6 ms·
Why String Theory Is Both a Dream and a Nightmare
- m4r35n357 7y agoThe answer is yes. Now what is the question? BTW article paywalled; - DR.
- papreclip 7y ago"only makes predictions that can't be tested" has always placed string theory outside the realm of science in my mind
- tzs 7y agoDoesn't that make what is or is not science somewhat up to chance? Suppose you develop a theory in order to explain the known results of experiments K1, K2, and K3. You have tuned any tunable parameters to make sure you theory is right for K1, K2, and K3. Then you calculate what results you would expect from your theory in other situations, S1 and S2. S1 and S2 were not taken into consideration when you developed the theory. It seems strange to me for whether or not your theory is "science" to depend on whether or not someone happens to have already looked at S1 and S2. Suppose on Earth the correct results for S1 and S2 were already known when you developed your theory. Then we discover there is intelligent life on Mars and their scientists have developed the same theory at about the same time, but no one had ever looked into S1 and S2 there until after the theory called attention to them. So the theory is not science on Earth but it is science on Mars? Does it cease to be science on Mars when we inform them that we knew the correct results for S1 and S2 before anyone on Earth or Mars developed the theory? If someone had come up with General Relativity in 1680, a few years before Newton's Philosophiæ Naturalis Principia Mathematica was published in 1687, would Newtonian gravity have not been science? (I'm assuming that at the time the small differences between Newtonian gravity and GR would be below what they could detect experimentally).
- papreclip 7y agostring theory doesn't have experiments. that's my point
- btilly 7y agoWhenever science proceeds in advance of experiment, it becomes religion. When people's careers are dependent on others taking their ideas seriously, they will proselytize regardless of evidence or lack thereof. I don't mind that people enjoy string theory. I do mind that we offer research positions into it, tenure, grants, and everything else that goes with it. And spend literally billions of dollars on equipment for ever more ambitious experiments that have turned up nothing. The history of science shows that money spent on research is repaid to society many fold. However there is an element of prepared serendipity. Many small grants for many small lines of research are much more likely to produce useful results than a few mega-projects. If half of what we have spent on particle accelerators was spread out across fluid dynamics, condensed matter physics, and other areas where there are a lot of open questions that are amenable to experiment, how much greater would the returns have been? If you doubt me, consider this. We spent around $5 billion on the LHC. Its signature success is the Higgs Boson. Which came out basically to what theory said, and measurements of which narrowed down a few parameters of the Standard Model. CERN is already laying plans for the successor, which will cost several times as much. There is nothing that has happened in the last 50 years which provides evidence that it will find any new particles. How many people can intelligently describe what the Higgs boson is? An intelligent description should include what symmetry breaking is, what the Higgs boson has to do with it, and why the standard model has so many free parameters. Of those people, how many can actually explain what we have learned about the rest of the model from the research at the LHC? Of those people, how many can explain how this improved understanding affects any observable macro phenomena that affects technology? Would it make sense to scrap the planned particle accelerator, and instead give $1 million to every person who actually understands the Standard Model and current research to devote their lives to something else? I admit that it sounds crazy. But I'd take an even money bet that we would both save money and see more useful returns on investment if we took that crazy course.
- tomatocracy 7y agoYes. The primary issue with string theory I have is that it seemed for a long time to suck in large numbers of very talented theoretical physicists because it was a fashionable field - I saw many contemporaries of mine who went into theoretical physics go down this route. It's not just experimental physicists and the big budget costs that comes with particle accelerators. Theoretical physicists of course cost a lot less than the LHC but they are quite a scarce resource nonetheless - especially very talented ones - and I wonder what could have been achieved had many of them been working in different areas of physics or even in different fields altogether.
- miscPerson 7y agoIt seems to me that string theory was the right idea, wrong implementation. After all, Microsoft is building their quantum computing efforts around TQFTs, which are essentially what string theory is about — “(quasi)particles” are a tangle of the underlying field, and interactions are the results of those tangles interacting. I’m pretty sure we’ve measured anyons and other quantum vortex knotting behavior in everything from photons to matter waves. Then loop quantum gravity is trying to implement many of these same ideas, to reduce all of it to different tangle modes in the same field.
- lidHanteyk 7y agoI've recently enjoyed a lecture series on string theory [0] and it seems to me that string theory is primarily a series of observations and thought experiments. The original context of string theory was in the understanding that, if we are exploring quantum mechanical ideas about waves and particles, then mathematical ideas about strings and waves can be used to simplify some of the computations. String theory does not need to be connected to the heart of group theory [1], although it might be. It doesn't need to be connected to 26 dimensions [2] or 10 dimensions [3][4], but we know that [1][2][3][4] are deeply connected already, and so if it relates to any of them, it must relate to all of them. We should be careful about the degree to which we get "lost in math", I suppose, but only in that we need to avoid wrong-way reductions [5]. We should be careful to not let string theory lead us to generalizations that are beyond experiment. As the article says, we have falsified some of the low-energy predictions of some string theories [6], and we should continue designing experiments that can challenge theoretical predictions. [0] https://www.youtube.com/playlist?list=PLA2FDCCBC7956448F https://www.youtube.com/playlist?list=PLA2FDCCBC7956448F [1] https://en.wikipedia.org/wiki/Monstrous_moonshine#Conjectured_relationship_with_quantum_gravity https://en.wikipedia.org/wiki/Monstrous_moonshine#Conjecture... [2] https://en.wikipedia.org/wiki/Leech_lattice#Applications https://en.wikipedia.org/wiki/Leech_lattice#Applications [3] https://en.wikipedia.org/wiki/E8_lattice https://en.wikipedia.org/wiki/E8_lattice [4] https://en.wikipedia.org/wiki/E8_(mathematics)#Applications https://en.wikipedia.org/wiki/E8_(mathematics)#Applications [5] https://meaningness.com/wrong-way-reduction https://meaningness.com/wrong-way-reduction [6] https://en.wikipedia.org/wiki/Supersymmetry#Current_status https://en.wikipedia.org/wiki/Supersymmetry#Current_status
- deleted 7y ago[deleted]
- chrispeel 7y agoI'm curious; what do physicists think of the use of quantum information theory as a tool that could shed light on quantum gravity? See Patrick Hayden[1] for one person trying this. He told me that his work using quantum information doesn't require string theory. [1] https://web.stanford.edu/~phayden/ https://web.stanford.edu/~phayden/
- 6gvONxR4sf7o 7y agoWhen people say string theory makes untestable predictions, do they mean: 1) The ways in which its predictions differ from the standard model cannot be tested, while the rest of its predictions match up with all tested physics thus far. 2) or, none of its predictions can be tested? People say it's untestable so it's not science, but that only really makes sense in scenario two. In scenario two, it still provides testable predictions that just happen to match other models too.
- blablabla123 7y ago> People say it's untestable so it's not science In that negative viewpoint it's still science, just another branch: Philosophy (Metaphysics) and still Mathematics of course ;-) No expert in String Theory, but the bottom line is that the strings are really small. (~ Planck Length) So directly measuring anything is not going to work. It's more like 1), but known predictions assumed by Standard Model are baked into the parameters.
- contravariant 7y agoRegarding (1), at this point I believe that String theory is still incomplete. It can make some broad predictions (parts of which might be more or less testable, but most will be in the Planck-energy scale), but so far it's proven difficult to fill in all the gaps and get something equivalent to the Standard Model. Basically you've got a few too many degrees of freedom and most of the predicted behaviour is well beyond the energy scale that we can reach experimentally.
- T-A 7y agoThe way I'd put it is 3) In its current state, you can get string theory to "predict" just about anything. The reason is the enormous amount of string theory vacua, each giving rise to different "laws" of low energy physics. You've probably seen the old estimate that 10^500 such vacua exist. That turned out to be a slight underestimate: https://arxiv.org/abs/1511.03209 https://arxiv.org/abs/1511.03209 Even if you try to narrow down your search to vacua with the same rough features as the Standard Model (types of particles and interactions) you end up with numbers like 10^723: https://arxiv.org/abs/1810.00444 https://arxiv.org/abs/1810.00444 (Disclaimer: what follows is a caricature meant to illustrate the magnitude of the problem, not a rigorous argument.) So in principle you can imagine performing lots of precision experiments to measure a bunch of quantities which can be derived from string theory, and then run through all those 10^723 vacua to see which ones match your data. It will take a while. Can you derive precise parameters of low energy physics from string theory vacua at a rate of one per second? The number of seconds since the big bang is less than 10^18. You do the math. And even if each quantity you measure can discriminate between two halves of the remaining search space, narrowing those 10^723 alternatives down to 1 will require more than 2400 such mutually independent quantities to be measured (10^723/2^2401 ~ 1). Alas, once you fix the rough features of the Standard Model, it has only about 25 free parameters. So, even given all the experimental data you need and eons to run your search, you will not be able to nail down one string theory vacuum as the one we are in (assuming that string theory is correct), if all you know about experimentally is the Standard Model. That only reduces the uncertainty about which string theory vacuum we are in to 10^723/2^25 ~ 10^715 different alternatives. You need to discover new physics at higher energy, to bring in more free parameters to use in your search. Something like 2376 (!) new free parameters. Only then will you be in a position to finally say that future discoveries in particle physics will be able to decisively rule out string theory (or not). Until then, whatever comes out of an experiment will just tell you that some vacua are out, but you will have plenty left.
- iamcasen 7y agoWhy not base physics on the idea that "particles" are just spherical standing waves with a high energy density in the center? The math is simple enough for electrons at least and explains enough of the standard-model paradoxes that it is compelling. People seem to have their fingers in their ears about all the known paradoxes highlighted in quantum mechanics. Makes sense to me that there is not a duality, it's just waves.