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Is It Time to Discard the Whole Dark Energy Contrivance?
Posted by Guy Pirro on 4/22/2017 7:18 PM


Our universe was formed in the Big Bang, 13.8 billion years ago and has been expanding ever since. This is an image of Galaxy Cluster LCDCS-0829, as observed by the Hubble Space Telescope. This galaxy cluster is speeding away from us due to the expansion of the Universe. Amazingly, if the expansion continues at the current pace, in a few billion years this galaxy cluster will become unreachable, even at the speed of light. (Image Credit: ESA, NASA, Hubble Space Telescope)


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So what is Dark Energy? Well, the simple answer is that we don't know. It seems to contradict much of our understanding about the way the Universe works.

We all know that light waves (a form of radiation) carry energy. You feel that energy the moment you step outside on a hot summer day.

Also, Einstein's famous equation, E = mc^2 teaches us that matter and energy are interchangeable -- merely different forms of the same thing. We have a giant example of that in our daytime sky: the Sun. The Sun is powered by the conversion of mass to energy.

However, energy is supposed to have a source -- either matter or radiation. But the idea behind "Dark Energy" is that space, even when devoid of all matter and radiation, has a residual energy. And this "energy of space," when considered on a cosmic scale, leads to a force that increases the expansion of the universe -- At least, that's according to the current conventional wisdom.

Perhaps Dark Energy results from weird behavior on scales smaller than atoms. The physics of the very small, called Quantum Mechanics, allows energy and matter to appear out of nothingness, although only for the tiniest instances. The constant brief appearance and disappearance of matter could be giving energy to otherwise empty space.

It could also be that Dark Energy creates a new, fundamental force in the universe -- something that only starts to show an effect when the universe reaches a certain size. Scientific theories allow for the possibility of such forces as well. The force might even be temporary, causing the universe to accelerate for some billions of years before it weakens and essentially disappears.

Or perhaps the answer lies within another longstanding unsolved problem -- how to reconcile the physics of the large with the physics of the very small. Einstein's theory of gravity (General Relativity) can explain everything from the movements of planets to the physics of black holes, but it simply doesn't seem to apply on the scale of the particles that make up atoms. To predict how these small particles behave, we need the theory of Quantum Mechanics. Quantum Mechanics explains the way small particles function, but it simply doesn't apply on any scale larger than an atom. The elusive solution for combining the two theories might yield a natural explanation for Dark Energy, but we just don't know.

We do, however, know this -- Since space is everywhere, this so-called Dark Energy force appears to be everywhere, and its effects increase as space expands. In contrast, gravity's force is stronger when things are close together and weaker when they are far apart. Because gravity weakens with the expansion of space, it is believed that Dark Energy now makes up about 68 percent of all of the energy in the universe.

It sounds rather strange that we have no firm idea about what makes up 68 percent of the universe. It's as though we had explored all the land on the planet Earth and never in all our travels encountered an ocean. But now that we think we've caught sight of the waves, we want to know what this huge, strange, powerful entity really is.

The strangeness of Dark Energy is perplexing. It shows us that there is a gap in our knowledge that needs to be filled. We have before us the apparent evidence that the cosmos may be configured vastly differently than we imagine. Dark Energy both signals that we still have a great deal to learn, and shows us that we stand poised for another great leap in our understanding of the universe.

But what if there is an alternative explanation for this enigmatic Dark Energy? What if it does not exist at all? That is what a Hungarian-American team of researchers is starting to conclude. The researchers believe that today's standard models of the universe fail to take account of its changing structure. Once that is done the need for Dark Energy disappears.

Our universe was formed in the Big Bang, 13.8 billion years ago and has been expanding ever since. The key piece of evidence for this expansion is Hubble's law, based on observations of galaxies, which states that on average, the speed with which a galaxy moves away from us is proportional to its distance.

Astronomers measure this velocity of recession by looking at lines in the spectrum of a galaxy, which shift more towards red the faster the galaxy is moving away. From the 1920s, mapping the velocities of galaxies led scientists to conclude that the whole universe is expanding, and that it began life as a vanishingly small point.

In the second half of the twentieth century, astronomers found evidence for unseen Dark Matter by observing that something extra was needed to explain the motion of stars within galaxies. Dark Matter is now thought to make up 27 percent of the content of universe (In contrast, ordinary matter amounts to only 5 percent).

Observations of the explosions of white dwarf stars in binary systems, so-called Type Ia supernovae, in the 1990s then led scientists to the conclusion that a third component, Dark Energy, made up 68 percent of the cosmos and is responsible for driving an acceleration in the expansion of the universe.

In their new work, the researchers (Gabor Racz and Laszlo Dobos of Eotvos Lorand University in Hungary and Robert Beck, Istvan Szapudi, and Istvan Csabai of the University of Hawaii) question the existence of Dark Energy and suggest an alternative explanation. They argue that conventional models of cosmology rely on approximations that ignore its structure and where matter is assumed to have a uniform density.

"Einstein's equations of General Relativity that describe the expansion of the universe are so complex mathematically, that for a hundred years no solutions accounting for the effect of cosmic structures have been found. We know from very precise supernova observations that the universe is accelerating, but at the same time we rely on coarse approximations to Einstein's equations, which may introduce serious side effects, such as the need for Dark Energy, in the models designed to fit the observational data." explains Dr. Laszlo Dobos at Eotvos Lorand University.

In practice, ordinary and Dark Matter appear to fill the universe with a foam-like structure, where galaxies are located on the thin walls between bubbles and are grouped into superclusters. The insides of the bubbles are in contrast almost empty of both kinds of matter.

Using a computer simulation to model the effect of gravity on the distribution of millions of particles of Dark Matter, the scientists reconstructed the evolution of the universe, including the early clumping of matter and the formation of large scale structure.

Unlike conventional simulations with a smoothly expanding universe, taking the structure into account led to a model where different regions of the cosmos expand at different rates. The average expansion rate though is consistent with present observations, which suggest an overall acceleration.

Dr. Dobos adds "The theory of General Relativity is fundamental in understanding the way the universe evolves. We do not question its validity. We question the validity of the approximate solutions. Our findings rely on a mathematical conjecture which permits the differential expansion of space, consistent with General Relativity, and they show how the formation of complex structures of matter affects the expansion. These issues were previously swept under the rug, but taking them into account can explain the acceleration without the need for Dark Energy."





If their findings are upheld, it could have a significant impact on the direction of future research in physics. For the past 20 years, astronomers and theoretical physicists have speculated on the nature of Dark Energy, but it remains an unsolved mystery. With the new model, this team of researchers expect at the very least to start a lively debate.


For more information:

http://www.ras.org.uk/news-and-press/2968-explaining-the-accelerating-expansion-of-the-universe-without-dark-energy

http://hubblesite.org/hubble_discoveries/dark_energy/de-what_is_dark_energy.php

https://www.astromart.com/news/news.asp?news_id=1543

https://www.astromart.com/news/news.asp?news_id=1474

https://www.astromart.com/news/news.asp?news_id=1293

https://www.astromart.com/news/news.asp?news_id=1227

https://www.astromart.com/news/news.asp?news_id=1224

https://www.astromart.com/news/news.asp?news_id=1020

https://www.astromart.com/news/news.asp?news_id=855

https://www.astromart.com/news/news.asp?news_id=794

http://curious.astro.cornell.edu/about-us/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/616-is-the-universe-expanding-faster-than-the-speed-of-light-intermediate

http://curious.astro.cornell.edu/the-universe/cosmology-and-the-big-bang/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/1066-can-two-galaxies-move-away-from-each-other-faster-than-light-intermediate

http://curious.astro.cornell.edu/about-us/97-the-universe/galaxies/cosmology/1069-do-galaxies-that-are-receding-from-us-faster-than-the-speed-of-light-disappear-from-our-observations



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