Every now and then, a sci-fi-like vision of the future bubbles up from the world of technologists and venture capitalists.
The latest of these is called "the metaverse".
Depending on who you talk to, it's either a utopia or dystopia.
Some say it's overhyped - won't get off the ground or is already obsolete - while others say it's an inevitable future, and nothing short of revolutionary.
But probably the most important thing you should know is that it's attracted a tonne of investment.
And a host of powerful corporations think you'll be inhabiting and using it fairly soon.
If that's news to you, that's no problem. They're building it anyway.
So what's it all about?
'The successor to the internet'
Two months ago, Facebook's Mark Zuckerberg shared with his employees a new, ambitious vision for the company.
The "overarching goal" of all the company's divisions, from ad sales to virtual reality, was to "help bring the metaverse to life".
The trillion-dollar social media company would transition to "a metaverse company".
"In many ways, the metaverse is the ultimate expression of social technology."
The metaverse he imagined was a virtual environment where users (via digital avatars) could interact with each other in real time.
In this vast and immersive one-stop shop, users can play games, buy digital commodities including real estate, go to school, watch the news, meet people, and so on.
From one perspective, it's the next version of the internet.
From another, it's just a better version of the online world Second Life, which launched in 2003 (and is still puttering along).
Meanwhile, other companies have also been telling us about the coming of the metaverse.
Tim Sweeney, boss of Epic, which makes Fortnite, recently said the company aimed to build "something like a metaverse from science fiction".
Microsoft chief executive officer Satya Nadella has said his company is working on building something called the "enterprise metaverse" where "the digital and physical worlds converge".
David Baszucki, the founder of the $US41 billion gaming platform Roblox, recently wrote: "The metaverse is arguably as big a shift in online communication as the telephone or the internet."
Heady stuff! But beyond the hype, the idea of the metaverse is an old one.
William Gibson introduced the concept of a virtual collective "cyberspace" in the 1984 novel Neuromancer, and Neal Stephenson coined the term itself in the 1992 novel Snow Crash.
As it happens, both these novels are dystopias where people take refuge in virtual universes to escape crumbling societies.
Now internet technology has advanced to the point where we can (maybe) build the metaverse for real.
A convergence of gaming, social, and commerce
In August, Zuckerberg launched a new virtual reality (VR) app, Horizon Workrooms, that was billed as part of his realisation of the metaverse.
Many reviewers said it was boring.
It's a bit like Zoom, but with virtual reality. Users (wearing a $US300 Oculus headset) choose a legless cartoon avatar and then sit at a virtual conference room having virtual meetings with co-workers.
More than one reviewer wondered why anyone would bother with the hassle of an expensive headset and arduous set-up process.
"Never in my life have I gone to an office and thought, "If only this could become an intense VR application!" a reviewer for New York Magazine wrote.
So not everyone's sold on the metaverse idea.
But it's early days and other parts of the metaverse will be designed to be more fun.
Think of the metaverse as an extrapolation and convergence of many existing parts of the internet, said Nick Kelly, a senior lecturer in interaction design at the Queensland University of Technology.
"There's a gaming track, there's a social network track, and there's the blockchain track, which is the economic side of things" he said.
"People are starting to think, 'what happens if you bring all these things together?' And we're getting pretty close to visions that we see in sci-fi books and sci-fi movies."
In April, Epic Games raised $US1 billion in funding to invest in the metaverse.
Epic makes Fortnite, which looks like a proto-metaverse: as well as a hugely popular game, it's a social network, a virtual showroom for intellectual property, and a marketplace for in-game currency.
In Fortnite, for example, Disney-approved Star Wars avatars rub shoulders with avatars wearing NFL-approved player uniforms. These in-game items have been bought with Fortnite's "V-Bucks".
"That's the vision that the big tech companies promote," Dr Kelly said.
"When you hear people talk about the metaverse, they'll get excited about things like intellectual property being able to be transferred from a movie into all of the different worlds that you're a part of.
"Your friends are seeing the things that you've bought and everybody is able to buy these things with a cryptocurrency."
One big shopping mall?
But these visions, he adds, may not come to pass.
Or they may come to pass, but turn out to be not so great.
A metaverse administered by Facebook might not be a place you want to go.
"One possibility is the metaverse looks something like Facebook 2.0 and people don't really love it," Dr Kelly said.
"Facebook's business model is about advertising and covert surveillance.
"The more time that we spend in virtual worlds, and the more that our human interactions are mediated by an online platform, that could increase the degree to which we are advertised to, and the way that data from us is extracted."
For the record, Zuckerberg says the metaverse he imagines won't be owned by anyone and will be operated by many different players.
He also says Facebook won't data mine conversations in Horizon Workrooms.
At the same time, the metaverse he describes sounds like one great shopping mall and interactive advertising experience.
"I think digital goods and creators are just going to be huge ... in terms of people expressing themselves through their avatars, through digital clothing, through digital goods, the apps that they have, that they bring with them from place to place," he said in July.
"Being able to basically have your digital goods and your inventory and bring them from place to place, that's going to be a big investment that people make."
Building the augmented and virtual reality technology to power a metaverse will cost Facebook billions, the company says.
It'll need to sell a lot of virtual magical swords to earn that back.
You can build it, but will they come?
The prize seems sweet to investors, but can fickle consumers be won over?
People have been expecting virtual reality, for example, to become ubiquitous for the last 20 years, yet it remains a novelty, even in gaming.
The same is true for VR's cousin: augmented reality.
About a decade ago, Google invested millions in developing "Google Glass", AR headsets that now gather dust on shelves.
The failure of the metaverse idea would be "a repeat of Google Glass on a much grander scale," said Dave Karpf, a media academic at George Washington University who has been critical of the hype.
"Funding would dry up for a while ... but after a decade or so, I'm sure technologists and venture capitalists would decide 'this time will be different' and would start throwing money at the idea again.
"The metaverse idea cannot fail. It can only be failed."
At the root of the problem, he said, is the stubborn unpopularity of virtual reality.
"We've had access to affordable VR headsets for several years now ... people are still really only using them for video games (and, I suppose, porn).
"That suggests to me that VR is mostly a novelty product."
Dr Kelly said this might turn out to be true.
"When you get down to it, people are rather attached to the physical world," he said.
Or it may succeed, in which case we should be thinking about what kind of metaverse we want to build and inhabit.
"Very often these dialogues become, 'this is the future, it's coming towards you'. It doesn't have to be like that."
The future of the internet can be shaped, he said. It could be designed to make human lives better.
Or it could be just another place to hook attention, mine data and sell commodities, Dr Karpf said.
"The things that are likely to make the metaverse bad if it were to take off, are the same things that make other parts of the internet experience bad (broadly, surveillance capitalism)," he wrote by email.
"[The metaverse] could either make things better or worse, depending on the incentives we build into it."
- ABC