“A supermassive black hole is a time machine. But of course, it’s not exactly practical. It has advantages over wormholes in that it doesn’t provoke paradoxes. Plus it won’t destroy itself in a flash of feedback. But it’s pretty dangerous. It’s a long way away and it doesn’t even take us very far into the future. Fortunately there is another way to travel in time. And this represents our last and best hope of building a real time machine.”
Hawking says: “Although I cannot move and I have to speak through a computer, in my mind I am free. Free to explore the universe and ask the big questions, such as: is time travel possible? Can we open a portal to the past or find a shortcut to the future? Can we ultimately use the laws of nature to become masters of time itself?”
Several of the planet’s leading scientists, including Charles Liu (author of “One Universe: At Home In The Cosmos”), Brian Greene (of “The Elegant Universe”) and Michio Kaku (“Hyperspace”) float a raft of objections to the concept of time travel. True to Clarke’s statement, sometimes affectionately known as “Clarke’s Law”, each objection seems more like reason to expect time travel than rule it out.
Professor Greene states that all time-travel theories operate at the very boundaries of known physics, and are therefore unlikely to work. As opposed to, say, the boundaries of our understanding being where new discoveries are made. As Sir Clarke said years ago: “The only way of discovering the limits of the possible is to venture a little way past them into the impossible”.
The other chief objection is the incomprehensible amounts of energy required to punch a hole in spacetime, or stabilize a wormhole, or engineer a double-cosmic-string-ring (yes, that’s a real astrophysical concept) capable of bending space hard enough to let us pop back to the past. One point eighty-one jigawatts just isn’t going to cut it here, whatever “jigawatts” turn out to be, and most calculations show that powering a time machine with a lightning strike would be like powering a sixteen-wheeler with a bag of jelly babies. (So it seems Marty won’t be getting back to the future after all).
Of course, the idea of lighting up New York would have had you committed to a mental home in the early eighteenth century. Pre-electricity, schemes were being suggested to transport the increasing numbers of people to the scant available heat and light in times of need.
Understand: the amount of energy we now take for granted was so vast, so utterly unimaginable to people in the past that they were preparing to restructure their whole society rather than even attempt to generate it. Of course, this doesn’t guarantee that we’ll be able to pop back and tell them. The false argument of past scientific ignorance, the “didn’t scientists used to think the world was flat” gambit fails because we know so much more now. The key to progress is our cumulative knowledge, developed and refined by generations of researchers into a vast, accurate body of knowledge. We are far more likely to be able to find what’s possible than at any point in history. What we know so far is probably right, and allows us to make predictions about what might be possible.
But until we can explain absolutely everything, we should still steer clear of saying something is impossible. Here’s what our beloved Professor Hawking says about time travel in a post on The Daily Mail:
“Time travel was once considered scientific heresy. I used to avoid talking about it for fear of being labeled a crank. But these days I’m not so cautious. In fact, I’m more like the people who built Stonehenge. I’m obsessed by time. If I had a time machine I’d visit Marilyn Monroe in her prime or drop in on Galileo as he turned his telescope to the heavens. Perhaps I’d even travel to the end of the universe to find out how our whole cosmic story ends.
“To see how this might be possible, we need to look at time as physicists do – at the fourth dimension. It’s not as hard as it sounds. Every attentive schoolchild knows that all physical objects, even me in my chair, exist in three dimensions. Everything has a width and a height and a length.
“But there is another kind of length, a length in time. While a human may survive for 80 years, the stones at Stonehenge, for instance, have stood around for thousands of years. And the solar system will last for billions of years. Everything has a length in time as well as space. Traveling in time means traveling through this fourth dimension.