On June 28, 2009, famed English astrophysicist Stephen Hawking threw a party. He was the only one there, and no one else came – but that’s exactly what he expected.
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The reason why no one came was because Hawking hadn’t sent out any invitations – yet. He rented a space at Cambridge University in the UK, decorated it with balloons and streamers, set up food and drink and then sat and waited for a few hours before leaving. Only then did he send out the invitations.
Hawking’s party was no ordinary event – it was a time travel party, held for future descendants should they ever crack the mystery of time travel. His experiment was in ode to one of the biggest puzzles faced by modern physics.
But why do scientists believe it to be possible, and even probable?
According to a December 2023 report in US-based Discover Magazine, the general theory of relativity offers several scenarios that allow travel to the past, since it posits that gravity is the bending and curving of time and space in response to matter and energy. In this case, time travel is just about finding the right curvature of spacetime.
For instance, one scenario talks about a long cylinder, which rotates fast enough to allow you to travel a corkscrew path around it, to land in the past. Another scenario is the creation of a wormhole, so that you can go through one end in the present, and end up in the past on the other.
Unfortunately, no such long cylinders exist naturally in the universe, and wormholes need exotic matter with negative mass to stabilise themselves – this mass doesn’t exist, as far as scientists can tell. So, it appears that every time astrophysicists try to conjure a time travel setup in general relativity, something in the universe prevents its realisation. Still, no hard and fast rule outright prevents it from being possible, so scientists persevere.
Like many others, Hawking believed that the solution to the problem would come in the form of an advanced theory of gravity, which has yet to be discovered. If this is likely in the future, that means our descendants will one day figure out time travel. If they do, historical records offer an open invitation to Hawking’s 2009 party – one they can use to visit him, and prove him right.