QED, squeezing light and just call me the 'Destroyer'

Now Mugwump may look cute but beneath that 'butter would not melt in my mouth' demeanour, he is built like a small tank. The feline equivalent of a Staffordshire Bull Terrier. A neck like Mike Tyson and shoulders and forelegs to match! I am not sure why but when I first refill the litter tray he goes through a ritual of maniacally pawing at the fresh litter in a usually successful attempt to spray the contents (it's not been used yet) of fresh litter all over the floor (radius from litter tray about 1 metre). He attacks it in what seems like a frenzy of frantic digging.

This would be all very well, just sweep it back up and put it back in the litter tray, you say; but for one thing. In his zeal to spread cat litter everywhere he usually manages to break the side of the tray, either cracking it so the next frenzy will rip a great chunk out of the side or simply bypassing the initial cracking phase and moving straight into 'oh I appear to have punched a great hole in the side' phase. This of course renders the tray an unsuitable receptacle for keeping cat litter in. Structural integrity has been compromised and in Scotty's words: "Shields have failed, Captain! The next shot will open us up like a can opener!"

Up to Christmas he had demolished three trays in this fashion. I do now however seem to have beaten him. His litter tray is now a 6" deep underbed storage box made of quite dense, thick, softish (not brittle) plastic! In the ten days it has been in use, not only has all the litter remained in the tray but there's not a crack to be seen! Success! There is only one snag. You need to use twice as much cat litter!

So, QED. Before moving into looking at what 'really' happens when a photon goes from (a) to (b) we will, as does Dick, look at the strange things that happen when you squeeze light. So, how do you squeeze a photon? Essentially you 'limit' its potential paths to your detector. We saw how, in the Penguin's last QED post, light (photons) can seemingly be 'reflected' from a non existent portion of a piece of glass. Although the probability of the photon not moving in a straight line path at 45 degrees to the horizontal is significantly less than the probability of it doing so, the probability of it going by this strange path does exist. You have limited its options, squeezed it, by removing part of the mirror and so it gets forced into more bizarre behaviour, if you are going to detect it.

You can also look at this in another way using a variant of the two slit experiment. Place a photon gun in front of a screen with two tiny pin holes, (a) and (b), a set distance apart in front of your photon gun. Place a detector (c) behind the screen in a straight line with the gun and pin hole (a). Fire the gun, one photon at a time, and you will get detections at (c), say 2%. Now cover hole (a) and fire another burst of photons, one at a time. Now since hole (b) is offset relative to the straight line path, you would think no photons would be detected at (c), since the photon would have to move in a dog leg path to get there; first up at, say 30 degrees, then down after it traverses the hole at the same angle. The two dog legs making an ultimately straight line. Well, you'd be wrong! Experiment 'proves' that this dog leg is exactly what happens. The probabilty is less but it remains a probablity nonetheless.

Now this all seems so counter-intuitive and contrary to the 'high school' physics we might have been taught that it's hard to get your head round. Light travelling in 'curved' paths (Forget relativity here for a moment, since light does travel normally in geodesics - curved paths - in four dimensional space time.) It's as though the light photon manages to bounce off the edge of the small hole to get back on the 'straight line' track to the detector that it would have taken if hole (a) had been open.

The reason this all seems counter-intuitive is that we imagine the photon as a single, structurally coherent 'particle' with an integrity in time, like a tennis ball. Photon (1) goes from 'gun' to hole (a) to detector (c). The reality is that the photon which arrives at the detector is not the same photon which left the gun, although, since all photons are identical, it may as well be the same photon. Therein lies the problem with trying to see things at a quantum level in the same way that we perceive things at our 'macro' level. Feynman's genius was to see that the way light interacted with matter had a profound effect on what was observed. THE photon does NOT remain coherent or intact for its journey from gun to detector. We'll look in the next QED post at how this happens.

Finally, in the wake of the Israeli 'invasion' of Gaza in an attempted 'clean up' of Hamas, which will almost certainly fail; when are politicians going to wake up to the realisation that military intervention solves nothing? Whatever the hawks may say, the twentieth century is littered with examples of the constant failure of a military solution to SOLVE anything whatsoever. It seems a pity that innocent blood is highly likely to be shed in the name of what is, after all, little more than a PR stunt! One would have thought that after Iraq and Afghanistan in recent years, the Israelis could have worked out in advance that this isn't going to work, except in the very short term.