As a minimum, as it does not include gravity anymore, it is an argument for the restricted idea “Research on String Theory is Largely a Waste of Time for Quantum Gravity”.

What drives us to pursue TOE? I came onto this blog asking Google “benefits of knowing the theory of everything”. Behind this search are my questions such as: What specific physical elements or properties will be inter-related? How will they be related? That is, what form of theory-less equations and supporting statements will do this? Perhaps TOE will not be “completely” defined, but what would be sufficient to point us in the “correct?” assured direction?

My points would be:

1) Its not a theory - no equations, no way of proving true / false
2) Its not one theory, its 10^500 or more, if you subscribe to the landscape, with so many theories one is bound to describe our universe, you just need to plug in the right 500 numbers (as opposed to a factor of ten less constants in the SM)
3) Its not background independent, so can never describe a changing spacetime geometry as required by GR
4) It moved from a hadron theory to a quantum gravity theory because it described the graviton. But gravity is not a force in GR, it’s paths through a changing geometry to preserve minimal PE, why do we even need a graviton?

A large number of theoretical physicists have tried for a few decades now to understand what string theory implies about reality without success. This isn’t to say that we’ve learned nothing at all about string theory. But what we have learned hasn’t told us anything about any observations we might make, despite the very large number of man-hours employed in understanding it. So string theory is definitely “very hard”. But whether or not it’s too hard is clearly a judgment call.

I guess I haven’t heard of any more promising theory for quantum gravity, so I don’t see why theorists shouldn’t keep trying to understand string theory. From what I understand, we are essentially guaranteed to understand more about mathematics anyway just by pursuing string theory, mathematics that will be useful whether or not string theory turns out to be accurate.

What is too hard? I mean any problem you don’t know the algorithm to solve is hard. Beyond that, how do you differentiate the levels of hardness?

It is all in the realm of unknown and the main attribute of it is being unknown So we just do not know how hard it is. There is a chance someone tomorrow ( or next year) will show all of us how simple (OK, not that hard) it is.

I am just trying to be optimistic here.

Great blog. Just subscribed.

This would be equivalent to if for “God exists” argument he argued for an existance as an idea rather then as people think he exists as part of/the creator of reality. It is disengenous to pretend he is arguing about the same thing as Woit, Smolin and others.

plausible scenarios in which one will ultimately be able to extract highly predictive statements about particle physics (but not, say, the cosmological constant) from the theory.

to
This seems perfectly sensible. I’d only add that this is only half of the story. High predictivity leads to predictions which, even more importantly, must be correct. This is where experimental data comes in, and it is as relevant to ST as it is to any other theory. After all, the way to natural laws is paved with good theories.

And there are equally plausible scenarios in which one will ultimately be able to extract highly predictive statements out of Jello Theory in which we posit the universe is made of tiny clumps of jello. Just because we don’t *know* what the Jello Theory really *is* yet or how to connect it to the real world doesn’t mean people shouldn’t wonder about it. After all, it could turn out to be highly delicious for all of us!

is because it’s just too hard.

I guess you’re going to tell us next that your worst defect is being too smart….

In the meantime, the advent of sexy new data from the LHC and

This is the part I just cannot understand. I’ve heard similar statements from many string theorists. They don’t seem to realize it just does not make sense. It’s like saying, “in the meantime, people will keep playing with science, while we await the second coming of Jesus Christ”. Well, it’s not at all obvious that Christianity is the true theory and science is just a pastime to make the wait less boring.

Since we don’t know how this will play out, it’s perfectly plausible to posit a worst-case scenario (the String Theory Landscape will turn out to be entirely unpredictive about particle physics) and ask whether it would still be worth working on String Theory.

But if you’re going to do that, you need to weigh all the other reasons to be interested in String Theory (e.g., the applications of AdS/CFT to RHIC physics), as opposed to simply looking at those things which may or may not have motivated people to take up the subject 20 years ago.

A suggested starting point relative to the use of string theory: why knowledge?

And you take it on FAITH that any such connection exists. There are no guarantees that M-Theory, once we’ve figured out what it is, will provide any connection to the real world. There are no guarantees that M-Theory will turn out to be an adequate model of real world physics. It might just be an elaborate contraption that thousands of physicists have wasted hundreds of man years of time to find out it is just a fantasy model of a non-existent universe.

Also did you mean to imply that my bias was making me read into Sean’s argument an argument against not being a waste or that it was Sean’s bias making his argument counterproductive? I suppose both did exist, but I still maintain that the argument is of that nature. For instance after making the point that it seems to fail to make predictions about standard model parameters, why would you then dismiss this entirely, instead of just moving on to why the quantum gravity aspect is a waste of time as well(because it hard.) While his argument would still stay the same, it is obviously more persuasive to simply argue againsts both possible benefits then to argue against one, then make the argument your adversary might make(will that doesn’t matter because…) before then going on to argue against that as well.

The second half of his argument, is essentially arguing that the non-perturbative theory can be found or at least well understood enough to connect with reallity(testable predictions), something that alone would be considered an argument in favor of string theory research, but then goes on to say that since it is hard it might take a long time perhaps even centuries(though this seems presented as an extreme case) and so we shouldn’t even bother.

All he has to do is add to the end “… too hard, one would think, however it could very well not take that long.” and now we have a clear argument for it not being waste, simply by stating something that had already been implied in the precceeding paragraph.

\int_{M}R

One can simply introduce a number of extra terms, to form a naive perturbation expansion for a theory of QG:

\int_{M}(R + epsilon L_{1}g + epsilon^{2} L_{2}g + …)

where epsilon is your “planck scale” parameter and the L_{i} are differential operators acting on the metric g (maybe my notation is a bit off, but you get the idea). It is clear that this is legitimate if you are considering low energy physics, eg particle physics, since then quantum effects will be perturbations about the norm, provided the L_{i} are bounded operators.

But then we now have an action, or rather, a whole family of actions, that all “include gravity”! So, if I follow your reasoning correctly, these must all be valid theories of quantum gravity.