Dear Dr. Fringe, is time travel possible?
That depends on what you mean by ‘time travel’!
According to Einstein’s theory of relativity, time is relative to the observer or object experiencing it. For instance, if you were to set two clocks at exactly the same time here on Earth, and then you were to send one of those clocks into orbit, the clock in space would be slightly ahead of the clock on Earth. This is because the force of gravity, being larger when closer to the Earth, actually has an effect on the passage of time.
The phenomena itself is known as time-dilation, a very real, very important fact of the universe. For example, all of our GPS satellites are required to account for this difference in time. If they did not, their locations would eventually be incorrect, and anyone using a GPS would eventually find themselves lost!
Remember that scene from the blockbuster film Interstellar? When the team of astronauts arrive on the planet near the supermassive black hole ‘Gargantua’? This was the reason why an hour on that alien planet was seven years back on Earth–the immense gravitational influence of Gargantuan was warping space-time itself!
So yes, in a sense, time travel is sort of possible, but not in the way that you’re probably wondering.
As for traveling back in time (Like you see in movies like The Time Machine) some scientists believe it may be possible if a hypothetical “negative mass” exists. As physicist Ethan Seigel describes in his article for Forbes, if some advanced civilization in the far future were to accumulate enough positive energy to bend space-time in one direction with a supermassive black hole, and then do the same but with negative energy (thereby bending space-time in the opposite direction), they could bring the two opposing, supermassive black holes together to create a quantum wormhole. These wormholes, according to American theoretical physicist Kip Thorne and his colleagues, could hypothetically allow for the creation of Closed Time-like Curves (CTC’s), the experience of which is effectively described in the Stanford Encyclopedia of Philosophy:
“A CTC can be thought of as the world line of some possible observer whose life history is linearly ordered in the small but not in the large: the observer has a consistent experience of the “next moment,” and the “next,” etc., but eventually the “next moment” brings her back to whatever event she regards as the starting point.”
Another highly hypothetical means of time travel was proposed by American astronomer Frank Tipler in 1974. Tipler suggested that if one could accumulate a material that is at least ten times the mass of our sun, then roll that material into a thin cylinder shape that is infinitely long and spin it at least a few billion revolutions per minute, one could, within the parameters of the theory of relativity, create a time machine that does not require negative mass. The vehicle that would enter this time machine would have to follow a carefully planned spiral trajectory along the surface of the cylinder to enter the very same CTC as described by Thorne; they could then effectively go back in time by as much as billions of years.
So, within the realm of hypothetical possibilities and borderline impossibilities, time-travel is perhaps possible! Unfortunately, this won’t be happening within any of our lifetimes. The amount of energy, resources, and time required to build any such device is far beyond any of humanity’s current capabilities.