The Big Crunch

The Big Crunch is one suggested theory for how the Universe may end. The Friedmann equations, which physicist Alexander Friedmann derived in 1922, are what gave rise to the concept of the big crunch. Under the presumption that the Universe is homogeneous and isotropic, these equations relate to the Universe’s expansion or contraction. The force of gravitational attraction and the outward momentum created of the big bang were thought to be the two principal forces that determined whether the Universe would expand or contract. The Universe would then  rather simply constrict if gravity were to overpower expansion. This happens when the Universe’s actual density exceeds the critical density determined by the Friedmann equations. For comparison, our cosmos has a critical density of roughly 5.9 protons per cubic meter and an actual density of roughly 1 proton every 4 cubic meters. Exceeding the critical density would result in the collapse of the cosmos or the creation of a super-dense black hole.

The Big Bounce

Then, you might be curious as to what occurs after collapse. Many scientists believe it would just “bounce” back, also known as ‘the Big Bounce’. When the Universe collapses it will become the size of a Planck’s length, or roughly 10-35 m. The Universe’s Volume is very close to 0 at this scale, Therefore as the Universe still has Mass it’s density is almost infinite. In that situation, the processes of the Big Bang such as inflation would all repeat again recreating the Universe. This is currently theorised to be due to Loop Quantum gravity. The Universe could repeat itself endlessly as a result of this process, restarting time and time again. Possibly, our own Universe is not the first in this cycle simply just another repeat in a long line of repeats. It is also speculated that every time the Universe begins again, it will be the same Universe i.e., the timeline we exist in today will be the same timeline in the new Universe and all the events of our timeline will once again occur in the new Universe.

Dark Energy

The Big Crunch as a thoery was acceptable up until two international teams of scientists discovered dark energy in 1998. The real driving force behind expansion. In 2004, more in depth measurements of dark energy were possible thanks to the Chandra X-ray observatory. They discovered that although dark energy has a fixed value, the amount of dark energy is increasing as the Universe gets bigger. This measurement suggests that the Universe is always expanding. There is little room for a Big Crunch in an expanding cosmos. However, we still don’t fully understand dark energy. Fortunately for us, the Nancy Grace Roman space telescope is set to launch in May 2027. The Nancy Grace Roman telescope’s objective is to learn more about the origins of dark energy and its function in the early cosmos. While the likelihood of the Big Crunch is currently minimal, there is still a possibility that with greater knowledge of the universe, collapse could still be possible. This is something that the Nancy Grace Roman will hopefully clarify.



Dr. Edward  J. Wollack(2015) What is the Ultimate fate of the Universe? -Nasa

William Harris(2021) How the Big Crunch Theory Works – How stuff works

Ashley Balzer(2020) Nasa’s WFIRST will help uncover the Universe’s fate -Nasa

Anna Heiney(2004) Chandra Discovery Sheds Light on Dark Energy – Nasa

Britt Grisworld(2014) What is the Universe Made Of?-Nasa

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