Cosmological Constant: Expanding Universe & Data Contradiction

In summary: I would like to add that as far as I know we add cosmological constant to ensure the derivative of energy tensor equals zero.
  • #1
mertcan
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hi, I have been watching some "world science festival" videos on youtube, also there were a conversation pertain to whether or not the cosmological constant should be a constant. As far as I know, our universe is expanding with a positive acceleration measuring the red shifts, and it implies that net total energy should not be constant in a given time. Nevertheless, there was a situation that a guy in videos said that data they had acquired resembled the cosmological constant. Is not there a contradiction??. Because they say both the our universe is expanding and data they had acquired resembled the cosmological constant (static universe, net total energy is constant).
 
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  • #2
No, there isn't a contradiction. The universe could be expanding without a cosmological constant whatsoever.
Presence of dark matter causes the expansion to accelerate, and if it's in the form of a cosmological constant, this acceleration is constant.
Models with changing dark matter result in acceleration of acceleration of the expansion.
 
  • #3
Bandersnatch said:
No, there isn't a contradiction. The universe could be expanding without a cosmological constant whatsoever.
Presence of dark matter causes the expansion to accelerate, and if it's in the form of a cosmological constant, this acceleration is constant.
Models with changing dark matter result in acceleration of acceleration of the expansion.
I would like to add that as far as I know we add cosmological constant to ensure the derivative of energy tensor equals zero. I mean, if cosmological constant (even if the dark matter result in it) is constant, then Does not the derivative of energy tensor equal zero? ( static universe )
 
  • #4
Bandersnatch said:
Presence of dark matter causes the expansion to accelerate

No, the presence of dark energy causes acceleration. Dark matter is a regular matter component which causes deceleration. Dark matter and dark energy are very different concepts.

mertcan said:
Because they say both the our universe is expanding and data they had acquired resembled the cosmological constant (static universe, net total energy is constant).

Einstein's introduction of the cosmological constant was to get a static universe. However, this only occurs for a very particular value for the cosmological constant and the solution is anyway unstable. There is no contradiction in having a cosmological constant and an expanding universe.
 
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  • #5
Orodruin said:
No, the presence of dark energy causes acceleration
A slip of mind. An embarrassing one nonetheless.
 

FAQ: Cosmological Constant: Expanding Universe & Data Contradiction

1. What is the cosmological constant?

The cosmological constant is a term in Einstein's theory of general relativity that represents the energy density of empty space. It is denoted by the Greek letter lambda (Λ) and was originally introduced by Einstein to mathematically balance the equations of his theory to account for a static universe.

2. How does the cosmological constant relate to the expanding universe?

The cosmological constant plays a crucial role in the expansion of the universe. In the early 20th century, it was believed that the universe was static and unchanging. However, observations made by astronomer Edwin Hubble showed that the universe is actually expanding. The cosmological constant is now used to explain this expansion and is thought to be responsible for the accelerated expansion of the universe.

3. What data contradicts the cosmological constant?

Recent observations of the universe have shown that the expansion of the universe is accelerating at a faster rate than originally predicted. This contradicts the original understanding of the cosmological constant, which was thought to be a constant value. This has led to the development of new theories, such as dark energy, to explain this discrepancy.

4. How does the cosmological constant affect our understanding of the universe?

The cosmological constant has had a significant impact on our understanding of the universe. It has played a crucial role in the development of the Big Bang theory and has helped us understand the expansion of the universe. However, the recent data contradiction has challenged some of our previous assumptions and has prompted scientists to develop new theories and models to better explain the behavior of the universe.

5. What research is being done on the cosmological constant?

Scientists are continuously studying the cosmological constant and its role in the expansion of the universe. This includes observational studies using advanced telescopes and satellites, as well as theoretical studies using computer simulations and mathematical models. The goal is to better understand the nature of the cosmological constant and its implications for our understanding of the universe.

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