Quantum Cosmology: Birth of a Universe

Most of us are familiar with the typical high-school explanation for the origin of the Universe; it started with a “Big-Bang”. But, like much of the science you learn in school, this is a gross over-simplification. The Big-Bang Theory simply describes the rapid development of our Universe into its modern form and is not the ACTUAL origin of the Universe. But this still leaves a lot of questions. What did the Big-Bang come from? Where did “what it came from” come from? It turns out fundamental physics just may have the answer. However, to understand quantum cosmology we first need to understand a bit of quantum physics…

 The underlying principle of nearly all of quantum physics (physics of smaller-than-atom particles) is the Heisenberg Uncertainty Principle, or Uncertainty Principle for short. Basically it states that you cannot know both the position of a particle and its momentum at the same time, because as you gain information about one, you lose information about the other. Its equation is:

“Uncertainty in position multiplied by uncertainty in momentum is equal to or greater than Plank’s constant divided by 2 pi.”

The reason why this is so fundamental to quantum physics is because it doesn’t just apply to position and momentum. It applies to many other things, such as the energy of a particular point in space and the time in which it is observed (observed here doesn’t refer to human interference. It refers to the interaction of a quantum system with a classical one). Therefore, the equation can be re-worded as:

"Uncertainty in the energy of a system multiplied by uncertainty in the time it is observed is equal to or greater than Plank's constant divided by 2 pi."

Now that we’ve looked at the basics behind quantum physics, let us look at some of the possible hypotheses to explain the origin of the Universe:

#1: Vilenkin Tunneling

What the above equation actually implies then is that the energy of a vacuum (empty space) can actually contain energy, which simply spontaneously “pops” into existence. Of course, to satisfy the uncertainty principle, this energy (E) then has to disappear within a quick enough amount of time (t).

However, if this phenomenon is constantly occurring, it would mean that energy is constantly (at an extremely rapid speed) being created and then destroyed. This means that a vacuum containing no pre-existing matter or energy still has short-term energy, which’s constantly appearing and disappearing. So the energy level of a vacuum’s constantly fluctuating. Are you keeping up so far? Good.

Special relativity tells us that energy, at high enough levels, can turn into matter (E=mc2). Therefore, when the energy of a vacuum randomly fluctuates to a high enough level, particles will materialize from the energy. These are what we call “virtual particles”.

Interesting: Some physicists also describe virtual particles by referring to a phenomenon known as “quantum tunneling”, where a particle may “tunnel” through a barrier it normally shouldn’t be able to (in this case, the barrier is an energy one preventing a particle coming into existence). The way it works is that a particle can “borrow” energy from its surrounding system, and thus tunnel through the barrier. This phenomenon is rare but possible thanks to the uncertainty principle. However, this is just another way of describing the same virtual particles, and is thus not all that important to know.

Of course, they’re called “virtual” particles as they too have to satisfy the uncertainty principle. They can only exist within a specific time frame before they have to disappear. Therefore, virtual particles always materialize in pairs; one matter and one anti-matter version (to annihilate each other). There’s also the problem of “what are the actual particles themselves popping into, if space-time doesn’t exist yet?”

The solution to the 2^nd problem is Vilenkin Tunneling. Since time and space do not exist independently of the universe, the tunneling must be from nothing. And by 'nothing' I do NOT mean empty space. I mean a state where space and time had yet to exist!





A basic diagram explaining how the particles come into existence into... nothing.

Of course, there’s still the 1^st problem of avoiding annihilation. Well, generally speaking, virtual particles will usually annihilate each other soon after creation. However, if inflation (which will be talked about further in a future article; "Big-Bang: Cosmic Evolution") is invoked, the particle can escape snnihilation by expanding exponentially. This inflating particle is what we now call... the Universe.

#2: Hawking-Hartle Model

Stephen Hawking’s and James Hartle’s “no-boundary” proposal states that time has no defined limit or boundary. Instead, time starts over.

The model states that in the beginning (pre-Big-Bang), there were actually 4 dimensions of space, and a quantum fluctuation (uncertainty principle) caused one of those states to decohere (act classically) and become time, thereby marking the beginning of the Universe and leading to the Big-Bang. 

Interesting: The model is also similar (yet different) to the cyclic models as it says the Universe repeats itself. Imagine a video that replays when it’s finished. The video itself isn’t infinite; it’s finite in size (it may be an hour long). But it continues to play over and over again. Our Universe is a replaying video. That means history, the creation of the Universe, Earth, humans, the Internet and your birth (as well as the end) will be replayed forever. Time behaves like any other dimension of space. It is finite, yet boundless and without any defined limit.

#3: Cyclic Models

This model of the Big-Bang proposes that not only is the Big-Bang eternal in the future (i.e. will continue forever), but is past infinite as well (negative infinity), and thus had no actual cause. Examples include the most recent Baum-Frampton Model and the unique inflationary/cyclic Aguirre-Gratton model. I would go into detail about how these eternal Big-Bang models are possible, but the arguments for it are mostly mathematical and difficult to explain.

A diagram of de Sitter space-time (vacuum solution of how space’s structured, according to General Relativity). To summarize it, if one assumes the space to be divided into 2 sections which can’t interact with each other… it’s mathematically possible for inflation to extend infinitely into the past, according to the Aguirre-Gratton model.

So there you have it… 3 possible hypotheses for the creation (or that at least try to explain the creation) of the Universe. Vilenkin tunneling IS still a hypothesis, but it’s the one most supported by physicists. In the next article we’ll look at the Big-Bang, and how the Universe developed from its humble origins into its modern form.

Acknowledgements

Thanks to Hasan Mohammad for co-authoring and editing this article. You can read his own science-related blog here: http://hasansthoughts.blogspot.com.au/