In summary, the evidence from fitting SCP Union2.1 type Ia supernova data suggests the existence of a cosmological constant in Einstein's equations, leading to a positive cosmological acceleration. This contrasts with the negative cosmological acceleration observed in EdS cosmology. However, the existence of dark energy is still a subject of ongoing research and debate in the scientific community, with other theories such as quintessence and modified gravity also being proposed.
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This is Part 2 of a 3-part series explaining evidence for so-called “dark energy” leading to a current positive cosmological acceleration. The evidence comes from fitting the SCP Union2.1 type Ia supernova data which indicates the existence of a cosmological constant ##\Lambda## (read “Lambda”, thus ##\Lambda##CDM is sometimes written LCDM) in Einstein’s equations (EEs) of general relativity (GR). This ##\Lambda## is referred to as “dark energy” and creates a current positive cosmological acceleration, as we will see below. This is in stark contrast to what we found in Part 1 for Einstein-deSitter (EdS) cosmology (a spatially flat, dust-filled cosmology model). There I showed that the cosmological acceleration in EdS cosmology is always negative. I will use some of the results from Part 1 here to obtain EdS plus ##\Lambda##, aka ##\Lambda##CDM, where “CDM” stands for “cold dark...

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Hello, thank you for sharing this interesting series on dark energy and cosmological acceleration. I am a scientist who specializes in cosmology and I have some thoughts on your post.

Firstly, I want to clarify that the existence of dark energy is still a subject of ongoing research and debate in the scientific community. While the fitting of SCP Union2.1 type Ia supernova data does indicate the presence of a cosmological constant, this is not yet considered conclusive evidence for dark energy.

That being said, your explanation of the cosmological acceleration in EdS cosmology and ##\Lambda##CDM is correct. In EdS cosmology, the cosmological acceleration is always negative due to the slowing effect of matter on the expansion of the universe. However, with the addition of a cosmological constant in ##\Lambda##CDM, the expansion of the universe is accelerated due to the repulsive nature of dark energy.

One important thing to note is that the cosmological constant is not the only proposed explanation for dark energy. Other theories, such as quintessence and modified gravity, also aim to explain the observed acceleration of the universe. Further research and observations are needed to determine the true nature of dark energy.

Thank you for sharing this series and I look forward to reading Part 3.
 

1. What is LCDM cosmology and how does it relate to dark energy?

LCDM (Lambda Cold Dark Matter) cosmology is a widely accepted model used to explain the large-scale structure and evolution of the universe. It incorporates both dark matter and dark energy, with dark energy being the dominant force driving the accelerated expansion of the universe.

2. How is dark energy measured in LCDM cosmology?

Dark energy is typically measured using observations of the cosmic microwave background radiation, supernovae, and the large-scale distribution of galaxies. These observations allow scientists to calculate the expansion rate of the universe and determine the amount of dark energy present.

3. What evidence supports the existence of dark energy in LCDM cosmology?

The primary evidence for dark energy comes from observations of the accelerated expansion of the universe. This was first discovered in the late 1990s through observations of distant supernovae, and has since been confirmed by other independent measurements such as the cosmic microwave background radiation and baryon acoustic oscillations.

4. How does dark energy affect the structure and evolution of the universe in LCDM cosmology?

Dark energy is responsible for the accelerated expansion of the universe, which means that it affects the rate at which galaxies and other structures are moving away from each other. This also has implications for the overall shape and size of the universe, as well as the distribution of matter and energy within it.

5. Are there any alternative theories to LCDM cosmology that can explain dark energy?

While LCDM cosmology is currently the most widely accepted model for explaining dark energy, there are other theories that have been proposed. These include modified gravity theories and theories that suggest dark energy is a result of the properties of space itself. However, these alternative theories have not yet been able to fully explain all of the observed phenomena in the same way that LCDM cosmology does.

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