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Timvanhoomissen
Is there more to our universe than what we can observe? If so, does that mean that photons from the CMB are traveling towards us from beyond our cosmological horizon?
To expand a little bit upon Chronos point, over time we'll be able to see CMB photons that were emitted from a little bit further away. But not very much further. Due to the way the expansion is likely to progress in the future, we'll only ever be able to see a finite distance.Timvanhoomissen said:Is there more to our universe than what we can observe? If so, does that mean that photons from the CMB are traveling towards us from beyond our cosmological horizon?
That which is beyond the horizon by definition cannot be seen.Timvanhoomissen said:Is there more to our universe than what we can observe? If so, does that mean that photons from the CMB are traveling towards us from beyond our cosmological horizon?
Chronos said:No. We can only see as far as photons could possibly have traveled since the universe originated. This distance is commonly referred to as the particle horizon. On a more practical note, we can only see back as far as photons were able to freely travel through the universe. This is commonly referred to as the surface of last scattering which came into being when the universe was about 380,000 years old. We are pretty confident the universe existed prior to its 380,000 birthday, but, we cannot detect photons emitted prior to that time because the universe then was filled with a hot plasma that is opaque to photons . We could, however, in theory detect neutrinos and gravitational waves emitted when the universe was very much younger. Neutrinos were emitted when the universe was only a couple minutes old and gravitational waves should have been emitted about the same time as when the big bang occurred.
Chronos said:Yes, CMB photons we observe in the future will originate from more distant regions of the universe. This, however, has little to do with the cosmic event horizon. Curiously enough, while the particle horizon never stops increasing, the cosmic event horizon actually shrinks as the universe ages! This is because the particle horizon applies to photons emitted at t = 0 and the cosmic event horizon applies to photons emitted at t = NOW. About 5 billion years ago, expansion of the universe began to accelerate. This means photons emitted NOW in regions that are already receding superluminally will never be able to reach a region that is receding subluminally, and hence us. CMB photons, however, were emitted long before expansion began accelerating so they will eventually reach us.
The CMB, or cosmic microwave background, is the oldest light in the universe. It is a remnant of the Big Bang and provides a snapshot of the universe approximately 380,000 years after it was created. Studying the CMB allows us to better understand the early universe and its evolution.
Scientists have observed a phenomenon called the CMB dipole, which is a difference in temperature across the sky of about 3 millikelvin. This dipole is caused by the motion of our galaxy through the CMB. By measuring this motion, we can determine that the CMB photons we observe are indeed coming from beyond our cosmological horizon.
The cosmological horizon is the maximum distance from which light can reach us in the observable universe. Beyond this distance, light has not had enough time to travel to us since the beginning of the universe. Understanding the cosmological horizon helps us determine the size and age of the universe, as well as the origin of the CMB photons we observe.
No, it is not possible for us to reach the source of the CMB photons beyond our cosmological horizon. The universe is expanding at an accelerating rate, meaning that the distance between us and these photons is continually increasing. Additionally, the speed of light is the fastest speed at which anything can travel, so we are limited in our ability to reach these distant sources.
The fact that the CMB photons are coming from beyond our cosmological horizon has significant implications for our understanding of the universe. It confirms the Big Bang theory and provides evidence for the expansion of the universe. It also allows us to study the conditions of the early universe and make predictions about the evolution of the universe in the future.