A Quantum Fluctuation

Hello to those of you still reading despite the rather large hiatus RTU has been experiencing. To reiterate I am currently studying for my MSc degree in Theoretical Physics and with seven exams looming on the horizon I have had to neglect all forms of activity aside from burying my head in lecture notes.

Today I felt like breaking that silence to come to write about a process, that I like to think embodies the phrase ‘making a mountain out of a molehill’ in the truly cosmic sense. How, quantum fluctuations in the dawn of the universe were the seeds that developed into the stars, nebulae and galaxies we see today. The origin of such rich complex structure can be traced back to tiny quantum fluctuations in those first moments of our universe.


The paradigm most accepted by cosmologists today for describing the early universe is inflation. This is the idea that the early universe underwent a period of rapid expansion, small patches of spacetime were vastly stretched out and the universe grew at an accelerated pace. The theory of inflation is proposed for many reasons, including it’s ability to explain why the universe is observed to be flat and why it is observed to be homogenous. By a homogenous universe we mean it is, on large scales, the same in every direction we look. For example when we measure the Cosmic Microwave Background radiation (for our purposes here think of this as the background temperature of the universe) it is the same on every patch of the sky. Inflation allows these patches that are so far flung apart to have been able to be close enough together and ‘talk’ to each other in the early universe that they could have equilibrated their temperatures. I hope to do a more detailed post on the workings of inflation later. The only idea we need today is the rapid expansion of spacetime and the idea that the driver of inflation is a field. For a recap on the idea of a field see What is a Field?

Now as we know that the universe was undergoing such a rapid expansion, logically it must have been much smaller in the past. At very early times the universe was so small that the theory that ruled the realm was the theory of the small, Quantum Mechanics. If you want a refresher on Quantum Mechanics see the Laws of Quantum. In quantum physics, a quantum fluctuation is the temporary change in the amount of energy in a point in space, as explained in Werner Heisenberg’s uncertainty principle. Now this point is a little tricky but essentially what happens is that the field driving inflation experiences these quantum fluctuations, and everything else at this time is rapidly expanding, these quantum fluctuations are blown up too.


Now every point in spacetime has a region around it that contains events that can effect it. What I like to do is think of this region as a sphere, with the point of interest at the center. This region is called the Hubble radius (see point two in The Horizon and Beyond). These quantum fluctuations get blown up so large that they exit their initial Hubble radius and for the moment we put them to one side, worrying about what is inside only.

Now time progresses in the universe’s expansion, inflation ends and we enter the region thought of as the standard big bang cosmology, temperatures heat up, and particles emerge from the primordial soup that existed. For a punchy recount of these  stages of the universe see A brief history of the universe. In short, electrons fly around and eventually combine with nuclei to form atoms and small structure begins to come in existence. All the while the universe is still expanding, but at a much slower rate as when compared with during inflation. This means the Hubble radius or sphere that we were imagining earlier is also increasing and eventually it gets big enough that those quantum fluctuations outside that we now like to call cosmological perturbations (because they certainly aren’t quantum anymore!) get re-engulfed by the sphere.


[Replace the ‘co-moving horizon’ term with the ‘Hubble radius’ we were talking about, there is a subtle difference but for our purpose the concepts are interchangeable]

The perturbations affect (or if you’re well versed in the language of physics couple to) the density of the existing matter and then as a result experience the force of gravity, subsequently undergo gravitational collapse and this process over time is what forms the large scale structure in the universe today.  It was the quantum mechanical fluctuations in the initial universe that broke the initial smoothness if you like of the universe and provided the initial ‘clumpiness’ that when when coupled to the density of matter, over time caused a coalescing of matter into beautiful structures such as stars, planets and galaxies. The complexity that we see all around can be traced all back to simple fluctuations, that acted as the seeds of structure for the universe and in turn, essentially of life.


18 responses to “A Quantum Fluctuation

  1. A dense metaphysics, but an interesting reading as always. Keep posting even after a long “hiatus”. The birth of universe and the related studies, I call them the Science of God, where He or She has altogether a different perspective based on scientific, empirical and rational studies and observations.

    Liked by 2 people

    • Yes this post was a lot denser than usual with less explanation, I will work on that next time when less rushed. Thank you for reading and for your appreciation despite our different beliefs.

      Liked by 1 person

  2. Maybe you can help me with a problem i’ve always had.
    The Big Bang was an emergence of particles from a primordial soup, which, would i be right in saying, were in a void of sorts, because nothing essentially existed. As you say (& by the way i am not quarreling with this theory) “…electrons fly around and eventually combine with nuclei to form atoms and small structure begins to come in existence.” But this surely must have taken place in a void of sorts, as i said.
    Does this in any way remind you of what the double slit experiment teaches us about the actions of matter (for want of a better word, excuse my terms) in relation to our observation of it? For me it does & i often wonder why matter at the birth of everything happened by by something of its own volition, but now our consciousness orders it?
    i realize this sounds like New Age nonsense, but it is a problem i have never heard addressed & for me at least, it seems a problem. Perhaps you can put me right.

    Liked by 3 people

    • Firstly, what humanity can empirically sense or measure, is only a small fraction of a greater whole. Nature moves according to common patterns, so that what goes on at a larger scale should also go on at a smaller scale. If I was to drop red dye into a glass of water, I would note that the red dye would spread outwards to all parts of the water, limited only by the limits of its container. For all I know the universe could have a limit like the water container, and what is seen as something in expansion is the red dye, but it is operating in an invisible additional substance like the water in the container.

      Another issue to consider is that an object could exist in multiple dimensions at the same time, with each dimension giving it a greater complexity.

      Also, all things have a potential side, and a kinetic side. The potential side is invisible, but has many possibilities, whereas the kinetic side has only one visible, limited and fixed possibility.

      In addition, all objects in the universe are fractals, which mix, separate, join at both the potential and kinetic level; questions then arise how fractals operate at different dimensions of the universe from 1D, to 2D to 3D on the potential and kinetic level, and how these cycle and feedback into each other.

      Nature is not linear, the linear brain can obscure or confuse what is really beyond the human senses and brain information processing systems.

      Liked by 1 person

      • Well what happens at the small & larger levels is what i am getting at. I can’t much to my chagrin, understand what the rest has to do with my problem, but that the small & large don’t seem to agree in my case is the issue at hand, i think.


    • Hi there, sorry for the slow reply. Apologies if I don’t answer your question correctly but I think the jist of what you’re asking is how particles could appear at the beginning out of essentially nothing? Nobody understands the workings of the very early universe but what we do believe is that the universe was driven by a field which experiences vacuum fluctuations as this post outlines. Such fluctuations can also produce particle/antiparticles pairs, hence particles come into existence as a result. I’ll try write a post on this process in more detail soon. Why the early universe had an imbalance between the matter (particles) and antimatter (antiparticles), so they did not completely annihilate each other is due to a process called Baryogenesis, for which the reasons are still not clearly understood in Cosmology! This then led to the creation of atoms with the electrons and nuclei as described (see https://en.wikipedia.org/wiki/Baryogenesis)

      Liked by 1 person

      • Don’t worry about slow replies, thanks for replying, i am, sorry to say, not finished with you yet though, haha.
        So, do you personally see any links between the macrocosmic event & the microcosmic in my example? Or would you say there is no link between how observation affects matter say, this instant & the instant of the Big Bang? i don’t mind you telling me what you really think,, i won’t be offended if you tell me it is a load of crap, i don’t offend easily. i understand it isn’t a technical question, but i think it should be addressed, perhaps it isn’t a question for scientists, maybe its a question for a philosopher of science.


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  6. The universe having “come into being” some 13.8 billion years ago, instead of always having been here, more or less as it is now as we always thought, leads to the thought that there’s no reason why universe-creation hasn’t occurred countless times before, and may still be occurring. Why should we assume that our universe is the only one?


  7. Is big bang going big bust? I hear the latest from James Webb shows mature galaxies as far out (or back) as they can see.


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