Measure the size of the world and, by the way, of the universe

The year is 1792 when two French astronomers leave Paris traveling in opposite directions.

One goes to the North, the other goes to the South.

They have a mission: to measure the size of the world.

It will take 7 years and thanks to them, among others, we have the meter and a universal language of measurements: the International System.

The International System arose in the shadow of the French revolution: universal rights demand universal measures and so that the standard pattern of measurement was not the result of a nation or a group, they used as their fundamental unit the measure of the world itself, or more specifically, the meridian arc that connects Dunkirk with Barcelona.

They proposed this measurement in order to define the meter as one ten millionth of the distance from the North Pole to the equator.

The meter would be invariable because the Earth is.

The measure of the meter was forged in a platinum bar and since then, with its pluses and minuses, most of the nations have adopted the International System of Measurements or metric.

The mistake of not doing so has been paid dearly, for example, by the Americans: it is worth mentioning 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 unit systems caused an error in his path.

The satellite ended up closer to the planet's surface than expected and was destroyed in its atmosphere.

The expansion of the cosmos is determined with a distant light source, and we obtain that the universe is expanding at 74.02 kilometers per second every 3.26 million light-years, unimaginably fast at our mortal human scales.

It is clear that a measure like the meter is of no use to us once we leave Earth and face the enormous distances we drive in the universe.

But the idea of ​​universal patterns does.

And years ago we had a little problem, rather a big problem, in fitting together different standards of measurement when trying to determine how the universe itself has grown.

To measure how the universe has grown, you just have to measure how fast the galaxies are moving away (which is relatively easy thanks to the cosmological Doppler effect) and how far away they are from us (this is the hardest part).

In principle, the history of the expansion of the cosmos can be determined using a simple trick: we take a light source of known brightness, if its light is weaker, it is further away.

Now we would just have to wait, literally, since we use a certain type of supernovae and we have to wait for them to explode, for those light sources to be turned on in different galaxies.

A collection of those measurements, over a sufficient range of distances, would produce a complete historical record of the expansion of the universe.

Indeed, we have managed to measure that value with the greatest possible precision using type Ia supernovae and Cepheids, and we obtain that the universe is expanding, citing a recent and precise measurement, at a speed of 74.02 kilometers per second per megaparsec.

A megaparsec is one million parsecs, or approximately 3.26 million light-years, so the expansion in units that you may 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 fill pages. of zeros, making it almost unimaginably fast on our mortal human scales.

And with that value we would be rather happy, if we were to refine its errors by measuring, for example, another class of signals such as the Cepheids with GAIA.

But it so happens that we can also determine the expansion of the universe when it was young and the value that is obtained is different.

Here is the problem.

This independent method is based on the cosmic microwave background, which, simply put, would be the photograph in the form of a glow that permeates the entire sky and that the Big Bang left us at 379,000 years ago when the universe was only a hot and dense plasma. .

The best measurement of early age expansion has been provided by the Planck space telescope and according to Planck the universe should be expanding a little slower 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, different from measurements when the universe was young (measured by the Planck telescope) and although the difference is 10% it may seem very little, let's think that we are talking about the greatest thing there is, the cosmos.

If the difference is due to measurement errors in both methods, refining them is not easy, cosmologists would have to do something they don't like very much and that is study stars to understand them.

There are new determinations of the Hubble constant with 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 get the different measures to agree, it will be clear that something is wrong and then we may have to invent something totally new.

Or maybe not, and it is enough for us to better understand the stars, the places where they are formed and their endings.

The alternative is the most exciting, so let's dream then, if the difference is not due to systematic errors, if it is real, it would imply physics beyond the standard cosmological model: rising dark energy, non-zero curvature, early dark energy , perhaps a new relativistic particle (dark radiation).

Sounds good right?

Let's wait and see what the new measurements with the James Webb telescope tell us.

Cosmic Void

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