**Ask a monkey a physics question thread**

[MadMojoMonkey]

That looks like a pretty good discussion, but I didn't read too much of it. You should read up on the "EPR paradox" to get an overview of what Quantum Entanglement is. I wrote a paper about it, so I can go on at length about EPR if you're curious.

The Standard Model is basically, "What we've figured out so far". It is the most widely tested collection of predictive ideas in the history of humanity. Its counter-intuitive elements of Quantum Mechanics have been so refuted and tested to the point that we now know that the predictions are accurate to something like 35 decimal places. No other predictive theory in history shows that kind of accuracy and precision.

It's hard for me not to say, "The Standard Model is what we know is right." However, that's no way to talk about scientific theories. We know that there is always a non-zero chance that they're incorrect, or incomplete. This openness to the revision of the Standard Model is its inherent strength. If anything is shown to disprove a part of the Standard Model, that disproved part is thrown out.


String Theories are nipping at the boundaries of the Standard Model. There is plenty that the Standard Model doesn't explain, or explains poorly. String theories are trying to find explanations that can make sense of the things in the Standard Model that are still incomplete.

String theories are taking the idea that particles behave like waves to posit that they look like waves because some physical thing is waving.
That makes sense to me.
They suppose the thing that is waving is a string of some sort with a thickness many times smaller than the diameter of a proton.
That also makes sense to me.
Unfortunately, there is no way to measure anything that tiny. Even if it's length spans the universe, the thinness of it makes it invisible to any known detection method.
So one problem with string theories is that their fundamental premise is unobservable.

Another problem is that in order to be included in the Standard Model, a string theory would have to make a prediction that is not made by a preexisting portion of the Standard Model. It has to provide "new" or "unique" insight into the nature of the universe to be added to the current explanation.

No string theory has yet predicted anything that is not predicted already and which is also observable.

There's no reason to assume that these theories will or wont come to greater fruition, but decades upon decades of work on string theories has not yet yielded new physics.

[wufwugy]

Another problem is that in order to be included in the Standard Model, a string theory would have to make a prediction that is not made by a preexisting portion of the Standard Model. It has to provide "new" or "unique" insight into the nature of the universe to be added to the current explanation.

No string theory has yet predicted anything that is not predicted already and which is also observable.

This is mainly the area I'm looking for clarification on. If string theory doesn't predict anything that isn't also predicted by the standard model, then how is it distinguishable from the standard model? If not, doesn't this make string theory the god of the gaps, where it kinda just makes stuff up about what can't be known?

[MadMojoMonkey]

If string theory doesn't predict anything that isn't also predicted by the standard model, then how is it distinguishable from the standard model?

First of all, there are many string theories, not just 1. Different theoreticians are taking different assumptions about the properties of the strings.

They're different from the Standard Model because they do not fully overlap. When a string theorist is doing his research, he first assumes physical properties of the strings. Next, he tries to show how strings with these properties would look like anything already described in the Standard Model. Then, he tries to see what else the string theory says.

So the idea that string theories are equivalent to the Standard Model is a misunderstanding. They only agree with the Standard Model in so far as the fundamental assumptions have been tweaked to force agreement somewhere.

Once the theorist can demonstrate that he's describing something physical, then he looks to see what else it describes. If it makes predictions that are at odds with the Standard Model in any way, that particular string theory is discarded.


So it's like the string theory starts out by tracing the Standard Model, then tries to color it in while staying inside the lines.

If not, doesn't this make string theory the god of the gaps, where it kinda just makes stuff up about what can't be known?

I don't think that a fair description. String theorists are not throwing up their hands and calling it "magic" or "god's work". They're working their asses off to try to find a portion of their theory that can be tested. They're not just throwing out some nonsense that can't be openly refuted and claiming to be the next Einstein.

String theorists are motivated by the fact that the Standard Model is incomplete. Not only is it incomplete, but also there's no clear hint as to which direction to hunt for the ideas that will complete it. The Standard Model is an open ended collection of ideas that explain a whole heap of a lot, and quite well. However, it doesn't explain everything, and has some glaringly frustrating omissions (like resolving QM with GR). String theories are guesses as to what the next step might be...

If anything, string theories are trying to chase down the God of the Gaps to kill it.

[wufwugy]

So it's like the string theory starts out by tracing the Standard Model, then tries to color it in while staying inside the lines.

How does it do this without making predictions?

So if I have you right, string theories are something like this: take all the math of the standard model, add more math, if it changes the standard model discard it, if it doesn't keep adding math. All the while making no falsifiable predictions.

I know I must be reading this wrong. I was struck by a comment in the reddit thread about how something posited by string theories and was supposedly proven (I think it was Higgs) was also posited by the standard model. This makes me wonder what string theories actually do. Could it be that anything predictable would just be a part of the standard model?

[MadMojoMonkey]

How does it do this without making predictions?

This is sticky, I know. String theories do make predictions.

So far, string theory predictions all fall into one of these categories:
A) The prediction is new, has been observed and the prediction is false
B) The prediction is old, has been observed and the prediction is true
C) The prediction is new, but can not be observed.

The compelling category for serious attention from the physics community at large would be
D) The prediction is new, and can be observed, but has not yet been observed.

If a string theory (or any theory) makes a prediction that falls in the D category, then that will be something to get excited about.

So if I have you right, string theories are something like this: take all the math of the standard model, add more math, if it changes the standard model discard it, if it doesn't keep adding math. All the while making no falsifiable predictions.

I don't know. In practice it might seem like that to a casual observer. It might even actually be like that at times to the theorist.

It's not about adding math. It's about adding a new idea.

Math is a tool of symbolic logic. It is invaluable to physics because the inductive and deductive statements you can make are all readily symbolized. So once you learn how the symbols interact, you have a time saving tool that when you give it (mathematics) a statement, it gives you back equivalent statements. Those return statements may or may not be at all intuitive, but they are always as "true" as the input.

As such, math is a great tool for physicists to use. The ability to generate equivalent statements from any input is why it's so amazing.

So it's not about "adding math". Except in the sense that adding an idea, then using symbols to describe the idea, then using math to manipulate those symbols.... that clearly involves using math... but the math is just shorthand for sentences, and sentences are just expressed ideas.

I know I must be reading this wrong. I was struck by a comment in the reddit thread about how something posited by string theories and was supposedly proven (I think it was Higgs) was also posited by the standard model. This makes me wonder what string theories actually do.

The Higgs Boson has absolutely nothing to do with string theory.

String theories hypothesize a substructure to all existing particles. String theories attempt to explain things which are observed and unexplained by adding the idea of a sub-structure. Specifically, that the substructure is unfathomably tiny strings, whose vibrations look like particles and forces.

String theory could offer an explanation for the sub-structure of a Higgs boson, but the Higgs boson was predicted without using string theory.

If a string theory could explain the whole of the Standard Model without error, and without predicting things that are "false", then that would be a huge thing.

It would mean that we have 2 seemingly equivalent frameworks to use as accurate descriptions. Which means that there would be a higher likelihood that strings are a valid description for the sub-structure of everything.

Could it be that anything predictable would just be a part of the standard model?

That's the idea. If the preexisting theories are shown to be less robust than a new theory, then the old theory is out and the new theory is in.

If a string theory effectively unifies all known matter and forces and their interactions into one single theory, then there's a great chance that theory's name would stick around.

[wufwugy]

If a string theory could explain the whole of the Standard Model without error, and without predicting things that are "false", then that would be a huge thing.

So is it true that all string theories so far have not been able to explain the current standard model without also positing things that are known to be false? Or have some created a framework that explains everything but isn't testable so there's no way to know? If not, what's the furthest that a theory has gotten? Like has there been unity of the four forces but only in an unfalsifiable way? Or has every unity of the forces done things like posit additional unknown forces?

Related question: is there a way to know if something is true based exclusively on the math? Or is it that math can operate within its own systems, so even a mathematical model that explains every known thing perfectly may still be false?

[BorisTheSpider]

Related question: is there a way to know if something is true based exclusively on the math? Or is it that math can operate within its own systems, so even a mathematical model that explains every known thing perfectly may still be false?

I'll wait for MMMs answer as far as the physics goes, but as an interesting tangent:

http://en.wikipedia.org/wiki/G%C3%B6...eness_theorems

http://en.wikipedia.org/wiki/Entscheidungsproblem

One of the themes of early 20th century mathematics was the attempt to prove that our systems of mathematics were internally consistent - that is to say, if we had a set of axioms and a system such as the natural numbers, that we could, in theory at least, prove that every true statement in that system was true, or that we could, in theory at least, construct a hypothetical "maths machine" that could take a statement and decide it's truth or falseness. In many ways, this parrallels newtonian physics - the idea that even if only in theory, we could predict/understand all the physical phenomena in the universe.

Both physics and maths turned out to be more subtle than was believed, physics with the discovery of relativity and quantum theories, and mathematics with Godel/Turing and the work done on computability/decidability and the discovery that, to state Godels theorem in the plainest way, if a mathematical system is internally consistent then it must not be complete (there must be things we can't state or prove within it), and that quite aside from that a system can't be used to prove it's own consistency.

[MadMojoMonkey]

So is it true that all string theories so far have not been able to explain the current standard model without also positing things that are known to be false?

Some string theories make predictions that are known to be false. E.g. if it predicted that an electron should have a mass of a star, that would clearly be a poor description. Most make predictions that are unable to be determined as true or false.

Or have some created a framework that explains everything but isn't testable so there's no way to know?

As far as I know, no string theory completely overlaps with the Standard Model... they don't even come close.

If there was a string theory that did "explain everything", then it would be of great interest.

If not, what's the furthest that a theory has gotten?

I don't really know. Not so far as to reconcile even one chapter of a physics book, much less all the chapters in all the physics books.

I'm not current in the field and people with PhD's in physics are working on these theories. When I do try to read them, I don't get far. I don't really speak the language enough to even figure out which little nibble on the edge of current theory they're attempting to elucidate.

Like has there been unity of the four forces but only in an unfalsifiable way?

Not to my knowledge.

Or has every unity of the forces done things like posit additional unknown forces?

I really don't know.

Related question: is there a way to know if something is true based exclusively on the math? Or is it that math can operate within its own systems, so even a mathematical model that explains every known thing perfectly may still be false?

I'd argue that the qualities of "truth" and "falsehood" only exist in math, and math-like logical systems. Without a rigorous logical framework, the ideas of true and false are meaningless.

Science is never true or false. Science isn't really concerned with truth and falsehood, just an honest account of observation. Which brings up a whole bonanza of questions.

If someone hallucinates something, observing it, does that mean it's "real"?
If something is observed by many... does that make it "real"?
If something is unobserved... can it be "real"?
Is a sense of shared subjective observation indicative of an "objective reality" that is observed?

Science can't even answer simple questions like those... so the idea that it's going to reveal some deeper truth about anything is, I think, off base.

The magic of math is that you can give it a statement and then work some mathemagic and return another statement. Whatever the truth of the input statement is identical to the truth of the output statement.