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Despite ongoing research, we still know little about the universe’s earliest moments. tychay

‘Melbourne researchers rewrite Big Bang theory’ … or not

Earlier this week, headlines in several major newspapers screamed: “Melbourne researchers rewrite Big Bang theory”. You might think this is a reference to a new script for a popular TV show, but as a cosmologist, such words quickly pricked my interest.

Reflecting on the story in the cold light of day left me reassured that my textbooks are not about to be rewritten, and that our current understanding of the birth of our universe, the Big Bang, remains as sturdy as ever.

It is important to begin with the science behind the story, from a paper in the prestigious journal Physical Review D by University of Melbourne postgraduate researcher James Quach.

The underlying idea is very profound, questioning the very nature of space-time itself. Quach suggests space-time is not smooth and continuous, but rather discrete and chunky*, made of fundamental building blocks in the same way matter is made of atoms – an idea dubbed “quantum grafity”.

Before thinking about the implications of chunky space-time, we need to look at the grander media statements. The claim is that there was a time, a time before what we understand as “time”, where this chunky structure of the universe was hot, buzzing around with no underlying structure, where space and time, as we know them, didn’t exist.

In the same way water freezes into ice, changing its internal “formless” liquid structure into solid ice with crystals lining up together, in this picture the universe was born in a “phase transition” when structureless dimensions crystalised into the space and time that we know today.

In this picture, our universe was not born in a Big Bang, but a Big Chill.

Exciting stuff!

But does the media hype match up with the realities of the research? Interestingly, the paper does not claim that the Big Bang theory is about to be banished. Even more surprising, the paper does not contain any cosmology. So what is going on?

First, a little background. I’ve written on The Conversation before about what the Big Bang theory means to a practising scientist, and it is more than the flash that “brought the universe into being”.

In fact, it represents an immense body of evidence which show that “the whole universe was in a hot dense state” and that the universe has been continually expanding and cooling throughout cosmic history.

Gravity was then able to drag matter together to form the stars and galaxies we see around us.

The signature of this early heat is still visible as the Cosmic Microwave Background (CMB) radiation, and tells us that in the earliest few minutes this immense fire forged the first light elements.

We can use our current understanding of the laws of physics to see into earlier and earlier times in the universe, until we hit a wall in our understanding – an epoch when the role of gravity and quantum forces had an equal part to play in what came before.

And this is where our current physics breaks down. We don’t have a “Quantum Theory of Gravity” that allows all the forces to play nicely together, and so we don’t know what happened in the tiniest fractions of a second at the “start” of the universe.

Before this time, it could have been an unstructured sea of chunks, just as in the media reports, but it could also have been one of many other ideas and hypotheses that have been floating around for many decade.

For instance, we could be nothing more than a quantum pimple on a previously existing universe or our cosmos could have been formed when older universes collided in “multi-dimensional” space-time.

My best bet is that it will turn out to be something we haven’t even thought of yet.

So, what does Quach’s research really tell us? If – and it is a big if – the idea of crystalline space-time is correct, then the universe could still be chunky today, and as light travels from “out there” to our telescopes it is constantly bounced back and forth.

Our observations of distant objects could contain the signature of chunky space-time, and support for the crystalline space-time structure.

But unfortunately, “quantum grafity” is not the first theory to suggest space-time may not smooth. Others have proposed that, on the smallest scales, the universe might be foamy, while others have posited the universe might contain immense space-time fractures left over from its turbulent youth.

And people have searched for these signatures in our observations of the universe. Alas, for all of these ideas, all we’ve shown is that cosmic space-time is as smooth as the proverbial baby’s bottom.

Even if the ideas of “quantum grafity” (or myriad other ideas) prove to be correct, it will reveal what happened in the earliest moments of the universe. But after gravity and the other forces go their separate ways – when the cosmos was less than one billionth billiont billonth of a second old, the subsequent growth must recreate the universe of the Big Bang.

Revealing what happened at the instant of genesis will only add to the Big Bang, not rewrite it.

I commend Quach’s research, as we must continue to explore ideas, even those that seem wacky and out-there. But it is a shame the AAP press release (and the resulting newspaper story) did not reflect the reality.

I guess a headline such as “Melbourne Researchers have a neat idea that might have observational consequences that may reveal the nature of the space and time, and could potentially point us in the right kind of direction in understanding a quantised picture of gravity and hence reveal what really happened at the very start of our universe” just doesn’t have the same ring about it.

It’s a shame, as it reflects the way that most of science is actually done. Sensationalist journalists just don’t seem to understand this.

For further analysis of James Quach’s research and the newspaper stories that followed it, check out this blog post by Luke Barnes, a postdoctoral researcher at the University of Sydney.

* UPDATE: So, how lumpy is space-time? It just so happens that a new press release has been published, focusing at one of the largest explosions in the universe, a gamma ray burst that was observed in 2007.

The explosion actually occurred 7 billion years ago, and the high energy gamma-rays it produced have traveled an immense distance through the universe to arrive at our telescopes. By noting that the gamma-rays arrived at the same time, the researchers concluded that they could not have been scattered by pixellated space-time on their journey.

While the sample size is small with only three gamma-rays detected, the researchers conclude that travelling through space-time is more like sipping smooth whiskey than bouncing around a bubbly brew.
Further reading:
‘Rewriting’ the Big Bang theory – a personal perspective

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