In this edited excerpt from “The Little Book of Cosmology” (The Little Book of Cosmology, published by Princeton University Press and reproduced here with permission from the publisher), physics professor Lyman Page explains how our model of the universe relies solely on six parameters.
How do we study the universe as a whole?
My work focuses on Microwave background radiation (CMBThe faint energy remnants of the Big Bang – and how they are measured could guide our path toward understanding the universe.
But there are many other ways to study the universe, and physicists who study this universe specialize in everything from general relativity to thermodynamics to elementary particle theory.
We make observations in nearly all wavelength systems accessible to measurement and with the latest particle detectors.
The observations come from the vicinity and from the most distant places in space.
All this evidence and theory can be put together in a surprisingly simple modular model of cosmology, which it just possesses Six parameters.
These are the numbers that define the entire universe.
File content UNeverso
The The first three parameters They tell us about it Content Universe.
We describe them as fractions of the total material and energy budget, such as the components of the pie chart.
The first parameter describes how much An ordinary substance is atoms In the universe, and she says that they only represent 5% Universe.
Describes the second parameter Dark matter, Sort of a new fundamental particle that we still don’t understand, and that account for 25% of the universe.
Surprisingly, the amount of dark matter, which we can infer from our measurements of subtle temperature fluctuations in the cosmic background radiation, is consistent with the value extracted from observations of the motions of stars and galaxies.
However, the value we get from the CMB measurements is more accurate.
Our measurements also tell us something else.
Because the CMB comes to us from the separation age, when the early universe cooled enough to release the photons from the hot plasma that bound them together for several hundreds of thousands of years after the Big Bang, causing the universe to become transparent, we can see that Dark matter is clearly in UEarly universe.
Moreover, we can see that the atoms, the substance that we are made of, represent only a sixth of the total mass of the universe.
The third parameter is The cosmological constant, The mysterious dark energy that underlies the accelerating expansion of the universe.
This represents 70% of the total matter and energy budget in the universe. We also don’t know what this dark energy is, but we do know that it exists, because we have directly measured its existence through cosmic acceleration.
Stars and galaxies are forming
The fourth parameter is Visual depth, Or how opaque the universe was with respect to the photons traveling through it.
This is the most astronomical of all the parameters of the Standard Model of Cosmology.
By this, we mean that it captures our scant knowledge of the complex process of formation and the subsequent explosion of the first stars and the formation of the first galaxies in the universe.
The intense light from these first stars and galaxies broke the hydrogen that was prevalent in the universe into its constituent protons and electrons, causing the universe to re-ionize.
In this process, about 5-8% of the photons of the cosmic background radiation, the photons that were released at the moment of decoupling, were scattered again.
To use the analogy, bearing in mind that the universe was previously transparent, it is as if a little bit of fog has entered.
Not much, you can still see a distant coastline, but visibility is reduced. Interestingly, to determine the optical depth of the universe, a CMB was taken.
Polarization, along with intensity and wavelength, is one of the three properties of a light wave.
Polarization determines the direction in which the light wave is oscillating.
For example, the light reflected from the hood is polarized horizontally. That is, the light wave oscillates horizontally from side to side.
Polarized sunglasses block this trend from wobble and its associated reflection.
Likewise, the electrons emitted from the reionization process are scattered and polarized by the CMB photons.
If you can look at the CMB with or without polarized “sunglasses”, you’ll see that they look a little different.
Describe the last two parameters Small fluctuations origins That gave rise to all of the structures we observe today in the universe.
If we had a complete model of the universe, a model that started with small quantum fluctuations and successfully predicted fluctuations of matter in spheres 25 million light-years in diameter, then we could get rid of one of these two criteria.
Unfortunately, although we have a very successful draft to understand how the universe evolved, we don’t know all the connections yet, so we need them as a parameter.
its name Spectrum of Primordial Force It describes the fluctuations in the density of the universe in three-dimensional space.
At the beginning of the universe, these fluctuations were small, but as the universe expanded, these differences in density became large throughout the universe.
As there were slightly denser regions in the primitive universe, matter continued to clump together, and now we can see galaxies or galaxy clusters; In other cases, where the density is lower, we see almost nothing.
The remaining parameter is called Spectral numerical index It’s the hardest to understand, but it’s also our best window into the birth of the universe.
It tells us how the primitive fluctuations, the small changes in energy that existed in the early universe, depended on the angular scale.
To understand this better, let’s use a musical analogy.
This last cosmic parameter allows us to distinguish between “white noise” and, for example, “pink noise”, where low tones (similar to large angular scales) have a somewhat higher magnitude than high tones (analogous to small angular scales).
Using the CMB, we found that the initial fluctuations were slightly greater in amplitude on the large angular scales than on the smaller scales.
In other words, Primal Cosmic Noise is slightly pink.
With these six criteria, We can calculate properties not only from The CMB, but also whatever cosmic measure we want to do.
We can, for example, calculate the age of the universe: 13.8 billion years (there would be an approximate difference of 40 million years).
The most restrictive observation is that of the CMB variance: subtle fluctuations in temperature.
However, the standard model for cosmology corresponds to all measurements, from all fields of physics and astronomy.
In short, regardless of how we look at the universe – with the probes of galaxies, through the exploding stars, through the abundance of light elements, across the velocities of galaxies or via the CMB – we need only the six parameters described above, and the known physical processes, to describe the universe that we observe .
What does it mean to be able to describe something so simple and quantitative? This means that we understand how the parts of the universe fit together to form a whole.
We understand some deep links in nature.
This means that we can be proven wrong, not with different arguments, but with Best quantitative model It describes more aspects of nature.
There are few systems that scientists have studied that can be described simply, completely, and with such precision.
We are fortunate that the visible universe is one of them.
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