Trinh Manh Do

A homogeneous universe

Why is the universe homogeneous?

In the standard Big Bang theory, when we go back in time, the current distance between any two points in space would decrease significantly. The current light signals between these two would also take a much shorter amount of time to approach the other. This case can be explained based on the gravitational force. If it was a sucking force, the universe expanding rate would theoretically decrease. The opposite however had occurred during the inflationary phase, the gravitational force was a pushing force which increased the expanding rate of the universe exponentially. This phase is described mathematically by a particular equation named Hartle-Hawking.

At the beginning of the inflationary phase (10^-35s after the Big Bang), the universe was slightly larger than a hydrogen atom. As a result of that, all regions in the universe could easily associate with each other and coordinate their most basic characteristics until they are extremely homogeneous. At the end, when the universe’s clock pointed 10^-32s, the universe inflated to a dimension of a galaxy cluster which is normally a group composed of more than 10 large galaxies. It is now bigger than 10 thousand billion billion billion billion times when compared to the size of a typical hydrogen atom. From here, it can be simply noticed that the different regions of the universe could no longer able to communicate with the other after this phase. Therefore the basic properties of the cosmos are considered to be extremely homogeneous.

In order to create a structural homogeneity, the inflation strongly associated with a “close ally” named the uncertainty principle. It is any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, such as position X and momentum P, can be determined simultaneously. This principle was first introduced in 1927 by a German physicist Heisenberg and started dominating the extremely tiny quantum world. It states that the more accurately the position of some particle is determined, the less precisely its momentum can be known and vice versa.

 XY >= h/(4pi)

Warner Heisenberg (1901-1976)

On the other hand, we have been told that our knowledge about the quantum world would be limited on the way approaching something called an absolute understanding. Such as, we can’t accurately measure the speed and the location of a particle in the same time. Or you will know exactly the speed and nothing about the location, or vice versa. This is called by the blurred quantum.

The “blur” is applied to explain the quantum energy field causing inflation. If we knew exactly how much energy was produced at a particular point of the field, we would define the variation of the particles in the field less accurately. This equivalent process directly relates to any quantum fluctuation happened in the field during this phase. Based on this, it is the cause of a huge amount of the particles and anti-particles appeared and then disappeared periodically in space.

The blurred quantum plays an important roles on making the cosmos homogeneous. By expanding space exponentially during the inflation, these infinitesimal fluctuations were amplified to a size of the Solar system. Due to that, the inflation has allowed quantum fluctuation to leave the subatomic world and to approach a new world with a larger scale.

The astrophysicists and the cosmologists discovered these quantum fluctuations in the structure of space by detecting the microwave background radiation, which is known as the remain temperature coming from the primitive universe. It is particularly expressed through some little smaller fluctuations and was called by the galactic seeds. Billion years later, based on the gravitational field, those galactic seeds suck the ambient particles, increase their mass, and finally give birth of hundreds of billions of galaxies in the observable universe. Each galaxy are decorated by hundreds of billions of star. That’s how the sky looks like nowadays.

Tonight, let’s observe the sky. Those stars and galaxies are naturally homogeneous combination of something incredibly small and the very large.

Trinh Manh Do

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