Why do galaxies in the universe accelerate their expansion instead of shrinking under the action of gravity?
For the first question, many people have heard of The Big Bang Theory. Maybe many people think that the big bang theory is the first question? How did the universe come into being? ? The answer. Is that really the case? The answer may disappoint you: no?
Unsolved Mysteries of the Universe In modern cosmology, the Big Bang theory, including inflation theory, explains what happened in the universe after BIGBANG 1 Planck time, as if scientists were watching. But in fact, at present, the initial stage of BIGBANG is only about 1 sec after BIGBANG, and what happened to BIGBANG in 1 sec is actually not so sure.
The reason is that the current physical theory does not know much about the physics of ultra-high energy States in the early universe. In the current theory, in the early days of BIGBANG, the four kinds of interaction forces in nature were unified, and with the continuous decrease of energy state (temperature), the four kinds of interaction forces were separated one after another. About 10- 12 seconds after the Big Bang, the temperature of the universe dropped to about 10 15 degrees, and the last two forces in nature: electromagnetic force and weak force finally separated.
After that, the evolution of the universe is probably relatively certain. But before that, the evolution of the universe is uncertain.
In fact, a basic question: why did the Big Bang happen, that is, why did the universe expand? As far as I know, the current theory cannot be answered. This problem is somewhat similar to Newton's first driving force. Newton said that at the beginning, God only needed to push and the universe would automatically circulate, so God didn't need to participate in the operation of the universe. It's probably the same now. We need an initial expansion? Force? As long as the universe begins to expand, can the next thing be left to the laws of physics? But why does the universe expand? What is the force that causes expansion? Don't you know?
Although some theories try to give an explanation, they are not widely recognized.
Although I say this to make everyone accept the reality, since I want to answer this question, I will be scolded to death by you if I say nothing after a lot? So I won't say why the universe is expanding. Let me talk about some theoretical explanations about accelerated expansion.
Dark energy is just a name? An unknown energy will produce a strong negative pressure. Is this really happening? Believe it or not, I don't believe it anyway.
Cosmic constant In order to maintain the static universe, Einstein added a constant term to the gravitational field equation, which made space produce a repulsive force to resist gravity. This is the property of space itself, and no other unknown mechanism is needed.
Gravitational escape there is a theory that gravity escapes to an extra dimension on a large scale, which leads to a significant decline in gravity on a large scale? Looks more sci-fi? This theory is based on the extra dimension in string theory, which may be curled up in the micro field, but it may also be a macro dimension. This theory is complicated, and it needs at least an independent article to explain it clearly, so I will skip it here.
Critical distance of gravity A critical distance of gravity will fail, and gravity will no longer spread to infinity. When gravity reaches this distance, it will gradually disappear. This is the most reliable explanation I think? I think the most reliable is purely personal opinion, because it's a bit like my own folk theory? I think gravity will reverse to repulsion after exceeding the critical distance? Personal opinion, don't take it seriously? )
So which explanation do you think is more reliable? Still think it's not reliable? Do you have a more reliable explanation? Tell me about it.