We all know how the universe began. For those who don’t know, please come out from beneath the rock you’ve been living under. The Big Bang Theory is far more than just a television show that stereotypes people who love science. To be honest, however, the term ‘Big Bang’ can be very misleading at times. In theory, there was no actual ‘bang’, per se, at least not in the “explosion-with-debris-flying-everywhere-to-create-the-universe” sense.
Once upon a time, almost 14 billion years ago, there was a singularity. For some as yet unknown reason, that singularity then expanded into the infinite everything of the universe in an inconceivably fast moment. For the past 13.8 billion years or so, the universe has continued to expand. I know what you must be thinking – how can infinity expand? Well, it can if it is inherently (and limitlessly) stretchable. In other words, some infinities ARE bigger than other infinities.
The question that naturally arises from this theory of an ever-expanding, infinite universe is: when will it stop expanding? And if it does, what would be the cause of it stopping? Logically, or rather, cosmologically, this would be the point where the universe begins to die.
THE BIG CRUNCH
If the critical density of the universe is high, then the force of gravity would give rise to a positively curved, or a closed, universe. It is assumed that at some point, the gravity of the dense universe would overpower the expansion forces and pull it all back inward, like a sad balloon having the air sucked out of it after a disappointing birthday party. The Big Bang would be countered and negated by the Big Crunch, which would bring the universe back into a singularity. At that point, it is theorized that the singularity could then expand again, giving birth to a newer, more exciting birthday par– *ahem* — universe. This theory has a certain elegance to it, but as we know, the universe is under no debt to make sense to us.
THE BIG FREEZE
If the critical density of the universe is low, however, then the effect of gravity would never be able to hold the universe in a closed shape (such as the aforementioned balloon). This would lead to a negatively curved, or an open, universe. Gravity, in this case, would not be able to restrain the expansion of the universe. The universe would continue to expand until it runs out of energy. Everything would eventually stop spinning and flying through space and slow to a whimpering death, which is why this potential endgame is called the Big Freeze.
If the critical density is just right, the expansion of the universe will go on forever, but would slow itself down, causing a flat universe. With the use of the WMAP spacecraft, it was discovered that the actual density of the universe would lead to a flat universe. However, that’s not the only breakthrough discovery in the possible death of our universe. In 1998, a team of astronomers observed distant supernovae to get a sense of how fast the universe was slowing down. To their surprise, they discovered that rather than decelerating, the universe was actually accelerating! Thousands of scientists around the world groaned as one, realizing that they needed to find a better theory!
Credit: Rob Byron
The question, obviously, is what mysterious force could be speeding up the process of expansion? Scientists know next to nothing about it, and therefore call it Dark Energy, which presumably constitutes 68% of the universe. It behaves like an anti-gravitational force, pushing the universe towards expansion. The weirdest part about Dark Energy is that it seems to be a Cosmological Constant – as the volume of the universe increases, Dark Energy expands to keep its energy density constant.
In other words, Dark Energy keeps growing as the universe expands, but matter (5% ordinary matter and 27% dark matter) doesn’t. In fact, all matter will eventually be converted into energy. According to this logic, or rather, cosmo-logic, the universe will reach a stage of maximum entropy, where energy is evenly spread throughout. If there is no difference in energy, then there will be no work. Thus, the universe will finally cease to function. This scenario is called the Heat Death of the Universe.
However, don’t you worry about this happening anytime soon! Sure, the universe is going to sputter and die in a utopian state of thermodynamic equilibrium, but that is going to happen in a googol years (10 raised to the 100th power), and that is incomprehensibly far away from today. There is a very small chance that humanity would be around to witness any of the demise. Don’t start scribbling out bucket lists just yet! The universe isn’t going anywhere anytime soon. Phew!
- Big Crunch – Wikipedia
- Universe Today
- Heat Death Of The Universe – Wikipedia
- Distant Aupernovae Are Revealing The Crucial Time When The Expansion Of The Universe Changed From Decelerating To Accelerating – University of California, Irvine
- Scientific American