# If the Big Bang theory is true, what caused it to explode?

According to the Big Bang theory, all the matter in the universe was amassed together at one single point. If this was the case, why was it able to explode? The density of the mass would create a tremendous gravitational pull, stopping any explosion from happening.

• @HalHollis, not remotely?? I think to the average lay person, it's pretty close. And if that is so wrong, it's the fault of physicists for making it appear true. – Tom B. Mar 6 '18 at 19:04
• – Qmechanic Mar 6 '18 at 19:06
• @TomB., it's not as if PSE hasn't tried to remedy this misconception. For example, see this highly upvoted question: Did the Big Bang happen at a point? -"The simple answer is that no, the Big Bang did not happen at a point. Instead it happened everywhere in the universe at the same time. Consequences of this include:" – Hal Hollis Mar 6 '18 at 19:06
• @HalHollis Yes, but those answers also say that the distance between all points approaches zero the farther back you go, don't they? They also refer to incredible (if not infinite) densities, etc. so it seems like a very good question nonetheless. – Tom B. Mar 6 '18 at 19:14
• @HalHollis And honestly, I suppose I have a pet peeve regarding comments that criticize good faith questions for no apparent reason. – Tom B. Mar 6 '18 at 20:26

The Big bang cosmological model is based 1) on general relativity and 2) on quantum mechanics. Using known particle and nuclear physics processes the history of the universe is built up as seen below.

General relativity has solutions with singularities which are both attractive, as in black holes, and "explosive" as in the first Big Bang model. In GR energy is not a conserved quantity in general, so it can be postulated out of nothing.

The beginning of time is in the present model above modified with the quantum mechanical fuzzines seen in the plot. Quantum mechanics also contributes to the inflation period, where the inflaton field homogenizes the energy soup. After that, known particle physics and then nuclear physics are used to model the history of the universe as we observe it now.

According to the Big Bang theory, all the matter in the universe was amassed together at one single point.

So it is not one point at the present standard BB model, it is a fuzzy region in the beginning of time.

If this was the case, why was it able to explode?

For the same reason that a bomb explodes: the cohesive gravitational forces are very much smaller than the kinetic energy of the broken parts. In the case of the big bang the radiation motion of various quantum mechanical entities is very much stronger than the attractive gravitational interaction of these entities to each other.

The original explosion is allowed by the mathematics of general relativity, as stated above, there are many types of singularities in GR. In the present model the quantum mechanical nature contributions fit and thus explain the observations as seen in the cosmic microwave background data.

The density of the mass would create a tremendous gravitational pull, stopping any explosion from happening.

At the beginning it is an energy soup, it is not mass but a lot of radiations with quantum mechanical entities.

• do you know what that time line is between "neutral hydrogen forms" and "modern universe"? – Tom B. Mar 6 '18 at 20:31
• @TomB. It could be "Structure formation and the associated Epoch of Reionization", at $t \sim$ a few 100 Myr, which arguably changes the Universe from being boring to interesting. But the outward curvature of the "edge" of the Universe (the white, horizontalish lines) indicates the accelerated expansion which started at $t \sim$ 10.2 Gyr. The t axis is not scaled consistently, so it's difficult to tell. – pela Mar 6 '18 at 22:16
• @TomB. this chart background.uchicago.edu/~whu/SciAm/sym2.html gives it as 3o0.000.000 years from the CMB at 380.000years. very large errors are involved in these estimates , and also dependent on the models used. – anna v Mar 7 '18 at 6:52