# Closed Universe for Housewives

The idea of ​​writing a note arose after reading an article on a closed universe here. Actually, even sooner after reading one of the comments on the article:
Trying to explain something to someone through formulas ... bad job. Who can translate this article to the level of housewives?
Well, my dear Housewives (as well as their husbands and children), let's get started?

In the kitchen, we are already waiting for simple tools: a huge piece of elastic thin rubber film, several watermelons and apples. Let's try to create a visual simplified model of gravity according to Einstein, and then try to simulate a closed Universe (what really there!). We fix the film at the edges (for example, to the walls of the kitchen) at a certain level above the floor.

1. Put the watermelon on the film. Under the weight of a watermelon, the film bent, a cavity formed, in it lies a watermelon. Perfectly. Housewives have already guessed that the film is the same space-time that is deformed (bent) by gravitating objects. So yes - it is distorted!

2. Throw the apple in the direction of the funnel. If the speed of the apple was relatively high or it rolled far from the funnel (touched the edge), the "center of gravity" (watermelon) only slightly distorted the "orbit" of the body (apple) and it rolled further. And if you run the apple slower and so that it falls into the funnel? The apple began to revolve around a watermelon! Here it is, the world's first kitchen satellite! And a clear example of movement in a gravitational field along a closed path. And the “satellite” after several revolutions fell onto the “center of gravity”. Everything is as in life, did you notice dear Housewives? Seeing the atmospheric resistance was great, did not last long in orbit.

3. And what if you throw there, in the funnel, another watermelon? Boom! Vibrated something like a blow! (Ripe? Unripe?) The vibration was transmitted to the film. Ripples ran across the film. My dear housewives may not know, but their husbands must know: hypothetical gravitational waves are ripples on the surface of four-dimensional space-time. So scientists believe. And the attempts to register gravitational waves themselves are based on a simple idea: a gravitational wave makes material bodies oscillate (tremble). Oh, well, they didn’t guess: before throwing a watermelon, it would be necessary to put a pea probe on the film. And look - the ripples on the surface of the film makes it (the pea) tremble? Yeah ... well, we threw a watermelon ... how much information to think about. By the way, hypothetical gravitational waves arise, including, at the mergerwatermelon stars. That is, our primitive model turned out to be surprisingly informative and adequate.

4. Well then? Now we know what gravity is from the point of view of general relativity; we know how curved space looks like time. But do not we swing at the creation of a closed universe, eh? In the process, we will be forced to lie a little, compose, embellish reality, but ... but ... it's all for scientific purposes, right? We begin to lie to simulate ... Imagine that our watermelon got heavier ... it’s even scary to imagine how heavy it gets ... the film stretches more and more ... the floor of the kitchen is mentally removed ... it goes down, the film stretches ... and the neck above ... it narrows and narrows. Keep lyingto simulate. (The nose grows - like Pinocchio). The neck closed. Everything! The closed universe is created! The world of watermelon is a separate closed Universe. And the geometry in it is Rimanov, as expected. The sum of the angles of a triangle is more than 180 degrees. All parallel intersect. The inhabitants of the outer film-universe (they are two-dimensional) by no means can detect this watermelon universe - the neck closed, smooth in this place, as if nothing had happened. Well, this is how gravity acted on the geometry of space - time ... bent ... deformed ... and as a result we got a world that became self-enclosed.
Phew! We are tired of the act of creation! The creator - and he created it is not clear how many days ... and created it is not clear what. We are not even sure that something is closed. There is an offer to take a break, cut a watermelon, have a bite, and remember everything we know about our Universe:

• the true dimensions of the universe cannot be determined, but the fundamental limit of the range of observations is 46-47 billion light years
• the topology of the Universe - the flat world of Euclid (up to a percentage)
• she was “born” like that - even more “flat” than now
• the density of the universe is close to the so-called critical
• the topology of the universe (“curvature”) is determined by observations of supernovae and RI fluctuations
• the postulate about the closure of the universe does not contradict the observed data, but there is no direct evidence of closure
• for 5 billion years, the Universe has been expanding rapidly - starting from the moment when the repulsive forces began to prevail over gravity, which restrained the expansion process (gravitational forces began to weaken in the process of expansion due to an increase in the distance between gravitating masses)
• it seems that this expansion is for a long time and seriously, that is, it will continue indefinitely
• it is not possible to directly measure the density of the Universe - we cannot adequately estimate the mass of matter and energy in a certain volume or in the whole Universe
• One can only guess about the true size of the Universe - we do not know how much it inflated in the inflationary stage
• the nature of dark energy, which makes a predominant contribution to the mass of the Universe (+ is responsible for the accelerated expansion of the Universe) is not yet clear, but it can be vacuum energy, the equation of state of which is such that the density and pressure enter with different signs
• the nature of dark matter, which makes a significant contribution to the mass of the Universe, is also not clear - this is most likely a new class of heavy stable particles that weakly interact with the outside world
• ordinary (baryonic) matter that makes the minimum contribution to the mass of the Universe is predominantly intergalactic clouds of gas (the “visible” part of this matter is only 10% of the total mass - and these are stars)

As you may have guessed, dear Housewives, the author does not bear any responsibility to readers for the desire to eat a watermelon (or go stupidly to eat in the kitchen) during the reading process.
Any requests to send a watermelon or transfer money to purchase a watermelon in order to simulate a closed universe will be ignored.