String theory: Is dark energy even allowed?

To our resident Physicists (who happen to be Catholic) please explain this one:

In string theory, a paradigm shift could be imminent. In June, a team of string theorists published a conjecture which sounded revolutionary: String theory is said to be fundamentally incompatible with our current understanding of ‘dark energy’. A new study has now found out that this conjecture seems to be incompatible with the existence of the Higgs particle.

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Ahem. One of them is not a catholic.

Really, they look Catholic. :rofl:

I think it’s unfair to ping me while not pinging simultaneously the non-Catholic physicists :stuck_out_tongue: @dga471 @pevaquark.

Let me preface that I am not a string theorist, my realm is classical and relativistic physics. As such, my views might be outdated or I might make some mistakes in the explanation.

First of, let me explain the context of the problem:
The Universe that we live in is accelerating in its expansion - i.e. cosmological constant is positive. We often call such a universe a de Sitter (in short dS) Universe.

As is famously known, string theory have a huge number of dimensions that are somehow not apparent in our everyday 3 spatial + 1 temporal dimensional existence. As such, a large amount of business amongst the string theorists is compactification, the reduction from the many dimensions of string theory to the 3+1 that we experience in our daily life.

Indeed, it was a triumph of string theory when it was proven that the many dimensions of string theories can be compactified to 3+1 dimensions producing the flat spacetime of special relativity (called Minkowski) and even a universe with decelerating expansion (non-imaginatively called anti-de Sitter, or adS).

However, because our Universe is closest to dS, it is considered important to be able to compactify to produce dS. There are many technical problems in this challenge, and indeed it might be possible that string theory cannot be compactified to dS.

Given these challenges, Vafa (super famous string theorist at Harvard) and collaborators wrote a paper giving a bold conjecture: what if no consistent theory of quantum gravity (and therefore string theory) can produce dS. This is the paper that is the impetus of the Denef et al. paper that is covered by Science Daily.

Denef et al. points out that: suppose we entertain Vafa’s conjecture. Would this wreck havoc on other physics we know? The answer is yes: if Vafa’s conjecture is true, then the Higgs field cannot exist. However, as we know, the Higgs field has been experimentally confirmed.

Therefore:

  1. Most probably Vafa’s conjecture is wrong
  2. If Vafa’s conjecture is true, actually there is still a way to produce the Higgs field, but it is fine-tuned. This is a philosophical issue - we have other examples of fine-tuneness in physics and a lot of physicists are not bothered by this.
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Sorry, I was favoring one type of Christian over another because of family and genetic tradition as most of my GA’s were Catholic. :grinning:

Does this say that string theory is not correct?

Nope, I don’t think so. First of, Vafa’s conjecture is a conjecture - it is not rigorously proven (more of an educated guess). Secondly, as stated in point 2), there is still an out, although it might be fine-tuned.

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Happy to introduce the latest physicist to join up: @david.heddle, who blogs at:

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