An alternative explanation for the discrepancy is the part of the Universe we live in is somehow different or special compared to the rest of the Universe, and that difference is distorting the measurements. But astronomers think they are getting close to pinpointing what the Hubble Constant is and which of the measurements is correct.
One is the ESA's space observatory Gaia, which launched in and has been measuring the positions of around one billion stars to a high degree of accuracy. Scientists are using this to work out the distances to the stars with a technique called parallax. As Gaia orbits the sun its vantage point in space changes, much like if you close one eye and look at an object, then look with the other eye it appears in a slightly different place.
So, by studying objects at different times of the year during its orbit, Gaia will enable scientists to accurately work how fast stars are moving away from our own Solar System. Another facility that will help answer the question of what the Hubble Constant's value is the James Webb Space Telescope, which is due to be launched late in By studying infrared wavelengths, it will allow better measurements that won't be obscured by the dust between us and the stars.
If they find that the difference in the Hubble Constant does persist, however, then it will be time for new physics.
And although many theories have been offered up to explain the difference, nothing quite fits what we see around us. Each potential theory has a downside. For example, it might be there was another kind of radiation in the early universe, but we have measured the CMB so accurately this does not seem likely.
Another option is that dark energy could be changing with time. It has forced scientists to dream up new ideas that could explain what is going on. Depending on what these new telescopes reveal, Beaton and Freedman could well find themselves in the midst of a mystery worthy of an Agatha Christie novel after all. Join one million Future fans by liking us on Facebook , or follow us on Twitter or Instagram. As space expanded, the universe cooled and matter formed. One second after the Big Bang , the universe was filled with neutrons, protons, electrons, anti-electrons, photons and neutrinos.
During the first three minutes of the universe, the light elements were born during a process known as Big Bang nucleosynthesis. Temperatures cooled from nonillion 10 32 Kelvin to 1 billion 10 9 Kelvin, and protons and neutrons collided to make deuterium, an isotope of hydrogen. Most of the deuterium combined to make helium , and trace amounts of lithium were also generated. The heat of creation smashed atoms together with enough force to break them up into a dense plasma, an opaque soup of protons, neutrons and electrons that scattered light like fog.
Roughly , years after the Big Bang, matter cooled enough for atoms to form during the era of recombination, resulting in a transparent, electrically neutral gas , according to NASA. This set loose the initial flash of light created during the Big Bang, which is detectable today as cosmic microwave background radiation. However, after this point, the universe was plunged into darkness, since no stars or any other bright objects had formed yet.
About million years after the Big Bang, the universe began to emerge from the cosmic dark ages during the epoch of reionization. During this time, which lasted more than a half-billion years, clumps of gas collapsed enough to form the first stars and galaxies, whose energetic ultraviolet light ionized and destroyed most of the neutral hydrogen. Although the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity, about 5 or 6 billion years after the Big Bang , according to NASA, a mysterious force now called dark energy began speeding up the expansion of the universe again, a phenomenon that continues today.
A little after 9 billion years after the Big Bang, our solar system was born. The Big Bang did not occur as an explosion in the usual way one think about such things, despite one might gather from its name. The universe did not expand into space, as space did not exist before the universe , according to NASA Instead, it is better to think of the Big Bang as the simultaneous appearance of space everywhere in the universe.
The universe has not expanded from any one spot since the Big Bang — rather, space itself has been stretching, and carrying matter with it. But in all cases, the early dark energy must disappear after a few hundred thousand years, during an epoch known as recombination.
Alongside early dark energy, theorists have put forward other exotic forms of dark energy — such as quintessence and phantom dark energy — that also change as the universe ages. While these extensions to the standard model relieve the Hubble tension, they are regarded by many cosmologists as fine-tuned — opportune mathematical additions that have no clear justification. For example, most cosmologists think space exponentially expanded at the start of the Big Bang during a period known as inflation, which was driven by a different kind of dark energy than the one that exists today.
But in a preprint submitted to Physical Review D in March, Barker and three co-authors acknowledge that much more analysis is needed to see if the model can describe not only how the universe expands but also how structures like galaxies and clusters evolved. With contemporary telescopes offering a glut of impressively precise data on such structures, devising a theory that matches all the observations is no mean feat.
Even with the extra freedom, most of the nonstandard models only reduce the Hubble tension rather than eliminating it. In the coming years, the Euclid telescope and others will meticulously map how gravity and dark energy have shaped cosmic evolution.
Meanwhile, gravitational waves emitted from colliding neutron stars offer a new way to measure the Hubble constant. The new data will rule out some of these novel solutions to the Hubble tension, but new cracks in the standard model may appear.
For now, many cosmologists are loath to complicate the model when it otherwise works so well. She added that even if the Hubble tension turns out to be nothing more than an accumulation of errors, this search for new physics may not be in vain.
So far, astronomers have confirmed only one—but on the morning of April 25, LIGO may have detected another. That said, pinpointing the waves' origins in the sky proved challenging, which is complicating follow-up measurements with telescopes. Meanwhile Riess and astronomers around the world are working to make their measurements of the Hubble constant even more precise, in the hopes that even a small discrepancy could unlock a massive new clue to how the universe works.
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