Posts tagged roger penrose
Posts tagged roger penrose
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.
In physics and cosmology, the anthropic principle is the philosophical argument that observations of the physical Universe must be compatible with the conscious life that observes it. Some proponents of the argument reason that it explains why the Universe has the age and the fundamental physical constants necessary to accommodate conscious life. As a result, they believe that the fact that the Universe’s fundamental constants are within the narrow range thought to allow life is not remarkable.
The Strong Anthropic principle as explained by Barrow and Tipler (see Variants) states that this is all the case because conscious life, in some sense, needed to exist. Critics argue in favor of a Weak Anthropic principle, which states that the universe’s fine tuning amounts to selection bias; in an infinite universe, some worlds might evolve conscious life. Douglas Adams used the metaphor of a living puddle examining its own shape, since, to those living creatures, the universe may appear to fit them perfectly (in fact, they simply fit the universe perfectly).
“The argument can be used to explain why the conditions happen to be just right for the existence of (intelligent) life on the earth at the present time. For if they were not just right, then we should not have found ourselves to be here now, but somewhere else, at some other appropriate time. This principle was used very effectively by Brandon Carter and Robert Dicke to resolve an issue that had puzzled physicists for a good many years. The issue concerned various striking numerical relations that are observed to hold between the physical constants (the gravitational constant, the mass of the proton, the age of the universe, etc.). A puzzling aspect of this was that some of the relations hold only at the present epoch in the earth’s history, so we appear, coincidentally, to be living at a very special time (give or take a few million years!). This was later explained, by Carter and Dicke, by the fact that this epoch coincided with the lifetime of what are called main-sequence stars, such as the sun. At any other epoch, so the argument ran, there would be no intelligent life around in order to measure the physical constants in question — so the coincidence had to hold, simply because there would be intelligent life around only at the particular time that the coincidence did hold!”
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.
This is a story of the search for the beginning of time.