What possible experiments will falsify String Theory?

In summary: The main focus now is on improving its ability to make predictions, which requires learning how to calculate detailed properties of realistic vacua. Another issue is the challenge of judging a hypothesis generator, as most hypotheses are likely to be wrong. Some suggest evaluating it based on efficiency and speed of learning, as well as its ability to generate stronger hypotheses from rejected ones without completely abandoning the framework. However, string theory has also faced criticism for being a "tower of conjectures" with no substance beyond mathematical elegance. While it cannot be falsified as a whole, specific models based on string theory can be falsified. This has led to debates about whether string
  • #1
MathematicalPhysicist
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Or will confirm its predictions?

As far as I can tell, you can only raise the bar on the energies required from the accelerator, but you cannot give an upper bound, where beyond it the theory is doomed...

This isn't science... we might as well say we need infinite energies. 🙃
 
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  • #3
I think there are no experiments that can falsify string theory, because the theory is not well enough defined to make any quantitative predictions. It is not a theory in the sense of general relativity or quantum field theory, it is more of an idea or a set of concepts.
 
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  • #4
The main thing needed is to improve its ability to make predictions, i.e. we must learn how to calculate the detailed properties of the realistic vacua.
 
  • #5
It's been mentioned many times, but I think the issue of falsifiability is only part of the problem, and at the present not the biggest one. Popper would probably disagree but it seems to me that string theory is a conjectured toolbox that is used to generate hypothesis. So how do you judge an "hypothesis generator"? It can not be falsified, because most hypothesis are presumably wrong anyway.

I would probably judge if from it's effiency or speed of learning, which includes an ability to constructively deform rejected hypothesis in a way that a new hypothesis is generated, stronger than the rejected one, without killing the whole machinery. But string theory seems to have stalled itself but too many options, and some constraints missing. This stalled progress, rather than lack of falsifiability is the current problem from my perspective at least. As something gets complex enough, the question is less wether you are right or wrong, the challenge is how to optimize progress and learn at an optimal pace.

/Fredrik
 
  • #6
Fra said:
It's been mentioned many times, but I think the issue of falsifiability is only part of the problem, and at the present not the biggest one. Popper would probably disagree but it seems to me that string theory is a conjectured toolbox that is used to generate hypothesis. So how do you judge an "hypothesis generator"? It can not be falsified, because most hypothesis are presumably wrong anyway.

I would probably judge if from it's effiency or speed of learning, which includes an ability to constructively deform rejected hypothesis in a way that a new hypothesis is generated, stronger than the rejected one, without killing the whole machinery. But string theory seems to have stalled itself but too many options, and some constraints missing. This stalled progress, rather than lack of falsifiability is the current problem from my perspective at least. As something gets complex enough, the question is less wether you are right or wrong, the challenge is how to optimize progress and learn at an optimal pace.

/Fredrik
It seems like a tower of conjecutres with no substance, but mathematical elegance.
 
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  • #7
MathematicalPhysicist said:
It seems like a tower of conjecutres with no substance, but mathematical elegance.
I have no problem with conjectures per see, but the ones in string theory is not attracting me. When I try to see positively on string theory, I always get myself into a corner which is outside the whole point of string theory in the first place.

/Fredrik
 
  • #8
How can you falsify quantum field theory (QFT)? You can't! You can falsify specific models like QED or the Standard Model, but you can't falsify QFT as such. That's because QFT is a framework, not a theory. It's often argued that string theory is also a framework, not a theory. That's why you cannot falsify string theory, but you can falsify some specific models based on string theory.
 
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  • #9
So @Demystifier do you say that it's not possible to falsify every model from String theory, because there are an infinite number of such models?

So why do we call them "theories"?
I mean there aren't models of GR, right?
 
  • #10
MathematicalPhysicist said:
So @Demystifier do you say that it's not possible to falsify every model from String theory, because there are an infinite number of such models?
Yes.

MathematicalPhysicist said:
So why do we call them "theories"?
Because the word "theory" has several slightly different meanings in different contexts. In "string theory", "theory" means any sophisticated system of thought. In "evolution is just a theory", "theory" means something not yet proved.

MathematicalPhysicist said:
I mean there aren't models of GR, right?
It depends on what exactly do you mean by GR. If by GR you mean a principle that spacetime geometry is governed by general covariant equations of motion, then theories of gravity with higher powers of ##R## are alternative models of GR.
 
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  • #11
Demystifier said:
Yes.Because the word "theory" has several slightly different meanings in different contexts. In "string theory", "theory" means any sophisticated system of thought. In "evolution is just a theory", "theory" means something not yet proved.It depends on what exactly do you mean by GR. If by GR you mean a principle that spacetime geometry is governed by general covariant equations of motion, then theories of gravity with higher powers of ##R## are alternative models of GR.
So the work for string theorists are secured for another millennia... unless funding will be cut.
 
  • #12
MathematicalPhysicist said:
So the work for string theorists are secured for another millennia... unless funding will be cut.
... or unless they run out of new ideas.
 
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  • #13
MathematicalPhysicist said:
So @Demystifier do you say that it's not possible to falsify every model from String theory, because there are an infinite number of such models?
Demystifier said:
Yes.
Why? What if they all predict the same for one specific question and it is not what experiment shows.
 
  • #14
martinbn said:
What if they all predict the same for one specific question ...
In that case string theory would be more than a framework. Viewing string theory as just a framework is one perspective, not the only existing perspective.
 
  • #15
Demystifier said:
How can you falsify quantum field theory (QFT)? You can't! You can falsify specific models like QED or the Standard Model, but you can't falsify QFT as such. That's because QFT is a framework, not a theory. It's often argued that string theory is also a framework, not a theory. That's why you cannot falsify string theory, but you can falsify some specific models based on string theory.
What about the predicted particles? Has 13 years work at the LHC not put a dint in it? (Lay level)
 
  • #17
Demystifier said:
In that case string theory would be more than a framework. Viewing string theory as just a framework is one perspective, not the only existing perspective.
Why? It just so it happened that all the theories in this framework have the same prediction. I mean one prediction, all the other predictions can be very different.
 
  • #18
martinbn said:
Why? It just so it happened that all the theories in this framework have the same prediction. I mean one prediction, all the other predictions can be very different.
I don't think that string theory is such theory. Or if you suggest that it is, then what that single prediction would be?
 
  • #19
pinball1970 said:
What about the predicted particles?
Which ones? If you mean particles of minimal SUSY extension of the Standard Model, that's not exactly a unique prediction of string theory.
 
  • #20
Demystifier said:
I don't think that string theory is such theory. Or if you suggest that it is, then what that single prediction would be?
I am not saying that. I am just saying that it is a possibility. If you claim that it is not the case can you prove it?
 
  • #21
Demystifier said:
How can you falsify quantum field theory (QFT)? You can't!
You can. Show that CPT is not an exact symmetry. It's an exact symmetry of every QFT.

String theory requires extra dimensions, but finding these - or showing they don't exist - could need an accelerator reaching the Planck energy. As long as we don't have that I'm not aware of possible measurement results that would specifically rule out string theories without breaking everything else.
pinball1970 said:
There is discussion about a new LHC. 100KM to look for these particles. Is this justified in your view? This https://www.nature.com/articles/d41586-019-00173-2 @Demystifier Also @mfb
That's independent of string theory.
 
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  • #22
Demystifier said:
How can you falsify quantum field theory (QFT)? You can't! You can falsify specific models like QED or the Standard Model, but you can't falsify QFT as such. That's because QFT is a framework, not a theory. It's often argued that string theory is also a framework, not a theory. That's why you cannot falsify string theory, but you can falsify some specific models based on string theory.
QFT is a framework, but you can falsify all QFTs at once e.g. by finding correlations such that ##\left|CHSH\right| > 2\sqrt{2}##. A similar thing may be happen in another framework. However, my understanding is that today string theory is not even a framework anymore. While in the early days, there were just a couple of concrete string actions that were in some sense dual to each other and the only freedom one had was the choice of compactification of the extra dimensions, today, there is no longer such a strict definition of string theory anymore. For example, most people working in holography count themselves towards the string theory community, even though the ties between holography and string theory (in the strict sense) are pretty loose. So the question in the OP may be ill-posed.
 
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  • #23
In his books Brian Greene says that we can look out for macroscopic strings those that are stretched to large sizes by inflation. They can give out gravitational waves that we can detect.

Theres some talk that looking for anomalies in the cosmic microwave background can be evidence that our universe bumped into another brane in the past proving braneworld.
But i do not know whether these techniques provides definitive evidence,
 

Related to What possible experiments will falsify String Theory?

1. What is String Theory and why is it important?

String Theory is a theoretical framework that attempts to explain the fundamental nature of the universe by proposing that the most basic building blocks of matter are not particles, but tiny strings. It is important because it has the potential to unify all of the known laws of physics and provide a complete understanding of the universe.

2. What are the main predictions of String Theory?

String Theory predicts that there are more than three dimensions of space, that gravity is a fundamental force that can be explained by the interactions of strings, and that there are multiple universes or dimensions beyond our own.

3. How has String Theory been tested so far?

String Theory is still in the theoretical stage and has not yet been tested through traditional experiments. However, some aspects of the theory have been indirectly tested through observations of the universe, such as the existence of extra dimensions and the possibility of multiple universes.

4. What are the potential experiments that could falsify String Theory?

There are several potential experiments that could falsify String Theory, including finding evidence that particles are not made up of tiny strings, discovering more than three dimensions of space, or proving that gravity cannot be explained by the interactions of strings.

5. What would happen if String Theory is falsified?

If String Theory is falsified, it would mean that we need to rethink our understanding of the fundamental nature of the universe. Scientists would have to come up with new theories and frameworks to explain the laws of physics and the workings of the universe.

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