BIG BANG MODEL OF OUR UNIVERSE
There are many models for understanding how the universe started and how the present universe formed in which we are living. The very successful model in describing our universe is the big bang model. Astrophysicists predicted that the big bang occurred 13.8 billion years ago. The name suggests that all the matter was ejected out with a bang but this is not the scenario but the explanation of the big bang theory is something different than the name suggests. It is rather the expansion of the space itself. The big bang model predicts that the universe formed from the singularity. All space and time are contained in a singularity.
And there is no meaning of space and time before the singularity.
(Singularity is where all the physics laws break down)
Therefore, time started when the big bang occurred, the time before the big bang is meaningless or undefined. The space between any two galaxies is expanding and the acceleration of the expansion is driven by dark energy which we still do not know what it is.
There was a time when many of the astrophysicists were against the big bang and supporting the steady-state model (we are not actually going deep and knowing what is a steady-state model but the basic idea is universe was homogeneous and isotropic and there is no origin and no singularity from which the universe was formed.) but after the discovery of some pieces of evidence supporting the big bang model, it is accepted universally by all physicists and astronomers.
The main three predictions of the big bang model are
- the universe is expanding with correlation with the distance (more farthest galaxies are drifting away with more speed)
- The present universe should be filled with radiation of the early universe
- The universe should contain approximately 75% hydrogen and 25% helium (some amount of helium)
surprisingly these three were proven to be true and support the big bang model to some extent.
why did I say some extend? because the big bang model doesn’t explain some of the facts of the universe.
the three questions which cannot be answered by the big bang model are:
- how the matter exceeded the anti-matter (when matter and antimatter combine, they annihilate and releases energy if all matter and antimatter annihilated in the early universe then galaxies and stars wouldn’t form and I would not be able to write this blog)
- how the structure is formed in the universe (formation of galaxies and stars)
- why did the big bang occurred and what triggered the big bang to happen?
The first prediction was confirmed by Edwin Hubble in 1924. he discovered that all the galaxies are moving further away from each other (which means galaxies are redshifted). Expansion of space does not mean that galaxies are moving farther away from each other to fill the empty universe. The space between any two galaxies is increasing. Some galaxies which are comparatively nearer to us are blue-shifted due to the dominance of the gravitational force between galaxies. Hubble proved that expansion of the space correlates with distance. (speed is directly proportional to the distance)
This is a great triumph of the big bang model.
The second prediction was confirmed in 1965 by two scientists in bell laboratory the discovery of cosmic microwave background (CMB). CMB is the radiation from the early hot and dense universe.
The radiation gradually decreased energy and now we see them like microwaves. Due to the expansion of space wavelength got stretched to the wavelength of microwaves. After the cosmic microwave background was discovered steady-state theory was ruled out.
We know that nuclear fusion occurs in the core of the sun (nuclear fusion is the formation of helium from hydrogen)
Since the early universe was very hot and dense big bang model predicts that nuclear fusion must occur in the early universe. Then we must be able to detect a certain amount of helium in the universe. astrophysicists calculated that the present universe contains approximately 75% hydrogen and 25% helium. This is the third prediction in the big bang theory.
but there are many facts of the universe that cannot be explained with the big bang model.
Therefore, this model is not an ultimate model of the universe.
In the future, we may develop a model that may explain all the questions.