There are two ways to travel through time: you could go forward, or you could go back. The crazy thing is, people are traveling forward in time as you watch this video. Traveling to the past can be a bit more tricky due to universe-ending paradoxes. But new research suggests time travel in both directions is not only possible but safe as well. The question is: would you do it? At the most basic level, time travel is all about speed, space, and gravity. For example, a second for someone standing on Earth will be different from a second for someone who is moving close to the speed of light or near a black hole.
And although we don’t have the technology to go that fast yet, according to mathematics and science, this is how time works. We can even observe time shifts in action above our world right now as time travelers whiz by at 17,130 miles per hour. Where are these intrepid explorers of time you may ask? On the International Space Station. That’s right, flying above your head right now is the crew of the International Space Station and they are technically traveling both through time and space. The reason for this is that they are moving much faster than we are here on Earth. The faster someone is moving; the slower time goes for them relative to someone who is standing still or moving slowly.
This is just how the universe works. Therefore, the astronauts on the International Space Station are experiencing time slightly slower than you are on Earth. To be fair, it is not much slower, but it is still happening. Scott and Mark Kelly are both astronauts for NASA. They are also identical twins. However, Scott has spent 520 days in orbit while Mark has only logged 54 days in space. Since they are identical twins they were born on the same day only six minutes apart. But Scott’s additional time circling the planet at high speeds means he is technically 5 extra milliseconds younger than his twin brother who has spent more time on Earth. Mark has traveled 5 milliseconds forward in the future from his perspective.
This is an imperceptible amount of time, but it is cool to think about. Not only is time travel real, but it’s happening whenever someone is in orbit above the planet. The speeds at which our current spacecraft move are nowhere near fast enough to travel a significant amount through time, but this may not always be the case. If you were an astronaut on the first-ever spacecraft to travel 99.999% the speed of light, you would time travel into the future in a significant way. At this speed, every second on Earth is just under 20 hours for you on the light-speed spaceship. This means that if you traveled just under the speed of light for one day you would have been speeding along for 86,400 seconds.
When you return to Earth and stop moving you will only have aged one day, but on Earth, 72,000 days will have gone by. In simpler terms, you would have traveled about 197 years into the future. This form of time travel is theoretically possible once the technology exists. However, until then, the primary source of human time travelers will be anyone who orbits the planet at high speeds. Traveling forward in time is the easy part. It is traveling backward in time that leads to some problems. That being said, you are somewhat of a time traveler yourself every time you look at the night sky. Since everything in space is far away, it takes a long time for the light from stars to reach us here on Earth.
This means when you look at stars you are looking back in time at how that star looked hundreds, thousands, or even millions of years in the past. For example, the North Star, also called Polaris, is located in the handle of the Little Dipper or Ursa Minor constellation. Polaris is approximately 323 light-years away from where you are standing when you go stargazing. Whenever you see Polaris, you are looking 323 years into its past. If Polaris exploded right now, it would not disappear from our night sky for another 323 years. And if you want to time travel a little closer to home, all you need to do is look at the moon. Whenever you observe the moon, you are looking into the moon’s past by about a second.
This is because it takes the light reflected from the moon around 1.3 seconds to reach Earth. So, observing the past isn’t so hard, but traveling to the past is a whole other animal. One way that someone could travel back in time is by using natural phenomena in space called wormholes. It is hypothesized that these “tunnels” connect two different points in the universe. But wormholes may not just connect space; they might connect various points in time as well. To be clear, no wormholes have ever been found, but science seems to suggest that they are not only possible but may be more common than we think. When talking about the universe it is important to remember space and time are closely intertwined. They are sometimes treated as one variable called space-time.
The way a wormhole may work is that a massive amount of gravity folds space-time in on itself and connects two points that are incredibly far apart making traveling between them almost instantaneous. If this is the case, the wormhole might do the same thing to two points in time as well. Therefore, if traveling through a wormhole is possible without being crushed by gravity, torn apart by interdimensional turbulence, or being blinked out of existence by some unknown force, time travel may be possible by entering one end of a wormhole and coming out the other. But wormhole time travel leaves us with a couple of problems.
First and foremost we haven't found one yet, and second, we have no idea what would happen once inside of the wormhole. However, there is some good news; scientists have been cooking up other ways to travel through time. One idea is by using what is called a Tipler Cylinder—named after the astronomer who proposed it—or an Infinite Cylinder. This time machine consists of a very long, indestructible tube. The tube would be filled with matter equal to 10 times the mass of our sun which would create a very dense spaghettified black hole. The whole cylinder containing the stretched-out black hole would then be spun billions of revolutions per minute.
The rotation of the elongated black hole would cause space-time to distort in a way that would allow a ship traveling on a precise trajectory through its ripples to travel back in time and end up in the past. The researchers who are studying this form of time travel have concluded the only way the device would work is if the cylinder was infinitely long, or made out of some unknown material that could contain the black hole and allow for it to somehow curve back in on itself. So, we are a long way from making the Infinite Cylinder a reality. This type of time travel would be on a “closed time-like curve” meaning that to avoid any sort of paradox the time travelers who went back in time would have previously existed wherever they ended up.
It is incredibly confusing, and science has found no way to explain this phenomenon yet, but the time travelers would somehow need to be part of the past and the future at the same time. Trippy right? Another cutting-edge theory in the quest for time travel comes out of the Technion-Israel Institute of Technology. It is here that theoretical physicist Amos Ori came up with the idea of making a time machine out of space itself. His vision consists of creating an area in space that is wrapped in itself like a donut. This would create a donut-shaped vacuum where timelines would collapse in on one another by using gravitational waves to manipulate space-time. Therefore, a time traveler could enter the timeline at one spot and exit at some point in the past.
There is a catch to this type of time machine, however. The time traveler could only travel as far back as to when the time machine was turned on. This is because time would only be able to fold in on itself as far back as the first instance of time within the donut-shaped space vacuum. Another key challenge would be to control the gravitational fields at will. This is theoretically possible, but we are nowhere near having the technology right now. To send someone back in time, they would need to be launched through the vacuum while the gravitational field within it was simultaneously shifted to allow the traveler to loop back to an earlier point in the timeline.
Without the precise control of gravitational waves to manipulate space-time the donut-shaped time machine wouldn't work. Putting aside the technical issues that need to be overcome before time travel is possible, there is another problem that has been plaguing scientists since they first thought of traveling back through time. This is the paradox. When traveling backward in time all kinds of crazy things can happen. The most famous is the “grandfather paradox.” It goes like this: if you are a time traveler who goes back in time and kills your grandfather then you would never have been born, and therefore, you could never have gone back in time to kill your grandfather in the first place.
Paradoxes like this have led many scientists to conclude that time travel to the past is impossible, or that the chances of a paradox happening may be so likely that it would end the entire universe. But recently researchers have been looking at these timeline inconsistencies in a new way. It is now hypothesized by some that if a paradox were to occur the universe would fix the problem itself. Take the “grandfather paradox” for example. If you went back and killed your grandfather, thus making it impossible for you to be born in the first place, the universe might adjust and you find out that the man you killed wasn't your grandfather at all.
Perhaps you were adopted and you just never knew. Scientists who believe that paradoxes will naturally correct themselves claim that this allows for time travel to the past without causing the universe to be destroyed by inconsistencies in the timeline. Whether this is true or not, it at least allows scientists to make calculations and theories about time travel to the past. When it comes to time travel there are some key takeaways. Traveling to the future is theoretically easy; all you need to do is go fast. Traveling to the past is hard and takes some fancy math, a lot of gravity, and technology we don't have yet. Not to mention that if paradoxes don't naturally fix themselves, traveling back in time could end the entire universe.
