If you consider time, it is easy to quickly get lost in the complexity of the subject. Time surrounds us – it always exists and is the basis of how we record life on Earth. It is the constant that holds back the world, the solar system and even the universe.
Civilizations have risen and fallen, stars have been born and extinct, and our one method of tracking every event in the universe and on Earth has compared them to the present with the regular passage of time. But is it really a constant? Is time really as simple as moving from one second to the next?
About 13.8 billion years ago, the universe was born, and since then time has flown by until now, controlling the creation of galaxies and the expansion of space. But when it comes to comparing time, it’s scary to realize how little of it we’ve actually experienced.
Earth could be 4.5 billion years old, but modern people inhabited the planet for about 300,000 years – that’s only 0.002% the age of the universe. Do you feel small and insignificant yet? It gets worse. We have experienced so little time on Earth that in astronomical terms we are completely insignificant.
In the 17th century, a physicist Isaac Newton saw time as an arrow shot from a bow, traveling in a straight, straight line and never deviating from its path. For Newton, one second on Earth was the same duration as that same second on Mars, Jupiter or in deep space. He believed that absolute motion could not be detected, which meant that nothing in the universe had a constant speed, not even light. Applying this theory, he could assume that if the speed of light can vary, then the time must be constant. The time must be marked from one second to the next, with no difference between the length of any two seconds. This is something that is easily thought to be true. Every day has about 24 hours; you don’t have one day with 26 and one with 23 hours.
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However, in 1905, Albert Einstein claimed that the speed of light does not vary, but rather it is constant, traveling at about 186,282 miles per second (299,792 kilometers per second). He claimed that time is more like a river, declining and flowing depending on the effects of gravity and spacetime. Time would speed up and slow down around cosmological bodies with different masses and velocities, and so one second on Earth was not the same duration all over the universe.
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This posed a problem. If the speed of light was really constant, then there must have been some variable that changed over great distances across the universe. With the universe expanding and planets and galaxies moving on a huge scale, something had to be given to allow for these small fluctuations. And this variable had to be time.
It was Einstein’s theory that not only was believed to be the truth, but also proved to be completely correct. In October 1971, two physicists named JC Hafele and Richard Keating began to prove its validity. To do this, they flew four Caesarean atomic clocks on aircraft around the world, east and then west.
According to Einstein’s theory, compared to terrestrial nuclear clocks – this time at the US Naval Observatory in Washington – Hafele and Keating’s air clocks would be about 40 nanoseconds slower after their eastern voyage, and about 275 nanoseconds faster after a journey. to the west, due to the gravitational effects of the Earth on the speed of the planes, according to their 1972 study in the journal Science. Incredibly, the clocks did make a difference when traveling east and west around the world – about 59 nanoseconds slower and 273 nanoseconds faster, respectively, compared to the U.S. Navy Observatory. This proved that Einstein was right, specifically with his theory of time dilation, and that time actually varied across the universe.
What happens during time dilation?
What does the theory of special relativity mean over time? Take a look at our explanation of special relativity first to really understand time.
Newton and Einstein, however, agreed on one thing – that time is moving forward. So far there is no evidence of anything in the universe that is capable of avoiding time and moving back and forth at will. Everything ultimately progresses over time, whether at a regular pace or slightly deformed if approaching the speed of light. But why is time moving forward? Scientists are not sure, but they have several theories to explain the single-track “mind” of time. One of these brings the laws of thermodynamics, specifically the second law. This says that everything in the universe wants to move from low to high entropy, or from uniformity to disorder, starting with simplicity at the Big Bang and moving on to the almost random arrangement of galaxies and their inhabitants in the present. This is known as the “arrow of time”, or sometimes “arrow of time”, probably created by the British astronomer Arthur Eddington in 1928, said analytical philosopher Huw Price at Séminaire Poincaré in 2006.
Edington suggested that time was not symmetrical: “If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow points to the future; if the random element decreases, the arrow shows to the past, “he wrote in”The Nature of the Physical World“in 1928. For example, if you were to observe a star almost uniformly, but then see it explode like a supernova and become a scattered nebula, you would know that time has moved from equality to chaos.
Another theory suggests that the passage of time is due to the expansion of the universe. As the universe expands, it draws time with it, for space and time are linked as one; but this would mean that if the universe reached a theoretical limit of expansion and began to contract, then time would be reversed – a small paradox for scientists and astronomers. Would time really move backwards, with everything going back to an era of simplicity and ending with Big Crack? We’re unlikely to find it around, but scientists may be wondering about what might happen.
It is incredible to think about the progress made by humanity in our understanding of time over the past century. From antique clocks to modern sundials atomic clocks, we can even track the passage of a second more closely than ever before. Time remains a complex issue, but thanks to scientific visionaries, we are closer to unlocking the secrets of this not-so-constant universal constant.
The importance of Einstein’s theory of special relativity
That of Einstein theory of special relativity depends on one key fact: The speed of light is the same no matter how you look at it. To say this in practice, imagine you are driving in a car at 20 mph (32 km / h), and you are passing a friend who is standing still. As you pass them, you throw a ball in front of the car at 10 mph (16 km / h).
To your friend, the speed of the ball is combined with that of the car, and so seems to travel at 30 mph (48 km / h). As for you, though, the ball is traveling at only 10 mph, as you’re already traveling at 20 mph.
Now imagine the same scenario, but this time you pass your motionless friend traveling at half the speed of light. With some imagination, your friend can observe you as you travel past. This time you illuminate a beam of light from the windshield of the car.
In our previous calculation we combined the speed of the ball and the car to find out what your friend saw, so in this case your friend sees the ray of light travel at half and half the speed of light. ?
According to Einstein, the answer is no. The speed of light always remains constant, and nothing can travel faster than it. In this case, both you and your friend are observing the speed of light traveling at its universally agreed value at about 186,282 miles per second. This is the theory of special relativity, and it is very important when talking about time.
Time: The fourth dimension of the universe
It was once thought that space and time are separate, and that the universe is just an assortment of cosmic bodies arranged in three dimensions. Einstein, however, introduced the concept of a fourth dimension – time – which meant that space and time were inextricably linked. The general theory of relativity suggests this spacetime expands and contracts depending on the momentum and mass of nearby matter. The theory was solid, but only proof was needed.
That proof came politely from NASA’s Gravity Probe B., which proved that space and time were indeed linked. Four gyroscopes they were directed in the direction of a distant star, and if gravity did not affect space and time, they would be locked in the same position. However, scientists clearly observed an effect of “frame traction” due to the Earth’s gravity, which meant that the gyroscopes were slightly pulled out of position. This seems to demonstrate that the fabric of space itself can be altered, and if space and time are linked, then time itself can be stretched and contracted by gravity.
How long is a second?
There are two main ways to measure time: dynamic and atomic time. The first depends on the motion of celestial bodies, including the Earth, to track time, whether it is the rotational time of a distant rotating star as a pulsar, whether the motion of a star across our night sky or the rotation of the Earth. . However, a spinning star is unbearable, difficult to observe, these methods are not always completely correct.
The old definition of a second was based on the rotation of the Earth. As the sun one day needs to rise in the east, set in the west, and rise again, a day was almost arbitrarily divided into 24 hours, an hour into 60 minutes, and a minute into 60 seconds. However, the Earth does not rotate uniformly. Its rotation decreases at a rate of about 30 seconds every 10,000 years due to factors such as tidal friction. Scientists have come up with ways to explain the changing speed of the Earth’s rotation, introducing higher seconds, “but for the most accurate time you have to slow down even more.
Atomic time depends on the energy transition within an atom of a certain element, usually cesium. By defining a second using the number of these transitions, time can be measured accurately to lose a tiny fraction of a second in a million years. The definition of a second is now defined as 9,192,631,770 transitions within a cesium atom, American scientist reported.
Atomic clocks: The most accurate track of time
The most accurate clock in the universe would probably be a rotating star like a pulsar, but on Earth atomic clocks provide the most accurate trace of time. The entire GPS system in orbit around the Earth uses atomic clocks to accurately track positions and relay data to the planet, while entire science centers are set up to calculate the most accurate measurement of time – usually by measuring transitions within a cesium atom.
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While most atomic clocks rely magnetic fields, Modern clocks use lasers to track and detect energy transitions within cesium atoms and maintain a more defined duration. Although cesium clocks nowadays usually conserve time around the world, strontium clocks promise twice as much accuracy, while experimental design based on charged mercury atoms could reduce differences even more than less than 1 second lost or gained in 400 million years.