Is time travel possible?
The novel 'The Time Machine' by HG Wells released in 1895 was based on the concept of time travel. Introducing time as a fourth dimension, this novel predates Albert Einstein's theory of relativity. This novel said that it is possible to travel through time parallel to the other three dimensions.
Everyone can travel through time. Whether we like it or not, we do it. For example, we travel a year through time between birthdays. But it's just that our movement through time is always at roughly the same rate or speed, one second per second. One second per second is like saying one foot per second. But when we hear time travel, we think of traveling faster than one second per second. We have been seeing this in science fiction movies and novels. Is it really possible? Science says yes.
How is time travel possible?
A hundred years ago, Albert Einstein proposed a new concept of how time works. He called it relativity. His theory states that space and time are interrelated. He said one more thing. The universe has a speed limit. That is the speed of light. Nothing can travel at the speed of light (186,000 miles per second). But what does this have to do with time travel?
As far as science fiction writers are concerned, time travel is the subject of their imagination. Their portrayal of time travel involves characters traveling to the future and the past by sitting in some vehicles and machines.
According to the theory of relativity, if we travel faster then our movement through time slows down or our experience of time slows down. In other words, it slows down our aging process. Scientists have done many experiments to prove this to be true. One of them is like this. Two clocks are set at the same time. One of them is placed on the Earth and the other on an airplane flying in the same direction as the Earth rotates. After the plane returned from its round-the-world journey, scientists compared the time on the clock inside with the time on Earth. The time on the clock in the high-speed plane was slightly behind the time on the ground. What we can understand from this is that the clock on the plane traveled slower than the clock on the ground at a rate of one second per second in time.
Time travel in science fiction movies
Let's look at another example. If a spacecraft could travel at 99 percent of the speed of light, it would travel a distance of one light year in one year. While this is understandable, the strange thing is that for the passengers inside that spacecraft, their journey would have taken only seven weeks. This is due to time dilation as a result of relativity. Consequently, the astronauts would have arrived about ten months earlier in the future.
As far as science fiction writers are concerned, time travel is the subject of their imagination. Their portrayal of time travel involves characters traveling to the future and the past by sitting in some vehicles and machines. The idea of traveling back and forth through time to see the future and change the past can only be seen in science fiction. In real life, we don't know of anyone who has ever traveled back and forth in time. As noted scientist Stephen Hawking pointed out in his book 'Black Holes and Baby Universes', “The best proof that such time travel is not possible and will never happen is that we have not yet been invaded by visitors from the future.”
Actual time travel
Science favors small forms of time travel or time bending. Einstein's special theory of relativity states that time is an illusion, or sensation, that moves relative to the observer. A person traveling at a speed that is close to the speed of light would experience time and the resulting aging, boredom, etc. much slower than someone who is sitting still. In this regard, a study of two astronomers who were twin brothers is famous. They are Scott Kelly and Mark Kelly. Scott Kelly spent 520 days in space and Mark Kelly spent 54 days. This difference in duration resulted in a difference in their ages by milliseconds. It was caused by the difference in the speed of time that they experienced during their lifetime. Scott said that he was already born six minutes later than Mark, but the age difference increased to six minutes and 13 milliseconds due to space travel. The age difference between Scott Kelly and Mark Kelly was increased by milliseconds because Scott was in Low Earth Orbit (LEO, less than 1000 km above the Earth's surface, orbiting very close to the Earth).
Is time travel possible in everyday life?
Getting into a time machine and traveling back or forward a hundred years does not fit into current scientific logic. For the time being, it can only be experienced through movies and novels. But even if we don't know it, sometimes there are occasions in our lives where the concept of time travel becomes relevant. For example, GPS satellites are very helpful in our daily life. Most of the time we rely on GPS when going to a new place. Space agencies, including NASA, rely on highly efficient and accurate GPS to locate satellites in space.
A wormhole can be described as a shortcut from one point in space-time to another.
But did you know that time travel can be experienced with these GPSs? Our location on Earth can be accurately determined by a network of GPS satellites orbiting the Earth at very high altitudes. GPS satellites orbit the Earth at a speed of 14,000 kilometers (8,700 miles) per hour. Because of this, the clocks on GPS satellites tend to lag slightly (microseconds) behind those on Earth. Meanwhile, the altitude at which these satellites orbit is about 20,200 km (12,550 mi) above the Earth. According to Einstein's theory, clocks closer to those with larger gravitational masses would sense time more slowly. But at the height of the satellites, the Earth's gravity is relatively weak. So clocks on GPS satellites run faster than those on Earth. The combination of these two phenomena causes clocks on GPS satellites to sense time faster than one second per second. This means that GPS on the satellites and those on Earth who rely on GPS experience time at different rates. But scientists use some numbers to adjust the time on GPS clocks so that the difference is not felt by those on Earth. If this is not possible then there would be big problems. GPS wouldn’t be able to accurately determine their location or your location. A difference of microseconds in time, however, can result in a difference of miles per day. Just think about that situation. Even though you are very close to your destination, the GPS will tell you that there is still a long way to go.
Dramatic time travel thoughts
Even GPSs have very mild time travel effects. But for time travel to cause a dramatic difference of hours, months, or sometimes decades, there must be the influence of very strong gravitational fields. For example in black holes. The super-strong gravity of black holes bends space-time tremendously and folds it into itself. One such occurrence is a wormhole. We are familiar with this concept from science fiction movies. Einstein's theory of relativity was actually the first to come up with the idea of a wormhole. A wormhole can be described as a shortcut from one point in space-time to another. It's easy to think of us going down a black hole and coming out of another black hole in another world. But using a wormhole as a shortcut is not at all practical as Hollywood movies say. Because black holes have much more gravity than we can think. Its gravity has the ability to disintegrate anything that enters it.
At the same time, don't think that going through the black hole and the wormhole and landing in another world or another time are just imaginary ideas. Since we are thinking about the 4D world that includes the dimension of time, there is a possibility that the way out of the wormhole sometimes opens at some point in the past.
But these are only possibilities, that science cannot completely prove or disprove. Things that we think impossible can happen in any corner of such a vast universe. If the laws of physics support time travel, there would still be some paradoxical scenarios that defy common logic. Scenarios we cannot even imagine would happen. For example, killing Hitler in his youth or killing one of our own great-grandfathers.
What did Stephen Hawking say?
Hawking has always been skeptical of the idea of time travel into the past. He was concerned not with disproving time travel, but with the paradoxes or contradictions that it created. Such thoughts lead him to the concept of 'chronology protection conjecture.' It was the assumption that as-yet-unrecognized laws of physics, which could be discovered someday, preclude the concept of time travel into the past (its technical name is closed temporal-like curves). Until proven, it can only be seen as an intellectual's guess.
In 2009, Stephen Hawking threw a champagne party (which was broadcast on the Discovery Channel) to prove his point. But Hawking publicized the party only after it took place. This was his explanation for doing so. If time machines ever exist, someone from the future will read Hawking’s ad and walk back through time to that party. But no one such person from the future came to the party. This is not to say that there is no scope for time travel. But let's say it's unlikely to become a common occurrence on Earth.
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Turning the Clock: The Story of Time Travel