# What is the explanation for rapid inflation just after the big bang?

I often hear about cosmic inflation occurring rapidly after the Big Bang, but have never came across any explanation for it. What supposedly caused this inflationary period in the early universe? Also, my assumption is that the laws of physics, i.e. light speed and relativity, did not exist during inflation, but were after effects. Is that a correct assumption? Thanks!

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Have you read the wikipedia article? (en.wikipedia.org/wiki/Inflation_(cosmology)) – Tracy Cramer Jul 9 '14 at 23:21
Afaik, there is no physical reason for it. Inflation is a model to explain some observations, but I never heard about forces or conditions which caused it. I hope someone more expert can say something. – Py-ser Jul 10 '14 at 7:17
Well, what forces "cause" electromagnetism for instance? The inflaton field changes state and releases energy - that energy release results in "inflation". – adrianmcmenamin Jul 12 '14 at 14:27

With normal matter, the strength of gravity depends on the stress-energy tensor, which, in an isotropic homogeneous universe, has trace of $\rho + 3p$. Note that the pressure from relativistic particles (photons and neutrinos) enhances the mass density in slowing down expansion. In inflation theory, it is assumed that there was a scalar field (perhaps) in a small section of the universe that began in a false vacuum state. That is, the field's energy density remained roughly constant as the universe began to inflate, and therefore the total energy of this field grew as the volume of the universe grew. The field's pressure was negative and greatly overwhelmed the inward force of the density of normal matter and pressure. It is this negative pressure that rapidly expanded this section of the universe by many factors.