When Professor Ronald Mallett was 10 years old, his father died of a heart attack. This triggered a desire to travel back through time so he could save his father's life. Now 72 and a leading US physicist, he is researching ways to make time travel a reality
Professor Mallett, you’ve devoted your entire career to the subject of time travel. Has it paid off?
I think so. In several experiments, Einstein presented the effect of speed on time. Subatomic particles live approximately 10 to 20 times longer when they move at the speed of light. If anything will be travelling into the future, it will be such particles first of all. However, if we one day have spaceships that can travel at nearly the speed of light, then we will be able to do so, too.
What are the physical principles that time-travel research is based on?
Mainly, Einstein’s general theory of relativity. According to this theory, time is influenced by gravitation. From this, you can see the possibility of time travel to both the past and the future.
How does that work?
Imagine a tensed rubber sheet, a bit like a small trampoline. If you threw a bowling ball on to the sheet, it would sag. A marble placed on the rubber sheet would roll towards the bowling ball. If you imagined the rubber sheet to be transparent then it would appear as though somehow the bowling ball was directly pulling on the marble. You could get the marble to orbit the bowling ball by giving the marble a little sideways motion.
According to Einstein’s theory, space is like the transparent rubber sheet, the sun is like the bowling ball and the Earth is like the marble. The Earth circles the sun because the sun distorts the empty space.
Could you explain this using everyday objects as examples?
Imagine a cup of coffee, where the coffee in the cup represents empty space and the spoon a circulating laser beam. Just as the spoon sets the coffee in motion, the beam will set the space in motion, but unlike with the coffee, you can’t actually see this with empty space. If I were to throw a coffee bean into the cup while stirring the coffee, the coffee would swirl the bean around. The same would happen if I were to throw a subatomic particle into the empty space that I’d set in motion with the laser beam. You can see the influence of the twisting movement on the particle, even though you cannot see the twisting itself actually happening. Because space and time are related, the movement of space could lead to the movement of time.
If we imagine time as a line, running from the past through the present and into the future, then we could go from the past to the present and the future and back to the past, by forming the time line into a loop.
Again using Einstein’s gravitational field equations, I was able to show that loops in time could be formed by circulating a laser beam, which could theoretically allow time travel back to the past. This work was subsequently published. So I was able to mathematically achieve my lifelong goal by showing the theoretical possibility of a laser-driven time machine.
What practical uses could developing such a time machine fulfil?
I believe that one day it could be used as an early warning system to inform people about impending catastrophes, such as hurricanes, tsunamis, floods or earthquakes. Thousands of lives could be saved.
Time travel with particles is one thing – but when and how might people be able to do it?
Serious research is really expensive, and a lot of money is required for the experimental phase. A major project financier is already involved in this. Once the space twisting by light has been demonstrated then the next phase can commence, which is to use the twisting of space by light to induce a twisting of time that would lead to time travel back to the past. The ultimate aim is to send messages to the past. All this research will take millions of dollars and many years.
What about the paradoxes that would develop from time travel?
Einstein’s general theory of relativity works for both the past and future. Paradoxes could only occur with journeys into the past, for instance if the time traveller were to change something that would lead to a completely different time line.
This is where quantum physics comes into play. In 1957, Hugh Everett III showed us that our universe may be one of several parallel universes that are similar but not identical. Later on, David Deutsch put this in more concrete terms: according to him, you could arrive in a parallel universe at a point in the past. If you were to intervene in the events of that universe, this would not influence the particular universe that you come from.
You have said that this is the century of time travel. Why?
So far in this century, new scientific and technical discoveries are being identified at a much faster rate than in any previous time in history. If the will is there, these developments could allow for time travel before the 21st century is over.