Discussing Predictions of the LHC: String Theory, LQG, and Beyond

[Arituay]

Hello all. I am a layperson that is very interested in science. I am particularly intrigued with what results the LHC will produce and how they affect the various existing theories. I was thinking that a central thread that links to and discusses various predictions on what the LHC will find would be useful so that when results start coming out we can see how the predictors fared. I realize this thread might be a bit early since any results will trail the actual start of experiments by months or more, but I am feeling impatient.


Note: This thread is NOT for discussion/predictions of existential risks involving the LHC, there are other threads for that.


Below are portions of an article from Seed Magazine that lists various predictions for the LHC (I am unsure of the custom here on this forum regarding fair use, so I won't post the whole article in case that is considered bad form).

(it says I can't post urls until I have at least 15 posts, below is my attempt to at least get the text of the url into the post for reference purposes- just put dots in place of the spaces)
www seedmagazine com/news/2006/07/why_a_large_hadron_collider.php?page=all&p=y

Why does the Universe Expand?

It will be more than 30 years since last we explored really new high-energy territory in physics. With our previous record-holding accelerator, we moved from fixed targets to head-on particle collisions, and had a four-fold increase in energy. The LHC will give us another near 10-fold boost, bringing us to energies where all theoretical fantasies are possible. This large step is effectively enhanced by a huge increase (about 100-fold!) in luminosity—the number of head-on collisions per second of protons with protons. In effect, the reach of the LHC is the largest incremental increase in observational power in history.

The intensely luminous LHC will surely help us to understand what has become one of the most profound puzzles in modern memory—the accelerated expansion of the universe. LHC is a shimmering example of humankind's age-old need to explore new frontiers. The long-simmering concern over the weakness of Einstein's gravity may well be confronted. However, what is for sure is that the LHC, with its awesome reach, will answer all of our current astro-particle problems and—if history is any guide—expose new truths undreamed of in our philosophies.

—Leon Lederman, Nobel Prize winner, Fermi National Accelerator Laboratory

What Is Dark Matter?

For over 50 years, CERN has been a wonderful example of European collaboration. It is now a true "world laboratory," destined to be the focal point of interesting particle physics for at least the next decade. I'm hoping that it will clarify the nature of the particles that constitute the "dark matter" in the universe.

—Sir Martin Rees, Cambridge University, president of the Royal Society and Astronomer Royal

How Is Symmetry Broken?

One of the big mysteries of physics is why the electromagnetic and weak interactions, which are two of the main elementary particle forces, are so different. We literally see electromagnetic effects with our eyes in the form of light. On the other hand, it takes sensitive modern equipment to detect and study the weak interactions. Yet the modern Standard Model says that at a fundamental level, these two forces are on an equal footing, described by very similar equations (Maxwell's equations for electromagnetism, the Yang-Mills equations for the weak interactions). The difference between these two forces only arises from a process of "symmetry breaking," whereby nature spontaneously picks one force over another—even though fundamentally they are equivalent. The LHC will tell us whether this notion is correct, and if so, how it works.

Understanding how the symmetry is broken is the key to understanding how the weak and electromagnetic interactions are unified in nature. This is believed to be an important step toward understanding a broader unification of the laws of nature.

—Edward Witten, Fields Medal winner, Institute for Advanced Study, Princeton University

Why 26?

Our theory of particle physics has 26 pure numbers in it. Why do they have these particular values? How did the universe begin? Or did it?

—Max Tegmark, MIT, scientific director, Foun-dational Questions Institute

Is The Universe Anthropic?

I see only two possible outcomes of the LHC project—either there will be low energy supersymmetry, or there won't. If there isn't, I would expect that the minimal Standard Model will prevail. In either case, the Higgs particle—a still-hypothetical particle postulated in the 1960's—will be shown to exist, thus explaining the fundamental particles' masses.

The main conceptual issue is the one having to do with fine-tuning. Conventional wisdom that has prevailed since the early 80's is that the pure Standard Model requires ultra-fine-tuning to keep the masses of elementary particles, such as quarks and electrons, from being sucked up to the higher energy unification or Planck scales. (It's called the "gauge hierarchy" problem.) There have been several solutions proposed including technicolor and extra dimensions (really the same thing), but they don't look viable. Supersymmetry can prevent the gauge hierarchy disaster, which is indeed a disaster: Were it to have existed, it would certainly have precluded life as we know it.

Similar logic says that the cosmological constant should also be sucked up to some large scale, which would also have proved disastrous to life. At the present time, the only explanation for the size of the cosmological constant is the anthropic principle—the dreaded "A word" that means if the universe weren't as it is, we wouldn't be here to observe it. So for me, the big question is whether the gauge hierarchy fine-tuning is similar to the cosmological constant fine-tuning, or if it has a more conventional supersymmetric explanation. Either will be incredibly interesting.

—Leonard Susskind, Stanford University,
author, The Cosmic Landscape: String Theory and the Illusion of Intelligent Design

See the article for more predictions. What do you all make of those predictions? What do LQG and string theory predict will happen at the LHC?

 

[humanino]

Hi, and welcome to PF

First thanks for the link, very interesting. I guess everybody here will have its own preferences, but honestly it will be difficult to follow up from such great names !

Personnaly, I was very interested by the fact that Witten did not mention anything exotic, that Weinberg only says he hopes to see more than just the single neutral Higgs (worst scenario), and that Schwarz goes even further, stating he speculates nothing speculative will be found.

What about unparticles ?

edit

What do LQG and string theory predict will happen at the LHC?

Maybe the other thread on string/LGQ would have been better for that...

 

[sir-pinski]

First of all, I find it admirable that as a layperson, you are interested in and eager to learn about the latest developments in science, particularly in the field of particle physics. The Large Hadron Collider (LHC) is indeed a groundbreaking experiment that has the potential to revolutionize our understanding of the universe.

In terms of predictions for the LHC, there are several theories that are being tested, including string theory and loop quantum gravity (LQG). Both of these theories are attempts to reconcile the two pillars of modern physics - general relativity and quantum mechanics.

String theory predicts that at high energies, particles will not be point-like, but rather made up of tiny strings vibrating at different frequencies. This theory also predicts the existence of extra dimensions beyond the three spatial dimensions we are familiar with. The LHC will be able to test these predictions by looking for evidence of string-like behavior in the collisions of particles.

On the other hand, loop quantum gravity proposes a different approach to unifying general relativity and quantum mechanics. It suggests that space and time are not continuous, but rather quantized, meaning that they are made up of tiny discrete units. This theory also predicts that at extremely high energies, space and time will become "fuzzy" and no longer follow the laws of classical physics. The LHC may be able to detect these deviations from classical physics, providing evidence for loop quantum gravity.

Apart from these specific theories, the LHC will also be able to test other predictions such as the existence of supersymmetry, which could help explain the hierarchy problem mentioned in the article. Other predictions include the discovery of the Higgs boson, which is crucial for the Standard Model of particle physics, and the search for dark matter particles.

In terms of the predictions mentioned in the article, it is important to keep in mind that they are just that - predictions. The LHC may confirm some of these predictions, but it may also provide unexpected results that challenge our current understanding of the universe. That is the beauty of science - constantly pushing the boundaries and expanding our knowledge.

In conclusion, the LHC is a remarkable experiment that has the potential to answer some of the most fundamental questions about the universe. It is an exciting time to be interested in science, and I look forward to seeing what discoveries and insights the LHC will bring.