Out of the Cave

I know... Where the heck have I been? Well, I took a week off and away from anything having to do with physics to reflect on accepting a faculty position. I'm not going to say where it is, but I'm happy to say that I accepted a position. Then there was all of the running around I had to do that I didn't do while I was travelling around for the last four months non stop (such as paying bills and such)

But I still managed to finish up my three year long project on the cosmological constant problem. This problem is reputed as being the 'biggest embarassment in physics' It has haunted all of the greats and all of the insignificants such as Einstein and yours truly respectively. What is the cosmological constant problem? Well my friend Sean Carroll wrote a great piece on the cosmological constant problem. Just do a Google search on Sean (Sean Carrroll Cosmological Constant).

But if you have little patience, let me say a few words. The cosmological constant problem can be understood best from Einstein's theory of general relativity. Schematically(very much so) the theory
states Geometry = Matter & Energy , or in other words space-time curvature/gravity is dynamically
related to matter and energy. The theory is able to make this mathematical relationship concrete with the help of some powerful insights from a branch of mathematics called Differential Geometry; which allowed Einstein to make this relationship independent on the choice of space-time points(or frame of reference)-this is known as the principle of General Covariance.

Now, Einstein realized that he could freely add a constant (hence the name cosmological constant) without violating any of these principles in his theory. Moreover you're free to put it on either side of the equation, but the constant carries different meanings depending on if its on the matter energy side of the geometry side.

Here is where the trouble begins. We once thought that the cosmological constant was zero, now we actually measure a non zero value (exculding the issue if its really a time dependent component of dark energy), the value is extremely small (the energy density is 10^{-33} electron volts^{4}). The problem is that everything in our universe has 'quantum fluctuation' whose zero point fluctuation contributes to the cosmological constant. If we use quantum field theory to the same level of accuracy that we confirm at accelerators, we find a disgraceful disagreement between theoretical and the observed value of the cosmological-how bad? 10^{120} orders of magnitude- It takes longer that the lifetime of the universe to count this number! (which crazy fool would want to do this?)

So what happened to this large cosmological constant?

Or did we get it all wrong? If we did, which theory should we throw out, general relativity or the Standard Model? Clearly we shouldn't throw out either( otherwise get rid of GPS or your cell phone). Some people, like my colleague and guru Lenny Susskind (the inventor of string theory) and Steve Weinberg (co inventor of the Standard Model of particle interactions) state one possible solution is that the cosmological constant is anthropically selected.
Now, these cats are genuises (I mean it!) and they may be correct. But in the meantime it does not hurt to seek a 'dynamical' way to explain that the cosmological constant does not gravitate the way that
the Einstein equations dictate. In other words perhaps there is a way that the quantum theory of gravity deals with a huge cosmological constant. This is what I've been thinking about for the past three years. Now I'm out of the cave with an answer.

Whats the answer?

I'll tell ya tomorrow.

Comments

[Mark Trodden]

Hey Stephon, congratulations on the faculty job. Let me know where you're heading. Cheers

[big fool]

congratulations on both great achievements! really excited to look at the arxiv tonite. but is lenny the inventor of string theory? was it not veneziano? his first paper seemed to appear earlier than lenny's first paper, my investigation is very crude.

[David Dooling]

Hi Stephon,
That's awesome.

BTW did you have something to do with me not getting my security clearance yet?

[Sean]

Stephon, congratulations! What is this about not saying where it is? Being on the faculty somewhere is not something you can really keep secret indefinitely.

[Stephon]

Sean, thanks! Its Penn State.

[Stephon]

Mark, thanks, its Penn State.

[Gordon Watts]

Congradulations on the job!