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micomaco86572
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What is the difference of cosmological horizon and particle horizon in cosmology?
chronon said:Take a look at http://www.chronon.org/Articles/cosmichorzns.html and http://www.chronon.org/articles/Cosmological_Event_Horizon.html on my website
I think that 'people' are sometimes confused about the issue, but that would be the most reasonable interpretation of cosmological horizon.micomaco86572 said:the cosmological horizon people often talk about actually means the the cosmological event horizon, doesn't it?
Well a freely coasting a universe without large scale gravity or cosmological constant - the (0,0) universe, also known as the Milne universe - doesn't have particle horizons. If you transform to conformal coordinates (See http://www.astro.ucla.edu/~wright/cosmo_03.htm#MSTD) then the conformal time goes back to minus inifinity.micomaco86572 said:You said:"for particle horizons to occur the rate of expansion of the universe (the derivative of the scale factor with time) must be infinite at time zero.", why?
In cosmology, horizons refer to the boundaries of the observable universe. These are the furthest points that we can see in the universe due to the finite speed of light and the expansion of the universe. Beyond these horizons, the light from distant objects has not had enough time to reach us and therefore cannot be observed.
Scientists use various methods to estimate the size of the observable universe. One way is to measure the cosmic microwave background radiation, which is the leftover radiation from the Big Bang. By analyzing the patterns in this radiation, scientists can calculate the size of the observable universe to be about 93 billion light-years in diameter.
Yes, there are three types of horizons in cosmology: the particle horizon, the event horizon, and the cosmic horizon. The particle horizon is the furthest distance from which particles of light could have traveled to Earth since the beginning of the universe. The event horizon is the boundary around a black hole from which nothing, including light, can escape. The cosmic horizon is the boundary of the observable universe.
Yes, the size of the observable universe can change over time. This is due to the expansion of the universe, which is causing the horizons to move further away from us. As the universe continues to expand, the observable universe will also increase in size. However, the rate of expansion is not constant and may change in the future.
The concept of horizons is closely related to the Big Bang theory. In fact, the idea of an observable universe with boundaries is a key prediction of the Big Bang theory. According to this theory, the universe began as a singularity and has been expanding ever since. As the universe expands, the horizons also move further away, limiting our ability to observe the universe beyond a certain point in time.