The CMB is remarkably uniform, it has a temperature of 2.725 degrees Kelvin above absolute zero.
Whatever the direction of the Universe, observe the satellites to the east, west, south or north, temperature is the same, it is measured at 2.725 degrees Kelvin. This implies that matter, any observable matter around us, has been in contact at some point to share this information.
2.725 Kelvin is the temperature balance between Big Bang universe hot and cold of the observable universe today.
It took 13.73 billion years to reach this equilibrium temperature. There is 13.73 billion years, a tremendous explosion of light, Big Bang, gives rise to the space, time, matter, a burning chaos of unimaginable heat, a shapeless pulp will swell, s' extend in all directions and cool slowly.
If we pour a glass of boiling water in a spherical tank of cold water, it will take some time for the temperature of the water molecules is balanced.
This will depend on the collisions between the molecules of cold water and hot water molecules.
The hot water molecules more energy will transfer energy to molecules of cold water, losing its own energy. The temperature is the expression of this molecular agitation.
The molecules faster, hotter, transmit energy to the molecules slow cooler.
The time required for the temperature of the water molecules, balanced, called the equilibration time.
In the example of water molecules, it is understood that to reach this equilibrium temperature, all water molecules were at one point in contact.
Our space is also in thermal equilibrium.
In our observable universe, cosmic radiation has 13.73 billion years to reach its equilibrium temperature.
Our horizon is the end of the aquarium, it is 13.73 billion years and we observe from the center of the aquarium.
In other words, on the horizon, all the molecules are the same distance from us.
This is where there is a problem with the Big Bang, as between molecules located at the north end and the molecules situated at the southern end, the distance is twice as large.
Now the horizon for all objects in the system, is only 13.73 billion years. Particles located at the north end and the particles located at the southern end, can not know because they are outside their respective horizon.
Nothing can travel faster than light, they have never been in contact yet the temperature is the same with surprising accuracy, of one hundred thousand (data COBE, Cosmic Background Explorer).
What is this mystery? Scientists have called "the problem of the horizon".
Should we review the theory of Big Bang?
How these regions of the universe, apparently disconnected from the standpoint of relativity, could exchange information.
The explanation could be given by cosmic inflation, which is a cosmological model where the observable universe has experienced a boom very violent.
This cosmological model explains both the problem of the horizon and the flatness problem.
This happens in the era of Planck, the cosmic clock strikes the first blow to 10-43 seconds.
The universe is a seething vacuum energy dense incredibly hot, then it is assumed, it swells suddenly, it's cosmic inflation. The universe is expanding so violent and 10-32 seconds, the first elements of matter and antimatter, are emerging.
Elementary particles and their antiparticles, quarks, electrons, neutrinos, photons, which are the constituents of the cosmic soup, are at this time, contact.
The initial region is initially homogeneous, then we will end up with a homogeneous region, in the observable universe as a whole.
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Image: The density fluctuations of 1/100 000th of Kelvin are treated in the microwave radiation fossil 2.73 K.
They show that about 380 000 years after the Big Bang, there were heterogeneous areas in the world, with a size between 100 and 1000 Mpc.