The long-running debate has been rekindled by the suggestion that dark energy, which is 70% of all the stuff in the universe, may not be real. The theoretical inventions of dark energy and dark matter allow us to explain observations that we don’t otherwise know.
Gravitation appears stronger than we can explain using only light-emitting particles. We add dark matter particles to 25% of the universe’s mass-energy. These particles have not been detected directly. Gravity appears to be weaker on the larger scales at which the Universe expands than it would in a universe that contains only particles, ordinary and dark matter. We add dark Energy to the equation, which is a weak antigravity force that acts independent of matter.
A Brief History Of Dark Energie
Dark energy is as old as general relativity. It was include by Albert Einstein 100 years ago, when he apply relativity to cosmology. Einstein wanted to balance the self-attraction of matter and anti-gravity at the largest scales. He couldn’t imagine the Universe starting from a point and didn’t want it to change over time.
In 1917, almost nothing known about our Universe. It was discuss that galaxies could be objects at great distances. Einstein was face with a dilemma. His theory’s physical essence, summarized decades later in a well-known textbook, is:
Space tells matter how it should curve and matter tells it how to move. This means that space is naturally incline to contract or expand, and bend with matter. It is never still. Alexander Friedmann, who kept the exact same ingredients as Einstein in 1922, realized this. He did not attempt to balance the amounts of dark energy and matter. This suggested a model that allowed universes to expand and contract.
If only matter were present, then the expansion will always slow down. It could accelerate if anti-gravitating, dark energy was present. Many independent observations suggest that there should be accelerate expansion in a Universe with 70% dark energies since the late 1990s. This conclusion is based upon an old model of expansion, which has not changed since 1920.
Standard Cosmological Dark Model
Einstein’s equations can be fiendishly complicate. They are not just more complicated than those in Isaac Newton’s theory gravity. Sadly, Einstein didn’t answer some of the most basic questions. These questions include: On what scales can matter tell space how it curves? Is there a larger object than a single particle that can move in response to this question? What is the correct scale?
The 100-year-old approximation, introduced by Einstein & Friedmann, that the Universe expands uniformly on average, avoids these problems. As if all the cosmic structures could put through blenders to create a featureless soup. This homogenizing approximation was valid early in cosmic history. The cosmic microwave background, the relic radiation from the Big Bang, shows that the Universe was less then a million years old when there were very few variations in matter density.
The universe isn’t homogeneous. Gravitational instability was responsible for the growth of stars and galaxies. Finally, a large cosmic web emerge, dominated by vast voids that were surround by galaxies sheets and thread with wispy filaments.
Standard cosmology assumes that the background expands as if there are no cosmic structures. Then, we do computer simulations with only Newton’s 330 year old theory. This creates a structure that is very similar to the observed cosmic web. It requires dark energy and dark material to be include. The model still has problems, from anomalies to tensions, even after it was able to invent 95% of the energy density needed to make everything work.
Standard cosmology further states that the curvature space is to be uniform across all places and independent of matter. This is in contradiction to Einstein’s fundamental idea that space curves because matter tells it how. There is not enough general relativity to be useful. You can summarize the standard model as follows: Friedmann tells time how to curve, Newton tells matter what to do.
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