2020-07-06

This is why we can never know everything about the universe

By yqqlm yqqlm

Speaking of ambition, there is nothing more than knowing everything about the universe. This is the ultimate scientific dream:not only to understand as comprehensively and deeply as possible the laws governing reality, but also to understand how every particle that exists exists from the moment the universe was born to the present.

But this dream is not necessarily what we can achieve, even with good equipment and ideal observation methods is difficult. Despite the vastness of the universe, the part of the universe that we can observe now and in the future is still limited. In our observable universe, the number of particles is limited, the energy is limited, and the information we can collect is also limited. Here is what we know about the scientific limits of knowledge.

After the Big Bang, the universe is almost completely uniform, full of matter, energy and Radiation is in a state of rapid expansion. Over time, the universe has not only formed elements, atoms, clusters, and star clusters, and formed stars and galaxies, but has been expanding and cooling throughout the time. No one can match it, but the universe has not taught us everything, including (especially) the beginning.

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Think about the Big Bang, The universe we live in today is produced and expanded in a state of high temperature and high density and then cooled and finally formed. Recall that moment 13.8 billion years ago. Even if the structure of the space itself is expanding, even if light can travel through the space at the ultimate cosmic speed (speed of light), the distance we can see is limited.

No matter how fast the structure of the universe expands, how fast the light travels, and how much time has passed since the Big Bang, these properties are not infinite. Therefore, we can only see a limited distance and only a limited amount of matter in the observable universe. The information we can get is limited.

From our point of view, the size of the observable universe may be 46 billion light-years, but there are definitely more unobservable universes, and may even be infinite. Just like our universe. Over time, we will be able to see more galaxies, and the final discovery will be about 2.3 times the amount of star coefficients we can currently see. Even the parts we have never seen before, there are things we want to know. What we do is not in vain.

Many discoveries in human history enable us to better understand the universe around us. Although we do not know everything, there are a large number of sources of knowledge that enable us to draw far-reaching conclusions about our universe. We know that the universe is composed of matter, energy, radiation, etc.

We know how many planets (about 400 billion) in our galaxy and how many galaxies (about 2 trillion) in the entire visible universe . We know how the universe is clustered into clusters of galaxies, galaxy clusters, and superclusters, and how they are separated by huge cosmic space. We know the scope of the universe that defines these structures, and how the universe has evolved over time.

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Caused by baryon acoustic oscillations The aggregation model proves that the probability of finding a galaxy within a certain distance depends on the relationship between dark matter, normal matter and all types of radiation including neutrinos. As the universe expands, this characteristic distance also expands, which allows us to measure the Hubble constant, dark matter density, and other cosmic parameters that change over time. The large-scale structure and Planck data must be consistent.

This theory is perfectly combined under the framework of the Big Bang and General Theory of Relativity, which is wonderful. When we find that the measured distance of a galaxy is related to its apparent rate of decay from us, it offers an interesting and revolutionary possibility. Perhaps these galaxies are not all far away from us, but the structure of the space itself is expanding.

If this is the case, then the universe will not only expand but also cool down, as the wavelength of light will be stretched to lower and lower energy levels over time . We should see a kind of residual luminescence whose special properties can be traced back to the earliest era:the cosmic microwave background. We should see a developing cosmic structure. We should find that the earliest gas cloud should have a certain proportion of light elements, and no heavy elements at all.

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The visual history of the expansion of the universe includes what’s called the Big Bang The state of high heat and high density, and the subsequent growth and formation of the universe structure. A whole set of data, including observations of light elements and the microwave background of the universe, leaves only the Big Bang as a reasonable explanation of everything we have seen. As the universe expands, it also cools, allowing ions, neutral atoms, molecules, gas clouds, stars, and galaxies to form.

All these predictions and more predictions about the early universe have been confirmed. This forms the present-day universe, and we know that our universe begins in a hotter, denser, more uniform, and faster-expanding state:what we know as the Big Bang.

Therefore, it is easy to think that the Big Bang is the beginning of the universe. You may think that if we can understand the origin of the universe and the laws that govern reality, we can know everything that happens in all beings. All we need to do is use the laws of physics to infer. However, when we naively infer the initial stage of the universe and compare what we expected with what we observed, we will find that this is not the case.

If the density of the universe is slightly higher, it has collapsed again; if its density is slightly lower, it will expand faster and become larger. The Big Bang itself did not explain why the initial expansion rate at the birth of the universe so perfectly balanced the total energy density, leaving no space for the curvature of space at all. Our universe looks perfect and flat in space.

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There are some very important questions here, if you try Returning to the initial state of the universe, unless the initial expansion rate and initial energy density of the universe reach a perfect balance, the universe will expand to annihilation, or refold almost immediately, and will never form stars or galaxies.

Unless something makes the temperature the same everywhere in the universe-this is something that has been proven-the universe should have different temperatures in different directions. According to past inferences, the universe should have been full of high-energy residues that have never been detected.

However, when we observe our universe, it does have stars and galaxies, the temperature in all directions is the same, it does not have these high-energy miserables. In the above picture, our modern universe has the same properties (including temperature) everywhere, because they all originate from an area with the same properties. In the middle panel, there can be spaces with arbitrary curvatures that are expanded to such an extent that we cannot observe any curvature today, thus solving the problem of flatness. In the bottom panel, the original high-energy legacy was swelled away, solving the problem of high-energy legacy. This is how inflation solves the three major problems that the Big Bang cannot explain alone.

The solution to these problems is the cosmic inflation theory, which replaces The concept of singularity and predicted the initial conditions that the Big Bang itself cannot predict. In addition, the inflation theory has made six other predictions for the phenomena we have seen in the universe:

The maximum temperature reached in the high temperature explosion is much lower than that of Prang Gram energy scale.

Since the Big Bang, fluctuations beyond the horizon, or temperature/density fluctuations on a larger scale than light, are possible.

Density fluctuations are 100%adiabatic and 0%constant curvature.

The range of density fluctuations is almost completely immobile, but the fluctuation range is slightly larger in a large range than in a small range.

A near-perfect flat universe with a quantum effect of curvature of 0.01%or less.

A universe filled with primitive gravitational wave background should leave its mark on the afterglow of the Big Bang.

The first five have been confirmed or as far as possible within our maximum observation capability, and the sixth hypothesis is still difficult to be confirmed by observation.

The fluctuations in the cosmic microwave background are composed of the cosmic background detector (large range), Wilkinson microwave anisotropy detector (medium range), and Planck (small Range), not only consistent with the quantum fluctuation set of constant scale, but also the magnitude is so low that it cannot be generated from any high temperature and high density state. The horizontal line represents the initial spectrum of the fluctuation (inflation), and the swinging section on the left and right represents how the gravity and radiation/matter interaction formed the early expanding universe. There is some key evidence in the background of the cosmic microwave to prove the existence of inflation.

But now we have a problem. An important one concerns our problems. We can observe our universe and use the available evidence to construct the concept of the Big Bang, and then make new predictions to test the authenticity of the Big Bang.

The unexplained problem about the Big Bang is to help us perfect the theory of inflation and thus replicate the success of the Big Bang theory. Explain these questions and make new predictions about the observable consequences.

The above are all brilliant examples of scientific success. But you should want to get more. The next question about our origin is, of course, where does cosmic inflation start?

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Our history of the universe has been perfectly explained by theory, But only at the qualitative stage. This is through observation to confirm the events that have occurred in different stages of the universe in the past, such as how the original planets and galaxies were produced, and how the universe expanded slowly. Before the Big Bang, the traces left behind left an imprint of expansion in our universe, which provided us with a unique method for testing the history of the universe.

Is cosmic inflation an eternal state in the past, that is to say it has no origin until it ends and creates the Big Bang?

Or does inflation have its origin, which emerged from a non-inflationary spacetime in a limited time in the past?

In other words, inflation is a small part of a cyclic state. Will the distant future universe experience inflation again?

These questions sound interesting, difficult, and persuasive, and also raise some interesting possibilities. Of course, knowing where our universe came from is not just describing the big bang, but also knowing where the big bang came from. If the origin is inflation, then we want to know where inflation comes from.

The contribution of gravitational wave residues caused by inflation to the B-mode polarization in the cosmic microwave background is known, but its amplitude depends on a particular inflation model. The B mode in these gravitational waves from inflation has not been observed, which is also the only one of the six predictions of inflation that is not supported by strong observation data.

But we have no way of knowing. This is where we are basically restricted by the information in the universe, and it is also the only way for us to understand the universe itself. In our universe, nothing we observe can make us distinguish these three possibilities.

Except for the most elaborate inflation model (some of which have been excluded), in all models, only the last 10^-33 seconds of inflation will be Affect our universe. Inflation has grown exponentially, erasing any information that has occurred before, separating it from anything we can observe, because the key information has expanded beyond our observable universe.

We can describe the history of the universe from the end of inflation and the beginning of the thermal explosion. Dark matter and dark energy are essential components of the universe today, but when they are produced is inconclusive. We have a general view of how the universe originated, but it is often corrected by the appearance of more detailed and excellent data. It is worth noting that any information about the beginning of inflation or 10-33 before the end of inflation does not exist in our observable universe.

All that’s left is a huge universe

  • The radius is 46 billion light years
  • Contains about 20,000 100 million galaxies
  • about 10²⁴ stars
  • 10⁸⁰ atoms
  • about 10⁹⁰ photons

The total energy contained in all particles, antiparticles, radiation quanta, and even in a vacuum is about 1054 kg, including dark matter and dark energy

But these astronomical numbers are still limited. In addition, they do not contain any information about the early inflationary universe. Most feasible inflation models have no testable, observable signs of the beginning of inflation, so we have no way of knowing how the universe came about.

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Currently known overviews of basic elementary (and composite) particles and forces. Some of the ideas presented are still speculative. If our goal is to know everything about our universe, then unfortunately we only have our own universe for observation and information. If the necessary signs have been eliminated by the movement of the universe itself, then we may never know the truth.

The total amount of information we can obtain in the universe is limited, and the same is true for the knowledge we can obtain. The energy we use, the particles that can be observed, and the measurements we can make are limited. But this does not mean that we are out of business, or no longer thinking about learning what we can get. We should improve our knowledge as much as possible, the more the better.

There is still much to learn, and there are also many things that science has not revealed. As long as we continue, what is now unknown may also become known in the near future. But what is known is limited, indicating that we may never know something. The universe may be infinite, but our understanding of it will never be infinite.

Author:Ethan Siegel

FY:Tommy Xie

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