Why the Big Bang is Still Happening | Unveiled

Why the Big Bang Is Still Happening

Many great thinkers have pondered the Universe's origin and fate, but some of our biggest questions remain unanswered. While often mistaken for a singular event, the Big Bang is actually still ongoing.

This is Unveiled, and today we’re answering the extraordinary question; Why is the Big Bang still happening?

Most people have heard about the Big Bang, but what does the theory actually entail? A common misconception is that the Big Bang explains the inception of the universe, but that’s not actually the case. Since the dawn of mankind, we’ve sought to understand the cosmos, but why there’s something rather than nothing remains a mystery! The Big Bang suggests that – 13.8 billion years ago – everything in existence was packed into a point of infinite density and temperature. Eventually, the floodgates opened and the Universe spread out. Along with progressively cooling down, the Universe has continued to expand ever since.

This point of infinite density and temperature is known as a singularity. Singularities are also thought to exist WITHIN our universe, at the heart of black holes. Because black holes have so much mass, their gravitational pull drags everything nearby towards them - even light. The gravitational singularity at their centre possess near-infinite density. The Big Bang theory posits that the universe was once compressed into the ultimate singularity, one with a high enough mass and gravity to hold all matter within a single minuscule spot. In a singularity, matter, energy, and everything in between is squashed together. Along with everything else, this initial singularity also encompassed time and space, which were indistinguishable from each other.

A singularity stores an insane amount of heat and, at a certain point, the universe began to expand and cool down. What triggered this expansion? The Big Bang theory doesn’t attempt to answer this question, but the model does provide an account of the universe's history and possible future.

Despite the theory’s name, the Universe probably did not launch with a literal bang. Rather, it was a rapid expansion of spacetime, during which the building blocks for what we see in the universe were created. Rather than everything flying away from a central point, everything in the universe is getting further away from everything else. In other words, the scale of space itself is increasing. Physical matter, on the other hand, is finite.

The Big Bang theory can be traced back to Albert Einstein's general theory of relativity, which – in turn – stemmed from Einstein having an issue with Isaac Newton's law of gravitation. General relativity states that gravity is the outcome of mass bending space and time, although this only becomes truly noteworthy when gigantic bodies are involved. Einstein originally backed a static Universe, but other researchers, most notably Belgian priest Georges Lemaître, derived solutions to his equations that implied an expanding cosmos.

The first to actually OBSERVE that the universe is expanding was American astronomer Edwin Hubble, building on the work of countryman Vesto Slipher. In 1917, Slipher had observed that distant galaxies are getting further away from Earth. In 1929, Hubble realized that not only are these galaxies receding, they’re moving away at a speed proportional to their distance from us. How can we tell? Well, the secret lies in light.

Like sound, light travels in waves. Think about the way a car sounds when it speeds past us. As it approaches, there’s less and less time between the arrival of each sound wave. Then as the car moves away, the opposite occurs; the frequency of the waves becomes lower. The phenomenon is known as the Doppler Effect, and it works with light too, except that instead of a shift in pitch, there’s a shift in color. When an object is moving towards the observer, the color shifts towards the blue end of the spectrum. When it’s moving away, a red-shift is observed. Distant galaxies are all red-shifted, meaning that they’re all moving away from the Milky Way. By observing a cosmological red-shift, Hubble learned that the universe is expanding.

Unlike the Doppler Effect, this red-shift is not due to the two bodies moving away from each other, but occurs because the space between them is expanding. Light from the Milky Way's closest spiral galaxy neighbor needs more than 2 million years to reach Earth. While traveling, the light’s wavelength expands and the more distant a galaxy, the longer the red-shift. Therefore, galaxies further away are receding at a faster rate.

Although the red-shift is the most convincing data supporting the expansion theory, it’s hardly the only piece of evidence. About 380,000 years after the Big Bang, the universe had expanded and cooled enough for atoms to form. This left fewer free electrons bouncing around, meaning that the electromagnetic radiation from the Big Bang was no longer being scattered. Known as the Cosmic Microwave Background, this ancient light is still observable nowadays throughout the entire Universe. CMB is essentially a remnant from the Universe's infancy. Over the last 13.8 billion years, the CMB has cooled considerably; more importantly, the radiation's temperature is generally the same regardless of location, be it the edge of the Universe or the Milky Way.

OK – so the Universe is expanding. But to what end? Will things ultimately slow down? Or is there no end in sight? Originally, scientists believed that due to the total mass of the universe, gravity might reduce the rate of expansion, perhaps even reversing it into a Big Crunch. However, in 1998, observations of distant supernovae led to the discovery that the universe’s rate of expansion is actually accelerating!

Why is this happening? At this point, little is truly known, but some scientists believe that dark energy may be responsible. While stars and galaxies are huge, normal matter only makes up around 5% of the universe. The rest is believed to be dark energy and dark matter, although both remain enigmas. Dark energy alone comprises around 68% of what’s out there. One theory is that dark energy is actually a property of “empty” space, and that the amount of dark energy increases as the universe stretches. In turn, this energy causes the rate of expansion to increase, creating a cycle where constant acceleration is the only option. This could mean that rather than a Big Crunch, we’ll really be facing a Big Rip. As the expansion accelerates and galaxies drift further apart, the universe could be stretched until atoms begin to split apart.

Regardless of what the future holds, the Big Bang is a continuous process, dating back to the Universe's inception. The observed red-shifted light emitted by galaxies, along with the progressively cooling cosmic background radiation, show that the Universe is only getting bigger. And that's why the Big Bang is still happening.