Comment by Steuard | Hacker News Reader

Comment by Steuard | Hacker News Reader

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I really don't agree with that conclusion, though I recognize that it's not far from the traditional definitions of science.

The point is, let's pretend for the sake of argument that this article's main idea winds up being absolutely true: imagine that someone produces a rigorous mathematical proof that any consistent physical theory that incorporates both quantum mechanics and gravity (general relativity) must be some variety of string theory.

Now, we live in a universe where quantum mechanics is an experimental fact, and we live in a universe where general relativity is an experimental fact (each within their own domains of experimental accessibility). Would it truly be unscientific at that (thus far imaginary) point to conclude that string theory was a correct description of reality? The only alternative that I could see would be to abandon the idea that mathematics is able to describe our universe at all. And that doesn't feel like science, either.

[Note: As a professional string theorist, I'm hardly a disinterested party. But it does mean I spend a lot of time thinking about this stuff.]

If GR and QM can be derived from string theory, but the base theory doesn't provide any extra prediction of its own or simplifies the other two theories, then what good does it serve? Can we at that point say it's a "correct description of reality" or just a clever mathematical trick?

> doesn't provide any extra prediction

But it does. It predicts extra dimensions and it predicts supersymmetry. However it might be that these are only visible beyond our achievable energy levels such that we cannot verify them. The goal would then be to find what other indirect (as in not actually observing the strings) feature string theory predicts, that is hopefully within our reach, and verify that.

So it is unfalsifiable unless it speaks more clearly? Well, make the effort.

I'm not really sure what your point is. People are making the effort, both experimentally and theoretically. The LHC had some minimal potential to discover supersymmetry, but it has not done so thus far. This does not suffice as a disproof, though, due to the low energy levels. Simultaneously, string theorists have long labored to find more indirect effects that could be detected.

"Make the effort" is like complaining that cancer hasn't been cured because people just haven't tried hard enough. It's one of the hardest intellectual problems the human race has ever faced.

Not exactly. I mean, claiming that the LHC had "minimal potential" after all the "we shall see when the LHC shows the data" is quite disingenious.

The "effor" has nothing to do with cancer and has a lot to do with the REAL WORLD we live in. Physics either talks about REAL experiments or is otherwise void of value.

There are lots of speculative nonsensical theories which can be brought up and have no relation to the real world. As long as they are not falsifiable, they are not Physics.

> I mean, claiming that the LHC had "minimal potential" after all the "we shall see when the LHC shows the data" is quite disingenious.

The potential for discovering supersymmetry through the LHC was indeed minimal. There is nothing disingenuous about that.

The LHC is conducting a vast number of experiments on a vast array of topics. Perhaps the main goal was to uncover the Higgs boson, which unlike supersymmetry could be disproved if it wasn't found by the LHC.

> The "effor" has nothing to do with cancer

It's an analogy...

> As long as they are not falsifiable, they are not Physics.

They are theoretical physics, though.

Again, I don't know what your overall point is. That we should just all give up and end theoretical physics right now for good?

The bottom line is that if you think people aren't putting in the effort, you're wrong. That's my my point here.

In that hypothetical it might be a reasonable conclusion, but it would still be an unscientific one, since it would depend purely on your understanding of a concept rather than empirical evidence. And this distinction would only matter to a philosopher, since the conclusion would have no practical implications either way.

I don't agree that it would be completely independent of empirical evidence. In fact, it would be relying on a vast body of empirical evidence: the century or more of data that has been collected to verify general relativity and quantum mechanics.

It would be an indirect conclusion, but mainstream physics is already filled with those (e.g., the existence of black holes).

Here's the problem: I could easily make up another theory based on quantum mechanics and relativity, with the same amount of empirical support (none). The trivial other theory would not be in the form of math, but pure math is not a sufficient condition for scientific theories like quantum mechanics and relativity, and there would be no other meaningful difference.

> I could easily make up another theory based on quantum mechanics and relativity [...]. The trivial other theory would not be in the form of math[...]

Can you clarify that at all? I honestly don't know how to reconcile your first sentence with your second one: you clearly mean something different by some of those words than I do, but I can't puzzle out what.

Are you suggesting that you'd make up a theory that said, for example, "The universe looks behaves according to quantum field theory in the following set of circumstances: [long list of conditions], and behaves according to general relativity in the following distinct set of circumstances: [other long list], and consists of a troupe of dancing angels under all other circumstances [including, for example, black holes and the early universe]." Because I'd hesitate to call that (or anything like it) in any sense a scientific "theory". It has zero explanatory power, because it's an archetypical example of "overfitting the data": it's a description of reality, not an explanation, and there is literally zero reason to expect anything that you used to fill in the gaps between the observed data to be true.

If that is the sort of thing you're talking about, then it sounds like your main claim is that there's no meaningful difference between that and (in our imagined case) a unique mathematical framework that gave rise to both quantum and gravitational observations as distinct limiting cases (while also making explicit claims about how the universe must behave in possibly-unobservable situations like black holes and the early universe). I don't really know how I would answer such a claim (if it's what you're trying to suggest), except to suggest an upgrade to a philosophical system that isn't deliberately obtuse. (I know that there is no a priori reason to expect the universe to have a mathematical description. But by this point, given the truly amazing success of those descriptions to date, the burden of proof really does have to rest on anyone who claims that those successes are just some sort of coincidence.)

My main point is that there is only one meaningful difference: the presence of the unique mathematical framework. This alone would not be sufficient to put that theory in the category of science.

Why? It comes down to the basic requirement that the theory should make some new and falsifiable prediction. Without that, the theory would at best be a mathematical unification (admittedly quite an impressive one). If using it isn't substantially better than using the older theories, all you've really done is invented a mathematical object that behaves like relativity in one context and quantum mechanics in another (and doing that without introducing loads of hidden variables seems to be enormously difficult). There is only something noteworthy and new in that mathematical sense. Is it interesting? Absolutely. Is it a scientific theory? Not really.

That is not the problem.

Any predictive unification of quantum field theory and general relativity will be mathematical in nature.

A unification which is not mathematical is guaranteed to never be predictive and to never aid in the construction of a unified theory which is predictive, because the problems to be solved here are indeed entirely mathematical (divergent integrals).

String theory is a unification which is mathematical. Its direct empirical support is indeed currently none. However, as Hawking stated, it remains the only serious viable theory of everything right now. Every other competing theory has been found to have serious intrinsic issues, let alone lack of experimental support.

People take string theory seriously not because it's some vague unification. They take it seriously because it solves extremely difficult mathematical problems. Even if it turns out to be wrong, it is fairly likely that the mathematical insight gained will be invaluable. Indeed, it has even led to at least one awarding of the Fields Medal for advances in pure mathematics, to Edward Witten.

Your point about the need for prediction is relevant, but string theory is currently in the class of ideas which have no prospect of making meaningful predictions anytime soon. You might want to argue that the mathematical formulation makes the possibility that this will change in the future more likely, but I honestly don't see how that follows.

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