Posts tagged CMB
Posts tagged CMB
Everything holds together, our new picture of cosmology is that we live in a universe dominated by nothing. The largest energy in the universe, 70% of the energy in the universe, resides in empty space. And we don’t have the slightest idea why it’s there.
This is absolutely wonderful.
When we say that the universe is flat, what does that really mean? The possible topologies of space-time are: open, flat and closed. A useful parameter when talking about the curvature of the universe is the density parameter given by omega (Ω) where Ω = Ωm + Ωrel + ΩΛ. The first term is the mass density given by ordinary, baryonic matter. The second term is the equivalent mass density of relativistic particles made up of electromagnetic energy and neutrinos. The last term is the effective mass of the universe dominated by dark energy (the cosmological constant.) The density parameter of the universe is given by the density divided by the critical density to result in a flat universe. If the density in the universe is exactly equal to the required density to inhabit a flat universe, Ω will be equal to 1. Current measurements give that Ω = 1.005 +/- 0.0007. Our universe is nearly flat! This can be seen using the Cosmic Microwave Background using a simple relationship.
Since the fluctuations in the CMB data are standard rulers, the curvature of the universe will determine the angular size of the fluctuations and thus the apparent size of the fluctuations will suggest the curvature of the universe. In an open universe, the curvature of space-time will distort light such that the fluctuations will seem smaller than they really are. On the contrary, in an open universe, the fluctuations will seem larger than they really are. In complete accordance with simulations of a flat universe, the fluctuations of the CMB data signify a flat universe: the universe has nearly exactly the critical density to result in a flat universe.
Cosmology is in a golden era, with extraordinary advances, both experimental and theoretical, coming every year. The aim of this project is to cast some of the most recent developments in a novel and engaging manner, choosing sound as the primary vehicle. Perhaps, with this experiential access to Nature, the excitement which is almost palpable in the astronomical community, can be felt more widely.
The project has also allowed me, a non-cosmologist astronomer, the opportunity to follow more closely what is, I think, a precious time in the history of science — indeed, in human history. With each passing year, the biography of the Universe is being penned in an ever firmer hand. In fact, since we are of the Universe, it is really an autobiography. Let’s now turn the first pages, and read about our birth and first year of life….
By Ron Cowen
Most cosmologists trace the birth of the universe to the Big Bang 13.7 billion years ago. But a new analysis of the relic radiation generated by that explosive event suggests the universe got its start eons earlier and has cycled through myriad episodes of birth and death, with the Big Bang merely the most recent in a series of starting guns.
That startling notion, proposed by theoretical physicist Roger Penrose of the University of Oxford in England and Vahe Gurzadyan of the Yerevan Physics Institute and Yerevan State University in Armenia, goes against the standard theory of cosmology known as inflation.
The researchers base their findings on circular patterns they discovered in the cosmic microwave background, the ubiquitous microwave glow left over from the Big Bang. The circular features indicate that the cosmos itself circles through epochs of endings and beginnings, Penrose and Gurzadyan assert. The researchers describe their controversial findings in an article posted at arXiv.org on November 17.
The circular features are regions where tiny temperature variations in the otherwise uniform microwave background are smaller than average. Those features, Penrose said, cannot be explained by the highly successful inflation theory, which posits that the infant cosmos underwent an enormous growth spurt, ballooning from something on the scale of an atom to the size of a grapefruit during the universe’s first tiny fraction of a second. Inflation would either erase such patterns or could not easily generate them.
“The existence of large-scale coherent features in the microwave background of this form would appear to contradict the inflationary model and would be a very distinctive signature of Penrose’s model” of a cyclic universe, comments cosmologist David Spergel of Princeton University. But, he adds, “The paper does not provide enough detail about the analysis to assess the reality of these circles.”
Penrose interprets the circles as providing a look back, past the glass wall of the most recent Big Bang, into the universe’s previous episode, or “aeon,” as he calls it. The circles, he suggests, were generated by collisions between supermassive black holes that occurred during this earlier aeon. The colliding black holes would have created a cacophony of gravitational waves — ripples in spacetime due to the acceleration of the giant masses. Those waves would have been spherical and uniformly distributed.
According to the detailed mathematics worked out by Penrose, when the uniform distribution of gravitational waves from the previous aeon entered the current aeon, they were converted into a pulse of energy. The pulse provided a uniform kick to the allotment of dark matter, the invisible material that accounts for more than 80 percent of the mass of the cosmos.
“The dark matter material along the burst therefore has this uniform character,” says Penrose. “This is what is seen as a circle in our cosmic microwave background sky, and it should look like a fairly uniform circle.”
Each circle has a lower-than-average variation in temperature, which is just what he and Gurzadyan found when they analyzed data from NASA’s orbiting Wilkinson Microwave Anisotropy Probe, or WMAP, which scanned the entire sky for nine years, and the balloon-borne BOOMERANG experiment, which studied microwave background over a smaller fraction of the heavens.
Because the team found similar circular features with two different detectors, Penrose says it’s unlikely he and his colleagues are being fooled by instrumental noise or other artifacts.
But Spergel says he is concerned that the team has not accounted for variations in the noise level of WMAP data acquired over different parts of the sky. WMAP examined different sky regions for different amounts of time. Maps of the microwave background generated from those regions studied the longest would have lower noise and smaller recorded variations in the temperature of the microwave glow. Those lower-noise maps could artificially produce the circles that Penrose and Gurzadyan ascribe to their model of a cyclic universe, Spergel says.
A new, more detailed map of the cosmic microwave background, now being conducted by the European Space Agency’s Planck mission, could provide a more definitive test of the theory, Penrose says.
Explanation: Seen from our edge-on perspective, the Milky Way Galaxy sprawls across the middle of this false-color, all sky view. The expansive microwave map is based on 1 year’s worth of data from instruments onboard the sky-surveying Planck spacecraft. Remarkably, the bright stripe of gas and dust clouds along the galactic plane and the galaxy’s enormous arcing structures seen at microwave energies are hundreds or thousands of light-years away, while the mottled regions at the top and bottom represent the Cosmic Microwave Background (CMB) radiation, some 13.7 billion light-years distant. Left over from the Big Bang, fluctuations in the CMB reflect the origins of structure in the evolving universe. Analyzing the microwave data, Planck scientists plan to separate the contributions of the Milky Way and CMB radiation. The work will ferret out the characteristics of the CMB across the entire sky and glean information about the make up of our Milky Way Galaxy.
The current cosmological consensus is that the universe began 13.7 billion years ago with the Big Bang. But a legendary physicist says he’s found the first evidence of an eternal, cyclic cosmos.