New Study Suggests Dark matter predates the ‘Big Bang’ — but what does that actually mean?
New research suggests that dark matter predates the Big Bang, but that finding has been somewhat misrepresented in the mainstream media. I spoke to researcher Tommi Tenkanen to clear up the misapprehensions.
Current estimates suggest that dark matter currently comprises 80% of the matter in the known universe, but despite that, scientists don’t actually know what it is. Thus, this leaves a huge gap in our knowledge of the universe and makes dark matter one of the biggest mysteries in science.
As such it’s little surprise that new research into the subject is a hot topic both in the scientific community and for casual readers.
Likewise, the origins of the universe and the so-called ‘big bang’ go to the fundamental question all of us have asked at some point: “Why is there something rather than nothing?”
As you can imagine, that means that a study which unities both the ‘Big Bang’ and the nature of dark matter is guaranteed to cause a stir — especially if it seems that research flies in the face of our current understanding of both.
We all love a mystery, after all.
Enter new research from John Hopkins University, helmed by a postdoctoral fellow in Physics and Astronomy at the Johns Hopkins University, Tommi Tenkanen. The study — published in the journal Physical Review Letters D — only promises to add to these enigmas, as it seems to show that dark matter is older than the Big Bang.
To some audiences, this may suggest that dark matter is older than the universe itself — as lay audiences often interpret the ‘Big Bang’ as the origin of the universe.
For an example of this, consider how the UK’s Daily Express reported the study: “ Now a groundbreaking study has revealed dark matter maybe even more bizarre than first thought, as its origin may have actually pre-dated the beginning of the Universe — the Big Bang.”
The problem is, the origin of the universe isn’t what cosmologists mean when they say ‘the Big Bang’.
In addition to this seemingly counter-intuitive piece of information, the study presents new ideas about how dark matter could have formed and how astronomers can finally identify it. Whilst this aspect of the research may not initially sound as ‘sexy’ as the more headline-grabbing element, it may be the most significant finding presented by the paper.
Tenkanen, the study’s author, explains further: “The study revealed a new connection between particle physics and astronomy.
“If dark matter consists of new particles that were born before the big bang, they affect the way galaxies are distributed in the sky in a unique way.”
This connection may — in addition, to revealing the nature of dark matter — may give us hints about what came before the Big Bang, Tenkanen adds.
This is the important part of the study and it has been missed by many editors and thus isn’t getting communicated to readers.
So why was coverage like the that found in the Express inaccurate?
To examine that, we have to consider what the phrase ‘before the Big Bang’ even means.
The ‘big bang’ — not big, not a bang, and not the beginning
It’s vital to point out that despite the meaning it has garnered in common parlance, the ‘Big Bang’ does not refer to the origin of the universe.
What the term Big Bang— coined in a derogatory fashion by Fred Hoyle, a British astronomer who rejected the theory — actually means when used by cosmologists and other scientists is a period of rapid inflation that occurred in the very early universe.
In addition to this, the Big Bang almost certainly wasn’t a ‘bang’ of any description — more comparable to the rapid inflation of a balloon that an explosion — it couldn’t be described as ‘big’ either — originating from a single, infinitesimally small, point.
Considering that, the headline ‘… predates the Big Bang…’ becomes instantly less counter-intuitive. And that’s not to devalue Tenkanen’s research. In fact, it’s something he is keen to point out himself.
He tells me: “What cosmologists nowadays mean by the Big Bang is an epoch roughly 13.8 billion years ago when the universe was compressed into a tiny volume.”
“Because of the huge compression, molecules and atoms were decomposed into smaller elementary particles that formed a hot soup scientists call a heat bath.”
Thus not the beginning of the universe, just close to it.
Tenkanen points out that researchers have this information because the so-called Cosmic Microwave Background (CMB) radiation — which has been measured exceptionally precisely — is a clear image of that state.
He continues: “However, properties of this CMB radiation suggest that before the heat bath formed, the universe was in a different state cosmologists call cosmic inflation.
“Nobody knows what happened before inflation or in the very beginning — if there was any. In any case, in modern terms, inflation preceded the Big Bang epoch.”
With that cleared up, we can examine what Tenkanen’s study actually says and why it’s still an important piece of research.
Diverging from current expectations about dark matter
Despite not delivering shocking implications about the origin of the universe, the paper does present new ways of thinking about dark matter, and the epoch in which it came to be.
Current theories regarding the origins of dark matter suggest that it could be a ‘leftover’ substance from the big bang, but experimental searches that take this into account have failed to deliver positive results.
Tenkanen explains why he thinks this is: “Most models for the properties and origins of dark matter assume it consists of new elementary particles that were leftover from the hot soup of particles in the Big Bang.
“While other researchers have suggested in the past models where dark matter originated from cosmic inflation — an era that indeed preceded the Big Bang epoch — those models predict very different observational signatures if any.”
Tenkanen suggests that this lack of evidence may be because these ideas are incorrect, stating that if dark matter was truly a remnant of the Big Bang, then researchers should have seen a direct signal of dark matter in particle physics experiments already
The key aspect of Tenkanen’s study, as he puts it, is that not only could enough scalar particles have been created during inflation that they could constitute the dark matter but also that they leave a unique imprint on the large scale structure of the universe. Specifically, that means on the distribution of galaxies and galaxy clusters.
He adds: “The study predicts there are more galaxies and galaxy clusters in the universe than in scenarios where dark matter is a remnant from the Big Bang.
“This makes the hypothesis testable with astronomical observations in the near future.”
Also, Tenkanen says, the model put forward by his research “is mathematically the simplest possible model for dark matter.”
None of this constitutes a total rethink of dark matter, the research still holds that dark matter is composed of particles, but it does call for investigating if different dark matter models can have observational consequences that may have been previously overlooked.
Why chose to explore a different model of dark matter?
Tenkanen explains how the path towards his PhD led him to explore a different model for dark matter rather than pursuing current, and perhaps better-established ideas.
He says: “Having studied both cosmic inflation and particle dark matter since the beginning of my PhD, so it was natural to ask if these two things have anything in common.
“In fact, a major turning point was an article I wrote last autumn together with researchers in Imperial College London. It was on a very similar model but in a slightly more complicated mathematical framework.”
In this new study, Tenkanen was able to simplify these earlier calculations and also make a novel prediction regarding observational consequences of the scenario.
The study leaves many avenues open to future researchers. In particular, researchers may wish to explore if there are other models that see dark matter created in a similar fashion of Tenkanen’s.
In addition to the theoretical, the study opens up observational and experimental opportunities to be capitalised upon.
Tenkanen says: “On the observational side, I hope astronomers will look for the predicted imprint of dark matter in the large scale structure of the universe.
“A great thing is that we will learn more about that when the Euclid satellite is launched into space in 2022. I’m excited to see what they will find.”
The researcher concludes: “On-going and near-future surveys of the large scale structure of the universe hold great promise in revealing more about the nature of dark matter, as dark matter is known to play a key role in its formation.
“Details of how that happened will certainly tell more about dark matter, also in cases where dark matter is too elusive to be seen in particle physics experiments.”
Original research: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.061302