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What Does Quantum Physics Have to Do With You?


“…received an innumerable quantity of exact replies concerning matters about which I had not asked.”

— Leo Tolstoy (on what invariably happens when asking scientists about the meaning of life)

“It is sometimes said that scientists are unromantic, that their passion to figure out robs the world of beauty and mystery. But is it not stirring to understand how the world actually works — that white light is made of colors, that color is the way we perceive the wavelengths of light, that transparent air reflects light, that in so doing it discriminates among the waves, and that the sky is blue for the same reason that the sunset is red? It does no harm to the romance of the sunset to know a little bit about it.”

— Carl Sagan

The pursuit of happiness is of such paramount importance to us that the founding fathers of the United States mentioned it in the Declaration of Independence as one of the self-evident truths. We might follow different paths on this road to happiness, yet most of the ingredients are common to us all. Some of the ingredients are obviously of a great evolutionary value, such as having children and finding a suitable environment in which to raise them.

Other ingredients are of a less tangible nature. We yearn to understand our origins, and this includes the origin of life, the origin of the universe and the meaning of it all. None of these are of any immediate biological value, per se (as the existence of other living creatures illustrates) and yet we all feel that they are sometimes as important as our biological needs and on occasion even more so.

Trying to understand who we really are seems to make us happy. This thirst for understanding is undoubtedly common to all humanity. I am an atheist, but what follows is not a piece on “science versus religion or philosophy”. Rather, it is about viewing science, and quantum physics in particular (I’ll come to this shortly), as an integral part of our endeavor to understand what this is all about. And I do believe that science has produced a power which is able to claim: “Whoever drinks the water I give them will never thirst again.”

Two features seem to me common to all human activity aimed at understanding the world, be it through science, philosophy, religion or art.

One is the feeling of transcendence. Put very simply, we all feel – at one point in life or other – that there is more to the universe than meets the eye. It can’t just all be about what we can see or hear or touch or feel.

The notion of transcendence was probably most forcefully and poetically expressed by the Ancient Greek philosopher Plato, who in his classic book The Republic, has the main protagonist Socrates explain the allegory of the cave. In probably one of the most beautiful paragraphs every written in Western philosophy Socrates says:

And now, let me show in a figure how far our nature is enlightened or unenlightened: –Behold! human beings living in a underground cave, which has a mouth open towards the light and reaching all along the cave; here they have been from their childhood, and have their legs and necks chained so that they cannot move, and can only see before them, being prevented by the chains from turning round their heads. Above and behind them a fire is blazing at a distance, and between the fire and the prisoners there is a raised way; and you will see, if you look, a low wall built along the way, like the screen which marionette players have in front of them, over which they show the puppets…And do you see, I said, men passing along the wall carrying all sorts of vessels, and statues and figures of animals made of wood and stone and various materials, which appear over the wall? Some of them are talking, others silent. Like ourselves, they see only their own shadows, or the shadows of one another, which the fire throws on the opposite wall of the cave.

Plato, speaking through Socrates, is implying that we, like his prisoners, only see shadows of appearances of real objects and hardly the actual fundamental nature of what is causing them. To grasp the real nature we need to free ourselves from the chains and leave the cave.

Physics, more than any other human activity, seems to me to be able to reveal the non-obvious aspect of the universe. And quantum physics in particular, is not just the most accurate description of natural phenomena, but at the same time is the most counterintuitive. It shows us more than any other pursuit that we are very akin to Plato’s prisoners in the cave and require a deep insight, arrived at after a long and laborious search, regarding what the ultimate underlying reality really is.

Basing our world view on just what our sense are telling us, we are naturally inclined to be materialistic. What you see is what you get. We perceive that the world is populated by stuff, such as tables, chairs, trees, rocks, animals and so on. All this stuff can be seen, touched, heard and felt. However, quantum physics teaches us that matter is mainly void and that its properties are best described by a mysterious function – the Psi function, of which we certainly have no direct experience.

In the quantum world, objects exist in many different places at the same time and their physical states can be more correlated than is classically allowed. These correlations are known as entanglement and allow us to achieve technological feats, such as teleportation, that are impossible classically. But to see these intrinsically quantum phenomena requires us to leave the imprisonment made by the cave of classical physics and use refined technology that allows us to interact with the quantum world. Transcending the world of classical physics has probably been the greatest triumph of the scientific method to date. The bonus of our impulse to leave the cave, of course, is the astounding development of our technology, which also contributes to our increased wellbeing.

The other aspect of nature that all humans are surprised and impressed by is its order and simplicity.  It is actually remarkable how far Occam’s razor, “assumptions should not be multiplied beyond necessity”, can be taken when trying to understand natural phenomena. It is simply mind-blowing how much actually follows from a handful of physical principles. The principles are currently those of quantum physics and general relativity, though I strongly believe that the latter will be reduced to the former. I will not expand on this issue here as I have written more extensively about it elsewhere.

On small scales, quantum physics explains the structure of matter (and how the void that is dominant can still give rise to the solidity we feel), the laws of chemistry and through it hopefully one day it will also explain the laws of biology. How far this can go is by no means clear, but it has already gone quite the distance. There are even some claims that life is a necessity given the laws of physics.

On the other hand, we have large structures such as galaxies, their clusters and so on. It is plausible that the biggest scale structure too can be explained through the laws of quantum physics. Some accounts of the universe are based on the quantum tunneling of the universe into its own existence. These accounts are currently fully compliant with the existing astronomical observations.  The small quantum jitters at this early stage of the universe are then amplified by a rapid expansion and are believed to lead to all the structure we see around us.

In fact, there is a formal way according to which quantum physics is a better compressor of data than classical physics. Namely, if we try to observe a certain process (say we detect photons and register the sequence of clicks in the detector), then the sequences of outcomes are in general more efficiently mimicked quantumly than classically. Quantum physics can reproduce our observations with less information than classical physics!

Interestingly enough, and as my recent work with my colleagues from China and Australia suggests, the quantum compression might also be able to explain the difference in the dynamics of entropy (which quantifies disorder in the universe) and complexity (which tells us how compressible the universe is). Namely, the universe is meant to start in a very ordered (low entropy state) and continue towards maximum entropy just as the second law of thermodynamics stipulates. For complexity, however, the universe starts in a simple state, and ends in a simple state. Sometime within these two extremes (now?) it is meant to be reach a maximum complexity. It might not be surprising that creatures like us, capable of understanding the universe, arise during this most complex epoch. And understanding where we come from and why would of course bring a great deal of satisfaction.

Though we all feel awe at the existence of order in the universe, this fact can also lead to the uncomfortable fear of determinism. If physical facts fix all the facts in the world, does that not mean that all our actions are predetermined?

This, of course, is a deep question to which science has no answer at present. Suffice it to say that quantum physics certainly destroys Leibniz’s “principle of sufficient reason” according to which everything that happens must have an underlying cause. The most elementary events in quantum physics are, as far as we know, intrinsically random and happen without any prior reason. However, whilst this might help us alleviate our fear of determinism, it is certainly not enough to guarantee any free will. I am personally happy to live with that state of affairs, but I am also confident that we will discover more on this very issue in the years to come.  And, to paraphrase Sagan, any new understanding can only add to the beauty of the world.

It is said that at the entrance to Plato’s academy, the world’s first university in the modern sense of the word, it was inscribed: “Do not enter if you do not understand geometry.” After two and a half millennia I feel we can afford to be a bit presumptuous to suggest a small correction to the great Plato: “Do not enter if you do not understand quantum physics (and, possibly optionally, geometry).” This might not satisfy Tolstoy, but, as far as I am concerned, it is the road to all emotional and intellectual fulfilment.

Discussion Questions:

1) Should quantum physics be taught much earlier in school and as part of general education?

2) Even if it were not for the purpose of intellectual fulfillment, quantum physics is still the basis of current technology and will almost certainly dominate the future technology. Should the public be better informed about it?

3) Does quantum physics indicate that the ultimate nature of reality might be transcendental, in the sense of beyond the human rational power of understanding?

Discussion Summary

Two interesting questions have emerged from the discussion following my essay, “What Does Quantum Physics Have to Do With You?” The first one, broadly speaking, is the question of how much our psychology colors the way we understand the world and, in particular, – and this is where I think things get interesting – the way we do science. We scientists would, of course, like to think that all human imperfections, though clearly present in the scientific practice, cancel out in the long run through experimental verification and falsification and that all that remains is truth (or closer and closer approximations to it). However, in the same way that it is clear that other apes have a more limited grasp and understanding of reality than we do, it might well happen that evolution will produce a species whose command and understanding of reality will far outstrip our own. Whatever they discover might be transcendental to us in the same way that apes will never “get” quantum physics. But is there a way of testing this? All sorts of psychological experiments confirm our human bias and the field of behavioral economics – with its many Nobel Prizes – is based on our misjudgments due to various psychological biases. However, can it be that the laws of physics suffer from the same biases? That would be truly astonishing (I doubt that any physicist would ever really bet on this), but what I would like to ask if there is a scientific way of revealing that bias in the same way that the economists such as Daniel Kahneman reveal our bias to making wrong inferences due to our human evolutionary idiosyncrasies. Might the differences between the observer and the observed – the subject that is very topical in quantum physics and has been for a long time- also belong to this category? This is I think a very difficult question and I for one do not even know how to begin to tackle this issue.

The second big question that has emerged from the discussion is, in fact, just within the confines of quantum physics itself. I am a big fan of the idea that quantum physics implies that locally things are random but globally they are not (this view is sometimes called “the Church of Higher Hilbert Space”, because quantum states live in the so called Hilbert Space and the word Church indicates that the Higher Hilbert Space is our belief and not an experimentally established fact). In fact, we can understand the entropy of an object (which quantifies its randomness) through the amount of entanglement it shares with the rest of the universe. So, fascinatingly, while the entropy of the whole universe might well be zero (meaning there is no randomness at the highest level), we all see finite entropy locally (i.e. randomness arises precisely because we ignore all the entanglements with the rest!). My question here is to do with the tension between the order we observe all around us (the existence of well-defined laws that cannot be circumvented even by us humans) and the disorder we believe exists at the most fundamental level of experimentation and as predicted by quantum physics.  Is the universe fundamentally completely random or is it in fact incredibly ordered and structured?  The two – ordered and random – are not necessarily mutually exclusive, as was already speculated on by the Ancient Greeks. Some of them argued that order can arise out of chaos. Darwin also presented a powerful case that biological order can arise out of no (or very little) order. So it is an old question, perhaps stated in a more modern language here. Again, is there a scientific way of experimenting and determining which is the case? More specifically, is there a way we can bridge the gap between the macroscopic and the microscopic (the microscopic randomness frequently gets amplified to become a macroscopic determinism)? I believe this is one of the biggest outstanding problems in science at present. I have been promoting the idea that the concept of information might help here and is a deeper concept than many others we have in science today. It somehow feels that it ought to be prior to other concepts such as matter and energy and space and time. Furthermore quantum information is capable of being created out of nowhere as it were. We can start with no information (or with maximum information) and make a measurement that creates (new) information. Having said that, it is certainly not possible to formally derive the rest of physics from information alone. In many ways this is work in progress and very important at that.

New Big Questions:

1. Does our psychological makeup affect the truth value of our physical theories?

2. Is there a way in which we can test if certain features of our universe (such as its temperature and time) are consequences of entanglement at a higher level?