# How to Build a Time Machine

Since the publication of the science fiction novella “The Time Machine” by the British writer Herbert George Wells in 1895, topics related to time travel have been talked about and lasted for a long time. So, can human beings realize time travel and travel in time?
What is time and space?
Before building a time machine, we must first understand time itself and figure out what time is.
When you are comfortably bathing in the warm spring sun, have you ever thought that this is actually the sunshine 8 minutes ago? Because it takes about 8 minutes to “run” the distance of about 150 million kilometers from the sun to the earth, even for light. So, all we see is the past sun.
For a long time, people have generally believed that if it is 15 o’clock here, then it must be 15 o’clock on the moon, and it is even 15 o’clock everywhere in the universe. But in fact, it is impossible for you to set your watch to the universal standard time.
Many people believe that the speed at which time passes is the same as the speed of time. Under the razor clam W⒁猓 core is very bad toughness  Ye Mata caries  for suitable potential Jiong Jun   write reed.  The
reason why the GPS satellite navigation system can play a role is to calibrate the clock on the satellite every day. Time has no absolute value, and the speed is different in different places.
Therefore, people who want to time travel must abandon the traditional view of time and treat time as a dimension. Most people think that we live in three-dimensional space, but in fact we live in four-dimensional space. In addition to the three axes of length, width, and height in ordinary three-dimensional space, there is an additional time axis. Of course, thinking about time as a dimension doesn’t sit well with us.
Simply put, we make an appointment with our friends to meet on a certain floor of a certain building, and we must also make an appointment to meet at the same time. The fourth dimension of time is closely intertwined with other three-dimensional spaces, and physicists named these four dimensions “space-time”. Therefore, to be precise, the macroscopic world we live in is actually three-dimensional space and four-dimensional space-time.
Most scientists now believe that time, like space, is not invisible, and that they are structures that can be stretched, even tied in knots. If so, time travel might not sound so ethereal. In other words, if we could find a way to manipulate the fabric of space-time, we would be able to achieve real time travel.
Speed ​​Time
Machine Most of us live in normal time and space, but it is not alarmist that there are already time travelers among us. In fact, the astronauts on the International Space Station and the Chinese Space Station have already started time travel into the future.
You must be wondering, how did they manage to enter the future?
They mainly rely on speed. The space station orbits the earth at a speed of more than 27,000 kilometers per hour, and some people have lived in the international space station for hundreds of days and nights. By the time they return to Earth, they will have moved into the future by about 1 microsecond, or a millionth of a second. Therefore, we can also think of the spacecraft as a time machine, and its super fast travel speed can slow down time.
So, can time be manipulated?
Scientists hypothesize that a “light clock” with light moving vertically up and down is placed on the dashboard of a car, and when the car passes by, the light in the light clock seen by passers-by moves diagonally. Therefore, a person looking from outside the car sees the light traveling a longer distance. However, the speed of light remains the same for people inside and outside the car. Time is distance divided by speed, so people in cars spend less time. In other words, time passes more slowly for people traveling at high speeds. Scientists call this phenomenon “time dilation.”
The world’s largest particle accelerator of CERN is located in Geneva, Switzerland. For nearly half a century, scientists from more than 80 countries around the world have studied and experimented with time travel here. Now, they have discovered a useful time-traveling particle called a meson. The high-energy particles come from cosmic rays that bombard Earth’s atmosphere, but only last about a millionth of a second.
Scientists use particle accelerators to push mesons so that their speed is close to the speed of light, and their lifespan will be extended accordingly. That is to say, the time corresponding to the meson is getting slower and slower, while the time outside the accelerator is still the same as usual. In a sense, mesons have entered our future.
But using speed as a time machine is still fraught with obstacles. It turns out that mass corresponds to a certain amount of energy, and when the momentum of an object increases, its mass also increases. If an object moves close to the speed of light, the added mass will be close to infinity. For example, when a meson moves at a speed close to the speed of light, its mass is more than 7000 times that of when it is at rest.
Therefore, energy is one of our biggest stumbling blocks to time travel. Simply put, we are currently unable to get a human-sized object to travel anywhere near the speed of light. Even with all the energy known on Earth, we can’t get a rocket to travel anywhere near the speed of light.
Gravity Time
Machine There is no unparalleled road. We certainly have another way to achieve time travel, and this method can not only take people into the future, but also take people back to the past. The method recognized by scientists to leap forward in time, in addition to relying on speed, is to rely on gravity.
Simply put, gravity demonstrates how mass bends (or distorts) the fabric of space-time. Assuming that the mass of an object is large enough to compete with stars and black holes, it can greatly bend space-time. The more massive the object, the greater the effect of shocking or bending the fabric of space-time. The Hubble Space Telescope has shown that light bends its path as it travels through the Milky Way, proving that mass can bend space-time. And the curvature of space-time will help us build time machines, because when gravity bends space-time, it has an actual effect on the passage of time.
Time passes more slowly on the first floor of a skyscraper than on the top floor. Because the closer to the surface of the earth, the stronger the gravity, the more curved space-time, and the slower time passes. Although this is a very small difference, if you stand on the top floor for 100 years, then your watch will run 5/100,000ths of a second longer than the watch on the first floor. So, in a sense, the earth itself is a time machine.
This effect is even greater if we change the scene to space. In orbit at great distances from Earth, time passes at a different rate than it does on the surface, which is important for GPS. We have to keep the ground and satellite clocks in sync for these systems to function properly. And because the gravitational field where the satellite is located is relatively weak, the time there passes faster, with a difference of about 50 microseconds in one day. Sat nav doesn’t work if we don’t correct for the difference in rate of time passing.
Earth’s gravity and the amount of warping it causes to space-time isn’t enough to help us travel back in time, but there are places in the universe where gravity has warped space-time significantly. Space-time is mostly flat, but in a black hole it curves sharply. The gravity of a black hole stretches and bends the space-time around it, making it an incredibly deep cone. Because its gravity is so strong, time inside a black hole slows down considerably.
For those who want to time travel, entering a black hole may be a way to achieve their wishes. However, in a black hole you are bound to hit a singularity, which is the densest point in a black hole. Therefore, you will be crushed to pieces at the singularity.
However, scientists soon discovered cosmic strings, thin, long, highly energy-concentrated tubes that were hypothesized to form during the Big Bang. It is speculated that a 1-meter-long cosmic string would have a mass greater than that of the Earth, so it would also warp space-time. Therefore, if two infinite cosmic strings pass by each other, a time machine can be created. Scientists assume that there is a spaceship traveling faster than the speed of light, orbiting around the two cosmic strings, then it can come back before it sets out.
However, according to the current cosmic string theory, it takes about half the mass of the Milky Way to go back to 1 year ago. And to control such a large mass, it is necessary to have the ability to dominate the energy of the entire galaxy.
The various theories of time travel may seem far-fetched, but for more than a century scientists have combined knowledge and imagination to try to prove that time travel will happen. Someone may have traveled only microseconds into the future, but scientists who study time travel are still moving on.
Because every great adventure actually starts with a small first step.