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Can String Theory Accommodate Inflation?
David Shiga writes "String theory is the leading contender for a "theory of everything" that could unite all the forces of physics. But a recent study suggests that it may be more difficult than scientists had hoped to square string theory with inflation — the widely accepted notion that the early universe had a period of especially rapid expansion. Some say this could even lead to the abandonment of either string theory or inflation, though no one is ruling out a possible resolution yet."
It is said that papers in string theory are published at a rate greater than the speed of light. This, however, is not problematic since no information is being transmitted.
Does string theory incorporate the inflation of meatballs and saucy noodles (i.e. strings) due to FSM?
"String theory is the leading contender for a 'theory of everything' that could unite all the forces of physics. [citation needed]"
Yet another post validating this argument
(yeah, yeah, it's old. So sue me)
I've never understood how string theory could ever be validated, except through funky math invented for the purpose. It's my understanding that if you enlarged an atom to the size of the universe a string would be about 50 feet long (about a planck length). How is that ever going to be testable in practice? From all I've read, the energy required is just not possible, ever.
Um...physics has completely turned upside down in the last century and has changed pretty dramatically over the last 20 years. What kind of remote island are you living on that you're so out of touch and think that 'different' approaches never get funding? If you've never bothered to look at current research then you really don't have any right to speak, and it's obvious that you haven't. For example there has been ongoing debate for many years now between people who are searching for dark matter and proponents of MOND. There's nothing more annoying than pontification from ignorant armchair physicists.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
This is a vindication of us old school proponents of char* theory.
Momentarily, the need for the construction of new light will no longer exist.
no one is ruling out a possible resolution yet.
Ah-hem, I am. Please let the record reflect that I was the first to do so.
done. wake me up when there are more scientific milestones up for grabs.
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The fact is that what string theory aims to explain (the very fundamental nature of the universe; the events just after the big bang; the reconciliation of quantum mechanics and general relativity) are effects that are inherently difficult to measure. (Otherwise these questions would have been asked long ago.) The fact is that we are not yet able to measure at the extreme energies where string theory becomes relevant. So, the fact is that string theory does make predictions, but it is difficult for us to test these predictions yet.
Efforts are being made, however. Increasingly sensitive measurements of large-scale cosmological phenomena, and ever-more-powerful particle accelerators may give us experimental information about string theory. Already, in fact, a wide variety of "string theories" have been discarded because they do not match the accelerator data. That is, we are placing bounds on the theories, based on experiments. This is how science works.
Also important to keep in mind is that string theory meshes with our currently established theories (which, it goes without saying, have been verified experimentally to a very high precision). The agreement is not yet perfect (as TFA points out), but it's important to keep in mind that of the millions of crazy theories you could write down to explain "the universe," very few of them can reproduce more conventional theories (e.g. electromagnetic interactions) in the appropriate limits. The fact that string theory meshes with established knowledge is the thing that keeps physicists "hopeful" that they are going down the right track. That doesn't mean the theory is right, but it shows that it fits in with our current scientific understanding. That's how science works: by developing more detailed theories that nevertheless reproduce the more basic theories. That kind of exaggeration isn't very useful. Ultimately string theory aims to explain the universe through verifiable (falsifiable) predictions. These observations are difficult to make, but are being attempted. If the observations contradict string theory, physicists will discard it. If a better theory comes along that explains observations, physicists will gladly use that theory instead. Until that happens, there is no reason to ignore our current "best guess."
String theory is the leading contender for a "theory of everything"
Actually, not it's not. For this to be the case, it would have to predict something that is experimentally verifiable. Which has yet to be the case. All it is now is some really messy math. And even that's giving it something b/c most of it is the typical hand-wavy (read: non-rigorous) "math".
Quite frankly, the only good thing that I see here is that there might be an end to String Theory a.k.a. the "theory" that sucks up most of the money for research even though more than 3 DECADES have gone by without /one/ bloody experimentally verifiable prediction. Perhaps after this is all said and done with, we can spend some money on some actually *promising* areas of research.
String theory isn't science, but it isn't religion either. It's math. Someday it may become science.
Damning string theory is a bit like damning Reiman Calculus was in the 1890's. It was of no existing use. Eventually, though, Einstein found a use for it. That may happen with string theory. Or, of course, it may not.
It is interesting that the math can be mapped onto what is known about the universe. That makes it interesting. But it can't be tested, only particular mappings can be tested. So it's math rather than physics.
I think we've pushed this "anyone can grow up to be president" thing too far.
Dark matter is certainly a bizarre hypothesis, and the question you ask is natural - couldn't we just be wrong about gravity? It's somewhat easier to believe that Einstein's general relativity is modified than that the universe is filled with so much mysterious, unseen "stuff". This is the basic idea behind MOND (MOdified Newtonian Dynamics) theories, which has received a good bit of thought among physicists.
MOND doesn't look like the right solution, however. The last 2 or 3 decades have provided an enormous amount of observational data about the structure of the universe (large scale structure, galactic dynamics, gravitational lensing, light element abundances, the cosmic microwave background...), all of which is basically consistent with the simplest dark matter model ("cold dark matter") and inconsistent with any modified gravity theory. We don't need to imagine any particularly exotic properties to the dark matter, it just needs to be something that doesn't interact with electromagnetic forces (just like a neutrino only much heavier). Even very complicated MOND models fail to match observations, however (unless you add in a bunch of dark matter anyway).
Perhaps the most striking example is provided by observations of the Bullet Cluster last year. Basically we've found a pair of colliding galaxy clusters where the collision has separated the dark matter from the ordinary matter somewhat. Skipping over the details, this provides dramatic evidence that dark matter is real "stuff" - in essentially any modified gravity theory without dark matter, the gravitational forces still have to be coming from the same place as the visible matter! This is a very general argument, and observations like this have more or less put the nail in the coffin of MOND theories.
Astrophysicists are almost universally convinced at this point that something like dark matter exists. We're starting to map its distribution in detail throughout the universe, and the next major challenge will be determining its makeup - either by production in an accelerator or detection in dedicated experiments.
They'll just add 5 more dimensions.
___
If you think big enough, you'll never have to do it.
String theory should be discarded. It's a fanciful religion that explains nothing, but creates a lot of stuff that needs explaining.
It explains everything we have ever observed. However, this is not enough. String theory will not come into its own until it makes a prediction of a phenomenon we have NEVER observed before. Only then will it prove more useful than current theories.
Now, it's easy to construct a theory which explains everything ever observed -- simply enumerate the universe and say "that's it." But that's not what string theory is. Tomorrow, somebody could discover something in the math that actually makes a testable prediction about something we've never seen before. You have not asserted a single reason why this could not be the case.
I'm not a string theorist, but I am a cosmologist. Here are some thoughts:
Inflation has not been "confirmed" in away way. It's the best explanation for a very very limited number of datapoints we have on the "early" Universe. Very smart people (e.g., Sean Carroll, now at CalTech) have made convincing cases that inflation is actually incoherent in important ways. I have spent quite a bit of time trying to come up with alternatives to inflation, and it's damn hard -- it "works" very well, in the sense that it solves a bunch of problems all at once that are hard to solve individually. But it does invoke plenty of nonstandard physics we've never seen in the Universe, let alone the lab.
Inflation and dark energy are deeply connected. They both require something called "negative pressure". Negative pressure is bizarre, and actually is from a Newtonian perspective a violation of the conservation of energy (in General Relativity, energy is not conserved -- rather a complicated combination of numbers some of which refer to what we'd measure as energy is conserved.) Negative pressure means that if you take a box of the stuff, and let it expand, at the end of the day there's actually more stuff in there than you started with.
String theory should better be known as "a collection of approaches." It does not have the coherence of, say General Relativity, which is a mathematically closed system. Talking about "giving up string theory" is kind of dumb -- essentially what you are saying is "do not try to do the following large class of calculation." There are definitely competitors to string theory, but none have captured the attention of a highly fractious community the way string theory has.
Not sure if anyone's still reading this thread, but I'm happy to talk more about it. Reply with questions if you like!
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## BEGIN STRING THEORY JOKE I'm a frayed knot. ## END STRING THEORY JOKE
Some versions of string theory do make a genuinely interesting prediction. They predict a particle that hasn't actually been observed. A large class of the most studied string theories require adding just this one particle to the standard model, and it has to have spin 2, and mass 0.
That's a great candidate for a graviton, which is also being predicted for some other reasons. When some of the most aestetically interesting versions of string theory turned out to predict not just any particle or whole family of particles, but that specific one, many physicists got more interested in those theories.
However, general and special relativity don't actually predict gravitons - Einstein was able to treat gravity as a strain inherent in space-time and not as something mediated by a particle at all, and get some very testable results. Quantum Mechanics doesn't really require Gravitons either. Actual particle accelerator experiments have satisfied various symmetry theories from just the particles observed, and this again doesn't include gravitons.
There's no practical way to build an accelerator that could even theoretically reach the energies needed to test unification of all four fundamental forces, and gravity is the odd man out that we have no expectation will be integrated by either accelerator experiments or astronomical observations.
Proof of a mediating particle for gravity would still not prove any of the string theorys, but it would give the likelyest of them some fairly strong support. For now, we're stuck - a theory looks mathematically beautiful, and actually makes a prediction, but we aren't sure yet if that prediction is ever going to become testable, and on the other hand we have no categorical proof the prediction is fundamentally untestable. A test would be nice, but so would a stronger reason for saying there could be no test than just that we aren't yet a type 2 civilization, with the energy of a whole galaxy to use, so we are limited by the economics of it.
Who is John Cabal?