Firstly a bit of blog news; on Wednesday Rationalising the Universe celebrated its first birthday – we have come far further in one year than I ever anticipated when I registered the site last year, in a Starbucks on Baker Street studying differential equations at 7:30pm. Over 2,500 follows, 20,000 hits and a feature on WordPress Discover, along with the addition of a new and highly talented author. Thank you to all who have interacted and contributed to the blog in the last year – with a particular mention to Jiisand and Kersten who keep me endlessly entertained with their comments, Richard Barker for the surprising mutual ground we share despite different lenses on the universe, Pearl for consistent and insightful comments from the start and Maths by a Girl for keeping my math game sharp several times a week.
I was encouraged to see the discussion on Mekhi’s post; it is comforting to know that there are many people out there who want to grapple with the things that matter, in a world where the trivial sometimes seems to dominate. The idea of reality only existing when observed was discussed heavily – should the reality humans know be dependent on us logging it? On the macroscopic scale the resounding answer is no – the tree does make noise in the forest regardless, but this reminded me of the problems with observer dependence in quantum physics. The tree falling in the forest, when discussed among physicists does not take much extension to transform into an elegant metaphor. Instead of developing these thoughts through comments I thought I would add an additional post, which blends with Mekhi’s work and with my analysis of Schrodinger’s cat. I will start where I finish; reality must not be observer dependent.
Aside from the fact a sandwich costs around £25, Copenhagen has another big problem; that is the Copenhagen Interpretation (or the Copenhagen work-around if you are feeling particularly cynical). Today, sitting in 2016 it is acceptable; the quantum realm exists in a foamy reality unless we look at it, collapse the wave function and fix reality. However there is the word we which implies a duty upon us to collapse the wave function or leave the quantum realm in its wavelike reality. When we go back to the very inception of the universe in which we reside, the hot big bang model gives a high energy dense soup of particles obeying, we presume, the quantum laws (albeit with some differences for the unification of the fundamental interactions depending on how far back you go). If we are to accept a reality in which particles only occupy their fixed point in space when an observer collapses the wave function – the more interesting point emerges, how do we have observers at all? For these primordial particles to collapse into single points in space and begin to clump into larger bodies, eventually making the stars which cooked us up; what initiated the collapse in an observer-less universe? (For a less rushed history of the universe see my Brief History of the Universe).
Despite the above; let us not forget that the wave function, along with quantum mechanics in general is arguably one of the most successful blends of theory and experimental progress ever known. The theory is less than 100 years old, and gives us a framework which agrees almost entirely to every experiment performed. So how can something both agree entirely to experiment, whilst at the same time not be quite right? It was Aristotle who lead us down the wrong path when he favored the use of logic alone declaring if you threw a stone upwards on a moving chariot it would land behind the chariot. This way of thinking, somewhat embarrassingly took until the days of Galileo to dispel – and since then the modern scientific method requires theories to be experimentally verified. So if the wave function is experimentally verified, it must be right? Well no – it can’t be right but that’s not necessarily doom and gloom; after all Newton was both wrong and experimental correct. Salvation for us lies, we hope, in a similar place that young Siddhartha Gautama found it – a middle way.
If you consider the vast number of quantum mechanical interpretations, objective collapse theories are closest (by a long way) to the Copenhagen Interpretation – this is a middle way that does not entirely depart from the central ideas but removes the observer problem. Collapse theories allow for the wave function and wave function collapse, however they allow the two to be objective (i.e. not dependent on the observer). The central pillar of any collapse theory is to allow wave function collapse to occur with a particle taking a fixed position without any observer present. How that collapse is actually initiated depends on your view point; Rodger Penrose for example believes the process is spurred on by quantum gravity and that there is an energy threshold beyond which the collapse will occur. Ghirardi–Rimini–Weber take a spontaneous collapse approach, introducing new terms to the wave function to allow for the objective collapse. If this is the case, then we imagine the probability would be very low; which need not be an issue in the very early universe where we have billions (and billions and billions and billions etc.) of particles to play with.
I don’t want to get too deep into the mechanisms by which a collapse could occur which an observer has not initiated; partly because they are heavily complex and require the full mathematics of the wave function (which I would not do justice) but also because there is much uncertainty. A much more fruitful discussion can be had around the benefits posed to quantum mechanics (and people worried about falling trees) if we can arrive at a position where we don’t just redefine what an observer is – we scrub them out entirely. The cat posed the interesting paradox where quantum mechanical processes were tied to macroscopic bodies to give a view of reality we are fairly sure does not exist. As exciting as it would be to think my entire body zooms into a wonderful state of superposition in an observer-less reality it seems unlikely. Under this new collapse approach, when we have large bodies we have so many particles interacting that their wave functions collapse like it’s going out of fashion; this does not require me to be looking at something to make it so. This is because the collapse of the wave function of one particle can set off the rest, so whilst the collapse of any one particle might take billions of years, the collapse of the wave function of a particle within my billion billion billion particles wouldn’t require such a wait. In fact, the wave functions could in theory not even form in my large conglomerate of matter giving a fixed view that my friends are used to observing.
There is a more mysterious application too – you may well have heard about the information paradox within a black hole. Particle goes into a black hole where (we assume) there are no observers. We accept that information is lost within a black hole. So if the particles information is the wave function, with the wave function collapsing on observation either the information is retained or there is an observer sitting in the black hole collapsing my wave function. Neither of these appeal; but if you start to allow for objective collapse then your paradox is resolved. There has been a flurry of research and calculations in this area; and it would seem possible that you can indeed modify the current Copenhagen Interpretation whilst preserving the experimental success of the theory to account for the rate of information loss within a black hole. This must be a holy grail for quantum mechanics – the removal of observer dependence, the solving of many paradoxes retaining the experimental success. The theories even give a nudge in the right direction for the mystery of dark energy.
So what does happen behind my back? Logically – nothing. The conclusions reached in Seeing is Believing are correct; order is preserved in the macroscopic world, do not be arrogant enough to think you can break nature with your little human body. The interesting metaphor of the quantum world throws up our faithful paradoxes of dead and alive cats and brings us the observer problem – the Copenhagen Interpretation it would seem is incomplete, currently accepted as the best we have. It does after all agree in the laboratory; and that is modern science. My view is that we place our faith in tweaking the model as described above; eliminating the problem of how anything exists in the first place and tackling some big issues in quantum physics. If this is to be propelled into the mainstream, the next steps must be to experimentally verify objective collapse. It is of course difficult to prove something does actually happen when you are not interacting with it, but the most hopeful candidate is to recreate the double slit experiment with more massive objects, in an attempt to eventually yield a result objective collapse comes into play. With experiments looking possible within the next decade and academic progress increasing at a tantalizing rate now is a good time to be entering the arena of quantum physics.