The Big Bang Theory describes how the universe expanded from an initial extremely hot and dense state approximately 13.7 billion years ago. As the universe rapidly expanded and cooled, simple subatomic particles formed, eventually combining to create the first atoms, mostly hydrogen and helium. Over billions of years, gravity caused clouds of these primordial elements to collapse and form the first stars and galaxies. Astronomical observations and mathematical models support this theory, including the cosmic microwave background radiation, Hubble's Law of galaxy redshifts, and the abundance of light elements found throughout the universe. While many aspects of the Big Bang Theory are well established, questions remain about what preceded this event and the ultimate fate of the expanding universe.

1. The Big Bang Theory
By Marina García, Jade Turner and
Marina Pascual 4º ESO B

2. The Big Bang Theory is the way we explain
what happen for the creation of our Universe.
It is the model that describes the early
discovery of it.

3. It occurred approximately 13,7 billion years
ago. And the Universe was extremely hot and
dense. There are many hypothesis surrounding
the Big Bang Theory, one of these is that
people tend to imagine a giant explosion, but
however it was not, it is a continuous
expansion.

4. After the initial expansion, the Universe
cooled enough to allow energy to be converted
into various subatomic particles, including
protons, neutrons and electrons.

5. The majority of atoms that were produced by
Big Bang Theory are hydrogen, helium and
traces of lithium.
Giant clouds of these primordial elements later
coalesced through gravity to form stars and
galaxies, and the heavier elements were
synthesized either within stars or during
supernovae.

6. Astronomers combine mathematical models
with observations to develop workable
theories of how the Universe came to be.
According to many experts, space did not exist
before the Big Bang.

7. The core ideas of the Big Bang, the expansion,
the early hot state, the formation of light
elements, and the formation of galaxies, are
deriver from these observations.

8. The mathematical support of the Big Bang
Theory includes Albert Einstein’s Theory of
Relativity along with standard theories of
fundamental particles.

9. What happened:
If we would have looked at the Universe one
second after the Big Bang, we would see a 10
billion degree mass of neutrons, protons,
electrons, positrons, photons and neutrinos.

10. What happened:
Then, as time went on, we would see the
Universe cooling down, the neutrons decaying
into protons and electrons, or combining with
protons to make an isotope of hydrogen.

11. What happened:
As it continued cooling, it eventually reach the
temperature where electrons combined with
nuclei to form neutral atoms.

12. What happened:
Before this ‘recombination’ occurred, the
Universe would have been opaque because the
free electrons would have caused light. But
when the free electrons were absorbed to form
neutral atoms, the Universe became
transparent, and that is why we nowadays see
the cosmic background radiation.

13. Evidence for the Theory:
1. We are sure that the universe had a beginning.
2. Galaxies appear to be moving away from us at
speeds proportional to their distance; this is called
‘Hubble’s Law’
3. If the universe was initially very hot, we should be
able to find some remnant of the heat (Cosmic
Microwave Background radiation).
4. The abundance of light elements, hydrogen and
helium found in the observable universe.

14. We do not know where it came from, why it is
here, or even where it is. All we really know is
that we are inside of it and at one time it did
not exist and neither did we.
One of the goals has long been to decide
whether the Universe will expand forever, or
whether it will someday stop, turn around, and
collapse in a ‘Big Crunch’.