Desperately Seeking Superstrings?
1986년 5월에 PHYSICS TODAY에 게재된 논문 'Desperately Seeking Superstrings?'는 초초string 이론의 현황과 문제점을 소개한다. 초스팅 이론은 고에너지物理와 중력을 설명할 수 있는 가능성을 열어놓았지만, 아직 실험적으로 검증되는 예측이 없고 현재 사용 가능한 데이터를 통해 표준모델의 확장을 제시하지 못하는 한계점이 있다.
초스팅 이론은 10차원 우주론에서 초간속도로 propagate 하는 초월성 string 의 특성을 연구한다. 이론은 particles 와 그들의 속성이 무엇인지, 그리고 어떤 매개 변수가 존재하며 adjustable 할 수 있는지를 정의한다. 그러나 years 동안 dozens 명의 최고 학자들이 노력해왔지만, 아직 하나의 verifyable 예측이 없으며 앞으로도 유망한 것은 아니다.
기존의 표준모델을 기반으로 하는 QCD 이론은 nuclear force와 particle physics를 설명하는데 잘 작동하지만, 높은 에너지 scale에서는 이론적 계산이 매우 어렵다. 초스팅 이론은 이러한 문제점을 해결하기 위해 제안되지만, 현재로서는 high energy scale에서 applicable 한 실험적인 방법이 없기 때문에 이론적 진위를 판단할 수 없다.
결과적으로, 초스팅 이론은 아직 현실성의 가능성을 열어놓았지만, 아직 이를 뒷받침하는 experimental evidence가 부족하며, 앞으로도 such a theory를 development할 기회는 낮다.
영어 요약 시작:
The article "Desperately Seeking Superstrings?" published in Physics Today in May 1986 discusses the current status and limitations of superstring theory. Although superstring theory offers the possibility to explain high-energy physics and gravity, it lacks experimental verification and fails to provide a consistent extension of the Standard Model.
Superstring theory is based on the properties of supersymmetric strings propagating in ten-dimensional space-time, and aims to define what particles exist and their properties, as well as the parameters that govern them. However, despite years of effort by dozens of leading researchers, no verifiable predictions have been made, and it remains unclear whether the theory is a viable explanation for high-energy phenomena.
Quantum Chromodynamics (QCD) is a successful theory that describes nuclear forces and particle physics at accessible energies, but its application to high-energy scales is computationally challenging. Superstring theory attempts to address these limitations, but currently lacks experimental methods to test its predictions at high energy scales.
In summary, superstring theory remains an intriguing possibility, but its viability is yet to be proven by experimental evidence, and it may not be a fruitful pursuit in the near future.
Desperately Seeking Superstrings?
arXiv:physics/9403001v1 [physics.pop-ph] 25 Apr 1986Desperately Seeking Superstrings?by Paul Ginsparg and Sheldon GlashowPhysics Today, May 1986Why is the smart money all tied up in strings? Why is so much theoretical capitalexpended upon the properties of supersymmetric systems of quantum strings propagatingin ten-dimensional space-time?
The good news is that superstring theory may have theright stuffto explain the “low-energy phenomena” of high-energy physics and gravity aswell. In the context of possible quantum theories of gravity, each of the few currentlyknown superstring theories may even be unique, finite and self-consistent.
In principle asuperstring theory ordains what particles exist and what properties they have, using noarbitrary or adjustable parameters. The bad news is that years of intense effort by dozensof the best and the brightest have yielded not one verifiable prediction, nor should anysoon be expected.
Called “the new physics” by its promoters, it is not even known toencompass the old and established standard model.In lieu of the traditional confrontation between theory and experiment, superstringtheorists pursue an inner harmony where elegance, uniqueness and beauty define truth.The theory depends for its existence upon magical coincidences, miraculous cancellationsand relations among seemingly unrelated (and possibly undiscovered) fields of mathemat-ics. Are these properties reasons to accept the reality of superstrings?
Do mathematicsand aesthetics supplant and transcend mere experiment? Will the mundane phenomeno-logical problems that we know as physics simply come out in the wash in some distanttomorrow?
Is further experimental endeavor not only difficult and expensive but unneces-sary and irrelevant? Contemplation of superstrings may evolve into an activity as remotefrom conventional particle physics as particle physics is from chemistry, to be conductedat schools of divinity by future equivalents of medieval theologians.
For the first time sincethe Dark Ages, we can see how our noble search may end, with faith replacing science onceagain. Superstring sentiments eerily recall “arguments from design” for the existence of asupreme being.
Was it only in jest that a leading string theorist suggested that “super-strings may prove as successful as God, Who has after all lasted for millennia and is stillinvoked in some quarters as a Theory of Nature”?The trouble began with quantum chromodynamics, an integral part of the standardmodel that underlies the quark structure of nucleons and the nuclear force itself. QCDis not merely a theory but, within a certain context, the theory of the strong force: Itoffers a complete description of nuclear and particle physics at accessible energies.
Whilemost questions are computationally too difficult for QCD to answer fully, it has had manyqualitative (and a few quantitative) confirmations. That QCD is almost certainly “correct”suggests and affirms the belief that elegance and uniqueness — in this case, reinforced by1
experiment – are criteria for truth.No observed phenomenon disagrees with or demands structure beyond the standardmodel. No internal contradictions and few loose ends remain, but there are some vexingpuzzles: Why is the gauge group what it is, and what provides the mechanism for itsbreakdown?
Why are there three families of fundamental fermions when one would seemto suffice? Aren’t 17 basic particles and 17 tunable parameters too many?
What about aquantum theory of gravity? Quantum field theory doesn’t address these questions, and onecan understand its greatest past triumphs without necessarily regarding it as fundamental.Field theory is clearly not the end of the story, so something smaller and better is needed:Enter the superstring.The trouble is that most of superstring physics lies up at the Planck mass — about1019 GeV – and it is a long and treacherous road down to where we can see the light ofday.
A naive comparison of length scales suggests that to calculate the electron mass fromsuperstrings would be a trillion times more difficult than to explain human behavior interms of atomic physics. Superstring theory, unless it allows an approximation scheme foryielding useful and testable physical information, might be the sort of thing that WolfgangPauli would have said is “not even wrong.” It would continue to attract newcomers to thefield simply because it is the only obvious alternative to explaining why certain detectorslight up like video games near the end of every funding cycle.In the old days we moved up in energy step by step, seeing smaller and smaller struc-tures.
Observations led to theories or models that suggested further experiments. Thegoing is getting rougher; Colliders are inordinately expensive, detectors have grown im-mense, and interesting collisions are rare.Not even a politically popular “SuperstringDetection Initiative” with a catchy name like “String Wars” could get us to energies wheresuperstrings are relevant.
We are stuck with a gap of 16 orders of magnitude betweentheoretical strings and observable particles, unbridgeable by any currently envisioned ex-periment. Conventional grand unified theories, which also depend on a remote fundamentalenergy scale (albeit one extrapolated upward from known phenomena rather than down-ward from abstract principle), retain the grand virtue that, at least in their simplest form,they were predictive enough to be excluded — by our failure to observe proton decay.How tempting is the top-down approach!
How satisfying and economical to explaineverything in one bold stroke of our aesthetic, mathematical or intuitive sensibilities, thusdisplaying the power of positive thinking without requiring tedious experimentation! Buta priori arguments have deluded us from ancient Greece on.Without benefit of theexperimental provocation that led to Maxwell’s equations and, inevitably, to the specialtheory of relativity, great philosophers pondering for millennia failed even to suspect thebasic kinematical structure of space-time.
Pure thought could not anticipate the quantum.And even had Albert Einstein succeeded in the quest that consumed the latter half of his2
life, somehow finding a framework for unifying electromagnetism and gravity, we would bynow have discarded his theory in the light of experimental data to which he had no access.He had to fail, simply because he didn’t know enough physics. Today we can’t exclude thepossibility that micro-unicorns might be thriving at a length scale of 10−18 cm.
Einstein’spath, the search for unification now, is likely to remain fruitless.Having a potentially plausible candidate “theory of everything” does dramaticallyalter the situation. But we who are haunted by the lingering suspicion that superstrings,despite all the hoopla, may be correct are likely to remain haunted for the foreseeablefuture.
Only a continued influx of experimental ideas and data can allow the paths fromtop and bottom to meet. The theory of everything may come in its time, but not until weare certain that Nature has exhausted her bag of performable tricks.3
출처: arXiv:9403.001 • 원문 보기