Zhuangzi once said: ”Once upon a time, I, Chuang Chou, dreamt I was a butterfly, fluttering hither and thither, to all intents and purposes a butterfly. I was conscious only of my happiness as a butterfly, unaware that I was Chou. Soon I awaked, and there I was, veritably myself again. Now I do not know whether I was then a man dreaming I was a butterfly, or whether I am now a butterfly, dreaming I am a man. Between a man and a butterfly there is necessarily a distinction. The transition is called the transformation of material things.”
These musings are attributed to a Chinese philosopher who died circa 286 BC. They are also thoughts that many of us ask ourselves at some stage of our lives. We quickly dismiss these questions as irrelevant, too philosophical or simply unverifiable and get down to brass tacks. After all, it is impossible to know if I am dreaming now, or more fashionably, if I am a program in a computer simulation. Or is it really?
I don’t know an answer to this question but I recognise it as an important one. Hell, it is the question to ask! Don’t you agree?
However difficult this question may be, it has variants which are perfectly verifiable in a laboratory. Let me discuss one of them. The one I particularly like.
We all know that there are only two types of particles in this Universe: bosons and fermions. We also know that certain conditions an even number of fermions can behave like a boson. The simplest example is the hydrogen atom H (atomic hydrogen) whose bosonic behaviour was confirmed by Bose-Einstein condensation in 1998 after 20 years of hard experimental work (Phys. Rev. Lett. 81, 3811 (1998)).
The question arises: Is it possible that all bosons we observe in the Universe are made of fermions? Are we being fooled into believing that there are fundamental bosons? More fashionably: Is there a device independent test to reveal the veracity of this claim?
I’d like to stress here the words “device independent”. This means that the test should not assume anything about the physics of the investigated particles, i.e., it should give a definite answer independently of any known physical theory.
In our recent paper in New Journal of Physics titled “Particle addition and subtraction channels and the behaviour of composite particles” (NJP 14, 093047 (2012)) we discuss this question. Check it out!