Horizon problem
The horizon problem is a basic problem in cosmology , which is raised by the standard model of the Big Bang and arose in the 1970s. It raises the question of how it can be that different regions of the universe , which are not in contact with each other because the distance between them is too great, can nevertheless have the same physical properties, such as a comparable temperature level.
This should not be possible if an exchange of properties (such as energy, temperature, etc.) can take place at the maximum speed of light and the individual areas were not available for more than 13.8 billion years (the universe is that old), to develop own characteristics. An explanation for the horizon problem is offered by the inflation theory , which was developed not least because of this problem. Another possibility takes into account a less accepted theory that the speed value of light could have changed over time.
Basic concept
If you look at the night sky, you are consistently looking into the past. The light of a galaxy that is ten billion light years away from the earth ( travel time distance ) took ten billion years to travel the long way to the earth's surface. If one now looks at a galaxy that can be observed ten billion light years away in one direction and then looks at another in exactly the opposite direction, the distance between the two galaxies is a total of 20 billion light years. This means that the light from one galaxy cannot have reached the other galaxy until today, since the universe has a verifiable age of 13.7 billion years and this period of time is not sufficient for the light to be able to cover the distance between the two galaxies . Expressed universally, it can be said that sections of the universe that are visible from earth remain invisible to other areas of space for the time being and must therefore lie outside the respective horizon of their observable universe .
According to basic physical theories, it is not possible that physical information can travel faster than light. The context information in this context means any kind of physical interaction. For example, heat usually flows from hotter to cooler areas, which in physical terms is a type of information exchange. Following this example, the two galaxies are unable to exchange any kind of physical information. In other words: they have no causal contact with each other. It should therefore be possible to conclude from this that they differ in terms of their physical properties or, more fundamentally, that different properties must be found in different areas throughout the universe.
Contrary to this expectation, however, the universe is in fact extremely homogeneous . For example, the cosmic microwave background radiation (CMB) that fills the universe has almost exactly the same temperature of about 2.725 K everywhere .
The temperature difference is so small that only recently has it been possible to develop instruments that can measure these differences. This fact poses a serious problem, because if the universe had started with only slightly different temperatures in different areas, then there should have been no way to reach the uniform temperature level that can be observed today. According to quantum physics, due to Heisenberg's uncertainty principle, this initial temperature difference should actually persist since the Big Bang, since on the other hand it can also be considered impossible that the universe has developed with exactly the same properties everywhere.
The extent of this problem can be regarded as relatively considerable. According to the Big Bang model, after its density had decreased due to its expansion, the universe eventually reached a point at which the photons in the 'mix' of particles were no longer directly compressed and instead they 'decoupled' from the plasma and moved into the Spread the universe like a 'firework of light'. Background radiation was probably born around 300,000 years after the Big Bang. The volume of the possible exchange of properties at that time corresponded to a diameter of 900,000 light years, based on the speed of light and the rate of expansion of space in this early universe. Now all of space is still at the same temperature, although it has reached an expansion of at least 46 billion light years.
inflation
A solution to this phenomenon, which could also explain some other basic questions such as the problem of the flatness of the universe, offers the inflation theory . Thereafter, between 10 −35 and 10 −32 seconds after the Big Bang, there was a small period of rapid, exponentially increasing expansion (called inflation ). During this phase of inflation, the universe expanded by an enormous factor faster than light and pulled the light with it in virtually all directions.
If this theory is correct, inflation solves the horizon problem by the fact that the entire universe was causally connected before this inflationary period and that the physical properties could interact and harmonize during this phase. It expanded so rapidly with inflation that these properties remained frozen across space ; from this point in time the universe was forced to an almost perfect homogeneity, since the information would no longer have a causal connection to change its properties. However, this also means that the observable universe is only a fraction of the actual cosmos.
As a consequence of such cosmic inflation, the anisotropy would have reduced during the Big Bang, but would not have completely disappeared. The temperature differences of the cosmic background radiation were also smoothed out by the cosmic inflation, but persist to a small extent. The theory predicts a broad spectrum for the anisotropy of the microwave background radiation, which is actually largely in line with the results that the WMAP and COBE space probes were able to provide science.
Variable speed of light
The Portuguese scientist João Magueijo and the American physicist Andreas Albrecht proposed a further solution to this problem in 1999. According to their thesis, the speed of light was not always the same, but shortly after the Big Bang it was 60 orders of magnitude higher than it is today. As a result, the different regions could have come into contact with one another, as their horizon would have been much wider before the distance finally became too great. In addition, far more time would have been available for the properties to be able to adapt to one another through interaction than the parameters that can be measured today would suggest. In addition, this theory demonstrates that a variable speed of light suppresses the density fluctuation, which supports the homogeneity of the universe.
However, this theory of the variable speed of light is rejected by most scientists, since the speed of light is one of the most important natural constants and forms the basis of Einstein's theory of relativity .
credentials
- ^ J. Casado (2003): A Simple Cosmological Model with Decreasing Light Speed . arxiv : astro-ph / 0310178
- ↑ Gravitational Lenses: Age of the Universe , Recalculated, astronews.com
- ↑ a b c Andrew Liddle: Introduction to Modern Cosmology , Volume 1. Wiley-VCH Verlag GmbH, 2009, ISBN 978-1-5274-0882-5 , p. 111.
- ↑ Dirk Evers: Space - Materie - Time , Volume 1. Mohr Siebeck, 2000, ISBN 3-16-147412-0 , p. 216.
- ↑ a b c d inflation . Retrieved July 15, 2010.
- ^ Charles Lineweaver, Tamara M. Davis: Misconceptions about the Big Bang . Scientific American . 2005. Retrieved November 6, 2008.
- ↑ Starkman, Glenn D. and Dominik J. Schwarz: Is the Universe Out of Tune? August 1, 2005.
- ^ Albrecht, Magueijo: A time varying speed of light as a solution to cosmological puzzles , Phys. Rev. D59, 1999, arxiv : astro-ph / 9811018 .
- ↑ Joachim Laukenmann: The universe is flat . World week. 2003. Retrieved July 1, 2014.