In Monster Field, 1938, fallen trees appear like the fossilised remains of giant creatures from prehistory. With great horse-like heads, and branches like a tangle of tentacles and legs, Paul Nash’s series of paintings and photographs serve as documents, bearing witness to the malevolent lifeforce that, unleashed by their undignified end, has taken hold of these apparently dead trees.

While the Turner Prize shortlist can reasonably be expected to provide some sense of British art now, the extent to which British art can or should attempt to reflect a view of British life is surely a moot point. Art that is socially or politically engaged can all too easily tend towards the artless, its functionality placing it uncomfortably close to pamphleteering, with the certainties of propaganda drowning out the possibilities of art.

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.

Today we amuse ourselves with Facebook clips of talking cats, but in the 1850s they had stereographs, pairs of identical photographs that, viewed through special lenses, become suddenly and gloriously three-dimensional. Vistas open up as if by magic, the illusion of space all the more beguiling for its transience. The act of looking through a special pair of glasses is a little bit like peeping behind a curtain, the intimacy of the encounter adding a slightly voyeuristic frisson to all manner of subject matter from landscapes to mock-ups of popular paintings.

The exhibition starts promisingly. You can help yourself to an orange from Roelof Louw’s pyramid of golden fruit. Its a reminder that, for the conceptualists, art was a verb not a noun. Focusing on activity rather than outcome, these artists were committed to the creative process rather than the end product. The idea was what mattered, and if it led to an open-ended exploration, so much the better.

The individual colleges of the University of Cambridge can call, when needed, on an astonishing international network of alumni for expert advice, consultation and financial support. Such is the backing for an exquisite new public gallery on the site of Edwardian stables in the grounds of Downing College there.

There are some wonderful things in this exhibition, and that’s no surprise: the British Empire endured for over 500 years and at its peak extended across a quarter of the world’s land mass. Preparing an exhibition of corresponding reach must have involved considering a vast range of objects, but choosing well is another matter entirely.

Tate Britain’s Duveen Galleries are currently filled with a hauntingly beautiful sound installation by Susan Philipsz (main picture). The Scottish artist won the Turner Prize in 2010 for a sound piece that didn’t really work at the Tate. Intended to be heard under the bridges spanning the River Clyde in Glasgow, the recording of Philipsz's fragile voice singing sad folk songs was largely drowned out by ambient noise.

This is Susan Hiller’s first exhibition since her Tate retrospective in 2011, and as it includes work from the 1970s to the present, it can also be seen as a retrospective of sorts. But since the selection was obviously governed by what was available for sale, it inevitably offers a piecemeal view of her achievements.

A finely honed and spacious selection dating from the 1950s to now, looks in acute focus at the work – a scatter of drawings, a print, but almost entirely paintings – of Frank Auerbach, (b 1931). An only child, he came without his family, from Berlin to England in 1939. His parents were murdered in the Holocaust. He is now one of the most remarkable painters of our time.