The universe began with a massive explosion called the “Big Bang”, and from the pure energy of the explosion came everything we know: you, me, Earth, and even the most fundamental of them all- space and time themselves were born out of the explosion. That’s what happened when the universe “exploded in to being”.

After the Big Bang, galaxies formed, in them stars, and around them planets. Soon the galaxies got farther and farther from other galaxies, and they continue to move farther from one another even now. The universe is in fact expanding.

The universe is so big that, in fact, the size of the entire universe is not known, cannot be known and will never be known. Scientists often use the term “observable universe”, since light from unobservable regions hasn’t had the time to get to us.

So what would happen if hypothetically the universe as we know it exploded again? I can’t think of any reason why the universe including empty space would explode, but let’s assume that all the stars in the universe exploded. That’s impossibly complex to think about too. So let’s dumb it down to ask: what if our sun spontaneously explodes spewing pure energy (total energy of the sun is 10⁴⁷ Joules) into space? 10⁴⁷ Joules is an enormous amount of energy!

Well, if you are on Earth, the first 8 minutes and 20 seconds after the explosion will be just a normal day, since it takes so much time for sunlight to reach us because of the large distance between us and the sun. But, after 8 minutes and 20 seconds, you will get a blast of radiation (or simply light) of energy 1.8*10³⁸ Joules, billion billion billion billion (1 followed by 36 zeros) times more powerful that your light bulb! This about a billion times larger than the energy required to vaporize our Earth, and will easily vaporize Earth. If Earth itself doesn’t exist, don’t worry about life. So, that is what happens when our sun explodes.

To imagine the whole observable universe exploding: lets do the math. Interestingly, googling showed our own Science Line read here for the number of stars in space: it looks like there are about 1 billion trillion (1 followed by 20 zeros) stars in the observable universe. Multiply the numbers, when all the stars, assuming that they are like our sun, in our universe exploded, they release 10⁶⁷ Joules of energy (1 followed by 67 zeros; a lot!). All of this energy will be spewed into space in the form of light.

These light rays will collide with one another and give rise to electrons, atoms, you (well, not the same you), etc... and a whole new universe that is ready to start (again) forming galaxies, stars and planets.

It is indeed mind boggling and humbling every time one thinks about the vastness and enormity of our universe.