It is incredible to think of the progress that human beings have made in understanding time since the last century. We went from ancient sundials to modern atomic clocks. Today we can follow the passage of a second more closely than ever, but time remains an extremely complex topic. Thanks to visionary scientists, we are getting closer and closer to unraveling the secrets of the one who claims to be the “master of everything”.
Time measurement is becoming more and more accurate.Source: Pixabay
The time for Newton
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Isaac Newton, in the 17th century, created the thesis that time is like an arrow shot from a bow, traveling in a straight and direct line – and never deviating from its path. For him, a second had the same duration anywhere in the universe and nothing had a constant speed, not even the light. So he assumed that if the speed of light could vary, time must be constant – going from one second to the next, with no difference in duration.
The weather for Einstein
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Albert Einstein, in 1905, stated that the speed of light does not vary, being a constant that travels at about 299,792 kilometers per second. For him, time – the fourth magnitude of the universe – was more like a river, leaking and flowing, depending on the effects of gravity and space-time. Time would increase and decelerate around bodies with different masses and velocities and, therefore, one second on Earth would not have the same duration in the entire universe.
But if the speed of light were really a constant, it would take a variable to change great distances across the universe. With its expansion and planets and galaxies moving on a gigantic scale, something would have to give in to allow these fluctuations – time. And after a brief passage from him, the theory proved to be totally accurate.
Proving time dilation
In October 1971, physicists JC Hafele and Richard Keating placed four cesium atomic clocks on planes to fly around the world, first to the east and then to the west. According to Einstein’s theory, when compared to atomic clocks on the ground, clocks in the sky would be about 40 nanoseconds slower after traveling east, and about 275 nanoseconds faster after traveling west, due to the gravitational effects of Earth at the speed of airplanes.
The study was published in 1972 in the journal Science and, iIncredibly, clocks made a difference when traveling east and west around the world: about 59 nanoseconds slower and 273 nanoseconds faster, respectively, compared to the US Naval Observatory in Washington, DC, where the clock was on the ground. Then Einstein he was correct in his theory of time dilation, and it was proved that time did indeed float across the universe.
Theories about time
Newton and Einstein agreed on one thing: time advances. So far there is no evidence of anything in the universe that is able to evade time and move back and forth at will. Everything moves forward in time, either at a regular pace or slightly deformed as it approaches the speed of light.
There are several theories on the topic. One is the second law of thermodynamics, which states that everything in the universe wants to move from low entropy to high entropy, or from uniformity to disorder: it started with the Big Bang – it is the “arrow of time”.
British astronomer Arthur Eddington suggested that time was not symmetrical: “If, as we follow the arrow, we find more and more the random element in the state of the world, then the arrow points to the future; if the random element decreases, the arrow points to the past ”, he wrote in 1928.
Another theory suggests that the passage of time is due to the expansion of the universe: as the universe expands, it pulls time with it – because space and time are linked as one. But that would mean that if the universe reached a theoretical limit of expansion and started to contract, time would reverse.
One thing is certain: each time we are able to measure time more accurately. Before we used only dynamic time, based on the rotation of the Earth, dividing a day in 24 hours, an hour in 60 minutes and a minute in 60 seconds – but the Earth does not rotate evenly. Leap years have been introduced to increase accuracy, but this is not an accurate measurement.
Atomic time – more accurate to this day – depends on the transition of energy within an atom of a certain element, usually cesium. Thus, time can be measured with the loss of only a small portion of a second in a million years. A second is now defined as 9,192,631,770 transitions within a cesium atom, according to Scientific American magazine.
Strontium clocks promise to achieve double precision and an experimental design based on charged mercury atoms could further reduce discrepancies in time measurement: to less than 1 second lost or gained in 400 million years.