What Are the Current Trends in String Theory Research?

[atyy]

Ooguri is funny. He says Hermann Nicolai exposed his secret spin foam past.

 

[tom.stoer]

You don't know what Witten is interested in and why.

That's why I am asking ;-)

String theory as of today suffers from many open issues; and I think perturbative finiteness is one of the minor ones b/c it goes away ones one understands its non-perturbative formulation in terms of unique fundamental d.o.f.. Therefore the question is if there's a strategy behind addressing these open issues, or whether this is simply fixing some minor problems.

 

[xristy]

In Witten's public talk during the Q&A he lists several discoveries like the Higgs and neutron starts that were viewed with skepticism and that took many decades to be discovered and then at 46:32 he says

Gravitational waves seemed hopelessly undetectable when Einstein first proposed - predicted them and the fact that eventually an incredibly story involving the binary pulsar made it possible to discover them was totally unforeseeable.

I've looked about but I don't see that LIGO or any other experiment has reported discovery of gravitational waves so I assume that Witten is simply suggesting they will surely be discovered but I'm not sure.

Have gravitational waves been observed or am I reading too much into Witten's statement?

 

[marcus]

In Witten's public talk during the Q&A he lists several discoveries like the Higgs and neutron starts that were viewed with skepticism and that took many decades to be discovered and then at 46:32 he says I've looked about but I don't see that LIGO or any other experiment has reported discovery of gravitational waves so I assume that Witten is simply suggesting they will surely be discovered but I'm not sure.

Have gravitational waves been observed or am I reading too much into Witten's statement?

A binary pulsar was observed to be losing energy at a rate consistent with the energy being carried off in the form of grav radiation.
I wil try to get a link for you.
I think that grav. waves have NOT been observed directly (as a periodic distortion of geometry.)

However the binary pulsar observation was widely accepted as proof that grav. waves are real. I personally was convinced FWIW. It seems to me smoking gun evidence.

You have two compact objects in rapid orbit and you time orbit precisely and you find it is SPEEDING UP.
So the two objects are spiraling in towards each other. They are losing energy. Where is this energy going?

Is there some kind of atmospheric drag? Well maybe that contributes somewhat but they are very massive very dense objects and you calculate that. You find it cannot be responsible for the main effect.

You may have read about this. It was big news, may have involved a Nobel prize.

It is a beautiful idea that geometry itself could have a kind of "viscosity" and dissipate energy by carrying it away in the form of waves. I'll try to find the link (though I think you may know what I'm talking about already.)

 

[atyy]

In Witten's public talk during the Q&A he lists several discoveries like the Higgs and neutron starts that were viewed with skepticism and that took many decades to be discovered and then at 46:32 he says I've looked about but I don't see that LIGO or any other experiment has reported discovery of gravitational waves so I assume that Witten is simply suggesting they will surely be discovered but I'm not sure.

Have gravitational waves been observed or am I reading too much into Witten's statement?

Maybe he is thinking about the indirect observation of gravitational waves by Taylor and Hulse's binary pulsar.

 

[xristy]

Thanks. I'm sure it was the indirect observation.

I noticed someone else recently referring to the indirect observation of the W in 1973 via the neutral current rather than referring to the decade later direct observation of the W.

 

[marcus]

Maybe he is thinking about the indirect observation of gravitational waves by Taylor and Hulse's binary pulsar.

Yes! for sure. I got a wiki passage that explains it adequately:
==quote Wikipedia==
The 1993 Nobel Prize was awarded to Joseph Taylor and Russell Hulse after they discovered two such stars. While Hulse was observing a new pulsar, named PSR B1913+16, he noticed that the frequency with which it pulsed fluctuated. It was concluded that the simplest explanation was that the pulsar was orbiting another star very closely at a high velocity. Hulse and Taylor determined that the stars were equally heavy by observing these pulse fluctuations, which led them to believe the other spatial object was also a neutron star.
The observations made of the orbital decay of this star system was a near perfect match to Einstein’s equations. Relativity predicts that over time a binary system’s orbital energy will be converted to gravitational radiation. Data collected by Taylor and his colleagues of the orbital period of PRS B1913+16 supported this relativistic prediction; they reported in 1983 that there was a difference in the observed minimum separation of the two pulsars compared to that expected if the orbital separation had remained constant. In the decade following its discovery the system’s orbital period had decreased by about 76 millionths of a second per year - this means that the pulsar was approaching its maximum separation more than a second earlier than it would have if the orbit had remained the same ...
==endquote==
http://en.wikipedia.org/wiki/Binary_pulsar