Dark matter probably doesn't exist either. These dark theories were invented to prop up the "Big Bang" which didn't happen 13.8 billion years ago. More like 50-100 billion years ago if that theory has any validity at all. 13.8 billion years is not enough time for all the required expansion and generations of stars to form, reform, and burn out. Those cold burnt out stars which didn't reform after each generation most likely make up the un-observable dark matter. Theoretical physics is more philosophy than science. When an experiment can not be recreated to prove a theory, it just becomes a popular opinion and not a fact. Computer models are simply tools and never proof of anything. When I worked with x-ray spectra we used about five models for various tests. Which model gave the correct answer? The one that came closest to our preconceived assumptions.

Please be aware that Einstein’s relativity theory has already been disproved both logically and experimentally (see “Challenge to the special theory of relativity” March 1, 2016 Physics Essays). The most obvious and indisputable evidence disproving special relativity is the existence of the absolute time shown by the universally synchronized clocks on the GPS satellites which are moving with huge velocities relative to each other (see Wikipedia on GPS: The GPS concept is based on time and the known position of specialized satellites. The satellites carry very stable atomic clocks that are synchronized with one another and to ground clocks.) while special relativity claims that time is relative (i.e. different on different reference frame) and can never be synchronized on clocks with relative velocities.
That is, our current Big Bang Theory, Standard Model of Particle Physics and other relativistic spacetime based theories are wrong. We should completely abandon all these theories.
Our visible universe is at least filled up with a fluid medium called aether, the waves of which is light or other electromagnetic waves. It is possible that more media coexist in the space too. Now we can measure the speed of aether through a modified Fizeau experiment shown on the paper mentioned above, which can be a starting point for the development of new physics theories for electromagnetic phenomena, particles, gravitation, cosmos, etc.
Regarding kinematic time dilation on the clocks on the GPS satellites, some people claim that the clocks are synchronized only in the earth centered inertial reference frame, but not on the frame of each satellite. If this were true, then there were kinematic time dilation between the clocks of different satellites observed on a satellite frame and this time dilation would accumulate. After a period of running, the time dilation should be significant. Now comes the contradiction: the clock of which satellite should be adjusted as all these clocks are still perfectly synchronized in the earth centered inertial reference frame? Any correction on one clock would break the synchronization. Therefore, the answer is obvious: all the clocks are still synchronized and don't need to be corrected except for those random drifts. There is no kinematic time dilation at all.
This conclusion has also been shown on Wikipedia: The GPS concept is based on time and the known position of specialized satellites. The satellites carry very stable atomic clocks that are synchronized with one another and to ground clocks.
That is, all the clocks are not only synchronized relative to the ground clocks, but also relative to one another. Therefore, all clocks show the same absolute time and special relativity is wrong.

Applying general relativity to the GPS problem results in a ten-fold increase in accuracy, from 10 meters to 1 meter.

Huh - and I thought GPS did in fact take into account relativistic time changes - but if @XinhangShen read about it on Wikipedia, well then it must be true!
So now I'm thinking that Earth really does sit on the back of a big turtle and everything else is bunk.

Could it be possible that there are pockets of empty space we can not detect or see? Like air bubbles in water are just pockets that take up space.

Dark matter exists and is controlled by cats. How else could an eight-pound cat feel like it weighs fifty pounds when it is standing on your chest? This phenomenon has been completely ignored by modern physics.

Is an "Electric or Plasma universe" possible?

XinhangShen, mnay experiments have been done PROVING that time is affected by speed and gravity. Since we are using WikiPedia as our source today . . . https://en.wikipedia.org/wiki/Time_dilation

As much as science disdains the philosophical , all of their theories are purely philosophical . This article is no different . 68% ? LOL....pluck another number out of the air . All science is sure of is what can be tested on a very local level . There are too many holes in the standard model to plug up , and dark matter is but another philosophical plug .The true nature of the Universe will remain inscrutable ,and since it can not be rolled back for study, the mystery will remain . Quantum Entanglement may be observed but never understood .

Too many people getting paid too much money making up theories that won't change the price of rice in China ...