# Can supersymmetry be considered a falsifiable prediction?

1. Nov 22, 2015

### Smattering

Hello everybody,

Recently, I read this interview with Edward Witten where he claims that supersymmetry is a falsifiable prediction of string theory.

But then again, I remember interviews with proponents of supersymmetry where they were asked whether the inability to find any hints of SUSY in LHC experiments is a set-back for SUSY. And almost all of them replied that the LHC experiments only tell us that we have to search for SUSY at higher energy levels.

Now, I wonder if there is an upper bound for the energy level to look at such that the SUSY proponents would admit the falsification of SUSY when no hints of it can be found at this energy level. Because if there is no such bound, then the SUSY proponents could always just reply that we must search at higher energy levels.

So my question is: Can supersymmetry be considered a falsifiable prediction, and if yes, how can you falsify supersymmetry?

Best regards,
Robert

Last edited: Nov 22, 2015
2. Nov 22, 2015

### Dr. Courtney

I think you make a good point that a theory or hypothesis needs to predict outcomes of specific experiments in order to be falsifiable.

I would want to require proponents to describe the experimental details of a case that would falsify supersymmetry, complete with a range of energies where their theories predict it to manifest.

Testable theories can provide these details.

3. Nov 22, 2015

### haushofer

I think with Susy it's not a matter of direct, once and for all, falsification, but a matter of credibility. It's an interesting question, maybe Richard Dawid's writings are useful for you.

4. Nov 22, 2015

### Smattering

Yes, that's exactly what I meant. Thank you for expressing this in a clearer way than I was able to.

5. Nov 22, 2015

Staff Emeritus
I wouldn't call supersymmetry a theory. I would call it either a framework for creation of theories or a property that certain theories have. The individual theories produced under the framework can be falsified, but how do you falsify a framework?

6. Nov 22, 2015

### Staff: Mentor

If you consider it a property of certain theories then it should be falsifiable as property and thereafter the theories based on it.
But wouldn't this imply non-existence of s-particles? And non-existence is hardly to verify.

7. Nov 22, 2015

Staff Emeritus
Not necessarily - the prediction may be well beyond experimental accessibility. A theory that there is a single licorice gumdrop in the center of the earth makes a prediction, but not one that is useful.

8. Nov 23, 2015

### Smattering

As mentioned in the original post, Edward Witten claims that supersymmetry is a *prediction* of string theory. So in the context of this thread, susy should be treated neither as a theory nor a property, but rather as a *prediction*. And a prediction which is not falsifiable would be worthless, wouldn't it?

9. Nov 23, 2015

Staff Emeritus
Superstring theory predicts SUSY. Superstring theory does not predict low-energy (i.e. experimentally accessible with today's technoology) SUSY. Those are facts. You can draw whatever philosophical conclusions about what is a real prediction you would like on that.

10. Nov 23, 2015

### Smattering

Predicting SUSY without specifying an upper bound on the energy level at which it can be observed is like predicting the apocalypse without specifying when it will happen.

By the way, here is the Witten quote I was referring to:

http://www.pbs.org/wgbh/nova/elegant/view-witten.html

So he definitly claims that SUSY is a *testable* prediction. In order to be testable there must be a way to disprove a prediction. Do you agree?

11. Nov 23, 2015

### Demystifier

According to string theory, the upper bound for SUSY is the Planck energy.

12. Nov 23, 2015

### Smattering

O.k. that is a word. Then, the upper limit for the apocalypse is when the sun becomes a red giant?

But if upper bound for SUSY is the plank level, we could just skip this detour and say that string theory predicts string-like particles at the plank length.

13. Nov 23, 2015

### MacRudi

very interesting interview. Thanks!
All famous physicists have basic principles in their thinking. Einstein said: "Gott würfelt nicht", Hawking said: "There are no naked singularities, because of a cosmic censorship" and Witten says: "If Stringtheory is wrong, then there must be a cosmic conspiracy" lol
But Witten also said here in this interview:

Witten: "You have to be open-minded because ideas come from different places. You can think about something in one way for a long time and it seems like the only way to think about it, but it really isn't. Somebody could make a suggestion that really sounds naïve. It might even be naïve, but it could have an important element of the truth in it. And it could be truth that one's overlooking. So it's really hard to state a general rule. If one could say the general rule about where to find inspiration, we would just teach it to our students and then science would be much more straightforward."

If SUSY is really needed for a Stringtheory, I would not say so. For HIS M theory maybe. We started out first as a pure bosonic theory. It is not really a strict prediction, when we look at all stringtheories alltogether.
We are talking the whole time about a phenomenology of particle physics. This is only an interpretation, like it was with buildingblocks in the greek ancient times, when we predicted that all elements were build out of fire, water, air and dust. In philosophy we would say it is kind of hermeneutic in language. Lagrangian speech is only kind of hermeneutic and doesn't seem to prove as kind of universal language. We are talking in lagrangian language the whole 20th century but never found fundamental basics for masses in neutrinos e.g. or can really explain quasiparticles.
The whole thing in our mathematic as language is that we need to find the right mathematic as language. The universal language. All other mathematic, what we spoke as language in the 20th century was kind of dialect spoken in a local field surrounding, but not really as universal language. If we are trying to see that particle physics is only kind of hermeneutics as phenomenology then we would find a way to think in other dimensions.

14. Nov 23, 2015

### Staff: Mentor

It's getting philosophic here. When I think about the instances these game changing ideas occurred in former times it seems obvious to me that two crucial events have to come together: a genius able to disregard existing tight bonded structures of thinking plus time and space to develop his/her concept without the need to consult established and honored scientists who will nothing left untried to bring him/her off his/her path.

My outside view often gets me the impression that current models only arise as a result of try and error. One theory after another are considered just to find the holy grail. If SM is too restricted, no prob let's grad the whole thing. Still too classic? No prob, I have some exceptional $E_n$ in hand. Too small? Extra dimensions are easily available. What? Still problems with the geometry? You will be surprised what topology and co-/homology will provide to you! Or the physicists' way: Not enough energy? Pimp the collider!
I admit that is a very naive point of view. And maybe the truth will be found in any cage of this bizarre zoo of theories. To me it seems urgent that a fundamental new idea is needed, not another dimension, gauge group, cohomology or energy.
I do not doubt the framework in general. It's too successful to drop. But maybe the thinking in symmetries is too narrowing down the whole thing.

P.S.: Unfortunately I'm not that genius. But I'm not a trisectionist, either.

Last edited: Nov 23, 2015
15. Nov 23, 2015

### MacRudi

If we are talking about fundamentals of mathematics it is pure philosophy, because we talk about logic behind the thinking. Logic was and is the only way to find reality.
Lemma of Zorn is e.g. pure philosophy to say that we should think in this logic. It is needed.
The same is with all axiomatic systems.
But to come back to the origin question I would say that Lenni Susskind is more on the path for predictions to prove that Stringtheory has something to do with reality, when he says that if we find our Universe is an Anti de Sitter spacetime. How can we find it?
Easy. If we find galaxies older than our big bang, then we know, that we are living in an anti de sitter spacetime. It is not a paradox, what might most say but the right prediction and calculation of a AdS Universe. If we find this paradox then we can explain it with an AdS Spacetime. And with explaining AdS Spacetime it is not a paradox anymore.
Very easy. I think this would be the best testable prediction for Stringtheory.

16. Nov 23, 2015

### haushofer

Maybe this business of falsification and freedom to 'tune models out of current experimental results' is a hint we need a new principle or guideline to replace the symmetries-guideline.

17. Nov 23, 2015

### MacRudi

yes this is the actual debate behind closed door

18. Nov 23, 2015

### Smattering

But this "prediction" has the same issue as those mentioned before: It can hardly be falsified, because if you do *not* find galaxies older than our big bang, then I could always claim that you did not search for them at the correct location. Actually it is even worse: Since our Hubble volume is growing with each year, even after you searched the complete Hubble volume, I could always claim that we should just wait another thousand years and then search again.

The problem with all these "predicitions" is that they claim something to *exist*. So in order to refute them, you would have to prove that whatever has been predicted does *not* exist. But as everyone knows, an *empirical* proof of non-existence implies exhaustive search. So you literarily have to scan the entire solution space. And in case of a solution space that is infinite or grows with time, it is downright impossible. This is why I have serious doubts that the claimed existence of something can be considered a *empirically* falsifiable prediction at all.

It is quite funny: Physics had its roots in philosophy, then it went through an empirical phase that lasted for approx. 300 years, and currently, it seems to go back into the realm of philosophy.

But then again, in order to practice empirical science, your objects of investigation must be observable with the tools of your time. And probably, modern physics has reached a point where most of the things that can be observed with present tools, can be explained sufficiently by existing theories. Thus, theoretical physicists focus on objects of investigations that cannot be observed with present tools. And without a sufficient experimental basis, you simply cannot practice empirical science.

19. Nov 23, 2015

### MacRudi

Yes we have this problem like we had since the ancient scientists of the old greek. We have deductiv theories and look for their predictions. But this is normal. General Relativity was the same.
And the chance to find in the near future Galaxies, which are older than the big bang I would say is much better than to find any SUSY. We found now more and more Galaxies which cannot exist just after Big Bang. So we only have to wait and see, what we will find. The possibility is much better, because our Telescopes are really classical instruments that are technical better and better. And we can find it very classically.
SUSY is only a construction out of a Lie Group, which cannot be found, because there are so many IFs and then, that we can only hope, that this theory behind it, has something to do with reality. (I have many doubts, and don't believe in it) Think of Higgs and Hierarchy Problem and so on.

Last edited: Nov 23, 2015
20. Nov 23, 2015

### Smattering

O.k., now you have drawn my interest. This might be a bit off topic, but why does AdS imply galaxies that are older than the age of universe as calculated by us? And what would this actually mean? Wouldn't it just mean that the universe was older than currently estimated?