# String theory predicts nothing?

1. Jan 6, 2006

### DaveC426913

I've read a lot of things to this effect, that string theory predicts nothing, or that it can't be disproven, and as such, many theorists argue it is doomed.

How is this so? Is it because the scales proposed are so incredibly tiny that we can't measure that small, even in the future? Is there some principle that prevents the theory from making predictions or being testable?

2. Jan 6, 2006

### MistyMountain

String theory predicts both everything and nothing at the same time.

It would be nice if it predicted something, but it doesn't predict anything. :)

Those who say they understand it must understand everything and nothing at the same time.

All this is giving me a hedache, so I am going to let someone smarter answer your question.

3. Jan 7, 2006

### DaveC426913

Yes, you didn't really shed much light on my question... :(

Any takers?

4. Jan 7, 2006

Staff Emeritus
If you read the popular books by string theorists, you will see that they claim that the reason string theory doesn't predict anything is that the energy scale is so high we couldn't observe what they predict.
But this is actually not the end of the story. Foes of string theory, who have become very vocal recently, assert that string theory predicts nothing, period. That there is no physical fact, at any energy, which if observed would confirm or falsify string theory. String theory is all about how strings and branes and so on behave, but efforts to connect this with other kinds of physics have come up short. And with the recent discovery that string theory predicts googles or infinities of inequivalent vacua, only one of which coreesponds to our world, and gives no recipe for finding which one that is, you can see that the non-prediction stakes have been raised. This has led the critics to jeer louder and the string physicsits, unwisely in my opinion, to circle the wagons.
So there you have it.

5. Jan 7, 2006

### marcus

that puts the situation in a nutshell---I would agree with sA about the wagons.

I'm becoming increasingly aware that there are alternatives to string which (although possibly less grand, elegant, attractive to some people) nevertheless DO make predictions.

so that we have the opportunity of proving some of these other theories wrong, if future empirical observations go against them. It is something to consider. the following is just my opinion.

PREDICTION ONE: Laurent Freidel and co-workers are developing a Quantum Gravity model that only works if there is a slight energy dependence of the speed of gammaray photons. Freidel's spinfoam QG is at the forefront of the spinfoam approach and (at least in the 3D case where it has been fully worked out) it REQUIRES this slight dispersion in photon speed. This should be observable by the GLAST satellite to be launched in 2007. I would say that, if GLAST does not observe a dispersion in Gammaray Burst photons, this will shoot down the leading spinfoam QG candidate.

A number of other QG approaches have also led their developers to expect some energy dependence---some type of DSR (deformed special rel)---and would be tend to be refuted along with Freidel's approach. I wont try to list all the authors and approaches that would be involved.

PREDICTION TWO: Loop Quantum Cosmology (LQC) as developed by Martin Bojowald has recently reached the stage where both the Bang and the Hole singularities have been removed and many of the researchers are saying that it LOOKS LIKE our Bang was really a Bounce.

On the BH side, they are saying that gravitational collapse leads to a Bounce. And on the BB side they are saying that our Bang was preceded by a contraction that looks mathematically similar to a BH collapse.

This was discussed a lot by the Friday papers at the October Loops '05 conference. It is looking like, in a Loop Gravity context, there is really only ONE thing, a bounce. And it makes a new region of the universe BRANCH OFF everywhere there is a black hole.

What this indicates to me is that a TYPICAL region of the universe is going to be one whose parameters are optimized for producing lots of black holes since such regions have more offspring. So this is NOT a hard and fast prediction, but it is looking increasingly likely that Loop Gravity implies that the parameters of cosmology/standard model are typically optimal for BH formation

So it challenges you: Can you find any parameter which if it were slightly changed would make BHs more abundant? Loop Gravity suggests that you can NOT find such a parameter. If you can, it would tend to refute Loop Gravity.

THIS IS CALLED cosmological natural selection, or the black hole natural selection hypothesis and IT IS ALREADY BEING TESTED. Because it predicts a nice low limit on the mass of neutron stars. So every time another neutron star is found, and astronomers measure its mass, we have a test. If they find one that is 2 solar masses or more, that would kill the idea (judging by what I've read) and even less, like 1.7 solar masses, if they were very sure of it.

-------------------------------------

so it is like deciding what girl to take to the prom. String is rich and has a nice car. But with Loop, even though she might not be so impressive at first sight, there might be more chance of empirical verification.

6. Jan 8, 2006

### alfredblase

Hmmm, ok, String Theory will eventually come up with something that QM does not as they are different theories.

If ST is not correct I should still think that QM is a false theory because one of QM's axioms is that all fundamental particles are point particles, i,e that they have no spatial dimention. This cannot be true as then massive fundamental particles would have infinite density. Rather what QM really states is that fundamental particles are so small that their dimensions can never be measured. This is no different to what ST does.

In conclusion, in choosing between taking a beautiful, if mysterious and rather unaproachable girl to the prom over an ugly, hypocritical slut, I choose the former (being ST) every time. =)

Last edited: Jan 8, 2006
7. Jan 8, 2006

### DaveC426913

I appreciate the info Marcus, but with all due respect, this thread is not about alternative theories. I'm interested in the failing of string theory.

"...string theory predicts nothing, period. That there is no physical fact, at any energy, which if observed would confirm or falsify string theory. "

How is this possible? Surely with enough probing and enough time (decades? centuries?) we should be able to confirm of falsify aspects if it?

Are opponents saying " there's no practical way in the near future" or are they saying "there is no way in principle" that we will be able to confirm or falsify string theory.

8. Jan 8, 2006

### Careful

**
If ST is not correct I should still think that QM is a false theory because one of QM's axioms is that all fundamental particles are point particles, i,e that they have no spatial dimention. This cannot be true as then massive fundamental particles would have infinite density. Rather what QM really states is that fundamental particles are so small that their dimensions can never be measured. This is no different to what ST does. **

You do not have to await the final failure of ST to know that that hypothesis is (in the end) incorrect. By the way, string theory should first reproduce the full predictions of the standard model implying that it could be falsified at the level where QFT is still happy.

**
In conclusion, in choosing between taking a beautiful, if mysterious and rather unaproachable girl to the prom over an ugly, hypocritical slut, I choose the former (being ST) every time. =) **

Nah, the beautiful, mysterious and unaproachable girl will not want to go with you to the prom. It is better to sit at a table from which you can eat as opposed to one which is only covered with golden plates :rofl:

9. Jan 8, 2006

### alfredblase

You guys are so impatient All you think about is sex, as long its got two legs u wanna do it now, "any hole's a goal" right? But man its well worth putting in the effort and waiting for that more special girl, cos u wont enjoy it otherwise. Let me explain:

You see, this illustates the whole thing, ST is still a very fledgling theory, despite all the funding it recieves, despite the decades people have been working on it. And that is because it is a very ambitious, complex and difficult theory. That doesn't mean its not well worth working and waiting for. Give it a proper chance man. U see this girl could show u tricks u never even dreamed of, shes got it all dude! hahaha

Last edited: Jan 8, 2006
10. Jan 8, 2006

### Careful

**You guys are so impatient All you think about is sex, as long its got two legs u wanna do it now, "any hole's a goal" right? But man its well worth putting in the effort and waiting for that more special girl, cos u wont enjoy it otherwise.**

:rofl: :rofl: You seem to forget that in order to appreciate when a girl is good, you first have to ride in many test models.

**
You see, this illustates the whole thing, ST is still a very fledgling theory, despite all the funding it recieves, despite the decades people have been working on it. And that is because it is a very ambitious, complex and difficult theory. That doesn't mean its not well worth working and waiting for. Give it a proper chance man.**

This is like the most silly excuse I have ever heard: (a) string theory is over thirty (b) did not produce one single physical result that is open to falsification (c) did not manage to reproduce the standard model (d) only reproduces GR perturbatively (while the strong field region is actually the interesting one) (e) an enormous amount of people are looking for it (f) despite of this lack of succes needs (i) extra dimensions (ii) supersymmetry (iii) calabi yau compactifications (with of course huge ambiguity here) ... (g) the landscape to cure the latter illness...

It seems to me that the girl you are waiting for isn't pretty at all, but an ugly tart which is covered inside a beautiful wedding cake :rofl:

Last edited: Jan 8, 2006
11. Jan 8, 2006

### alfredblase

ok, im gonna stop discussing this with you, because your sentences are crap and dumb, and show a lack of intelligence and understanding.

Last edited: Jan 8, 2006
12. Jan 8, 2006

### Careful

Really, what is objectively wrong with them ? Perhaps you could explain to us what *your* justification is for telling to people that string theory is the big catch´´ while it hasn't clearly lived up to any of the standards a physical theory requires. Actually, my view is that it is ok to do string theory, but the reason for it is negative alas (the lack of *clearly* superior alternatives).

13. Jan 8, 2006

### DaveC426913

Hello? I would like this thread to not be hijacked if you don't mind - at least until I've gotten an answer to my question. This is not about theories in competition, or which one os better. I just want to understand how string theory predicts nothing.

So far, the only thing I've seen that has addressed that is selfAdjoint's statement that "...the energy scale is so high we couldn't observe what they predict..."

Doesn't this just mean it's out of our reach? That's not the same thing thing as 'never'.

14. Jan 8, 2006

Staff Emeritus

Did you see my other statement? String theory has been accused of predicting NOTHING that can ever be checked! The string physicists have not really defended themselves against this charge.

15. Jan 8, 2006

### DaveC426913

I did see that, but that is not answering my question since it is part of my question.

How does the theory not predict anything about anything? The theory requires particles, their interactions and energies to behave certain ways, does it not? Predictions would put numbers to them, which can, in principle be verified or refuted.

By the way, if it doesn't predict anything, and its not modelled after observable physics, does that not mean it is not even a theory by definition? Wouldn't it merely be a hypothesis? Or a conjecture?

Last edited: Jan 8, 2006
16. Jan 8, 2006

### DaveC426913

I did see that, but that is not answering my question since it is part of my question.

How does the theory not predict anything about anything? The theory requires particles, their interactions and energies to behave certain ways, does it not? Predictions would put numbers to them, which can, in principle be verified or refuted.

By the way, if it doesn't predict anything, and its not modelled after observable physics, does that not mean it is not even a theory by definition? Wouldn't it merely be a hypothesis? Or a conjecture?

17. Jan 8, 2006

### DaveC426913

I did see that, but that is not answering my question since it is part of my question.

How does the theory not predict anything about anything? The theory requires particles, their interactions and energies to behave certain ways, does it not? Predictions would put numbers to them, which can, in principle be verified or refuted.

By the way, if it doesn't predict anything, and its not modelled after observable physics, does that not mean it is not even a theory by definition? Wouldn't it merely be a hypothesis? Or a conjecture?

18. Jan 8, 2006

### DaveC426913

I did see that, but that is not answering my question since it is part of my question.

How does the theory not predict anything about anything? The theory requires particles, their interactions and energies to behave certain ways, does it not? Predictions would put numbers to them, which can, in principle be verified or refuted.

By the way, if it doesn't predict anything, and its not modelled after observable physics, does that not mean it is not even a theory by definition? Wouldn't it merely be a hypothesis? Or a conjecture?

19. Jan 8, 2006

### DaveC426913

I did see that, but that is not answering my question since it is part of my question.

How does the theory not predict anything about anything? The theory requires particles, their interactions and energies to behave certain ways, does it not? Predictions would put numbers to them, which can, in principle be verified or refuted.

By the way, if it doesn't predict anything, and its not modelled after observable physics, does that not mean it is not even a theory by definition? Wouldn't it merely be a hypothesis? Or a conjecture?

20. Jan 8, 2006

### DaveC426913

I did see that, but that is not answering my question since it is part of my question.

How does the theory not predict anything about anything? The theory requires particles, their interactions and energies to behave certain ways, does it not? Predictions would put numbers to them, which can, in principle be verified or refuted.

By the way, if it doesn't predict anything, and its not modelled after observable physics, does that not mean it is not even a theory by definition? Wouldn't it merely be a hypothesis? Or a conjecture?