The greatest revolution in the scientific community, most often caused by a subtle difference between reality and expectations. 16th century, Copernicus made the Earth is not the center of the universe, his argument was based on a lot of people, but some of the movement of celestial objects esoteric minutiae. Today, a new scientific revolution, already 11 years ago with the discovery of the accelerating expansion of the universe began. Subtle differences in brightness of the supernova, gave astronomers concluded: all the material components constituting the universe, among them, 70% are completely unknown. That is, the space is filled with material which is different from any other ingredient - they always promote the expansion of the universe, unlike other substances that hinder expansion. This ingredient is called dark energy (dark energy).
10 years later, some of cosmologists still on the presence of dark energy was incredible, and even began to rethink those first so that they derive the basic assumptions of dark energy. One hypothesis is the product of the early scientific revolution - the Copernican principle (Copernican principle). This principle states that the location of the Earth is neither the center of the universe, nor any special. If we abandon this basic principle, we can explain these observations of a phenomenon but without resorting to dark energy picture of the universe, will surprisingly revealed.
Most people are very familiar with such a concept: our planet is but a cosmic dust, near the edge of the galaxy in a humble, around an ordinary star rotates. In our universe, at least similar to the billions of galaxies, even more than the distribution of a wide horizon of our universe (cosmic horizon, which we can observe the most distant border) - This leads us to believe that, in their own universe location is not unique in any place. However, there is little evidence to support such a humble view of the universe? How can we determine whether they are in a special position on it? Astronomers usually skip these questions, we assumed negligible is obvious, do not need to be further explored. Maybe we really are in a special place in the universe - to consider the possibility that many people seem to be unthinkable. However, this is some of the recent team of physicists around the world are seriously thinking perspective.
Ironically, assuming themselves insignificant in the universe, cosmologists to precisely provide a strong explanatory power. Summarized from the Copernican principle according to the cosmological principle (cosmological principle) stated: any time, point in any direction as viewed from space any, appearance of the universe are the same. This assumption allows us to put yourself in the corner of the universe to see what extrapolated to the entire universe. Cosmologists have made great efforts to cosmological principle-based, built up on behalf of the highest level of scientific cosmological model. Combined with modern science of space, time and matter of understanding, the cosmological principle implies: space is expanding, the universe is cold, which is filled with relics from the beginning of the hot universe - all these prophecies are astronomical observatory eleven confirmed.
For example, astronomers found that distant galaxies emitted light seems more red light than the hair of some nearby galaxies. This phenomenon is known as redshift (redshift) will be able to use the space for expansion ingenious explanation, because light will be with the expansion of space stretched accordingly. Microwave radiation detectors also found very early universe emitted - the cosmic microwave background (cosmic microwave background). This relic of the Big Bang primordial fireball, like a layer of curtain wrapped up in all directions of space, smooth almost flawless. To be fair, we can successfully explain these phenomena, since, as we humble attitude is a credit - assuming the more important their place in the universe, the more we can be "comprehensive" explore the universe.
Darkness falls
That being the case, why can not we complacent? If the cosmological principle really is so successful, why bother to question it? The problem is that astronomical observations have some very strange results. Over the past decade, astronomers found that distant supernovae to determine the extent of the redshift, the observed brightness is always darker than expected. Supernova redshift marked expansion of space since it exploded magnitude. Detect distant supernovae redshift luminous degree, cosmologists can infer that when the supernova explosion the size of the universe is much smaller than it is today. The higher the degree of redshift supernovae, when it exploded, the smaller the size of the universe, so from then until now, the greater the magnitude of expansion of the universe.
Supernova observations brightness provides us with a way to measure it to our distance so as to reveal the supernova explosion long ago there. If a supernova's redshift level has been determined, but its brightness and looks lower than expected, the supernova's distance will certainly farther than astronomers thought. Its light takes longer hair can reach us here, which means that the size of the universe from the time of the expansion to the present size, must have spent a longer time. Therefore, the expansion rate of the universe in the past must be slower than scientists previously expected. In fact, distant supernova looks very dark, so that the accelerating expansion of the universe must be to catch up with its current rate of expansion.
This accelerating expansion triggered a revolution in cosmology: the universe of time and space to attract the substance of the present structure, the expansion rate gradually slowed down, but the supernova data suggest that the opposite is true. If cosmologists accept the cosmological principle and assume that the accelerating expansion of the universe appears everywhere, we can come to a conclusion: the universe must be filled with a way to generate repulsive singular energy - dark energy.
In the standard model of elementary particles and forces physicists to describe, there is no consistent anything and dark energy. This is a not yet been directly observed substance, its nature is different from anything we have seen in the past, the energy density is lower than the most simple idea that we can make the 120 orders of magnitude (According to quantum field theory inferred vacuum energy, the energy density of dark energy is 10,120 times). For what dark energy might be, physicists have some ideas, but still pure speculation. In short, the dark energy, we can almost be said to be ignorant. Whatever dark energy might be, researchers are working on a series of ambitious and costly ground and space exploration missions, used to find dark energy and determine its nature. For many people, this is the most daunting challenges faced by modern cosmology.
Shining Path
Faced with such a strange, dark energy seems unlikely, some researchers began to rethink "the existence of dark energy," the derivation process, questioning the underlying assumptions of a time - we live in the universe is not the position in the end Mediocre, we observed the phenomenon can not be generalized to the entire universe? If you put aside cosmological principle, evidence of the existence of dark energy can not be explained by other means?
In traditional cosmology description, "cosmic expansion" refers to the expansion of the universe as a whole occurred. Talk like a balloon being inflated: we fill the balloon to say how much, referring to the size of the entire balloon, and not specific to each small balloon inflated number. However, we are seeing some bizarre gatherings of balloons, their expansion is not uniform. For example, an elongated balloon is inflated, the circle will be on the side of rapid expansion, then bulging portion to the other end will extend long past. Abandoned the cosmological principle in another cosmological point of view, the spatial non-uniformity can be expanded. A much more complex picture of the universe on this surface.
We might look at the following this model, which is the University of Cape Town (University of Cape Town), George Ellis (George Ellis), Charles Hellaby (Charles Hellaby) and Na Qimu Moose Tafari (Nazeem Mustapha) first proposed, and later by the French in Paris - Meudon Observatory (Paris-Meudon Observatory) Marie - Noelle Celestin Shourie (Marie-Noelle Clrier) further development: first, assume that each universe in deceleration of the expansion, because the material is always interesting space, preventing it expands then, suppose we live in a vast universe super giant hole (cosmic void) being - not inside a giant hole empty, only half the average density of matter elsewhere even third. A more open space area, contained within, less material can slow the expansion therefore, the internal giant hole expansion rate faster than in other places - the center of the most rapid expansion, the slower expansion close to the edge, because of the high density area outside the cave giant has begun to play a role in the vicinity of the edge. At any time, the expansion rate of the different parts of space are not the same, like those grotesque balloon inflated uneven expansion of the same.
Some contemplated in this uneven supernova universe erupted in different locations, some giant hole near the center, close to some giant hole edge, and some huge holes located outside. If we are close to the center of the giant hole, a supernova farther away from us, the slower the rate of expansion of the space around it. In the process of light propagation to us, the expansion velocity through the region faster and faster it sends. Each light through an area, the space expansion will stretch a little light, the cumulative effect of this had we observed redshift. Redshift produced after such a light in the universe propagation distance than at the same speed (ie our neighboring expansion rate) redshift whole expanding universe created slightly lower. In turn, such a light in the universe to achieve a certain redshift, it must be consistent with the propagation distance than the expansion rate of the universe in the light propagation distance longer - that is, the supernova must be farther away from us, thus it appears darker.
In other words, the model to changes in the expansion rate from the time of "transfer" to the space. In this way, the introduction of dark energy, cosmologists do not need to, be able to explain "supernova brightness darker than expected," the observed facts. To make this "alternative" interpretation works, we have to live in a truly cosmic scale to achieve huge hole. Supernova observations range has been extended to several billion light years away, occupy a large part of the entire universe can be observed. To explain these observations, the giant hole the size it must meet similar standards. No matter who's standards, which are enough to be called "great" the.
Far-fetched?
Such a giant hole in the universe how strange it? It seems a flagrant violation of the cosmic microwave background (astronomers observed microwave background intensity of the parties does not exceed the difference between the direction of 1/100 000), not to mention the galaxies in space seemingly evenly distributed. However, a closer look shows that these may not be sufficient evidence beyond a reasonable doubt the universe ruled the caverns.
Uniform background radiation intensity on the requirements of the universe looks almost the same in all directions. If the giant hole substantially spherical, we are from the giant hole in the center and close enough to the fact that these observations do not have any problems. In addition, the microwave background that there are some anomalies, may be able to use large-scale non-uniformity to explain.
As for the distribution of galaxies, the existing sky surveys also unable to detect distant galaxies enough, not enough to exclude a large size to be able to "simulate" the existence of dark energy super giant hole in the universe. The sky surveys found a size of about hundreds of millions of light-years of "small" giant hole in the material fibers and other structures, but we had been talking about the giant hole the size of a large magnitude would go. Galaxy Survey observations have not confirmed cosmological principle, which is currently a problem in the astronomical community debate. American David Hogg of New York University (David Hogg) and its partners made the analysis shows that the largest structures in the universe is about 200 million light- on a larger scale, the distribution of the substance seem uniform and smooth, and the universe consistent principles. But Italy Luomafeimi Center (Enrico Fermi Center) of Francesco Sylos La Bini (Francesco Sylos Labini) and his colleagues argue that the largest structure ever found, but it is found that these structures Galaxy Survey project a limited detection range to find the "maximum" structure only. Larger structures may range beyond the observation of these surveys.
Suppose you have a map showing the other side of the terrain, extending from one side of a road map within a radius of 10 km to. It follows that the longest road only 10 kilometers of the conclusion is clearly wrong. To determine the length of the longest road, you need a larger, clearly marked map of all roads starting and ending locations, so you can know the full scale of the road. Similarly, astronomers have to prove the cosmological principle, it must be a large-scale galaxy surveys, detection range must exceed the largest structures in the universe right. Existing sky surveys in the end big enough, this is a matter still under debate.
For theorists, the super giant hole is a difficult "digest" things. All available evidence suggests that galaxies and fiber, large-scale structures like the giant holes are from the microscopic quantum fluctuations of "bred" from the (cosmic expansion of these microscopic "seed" to enlarge the scale of astronomy), the universe theory can accurately predict the probability of a particular size structure appearing in the universe. The larger the size of the structure should be more rare. Large enough to "simulate" the probability of dark energy super giant hole in the universe appear no more than 1/10 100. Super giant hole may really exist, but the possibility can find one in our observable universe, it seems minimal.
However, the above reasoning there may be a loophole. The early 1990s, one of the authors of "standard model of the early universe," the United States of Andrei Linde of Stanford University (Andrei Linde) and colleagues show that despite the super giant hole very rare, but they are in the early universe expanded faster, eventually occupy the most space. Observers find yourself on the possibility of a super giant hole inside, probably did not so low. This conclusion shows that the cosmological principle (that is, we do not live in a special place) and between ordinary principle (principle mediocrity, that we are just ordinary observer of), does not always equate. It seems that in the ordinary common humanity, but also can live in a special place.
Detection giant hole
What observations can be determined, the accelerating expansion of the universe is driven by dark energy, we still live in a special place super giant hole in the center like? In order to test whether there is a giant hole, cosmologists need to establish an effective model to describe how space, time and matter responds to the surrounding environment. In 1933, a model of the universe Abbe Georges Lemaitre (Abb Georges Lema tre) was in line with the proposed a year later, Richard Tolman (Richard Tolman) also independently made the same model, the first after World War II by the Hermann Bondi (Hermann Bondi) further development and improvement. In their vision of the universe, the expansion rate depends not only on time but also on the distance to a particular location, and we now assume that this is exactly the same.
With Lemaitre - Tolman - Bondi model of the universe, cosmologists can predict a series of physical quantities can be observed. Let's look at the beginning astronomers deduced the existence of dark energy supernova. Astronomers observed the supernova more reconstruction cosmic expansion history more accurately. Strictly speaking, these observations can not rule out the giant hole model, because no matter what kind of observed supernova data, cosmologists can use the shape of a giant hole suitable to explain it. However, you want to do with dark energy absolutely no difference, this giant hole must have some very strange properties.
The reason is that the hypothetical dark energy driving the accelerated expansion will continue until today. If a giant hole to exact "simulate" this expansion velocity with the distance we must be far more sharply decline, and all must be so in any direction. As a result, it must be in any direction, as far away from us getting dramatically increase material and energy density. The density distribution of matter in the universe, it certainly looks like a sharp upside down witch hat, hat tip pointing to where we live. However, all hitherto observed structure of the universe, seems to have the opposite extreme: they are mostly smooth density distribution, and no reason not to be a "hat tip." Worse, the same year at Cornell University Ali van der Velde (Ali Vanderveld) and Buena Flanagan (Eanna Flanagan) has been proven, point to the place where we live "hat tip" must also singularity is a job, just like a black hole in the middle, like the ultra-dense area.
However, if this is more true giant hole has a smooth density distribution, it will leave enough to recognize the identity of the observer "fingerprint." Smooth voids still produce some of the observed phenomena, may be mistaken for the accelerated expansion, but there is no "hat tip" empty and dark energy will not be able to reproduce exactly the same result. Rather, seen on the surface of the expansion of "acceleration" with the red shift change by change, it will disclose the secret. We are one with Kate Rand (Kate Land, then at the University of Oxford, UK) co-authored the paper to prove: the existing hundreds of supernova observations, based on several hundred more supernova observations, it should be caverns and dark energy sufficient determination of who is right. Supernova observation project in a very favorable position, will soon be able to achieve this goal.
Supernova is not the only criterion for observation. In 1995, Princeton University, Jeremy Goodman (Jeremy Goodman) suggests another possible test methods - observation of the microwave background radiation. The best evidence of dark energy was not yet released, Goodman proposed aim of this approach, not to give any unexplained phenomena seek to explain, but for the Copernican principle itself, looking for evidence. His idea is to mirror as distant galaxies, from different locations to observe the universe, as according to the different celestial bodies in the same dressing room mirror. Microwave radiation encountered clusters of galaxies, a small portion will be reflected galaxies. These carefully measured the spectrum of the radiation, cosmologists can infer that the universe when viewed from one of these galaxies, the universe what it looks like. If changing positions will change the appearance of the universe manifested, which will provide strong evidence giant holes or similar structures.
Cosmologists have two teams this idea into practice. United States Dartmouth College (Dartmouth College), Robert Caldwell (Robert Caldwell) and Illinois Batavia City Fermi National Accelerator Laboratory Albert Stebbins (Albert Stebbins), research accurate measurements of microwave background the University of Madrid, Spain Juan Garcia - multi Bailey (Juan Garca-Bellido) and Aarhus University (University of Aarhus) of Troels Howe Ge Bole ( Troels Haugbolle) the direct observation of individual galaxies. Both groups did not detect the presence of the giant hole, they can only be limited to such a giant hole might have what kind of character. Scheduled for May 2009 launch of Planck (Planck Surveyor), this property will make a huge hole more restrictive, and may even completely exclude the presence of a giant hole.
University of Cape Town Bruce Bassett (Bruce Bassett), Chris Clarkson (Chris Clarkson) and Lvhui Qing (Teresa Lu) proposed a third method - independent measurements of the expansion rate at different locations. Astronomers usually used to measure the expansion velocity redshifts, but redshift is a celestial body to the cumulative effect of all the space between our regional expansion. Since all of these areas are added together, redshift can not distinguish between the expansion velocity changes with time or spatially variable. The best possible screening expansion effect elsewhere, only measure the expansion rate of a particular spatial location. The task is difficult but not yet completed. Observe the formation process at different locations on the structure of the universe, it may be a viable option. The formation and evolution of galaxies and clusters of galaxies in space depends largely on the local expansion rate. These objects of different positions, excluding the impact of other effects of their evolution, astronomers may be able to distinguish the subtle differences on the expansion rate.
Other possible
We live in a universe super giant hole inside, which appears with the "cosmological principle" situation with the fire, but there may be some trade-off situation. The universe on a large scale cosmological principle can be followed, but the galaxy sky surveys have found smaller caverns and material fibers may also work together to simulate the effects of dark energy. McGill University Diersabo Biswas (Tirthabir Biswas) and Alessio Notari (Alessio Notari), there was at the University of Padua, Italy Mara Valerio (Valerio Marra) and his collaborators at the University of Chicago, and this idea has been studied. In their model, the universe looks like Swiss cheese - uniform whole, but the interior is full of holes. Therefore, the expansion rate will be slightly different at different locations. Light emitted by distant supernovae in our arrival here before, will pass through a number of smaller caverns, changes in the expansion rate will be distorted on their brightness and redshift. But now it seems, the idea seems to be in deep trouble. Clifton, one of the authors and Oxford University Joseph statue Heights (Joseph Zuntz) cooperation proved to reproduce the effect of dark energy requires the presence of a large number of very low density of matter giant hole, and their distribution must also adhere to a particular way .
Another possibility is that dark energy is the illusion of mathematical approximations cosmologists conventional produce. To calculate the universe's expansion rate, we typically count the total amount of substances contained in a region of space, divided by the volume of space, an average energy density. We then substituted into an average density of Einstein's gravitational equations to determine the average speed of expansion of the universe. Although the density varies with location, but we treat it as minor fluctuations on overall averages.
The problem is that the average distribution of matter on behalf of the Einstein equation solver, substituting the real matter distribution with solving equations and then seek the geometric mean of the results, it is totally different. In other words, we are to average and then solve the equation, but in fact we should first solve the equation and then averaged.
The real universe, even if it is anything that is substantially similar to the real universe is substituted into the entire equation solver, the difficulty is that people can not imagine, so most scientists are resorting to average and then solving this relatively simple method. In order to determine how accurate this approximation in the end, the University of Lyon in France than Thomas Schell (Thomas Buchert) conducted a study. He introduced a set of additional items in cosmology equations used to represent the average of the first and then solve the error generated. If you can prove that these items is small, then the approximation is very if these items is large, approximate method on the poor. At present, this research has not come to the exact result. Some researchers suggest that these additional items may be enough to explain dark energy, some researchers have claimed that these items can be ignored.
Able to distinguish between dark energy and observational testing giant hole model, will soon be expanded. Pierre Astier, France University of Paris (Pierre Astier) led supernova Information Survey (Supernova Legacy Survey) and the Joint Dark Energy Task (Joint Dark Energy Mission) is currently being designed, the precise determination of the expansion history of the universe. Planck and a variety of ground and balloon-borne equipment will be more finely mapping the cosmic microwave background. Expected to be completed in 2020, jumbo radio telescope - square Kilometer Array (Square Kilometer Array), the census will help us to observe all galaxies within the universe.
This cosmological revolution is far from over.
(Author: Timothy Clifton, Pedro G Translation: Yu Chun)
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