Dark energy may disguise shape of universe

Dark energy may disguise shape of universe – physics-math – 03 August 2009 – New Scientist

WE LIVE in a special time. For the past two decades, most of my colleagues and I have been working under the assumption that we can know everything about the universe. We know the amount of matter and energy it contains. We know its shape is flat. We can trace its history from the earliest moments after the big bang and we can even predict its fate. Or at least we thought we could.

Why were we so confident? Exquisite measurements of the radiation left over from the big bang led us to believe that we could work out the curvature of the universe to within a few per cent. In doing so, we have determined how much energy the universe contains and that most of it is in an exotic form called dark energy, which is driving the expansion of space.

However, recent discoveries have left me wondering if these claims were premature. As we learn more about dark energy and its effect on the expansion of space and time, we find that dark energy and the shape, or geometry, of the universe are worryingly intertwined.

By changing our assumptions about dark energy we can radically modify our constraints on the shape of the universe. Equally, without a much more precise measurement of the geometry, it is impossible to determine the nature and evolution of dark energy. Our picture of the universe has, to some extent, been blown wide open again.

Cum funcţionează Universul – II

Cum funcţionează Universul – II

Să ne aducem aminte de exemplul din finalul primei părţi, cu pista a cărei lungime se măreşte constant şi să încercăm o paralelă cu modelul Universului în expansiune, care prezintă caracteristici asemănătoare.

Lumina de la marginile sferei de 42 de milioane de ani-lumină şi-a început călătoria spre locul unde Terra se va fi format acum în jur de 13.7 miliarde de ani. Dar pe parcursul călătoriei, spaţiul intermediar şi-a mărit dimensiunile de 1090 de ori, iar în prezent suprafaţa sferică de pe care lumina a plecat este la aproximativ 46 de miliarde de ani-lumină depărtare. Vorbim despre distanţa maximă până la care putem vedea în spaţiul cosmic în prezent, care poartă numele de orizontul nostru de particule.

Cum funcţionează Universul – partea I

scientia.ro

Este posibil oare ca galaxiile îndepărtate să se distanţeze de noi mai repede decât lumina? Şi, dacă da, ne-ar fi posibil totuşi să le observăm? În mod surprinzător răspunsul este în ambele cazuri un “DA” răsunător. Cum de este cu putinţă aşa ceva? Cum se poate ca ceva să se deplaseze cu viteze superioare vitezei luminii?

În acest film (partea 1) şi în următorul vom încerca să oferim o descriere corectă a Universului pe baza modelului LCDM1 (Lambda-Cold-Dark-Matter), cel mai bun model cosmologic existent astăzi. Odată tabloul construit, răspunsurile la întrebările din paragraful de început vor veni de la sine.

Entropy and our cosmic telephone number

arxiv blog
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How can the cosmos have the entropy we see today if the temperature was almost exactly the same everywhere after the Big Bang? The answer may lie in our “cosmic telephone number”

“So how could you take something with almost the same temperature everywhere and then make something really hot here and something else really cold? How did that happen?”

The answer, he says, is in two parts. First inflation, this is the mysterious process in which the universe increased its volume by many orders of magnitude in just a fraction of a second. In the process, this magnified any tiny fluctuations that may have existed before inflation. And second gravity, which magnifies any clumpiness by pulling clumps together to form bigger clumps. This eventually forms galaxies, stars, planets and living things like us.

But Tegmark goes on to say that the process of inflation implies that other parts of the Universe that are unobservable to us may have grown from much more uniform parts of the early universe and so be hugely uniform now. And that recent results in string theory hint that the laws of physics may be quite different on those regions.

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Building a theory of dark matter annihilation

arstechnica.com:
In a case of classic scientific theory building, researchers show that a whole host of anomalous cosmological observations can be explained by a single new force.

How the Big Crunch Theory Works

science.howstuffworks.com:
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Clearly, there’s no easy answer when it comes to predicting the fate of the universe. But let’s imagine for a ­moment th­at the density of the universe is above the critical value required to stop expansion. This would lead to the big crunch, which in many ways would be like hitting the rewind button on a VCR. As gravity within the universe pulled everything back, galaxy clusters would draw closer together. Then individual galaxies would begin to merge until, after billions of years, one mega-galaxy would form.

Inside this gigantic cauldron, stars would meld together, causing all of space to become hotter than the sun. Eventually, stars would explode and black holes would emerge, slowly at first and then more rapidly. As the end drew near, the black holes would suck up everything around them. Even they would coalesce at some point to form a monstrous black hole that would pull the universe closed like a drawstring bag. At the end, nothing would remain but a super-hot, super-dense singularity — the seed of another universe. Many astronomers think the seed would germinate in a “big bounce,” starting the whole process over again.

That’s not the only theory. A few cosmologists, led by Paul J. Steinhardt of Princeton University and Neil Turok of Cambridge University, have recently argued that the big chill and the big crunch are not mutually exclusive. Their model works like this: The universe began with the big bang, which was followed by a period of slow expansion and gradual accumulation of dark energy. This is where we are today. What happens next is highly speculative, but Steinhardt and Turok believe that the dark energy will continue to accumulate and, as it does, will stimulate cosmic acceleration. The universe won’t ever stop expanding, but will spread out over trillions of years, stretching all matter and energy to such an extreme that our one universe will be separated into multiple universes. Inside these universes, the mysterious dark energy will materialize into normal matter and radiation. This will trigger another big bang — perhaps several of them — and another cycle of expansion.

Origins Of An Infinite Universe? A Fractal Conversation…

www.zimbio.com

Principiul antropic (III): multiuniversurile – Prof. Al. Mironov

www.cronicaromana.ro

What Can Swiss Cheese Teach us About Dark Energy?

(PhysOrg.com) — About 10 years ago, scientists reached the astonishing conclusion that our universe is accelerating apart at ever-increasing speeds, stretching space and time itself like melted cheese. The force that’s pushing the universe apart is still a mystery, which is precisely why it was dubbed “dark energy.”
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The researchers at Fermi said these voids might lie between us and the
supernovae being observed, acting like concave lenses to make the
objects appear dimmer and farther than they really are. If so, then the
supernova might not be accelerating away from us after all. Their
theory claimed to provide a way in which dark energy might go poof.

New dark energy findings suggest Einstein’s theory is dead-on

www.tgdaily.com:
Washington (DC) – NASA held a phone-in press conference today wherein three astrophysicists reported the latest findings on dark energy. They have now “clearly seen” the effects of dark energy on the most massive collapsed objects in the universe. This new evidence has aligned scientists behind the central belief that 1) dark energy exists, 2) that it explains why we are seeing the universe expanding and accelerating, and 3) that Einstein’s General Relativity theory is correct – so long as the cosmological constant is applied (something Einstein himself called his “greatest blunder”).