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You say that Black Energy is something which is needed to overcome the gravitational pull of our expanding Universe. You say that the Universe would collapse into a singularity due to gravitational pull between galaxies. Yet, we see that opposite is happening and, therefore, there must be some Dark Energy, which keeps the Universe to expand.
Yet, you say that there is no problem with distant galaxies receding faster than speed of light because nothing pushes them -- it is space that appears between us en them. Thus, you say that the Universe expands due to new born space between the points in the universe, which can overcome some physical laws. Why cannot it then overcome the law of energy, needed to overcome the gravitational collapse of the Universe? If your new space can push the galaxies faster than speed of light, it can do so without any energy, I suppose. Why one but not the other?
Moreover, there is equal amount of galaxies on the left and on the right from you. This means that we do not even need any energy to maintain/expand the Universe. When the pull is equal from all the distances, we do not experience any force at all. The Universe is stable by itself, without any Dark Energy.
Finally, even if this my latter consideration is flawed and galaxies still tend gravitationally together despite of the uniformity and infinity of the universe, I would also like to point out that the energy means mass and, thus, Dark Energy can only increase the gravitational pull between the galaxies!
This is my naive counter argument to the popular explanations. Does it has any holes in it?
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closed as unclear what you're asking by knzhou, CountTo10, Gert, Numrok, sammy gerbil Aug 18 at 21:27
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First of all, Physics never intended to answer the question "Why?" but gives a more or less good approximation on the question "How?".
There are several confusions in your question and I'll try to point them but keep in mind that the name "Dark energy" comes from the fact we don't understand what it is.
1) You have to separate the objects (stars, planets, photons ...) evolving in the space-time and the space-time itself. What we call Universe is actually the space-time. Nothing seems to prove that physical laws such as conservation of energy can be applied on the space-time. The only things you can measure are the objects evolving in the space-time and that so far seem to obey physical laws as we know them on Earth.
2) Dark energy was first introduced by Einstein to overcome the problem of Static Universe, which was later discarded by the Friedmann's equations and at that time the idea of a cosmological constant (dark energy) was dropped. It was then reintroduced in the Gamow's Big Bang theory to explain the different epochs of the Universe. This doesn't come from nowhere, the main idea is to give an interpretation of Friedmann's equations with a few considerations and then prove some of the inherent predictions. Gamow predicted two main things, the different abondancies in the Universe (Baryogenesis) and the temperature of the Universe (Cosmic Microwave Background), based on the only assumptions that the fermions and bosons in the Universe obey some basic thermodynamic laws.
3) Both predictions where successfully proved by measurements. Especially the Cosmic Microwave Background, which appears to be a wonderful source of informations.CMB is conceptually a picture of the early Universe that we can still measure today as it is (redshifted of course). With good tools and considerations, it allows you to predict the different abondances present in the Universe, namely the Radiations, Matter, and Vacuum abondances (Dark Energy). So far nothing allows you to exclude the possibility of a Universe (flat or curved) expanding or collapsing. Well, confronting the different models (Big bang as well as models excluding Big Bang) you have with the observations you made from the Cosmic Microwave Background seems to tell that a flat expanding Universe in the Big Bang theory describes conveniently the data you have.
4) Well how can you explain a Universe in expansion. You said that distant objects are moving faster than light, this can be deduced (not observed because of causality) if you consider that the space-time expands and it's also true that space-time is created between us and those galaxies, well it means that some energy is added, obeying the same laws that we know, affecting those objects: this is Dark Energy. We don't know why it's there, we just know that our model needs a consideration like this and the very same model predicts other phenomena measured.
5)It's important to say that the Universe is not infinite or if you prefer, there's no pleasant theory considering an infinite Universe able to explain some simple considerations such as the fact that with all the stars surrounding us, there's no light in the sky during night. If the Universe was infinite, then light from all the stars would have had the "time" to reach us, making the night sunny as the day. (Big bang does explain that)
6) Last remark, your conception of Gravity is a bit too classical for such considerations. The main point behind the General Relativity is the paradigme change in the interpretation of Gravity. It says that gravity is not really a force as we understand it (something you could switch off and on as you want) but it's actually a property of the space-time (equivalence principle for further informations on that topic).
I hope this will help you, I intentionally put some technical words that are usually well explained on Wikipedia.
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