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The big bang

Article curated by Grace Mason-Jarrett

When we look to the night sky, we see darkness scattered with faint lights. Space, at first glance, appears to be vast and sparsely populated with stars appearing every couple of light years or so. Thanks to various telescopes like Hubble, we now know that our universe is interspersed with huge dust clouds, asteroids and comets. We can see planets orbiting other stars and stars orbiting each other, and we have found galaxies which could be as old as 13 billion years accelerating away from us[1]. Today’s universe is buzzing with activity - from watching all this, Astronomers are gradually piecing together what might have happened just after time began.

Most people will be aware of the Big Bang Theory – the theory that the universe began as a single point containing every piece of matter, so small it is actually dimensionless, and went from existing like this to being everywhere. The Big Bang theory doesn’t describe this event as an explosion as such, but rather the sudden appearance of the universe from a single point [2]. In an impossibly small amount of time space in the universe grew exponentially and protons and electrons gradually came together to form a type of hydrogen call deuterium. As the universe filled with deuterium, the atoms smashed into each other and broke up into a thick smog and light stopped being able to get anywhere. This era is known as the ‘Dark Ages’, a time where for 380,000 years astronomers simply see through the fog, and have very little evidence for what might have gone on then.

Eventually, all those smashed up atoms cooled down enough to start recombining - this is known as the ‘Epoch of reionization’, and suddenly light was able to travel again. The mist cleared and light once again filled every part of the universe. We can still find the light which was released at this time at any point in the sky, though now it is only at a very low frequency. This light - the Cosmic Microwave Background - is the best piece of evidence we have currently for uncovering the sequence of events which led up to us.

Before the beginning of time

What existed before the Big Bang? If we are to assume that the universe did indeed begin as this theory suggests, then we have a huge problem. In everyday life things happen as a result of cause and effect, a glass breaks on the floor because it fell off a table because someone knocked it because… and so on. Following this logic, something must have caused the Big Bang, therefore something must have existed before the Big Bang. How could we possibly ever see evidence of this? Or, if nothing did cause it - then why did it happen?
In the 20th Century Einstein came up with the theory that massive objects bend space-time. You can think of this like sheet stretched flat in the air – this is space-time. By putting a heavy ball on to this sheet (a massive star or black hole), the sheet will dip and stretch, creating a well at the position of the ball. In a similar way, this is how very heavy stars and other huge objects bend the fabric of time and space and we can see evidence of this in gravitational lensing effects. At points like this, time travels slower. Therefore, if we combine Einstein’s thinking with the Big Bang theory then all the mass of the Universe is contained in a single point and time simply stands still.
So, there are no dimensions in the pre-Big Bang Universe and no time for any history to be made. Without these constituents, scientists are left with very, very little to work with. That hasn’t stopped them from making educated guesses though. A branch of quantum theory known as loop Quantum gravity has made astonishing advances in addressing these sorts of questions.
Some of these theories sound like something out of Star Trek, involving 11 dimensions, strings, quantum jumping, worm holes, parallel universes, parent universes – the list goes on. If there was anything before the Big Bang, then evidence might be found in the Cosmic Microwave Background.
Delve deeper into cosmic microwave background.

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NASA/ WMAP Science Team
This diagram shows how scientists think the universe may have expanded from a single point into the vast space we see today. Image credit: Public domain

One theory which is rapidly gaining credibility due to developments in Loop Quantum Gravity – a branch of Quantum Theory which combines quantum theory with general relativity - looks at the issue of a singularity. What exactly is a singularity? In mathematical terms, a singularity describes a point where a certain property (e.g. mass, temperature, density) is infinite. Black Holes are examples of singularities with infinite density. It’s this definition which causes the maths to blow up and contradict physical laws. However, new theories suggest that singularities are actually gateways to other universes, leading to the idea that rather than there being a Big Bang our Universe began as a result of a Big Bounce from a ‘parent’ Universe which sent energy rocketing in all directions[3].


What about what happened just after the Big Bang (or Big Bounce)? At the moment, according to theories, we have an incredibly hot space with electrons, protons and other single particles whizzing about. As the Universe stretches out into space it cools down, taking energy away from the particles and they slow down enough to begin to start interacting with each other. Slowly they come together to form the first atoms and elements. The vast majority of the atoms we can detect in the universe were created very shortly after the big bang, in a process known as nucleosynthesis. Most of these atoms are Hydrogen and Helium, which formed in a specific ratio, along with tiny amounts of Deuterium, Lithium, and Beryllium (heavier elements are created later in processes within stars). For these elements to form in the ratio that they did, the medium in which they formed must have had a particular density, however scientists have found that this density would have been too low to allow the Universe to expand at the rate it was. So there must be another force at play here – but what?


From looking very carefully at the process of nucleosynthesis - how atoms heaver than Hydrogen form, scientists are able to predict exactly how much of each element should have been created in those first few moments. Hydrogen and Helium ratios comply with these predictions, but Lithium does not. In fact, only a quarter of the Lithium predicted to have been created is found today. One explanation could be that there is some process whereby the Lithium in stars is being destroyed or removed, however if this is the case then how is it that many different star types (which have different life spans and different rates of processes) have the same amount of lithium missing? Another solution might be to look at the prediction calculations again. If scientists calculate the involvement of theoretical dark matter particles, called axions, during the early processes in the universe then there would not need to be as much Lithium created[4].


This article was written by the Things We Don’t Know editorial team, with contributions from Jon Cheyne, Cait Percy, and Johanna Blee.

why don’t all references have links?

[1] Kramer M. “Ancient Galaxy Is Farthest Ever Seen.” (2013) space.com
[2] Chow D. “The Universe: Big Bang to now in 10 easy steps” (2011) space.com
[3] Dzier˙zak P., Jezierski J., Malkiewicz P. And Piechocki W., “The minimum length problem of Quantum Loop Cosmology” (2010) arXiv preprint
[4] Howk C.J., Lehner N., Fields B. D. And Mathews G. J., “Obervation of interstellar lithium in the low-metallicity Small Magellanic Cloud” (2012) Nature, 2012. DOI: 10.1038/nature11407

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