Is ST considered by mainstream physicists to be:
Pie in the Sky
A theory that’s worthy of more investigation
The real deal that we just can’t quite see yet, but coming soon.
From what I’ve read (not extensively) their are respected scientists who believers and who are nay sayers. I’m wondering where the scientific community as a whole stands on this issue?
On the one hand, it’s not a theory. A theory has to be testable, and the string model has so many free parameters and so few actual predictions (much less predictions at a realistically-testable scale) that the model can be adapted to match almost any experiment, so it can’t really tell us anything we don’t already know.
On the other hand, though, there has to be something that goes on when quantum mechanics interfaces with gravity, and problematic as the string model is, nobody really has anything better, either.
So we don’t really have a good answer, one way or the other.
I heard an interview with Michio Kaku on the Skeptics’ Guide to the Universe podcast recently. He was talking about M-Theory, which is apparently the most promising version of String Theory.
I don’t pretend to understand the physics, but he said that the common notion that String Theory was “untestable” was nonsense. He then went on to list at least five ways this could be done, all achievable in the near future (the LHC was involved in at least one of them).
Sorry for being unspecific, but I’ve no time to do a search on this.
Interesting article on this topic from Time magazine, The Unraveling of String Theory.
It’s difficult for the layman to judge what’s what when even physicists are divided.
Lee Smolin, one of the physicists referred to in the article, is one smart cookie. If he’s come down against string theory (as he clearly has) then it does make a person wonder.
Lee Smolin wrote the book on the subject The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next. It’s quite readable for something on a subject whose math even most physicists can’t get.
He’s a proponent of a rival theory called loop quantum gravity. That seems to be gaining in popularity.
Overall, though, string theory is still taken extremely seriously and this controversy seems to have energized its defenders into proposing more possible tests to get rid of that stigma of “untestable.”
When the Large Hadron Collider finally starts producing some results some of the proposed tests should get some real data and we might see some answers in the next decade. Yeah, I know, lots of “somes” and hedging going on in that sentence.
The Smolin book is good, as is the one by Woit - Not Even Wrong. You’ll find some very compelling arguments about the business and worthiness of string theory.
I’m sure when people call it untestable they mean it’s untestable today.
No, at least Smolin and Woit mean that it’s untestable even in concept. That is, any set of results from even purely theoretical experiments could be explained by some variation of string theory, which suggests that there isn’t really anyway to make falsifiable predictions with it.
This is just a way to say available data is lacking and that additional experiments will allow us to determine some of the parameters. The theory is only untestable if there are some parameters whose values can never be pinned down.
Quoth Petrobey Mavromihalis:
There are some variants of string theory which do predict plausibly-observable consequences-- One set of such variants predicts black holes at the LHC, while another (disjoint) set of variants might explain a certain type of mysterious noise at one of the gravitational-wave detectors, and if Kaku says that there are three other plausible situations, I’ll take his word on it. The thing is, though, even if those experiments fall through, all it means is that the One True String Theory isn’t any of those particular variants. And honestly, we don’t really have any a priori reason to favor those variants, beyond wishful thinking: Nobody would be really surprised if the scale of the extra dimensions doesn’t explain the gravitational hierarchy problem, or if the Universe isn’t holographic. Yes, in principle, if we can rule out enough cases, we can find the true one by process of elimination, but for the String Model, there are literally many googols of cases that need to be ruled out.
Quoth Exapno Mapcase:
Loop quantum gravity has many of the same problems as the string model, but less explanatory power. Both models would quantize gravity; the string model would also unify it with the other forces, while loop quantum gravity does not. We know for certain that there must be some way to quantize gravity, but it’s not at all a given that all the forces can be unified: Historically, the study of forces has tended towards ever more encompassing unifications (Archimedes unified gravity and levity, Maxwell unified electricity and magnetism, Glashow, Weinberg, and Salam unified electromagnetism and the weak force, and there are good indications that the electroweak force can be unified with the strong force), but it’s still possible that gravity really is different and can’t be unified with the others.
Personally, if I’m going to be taking a dose of snake oil, I’d rather take one that claims to cure as much as possible, so if I’m forced to choose, I reluctantly prefer the string model, but others prefer not to assume that gravity is unifiable without evidence, and so prefer loop quantum gravity.
I’d like to believe that gravity is quantized, but is there any actual evidence for it yet?
Just to be clear, quantizing gravity means that gravity is explained (in part, at least) by gravitons, right? Photon:Light :: Graviton:Gravity?
Not that it proves anything, but respected scientists at one time were dead set against Darwin, Walton, Einstein and practically every scientist that came up with a new theory. Sometimes they were right, often they were proven dead wrong. So it goes.
I spoke a bit too strongly, there. Let me rephrase that: The certainly exists some way to reconcile general relativity with quantum mechanics. There are no situations in the observable Universe at this time where both are relevant, so for practical purposes we can get away with just using one or the other (or neither) in any given situation. But conditions now are certainly such that a condition could arise where both are relevant. For instance, if you let a black hole evaporate, eventually (after a mind-bogglingly long time), it would get to a sufficiently small size that quantum effects would be relevant, and of course gravity is always relevant for a black hole. Whatever it is that happens to the black hole at that point, we can safely call it quantum gravity.
More or less, though a more precise analogy would be photon:electromagnetism :: graviton:gravity. That doesn’t really say much, though, since that’s pretty much just the definition of gravitons. Beyond that, we know almost nothing about gravitons or their properties .
Yes, and they were quite right to be dead-set against Einstein et al.-- That’s an essential part of how science works. The reason we pay heed to Einstein’s theories is that they have suffered the slings and arrows of outrageous peer review… And yet survived. The scientific community would be negligent in its duties to let any new idea off easily, and that’s true regardless of how good the new idea turns out to be.
No, it can also be untestable because the space of parameters is so large that even if one experiment pins down a few of them, there are still enough remaining degrees of freedom so that any result from any conceivable future experiment can also be fit to a possible set of parameters consistent with the parameters from the previous experiment…and so on and so on for any possible chain of experiments. The result is that you can’t test the experiment not because you can’t make any predictions, but that you’re theory basically makes every possible prediction. There is no test that you could make that could give you a result that would let you say “the theory is false”
This is what Smolin and Woit claim is the case with string theory. I have no idea if they’re correct or not, but I don’t think I’ve ever seen anyone refute their claims head on.
Good gawd
Is the “adjustability” THAT bad?
I would highly recommend reading this review by Sean Carroll, a real physicist. He reviews Smolin’s argument and disagrees with substantial elements, while acknowledging many of the problems with string theory. It’s really, really worth reading if you are interested in this topic, and it doesn’t require any physics background. It answers lots of the questions above - the adjustability of string theory, how respectable it is, etc.
KlondikeGeoff writes:
> Not that it proves anything, but respected scientists at one time were dead set
> against Darwin, Walton, Einstein and practically every scientist that came up
> with a new theory. Sometimes they were right, often they were proven dead
> wrong. So it goes.
Are you using the “They all laughed at Christopher Columbus” argument. It’s wrong. (Of course, in the case of Christopher Columbus, nobody laughed at him because they thought that the world was flat and he would fall off it. Some people opposed his first voyage because they knew it was too far around the world to get to Asia in a reasonably short voyage. Columbus was very inaccurate about the circumference of the Earth.) It’s hard to think of any major scientist who was strongly opposed when they first proposed their theories. Of course, in many cases other scientists pointed out (sometimes quite rightfully) that there were problems with their theories because they didn’t have sufficient evidence. Generally the scientific community came around reasonably quickly to accepting their theories once they got enough proof. No scientist laughed at the theories of the important scientists. They considered them carefully, often for decades, while they waited for evidence.
Incidentally, who is Walton? The only major scientist I can find named Walton is an Irish physicist named Ernest Walton, and I can’t find any evidence that anyone opposed his theories for any significant amount of time.
Most of that review amounts to arguing that loop quantum gravity is no better than string theory. OK, that’s a fair enough position to hold, and it’s certainly an area where sane, intelligent people can disagree, though I wish he wouldn’t lean as heavily as he does on the democratic argument (“string theory gets more support from the community, so we’re winning”). I will, however, take issue with this statement:
Of course the “proofs” in quantum field theories don’t meet the mathematical standard of proof. This is physics, not mathematics, so we use a physics standard of proof. QED is by all accounts a “realistic quantum field theory”, and it’s predicted a value for the gyromagnetic ratio of the electron which matches the experimentally-measured value to twelve decimal places: By the standards of any science (as opposed to pure mathematics), that’s about as close to a “rigorous proof” as you’re ever going to get. This is precisely the sort of thing we haven’t been able to get out of the String Model, Loop Quantum Gravity, or any other attempt at quantizing gravity.
