The universe is increasing quicker than idea predicts
Ryan Keeley, University of California, Merced
Astronomers have identified for many years that the universe is increasing. Once they use telescopes to look at faraway galaxies, they see that these galaxies are moving away from Earth.
To astronomers, the wavelength of sunshine a galaxy emits is longer the quicker the galaxy is shifting away from us. The farther away the galaxy is, the extra its mild has shifted towards the longer wavelengths on the pink facet of the spectrum. Thus, the upper the redshift.
As a result of the velocity of sunshine is finite, quick, however not infinitely quick, seeing one thing distant means we’re taking a look at the way it regarded previously. With distant, high-redshift galaxies, we’re seeing the galaxy when the universe was in a youthful state. So excessive redshift corresponds to the early instances within the universe, and low redshift corresponds to the late instances within the universe.
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However as astronomers have studied these distances, they’ve realized that the universe isn’t just increasing. Its fee of growth is accelerating. And that growth fee is even quicker than the main idea predicts it must be, leaving cosmologists like me puzzled and on the lookout for new explanations.
Darkish power and a cosmological fixed
Scientists name the supply of this acceleration dark energy. We’re not fairly positive what drives darkish power or the way it works. However we predict its conduct could possibly be defined by a cosmological constant, which is a property of spacetime that contributes to the growth of the universe.
Albert Einstein initially got here up with this fixed. He marked it with a lambda in his idea of general relativity. With a cosmological constant, because the universe expands, the power density of the cosmological fixed stays the identical.
Think about a field filled with particles. If the quantity of the field will increase, the density of particles would lower as they unfold out to take up all of the space within the field. Now think about the identical field, however as the quantity will increase, the density of the particles stays the identical.
It doesn’t appear intuitive, proper? That the power density of the cosmological fixed doesn’t lower because the universe expands is, after all, very bizarre, however this property helps clarify the accelerating universe.
The universe is increasing and the usual mannequin
Proper now, the main idea, or customary mannequin, of cosmology known as Lambda CDM. Lambda denotes the cosmological fixed describing darkish power, and CDM stands for cold dark matter. This mannequin describes each the acceleration of the universe in its late levels in addition to the growth fee in its early days.
Particularly, the Lambda CDM explains observations of the cosmic microwave background. The cosmic microwave background is the afterglow of microwave radiation from when the universe was in a hot, dense state about 300,000 years after the Big Bang. Observations utilizing the Planck satellite, which measures the cosmic microwave background, led scientists to create the Lambda CDM mannequin.
Becoming the Lambda CDM mannequin to the cosmic microwave background permits physicists to foretell the worth of the Hubble constant. The Hubble fixed isn’t really a relentless, however a measurement describing the universe’s present growth fee.
However the Lambda CDM mannequin isn’t excellent. The growth fee that scientists have calculated by measuring distances to galaxies and the growth fee as described in Lambda CDM utilizing observations of the cosmic microwave background, don’t line up. Astrophysicists name that disagreement the Hubble rigidity.
The Hubble rigidity
Over the previous few years, I’ve been researching ways to clarify this Hubble rigidity. The stress could also be indicating that the Lambda CDM mannequin is incomplete and physicists ought to modify their mannequin. Or, it might point out that it’s time for researchers to give you new concepts about how the universe works. And new concepts are at all times essentially the most thrilling issues for a physicist.
One strategy to clarify the Hubble rigidity is to change the Lambda CDM mannequin by altering the growth fee at low redshift, at late instances within the universe. Modifying the mannequin like this may also help physicists predict what kind of bodily phenomena is perhaps inflicting the Hubble rigidity.
For example, perhaps darkish power just isn’t a cosmological fixed however as an alternative the results of gravity working in new methods. If that is so, darkish power would evolve because the universe expands. And the cosmic microwave background, which exhibits what the universe regarded like just a few years after its creation, would have a unique prediction for the Hubble fixed.
However, my crew’s latest research has discovered that physicists can’t clarify the Hubble rigidity simply by altering the growth fee within the late universe … this complete class of options falls quick.
Creating new fashions
To check what sorts of options might clarify the Hubble rigidity, we developed statistical tools that enabled us to check the viability of your entire class of fashions that change the growth fee within the late universe. These statistical instruments are very versatile, and we used them to match or mimic completely different fashions that would probably match observations of the universe’s growth fee and may provide an answer to the Hubble rigidity.
The fashions we examined embrace evolving darkish power fashions, the place darkish power acts otherwise at completely different instances within the universe. We additionally examined interacting darkish energy-dark matter fashions, the place darkish power interacts with dark matter, and modified gravity fashions, the place gravity acts otherwise at completely different instances within the universe.
However none of those might totally clarify the Hubble rigidity. These outcomes recommend that physicists ought to research the early universe to know the supply of the strain.
Ryan Keeley, Postdoctoral Scholar in Physics, University of California, Merced
This text is republished from The Conversation below a Artistic Commons license. Learn the original article.
Backside line: Scientists have lengthy identified that the universe is increasing. However the universe is increasing quicker than idea predicts. So scientists try to give you new fashions to clarify what the usual mannequin of cosmology can’t.
