What is the basis of human belief regarding the Existence of independent objects? When it comes to the sciences the basis is often that classic (yet often misused) word ‘proof’ … but what is it that constitutes proof in the scientific world? Humans like to take what we can see as quite solid evidence for the proof of an external object’s existence. If we see a chair in front of us and then we sit down upon it and it performs its dutiful function of upholding our weight then we can quite confidently take this as proof that the chair actually exists. This is the commonly held philosophical viewpoint known as realism. But what about when it comes to objects like electrons, protons and quarks – we definitely cannot see these entities with a microscope, let alone the human eye, how then do we infer proof of their existence?  These quantum scale objects can be grouped under the term ‘unobservables’ and we will come back to them shortly.

There are other categories of entities such as ‘unobserved observables.’ Can you think of an object that we as homo sapiens have not observed but theoretically could be observed? A good example is a dinosaur – definitely big enough to see with the human eye yet unobserved due to extinction events long before our lifetime.  Why do we believe in dinosaurs? The belief derives from what philosophers like to call ‘Inference to the Best Explanation’ –  thanks to the skills of our paleontologist friends we find fossilised bones and teeth, which we can combine with our geological knowledge of the Earth millions of years and infer the best explanation; the existence of a creature composed of such pieces that would thrive in the conditions of the pre-historic earth. This is ‘Inference to the Best Explanation’ – taking all the data we know and constructing the most likely theory. Now what about total unobservables? How do we explain the existence of these entities?

So let’s take electrons, how do we follow this procedure of logical deduction to assume their independent existence? Well, the most pertinent school of thought in philosophy of science is called Entity Realism. We cannot see quarks directly however what we can see is the effects they have on larger entities. The proponent of Entity Realism, Ian Hacking, reasons along these lines. He argues that we understand the properties of the electrons and even though we cannot see them we can change variables in the system to manipulate their behaviour in order to produce effects on larger observables which we can can see. Now this manipulation of the unobservable entities and their produced effects is though to be proof enough of their existence. As long as we can manipulate and intervene on scientific entities in a laboratory to create phenomena we expect, we are justified to believe in their existence as the causal entities at work in the observed effects. This is similar to the Inference to the Best Explanation argument in that it uses a deduction process to assume the belief in the existence of an entity using pieces of information we can directly observe. As was the case with the dinosaur where we had the fossils, with the electrons we have the behaviour of the larger phenomena of which we know the electrons are the cause.

So Hacking summarises that “If science is able to use its posits as tools for experimentation, then the posits are real. If not, then they are merely hypothetical. An implication of this view is that one can be realist about electrons, but not about quarks or weak neutral currents”.

Overall I like Hacking’s argument a lot – relying on a degree of practically and what we can do in the physical world with entities in order to accept their existence. However both these arguments still rely on the ability of human observation and human manipulation to some degree. To me again this resounds with a degree of human hubris – why should the independent existence of objects rely on what we can see with our tiny eyeballs or what we can manipulate with our level of technology. If our technology so increases to be able to manipulate a quark, was the quark non-existent before? I think not. This reminds me of a similar philosophical line which equally gets on my grind ‘if a tree falls in a forest and no-one is around to hear it, does it still make a sound?’ Of course it does, unless you believe the laws of nature are entirely dependent upon the perception of a particular species living on one planet.

Now here is another problem with this way of thinking – there is a different type of unobservable, one which comes on the extreme opposite length scales to the quarks, electrons and protons – astronomical length scales. Can you guess what we are talking about this time? Black holes. Hacking concedes that his theory falls short on these scale ‘When we use entities as tools, as instruments of inquiry, we are entitled to regard them as real. But we cannot do that with the objects of astrophysics”. We cannot directly see a black hole and we certainly are not at the stage of advancement yet where we can manipulate its properties. All we can do is infer its existence from the effects it has on the objects surrounding it e.g the speed of gas clouds orbiting the region, glowing of matter and rapidly moving stars in the gravitational field.  But all this understanding depends on our theoretical models of the behaviour of matter, spacetime and gravitational fields being correct – all these things we assume to be correct but does this consistent direct proof of the black hole itself?

For decades the concept of black holes remained a theoretical construct, a by product of Einstein’s general relativity when Karl Schwarzschild worked out that for an object of any given mass, there was a specific radius at which light would be unable to escape. However now they seemed to have moved into the realm of reality as our astrophysical observations have increased in quality and we can see the effects on surrounding objects. So again we see the proof for their existence to be a case of Inference to the Best Explanation, like the case of the dinosaur. We use all the information we have  to deduce the most likely conclusion – the existence objects we call ‘black holes’ which have a class of properties which cause the observed behaviour. We draw this conclusion without direct observation or manipulation of the objects themselves. If you are an Entity Realist however you really can’t have it both ways… you can’t see or manipulate these astrophysical objects and thus have no ground for claiming they are real. For an Entity Realist like Hacking, Black Holes are not real.

So to re-cap the thoughts, when we leave the world of common everyday objects like chairs and tables to the tiny realm of the electrons of mammoth realm of black holes we need to accept different methods as opposed to directly observing to accept their existence. Both these methods depend heavily on the theory that applies to the realm, quantum theory for the quarks, electrons and positrons and general relativity for the black holes. But, here’s the big snag; who is to say our theories represent the true nature of reality, who is to say our theories are right? Our best theories regarding entities have been very wrong in the past – scientists once believed in something called phlogiston theory; the idea that water was an element, i.e. made up of one entity ‘the water element’ yet now we know it is made up of two hydrogen atoms and an oxygen atom. So previously  there was belief in the existence of a water element – now, after our theories have developed, we know this is false! This entity does not exist in the universe. So who is to say our theories won’t evolve in the future to disprove the existence of quarks, electrons and positrons or black holes for that matter? Belief based on theory and not direct observation requires faith in the current theory and thus, it can be argued, cannot be taken as proof.

So maybe it seems seeing after all, is the only way for humans to wholeheartedly believe, a belief that can exist without having to invest faith in the truth or accuracy of a scientific theory. This is not to say that objects don’t exist without our observation (remember a tree does make a sound when it falls in a forest)  but that we can never have the same degree of confidence in our personal human belief about them. As strong as our theories may seem how can we ever be sure about what goes on in the murky waters of the invisible…

[I should note that this article assumes the popular realist interpretation of the world – that objects and reality do exist independently of the mind and are not constructs of our consciousness. This is a fair assumption to make, unless we want to fall into the rabbit hole of the truly weird and wacky philosophy of reality. Musing for another post.]