Do we not often wonder what the Universe is made of and how it looked at the beginning? Or how does it expand or change its expansion rate over time? Had we known the answers to these questions, we would understand both the past and future of our universe better.
Mystery surrounds the measurement of the Universe as different methods provide discrepant answers, which remain arguably the biggest conundrum in modern cosmology.
Astrophysicists have created the largest-ever three-dimensional map of the Universe on July 19 this year, which may finally help to solve this cosmic mystery.
The Sloan Digital Sky Survey (SDSS), a project involving hundreds of scientists from around the world collected two decades of data and mapped the Universe with telescopes. It also filled the most significant gaps in our possible exploration of its history.
Cosmologist Kyle Dawson of the University of Utah, announced the SDSS analysis in a press release saying that, "We know both the ancient history of the Universe and its recent expansion history fairly well, but there is a troublesome gap in the middle 11 billion years. For five years, we have worked to fill in that gap."
The gap in the middle, 11 billion years that the astrophysicists talk about, actually began a few billion years after the Big Bang, SDSS found. Scientists can measure the rate of the universe's expansion before this with the help of Cosmic Microwave Background.
The SDSS press release stated, new results of detailed measurements of more than two million galaxies and quasars covering 11 billion years of cosmic time come from the extended Baryon Oscillation Spectroscopic Survey (eBOSS), an international collaboration of more than 100 astrophysicists that is one of the SDSS's component surveys.
According to Live Science, Redshift - a process by which light from the most ancient, distant galaxies is stretched by the expansion of the Universe, increasing its wavelength and shifting it toward the redder end of the spectrum – played a key part here.
The map has been designed keeping the Earth in the centre. As we look outwards, we see different stages of the Universe in a different time.
The survey revealed both surprising and non-surprising results which are equally important. As Forbes reported, it confirms several things that were generally thought to be true – but sheds a surprising light on many aspects of the Universe.
The largest 3D map ever can show how the Universe looked like in its infancy. Its expansion history over the last few billion years from galaxy maps and distance measurements can also be known now.
According to CNN, the map reveals the early materials that "define the structure in the Universe, starting from the time when the Universe was only about 300,000 years old." The map will help measure patterns in the distribution of galaxies providing several key parameters of the Universe to better than one percent accuracy.
The 3D map shows that the expansion of the Universe began to accelerate six billion years ago, and the Universe has only continued to expand faster and faster ever since. According to CNN, "dark energy" is the "mysterious invisible component" that has caused the acceleration.
The dark energy is incredibly consistent with the cosmological constant. Its energy density remains constant over time and it hardly evolves or varies through space. Dark energy, as SDSS mentioned, is consistent with Einstein's General Theory of Relativity but extremely difficult to reconcile with our current understanding of particle physics.
It makes up 70 percent of the Universe. The rest 30 percent consists of 25 percent of dark matter and only five percent of normal matter.
A non-surprising yet exciting confirmation of the study is that the Universe is incredibly spatially flat. This confirmation has driven away those speculations that rose last year that the Universe might be closed instead of flat. It is now confirmed that Universe' maximum allowable curvature is just 0.2 percent of the critical density.
There has been a discrepancy between researchers' measurements and collected data of measurement of the current rate of expansion of the Universe, also known as "Hubble's Constant". This has been the most surprising finding of all.
Forbes reported, teams that measure the distances to objects individually in "distance ladder" method consistently get values of 72-75 km/s/Mpc, but teams that use the Cosmic Microwave Background consistently get values between 66-68 km/s/Mpc. But the best result that the study found, yielded an expansion rate of 68.2 km/s/Mpc.
A question may arise, "how big was the Universe at a particular time?" The SDSS has shown that it can be measured exquisitely with data from the Cosmic Microwave Background.
"By combining SDSS data with additional data from the Cosmic Microwave Background, supernovae, and other programs, we can simultaneously measure many fundamental properties of the Universe," says Eva-Maria Mueller of the University of Oxford, who led the analysis to interpret the results from the full SDSS sample.
Will Percival, eBOSS's survey scientist said, "These studies allow us to connect all the measurements into a complete story of the expansion of the Universe."
However, this largest three-dimensional map still has some unsolved puzzles to solve – the puzzle of dark energy, the mismatch of local and early Universe expansion rate – to name a few.
The SDSS said in their statement that "they are nowhere near done with their mission to map the Universe," and have already begun building the hardware to start this new phase of mapping stars and black holes. The SDSS is looking forward to the discoveries of the next 20 years. They will hopefully solve the unsolved puzzles and maybe reveal even more surprises.