???? Is the Universe infinite? The answer may surprise you! The fact is that we will probably never know... Theoretically, it is impossible to answer this question. Although the theory of general relativity allows us to describe the evolution of the entire Universe since its birth, it tells us nothing about its geometric properties. Einstein's relativistic theory of gravitation only tells us that the curvature of the Universe is zero. What does this mean in concrete terms? Let's take three points in space-time. Now, let's connect these three points together. Without curvature, we do not get a pyramid, but a triangle, i.e. a flat object. A flat Universe, without curvature, and therefore infinite... This does not convince all cosmologists! ???? As a reminder, videos are published on SUNDAY at 6:00 PM. ------------------------- ???? The Observable Universe: The observable Universe is the name given to the visible part of our Universe in cosmology. As we have seen, the observable Universe is finite. Its boundary is called the cosmological horizon. This horizon is the limit of the Universe observable from a given point, usually the Earth. It can correspond to the limit from which electromagnetic radiation can be emitted or the limit from which a signal of any kind can be received, such as gravitational waves or neutrinos. The cosmological horizon can also be defined as the boundary between the visible part of the Universe, made up of objects whose light will have traveled for less than 13.7 billion years, and the invisible part of the Universe, whose galaxies are too far away for their light to have had time to reach us. However, saying that the cosmological horizon is 13.7 billion light years away is a simplification, since it does not take into account the expansion of the Universe. If we add the expansion of the Universe to the equation, we can say that the photons emitted by the cosmological horizon are now more than 13.7 billion light years away from us, because the expansion rate of the Universe is greater than the speed of light. In fact, the most distant signals that reach an observer on Earth come from the cosmic microwave background, a radiation that fills the entire Universe, but whose emission region is at the edge of the observable Universe. This region is known as the last scattering surface. Cosmological models estimate that the last scattering surface is 46.5 billion light-years away, due to the expansion of the Universe. The observable Universe can be described as a sphere with the Earth at the center. This is not geocentrism, the ancient physics model according to which the Earth was stationary at the center of the Universe. Our planet is at the center of the observable Universe, simply because the observers are on Earth! This is a relative notion. Observers located elsewhere in the Universe would not have the same observable Universe, but the radius of this sphere would be the same. The observable Universe is defined by what is observable and measurable. The further we advance in time, the more distant objects we can observe, when their light reaches us. The observable Universe is therefore expanding over time. The visible radius is larger by one light-second for every second that passes, or one light-year for every year that passes. We can also put it this way: light travels at a speed of 300,000 km/s. With every second that passes, we discover a new depth of space of 300,000 km. In just one year, we can discover several new galaxies. Objects at the edges of the observable Universe are observed in their primitive state, because they are the ones whose light took the longest to reach us - billions of light-years! And the further away the objects are, the higher their redshift, due to the expansion of the Universe. ------------------------- ???? Today's program: 00:00 - Introduction 00:58 - What is the observable Universe? 15:17 - Observing the Universe: the challenges ahead 22:04 - What is the size of the observable Universe? 29:50 - What's in the observable Universe? This channel is an official affiliate of the ORBINEA STUDIO network.