The hunt for dark energy

It is currently widely accepted that both space and time started with the Big Bang. The universe started as a small singularity that was infinitely dense and has continuously expanded since. This can be evidenced by an observed pattern called redshift (a result of the wavelength of electro-magnetic radiation increasing). However, gravity in simple terms works to pull objects together, so how come the universe is expanding? The answer is… dark energy. 

Dark energy is a relatively new concept and is thought to represent 95% of the universe, while the atoms that build galaxies, stars and planets are only 5%. The theory developed from observations in 1998 showing that the expansion of the universe was accelerating, where at the time physicists believed that the expansion would slow down due to gravity. This meant that something had to be opposing the force of gravity and later this was attributed to dark energy. 

However, over 20 years after its discovery, almost nothing is known about dark energy, it is still just a theory. This has been described as ‘embarrassing’ by academics such as Prof Ofer Lahav from the University College London. However, a new project based in the U.S hopes to help understand this mysterious force. 

A team of researchers plan to use a device called the dark energy Spectroscopic Instrument (DESI) that contains 5000 optical fibres, all acting as a telescope. It will be fitted onto the Mayall telescope in Kitt Peak Observatory in Arizona. Each telescope in the DESI will be able to capture light from a galaxy at peak intervals of every 20 minutes, so up to 360,000 galaxies a day. It will be able to map each galaxies distance from Earth and calculate how much the universe has expanded in the time it took the light to reach Earth, all at an accuracy triple that of any project done before. The project aims to observe a selected 35million galaxies to create a map of the universe. 

But what does this mean in terms of dark energy? The project will be able to calculate the rates of acceleration more accurately than ever before, helping to confirm the theory of dark energy, but will also help scientists understand how dark energy works to oppose gravity.  

The key to this is a concept called vacuum-pressure, a force created by subatomic fluctuations in space-time. Current calculations show that the vacuum-pressure should be larger than the force currently observed pushing galaxies apart. It is thought that the vacuum-pressure during the early universe was much greater than it is now, however if the study finds that the early vacuum-pressure was the same as it is now then theories start to become speculative, such as our universe being part of a ‘Multiverse’.  

What if dark energy does not exist? The study also hopes to test the currently accepted Einstein’s theory of gravity, as it is possible the theory is incomplete. The device will be able to see far back into the past and see how gravity built the galaxies we see.  

So much is still unknown about the universe and the laws of physics, hopefully this project will help develop more understanding into the universe we know.

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Mali Hitchcock Brown

January 2021
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