How many profound scientific truths are contained in one meter and one second? It may subvert your imagination

We live in a three-dimensional world, that is, everything we know has three spatial dimensions, namely length, width and height, which makes the world we see a three-dimensional world. Since the advent of Einstein's theory of relativity, people have realized that time and space are one in this world, and the time dimension runs through the three-dimensional space. Therefore, the world we actually live in is a four-dimensional space-time.

In the world we know, space is the extension of all material existence, while time is the process, order and continuity of material movement, which are not bound by people's will. People can only describe it by observing space and time and using certain tools.

This tool is the unit of measurement of time and space, and is the most basic tool for humans to understand the world.

In order to describe the size of various substances in the world, people invented scale units, such as millimeter, centimeter, meter, kilometer, etc., among which the most basic unit is meter; at the same time, in order to more accurately measure the nature of dynamic space-time, in addition to tools for measuring the size of matter, there must also be tools for measuring the movement process of matter, such as hours, minutes, seconds, etc., among which seconds are the basis.

Therefore, hours, minutes, seconds and millimeters, centimeters, meters and kilometers are the most commonly used units of measurement in people's daily lives.

With these units of measurement, we can almost measure the changes in various everyday things, such as an ant can crawl 1 cm in one second; the average person walks at about 4 kilometers per hour; a car can reach a speed of more than 100 kilometers per hour on the highway; the flight speed of an airliner is about 800 kilometers per hour, and so on.

These daily timekeeping and measurement units are sufficient for daily life for the general public. For example, 1 second is just a tick, and anything less than 1 second does not seem to have much meaning; and 1 millimeter is not even as big as a sesame seed, so it seems meaningless to subdivide it further.

However, in scientific measurement, these everyday units of length and time are far from enough. For example, it is very difficult to use commonly used units of measurement to describe some tiny things or even the microscopic world.

For example, in studying the insect world, scientists have found that different insects flap their wings at different speeds: flies need 3/1000 seconds to flap their wings, mosquitoes need 2/1000 seconds, bees need 5/1000 seconds, etc. Smaller things are even more difficult to measure, such as hundreds of millions of meters or hundreds of millions of seconds.

This description is very troublesome and inaccurate. In order to describe the microscopic world more accurately and conveniently, scientific research has given birth to increasingly detailed microscopic scales.

For example, the unit of length is below meters, centimeters, and millimeters, and is divided into micrometers, nanometers, picometers, femtometers, attometers, zemeters, and millimeters. 1 millimeter is equal to 1000 micrometers; 1 micrometer is equal to 1000 nanometers, and so on. 1 femtometer is 1000 trillionth of a meter.

Correspondingly, the time measurement units are also divided into smaller and smaller units. Below seconds are milliseconds, microseconds, nanoseconds, picoseconds, femtoseconds, etc. Each level is 1000 times smaller than the previous unit. For example, 1 second is equal to 1000 milliseconds, 1 millisecond is equal to 1000 microseconds, and so on. 1 femtosecond is 1000 trillionths of a second.

With these micro-units, it is much easier to describe the microscopic world. For example, the time interval for an insect to flap its wings can be described as: a fly takes 3 milliseconds, a mosquito takes 20 milliseconds, and a bee takes 5 milliseconds. Moreover, a more delicate and tiny microscopic world can be accurately described.

For example, human cells are only 5 to 200 microns in size, and bacteria are only 0.5 to 5 microns in size; viruses are more than a hundred times smaller than bacteria, only a few dozen to 100 nanometers in size; human DNA molecules are only 10 nanometers in size, but contain more than 20,000 genes and 3.16 billion base pairs.

The molecules, atoms, electrons that make up matter, and the photons that fill our world are even smaller units of scale. The diameter of a water molecule is about 0.4 nanometers, the diameter of a hydrogen atom is about 0.1 nanometers, and the diameter of the atomic nucleus is only about 1.7 femtometers.

With these tiny measuring tools, science continues to create high-precision measuring tools, such as femtosecond cameras. This camera can capture more than one trillion frames per second. Under this camera, the world's fastest speed of light becomes a snail, and those things at the millisecond, microsecond, and nanosecond levels that the human eye cannot distinguish, such as the sprint to the finish line of a 100-meter race and the unhurried 8-nanometer steps of motor proteins, are all clearly visible under the camera.

Modern quantum mechanics believes that the smallest scale that humans can understand is the Planck scale, that is, the Planck time and the Planck length. This is based on the inevitability of singularities deduced by general relativity, the existence of zero points in space and time, and the uncertainty principle of quantum mechanics, the degree of uncertainty depends on the Planck constant.

Planck's constant determines that the smallest unit of length is 1.6 times 10 to the negative 33rd power per centimeter, which is a scale 20 orders of magnitude smaller than the atomic nucleus; and the corresponding smallest unit of time is Planck time, which is approximately 10 to the negative 43th power per second, or one trillionth of a trillionth of a second.

The world that humans can or are currently aware of all started from the scale and time after the Big Bang.

Quantum mechanics concludes that anything shorter than this length and time cannot be accurately measured. Therefore, for modern physics, all theories fail at Planck spacetime, which is not the spacetime we can recognize, that is, it belongs to super-spacetime. For example, the inside of the black hole horizon and even the singularity, the Big Bang singularity and the things before it are the end of modern theories, or the end of spacetime, which humans cannot recognize.

Humankind's understanding of the laws of nature is still developing in depth in both directions, that is, it is constantly expanding towards the microscopic quantum world and the macroscopic depths of the universe.

Therefore, in addition to the units of measurement for the microscopic world, there are also units of measurement for the macroscopic universe.

Once you leave the Earth, it seems inconvenient to use the units of measurement that humans use to measure the Earth. The closest celestial body to the Earth is the Moon, which is about 384,000 kilometers away from us on average. Using kilometer-level units for measurement here does not seem to be a problem, but when you reach a farther place, it becomes a little inconvenient to use kilometer-level units for measurement.

For example, the Earth is about 150 million kilometers away from the Sun, so the average distance to Neptune is about 4.5 billion kilometers, and the average distance to Pluto is about 6 billion kilometers.

In order to facilitate the description of the distances between planets in the solar system, scientists have established an astronomical unit, abbreviated as AU, and set the average distance from the Earth to the Sun, 149.6 million kilometers, as 1AU. In this way, our average distance to Neptune is about 30AU, and the average distance to Pluto is about 40AU.

Modern scientific research believes that the gravitational range of the solar system's planetary system extends beyond Pluto. At the edge of one light year away from the sun, the sun's gravity forms an area called the Oort Cloud Belt, which is a densely populated area of ​​comets. These comets form a huge sphere that wraps around the solar system.

What does 1 light-year mean? It is the distance that light travels in one year. This is a unit of measurement for the larger scale of the universe. Outside the solar system, astronomical units are not effective for measurement, and light-years must be used.

The exact speed of light is 299,792,458 meters per second, or about 300,000 kilometers per second. There are 3,600 seconds per hour and 24 hours per day. Scientists have determined a Julian year to calculate light years, with 365.25 days per year. This means that each Julian year is 31,557,600 seconds, and the scale of light's movement in one year is 94,607,304,725,808 meters, or about 9.46 trillion kilometers.

This is 1 light year, a unit of distance, about 9.46 trillion kilometers. The gravitational radius of the solar system is about 1 light year, which is more than 63,000 AU when converted into astronomical units. Therefore, it is inconvenient to use astronomical units to measure outside the solar system. When measuring the distance between stars, light years are generally used.

There is also an astronomical distance unit that is larger than the light year, which is the parsec. The so-called parsec is a unit of measurement based on trigonometric parallax. It is called Parsec in English, abbreviated as pc. 1pc is about 206264.8AU, or 3.26 light years. However, in astronomical measurements, the more widely used unit of measurement is still the light year.

The standard cosmological model of modern astronomy holds that the universe originated from the Big Bang about 13.82 billion years ago. Due to the rapid inflation and expansion of the universe, the radius of the observable universe has now reached 46.5 billion light-years, and the observable universe contains about hundreds of billions or even trillions of galaxies.

The Hubble telescope has observed that the farthest galaxy is 13.4 billion light-years away from us, and the Webb telescope launched last year has further extended this distance by 200 million light-years, and found that the farthest galaxy is 13.6 billion light-years away from us. In other words, galaxies were widely formed within 200 million years after the Big Bang, which challenges the previous theory of the formation of the universe.

There are many methods for measuring astronomical distances, the main ones include the triangulation parallax method, the Cepheid period-luminosity relationship method, the galaxy spectrum redshift method, the Ia supernova standard candle method, etc., which will not be introduced one by one here.

Now there is a question that needs to be clarified. What is the basis of these scales for measuring time and distance? Are they accurate? We should know that a small mistake can lead to a big mistake. This is the most basic principle from ancient times to the present. In fact, we have already seen from the long introduction of the whole article that the most basic scale for measuring time and distance is meters and seconds.

Let us now briefly summarize how the meters and seconds used today came about and whether they are accurate.

The definition of meter originated in France. The original definition of 1 meter was: one ten-millionth of the distance from the equator to the North Pole, based on the meridian passing through Paris. Based on this length, a meter prototype was made of platinum and stored in the French National Archives. After several revisions, this platinum rod meter prototype was kept in the basement of the International Bureau of Weights and Measures in Paris, which stipulated that at 0 degrees Celsius and 1 standard atmospheric pressure, the distance between the two ends of the platinum rod was 1 meter.

However, this platinum rod rice prototype will still have extremely slight errors due to time, humidity, temperature, air pressure, etc.

As people's understanding of the speed of light becomes more and more precise, in order to make the speed of light an integer, the International Conference on Weights and Measures revised the definition of the meter in 2019, abolished the platinum rod meter prototype, and defined the meter as: "The distance traveled by light in a vacuum in 299,792,458th of a second" is 1 standard meter.

In other words, the exact value of the speed of light is 299,792,458 meters in a vacuum in one second, which is an integer. This is an extremely subtle correction to the scale of the original meter in the past, making the meter, the speed of light, and time a precise and unified measurement tool. Moreover, this standard meter is no longer a physical object, but the constant speed of light in a vacuum, and there will be no error.

There is also a most critical basic data here, which is seconds. Since the length of this meter is determined by the distance that the speed of light in a vacuum travels in 1/299,792,458 of a second, the accuracy of this "tick" of 1 second is the key among the keys. So, how are these hundreds of millions of seconds calculated?

Don't underestimate this simple "tick" of 1 second, there is a more sophisticated science behind it. The "second" currently used was determined by the 13th International Conference on Weights and Measures held in 1967, and is defined as: 9192631770 times the period of the electromagnetic wave radiated when the cesium-133 atom transitions between two hyperfine energy levels in its ground state.

What does this tongue-twisting sentence mean? Simply put, every atom has its own characteristic vibration frequency, and the radiation frequency corresponding to the transition between the ground state hyperfine energy levels of the cesium atom reaches nearly 9.2 billion cycles per second. The precise calculation of its transition of 9192631770 cycles is used as the definition of 1 standard second.

The timing tool made using the vibration frequency of cesium atoms is called a cesium atomic clock, and its error can be as low as within 1 second in 20 million years.

With this sophisticated "standard second" and "standard meter" tool, scientists have differentiated microscopic and macroscopic measurement tools on this basis, and the measurement and description of the world have become more and more sophisticated and accurate.

There is a lot of complicated knowledge about weights and measures, so I will stop here today and talk about it again later.

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