Image source [1]: The Hubble eXtreme Deep Field (XDF) was completed in September 2012 and shows the farthest galaxies ever photographed.
Hello friends, continuing with the previous post about cosmology [1].
Hubble's law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model. The motion of astronomical objects due to this expansion is known as the Hubble flow.
Hubble's law would tell us that the further away the galaxies are, the quicker they get away from us. If we turn back the expansion movement, the more distant galaxies would approach more quickly, the closest ones slowly, and all would arrive "here" at the same time. It is important to note that Hubble's law is only approximate, and only validates for nearby galaxies.
The relative expansion of the universe is parametrized by a dimensionless scale factor a. Also known as the cosmic scale factor or sometimes the Robertson-Walker scale factor, this is a key parameter of the Friedmann equations.
In fact physics and physical cosmology, Planck units are a set of units of measurement defined in terms of five universal physical constants, in such a way that these five physical constants take on the numerical value of 1 when expressed in terms of these units. Planck's time is usually identified with the frontier of our knowledge about the universe, requiring the previous times a theoretical physics still to be developed, although the first steps to transcend it begin to take place. The universe then had to have certainly peculiar properties. In Planck's time, the four basic interactions of nature (gravitational, electromagnetic, weak and strong) were unified. Max Planck was unaware of this period of the universe, but this takes its name because I build a system of units with which no universal constant appears (all are equal to one) and all the magnitudes of physics are dimensionless.
The relativistic language
General relativity uses a different language and interpretation although the equations that are obtained and, therefore, the conclusions that are deduced, are the same. Newton's cosmology, although it has actually been developed recently, without the intervention of Newton. It has a naive approach although of great introductory power and we have limited it.