There was nothing and nowhere 14 billion years ago. An entity the size of a subatomic particle swelled out of proportion in an instant, and from a complete vacuum, suddenly (it should be said) an entire universe emerged. Big Bang is the most used term for this unique event.
The spherical region, about 90 billion light years in diameter, which we call the "observable universe" (or "Hubble sphere"), is the only portion of space where light has had time to reach 13,8 billions of years since the beginning of the universe.
As the cosmos expands, things end up outside the Hubble sphere (and therefore out of our view) because the expansion of space has increased the distances between objects faster than light.
Three hypotheses about the universe
The universe is made up of three principles based on theory and observation:
- The laws of physics are constant and apply to all places and times.
- The cosmos is homogeneous, or more or less uniform in all directions (though not necessarily all the time).
- Humanity does not have a privileged observation point, not being exactly at the center of the universe;
These characteristics are consistent with the scientific deductions drawn from Einstein's theories. The theories of the great scientist imply that:
- The universe expands.
- The universe has emerged in the past from a hot and dense state, and in a limited time.
- The lighter elements, hydrogen and helium, were created in the first moments of time.
- Microwave radiation permeates all of space, a remnant of the phase transition that occurred when the hot early universe cooled enough for atoms to form.
What if some of the basic assumptions are wrong? Beyond the Big Bang.
If any of the astronomers' basic assumptions were wrong, the Big Bang theory would not explain the properties of this universe. Could it be that a Big Bang never happened? And what would have been in its place?
Here are three alternative theories.
The first is that steady state, one of the first rivals of the Big Bang theory. The steady state theory states that the universe continually generates itself in space to explain its apparent inflation. This type of universe would be infinite in length, with no beginning or end. However, a mountain of evidence uncovered since the mid-60s indicates this idea it is false.
The second is the theory ofeternal inflation. According to the notion of eternal inflation, the expansion of the universe goes on indefinitely: new universes are created somewhere in the multiverse, like infinite "bubbles". In these other universes there may be physical laws different from ours, indeed: according to this theory ours would be one of the few universes that completely follow the standard model of cosmology.
The third is called oscillating universe theory. It features an endless series of Big Bangs, followed by Big Crunches that restart the cycle, indefinitely.
If they seem stranger to you than the Big Bang, you will see in the future!
The conclusions of quantum gravity and string theory increasingly suggest that the universe is not what it appears to us. It could be a flat hologram projected onto the surface of a globe, for example. Alternatively, it could be an all-digital simulation performed on a huge computer system.
We will never know, right? Maybe.