Space Week

Deep Time: The Fate of the Universe

By Katie Bean

Everything in the universe is massive, without a doubt. Galaxies are rushing away from each other and stars are fusing hydrogen into helium at ferociously high temperatures and pressures. However, the once busy and blooming universe will eventually decay into a desolate, gloomy state after five distinct stages. What will happen at the end of the universe?

The beginning of the universe was inexplicably rapid. It inflated at an extremely fast pace and the temperatures were incredibly high. For some microseconds, only quarks (these make up protons and neutrons) could exist due to the scorching heat (Adams and Laughlin 1999, 4) These quarks annihilated with antiquarks, leaving the leftover matter to condense into protons and neutrons. Merely one second after the big bang, the temperature was 1032 Kelvin (Las Cumbres Observatory, n.d.) and atoms shot into existence after 20 minutes. Up until the universe was 1 million years old, it remained in the primordial era.

‘The Five Ages of the Universe’ states that the universe is currently in the Stelliferous Era, where stars are rapidly fusing hydrogen into helium at massive temperatures and pressures, including our sun. Our sun has a 12 billion year lifespan and is currently around halfway through it, allowing life on Earth to thrive with sufficient energy and light It is safe to say that we are not in much danger of being fried by our own red giant any time soon!

This lengthy era began when the universe was merely one million years old and will last until it is a trillion years old. (Adler 2020) Towards the end of the stelliferous era, the universe will become home to a multitude of supernovae and black holes as massive stars reach the end of their lives, as well as black dwarves from smaller stars. As this era ends, the universe will become much darker and gloomy.

Remnants of once burning, sizzling stars will provide a meagre supply of light during the degenerate era. It is highly unlikely that any life forms could exist during this desolate period of deep time, ranging from 1015 to 1039 years (Adler 2020) after the Big Bang sprang the universe into action.

Space will be dominated by hydrogen-abundant brown dwarves (commonly recognised as star failures that are too small to undergo nuclear fusion), white dwarves, black holes and perplexingly dense neutron stars. Galaxies will collide with each other, scattering the ashes of once blazing stars into various deserted areas of space. (Adler 2020)

Time drags onwards as we follow the second law of thermodynamics into a deeper state of disorder: the black hole era. When all the stars have decayed into nothingness, black holes assume dominance over the cold, barren universe. These cosmological superpowers have an especially eerie quality – as soon as anything passes the event horizon, it cannot escape. A black hole is an object or mass that has a radius smaller than its Schwarzchild radius (defined as Rg = 2GM/c2) (Swinburne University of Technology, n.d.).

Black holes come in different types: stellar (formed by the death of a massive star), intermediate (weighing around 1 to 100 times the mass of our Sun (Parks 2019)), supermassive (these are usually found in the centre of a galaxy) and miniature. We are often able to observe the accretion disc around the black hole, where some matter has not yet been completely sucked in; the forces acting on these particles produces strong gamma and x-rays. (Mastin 2009).

Figure 1. An accretion disk around the black hole Messier 87 (Ghosh 2019)

Although black holes may seem endless and almighty, they too must evaporate. This happens due to Hawking radiation because they give off subatomic particles and inevitably evaporate – most will have disappeared by the 100th cosmological decade (Adams and Laughlin 1999, 135).

This brings us to the last of the five proposed eras of deep time: the dark era. At this point, only some electrons, positrons and long-wavelength radiation will exist. Heat death would now be a possible end for the universe – the entropy will simply just remain the same as it could no longer increase and would have reached thermodynamic equilibrium. (Adams and Laughlin 1999, 182).

Nevertheless, there are countless theories concerning the universe’s rebirth: the ‘Big Rip’, the ‘Big Crunch’, the ‘Big Bounce’ and so on. One thing is for certain, though – the universe in which we live is miraculous and ever-changing. The fact that it could be a totally different place as time drags forwards is mind-bending!

Bibliography

Adams, Fred, and Greg Laughlin. 1999. The Five Ages of the Universe. New York: The Free Press.

Adler, Doug. 2020. The Degenerate Era. astronomy.com. https://astronomy.com/news/2020/03/the-degenerate-era-when-the-universe-stops-making-stars.

Ghosh, Pallab. 2019. First-ever black hole image released. bbc.co.uk. https://www.bbc.co.uk/news/science-environment-47873592.

Las Cumbres Observatory. n.d. The Early Universe. lco.global. Accessed October 7th, 2020. https://lco.global/spacebook/cosmology/early-universe/.

Mastin, L. 2009. EVENT HORIZON AND ACCRETION DISK. https://www.physicsoftheuniverse.com/topics_blackholes_event.html.

Parks, Jake. 2019. What are intermediate-mass black holes? astronomy.com. https://astronomy.com/news/2019/07/what-are-intermediate-mass-black-holes.

Swinburne University of Technology. n.d. Schwarzschild Radius. Accessed October Wednesday 7th, 2020. https://astronomy.swin.edu.au/cosmos/S/Schwarzschild+Radius.

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