Robin was moving away from theoretical physics and into the philosophy of physics, and there were many discussions with him and his friend Keith Roberts.
Once they had tried to set up a purely operational definition of Special Relativity, and when one of them objected that there was no such thing as a rigid body in relativity, Alan said, 'Well, let's call them squeegees'
It was that pleasant, unpompous way of being serious without being solemn that in 1948 was far from widespread in academic life, and was associated with the legacy of the Apostles and the King's milieu—though it came naturally to Alan.
There was another nice occasion when Don Bayley came for the weekend to see Alan and Robin, to be greeted with a toy steam engine that Alan had bought at Woolworths.
'I always lusted after things like this as a boy,' he said ruefully, 'but didn't have enough pocket money for them. Now I have got enough money, I might as well have it.'
They played with it for the afternoon.
Alan had told Robin that 'Sometimes you're sitting talking to someone and you know that in three quarters of an hour you will either be having a marvellous night or you will be kicked out of the room.'
It was not always like that, for the innocent Peter Matthews' cocoa sessions did not involve this stark dichotomy.
Nor was Alan accomplished in the necessary social game of words and eye-contact; he was too shy and brusque and lacking in confidence in his looks.
Cambridge did inspire him with greater interest in his appearance, and sometimes he would show Robin a photograph of himself at sixteen and say how handsome he looked then.
He was certainly not attractive in the Aryan-Brylcreem style of the 1940s.
To the fastidious, his open-necked, shabby, breathless immediacy came as messy and coarse, though there were redeeming features; he could put on a roguish charm which reminded people of his Irish ancestry, and besides his piercing blue eyes he had thick, luxuriant eyelashes and a soft-contoured nose.
But whatever his doubts and disadvantages he would pace round the courts of King's and invite young men in for tea.
Sometimes he struck lucky. In April 1948 he struck very lucky indeed, for Neville Johnson stayed for tea, and stayed many times.