time-translational symmetry would be a global symmetry but this "enhanced ER-EPR interpretation" turns it into a gauge symmetry because the "copies" of the history of the Universe are literally identified.
The ER-EPR picture may also have conceptual implications for the status of "soulmates". If two objects are quantum entangled, they are connected through a wormhole of a sort. (This is only possible for pairs of objects – triplets or greater groups of objects can't be entangled in the usual way, essentially due to the monogamy of the entanglement, but there of course exist generalizations of entanglement for triplets of objects, too. They could have other geometric visualizations.)
The information carried by our brains is probably classical; intrinsically quantum entanglement is probably not sustainable and our brains aren't quantum computers. But if you ignore this "detail", the Maldacena-Susskind picture may invite you into imagining that your brain is "literally" i.e. "geometrically" connected with the brain of your soulmate(s). And you may even suggest that such a connection is important even if you die very far from any black hole singularity. Any kind of death – e.g. erroneous death of a living person in the crematorium – may be interpreted similarly to the Hawking-radiation-vs-interior wormholes. The soul may be transferred elsewhere, perhaps even to a different universe.
The ER-EPR picture may have "opposite" implications, too. For example, eternal inflation in cosmology often requires some extreme processes (like the tunneling through the configuration space) that impose so brutal conditions upon the spacetime that any living object is inevitably destroyed. Eternal inflation theorists never cared. It doesn't matter whether all the organisms are inevitably killed and the degrees of freedom are brutally reshuffled; they would still believe that it makes a complete sense to connect the two different universes into a multiverse just like you would connect them in the absence of an extreme tunneling event.
I was always feeling uncomfortable about these "connections through Hell" (and therefore about the multiverse's being physically meaningful in general). I have had several reasons to doubt this simple-minded connectivity. One of them was that the "fabric of space" in a different vacuum is really a "different material" than the original "fabric" – much like a dimension and its T-dual dimension are made of a "different stuff" – and by the Lorentz symmetry in both spacetimes, the two time coordinates should be thought of as "different things", too.
Another reason for doubts was closer to the ER-EPR logic. My feeling was that the question whether the spacetime is smoothly continuing should be decided by some operational procedures – the degrees of freedom "before" should be similar to (highly entangled with) the degrees of freedom "after". The spacetime is smooth and connected iff the actual observables that depend on the location – the quantum fields – are continuously and slowly enough changing functions of the spacetime. But if all the observers are killed and all the low-energy (and other) data are hopelessly reshuffled in the extreme environment of Planckian curvature invariants and Planckian gradients of scalar fields, it means that there is no good operational way to show that the region "after" is really connected to the region "before" the quantum tunneling event. My positivist upbringing told me that if the hypothetical connection of the "before" world with the "after" world has no empirical consequences, even in principle, it's at least conceivable that this connection is physically meaningless and an accurate description of Nature denies it.
Now, I believe that the ER-EPR correspondence provides us with a more rigorous edition of the argument I would be making. Just like a wormhole connection is created in the presence of quantum entanglement, an extreme transition similar to quantum tunneling destroys any simple entanglement between "before" and "after" which means that the continuity of the spacetime becomes less genuine or useful. In fact, when your world is decaying due to quantum tunneling, it may be more "true" to continue or extrapolate the spacetime elsewhere, to a region (perhaps in a "completely different" universe) where the degrees of freedom are assembled more similarly to those before you were killed – you may want to believe that your universe is connected to a realm of your soulmates.
Sheldon's Christmas. I've watched all 146 TBBT episodes so far, about 3 times in average, but the Christmas hug episode may still be my most favorite one.
Now, we may ask: May it ever be legitimate to "tunnel your soul" into the mind of someone else whose brain is highly entangled with yours but who lives in a different environment? I am not sure whether those developments in quantum gravity that we already know about may justify such a far-reaching conclusion. The main problem is that it still seems to me that "a soul shouldn't be allowed to fake its environment". Leonardo DiCaprio (and his wife and his colleague) was creating his skyscrapers at all negative levels but I still think that the fabrication of the skyscrapers "by pure thought" should contradict the laws of physics at any level (unless we are thinking about a Tegmark-like "anything goes" world of all mathematical possibilities which seems vacuous to me).
Many sentences above were deliberately provoking and "somewhat surpassing" the claims that may actually be defended by the existing scientific insights. And I do believe that the predictions for "doable experiments", even in the presence of quantum gravity contributions, are unlikely to change relatively to the existing picture. Be sure that I am as conservative as you may get. But I can imagine that a future understanding of quantum gravity will profoundly change our understanding of the reality vs dreams, our understanding of our connections with our dreams and fantasies and with the creatures in this world and other worlds who are similar to us, and perhaps our ways to think about the spiritual issues connected with death. To put it more modestly, they may provide us with shocking alternative but "equally correct" ways to think about these issues.
While I find it extremely unlikely that any particular religious or science-fiction story will be confirmed including the finest details, it's conceivable that some of the profoundly new ways to think about the reality, dreams, and death will be much more similar to the spiritual pictures than what stubborn, prejudiced materialists will find comfortable.
Stay tuned and Merry Christmas.
P.S.: The Czech media just reported that the Norwegian Christmas revolves around the 1973 Czech fairy-tale, Three Nuts for Cinderella, co-starring some East German actors. It's not dubbed – all movies are professionally dubbed in Czechia (I do believe that the Czech dubbing of most movies sounds better than the original). It is aired as a voice-over that you know from amateurish early VHS and that you may watch. The tradition to air this movie – on Christmas Eve morning, 11 am – began in 1975 and a million of Norwegians (the most watched TV program on that day) have adjusted their daily schedule according to the TV schedule. In 1993, the TV attempted to eliminate the movie from the program. They shouldn't have done that! A million of citizens demanded "their Cinderella" to be returned and they asked the responsible TV managers to *beep* their *beep* *beep*. So the fairy-tale was returned to the schedule – more or less permanently. This year, the Norwegian press claimed that the actors starring as the prince and the Cinderella fell in love with one another in the real world, too. I didn't know. ;-)
Try my Christmas playlist but many songs have been deleted. Damn copyrights.