What is the universe like? Here is the answer you want

An unforgettable olfactory experience

What does space smell like? This is a very confusing question. And you might think that anyone who asks about the smell of space probably won't be able to come back alive, so this question seems to have become an unsolved case.

In fact, this question has puzzled scientists for a long time. Although there is no good result from smelling directly in space, we can still get the smell of space indirectly. That is, when astronauts complete a spacewalk, they will carry the smell of space for a short time when they return to the capsule.

Retired American astronaut Tony Antonelli still remembers the first time he opened the hatch in space. He said in an interview: "I had received ten years of training, but I was completely shocked the moment I opened the hatch. No one told me about the smell of space. The smell was strong and unique, completely different from the smell I smelled on Earth before. I don't know how to describe it. It was the smell of some kind of metal mixture.

Don Petit, an American astronaut, also described the smell of space in 2003: Every time we open the hatch to welcome the tired astronauts in, our sense of smell will be attacked by a special smell. At first I arranged where this smell came from, but then I noticed that its source was the astronauts' space suits, helmets, gloves and tools. Compared with metal or plastic equipment, textiles are more likely to be attached to this smell. Petit admitted that this smell is difficult to describe. The best answer I can give is a metallic smell, a very pleasant metallic smell, which reminds me of my hours of continuous welding work on the university bookshelf.

Based on the descriptions of astronauts, NASA is currently trying to replicate the smell of space for training purposes. It has completed the trial production of a space perfume sample and is raising funds through crowdfunding for mass production of the perfume. Judging from this project, everyone will also be able to have this unforgettable olfactory experience in the near future.

The shape of the debate

Does the universe have a boundary? Is it closed or open? What shape is it? Is it flat, spherical, or something else?

Closed Sphere Theory

As early as 1917, Einstein began to study the origin of the universe from the perspective of field equations. Einstein believed that on a cosmic scale, the distribution of matter should be uniform and isotropic. To this end, he proposed the famous cosmological principle. It was proven in real time that this principle was surprisingly consistent with later astronomical observations. Based on the cosmological principle, Einstein established a closed, finite, static universe model. This is also the first universe model that is relatively recognized internationally.

Open Infinity Theory

In 1922, a Russian scientist discovered that the universe is not necessarily static, but may be expanding, by solving Einstein's field equations. Based on the cosmological principle, he found that Einstein's field equations have three forms of solutions: expanding three-dimensional flat space, expanding three-dimensional spherical space, and expanding three-dimensional pseudosphere.

Subsequently, numerous astronomical observations have shown that the universe is very close to being flat in space, which means that no matter which dimension is removed, the resulting surface is infinite. In 1980, American scientist Guth proposed the inflation theory, which also explains the flatness of the universe very well.

Although the inflation theory plus the standard cosmological model of a flat universe is deeply rooted in people's minds and even becomes a consensus, we cannot rule out the possibility that we live in a spherical or hyperbolic world, because when the model is large enough, the scale we detect will account for a very small proportion, making no matter which model is used, the detected scale will look almost flat.

This is why early people believed the Earth was flat - the curvature of the Earth was too small to detect on the scales they were able to observe.

Theory of Closed Spheres, Phase II

In recent years, the theory of cosmic expansion has been widely recognized. However, an anomaly was discovered in the cosmic microwave background spectrum released in 2018. This phenomenon cannot be explained by the standard cosmological model based on a dynamic flat universe. This prompted DiValentino and three other cosmologists to re-examine the shape of the universe. They found that if the idea of ​​a dynamic flat universe in standard cosmology is abandoned and the static closed universe established by Einstein in his early years is returned, not only can this anomaly be well explained, but the Hubble constant crisis can also be greatly alleviated, which can kill two birds with one stone.

At present, this important idea has been published in Nature Literature in 2019.

The debate over the dynamic and static models of the universe, which had been dormant for many years, has begun again.

Changing colors

At night, when you look up at the starry sky, have you ever thought that the true color of the universe may not be the simple black in front of you?

In order to show us a more realistic image of the universe, NASA has been observing the universe for 26 years through the Hubble telescope. Through the photos that are constantly sent back, we see colorful images of celestial bodies in the universe, but what is the overall color of the universe?

Astronomers studied the colour of light emitted by 200,000 galaxies photographed to see what colour you'd get if you painted the entire sky over it and mixed it - a soft latte.

But scientists believe that the analysis of the color of the universe requires redshift surveys of countless stars, because based on existing theories, the universe is now in a state of accelerated expansion, and the distances of major stars are constantly changing. This change will affect the wavelength of light received by the telescope, and starlight can largely affect the color of the universe. In addition to the influence of cosmic expansion, since the color of starlight is a representation of its own temperature, hot stars tend to be blue, and cold stars tend to be red. With the accelerated death of short-lived and extremely active blue stars, the color proportion of stable stars that emit reddish light gradually increases. Therefore, over billions of years, the color of the universe has been gradually changing. For now, our universe contains a large number of stars dominated by red and blue colors, and there are also many colorful dust and gases, which are mixed to resemble the color of latte coffee.

An elusive sound

We all know that the propagation of sound requires a medium, and from common sense, space is a vacuum, so it is difficult for us to capture sound in space. If we only talk about hearing, space can be considered to be silent.

But space is not empty, but there are a small number of particles. It's just that the density is much lower than the atmosphere on the surface of the earth that we are familiar with. How low is it? There is a lot of air on the surface of the earth, and on average, there are 3×1020 gas molecules per cubic centimeter of the ground. In space, there are only 5 protons on average in the same size of space. Therefore, it is very difficult to obtain sound waves in space. The main method now is to collect, transform, and amplify various beams in space through scientific research equipment, and finally restore the space sound that we can hear.

In fact, space is also very noisy, and each planet has its own sound. According to the audio currently released by NASA, for example, in the solar system, the sounds of various celestial bodies have their own characteristics. Among them, Mars, Uranus, and Pluto belong to the "wind system": Mars sounds like the sound of the whistling cold wind on the cold land of the northeast, Uranus adds some swirls to the cold wind of Mars, and Pluto sounds like the vibration of a bare flagpole standing in the wind; the sun and Venus belong to the metal system: the sun emits an echo like a slender metal vibration, and the sound of Venus is lower than that of the sun; Mercury, the earth, and Neptune belong to the mechanical system: Mercury sounds like the roar of a motorcycle engine when it starts, the earth sounds like the roar left after a plane passes low, and Neptune sounds like the sound of snowflakes when an old black-and-white TV has no signal; Saturn and Jupiter belong to the horror system: their sounds are the background sound of the kind of chilling horror movies.

Everyone describes sound differently, so listen to these strange space sounds and only you will know what you are hearing.