“For me photography is a journey of discovery”, says Elton John. “I buy what I like and if it's not fashionable I don’t care. The more you collect, the more sophisticated your eye becomes.” He realised he had become a serious collector when, in 1993, he paid a record price at auction for Glass Tears, 1932 by Man Ray (main picture). This hauntingly beautiful close-up of a woman’s face is paradoxical because the droplets on her cheeks are obviously glass, yet one still tends to see it as an expression of sadness. 

The wilder shores of contemporary visual art are now ephemeral or time-based: performance, installation, general carry-on and hubbub. But once upon a time – say, the 1960s – it was the nature of objects, pared down to essentials, and often made from real materials sourced from the streets, builders’ yards and shops, that startled: the idea made manifest without old-fashioned notions of the hand-made, craft or manual skill.

It's 100 years since Georgia O’Keeffe first showed at Alfred Stieglitz’s 291 Gallery in New York, a hub of avant-garde activity, and the opening room of this major retrospective revisits the 1916 exhibition. Inspired by Arthur Dow’s emphasis on freedom of expression and Wassily Kandinsky’s book The Art of Spiritual Harmony, O’Keeffe made a series of drawings and paintings in which natural forms are abstracted to the point where they are only just recognisable.

Here comes the Switch House. The 10-story new build attached to the Gilbert Scott Bankside power station that was the first instalment of Tate Modern in 2000 opened to the public this weekend. Tate Modern’s expansion became almost a necessity as the original estimate of two million annual visitors became five million.

Mona Hatoum was born in Beirut of Palestinian parents. She came to London to study at the Slade School in 1975 and got stuck here when civil war broke out in Lebanon, preventing her from returning home. In effect, she has been living in exile ever since and the sense of displacement and unease induced by being far from home permeates much of her work.

The earliest known selfie is as old as the medium itself – literally. Hippolyte Bayard, one of the inventors of photography, pictured himself as a drowned man. His technique of photographic printing on paper had been upstaged by the daguerrotype, a metal plate alternative developed at the same time (1839) by Louis Daguerre. While Daguerre was showered with honours, Bayard was overlooked and, in disgust, he posed as a martyr to wasted endeavour; his hands stained with photographic chemicals, he slumps in a chair like a corpse newly dragged from the water. 

Sculpture that moves with the gentlest current of air! Sculpture that makes you want to do a little tap dance of joy! Or maybe the Charleston – swing a leg to those sizzling Jazz Age colours and shapes and rhythms. Look, that’s the queen of the Charleston right there – the “Black Pearl” of the Revue Nègre, Josephine Baker. She’s a freestyle 3D doodle in space, fashioned out of wire: spiral cones for pert breasts, that sinuous waist described by a single serpentine line. What a callipygous shimmy. And who’s that with the Chaplin moustache?

Pop went the easel, and more, as we were offered a worldwide tour – New York, LA, London, Paris, Shanghai – of the art phenomenon of the past 50 years (still going strong worldwide). We were led by a wide-eyed interlocutor, the bright-eyed and bushy-tailed Alastair Sooke, to the throbbing beat of – what else? – pop music, Elvis and much else besides.

It's impossible to overstate the reverence accorded the painter Agnes Martin by her fellow artists; in the panoply of American cultural goddesses, she is right up there with Emily Dickinson. Yet she is scarcely known in the wider world, partly because her work is relentlessly abstract, but also because she was deliberately evasive.

In 1967 when she produced Syncopated Rhythm (main picture), Sonia Delaunay was 82; far from any decline in energy or ambition, the abstract painting shows her in a relaxed and playful mood. Known as The Black Snake for the sinuous black and white curves dominating the left hand side, this huge, two and a half metre wide canvas is deliciously varied.