A few years ago there was an interview with the lad at Cern whose job it was to answer queries from members of the public concerned that the Large Hadron Collider would produce a blob of anti-matter which would suck the entire universe into a black hole somewhere in the vicinity of Geneva.
That's not going to happen, said your man, though as a scientist I never like speaking in terms of absolute certainty. Theoretically I could drop this pen and it would pass through the table. He dropped the pen. It hit the table. The universe is still here.
As with science so in sport. When Barcelona entered the 87th minute of their second leg against Paris Saint-Germain needing three goals, it was theoretically possible that they might get them. It was just logically impossible. They had, after all, scored just three in the previous 177 minutes of football against the same opposition. Then the pen fell. It passed through the table. And a little ball of footballing anti-matter christened, in the inclusive Brazilian manner, Neymar da Silva Santos Junior blew PSG's universe to smithereens.
When we talk about comebacks we usually say a team kept doing the right thing, kept plugging away, didn't let their head drop and other such formulations familiar to those of us reared on the stolid artisan language of British and Irish football. But this, the greatest comeback of all-time, was based on individual flair and inspiration. Our grandparents had the Matthews Final. We will always have Neymar's Night.
It began with the free-kick which reduced the goals requirement to two. Has there ever been a free which combined power with precision to such effect? Zico's against Scotland in 1982 perhaps. PSG 'keeper Kevin Trapp stood stock still as though there was something unfair about a shot this good. And still you didn't really think Barcelona were going to do it. The feeling was more like, 'What a bitter irony, they got the four goals they needed in the end but the away goal will put them out'.
Almost straight away, it seemed, Luis Suarez tumbled in the penalty area and a referee who showed signs, as refs sometimes do, of getting carried away by the momentum of the comeback pointed to the spot. You waited for Lionel Messi to step forward and do the needful for the second time in the game. Instead Neymar took the ball. It was a moment of great symbolic force, the Brazilian saying to his team-mates, "I'm the one you need now. I am the one who will carry us through. I am the one who knocks out PSG." We may come to see it as the moment when the torch was passed by the greatest player of our lifetime to his successor.
Time for another tribute to the Brazilian team of the eighties. Back then it was Socrates who'd approach the spot with a short casual stuttering run-up before despatching his penalty effortlessly past a mesmerised 'keeper. Now Neymar did his cover version before floating the ball home with a deft touch, his utter calmness gloriously inappropriate in the circumstances.
Because by now as we journeyed into five minutes of stoppage time everything was turning feverish and frantic.
The forecast had turned from impossible to unlikely. We told ourselves that Barcelona would probably get one chance. They did and Gerard Pique's header went straight at the 'keeper. Two crosses were cleared by the defence. The visitors almost broke away down the field only to be foiled by Barcelona 'keeper Marc-Andre ter Stegen making a tackle as he raced back towards his goal. Then he turned around and went back into the box, embracing the whole loony Marx Brothers vibe of it all.
With 30 seconds left Neymar got the ball 40 yards out. They yelled at him to lash it into the box but, like Chris Tarrant on Who Wants To Be A Millionaire, he didn't want to give us that. First he needed to dummy past a defender and then came a chipped delivery of such delicacy and finesse you knew a Barcelona player would get on the end of it. Sergi Roberto stretched acrobatically and even then the miracle was in danger, the volley could have gone over or hit the 'keeper and we'd have had the most heartbreaking so-near-but-yet-so-far story of all. In it went, impossible having become unlikely transforming in that instant to inevitable.
To do what Neymar did in those last seven minutes you need astonishing technique. But personality comes into play too. As the man went through his penalty routine the commentator echoed many of us by shouting 'stop the clock'. The fastidiousness seemed almost lunatic given the temporal situation. Yet Neymar knew what he needed to do and how he needed to do it. Technique alone can't account for the penalty, the dummy, and that last little chip. They're rooted in a desire deep down to express yourself and to entertain, to put on a display even at the most fraught moment, perhaps particularly at that moment. The metaphors of Sport As War or Sport As Art don't capture this most crucial aspect of the great sportsman's make-up. Sport as its best is really great popular entertainment. And to be a truly great entertainer, to bring joy to large numbers of your fellow human beings, can be one of the most noble callings there is.
Our football world has a suspicion of entertainment and a disdain for flamboyance. There are pundits whose first thought about Neymar would be that he doesn't track back. The League of Ireland is full of lads who track back, they track back in Sligo and Longford and Bray, they spend their lives tracking back. You can pretty much teach any fit young man to track back. But you can't teach him to do what Neymar does.
The puritan pragmatic creed which dominates thinking about football in this part of the world influences all of us to some degree. A part of us thinks when we see Neymar or Messi or Ronaldo flicking and stepping over and back-heeling that this is no time for the fancy stuff. But in Neymar's world it is always time for the fancy stuff. It is the fancy stuff which helps you defy the laws of footballing physics.
There's a saying that 'magic is just unknown science', which presumably derives from some philosopher or other. I got it out of an Irvine Welsh short story. So there must be a rational explanation for Barcelona's miracle comeback. It just looked like magic.
Liam Brady tried to explain it by invoking the motto about Barcelona being 'more than a club'. But that's confusing morality with aesthetics. As Oscar Wilde might have said had he been sitting between Didi Hamann and Richie Sadlier on Wednesday night, there is no such thing as a moral team, teams play well or badly, that is all. The 'more than a club' thing made more sense when Barcelona's largely home-bred team were going up against Real Madrid's Galacticos and the club still had the Unicef logo on their shirts. These days Barca have fully embraced the commercial side of the game. There is nothing more Galactico than that Messi/Suarez/Neymar front line.
Maybe it's more correct to say that Messi-era Barcelona have been 'more than a team'. One of the privileges of watching them is that the record books will never capture the utter thrill of watching them in action or how they have dominated the footballing landscape in the decade since the little man took over at the Nou Camp (and it is he rather than any manager who has defined the era. Pep Guardiola spent Wednesday night masterminding a scoreless draw against Stoke). The stats will show six La Liga titles and three Champions Leagues but they won't show how every season in both competitions was dominated by the question of who might stop Barcelona and how they might do it.
They won't show either that every year for the past ten years Barcelona have been the most entertaining team in the world and how at times it was like watching, on a weekly basis, that Brazil 1970 team our parents told us about. Like fools most of us watch more Premier League than La Liga but how many Saturday nights have there been when, flicking through the channels, we chanced upon Barca, the way they pass and move almost as instantaneously recognisable as their jerseys, and stayed glued to the screen, transfixed by the miracle of football being as good as football can be.
Not the least of Wednesday's triumphs was that Neymar suggested this utter sublimity does not have to end when Messi does. At the end Messi and Luis Enrique jumped up and down in tears like children, these men who have seen pretty much everything in football uplifted to the same kind of amazement filling living rooms across the world. You felt a twinge of pity for the poor Paris supporters who'd probably been throwing a few snails on the frying pan and cracking open the Blue Nun before the world turned upside down, but really the French side were as incidental to the drama as Rosencrantz and Guildenstern.
It was Neymar's night. It has been Messi's decade. It is Barcelona's game.
Sunday Indo Sport
These have been unhappy days in the era of late Arsene Wenger, and while the thrashing from Bayern Munich on Tuesday night posed the question how much worse it might get, the reassuring answer for the Frenchman was that the truly apocalyptic FA Cup shock was never on the cards.