A Sunday spent dipping at Slimbridge, reminiscences of a misspent youth and Sherlock Holmes and the strange case of the missing photon

Ruff

I spent Sunday morning at Slimbridge dipping a Citrine Wagtail that my good birding friend Nick had found the previous day. Although early access for members  is still restricted, Slimbridge very kindly put in place a guided entry system for members wishing to see the bird from the car park at 08:00. I arrived at 07:30 and managed to get myself booked onto the first tour of ten but, unfortunately, there was no sign of the bird from the Hogarth hide where it had been seen the previous day. I had a walk around the reserve and then went back to the Hogarth hide for a second look where I met my birding friend Ewan. We spent the next hour or so chatting and taking pictures of very confiding Ruffs and Green Sandpipers right in front of the hide. At one point we heard that the Wagtail had been spotted at the Kingfisher hide so we rushed around there only to find a small distant flock of what appeared to be Yellow Wagtails in amongst the cattle, a case of mistaken identity I suspect.

Ruff

Green Sandpiper

Ruff

If truth be told, I was a bit of a handful as a teenager and gave my poor parents a right old run around. I was constantly in trouble with the police and, looking back on it now, was probably saved from a much more troubled life by an emergent interest in science and maths kindled by some truly awesome teachers at school. Jumping back to the troubled bit, there are many stories that I’m now much too embarrassed to tell but one quite funny one that I’m happy to  tell springs to mind. I was fourteen and now living in Salisbury where we had moved to because of dad’s work. I was in with a fairly rough bunch of lads and our pride and joy were two battered mod style scooters which we would ride rather illegally around the back streets of Salisbury. One day we had the misfortune to ride by a parked police car which gave chase, we headed off the road and onto to the old Salisbury rubbish dump with the police car close behind. We abandoned the scooters and made our getaway across some adjacent fields. Much later we plucked up courage to go back to recover the scooters only to find a message from the police pinned to them; “if you would like your carburettors back they are at the local police station” Funnily enough, we never bothered!

It is often said that a good teacher can change a child’s life and that certainly happened to me curtesy of  my wonderful maths teacher, Mr Manners, to whom I owe an unpayable debt of gratitude. I remember being awestruck when I learned about trigonometry and how sines, cosines and tangents could be used to calculate the properties of geometric shapes. It was like an amazing puzzle to me that I simply had to unlock! Mr Manners took this keen and excitable student under his wing and told him about all sorts of wonderful things in maths that were not strictly on the school curricula. I remember him attempting to explain complex numbers based on multiples of the square root of minus one and my absolute amazement at this strange concept. Many years later when I was completing my PhD in quantum liquids, I managed to get in contact with Mr Manners, thanked him and was able to tell him what a profound effect he had on my life.

As a sixteen year old I became fascinated by Astronomy through watching the Sky at Night on TV and persuaded my parents to buy me a telescope. I spent hours at night in our garden, oblivious with the enthusiasm of youth to the freezing cold, marvelling at the wonders of Saturn’s rings, Jupiter’s moons and the Andromeda galaxy. I remember being awestruck by how insignificant I was in this great scheme of things, this small collection of chemicals ,the result of some fortunate accident in a primeval soup, staring out at the infinite universe and all its unknowable wonders.

I had hence planned to study Astronomy at University but, while at college, discovered the weird and wonderful world of quantum mechanics and  quickly changed to study maths and physics. I think it was probably an accumulation of amazing articles on quantum mechanics  I read that drove me this way but one in particular stands out. I remember reading about the so called double slit experiment and determined that I now simply had to study Physics.

The double slit experiment is one of the iconic experiments done soon after quantum mechanics was discovered that showed that this counterintuitive world was actual very real. If you combine two waves of any type, they could be sound, in water etc, of the same wavelength you will produce what we call an interference pattern based on how the two waves combine, i.e.  both are at a peak resulting in an increased peak or ,if a peak and trough coincide, to cancel each other out. We call this constructive and destructive interference.

In the classic two slit experiment a light beam is shone at a grating with two slits in it. When the two beams of light are recombined behind the slit you see a series of black and white lines corresponding to the constructive and destructive interference described above. From this we can deduce that the light is in fact an electromagnetic wave. But we also know from other experiments that light comes as particles or small packages called photons. Now imagine that you reduce the beam of light shining on the slits until only one photon is hitting the slits at a time. Presumably the photon will either go through one slit or the other and rather than form an interference pattern you will just see one dot behind one of the slits corresponding to which slit the photon has gone through. Well of course not, this is the counterintuitive world of quantum mechanics after all! Somehow the single photon of light has simultaneously gone through both slits at the same time and interfered with itself to form an interference pattern!

In this sense this single  photon of light has  demonstrated what is called wave particle duality in quantum mechanics, i.e sometimes it acts like a wave, sometimes it acts like a particle or even both at the same time!

Footnote – my blogs are posted with sometimes rather imaginative spelling and grammar due to my extreme dyslexia!