The year is 1792 when two French astronomers are leaving Paris and traveling in opposite directions. One goes north, the other south. You have a mission: to measure the size of the world. It will take 7 years and thanks to them, among other things, we have the meter and a universal measurement language: the International System.
The International System arose in the shadow of the French Revolution: universal rights demanded universal measurements, and in order that the standard measurement was not the product of any one nation or group, they used as their basic unit the measurement of the world itself, or more precisely the meridian arc that Dunkirk included Barcelona connects. They proposed this measurement to define the meter as one ten-millionth the distance from the North Pole to the equator. The meter would be unchanging because the earth is.
The measure of the meter was forged into an ingot of platinum and since then most nations have adopted the International System of Measurements or Metric with its advantages and disadvantages. The mistake of not doing this, for example, was paid dearly by the Americans: it is worth noting the loss of 125 million dollars and the disappearance of a satellite, the Mars Climate Orbiter, when two teams of engineers working with two different systems caused an error on its way . The satellite landed closer to the planet’s surface than expected and was destroyed in its atmosphere.
The extent of the cosmos is determined using a distant light source, and we get that the universe is expanding every 3.26 million light-years at 74.02 kilometers per second, unimaginably fast by our mortal human standards.
It is clear that a measure like the meter is no longer of any use to us when we leave the earth and face the enormous distances we travel in the universe. But the idea of universal patterns does. And years ago we had a little problem, quite a big problem, bringing different measurement standards together when trying to determine how the universe itself grew.
To measure how the universe has grown, all you have to do is measure how fast the galaxies are receding (which is relatively easy thanks to the cosmological Doppler effect) and how far they are from us (that’s the hardest part).
In principle, the history of the expansion of the cosmos can be determined with a simple trick: we take a light source of known brightness; if its light is weaker, it is further away. Now, literally, since we’re using a specific type of supernovae, and we have to wait for them to explode, we would just have to wait for these light sources to turn on in different galaxies. A collection of these measurements over a sufficient range of distances would provide a complete historical record of the expansion of the universe.
In fact, we have been able to measure this value with the greatest possible accuracy using Type Ia and Cepheid supernovae, and we get that, according to a recent and precise measurement, the Universe is moving at a rate of 74.02 kilometers per second per Megaparsec expands. A megaparsec is a million parsecs, or about 3.26 million light-years, so the extent in units you might be more familiar with would be 74.02 kilometers per second every 3.26 million light-years, and to express that in meters you would have to do the zero-filling of sides, making it almost unimaginably fast on our mortal human scales.
And at that value, we’d be pretty happy if we refined its errors, for example by measuring another class of signals like the Cepheids with GAIA. But it happens that we can also determine the expansion of the universe when it was young, and the value that is obtained is different. Here’s the problem. This independent method is based on the cosmic microwave background, which, put simply, would be the photo in the form of a glow penetrating the entire sky that the Big Bang left us 379,000 years ago, when the Universe was just a hotter dense plasma. . The best measurement of early age expansion was given by the Planck Space Telescope, and according to Planck the Universe should be expanding at a slightly slower rate than the other measurement gives us at 67.4 km per second per megaparsec.
Measurements of the constant from the current universe (measured by the Hubble and Gaia space telescopes) provide a value that differs from measurements when the universe was young (measured by the Planck telescope), and although the difference is 10%, he likes it appear very low. Let’s say we’re talking about the greatest thing there is, the cosmos. If the difference is due to measurement errors in both methods, it’s not easy to refine them, cosmologists would have to do something they don’t like very much, and that would be to study stars to understand them. There are new determinations of the Hubble constant using a different method of measuring the distance (using red giant stars) between the two values that would literally solve the problem.
If we don’t reconcile the various measures, it will become clear that something is wrong and then we may have to invent something completely new. Or maybe not, and it is enough for us to better understand the stars, the places where they form and their end. The alternative is the most exciting, so let’s dream then, if the difference isn’t due to bias, if it’s real it would imply physics beyond the standard cosmological model: ascending dark energy, non-zero curvature, early dark energy. maybe a new relativistic particle (dark radiation). Sounds good right? Let’s wait and see what the new measurements from the James Webb telescope tell us.
Cosmic Void is a section in which our knowledge of the universe is presented qualitatively and quantitatively. It aims to explain how important it is to understand the cosmos not only from a scientific point of view, but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that the universe is and is mostly empty, with less than one atom per cubic metre, although paradoxically there are trillions of atoms per cubic meter in our environment, inviting us to wonder about our existence and to contemplate the presence of life in the universe. The section consists of Pablo G. Perez Gonzalezresearchers at the Center for Astrobiology; Patricia Sanchez Blazquez, Full Professor at the Complutense University of Madrid (UCM); Y Eva VillaverResearchers at the Center for Astrobiology.
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