At the beginning of the 20th century, a young scientist named Albert Einstein examined the properties of light and mass and how they are related to each other. The result of his thoughts was the theory of relativity. His work has changed modern physics and astronomy as it is felt so far. Each student studies his famous E = MC2 equation to understand how mass and energy are related. This is one of the fundamental facts of the existence of space.
What is a cosmological constant?
No matter how deep Einstein's equations for the general theory of relativity, they represented a problem. He sought to explain how mass and light exist in the Universe, how their interaction can lead to a static (i.e. not expanding) Universe. Unfortunately, his equations predicted that it would either contract or expand, and this would happen forever, but would eventually reach the point where it would begin to contract.
This did not seem right to him, so Einstein needed to explain the way to keep gravity in order to explain the static universe. After all, most physicists and astronomers of his time simply assumed that this was so. So, Einstein invented the Fudge factor, called the "cosmological constant", which gave the equations order and led to a non-expanding and non-contracting universe. He came up with the sign "lambda" (Greek letter), denoting the density of energy in the vacuum of space. She manages the expansion, and her lack stops this process. Now a factor was needed to explain the cosmological theory.
How to calculate?
Albert Einstein presented the first version of the general theory of relativity (GR) to the public on November 25, 1915. In the original, Einstein’s equations looked like this:
In the modern world, the cosmological constant is equal to:
This equation describes the theory of relativity. Also a constant is also called a lambda member.
Galaxies and the expanding universe
The cosmological constant did not correct everything as he expected. In fact, it worked, but only for a while. The problem of the cosmological constant has not been solved.
This continued until another young scientist, Edwin Hubble, made a deep observation of variable stars in distant galaxies. Their flickering showed the distance to these space structures and much more.
Hubble’s work not only demonstrated that the Universe included many other galaxies, but, as it turned out, it was expanding, and now we know that the speed of this process changes over time. This greatly reduced Einstein's cosmological constant to zero, and the great scientist had to reconsider his assumptions. Researchers have not completely abandoned it. However, Einstein later called adding his constant to the general theory of relativity the greatest mistake in his life. But is it?
New cosmological constant
In 1998, a team of scientists working with the Hubble Space Telescope, studying distant supernovae, noticed something completely unexpected: the expansion of the universe is accelerating. Moreover, the pace of the process is not what they expected, and in the past were different.
Given that the universe is filled with mass, it seems logical that expansion should slow down, even if it were so insignificant. Thus, this discovery seemed to contradict what Einstein's equations and cosmological constant predicted. Astronomers did not understand how to explain the apparent acceleration of expansion. Why, how does this happen?
Answers on questions
To explain acceleration and cosmological ideas about this, scientists returned to the idea of the original theory.
Their latest assumptions do not exclude the existence of what is called dark energy. This is something that cannot be seen or felt, but its effects can be measured. This is the same as dark matter: its effect can be determined by the way it affects light and visible matter.
Astronomers may not yet know what this dark energy is. However, they know that it affects the expansion of the universe. To understand these processes, more time is needed for observation and analysis. Maybe cosmological theory is not such a bad idea? In the end, it can be explained if we assume that dark energy does exist. Apparently, this is exactly what scientists need to look for further explanations.
What was in the beginning?
Einstein's initial cosmological model was a static homogeneous model with spherical geometry. The gravitational effect of matter caused an acceleration in this structure, which Einstein could not explain, since at that time it was not known that the Universe was expanding. Therefore, the scientist introduced the cosmological constant into his equations of the general theory of relativity. This constant is used to counteract the gravitational pull of matter, and therefore it has been described as an anti-gravity effect.
Omega Lambda
Instead of the cosmological constant itself, researchers often refer to the relationship between the energy density due to it and the critical density of the universe. This value is usually denoted as: ΩΛ. In a flat Universe, ΩΛ corresponds to the fraction of its energy density, which is also explained by the cosmological constant.
Note that this definition is associated with the critical density of the current era. It changes over time, but the energy density due to the cosmological constant remains unchanged throughout the history of the universe.
Let us further consider how modern scientists develop this theory.
Cosmological evidence
The current study of the accelerating Universe is now very active, with many different experiments covering completely different time scales, length scales and physical processes. The cosmological model of CDM is created, in which the Universe is flat and has the following characteristics:
- energy density of about 4% of baryonic matter;
- 23% of dark matter;
- 73% of the cosmological constant.
A critical result of the observations that brought the cosmological constant to its modern significance was the discovery that the distant supernovae of type Ia (0 <z <1), used as standard candles, were weaker than expected in a decelerating Universe. Since then, many groups have confirmed this result with more supernovae and a wider range of redshifts.
We explain in more detail. Of particular importance in the modern cosmological concept are the observations that supernovae with an extremely high redshift (z> 1) are brighter than expected, which is the signature that is expected from the deceleration time preceding our current acceleration period. Prior to the 1998 release of supernova research results, there were already several lines of evidence that paved the way for the relatively quick adoption of supernova theory of acceleration of the universe. In particular, three of them:
- The universe was younger than the oldest stars. Their evolution is well studied, and their observations in globular clusters and other places show that the oldest formations are more than 13 billion years old. We can compare this with the age of the Universe, measuring its expansion rate today and tracing it to the time of the Big Bang. If the Universe slowed down to its current speed, then the age would be less than if it would accelerate to its current rate. A flat universe, consisting only of matter, will be about 9 billion years old - a serious problem, given that it is several billion years younger than the oldest stars. On the other hand, a flat universe with 74% cosmological constant would be about 13.7 billion years. Thus, the observation that it is currently accelerating has resolved the age paradox.
- Too many distant galaxies. Their number has already been widely used in attempts to estimate the deceleration of the expansion of the Universe. The volume of space between two redshifts differs depending on the expansion history (for a given solid angle). Using the number of galaxies between two redshifts as a measure of the volume of space, observers determined that distant objects seemed too large compared to the predictions of a slowing universe. Either the luminosity of galaxies, or their number per unit volume, evolved unexpectedly over time, or the volumes that we calculated were incorrect. Accelerating matter could explain the observations without invoking any strange theory of galaxy evolution.
- The observed flatness of the universe (despite incomplete evidence). Using measurements of temperature fluctuations in cosmic microwave background radiation (CMB), starting from the time when the Universe was approximately 380,000 years old, we can conclude that it is spatially flat within a few percent. By combining these data with an accurate measurement of the density of matter in the universe, it becomes clear that it has only about 23% of the critical density. One way to explain the missing energy density is to apply a cosmological constant. As it turned out, a certain amount of it is simply necessary to explain the acceleration observed according to the supernova. This was just the factor that is needed to make the universe flat. Therefore, the cosmological constant resolved a clear contradiction between the observations of the density of matter and CMB.
What is the point?
To answer your questions, consider the following. We will try to explain the physical meaning of the cosmological constant.
We take the OTO-1917 equation and take out the metric tensor g ab . Therefore, inside the brackets we still have the expression (R / 2 - Λ). The value of R is represented without indices - this is the usual, scalar curvature. If you explain on the fingers - this is the reciprocal of the radius of the circle / sphere. Flat space corresponds to R = 0.
In this interpretation, the non-zero value of Λ means that our Universe is curved on its own, including in the absence of any gravity. However, most physicists do not believe this and believe that the observed curvature must have some internal reason.
Dark matter
This term is used for a hypothetical substance in the Universe. It is intended to explain the mass of problems of the standard cosmological model of the Big Bang. Astronomers suggest that about 25% of the universe consists of dark matter (possibly collected from non-standard particles such as neutrinos, axions, or weakly interacting massive particles [WIMPs]). And 70% of the Universe in their models consists of even more obscure dark energy, leaving only 5% for ordinary matter.
Creationist cosmology
In 1915, Einstein solved the problem of publishing his general theory of relativity. She showed that anomalous precession is a consequence of how gravity distorts space and time and controls the movements of the planets when they especially approach massive bodies, where the curvature of space is most pronounced.
Newtonian gravity is not a sufficiently accurate description of planetary motion. Especially when the curvature of space departs from Euclidean flatness. And the general theory of relativity explains the observed behavior almost exactly. Thus, neither dark matter, which some suggested was in the invisible ring of matter around the Sun, nor the planet Vulcan itself, were necessary to explain the anomaly.
conclusions
In the early days, the cosmological constant would be negligible. In later days, the density of matter will be essentially zero, and the universe will be empty. We live in that short cosmological era when both matter and vacuum are of comparable magnitude.
In the framework of the component of matter, apparently, there are contributions from both the baryons and the non-baryon source, both of them are comparable (at least, their ratio does not depend on time). This theory staggers under the burden of its unnaturalness, but, nevertheless, crosses the finish line much earlier than competitors, it is so well consistent with the data.
In addition to confirming (or refuting) this scenario, the main task of cosmologists and physicists in the coming years will be to understand whether these apparently unpleasant aspects of our Universe are simply amazing coincidences or actually reflect the basic structure that we don't understand yet.
If we are lucky, then everything that seems unnatural now will serve as the key to a deeper understanding of fundamental physics.