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Why String Theory Is Not Science (forbes.com)
StartsWithABang writes: Earlier this month, a conference was held devoted to the question of whether untestable scientific ideas like string theory and the multiverse are actually science or not. While many opinions were stated and no one changed their mind, the answer is apparent: unless you're willing to change the definition of science to include "this thing that isn't science," then no, string theory is not science. It's a theory in the sense of a mathematical theory — like set theory, group theory or number theory — but it isn't yet a scientific theory. Of course, it could become science, but that would require that it actually do the things a scientific theory does: make testable predictions that can be validated or falsified.
What if their goal isn't to make a testable prediction that diverges from the current best theory, but merely to explain more elegantly what's already explained? Shouldn't that count as scientific progress too?
After all, heliocentrism didn't make any prediction that a sufficiently elaborate theory of epicycle couldn't explain, it merely stated that the equations of motion were simpler if you put the Sun at the center.
But that's not what string theory does. Instead, it predicts everything. No, not everything we have observed, EVERYTHING. No negative or positive finding tests string theory, it just suggests more knobs to twiddle. The one shining hope is that if we don't find supersymmetry, it is dead as a theory since it cannot accommodate a universe without.
It could be forgiven all of that if it made things more tractable, but it doesn't.
The condition for science is that it has to be testable in principle, NOT that it has to be testable within the limits of current technology. When Higgs came up with his theory there was no accelerator capable of testing it (although we did not know that at the time). So would that make the Higgs mechanism non-science until the 21st century when we built the LHC? Clearly not. So, unless String theory is completely untestable in principle, regardless of potential future technological advances, it is science albeit science which is currently impossible to test with current technology.
String theory is arguably not science not because it makes predictions we cannot test, but because it basically makes no predictions at all. Originally, when people realized the importance of 10-dimensional manifolds (i.e., of theories with 6 compact dimensions), there was a lot of excitement as people thought (and confidently said) that there would be one and only one suitable such manifold, which would have led to concrete (if maybe hard to test) predictions. But, now, there is a huge number (order 10^500) of such manifolds known, each basically allowing for a separate theory, and we have no idea which could be the right one.
Also, there is the pesky fact that predictions have been made about the foundations of string theory (that, for example, the LHC would detect the supersymmetric partners of existing particles), and they have not been born out by experiment,
Having said that, my personal feeling is that string theory is science, but science that is unlikely to be fruitful. Eventually, unless this changes, something else will come along, and it will cease to be the center of attention for theoretical physics.
The problem is that its equations are quite elegant and simple -- because its goal was to unify the fundamental forces... and by doing so, created so many variables, functions, and possibilities, you can describe just about any universe that might exist. Each particle exists in 11 dimensions with varying degrees of freedom -- and we have few hints at the shapes of those hidden dimensions. Pinning it down to our universe is hard -- really hard. Like 10 ^ 99 possibilities hard. And, there's still the possibility that it's wrong, but there are a very long list of possibilities to go through before they can figure that out. Even if they find one that matches perfectly, just because the math agrees doesn't mean it says anything about how the universe really works -- just that the math works.
But, say you want to describe fundamental forces -- easy... the equations for light, gravity, strong force, and weak force look identical in string theory except for a function tacked on the end -- same for particles and their properties. (Also, as the energy level reaches a certain point, the forces converge towards a point where they are all equal.... as if they are all aspects of the same force that split into different dimensions.)
The same sort of thing was done to predict the Higgs. Equations were written as if all particles were massless plus some function based on interaction with the Higgs. Without the Higgs, the equations were ugly and none of the equations for the particles looked alike, but factor in the Higgs, and they all fall beautifully into place as identical plus some Higgs function. So much was based on this math, that it was understood that it HAD to be right -- years before the particle from the field was discovered.
The irony is -- string theory is a bit like creating epicycles to make the Earth the center of the solar system in the sense that string theory was created to unify the forces -- and in doing so, necessitated the creation of multiple curled up dimensions. It made some things very easy by postulating something strange. Einstein described gravity as the curvature of spacetime, and this gave string theorists the initiative to do the same with the other forces. It may be right -- it's probably right... it looks right in how elegant the math is... but... there's no way to test it -- yet. The theory says more about what can be rather than what must be, so it'll be a while before it matures enough to be called true "science."
What if their goal isn't to make a testable prediction that diverges from the current best theory, but merely to explain more elegantly what's already explained? Shouldn't that count as scientific progress too?
An excellent question! Yes, more elegant explanations of existing phenomena are definitely a big part of science. The unification of electricity and magnetism is an example . But that unification led to new predictions that the non-unified models did not. Yet, even if string theory was able to make the same predictions as the standard model and no new predictions then, hell yeah, it is would be science. The problem is that it makes no predictions. Well, to be more accurate, it makes way too many predictions which is pretty much the same thing.
You see, explaining what has already been explained involves making testable predictions. String theory does not do this which is why it is not science. That doesn't mean it is worthless to pursue.
We don't see the world as it is, we see it as we are.
-- Anais Nin
Problem is, supersymmetry (SUSY) is the only theory that even attempts to explain why the masses of particles are as small as they are -- including the Higgs particle. Without SUSY, the Higgs, W, and Z bosons become nearly infinitely massive due to loops in their feynmen diagrams. It's the SUSY that cancels out infinities in a lot of equations to make the string theory results make sense.
Many expect SUSY particles (sparticles) to start showing up at a multiple of the Higgs mass -- say... close to the Higgs mass or an order of magnitude higher, but not much higher. Sparticles are a good candidate for dark matter, but they're unlikely to be detected by the LHC.
Also, we know that string theory can give the same answers as other quantum theories for known values... so it's not "wrong" so much as it's a different way to do the same math... but ST requires SUSY because it's a necessary result of the math. If you compute a universe that allows both bosons and fermions, then for each boson, there is complementary fermion and vice versa -- only SUSY predicts that they have the same mass, but clearly they don't -- so the symmetry is broken.
If no sparticles are found at higher energy levels, then someone will have to explain what's wrong with particle physics in general -- because the math works.... so, what is it about the math that is correct that we're incorrectly interpreting as reality? Even if string theory is discounted in favor of another theory... you can wipe out the theory, but not the math. The math is just a different formulation of a problem to get the same answer. If I say 3 + 2 = 5, and the 2 is the sparticle in my theory... then when we find sparticles don't exist, what the heck is it that I'm adding to 3 to make it 5 ?!?!? There must be some unknown physics that string theory is describing as super particles that may actually be something else we don't understand. We don't even know why the symmetry is "broken" in the current theory to begin with.