- #1
Cerenkov
- 374
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https://www.physicsforums.com/threads/what-are-the-best-parameters-for-lcdm.831858/
Hello.
In the above linked thread from 2015 Science Advisor Chalnoth replies to Earnest Guest.
First, the cosmological constant has been a component of General Relativity pretty much from the start. The way that General Relativity is derived, in fact, essentially requires the existence of the cosmological constant. Its value had long assumed to be zero because it has to take on a value smaller than about 10−120 in natural units in order for any gravitational collapse to occur. Theorists largely assumed that there must be some kind of symmetry that sets the cosmological constant to be zero. However, no such symmetry has been found. Our theories, in other words, seem to be telling us that the cosmological constant probably must exist, and therefore we really shouldn't have been all that surprised to see it occur. My questions pertain to the highlighted sentence.
1.
Is the gravitational collapse in question the phenomenon referred to by Roger Penrose in this paper? https://www.semanticscholar.org/pap...rose/faad1f4358fddf70df2e00c0a290b7e4501c27de
2.
What do the words 'natural units' refer to please?
3.
If possible, could someone please explain to me why the value of the cosmological constant has to take on such a small value for gravitational collapse to occur? Please note that my level of understanding is Basic, so I won't be able to follow any math.
If it's not possible to answer this question at a Basic level, I quite understand and I thank you for reading this. I am reconciled to not being able to follow a lot of what is posted in this forum. But my interest in these topics remains undimmed.Thank you for any help given. Cerenkov.
Hello.
In the above linked thread from 2015 Science Advisor Chalnoth replies to Earnest Guest.
First, the cosmological constant has been a component of General Relativity pretty much from the start. The way that General Relativity is derived, in fact, essentially requires the existence of the cosmological constant. Its value had long assumed to be zero because it has to take on a value smaller than about 10−120 in natural units in order for any gravitational collapse to occur. Theorists largely assumed that there must be some kind of symmetry that sets the cosmological constant to be zero. However, no such symmetry has been found. Our theories, in other words, seem to be telling us that the cosmological constant probably must exist, and therefore we really shouldn't have been all that surprised to see it occur. My questions pertain to the highlighted sentence.
1.
Is the gravitational collapse in question the phenomenon referred to by Roger Penrose in this paper? https://www.semanticscholar.org/pap...rose/faad1f4358fddf70df2e00c0a290b7e4501c27de
2.
What do the words 'natural units' refer to please?
3.
If possible, could someone please explain to me why the value of the cosmological constant has to take on such a small value for gravitational collapse to occur? Please note that my level of understanding is Basic, so I won't be able to follow any math.
If it's not possible to answer this question at a Basic level, I quite understand and I thank you for reading this. I am reconciled to not being able to follow a lot of what is posted in this forum. But my interest in these topics remains undimmed.Thank you for any help given. Cerenkov.
