That “we haven’t seen each other in a long time,” is it really a long time? If we think that a billion-year-old galaxy is a young galaxy, it must be recognized that we have not been together for so long. But if we compare it with the time it takes for a photon to cross a hydrogen molecule, an event that is measured in zeptoseconds, the smallest unit of time measured to date, we have had that beer forever.
Today as smart gadgets measure steps, heartbeats, even inhalations to the second, timing remains a first-class intellectual challenge.
Thus, Time, in capital letters, allows a fantastic game. A clock that marked all possible times would have to be immense and minimal.
A team of researchers from the universities of Frankfurt, Hamburg and Berlin have been able to measure the shortest amount of time to date. The unit used was the zeptosecond, which is equivalent to 0.000000000000000000001 seconds. At the other end of the scale, scientists estimate that about 4.5 billion years have passed since Earth was born. An endless period for our species, since recent data suggest that Homo sapiens emerged only about 190,000 years ago.
But the history of the Blue Planet is not so long if it is interpreted on the scale of the universe. For example, it falls short of the lives of the stars.
If you blink, you miss The Big Bang
Among those stars are white dwarfs. No one has seen the death of any because they are longer than the universe itself. Its existence would escape the understanding of the Earth itself if it were aware of time. At the other end of the timescale, where events are extremely fast, the universe also challenges our minds. According to the Big Bang theory, it took less than a thousandth of a second for elementary particles to appear.
If we could see the phenomenon in a laboratory, a blink at the wrong time would be enough to miss the creation of the new cosmos.
The human species has less than twenty galactic years of existence, which is equivalent to 4.5 billion earth years
In the universe, everything is a matter of scale. Overwhelming, but measurable. “When you talk about Astronomy, you have to change the time scale, the distance, the masses…”, observes the president of the Spanish Astronomy Society, Javier Gorgas. “If I say that a galaxy is one billion years old, my colleagues fully understand that it is very young,” he adds.
The cyclical dance of the stars sets the tone for the calendars. It takes Earth 365.25 days to go one revolution around the Sun, so we measure time in cycles made up of three 365-day years and another leap of 366 days. Astronomers use this division to study periods of thousands of years and gigayears. (each equals one billion years). The life of the stars and the age of the universe are periods that are well suited to this scale.
But careful measurement confirms that 365.25 days is too round a figure to be exact. You can take the Sun as a reference or look at the other stars. The result varies in both cases. The time that elapses between two steps of the Astro Rey through the meridian is equivalent to a solar day, while the time it takes for a star to occupy the same position in the sky with respect to the previous day is known as a sidereal day. The latter is 4 minutes shorter. The same principle is used to distinguish between solar year and sidereal year. The first lasts 365 days, 5 hours, 48 minutes and 45.9 seconds, while the sidereal is 20 minutes longer.
The hands of a clock move slower on the lower floors of a building
This lag is due to the precessional motion of the Earth. The North Pole is not fixed, but describes a wide circle every 25,776 years: each turn is called a Platonic year. The movement causes the point in space that points to the north of the Earth, from which the coordinates are defined, to move slowly over the millennia. The extra 20 minutes of the sidereal year correspond to the time it takes for the Earth to recover the deviation that accumulates each solar year due to the precession movement.
Finally, it can also be measured as a function of the time between two successive passages of the Earth through its perihelion. This period is 4 minutes longer than the sidereal year, and is called the anomalistic year.
The orbital waltz of the Earth and the Sun marks the passage of days and years that we clearly perceive, but only astronomical observations can unveil an even greater dance taking place in our own galaxy.
The Galactic Year
Our Solar System makes one revolution around the galactic center every 225 million solar years. Each spin is a galactic year, which is a difficult measurement to understand. “There are certain uncertainties about the duration of the galactic year, because the Sun could slow down when passing through an area of higher density and accelerate in other regions, but it is between 225 and 250 million years,” Gorgas details. The Earth and the Sun are about 20 galactic years old, and the universe about 60.
The Moon formed shortly after our planet’s first galactic year of life. The Earth’s crust solidified towards its third galactic year, and in the fifth, with more than a billion solar years behind it, the Earth welcomed the first prokaryotic cells. Eukaryotes, those that have a nucleus and are the ones that organize complex life forms, arrived seven galactic years later.
Hominids broke into history shortly before Earth turned 20 galactic years, that is, the 4.5 billion years it is now. But although astronomers move comfortably in thousands of years and in gigayears, there are also shorter scales that require more accurate measurements.
The Role of the Second
“It is complex to measure the passage of time very carefully,” says Gorgas. The Earth does not always rotate at the same speed with respect to the Sun, and the effects of the Moon’s gravity influence its path and, therefore, the length of the day, even if it is only in seconds. Therefore, for practical purposes, atomic clocks are used.
“The second can be defined by the half-lives of radioactive elements or based on basic questions of physics that are the same throughout the universe,” explains Gorgas. And atomic clocks provide the precision necessary to account for phenomena such as pulsars, which are neutron stars that are spinning in periods of thousandths of a second.
But even the second is not final. As predicted by the theory of relativity, time moves more or less quickly depending on the speed of the observer with respect to the object and the force of gravity. “It is something that worries modern physics,” admits Gorgas. For this reason, everyone looks towards the origin of the universe, when the laws that govern the large and the smallest scales of quantum physics coexisted for an instant.
Perhaps there are the keys to unraveling that partner that everyone claims to understand, even if they do not know how to define it.
Knowing if you are willing to make yourself known relatively soon in an experiment that is currently being carried out is a matter of time. But how much?
Time would pass slower for an astronaut flying at the speed of light than for the pilot of a sports car. If you are given a choice, it is a good option to work on the highest floors of the building, since gravity weighs in the hands of the clock and causes them to move more slowly on the lower floors. The same effect, predicted by the theory of relativity, is most striking in space. “Near very massive objects, such as neutron stars, time slows down, and near a black hole it stops altogether”, explains Professor of Astrophysics Javier Gorgas.