If in the future there is a spaceship that can fly one light year in one second, can it fly out of the universe?

This article is based on answering the weird questions from netizens. I think it’s fun and can stimulate my imagination, so I’ll talk about it. See the screenshot for the original question:

Let's first talk about the origin of 1 light year and how fast 1 light year is in 1 second.

Light-year is a unit of distance in the universe determined by the scientific community. It is the speed of light in one year. The speed of light refers to the speed of light in a vacuum, c=299792458m/s (meters/second). Because such a large scale does not need to be so precise, it is usually measured at 300,000 kilometers/second.

So how long is 1 light year? First, we need to determine how many seconds there are in a year. A year is determined by humans to be the time it takes for the Earth to revolve around the Sun, but there are two ways to calculate this time.

One is the sidereal year, which is the time interval between the Earth's orbit around the Sun and a certain star when the Earth is at the same position as the Earth. The sidereal year interval is not strictly accurate, because the right ascension and declination of stars will change due to precession. The current sidereal year is calculated based on the J2000.0 epoch, which is 365.25636 mean solar days, or 365 days, 6 hours, 9 minutes and 10 seconds.

One is the tropical year, which refers to the time interval between two consecutive passes of the sun through the vernal equinox. That is, the time it takes for the earth's orbit to return to a virtual vernal equinox along the ecliptic, also known as the solar year. The tropical year is calculated in advance when compiling the perpetual calendar, so the time interval of each tropical year is not exactly the same, so an average value is taken over a century. The length of this century is 365.242199174 days, that is, 365 days, 5 hours, 48 ​​minutes and 46 seconds.

So how do we calculate a light-year? The time intervals between these two years are different, and the time of each year varies at different times. How do we measure the length of a light-year? In order to have an accurate quantitative measurement, the scientific community has developed a Julian year for astronomy, which stipulates that an astronomical Julian year is 365.25 days, and a year is determined to be 365.25 days * 24 hours * 3600 seconds = 31557600 seconds.

In this way, the light year has an accurate scale: 1 light year (symbol ly) = 299792458 meters * 31557600 seconds = 9460730472580800 meters. Large-scale measurement generally uses 1 light year ≈ 9.46 trillion kilometers.

If it travels a distance of one light year in one second, it means it runs 9.46 trillion kilometers per second, which is 31,557,600 times the speed of light.

Let's talk about how big the universe is.

After Einstein's theory of relativity came out, the relative view of space and time began to replace the absolute view of space and time that had been followed since ancient times. Hubble also discovered the law of cosmic expansion, supporting the Big Bang theory. Since then, the Big Bang theory has become the standard cosmological theory in the scientific community, believing that the universe expanded from a singularity about 13.8 billion years ago.

This completely overturned the absolute cosmology that had been believed for thousands of years and followed even after the emergence of modern science in the era of Galileo and Newton. This cosmology believes that the universe has no beginning, no end, no boundaries, and time and space are fixed and unchanging. The modern cosmology believes that time and space are relative and changing, and the universe has a beginning and an end, and is bounded but not bounded.

So how big is the universe? Or what shape is it? So far, the scientific community has only conjectures, and there is no standard answer. The more unified view is that the universe exploded from a singularity, and through the stages of inflation and high-speed expansion, it is still expanding faster than the speed of light on a large scale. The calculated radius of the observable universe is about 46.5 billion light years.

This is just an observable universe. According to physical laws such as the speed of light, humans can only observe such a large space. According to Hubble's law, the expansion of the universe is isotropic, the farther away, the faster, that is, all directions look the same, and the expansion speed is proportional to the distance, the farther away, the faster.

Therefore, standing on the earth and looking around, the farthest you can observe is 46.5 billion light years away.

But there are two unobservable ranges in the universe, one is called the past horizon and the other is called the future horizon. The past horizon refers to the period of 380,000 years after the Big Bang, when the temperature and density of the universe were too high, and even light could not be emitted. During this period, the universe experienced a sudden expansion, so the expansion speed was extremely fast. However, due to the lack of electromagnetic wave overflow, humans cannot currently observe this space.

There is now a theory that it may be possible in the future to understand the state of the universe during this "dark" period through gravitational waves.

The future horizon is at the limit of our human observation ability. Galaxies are moving away from us at several times the speed of light, out of human observation. Therefore, humans will never know how big the universe is outside the observable universe, and what is happening there. So, how big the universe is, humans may never know.

After years of cosmic observations, the scientific community believes that there are approximately trillions to 10 trillion galaxies in the observable universe. Our Milky Way is just one of them, and the solar system is just one of the approximately 400 billion stars in the Milky Way.

The solar system is a planetary system with the sun as its core. The mass of the sun accounts for 99.86% of the mass of the entire system, which is 330,000 times the mass of the earth. The solar system has eight planets and hundreds of satellites, several dwarf planets, countless asteroids and comets, etc. The gravitational radius of the sun is about 1 light year. Don’t underestimate this small 1 light year. The farthest unmanned probe that humans have flown, Voyager 1, is flying out of the solar system at a speed of 17 kilometers per second. It will take more than 17,000 years to fly out of this 1 light year radius.

So, can one light year per second fly out of the universe?

The answer is definite: No.

We can do a simple calculation. If we fly at a speed of 1 light-year per second, it will take 196,575,521 years, or nearly 200 million years, to reach the edge of the observable universe with a radius of 46.5 billion light-years. However, if we fly out of the observable universe, a new observable universe will be formed with the spacecraft as the center, which will take nearly 200 million years to fly. How many observable universes are there ahead?

In the curvature of space-time in the universe, light is also bent and orbits around this curvature. Therefore, the spacecraft appears to be moving in a straight line, but it is actually moving in a curve and in circles, just like walking on the surface of the earth, moving in one direction without turning, and eventually returning to the starting point after circling the earth.

There is a saying in the scientific community that due to the curvature of the universe, if there is a telescope that can see infinitely far, looking forward in the universe, you will eventually see your own back. In other words, the light goes around and returns to the starting point.

Of course, if you are really traveling in a light-speed spaceship, you will not be able to feel the passage of time, as if you have traveled through the universe in an instant. This is the explanation of Einstein's time dilation theory, and it is also the essence of the relativity of space and time. The speed time dilation rate follows the formula: t'=t/√[1-(v/c) ^2]

In the formula, t' is the value of the velocity time dilation effect; t is the time recorded by the first clock of the low-speed observer; v is the speed of the second clock relative to the first clock; and c is the speed of light.

According to this formula, the faster the spacecraft is, the slower time passes. When the speed reaches the speed of light, time stops. Distance also has a length contraction effect. The faster the speed, the shorter the distance. When the speed reaches the speed of light, the distance is zero.

Some people may not believe this explanation, but the two predictions, or theories, of speed time dilation and gravity time dilation have long been proven to exist. Modern aerospace, as well as positioning and navigation in our daily lives, will be impossible if we do not take these two time dilation factors into consideration and make adjustments according to the theory of relativity.

However, Einstein's special theory of relativity limits the speed of matter movement. Any object with rest mass cannot reach the speed of light, let alone exceed the speed of light. Therefore, it is impossible for a spacecraft to reach the speed of light, let alone exceed the speed of light.

However, there are two theoretical supports for interstellar travel that can reach the destination at a speed greater than the speed of light. These are wormhole travel or warp speed travel. Although these two methods of travel are still in the theoretical fantasy stage, many people, including some scientists, believe that they can eventually be realized.

Although these two methods may reach the destination many times faster than the speed of light, neither of them actually allows the spacecraft to reach speeds above the speed of light. Instead, they are more like the "shortcut" in our daily life experience or the legendary "shrinking the earth" method, which uses some magical technology to make the journey shorter, and much shorter. For example, a distance of 100 light years becomes just a matter of seconds and can be covered in one step.

This way, there will be no time dilation effect, and people will feel that time is close to the normal passage of time. Therefore, even if this kind of interstellar travel is really realized, can human lifespan survive 100 million or even billions of years?

More importantly, the universe is in a huge space-time curvature. Theoretically, there is no space outside the universe, so all objects cannot break through the boundaries of the universe. This is what is called the universe is bounded but not bounded.

Specifically, the universe itself is synonymous with matter and time and space. Matter, time and space are a trinity and cannot exist independently. Time and space are constantly expanding due to the continuous expansion of the universe. Outside the universe that has not yet expanded, there is no time, space and matter. In this void, where can the spacecraft fly? This is a paradox in itself.

So, no matter how fast a spaceship is, it cannot fly out of the universe. What do you think? Welcome to discuss, thank you for reading.

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