A couple of months ago, the Smithsonian magazine featured an overview of string theory by Brian Greene. This led the readers into a physics debate. Bart Adler wrote, "Maybe if it was falsifiable, string theory would have some hope of being helpful to science. Instead it looks more like faith-based mathematics, barely distinct from religious beliefs."
I heard somewhere that String Theory would be testable by a particle accelerator the circumference of the solar system.
I don't know exactly if I was correct. But anyway, I mentioned on a forum about Ancient Greeks ideas of atoms and that technology, such as a particle accelerator, wouldn't come around until much later to examine the idea quite thoroughly. Maybe it's just how the science cookie crumbles sometimes.
String theory at present is the mathematical exploration of the idea that particles are not zero-dimensional as in quantum field theory. Like many mathematical disciplines it has application outside of the area of original interest, and is interesting in its own right. While there is no experimental evidence that compels string theory to be a good model of fundamental physics, but to say it is without application in physics ignores that it leads to good physics: http://en.wikipedia.org/wiki/AdS/CFT_correspondence AlphaNumeric got his PhD on exploration of String Theory-related topics.
Sometimes some faith in science aspects is required. We assume the Universe to extend much further beyond our Hubble volume, we assume homegenity and Isotropy, most assume some life elsewhere at sometime, or someplace, based on the astronomical numbers available of planets stars and galaxies. Sometimes new observations mean our "scientific faith" must change. Lots of scientists are abhorred at the idea of faith in science. :shrug: I don't see any harm in it at all. I see it as totally different to the mindless faith of religions. String theory and its derivitives has many wise and professional adherents to it, due to the beauty [ although difficult] of the maths involved. Ed Whitten for one. Obviously the problem is of course that as yet we are unable to observe at such incredibly tiny levels. Who knows what the future holds though. "Anybody who has been seriously engaged in scientific work of any kind realizes that over the entrance to the gates of the temple of science are written the words: 'Ye must have faith".' Max Planck:
If we have learned anything from the kind of science that has withstood the test of time, it is that any science is only as certain as its most fundamental assumptions. The fewer assumptions, the more enduring the science. A great number of assumptions were required to justify the foundational ideas of string theory, many of them wrong, but it is not yet a total loss. Assume strings have only the dimension of time, and a wave energy content that can propagate in only one direction (the arrow of time). 4D space time only exists in terms of a superposition of the virtual energy foam of the vacuum in an infinitude of directions from any point through which it propagates. Space as we perceive it is emergent from energy and time. Fields are another dynamic of strings. SR and GR just drop out of these assumptions, complete with length contraction and time dilation, for both energy and matter.
We have to "have faith" that the physical laws of the Universe wil be the same tomorrow as they are today. As such, we have no reason to doubt they would be, but that "faith" doesn't make us religious.
If you use the speed of light as the ground state of the universe, that math should be much easier. The speed of light ground state was chosen because in our universe, matter is net converting to energy. We do not observe energy net converting into matter. Yet we prefer to set the higher potential (matter/inertial) as the ground state due to long standing earth centric traditions. What we observe from the earth, is like looking from the top of the mountain compared to the C-level. This results in hidden potential energy that has to be incorporated making things too complicated. All the forces of nature, release energy. This causes the potential in matter to return to C; ground state. While mass burn in stars converts mass to energy; C. This shows C is at lowest potential. Gravity will cause matter to clump, because this allows space-time to contract in the direction of a speed of light reference; toward the point-instant. To resist gravity, means one has to move away from the point-instant direction; opposite direction of the C reference. The expansion of the universe is also consistent with a C ground state. The expansion red shifts energy in the direction of infinite wavelength which has the lowest potential. The C ground state does not require any assumptions that are not consistent with basic observations. The simplicity is all roads lead to Rome.Both gravity and the expansion return to C leading to clumping of matter and the red shifting of energy to maximize the lowering of potential. The only wild card is the speed of light reference, as the ground state, takes time to get used to. We have developed higher potential reference physics that is set high in the mountains. This has a different view than being grounded at C-level. The net result is some variables disappear at C-level because the potential in the mountains is higher than at C-level. This does take time to digest. One can glide from the mountains to C-level but not from C-level to the mountain. The last point is the C ground state is not the same as an energy reference since even energy sets a potential with the C ground state; expansion. Energy moves at the speed of light, but it is impacted by inertial reference which can alter wavelength and frequency. These are inertial reference dependent. Energy has two legs, one in C and other in inertial, thereby acting as the bridge back to C-level. Dark matter and dark energy, based on the assumptions, would be between energy and C-level but too would set a potential with the ground state and may act as an intermediate between matter, energy, and C-level.
I recollect that article a bit. Even Brian Greene starting to sound like it's time to stick a fork in it, though trying to redeem the years spent in terms of interesting by-products having fallen out of the venture. Lee Smolin has recently been going on a tear railing against a variety of views and these quasi-metaphysical theories in physics. The irony there is that in the past he worked a small extent on string theory himself (when not consumed with loop quantum gravity), and even asserted there actually were ways to test it. Lee Smolin: [...] Now I want to talk about the problem of quantum gravity and the two best developed approaches that have been proposed to solve it, which are called loop quantum gravity and string theory. [...] The really important news is that there is now a real chance of doing experiments that will test the new predictions of these theories. This is important, because we're in the uncomfortable situation of having two well-developed candidates for the quantum theory of gravity. We need to reduce these to one theory. We can do this either by finding that one is wrong and the other right, or by finding that the two theories can themselves be unified. (Of course, the result of testing the theories could be that both of them are eliminated, but this would be progress, too.) [...] The idea that you could do experiments to test the quantum theory of gravity was mentioned from time to time by a few people through the 1990s, but to our shame we ignored them. One person who proposed the idea forcefully is a young man in Rome called Giovanni Amelino-Camelia. He just ignored everybody who said, "You'll never probe scales that small. You'll never test these theories." He told himself that there must be a way, and he examined many different possible experiments, looking for ways that effects of quantum gravity could appear. And he found them. Now we know more than half a dozen different experiments we can do to test different hypotheses about physics at the Planck scale. Indeed, in the last year, several proposals about Planck scale physics have been ruled out by experiment. The key thing that Amelino-Camelia and others realized is that we can use the universe itself as an experimental device to probe the Planck scale. There are three different ways the universe gives us experimental probes of the Planck scale. First, there are accelerators in distant galaxies that produce particles with energies much higher than we can produce in even the largest human-made accelerators. Some of these ultra-high-energy cosmic rays have been observed hitting our atmosphere with energies more than 10 million times those we have ever produced. These provide us with a set of ready-made experiments, because on their way to us they have traveled great distances through the radiation and matter that fill the universe. Indeed, there are already surprises in the data which, if they hold up, can be interpreted as due to effects of quantum gravity. Second, we detect light and particles that have traveled billions of light years on their way across the universe to us. During the billions of years they travel, very small effects due to quantum gravity can be amplified to the point that we can detect them. Finally, the postulated inflation by which the universe expanded very rapidly at early times serves as a kind of microscope, blowing up Planck scale features to astronomical scales, where we can see them in small fluctuations in the cosmic microwave radiation. -- LOOP QUANTUM GRAVITY, edge.com, Feb23, 2003
I read at least two Brian Greene's books on string theory, and I found them fascinating. I'm not a physicist or a mathematician so there was stuff I couldn't understand crystal clear, but from what I got, string theory came from the necessity to make General Relativity and Quantum Mechanics work...did I get that right? Edit: When they try to find out <insert special physics term> using General Relativity and Quantum mechanics, the result is infinite...which doesn't appeal greatly to what we're trying to solve right?
Indeed. The key difference is that between reasoned faith and unreasoned faith. As I have often written, my dog has been unswervingly faithful, loving, kind and attentive for ten years. On the basis of this mountain of evidence, it is reasonable for me to have faith that he will continue to be so. The religionists, on the other hand, base their assumptions on legends from the Bronze Age, when scholarship as we know it was rare and rudimentary, when written language was a new technology that was known only by a few and had not yet had time to accrete volumes of literature, and when argument by authority was a respected way of learning. It is utterly unreasonable for anyone in the Post-Industrial Era to have faith in assertions that have absolutely no respectable evidence and which, furthermore, contradict much of what we have already learned from the application of evidence-based science. But to be fair, I (at least) have never seen a scholar of any branch of science insist that string theory has been proven true beyond a reasonable doubt and therefore deserves a place in the canon of science. I'm quite certain that they all consider this hypothesis to be based entirely on some extremely entertaining mathematics supported by a lot of enthusiastic arm-waving. And as I said earlier, the one thing for which I criticize them is, precisely, their use of the name theory, when it is only a hypothesis. Furthermore, I suspect that the String Hypothesis belongs in that messy corner of science called "cosmology," where physics, mathematics and philosophy converge in a big mess. Sure. But he was talking about reasonable faith, as opposed to unreasonable faith, as I described at the beginning of this post. Scientists are welcome--in fact urged--to have faith in the scientific method, and in the work of those who adhere to it--in good faith. Please Register or Log in to view the hidden image!
In physics no theoretical model is ever proven. We do experiments to test theoretical predictions. The problem for string theory is we can't test it's predictions with existing experimental technology. So what rpenner said in post #6 is what most scholars would say about the theoretical model. Saying it isn't a theoretical model is nonsense. Calling cosmology a big mess is illiterate nonsense.
Isn't that exactly how you "prove beyond a reasonable doubt" the veracity of a hypothesis, elevating it to the status of a theory? Just having fun. There surely is a dollop of philosophy in it: we have to figure out just exactly what we mean by words like "universe" and "space." Is what we refer to as our "universe" merely a Hubble volume tucked away in a corner of an infinite space-time continuum, so there may be lots of other universes that happen to be so far away, or so far in the past or future, that we'll never have a way to know of their existence? Or is it a space-time continuum that came into existence with the Big Bang, and may go out of existence if one day it collapses in on itself, and there's literally nothing outside of it? Or are both of these descriptions wrong?
A physics theory is a mathematical model of the behavior of a wide class of related phenomena. A well-tested physics theory precisely describes the human history of all observed behavior of all such related phenomena, usually within state-of-the-art measurement tolerances. But that does not prove the theory because it's possible for competing theories to live in the error margins of our most precise experiments with measurable differences between the two only in extreme physical conditions or other places rarely observed with precision. Likewise, a model can only ever describe behavior of observable phenomena. It cannot speak to what objects fundamental in the theory "really are" or unevidenced metaphysical "mechanisms" that might further "explain" the behavior. That's usually where crackpots go wrong, thinking that there needs to be explanations all-the-way-down even when the evidence only supports a finite amount of explaining. Since a physics theory is a mathematical model of the behavior of aspects of reality, and one that is not and cannot be proved to be exact, in the mathematically sense of "prove" a physics model cannot be proven. But a wrong physics model may certainly be disproven by accumulation of evidence that it does not precisely predict a class of phenomena which should certainly be within its domain of applicability. A stronger way to disprove a wrong physics model is by demonstration that another physics model is always as good or better. Nothing succeeds like success. That's another point where crackpots go wrong, preaching the supremacy of their ideas without clear and convincing demonstration that they are viable, competitive or better physics models. So while you can prove a physical theory is reliable under all past observation regimes, and for many people that will be good enough to bet trillions of dollars on it being very-nearly correct for all their future plans, it does not necessarily mean that the theory is even the best we can do with human observations. Newton, Maxwell and Einstein are lauded because they got the big picture mostly right first, but that doesn't mean that they were always right or that their conclusions were readily apparent based on the evidence. --- Cosmology makes observations on the visible universe, which is a three-dimensional light cone into the distant past, and assume that the universe-as-a-whole is uniform at large scales. This assumption, which cannot be proven, is supported by observation in that a diligent search has revealed no evidence that the universe has a spatial edge. It does however have a temporal edge and evidence of temporal change, the details of which support a specific physical model predicated on General Relativity and Quantum Field Theory both being reliable for billions of years. Thus the "universe" contemplated by cosmology is the spatial extension of the visible universe, along with its modeled past and future. While the two physical theories are not mutually compatible, the large-scale changes in the universe don't require their cooperation except for a tiny part of the first second, where current physics really doesn't give insight. This Big Bang cosmology does not presume that the universe started from a point, but rather that the whole of the space of the universe was filled with hot dense matter in the earliest of times and in that hot, dense soup, the forerunner of today's visible universe was a patch of space smaller than a hydrogen atom. Thus, while black holes are said to have time-like (time-extended) singularities where our present limited grasp of physics is unreliable, the Big Bang was a space-like (spatially-extended) singularity. Because General Relativity is a theory about an intrinsic property of space-time, called curvature, which relates how distances and elapsed time measures compare within the universe, it is silent on the large-scale topology of the universe. So the cosmological assumption that the universe is without spatial edge is compatible with both infinite and finite (but very large) models of unbounded space, but such questions of does the universe fold back on itself cannot be answered within the framework of General Relativity which doesn't talk about curvature in some higher-dimensional superspace. Also, no matter the topology of the universe, the cosmological assumption that there is no spatial edge means there is no spatial direction in which we may point to "outside the universe." If there is an "outside" to the universe contemplated by General Relativity and cosmology, it lies in some unevidenced higher spatial dimension. String theory is compatible with our universe lying on a 3-dimensional membrane in some high-dimensional space, but as I said the idea is as yet unevidenced.
No. Our universe is our universe. Not just the visible universe. You may hear some multiverse quacks saying that kind of thing, but it's sophistry. The word universe stems from uni as in unicycle and verse as in vice versa. It means "turned into one", or "everything". It's a nonsense to talk about multiple everythings. Nobody knows for sure, but my view is that space is expanding, and beyond it there is no space. There is no beyond it. There is no outside of it. As for branes in higher dimensional space, rpenner said there's no evidence. I say there's no evidence for heaven and hell and sweet baby Jesus either. This is rubbish. It's quantum field theory, not quantum point-particle theory. The electron is said to be an excitation of the electron field. String theory is rubbish too. It's now discredited and on the way out. See Woit's blog.
