Still traveling, but will be back soon. This week’s bogus “test of string theory” is described in a NASA press release about three satellite-based experiments that would look for violations of the equivalence principle. From the press release:
…it [a violation of the equivalence principle] could provide the first real evidence for string theory. String theory elegantly explains fundamental particles as different vibrations of infinitesimal strings, and in doing so solves many lingering problems of modern physics… The equivalence principle could offer one way to test string theory…
“Some variants of string theory predict the existence of a very weak force that would make gravity slightly different depending on an object’s composition,” says [Clifford] Will. “Finding a variation in gravity for different materials wouldn’t immediately prove that string theory is correct, but it would give the theory a dose of supporting evidence.”
…string theory makes a range of predictions about how strong this new force would be, so it’s possible that the effect would be too small for even these space-borne instruments to detect.
Does string theory predict violations of the equivalence principle? From a posting on Lubos Motl’s blog:
In reality, it will probably be impossible to falsify string theory because string theory is probably correct and you can’t ever falsify correct theories. 😉 But if string theory were wrong, there would be thousands of ways to falsify it, even in the very near future. Although string theory predicts many new phenomena whose details are not uniquely known, it also implies that many old principles are exactly valid. If string theory is correct, the superposition principle of quantum mechanics, Lorentz invariance, unitarity, crossing symmetry, equivalence principle etc. are valid to much higher accuracy than the accuracy with which they have been tested as of 2006.
If you believe that string theory is wrong, just prove any of the theories predicting all the bizarre phenomena like Lorentz symmetry breaking, breaking of unitarity, locality, rotational invariance, and so on. I think that all these things are badly motivated – but it’s mostly because I know that it seems that they can’t be embedded in string theory. If you don’t believe string theory, you should believe that anything can occur and every new test of Lorentz invariance has a potential to falsify special relativity. Every new test has a potential to falsify the equivalence principle. And there are dozens of such examples. Without string theory, all these laws are approximate accidental laws and symmetries. I assure you that string theory will pass every new test of this type and its foes will always lose. String theory allows us to redefine what proposals about new physics are reasonable and what proposals are not, even without the exact knowledge of the vacuum.
I guess it’s all right that I don’t have time to comment on this, since no comment seems necessary…
This paper from a 2005 conference on tests of the Equivalence Principle has a table (table I, p. 3) showing some experimental limits on deviations from the E.P.; briefly, these are – neutral bulk matter: 10^-12, atoms: 10^-9, neutrons: 10^-3 and charged matter (electrons): 10^-1. I guess that the new experiment (STEP) will be able to bring the “neutral bulk matter” limit down to 10^-17 – or not, depending on what it finds.
The neutral bulk matter tests involve systems where the electrical charges are in balance to a much greater extent than one part in 10^12, and I wonder whether one could not just say “case proven” here and concentrate on the limit for charged matter instead. Such experiments, though, seem to be hard to carry out as they require the measurement of tiny deflections of single electrons due to gravity. See here, for example.
‘I guess it’s all right that I don’t have time to comment on this, since no comment seems necessary…’ – Peter Woit
Glad that you are not wasting time on fruitless arguments.
Lubos is correct. Physics proceeds by asserting a theory is true and must be believed until it is disproved. Even when the theory is disproved, you must continue using it until a better theory comes along. It is very arrogant of certain people to assert that a person’s defense of extradimensional dogma isn’t physics. You must first prove string wrong, and provide the correct theory to go in its place.
anon, it should go without saying that what you’ve said is nonsense. Science doesn’t proceed via theories that -cant- be disproven nor bring much to the table.
I’d say a theory can’t be taken seriously unless it can propose a way in which it could conceivably be disproven, even if it has some amazing utility and explains many things. Unfortunately string theory fails all 3 of these tests so it’s even more useless than a generally unfalsifiable theory.
annon is obviously nothing but a troll.
Don’t waste time answering him.
‘There is an unwritten precept in modern physics… which states that in physics “anything which is not prohibited is compulsory”.’
– O. Bilaniuk and E. C. G. Sudarshan, Physics Today, May, 1969, p43.
You must first prove string wrong, and provide the correct theory to go in its place.
*Cough*. Gentlemen, it seems to me that the word you are looking for here is “sarcasm”.
Yatima, take the situation of the procession of the perhelion of Mercury, which was a weak point in Newton’s theory for centuries (it was eventually cleared up by general relativity).
The situation with string theory will be identical if it is found to disagree with experiments: you have to go on using string theory until a new theory comes along which reduces to string theory as an approximation. So even if it is experimentally ‘disproved’, we will continue to use string theory until we resolve the problem, which may take centuries!
However, as Lubos points out, it is more probable statistically that the landscape is not entirely false. Think of the 10^500 vacua as a lottery. Become a string theorist, and it’s like having 10^500 lottery tickets: you own virtually conceivable theory going. It’s a monopoly! 😉
I agree. Problem is: there’s every reason to suspect that ST will never be found to disagree, nor agree, with any experiment. That’s why it’s not (even) wrong.
I think it is stretching the term theory to call string theory a theory. Apparently wikipedia agrees:
http://en.wikipedia.org/wiki/Theory
“The term theory is occasionally stretched to refer to theoretical speculation that is currently unverifiable. Examples are string theory and various theories of everything.”
Also, from wikipedia,
“In physics, the term theory is generally used for a mathematical framework — derived from a small set of basic principles (usually symmetries – like equality of locations in space or in time, or identity of electrons, etc) — which is capable of producing experimental predictions for a given category of physical systems. ”
Where are string theory’s predictions? I don’t think string ‘theory’ is even a theory!
anon., I’m not sure if you understand how the scientific process works in physics, so let me just give you a quick run-down:
(1) Someone sees something and guys “Hmmm…why did that happen?”
(2) Another someone sets up a series of experiments and comes up with a bunch of data about what happened. Publish.
(3) A theorist sees this data and goes “Hmmm…I wonder if I can figure out why this happened…” Using existing theories, said theorist tries to explain the data.
(4) If every theorist decides “We dunno”, you start inventing a “new” theory.
The burden isn’t on experiments to falsify theory, it’s on theorists to try to come up with an explanation of an experiment using existing, thus far unfalsified, theories. String theory reverses the roles. Physics isn’t dictated by who has the cooler theory, it’s dictated by what God decided the universe should look like, and what the experimentalists consequently see.
“Physics … it’s dictated by what God decided the universe should look like, …” – Steve
Well, maybe your understanding of physics is about 500 years out of date. But thanks for your attempt to enlighten me 🙂
It’s interesting that a number of fairly eminent members of the general relativity community have made soothing overtures to the string community of late. Clifford Will and Thibault Damour are names to be reckoned with in the field of experimental tests of general relativity. I expect they believe variants of string theory can in principle be tested in the same way as Dicke’s scalar-tensor theory of yore. However, I fear they are getting involved in an elaborate and expensive version of whack-a-mole. They will be welcomed with open arms by a community desperate for external validation.
If correct theories are not falsifiable, then by Lubos Logic it follows that non-falsifiable theories must be correct.
I don’t know why string theory doesn’t just declare that it is all possible theories and then declare victory… It is getting close to that point now… another 10 years maybe and then they’ll do that.
String theory reminds me more of a Fourier series expansion that can fit anything than a physical theory.
Rick says
I’d say a theory can’t be taken seriously unless it can propose a way in which it could conceivably be disproven, even if it has some amazing utility and explains many things.
Isn’t it the case that any theory which has amazing utility can be disproved. If a theory doesn’t predict anything, then shouldn’t it be considered (like Borges’ Library of Babel) by definition useless.
I guess one should have expected Lubos to misrepresent the established usage (in discussions of the philosophy of science) of the word “falsifiable.” (Sigh…)
Great post. If Motl’s original text was absolutely hilarious, quoted in this context it’s irrepressible so… A masterpiece of polemical counterpoint…
This is wise and accurate. Physics proceeds via proof by assertion. Not only is no evidence required to demonstrate that any assertion made in physics confirms with observables, the very attempt to require evidence for any assertion in antiscientific and, indeed, anti-rational. The very essence of the rational skeptical mindset which characterizes the modern Western world is credulous belief in any unsubstantiated claim regardless of how many experimental observations it contradicts.
In other breaking new, the earth is cubical in shape, 12 = -1, and plogiston will soon replace gasoline in our cars, effectively ending the Peak Oil crisis.
Peter:
I hope this is not considered OT but it is somewhat related to the issue being discussed. Suppose someone wants to become a theoretical physicist. The person obtains a PhD at a good university with a well known advisor; then he/she is able to obtain several postdocs and finally he/she is able to receive a position at a top notch university or research center. My question is this: How does this person judge the success of their research career? By the number of papers published in PEER reviewed journals? By being a great teacher of up and coming other theoretical physicists? By obtaining research grants based on proposals reviewed by PEER occupied committees? By having their name appear in lay publications? Write a successful textbook or book for the layperson? Or win a Nobel Prize?
Other than the last criterion couldn’t everything also apply to say a person who desires to do research in say medieval Germanic literature?
Without some connection to the real world (RW) how does one define the success of one’s career as a theoretical physicist? Is it just PEER review?
Cecil,
If you manage to get a tenured position at a top-notch university, you’re more of a “success” as a theorist than 90 percent of the other people who got Ph.D.s in the subject. If you don’t consider that “success” you’re basically an insecure neurotic. Beyond that, once you have a permanent job allowing you to pursue what you want, all the different things you mention are possible things to work on and aspire to. Up to you to judge how well you succeed at what you try and do. Different people value different things, and the approval of certain very specific groups of ones peers is something different people care about to different extents.
I wonder if it is possible to concede a point to the string theorists: their theory is true and can’t be falsified. So why don’t we just move on. I don’t see the point of a theory which cannot be falsified. If a particular experiment can neither prove nor disprove a particular theory, then why even discuss the theory with respect to the experiment?
My daughter was required to design an experiment for her 8th grade science class. She decided to measure the some ill-defined difference between skimmed milk, 2% and whole milk, by bring the different samples to a boil. The measured variable was time to boil. If she were to claim that this experiment falsified string theory, how would a string theorist show that the experiment was not applicable?
Peter:
Thanks for the reply. But I was more interested in the research part of being a successful theoretical physicist. How does one judge that aspect of their career? After all discovering a new theory of nature does not happen that often. So in this age of ST, LQG and other estoric ideas how does one define being a “success” other than position? Which is usually governed by how your PEERS judge you.
I can’t contain my curiosity. What exactly does P.E.E.R. stand for?
Aaron,
I think it is “Person Expecting Endless Rubbish”
In other breaking news… 12 = -1
Ah, Z13.
When I clicked the link in “From a posting on Lubos Motl’s blog”
(which refers to http://motls.blogspot.com/2006/10/falsifiability-in-physics.html)
I arrived at http://www.physics.harvard.edu/~motl/crackpot-not-even-wrong.html.
I’m not familiar with string theory. But I am familiar with standards of civilized communication. Is this the famous Harvard university?
Cecil:
Medieval scholars designed ingenious ways to count the number of angels dancing on the head of a pin. No doubt, they earned respect from their peers, well-paid positions, and all that… at about the same time when Galileo and Giordano Bruno were grilled by inquisition, one of them quite literally. So, in those times “success” and “progress” were not synonyms. Do you think they are synonyms now?
ES:
That seems to be the issue.
I guess I need to be more more clear. If you are a theoretical physicist and do not contribute to a theory that makes connections to the RW can you be successful? Yes or no? Exactly what does a theoretical physicist do if there are data to support his or her pet ideas? You can teach, but what about the research? Or maybe theoretical physicist needs a different definition. (Of course I am not sure what a theorteial physicist actually does so maybe someone who is such an animal can define his or her job description.)
‘If you are a theoretical physicist and do not contribute to a theory that makes connections to the RW can you be successful? Yes or no?’ – Cecil
That’s the same as asking if string theorists are successes. Consider dictators who think they have the answer to everything, and suppress dissent. Fellow dictators may respect them, and financially they may be a success. That’s all that counts to them.
What would be a failure in their book is someone like Mallory who set off to climb Everest in 1924 and didn’t return. A ‘success’, in the dictator’s book, is a label attributed by others to someone who makes a vast fortune and acquires power and through that power, respect (though that may be respect through fear, rather than respect from genuine admiration).
Newton and Darwin both came up with their discoveries and held back from publication for decades until they had built up a convincing set of evidence to support them. They didn’t build careers on the back of revolutionary discoveries. Copernicus wrote his book when he was an old man. String theory is the very opposite of this tradition; it’s got no solid evidence yet it is deemed a popular success because it has acquired mainstream credibility.
Since money is always involved, I tend to see theoretical physics as a big fashion show. You can’t tell what is or isn’t successful before a substantial amount of time or generations have passed. I don’t think anybody can claim enough hindsight at present to carefully judge the situation in theoretical physics or the “success” of anything in a less relative way. Let the fashion show continue…and its models trip.
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