The story is What Did Tessimond Tell You by Adam Roberts. I read it in the Solaris Rising 1.5 ebook.
The story starts:
THE NOBEL WAS in the bag, and we were only a fortnight from our public announcement, when Niu Jian told he was quitting. I assumed it was a joke. But Niu Jian had never been a practical joker; and of course he wasn’t kidding now. The sunlight picked out the grain of his tweed jacket. He was sitting in my office with his crescent back to the window, and I kept getting distracted by the light coming through the glass. Morningtime, morningtime, and all the possibilities of the day ahead of us. The chimney of the boilerhouse was as white and straight as an unsmoked cigarette. The students wandered the paths and dawdled on the grass with their arms around one another’s shoulders. Further down the hill you could see the cars doing their crazy corpuscle impressions along the interchange and away along the dual carriageway. “You want to quit—now?” I said. “Now is the time you want to quit?"
Niu Jian decides to quit after speaking to the eponymous professor Tessimond who explains:
“Your theory,” I said again, in a just-so-as-we’re-clear voice, “is that the reason we move along the arrow of time the way we do is that we’re being drawn towards a supermassive temporal black hole?"
I looked at him, feeling distant from myself. “When we reach the actual temporal event horizon,” I said, “tidal forces will rip us apart.”
“Or rip time apart,” he said, nodding slowly. “Yes. Of course, that amounts to the same thing.”
“You’ve got the equations there,” he said, looking at my phone as it lay, like a miniature 2001 monolith, flat on the table. “But it’s hard to be precise. The scale is fourteen billion years; the calculation tolerances are not seconds, or even days. Years. I calculated seven years, plus or minus four. That was a decade ago."
The story ends:
Of course I never flew to Stockholm. Why would I waste three days away from my child? None of that matters.