The universe is not ashamed to reveal its age. There are many ways to find out how long it has been since the Big Bang.
It is estimated that 13.4 billion years have passed since then, with an error interval of 200 million years.
Hundreds of millions of years of uncertainty is no mean feat. However, this accuracy is declining, thanks to increasingly accurate cosmic timers.
To take advantage of the exact age of the universe, we take advantage of the fact that it is expanding, something we have known for almost a century.
This expansion creates phenomena with huge numbers. For example, an object close to our galaxy, the black hole Sagittarius A *, is moving at a speed of 80,000 km / s from one of its distant cousins, OJ287.
This basically happens in almost every black hole in the universe. They are moving away from each other at the same speed as their host galaxies.
However, confidence in scientific results depends on the repetition of experiments. And that’s something the universe doesn’t support.
How to measure time from the Big Bang
To compensate for this inability to repeat the experiments, we compared different data sources. This way, we were able to fine-tune our cosmic timers.
But after all, how can we measure the time that has elapsed since the Big Bang?
Our basic data is the Hubble factor. It is a set of data that indicates an increase in the average percentage of the universe over time. Suppose we can measure the growth itself and the rate at which it occurs. By combining the two factors, we get the time spent in this evolution. In other words, we have a cosmic timer at our disposal.
But let’s put this explanation in everyday terms. A revolutionary cosmetic product promises that a person’s eyelashes will be twice as long in 60 days. Following this logic, if we notice that the substance applied and the eyelashes have grown by 50%, that means that it will be a month since the application started, right?
The answer, however, may not be so easy. If we do not apply the product continuously every day, the growth rate of the eyelashes will slow down. We thus conclude that measurement time based on resizing can lead to errors.
To understand this transformation we need to know what happened on a daily basis. This is what we call controlling the experiment. But is that also a bad method of measuring the age of the universe?
When the universe was younger than the earth
In 1947, physicist George Gamow used data from the Hubble Factor to calculate the age of the universe at 2.5 billion years. Shortly afterwards, geologists dated the age of the Earth to 4.5 billion. How could the universe be younger than our planet?
Of course, the age estimate of the universe was incorrect. The problem was that they did not fully understand how to do this calculation. But it was well known that expansion usually decreases the density of the components of the universe. And, depending on the nature of each of them, this process takes place at different paces.
In the early stages of the universe, radiation prevailed. As the radiation dissipates very quickly, it was replaced by dark matter, as the density of this compound decreases more slowly.
All of this follows what is described in Einstein’s equations. The nature of radiation and dark matter causes the universe to slow down. This means that even though there was expansion in these stages, the pace was slowing down.
But that idea clashed with evidence found in other experiments. In them, the rate of expansion of the universe was increasing.
The advent of dark energy
There was a new component in the process that claimed prominence: dark energy.
Through one of these magical coincidences, the effects of different stages of the universe are offset. In other words, the original delay in the expansion rate was offset by the current acceleration. That’s why it makes sense to guess the age of the universe directly through the Hubble factor.
Again, this type of work requires measuring scale growth in the universe itself. To do this, we take advantage of the fact that the propagation extends the length of the electromagnetic waves that reach us from the stars.
It is called the corresponding effect slipping to red. This is done, for example, in spectroscopy using extensive catalogs with intensity and wavelength models. Thus, almost identical objects are identified with each other, but different depending on the depths of the universe.
It is important to note that the farther away these objects are in comparison, the longer the light will last. For example, the red light that reaches us from the farthest known galaxy, GN-z11, is ultraviolet.
The basis of cosmic timers
By calculating the red light displacement in a distant galaxy, we calculate the propagation that has occurred since each light beam was emitted. The calculation is then repeated with the same galaxy and the results are compared.
The next step is to average this difference in spread over the corresponding time interval. And that temporary window will be, in fact, the difference in the travel time of light, depending on whether it comes from one galaxy or another. This is equivalent to achieving the age difference between galaxies.
Thus, a force-creating technique is formed: cosmic timers. With this great idea, pardon the pun, it is hoped to arbitrate the debate over the values of the Hubble factor between measurements of the local universe and the deep universe.
A shortcut to the age of each star
Because galaxies have hundreds of billions of stars, you have to be very careful.
To obtain the ages of galaxies and stars, the overall demographic average must be used. And we don’t do it because we want to, but because we can’t do it any other way. It is very difficult to determine the age of each star.
Fortunately, providential tricks make this task easier. It consists in the successful use of a very accurate signal of the change in light intensity emitted at 4,000 angstroms. [uma unidade de medida de comprimento]. The technique depends on the presence of metals that heat the galaxy and allows the results obtained by means of cosmic timers to be rounded off.
In fact, we do not calculate the current Hubble factor in this way, but this is also the case for previous eras. By combining this knowledge with relativistic cosmology, we improve our understanding of dark energy. And the wheel keeps spinning and gives us answers about the components of the universe.
Today, we have only a small number of such cosmic timers. However, they are very accurate. However, there is high hope that these results will increase in future missions.
This would allow us to build a strong and informative catalog. The promising experiments I am referring to are EUCLID and Nancy Roman, missions launched by the European Space Agency and NASA, respectively.
They will certainly improve the chances of cosmic timers to position themselves as a key piece that will be able to measure not only the Hubble factor, but also the evolution of the universe itself.
These advances will increase our desire to tackle the biggest puzzle of all: how did the universe come into being? For now, we don’t know. But we can repeat what physicist James Clerk Maxwell said: “Fully conscious ignorance is the forerunner of real progress in knowledge.”
* This article was originally published in The Conversation. You can read the original version here.
This text was originally published here.
Ruth Lazkoz is Professor of Theoretical Physics at the University of the Basque Country – University of the Basque Country.