The theory that 'Isn't this world just a dream that humans have?'

The theory that ``the world we see is actually a dream dreamed by a brain floating in a tank'' is one of the most popular thought experiments. Based on this idea, Kurzgesagt, a scientific YouTube channel, has released a video explaining the concepts of existentialism and entropy.

You're a Dream of the Universe (According to Science) - YouTube

As far as humanity knows, people actually exist, living their daily lives as Earthlings in a universe that was born 14 billion years ago.

However, all of this may be just what you think. These ideas may sound far-fetched, but they are the inevitable result of scientific theory. To understand this idea, you need to understand three important concepts.

The first one is '

Arrow of Time '. Human beings can naturally distinguish between the past and the future. For example, if you put a drop of red ink in a glass of water, the ink will spread to every corner of the glass, but not the other way around. Who has ever seen ink naturally condense back into a single mass?

When you think of it this way, time always seems to flow in the direction in which the ink spreads. However, when you look through a microscope, all you see is ink molecules randomly colliding with each other, with no forward or backward movement. Everything here can change in the opposite direction. Despite this, humans tend to perceive that there is an arrow of time that moves things in one direction.

This arrow of time is actually a matter of probability. In the previous example, the ink molecules can spread everywhere. And just as the probability of winning the lottery increases the more lottery tickets you buy, the probability that the ink molecules will spread throughout the glass is much higher than the probability that they will be concentrated in one place.

In other words, the laws of physics do not prohibit ink from condensing in one place, it is just highly unlikely. Not only will the ink clump together, but it could also be shaped like a jellyfish or a human brain. This is the first concept.

The second is the concept of space. The universe, which was born 14 billion years ago, has produced countless stars and substances, but in other words, the universe is like a glass filled with a large amount of ink. All kinds of phenomena can occur as if in a glass, but the difference is that the universe appears to be accelerating and expanding due to dark energy.

There are a huge number of stars in the universe, but their number gradually decreases over time. It is thought that in about 100 trillion years, the last remaining star will disappear, and after that, it will become a dark space filled with dark energy for hundreds of millions to trillions of years.

There is an idea that a cosmic horizon (event horizon) is formed in the ``surroundings'' of the universe, which is dominated by dark energy. It is said that even light cannot reach the end of this line, but if we simply think about it based on this line, we can think of the universe as a sphere surrounded by lines, about 36 billion light years wide. Masu.

This sphere is like an inverted black hole, but since all black holes are known to emit small amounts of particles (Hawking radiation), this sphere is thought to emit particles in the same way.

Based on this theory, the universe is considered to be a closed sphere filled with particles, and particles with temperature move randomly within the sphere. In other words, if we think of outer space as water and particles produced by Hawking radiation as ink, we can think of the universe as a ``glass filled with water and ink,'' in which all kinds of phenomena can occur. there is. This is the second concept.

'Eternity' is a word that refers to an infinite world, and in an infinite world, events that are unimaginable by common sense may occur. The fluctuating particles collide over and over again, creating every possible combination of particles.

This is like asking a monkey to hit a typewriter. Monkeys type out strings of gibberish most of the time, but given enough time they should even be able to draw out the first act of Hamlet (infinite monkey theorem). Returning to the universe, it is also possible that particles moving randomly could give rise to what we now know as 'stars.'

If you think about it this way, the universe was not created by the Big Bang, but by chance due to random fluctuations of particles. And it's also possible that, like ink dropped into water, it exists for only a moment before it dissolves throughout the glass.

The universe in which humans exist happens to have humans, the Earth, and orbit around the sun, but it also might have dinosaurs riding snails and stars made of blueberries. . Physicists who live in such a world do not realize that the world they live in is strange because that world is common sense.

Although the probability of such fluctuations occurring in space is thought to be very low, the human brain is thought to have a higher probability of such phenomena occurring than in space.

Humans can think. You can learn about yourself and those around you. But at the end of the day, the human brain is just interpreting signals from our senses and imagining our own world. In other words, your brain may be the only thing that thinks the world is real. The brain can also be thought of as something floating alone in empty space.

For example, if we compare the probability that trillions or quintillions of people will be born in the universe through the fluctuations of particles and the probability that only our own brain will be born, the latter is overwhelmingly higher. In other words, the probability that you are just a brain is overwhelmingly, incomparably higher than the probability that you are a real human being.

However, there is a hole in this theory. I've talked about it a lot like a dream, but this is a hypothesis built without any understanding of the existing universe, and no one can prove whether or not there actually is a floating brain. Kurzgesagt concluded, 'It's just a thought experiment about what is possible in physics.'

in Science,   Video, Posted by log1p_kr