1. The black hole paradox
One of the biggest tasks in physics is known as the black hole information paradox.
According to quantum mechanics, information about the mass and structure of particles is constant, ie they cannot be destroyed. For example, if you burn two different items, it will be practically impossible to recover items from the ashes, but not completely impossible. The two ashes will differ from each other in mass and other characteristics, which means that even after burning the items, the ashes still carry some information about them.
The problem is that black holes absorb matter and then irradiate matter absorbed over time in the form of Hawking radiation. Unlike ash, Hawking radiation carries no information about matter: Hawking radiation is consistently the same, indicating that information about the universe in a black hole could be destroyed.
Stephen Hawking believed that particles that hit a black hole would eventually return to the universe, because if that was not the case, it would mean that most of modern physics would have to be reworked.
2. The fermi paradox
We know this paradox by the name of the Italian physicist, Enrico Fermi. The idea of the paradox is this: Observations of the universe indicate that the chances of life appearing in the universe are quite high, yet we can find no trace of life anywhere, where are the aliens?
There are about 400 billion stars and 640 billion planets in our galaxy alone, and a significant number of these planets are located in the vital zone around their own star, which means that life in the universe must have many chances to develop, yet we can not find traces of other civilizations.
3. Polchinsky paradox
Joseph Polchinsky is an American physicist who developed many different versions of the time paradox.
What if we roll a billiard ball into a time-space portal (sometimes called a wormhole) so that it hits itself in the past and does not allow the ball to bounce into the hole?
One option for this paradox is to travel in time and kill your own grandparents, in which case you can no longer appear and travel in time. Another version is this: If you go to the past to kill little Hitler, then there will no longer be a reason why you have moved to another century, and therefore this journey will not take place ?!
4. The Paradox of Wilhelm Olbers
This problem was first mentioned by the British Edmund Halle in 1720, and then independently of Halle, in 1742, a more precise formulation of this puzzle was made by the Swiss Jean-Philippe de Chezo (1781-1851), who gave an answer that did not differ much from that of Olbers.
Olbers’s photometric paradox is formulated as follows: If the universe is infinite, homogeneous, and stationary (astronomers were convinced of this in the eighteenth and nineteenth centuries), then there must be stars in all directions in the sky. That is, the whole sky should be full of shining star points and it should shine. In fact, the sky is dark and only individual stars can be seen on it.
Olbers explained this by absorbing light in the environment because space is partially filled with light-absorbing substances, such as interstellar clouds. However, with the advent of thermodynamics, this evidence has become controversial because as it absorbs light, the interstellar cloud will heat up and begin to glow on its own.
Finally, the Olbers paradox could be explained in the twentieth century. We now know (Hubble’s law, the universe is expanding, and the farther away the galaxy is from it, the faster it is moving away from us) that the universe has a finite age. The Big Bang is estimated to have occurred 13.8 billion years ago, meaning astronomers can see glowing objects at 13.85 billion light-years. That is why the number of stars is not infinite, although their number is huge, and therefore the stars are not visible in all directions. Yet we know that neither stars live indefinitely. In the direction of observation it may be a star, though it may not shine because it may be an age in which the thermonuclear fuel has long since run out. Any of the above explanations is quite sufficient to make the problem of Olbers’s paradox exhaustive, although there was no other explanation in those years other than the absorption of light by interstellar clouds.
5. The “red sky” paradox
Columbia University (USA) astronomer, David Kipping, so called. The “red sky” offers an explanation of the paradox, the paradox that follows – why not see the most common type of star in the sky – red gnomes? (Proceedings of the National Academy of Sciences).
Kipping used Bayesian statistics when the probability of the occurrence of the event under consideration depended on the understanding of new information about it. The scientist considered the probability of the emergence of a thinking observer with solar-type (spectrum class F, G or K) stars or red dwarfs. Red dwarfs are 5 times more common than mainstream stars and live up to 20 times longer. In addition, numerous Earth-type exoplanets have been discovered around them (how stars die).
The chance that a thinking observer will appear with a star that looks like the sun, and not a red dwarf, is 1/100. This is contrary to the principle of Copernicus, according to which humanity is not in any particular position in the world (Copernicus principle).
The scientist concluded that with red dwarfs, the probability of the appearance of thinking creatures may be very small, as well as the small time window required for the evolution of complex life or the small probability of the formation of planets compatible with life. One of these three options may explain the absence of a “red sky”, as the observer appears only far from the red dwarfs. As Kipping writes, all three options seem to be possible due to limited knowledge, only future astrobiological studies will help determine the exact cause of the paradox.