Posts tagged big bang theory
Posts tagged big bang theory
Short answer: no.
Long answer: click through the link.
WARNING! Quantum fluctuations lie ahead.
Guth says (p. 12-14, 271-276) that the person who first suggested that the universe and its associated space may have originated as a quantum fluctuation was Edward Tryon in 1973 in his paper Is the Universe a Vacuum Fluctuation? (Nature, vol. 246, p. 396-397, 14 December 1973.) As Tryon says in that paper:
In any big bang model, one must deal with the problem of ‘creation’. This problem has two aspects. One is that the conservation laws of physics forbid the creation of something from nothing. The other is that even if the conservation laws were inapplicable at the moment of creation, there is no apparent reason for such an event to occur.
Contrary to widespread belief, such an event need not have violated any of the conventional laws of physics. The laws of physics merely imply that a Universe which appears from nowhere must have certain specific properties. In particular, such a Universe must have a zero net value for all conserved quantities.
To indicate how such a creation might have come about, I refer to quantum field theory, in which every phenomenon that could happen in principle actually does happen occasionally in practice, on a statistically random basis. For example, quantum electrodynamics reveals that an electron, positron and photon occasionally emerge spontaneously from a perfect vacuum. When this happens, the three particles exist for a brief time, and then annihilate each other, leaving no trace behind.
If it is true that our Universe has a zero net value for all conserved quantities, then it may simply be a fluctuation of the vacuum, the vacuum of some larger space in which our Universe is imbedded. In answer to the question of why it happened, I offer the modest proposal that our Universe is simply one of those things which happen from time to time.
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.
byon February 8, 2011
Our Universe is an enormous place; that’s no secret. What is up for discussion, however, is just how enormous it is. And new research suggests it’s a whopper – over 250 times the size of our observable universe.
Currently, cosmologists believe the Universe takes one of three possible shapes:
1) It is flat, like a Euclidean plane, and spatially infinite.
2) It is open, or curved like a saddle, and spatially infinite.
3) It is closed, or curved like a sphere, and spatially finite.
While most current data favors a flat universe, cosmologists have yet to come to a consensus. In a paper recently submitted to Arxiv, UK scientists Mihran Vardanyan, Roberto Trotta and Joseph Silk present their fix: a mathematical version of Occam’s Razor called Bayesian model averaging. The principle of Occam’s Razor states that the simplest explanation is usually the correct one. In this case, a flat universe represents a simpler geometry than a curved universe. Bayesian averaging takes this consideration into account and averages the data accordingly. Unsurprisingly, the team’s results show that the data best fits a flat, infinite universe.
byon March 29, 2011
Robert Frost once wrote, “Some say the world will end in fire; some say in ice.” Likewise, some scientists have postulated that the universe could die either a dramatic, cataclysmic death – either a “Big Rip” or a “Big Crunch” – or a slower, more gradual “Big Freeze.” The ultimate fate of our cosmos has a lot to do with its shape. If the universe were open, like a saddle, and the energy density of dark energy increased without bound, the expansion rate of the cosmos would eventually become so great that even atoms would be torn apart – a Big Rip. Conversely, if the universe were closed, like a sphere, and gravity’s strength trumped the influence of dark energy, the outward expansion of the cosmos would eventually come to a halt and reverse, collapsing on itself in a Big Crunch.
byon February 17, 2011
How did the universe get its start? It’s one of the most pressing questions in cosmology, and likely one that will be around for a while. Here, I’ll begin by explaining what scientists think they know about the first formative seconds of the universe’s life. More than likely, the story isn’t quite what you might think.
In the beginning, there was… well, we don’t really know. One of the most prevalent misconceptions in cosmology is that the universe began as an immensely small, inconceivably dense collection of material that suddenly exploded, giving rise to space as we know it. There are a number of problems with this idea, not least of all the assumption implicit in an event termed the big “bang.” In truth, nothing “banged.” The notion of an explosion brings to mind an expanding tide of material, gradually filling the space around it; however, when our universe was born, there was no space. There was no time either. There was no vacuum. There was literally nothing.
byon March 9, 2011
Let’s recap. When we left off, the universe was a chaotic soup of simple matter and radiation. A photon couldn’t travel very far without bumping into and being absorbed by a charged particle, exciting it and later being emitted, just to go through the cycle again. After about three minutes, the ambient temperature had cooled to such an extent that these charged particles (protons and electrons) could begin to come together and form stable nuclei.
But, despite the falling temperature, it was still hot enough for these nuclei to start to combine into heavier elements. For the next few minutes, the universe cooked up various isotopes of hydrogen, helium and lithium nuclei in a process commonly known as big bang nucleosynthesis. As time went on and the universe expanded even further, these nuclei slowly captured surrounding electrons until neutral atoms dominated the landscape. Finally, after about 300,000 years, photons could travel freely across the universe without charged particles getting in their way. The cosmic microwave background radiation that astronomers observe today is actually the relic light from that very moment, stretched over time due to the expansion of the universe.
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.