What experiment would disprove string theory?

Question

String Theory is often criticised as not falsifiable, i.e. that there is no experiment that can disprove it. Therefore, critics of String Theory often equate it to pseudo-science, etc.  

However, string theorists believe that string theory is falsifiable. 

So could we have a comprehensive list of proposed experiments which could disprove string theory? 

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Albert

Comments

I saw a comment (seems to have vanished) to one of the answers that the view, heavily thrashed out in Smolin's book, that ST assumes a flat background whereas GR clearly accounts for dynamically bending spacetime is a bit moot insofar that GR could be construed of as being in a flat background with some fancy additions. Did this comment have any merit - could Lee Smolin truly have been unaware of such an interpretation? Or could it be something kind of trivial like the curved manifold of a GR solution can be embedded in a higher dimensional flat space (Whitney embedding). Comments anyone?

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user WetSavannaAnimal aka Rod Vance

Answer 1

String theory should come with a proposal for an experiment, and make some predictions about the results of the experiment; then we could check against the real results.

If a theory cannot come with any predictions, then it will disprove itself little by little ...

The problem is that, with string theory, this is extremely difficult to do, and string theorists have year in front of them to go in that direction; but if in 100 years we are still at the same status, then it would be a proof that string theory is unfruitful...

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Cedric H.

Comments

While a fair point, I don't think this really answers the question, as it will not be a disproof. :/

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user BBischof

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Certain ancient Greek philosophers theorized that matter came in chunks - the word 'atom' is Greek if I recall. They were right though it wasn't until only 100 years ago anyone could be sure. So a long time passing without verification should not discredit an idea.

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user DarenW

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Albert, you must have made a mistake in clicking because you clicked at this comment - which doesn't answer any of your questions, and what it says, is also incorrect - and you labeled it as the "right" answer to your question. Could you please fix your mistake? Thanks, LM

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Luboš Motl

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-1 There is no content in this answer.

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Erick Robertson

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Downvote for not answering the question.

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Robert McNees

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@Georg - the ancient philosophers had some great ideas, but no means to really verify them. Atoms (and all the subatomic goodies) with any nonzero amount of knowledge of their structure weren't real science until around 1900, give or take. Sure, earlier there were some good arguments for the idea of matter being "chunked", coming in units, but that's such a general fuzzy idea, with limited predictive potential.

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user DarenW

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@Eric Zaslow - yes, that second comment is pure opinion. What I expect is that string theory will fail due partly to other theories (perhaps unthought of at this time) being more fruitful, partly due to loss of interest and dissatisfaction with unanswered questions e.g "what are the strings made of?" and "why is string theory defined by an action principle?", and partly due to deep mathematical troubles, like how renormalization troubles killed certain theories in the past. But I am guessing...string theory (M-theory et al) may die in more interesting ways than anyone can guess today.

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user DarenW

Answer 2

Disprove string theory by empirically falsifying a string theory postulate. No postulate can be defended or it need not be postulated. Falsify BRST invariance and string theories collapse. Falsify the Equivalence Principle (EP) and the whole of physics needs a rewrite. No measurable observable violates the EP. All continuous and most approximately continuous symmetries bow to Noether's theorems.

You need an observable (so you know it is there) that is calculable (so you know how much) but not measurable, that is an absolutely discontinuous symmetry - and a test for its divergent consequences. Are shoes different from socks when given a left foot? By how much, yours versus mine? Quantitative chirality is calculated in any number of dimensions, J. Math. Phys. 40, 4587 (1999) and

http://petitjeanmichel.free.fr/itoweb.petitjean.freeware.html#QCM
(
Solution optical rotations ignore atomic mass distribution)

Chop a pair of shoes into mm^2 pieces. Sort them left versus right. Chirality is an emergent property. It depends on scale. To test the EP against a pair of shoes, one would need a shoe built on the smallest possible scale - a few atoms - and rather a lot of shoes to sum to a measurable divergence. Physics cannot do that, but chemistry can.

If anything can break string theory (we cannot be smarter than Luboš, but we can be orthogonal) then

Two geometric Eötvös experiments. 0.113 nm^3 volume/α-quartz unit cell. 40 grams net as 8 single crystal test masses compare 6.68×10^22 pairs of opposite shoes (pairs of 9-atom enantiomorphic unit cells, the test mass array cube's opposite vertical sides).

DO NOT bet your grade on that! Betting a December Swedish dinner is acceptable, especially if its main course is surströmming,

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Uncle Al

Comments

String theory is rigorously derived. One CANNOT disprove it within physics. That does not mean it is true. It means an experiment outside Official Truth is required. 1) "Particle physics is not mirror symmetric - shouted down, PNAS 14(7) 544 (1928), pnas.org/content/14/7/544.full.pdf+htm 2) "Particle physics is not mirror symmetric - Nobel Prize - but not for the experimenter, Phys. Rev. 105(4) 1413 (1957), prola.aps.org/pdf/PR/v105/i4/p1413_1

This post imported from StackExchange Physics at 2014-03-30 15:55 (UCT), posted by SE-user Uncle Al

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chiral violations of the Eotvos sort, if nonzero, are infinitesimal compared to actual different mass violations of the equivalence principle. This answer is saying "do an equivalence principle test",  but massless scalars can violate EP, and even a non-null result of an Eotvos test does not have bearing on the question asked here. This does not answer the question, and it doesn't answer the question in a particularly maddening way, namely by not explaining itself properly. The experiment that is proposed above is to test equivalence principle violations between chirally reflected objects, a test which could concievably fail (at teeny tiny unmeasurable rates) simply because of Weak interaction effects changing the mass of the objects infinitesimally, and then a teeny-tiny Eotvos violation converting the mass difference and composition difference into an EP violation. The result is obfuscated compated to standard Eotvos tests which simply start with extremely different compositions right at the beginning.

The statement "Eotvos experiment detects violations of EP, and therefore violations of string theory" is correct, but is not the aim of the question.