From of the universe is dark energy. The

From Hubble’s landmark discovery in1929 that the universe is not in fact static, but is rather in a constant stateof expansion, the problem of dark energy was inadvertently born. He observed aphenomenon called redshift, “the shifting of emitted electromagnetic radiation(such as visible light) towards the less energetic red end of the electromagneticspectrum”, while viewing other galaxies.1 This was irrefutable proofthat the universe was expanding. Building on this idea, an assumption was made thatwe now know to be false, that gravity pulling together the universe is slowingdown the rate of the universe’s expansion.

In 1998, it was discovered by twocompeting teams of scientists that the rate of expansion is actuallyincreasing. They did this by observing Type 1a supernovae. These occur when awhite dwarf exceeds a solar mass of 1.4 causing a nuclear chain reaction andexploding.2 These supernovae were usedbecause they always reach the same peak brightness (due to the uniform natureof the masses they occur at and the uniform way in which the reactions happen).From the brightness of a supernova, these scientists were able to discern howfar away the supernova was. They could then use the redshift of the supernovato work out what the relative size of the universe was when the supernovaemitted that light.

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3 Surprisingly, the resultsshowed that the supernovae were observed to be dimmer than expected, whichcould only lead to the conclusion that they have travelled further than theprevious rate of expansion would have suggested and thus the universe’sexpansion is accelerating. The concept of dark energy arose out of theinability to describe this occurrence. The conclusion was thus drawn out that73%4 of the universe is darkenergy.Theconcept of dark matter was first proposed in 1922 by Jacobus Kapteyn.5 Through his work on stellarvelocities, he realised that for stars to orbiting galaxies at the speeds thatthey were, the galaxy had to have a greater mass than the sum of its observableconstituents. He explained this by reasoning that the galaxy had some othermass that could not be observed. The problem of dark matter became morewidespread in 1980, when Vera Rubin published his results of his galaxyrotation curves.6 Galaxy rotation curves areplots of the radius of a star’s orbit from the centre of a galaxy against itsspeed.

The speeds of stars further fromthe galaxy’s centre were observed to be much higher than what had beenpredicted using the Keplerian formula. It became evident that visible mass didnot account for all the mass within the galaxy. He concluded that this missingmass was dark matter.Perhaps the most prominent piece of evidence to back this idea of dark matterwas 


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