Susskind on the cosmological constant.

In summary: Fine Tuning? But isn't that what creationists say? That the universe was fine tuned for us? Or at the very least, that it was tuned in a way that we could exist? And isn't that what Susskind is saying in his lecture? That the fine tuning is a problem?I don't think Penrose is saying that the fine tuning is a problem. I think he is saying that it can't be explained by a string theory multiverse, which is what he calls the alternative to an intelligent designer. He argues that the fine tuning is evidence for an intelligent creator.Susskind is saying something different. He is saying that the fine tuning is evidence against a string theory multiverse.
  • #1
Freeman Dyson
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I am watching a lecture by Susskind on his book The Cosmic Landscape. And he is going on about how "tuned" and unlikely it is. Largely based on work done by Weinberg. He said it was one of the biggest surprises in science and can't be ignored. How fine tuned the cosmological constant is. Is this true? I have read a little on here and people do not seem to be too big on him or string theory. And seem to side with Smolin. What do you guys think of this? Is this fine tuning really the problem that Susskind says it is?
 
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  • #2
Go to the Perimeter Institute site and download Penrose's inaugural lecture (it is one that he has given in various forms, so you'll probably recognize some or all of it). He also addresses the subject in Chapter 2 of the Philosophy of Vacuum, edited by Saunders and Brown. Expensive book, but highly recommended if you can borrow it or find a used copy.

http://streamer.perimeterinstitute.ca/mediasite/viewer/ [Broken]
 
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  • #3
turbo-1 said:
Go to the Perimeter Institute site and download Penrose's inaugural lecture (it is one that he has given in various forms, so you'll probably recognize some or all of it). He also addresses the subject in Chapter 2 of the Philosophy of Vacuum, edited by Saunders and Brown. Expensive book, but highly recommended if you can borrow it or find a used copy.

http://streamer.perimeterinstitute.ca/mediasite/viewer/ [Broken]

Thanks. I will look at that. Susskind almost seems to be setting up a false dichotomy between his string theory multiverse and intelligent design. The fine tuning HAS to be explained and his string theory multiverse are the only explanation short of a benevolent creator that tuned the universe for life.
 
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  • #4
Freeman Dyson said:
Thanks. I will look at that. Susskind almost seems to be setting up a false dichotomy between his string theory multiverse and intelligent design. The fine tuning HAS to be explained and his string theory multiverse are the only explanation short of a benevolent creator that tuned the universe for life.
If you look at Penrose's work, he poses some questions relating to unification quite clearly. If quantum theory predicts one thing, and classical physics (including GR) predicts another, how can divergences in observations be understood and reconciled? Penrose uses the metaphor of a mermaid who lives both above and below the water (a Universe that inhabits both quantum and classical domains). That may or may not be helpful to you (or to me), but it is a nice visualization - a way to frame the question that is inclusive of both domains - which is probably a good way to figure out which scientific domain may have to "give" a little or a lot before they can be reconciled, so a TOE might be viable.
 
  • #5
I also came across this from Weinberg:

A Priori Probability Distribution of the Cosmological Constant

Abstract

"In calculations of the probability distribution for the cosmological constant, it has been previously assumed that the a priori probability distribution is essentially constant in the very narrow range that is anthropically allowed. This assumption has recently been challenged. Here we identify large classes of theories in which this assumption is justified."

http://arxiv.org/PS_cache/astro-ph/pdf/0002/0002387v1.pdf" [Broken]

To be honest, the article is a little over my head. Anyone dumb it down a little?
 
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  • #6
My short version of this problem is that we are dealing with one point statistics, in that we have one Universe, and the conditions are what they are. If you want to argue about how likely those conditions were before you knew about our Universe, the answer you get depends completely on the assumptions you make. In the language of Bayesian statistics, the answer is dominated by the prior (which is the probability you assume before you observe the data).

There is a similar never ending bun fight in the literature around the probability of life forming. Some argue that the one data point we have (Earth) implies life will form very commonly in the Universe, some argue that the evidence of the timescales of evolution on Earth tell you it will be very rare. Others say that the one data point tells you very little. Again it all depends on the prior that is assumed (either implicitally or explicitally).

My own view is that the cosmological constant problem can't sensibly be answered using these kinds of arguements, and will require some other yet to be realized insight, which hopefully also points to new ways of verifying this new idea (e.g. predictions about experiments or observations that can be made but have not yet been done).
 
  • #7
Ok, I watched the Penrose lecture, which was very good. Penrose is one of my favorites. But this only compounds my confusion. Penrose is talking about the "fine tuning" of the initial entropy state of the universe. How "special" it is. How unlikely it is to happen by chance. So what are the implications of this? What would the universe be like if it were any different? Could life still arise?

This goes back to the Einstein question. Did the universe have any choice when doing this? What caused the initial entropy state of the universe?
 
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  • #8
Are you really Freeman Dyson?!
 

1. What is the cosmological constant?

The cosmological constant, denoted by the Greek letter lambda, is a term in Einstein's field equations of general relativity that represents the energy density of the vacuum of space.

2. Who is Leonard Susskind and why is he important in the study of the cosmological constant?

Leonard Susskind is a renowned theoretical physicist who has made significant contributions to the field of cosmology, particularly in the area of quantum gravity. He is known for proposing the string theory landscape and for his work on the holographic principle. Susskind has also written extensively about the cosmological constant and its implications in modern physics.

3. What is Susskind's argument about the cosmological constant problem?

Susskind argues that the cosmological constant problem, which refers to the discrepancy between the predicted and observed values of the cosmological constant, can be solved by considering the landscape of string theory. This landscape allows for a wide range of possible values for the cosmological constant, thus explaining its small but nonzero value in our universe.

4. How does Susskind's argument differ from other proposed solutions to the cosmological constant problem?

Susskind's argument differs from other proposed solutions, such as the anthropic principle, in that it is based on the landscape of string theory and does not rely on the existence of multiple universes. He also suggests that the cosmological constant may vary across different regions of the universe, which could potentially be tested through observations.

5. What are the implications of Susskind's argument for our understanding of the universe?

If Susskind's argument is correct, it could have significant implications for our understanding of the universe and the laws of physics. It would suggest that the cosmological constant is not a fundamental constant, but rather a result of the landscape of string theory. This could lead to a deeper understanding of the relationships between different physical theories and potentially help reconcile the discrepancies between general relativity and quantum mechanics.

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