Can humans travel through time, have you ever wondered?

In books and in movies, our favorite characters have time machines to travel to the past or to the future. But in real life it's not so easy.

Edward Farhi, director of the Center for Theoretical Physics at the Massachusetts Institute of Technology (MIT): "Changing the clock's speed is really consistent with the laws of physics. You can totally jump around. to the future".

However, according to Mr. Farhi, most physicists think we can travel to the future, but going back to the past is much more complicated and complicated.

The idea of time travel is derived from Einstein's theory of relativity, which states that the passage of time is relativistic, depending on how fast you are moving. The faster you move, the more time seems to slow down. That is to say, a person traveling aboard an extremely fast spacecraft will experience a two-week trip that seems to last 20 years with people on Earth.

In theory, in the above way, a person who wants to travel to a certain time in the future only needs to use a means of transport fast enough to erase that certain period of time.

However, this type of time manipulation only affects the rate at which time moves forward. No matter how fast your speed, time will only move forward. For this reason, scientists can't predict how humans might have returned to the past.

Some anomalous solutions to Einstein's equations reveal that time travel to the past is possible, but to do so may require the energy of the universe and the universe is possible. destroyed in the process.

And even if science can find a way to make the return to the past a reality, there are still countless logical paradoxes to be solved.

"For example, when you go back in time, you can prevent your parents from coming together and giving birth to you. That could be the end for it all," Mr. Farhi said.

Travel to the past

Traveling to the past is impossible. Even sending information back to the past is hard to imagine because it will change things that have already happened, but no one can change things that have already happened. For example, let's say you were swinging on a curved bar and fell and broke your arm. What if you could go back in time and tell yourself not to play it? If you do, you won't fall and you won't break your arm. But if you didn't break your arm, you wouldn't have to go back in time to tell yourself not to swing like that. So what will happen to your arm, is it broken or not?

If you find thinking like that really troublesome and complicated, many people feel the same way.

Time travel is a very difficult thought for most people to imagine. That's because when we think of time, we think of it as a straight line with many things happening one after another.

If we could go back in time and change something that happened, we would change the order of that line. That would break a rule called "causality".

Causality is the rule that a cause (for example, your actions) happens before there is an effect (the result of your actions).

In the example you play the swing bar, the cause is that you fell and as a result you broke your arm, the broken arm is because you fell.

Cause and effect is one of the unbreakable laws of the universe. Breaking this law will have unintended consequences for the universe and all of us. According to experts, because the universe has this law, it is impossible to return to the past, otherwise this rule will always be broken.

Travel to the future

Technically, we are always moving into the future, because time is always passing. For every second, we move one second into the future. But this happens to everyone, so that's not called time travel, right?

Believe it or not, the truth is that each person can perceive time passing at a different rate. The passage of time for a person who is moving very quickly is very different from that of a person who is standing still. This is a very complex idea, called "time dilation".

A person flying from Hanoi to Da Nang will find time passing faster than someone waiting for him or her at the airport for the duration of the flight. So why don't we notice this difference?

That's because you have to be moving much, much faster than the plane before you start to notice the dilation time. Even if you fly around the world, the time you feel is only a billionth of a second different from the person sitting at home.

The only way for scientists to know the expansion time is through extremely precise experiments to measure it.

However, time dilation can't help us with time travel either. If you were to fly around the world for more than 4 million years, the people on the ground would spend only 1 second longer than you.

How fast can we go?

If it all depends on speed then the answer must be to go faster. If you can go fast enough and long enough, through hundreds of ordinary years in just one short trip, it might feel like you're traveling into the future.

Unfortunately, the "fast enough" here has to be the speed of light, which is much faster than any human means available today. Light travel is about billions of kilometers per hour.

The fastest man-made object is the Parker Solar Probe of the US Space Agency. This ship was launched in August 2018. But its fastest speed is only 0.064% of the speed of light, which means light travels 1,000 times faster than this ship.

All of this shows that if people want to reach the future, there is still a very, very long way ahead.

Retrospective

So we can't time travel. But we can still look back at the past every night.

Light has a fixed speed. It travels extremely fast, but objects in the universe are also so far apart that light takes a long time to travel from distant stars and planets to our Earth. Light from the Sun also takes 8 minutes and 20 seconds to reach Earth, which means we saw the Sun in the past 8 minutes and 20 seconds. But remember never to look directly at the Sun because it can damage your eyes.

The closest galaxy to our Milky Way is the Canis Dwarf galaxy, which is 25,000 light-years away. This means that light takes 25,000 years from there to reach Earth. When we look at this galaxy through a telescope we see it from 25,000 years ago. So even if we can't time travel by ourselves, we can still look up at the sky every night and observe the past.

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