Late on this November afternoon, Julia came in through the dim foyer of her own home and passed into its darkened interior. Across the living room, no red pinpoints glowed from the panel of the answering machine, yet she was sure she had turned it on. She had begun to walk toward it when she saw a shape in the darkness, and then the shape moved. Adrenalin stunned her as lights blazed and voices shrieked, “SURPRISE!”

“So you were surprised, then,” Larry Scott says with a twinkle, shouting actually, for the kitchen is now a bedlam of music and voices and clamoring pots. Larry’s wife Sharon leans forward to listen, anticipating fun in Julia’s response.

“Way beyond surprise,” Julia says. With thumb and forefinger, she indicates a small space. “I came that close to a fatal heart attack.”

Actually, hysteria was closer than death. All at once, when the lights went on and the loved ones screamed, Julia gaped and threw up her hands as though confronted by a burglar with a gun. A camera flashed in her face. She jerked her elbows to her sides and her fists to her chest, jumping up and down and crying, “Oh! Oh! Oh!” in great gasps as she tried to regain control, and everyone whooped at the comical sight. Julia’s hands did not stop shaking for half an hour, yet now she is laughing as she extends a hand and makes it shake in illustration, for the tale gets better with each telling and is beginning to elicit gales of laughter when shared with late arrivals.

Without a doubt, this is a splendid assemblage. Good friends pack the chambers and channels of the townhouse’s first floor like commuters in the aisle of a rush-hour subway train. A knot of passengers fights for balance in the center of the kitchen, lurching forward and rearing back in merriment, subsiding again as the conversation rolls into the straightaway of some more sober interest.

Below the kitchen bulletin board, a nucleus of lawyers tries to give form to a legal discussion; it evaporates in a sudden gust of levity. Backed against the counter by the food processor, I nod and comment as Larry Scott describes the elk he has just bagged in the mountains north of Steamboat Springs, where Sharon is working for a small law firm and he has for six months been building an enormous mansion of fitted logs for a millionaire Texan. Sharon is seven months pregnant, but they have driven all the way down to Boulder for the party with offerings of elk steak and hamburger.

“I never shoot from any more than twenty yards,” Larry is saying, and I am watching groups of celebrants form and dissolve on the surging sea of bodies behind him, transient islands of joyous tumult, eagerly whispered gossip, and earnestly exchanged opinions. Plying the straits between them, others nudge drinks into empty hands, slap shoulders, tug strangers together in introduction, barge the wet vegetable byproducts of salad-making from sink to wastebasket, ferry cargoes of casserole to the oven and hors d’oeuvres to the dining nook at the kitchen’s far end, steam down a short hall lined with bookshelves, around the stereo, and into the living room, laden with desperately needed shipments of dips and munchables.

Cries of appreciation float back to the kitchen where Andy Gargano is peering into a huge, white-enameled pot at the miracle of his chili as it begins to bubble and steam; he dredges its muddy depths with a long wooden spoon. He picks another spice from the shelf above the stove and reads the tin with intense concentration, considering its potential impact. Beside him, Jim Weber works another burner, stirring a melted mixture of Velveeta cheese, cream cheese, pepper, and beer for a party dip. A newspaper food editor, Jim takes perverse delight in a gospel of “American classics” — Spam, Velveeta, corned beef hash from a can — as gourmet ingredients.

Andy’s girlfriend Christina Skinner thrusts her head between their shoulders and inhales. “Mmm,” she moans, rolling her eyes, then whirls away to search the unfamiliar cupboards and drawers, poking me aside with a good-natured growl to root in mounds of dirty dishes, plastic wrap, and discarded leaves of aluminum foil. She unearths a silver cake server and bears it off into the maelstrom around the dining table where her friend Donna Sedeniak, who stands by day behind a delicatessen counter in white cap and apron, slowly moves a small squeeze-tube over the birthday cake’s chocolate icecap, writing “Happy 30th Julia” in a thin line of transparent red.

All this I see in an infinitesimal space between two instants — the end of a joke I have made and the beginning of a motion toward the refrigerator — and I gaze in wonder. What magnificent creatures they are, these friends who populate the complex ecology of the life I share with Julia. Refreshed by their presence, confirmed by their affection, we rejoice in the sight and the sound of them. Their humor nourishes our spirits. Their minds are the nerve endings through which we monitor our world, and now we have drawn them close to extract their messages in words that leap between us like so many electrochemical pulses sputtering across the synapses of our communal brain.

What presumptuous liberties I take! What pompous extravagance of biological allegory! We physicists have the instinctive conceit that all wisdom accrues to us from the study of the universe at its most fundamental. Is not the human organism, after all, a matter of biology? Biology turns upon the molecule, the molecule upon the atom, the atom upon an obscure zoology of imagined particles and forces. During the week, I manipulate and contemplate those symbols and fancy myself, in moments of weakness, at the bottom of some larger understanding.

The physicist begins his studies in naiveté, believing nothing exists that cannot ultimately be described by equations or subdued by the power of rational thought. Then he follows that rational thought to its indistinct frontiers, probes them with mathematics and machines, and finds that his sphere of wisdom is but one small bubble in an infinite mystery.

Yet I wade through the living room refilling liqueur glasses from an unexpectedly popular bottle of Old Bushmills Irish whiskey and persist in fancying my home filled with swimming motes of life; a bloom of short-lived yuppie mayflies hovering in the air by a riverbank, dancing in clouds of themselves above the fast, cold currents of reproduction and oblivion; the genus homo exhibiting mass bonding behavior. What charming nonsense!

I keep it to myself, this analytical imagery so quaint and vulgar when compared with my Julia as she entertains our friends with tales of our trip to Europe. She stands by the pile of presents on the couch, her face glowing like the face of a child in a circle of adoring adults.

“Old man,” shouts Karl Nielson above the music, nudging my arm and holding out his glass, “I heard you went to Oktoberfest.” He tilts back his pale blond head, sly with anticipation. Standing close so he can hear me, I gratify him with a much practiced and now hilarious description of divinely drunken madness in the beer halls, how the German vomited and the American serviceman slipped and went down in it, how we filled ourselves with the potent beer and sickened ourselves on stomach-pumping rides along the carnival midway.

The chili and other hot dishes having arrived on the dining table, Andy Gargano’s voice rises in a bid for attention, but Karl has just steered us into shotguns and trap shooting and fails, like nearly everyone else, to take notice. “Come on, you swine,” Andy calls with mock resentment to no one in particular.

Feet thump on the wooden steps outside and stomp into the foyer’s welcome warmth, shedding snow. Carl Quinn and his wife Liza have come up from Denver with a dish covered by aluminum foil; Roger Green is here from Golden with his girlfriend Kristin Moeller and what appears to be some kind of pie. They drop the coats from their backs, shouting and waving with broad smiles. The house takes them in with the din of a cliffside rookery greeting a new flock.

“Was she surprised?” asks Carl Quinn, reaching out a long arm to shake my hand. “Oh Christ was she surprised,” I say, and wonder aloud whether a surprise party has ever caused a heart attack. Quinn receives my report, while Roger and Kristin receive Julia’s on the other side of the room, with grins of satanic delight and moues of sympathy for her fright. Christina Skinner — Julia’s best friend — stands by, relishing my every word and adding not a few of her own. For a month, Christina helped me plan the elaborate deception, inviting Julia to go this evening to a small party that did not exist, to throw her off the trail in case she suspected.

Quinn takes particular pleasure in his part, having invited us to spend this afternoon at a show in Denver, while Christina and some twenty hard-core conspirators entered our house with a key I had hidden on the porch, sending the cat in mad flight to an upstairs closet; they draped the rooms with crepe paper and balloons, turning off the lights to whisper and giggle as they waited. And then we came home, and Julia walked before me into the house and into a firestorm of affection that exploded like a revelation from the dark and the silence. Oh God, it was good.

“We really got her,” Christina exults with wicked triumph. Our guests now mill around the feast-laden dining table, filling their plates with food and plastic cups with wine or beer. Who are these intimates who surround us now, popping flashbulbs and burlesquing the “Happy Birthday” song with a noisy vitality so remarkable and enigmatic? A hundred years from now, no one will have any more knowledge of us than we have of those family connections in the rare, turn-of-the-century photographs that grandparents bequeath us: “your grandfather’s great uncle,” or “a friend of your grandmother’s family who ran a brewery,” and beyond that nothing. Two hundred years from now, we will all be equal in anonymity, ghosts of light and shadow on fading film, of color on ancient canvases, of ocher smudges on cave walls. Two million years from now, thinks the physicist to himself, whispers the silly, morbid fool to himself, we will have no more reality than the subatomic particle spawned in a nuclear accelerator, living and dying within one billionth of a second, as incandescent as these people, this room, the candle flames above this birthday cake, now burning, now gone.

Julia straightens up with flushed cheeks from the smoldering candles, and Donna Sedeniak hands her a knife. Julia positions it on the mud-brown icing. The cake wobbles as she tries to saw. “Don’t torture it, cut it!” says Jim Weber, and Julia breaks up laughing at her impotence, her wrist limp and the knife dangling in her hand.

“Julia,” says Karl Nielson, prodding me with his elbow, “did you know that every birthday is just another muffled drumbeat on the long march to the grave?” Julia backs away from the table and bends down, laughing harder. “If you want a bigger knife,” Karl suggests, “you could borrow the grim reaper’s blade; he’s standing right behind you.”

“Come on, you guys,” Donna says. She takes the arm of the helpless Julia and tries to guide her hand. Julia brushes her gently away. “I can do it,” she says, wiping her eyes with the back of a hand. She carves the cake and loads the moist wedges one by one on small plates, laboring, while others eat, until the cake is gone. She turns her head as I kiss her lightly and carry the knife away to the sink, where Liza Quinn is already working with her delicate arms in the dishwater.

“Dear Heloise,” Liza says, “If you can tell me an easy way to wash those brown stains out of my coffee mugs, you just may save my marriage.”

“You don’t have to do this,” I tell her.

“I want to,” she says. “We’re going to have to leave soon, and I want to do something.”

“Leave! Already? We haven’t opened the presents.”

“I’m sorry,” she says. “We’re so tired. It’s been an absolutely horrible week. Shall I pour this out?” She is pointing at one of the etched crystal liqueur glasses Julia gave me on my birthday, now sitting on the counter half-full of Old Bushmills. It’s the third time tonight I’ve found one of these. Who is wasting my fine whiskey?

Liza dries her hands as her husband appears beside us, praises the cake, and eases his plate into the soapy water.

“Liza?” he says. “Shall we?”

Julia catches them in the living room, protests, is understanding, expresses polite disappointment. “You know what happens to the first people who leave, don’t you?” she asks, affecting menace.

“Oh dear,” says Liza. “What?”

“We see them to the door.”

Shivering beneath the bright porch light, we wave them down the steps and into the night, exchanging a litany of fond goodbyes, “Wimps!” “Happy birthday, Julia.” “Thanks for coming.” “Our pleasure.” “Watch the road, not each other.”

We wait until we hear the car start and see its headlights blaze along the snowy curb, then give a final wave and step back into the warm foyer. From here I can see Terry Overstreet, a normally dour attorney, gone haywire in the living room, convulsing and bobbing to the stereo’s beat, raising his hands before him and rocking back to play an imaginary saxophone. Around him crazy fools are dancing on our oak floor with great clumps that make me fear for the neighbors downstairs. Jim Weber, in a quiet backwater against the far wall, stands close to Donna Sedeniak in an awkward advance that appears destined for success.

“The party ain’t over till it’s over,” Julia says, swaying slightly with the music. She turns to stand against me, locks her arms around my waist, leans back, and looks up with gleaming, sleepy eyes. “Let’s never let the party be over,” she says.

“Never,” I say, and wish again that I could save her, wish I could tell her that only three weeks remain before a drunken driver will swerve into her lane on the interstate and force her into the concrete structure of an overpass, force me through the snow and the cold and the dark to the hospital morgue, drive me back into my empty home where the telephone sits waiting in the silence; that I will often relive, revivify, resurrect this evening where I now and forever preside as genial host, cherishing this incandescent moment with the breathless amazement of a child lost in a fairy tale, surrounded by festival merrymakers he does not yet recognize as ghosts.