"We are the eternal survivors, riding through time!" Nik Turner, of Space Ritual, calls out, to huge applause and whoops and a noticeable absence of both spliff haze and derision, as he led his band into a song called 'The Ritual of the Ravaged Earth', with its chorus proclaiming that, "we're so tired of making love/it's so cold at the edge of time."

Well, he should know. Gong and Space Ritual are incarnations of bands that have been going for 40 years. 40 years! Granted, both bands have had more offshoots, reformations and splitters than the People's Front of Judea in that time, but they're still going, reworking old familiar songs, leaving others alone, using new (well, -er) technology. Including both bands' use of cheesy stock photos and strobe effects last seen on an epilepsy-inducing polygontastic virtual-reality screensaver and responding to contemporary events in sometimes-awkward style – as in Gong's new song about 'Banker Wankers' where the main thrust seems to be that the banking crisis would never have happened had hopped-up derivatives traders swapped weed for coke. And there was almost an attempt at rapping.

Not everything onstage is theatrically perfect. That's probably an understatement. Set lists for both bands seem plucked from a hat; tempos are all over the place. It's patronising to applaud someone for hanging around, in the same way it must really piss octogenarians off when some young kid is surprised they can speak in full sentences without dribbling on their shoes. But for every cringey moment, something great happens, because these are bands from another era that have chugged their way through everything that has happened over the last four decades and dragged it all behind them leaving music like sparkly-slimy snail trails. That last sentence was probably a cringey moment too. Can I just say: you had to be there?

Memory, especially when it comes to styles or ways of seeing that are linked to specific cultural moments, falls apart when translated into electron streams. A cavalcade of centuries of music and video exists, online, in the eternal now. It's flat, it can be copied infinitely, it's digitally perfect, it's immortal, it can travel the globe in nanoseconds. Being alive isn't like that.

Scientists now think that when you remember something, you really only recall the last time you remembered that thing, and memory works like a time machine or shortcut to that previous state. But each re-remembering can be laced with whatever you're experiencing at the (new) moment of recall: a hangover, pissing rain, the smell of crunchy leaves or bus fumes or anything else at all. Memories are always tainted - or tempered - by the body, and by the passing of time. Digital recordings don't circulate like memories, they circulate like bank transfers.

There are a few strategies to counter this and bring out the difference. Hauntology is a good start. There's a slew of interesting hauntology blogs out there, like the spectral dimension and k-punk's hive-mind Found Objects. These blogs harpoon vaguely paranormal but mostly just mislaid cultural artifacts, and yank them back through server-farm wormholes with enough recoil to send you reeling.

Quite a few of the links there are of a vintage and aesthetic stretching between post war-modernism and technological utopianism, and 70s broadcasts influenced by folk music and vague bowlcut'n'rollneck socialism - points of origin for both Gong and Space Ritual/Hawkwind. There are some late Victorian ruins, some megaliths, some folklore, melted tapes, some stuff found in skips.

Hauntological blogs work best when someone posts a link that harks back to something so long unremembered that being confronted with it again brings on the awareness of decay, the dissonance between the way you felt upon first encountering something and in the present. Done right, there's a real physical quease.

It's an awesome strategy, but there's also a whole lot missing between the present and our hauntological triggers: what happened between now and then? There wasn't a complete gap, and while the sudden memory-harpoon can trigger physical memory by stitching two moments in time together, what about listening to stuff by people who travelled that whole long slow distance between eras that now feel light years apart?

There's another way to deal with the way digital memory denies the body's memory, and that's watching long-term space rockers go about what they do best. Have you ever wondered what might have happened if, instead of developing total digitisation and almost instant worldwide communication, people had developed space travel first instead? In 1969 ARPAnet was more of a reality than Near Light Speed travel to other stars will likely ever be in our lifetimes, but a lot of science fiction of the day had it the other way round, and journeys to the star - or sideways on psychotropics, or both - were the future. Yes, this got silly, but there's a joy to the silliness of Gong's mythology of pot-head pixies in propellerhead suits, flights to planet Gong in teapots, and space witches. (Or a poignancy to the silliness of Hawkwind's interstellar lament, 'Spirit of the Age', where a young space-pilot moans about how on his return to earth his girlfriend will be 'about sixty by now' because when he left she was underage and her father wouldn't sign the order to freeze her until his return. Relativity can stretch time and fuck up your love life - talk about being haunted and still alive!) Long journeys into space are the opposite of instant gratification. There's time to think, dream, get bored, fall in love, fall apart and freak out.

Space Ritual is really Nik Turner's Hawkwind, though singer Dave Brock's Hawkwind, also still active, has the official rights to the name. It's kind of cool that these bands can keep going when people leave. Long journeys have their casualties. So many of the songs Space Ritual kept in their set were written by science fiction god Michael Moorcock and Robert Calvert, crazy space truckers both. They drive: No song played lasts less than ten minutes, and a few could soundtrack the average commute. Calvert's 'Steppenwolf' with its refrain "I am a MAN WOLF! I am a WOLF MAN!" warped into something that could have been 'Black Magic Woman' or anything else from Santana's back catalogue, for that matter - and it is just fine. This happens more than once: the Cartesian 'body and mind' existential angst of 'Brainstorm' goes the same way, into jam-band noodling that is only bested by Turner's hail-spasms of sax-blasts. (See the video below but be warned, all of the live videos linked to here have worse sound than you'd find in a tiled bank of toilets set under a motorway bypass, but that is kind of the point. This isn't music for screens.)

This stuff is so overblown it's beyond absurd, and it's supposed to be. Gong's lead singer Daevid Allen sure has fun with his costumes - the guy looks down at six-footers' bald spots and has the build of a rack-stretched heron, and he comes onstage in a catsuit painted with a skeleton, a moth-like moon man suit (seen here in 'Oily Way'), a vest printed with eyeballs, and shirts reading 'banker wankers' and 'no one knows i'm a lesbian'.

Both bands are joined by a dancer called 'Miss Angel' who camps it up like a Edgar Rice Burroughs Martian Princess, with costume changes that could have been nicked from the Flash Gordon wardrobe trailer and moves from Kate Bush's 'Egypt' video. At one point she has this gold fluttery cape with winged bits that looked like what would happen if the Lunar Lander grew a vagina. Chrome Hoof: you've got competition.

When Gilli Smyth, Gong's other driving force takes over the vocals, her 'Space whispers' sounded like really sexy whalesong picked up at Jodrell Bank. She sings a song about witches, and how witches are free and they can do what they want and, "Don't let people tell you you aren't magic, because you are, we all are!" There are cheers. Crazy, or crazy-humane? Yes, there are flutes. Yes, there are keyboards that sounded like the Doors. It's goofy and wrong-footed sometimes, but when it rocks, it rocks, because it's alive, because Gong's jazzy chants and Space Ritual's buzzsaw motorik drive and even Miss Angel's twirling glittery wings all churn up the sense-memory in realtime. So yay for the old flesh and continuous streaming flows of ever-updating recall; yay for witches, time-travellers, stoner rocketeers who are still on some long-term voyage out, fading out maybe, but definitely here. Still here.