What we think it will do is based on the success of the indirect approach in science. Darwin's evolution by natural selection, for example, gained early acceptance because without it nothing much in biology made sense. Later discoveries including genetics and a detailed fossil record reaffirmed that what makes the most sense can often be true.
But one of the most famous examples of why indirect science is a valid approach in modern physics was also an example of a rush to debunk something that didn't need debunking - Newton's gravity. We're talking now about the discovery of Uranus.
Sir William Herschel announced the discovery of Uranus in 1781, the first discovery of a planet(1) made using a telescope (2) - but there was a problem soon after, namely that it didn't follow a path that gravity said it should follow. No less than Astronomer Royal George Biddell Airy intimated that Newton might be wrong - without a new theory of gravity , the orbit of Uranus did not make sense, he believed.
It fell to French mathematician Urbain Jean Joseph Le Verrier to disregard the need for a new theory of gravity. Instead, "with the point of his pen" meaning mathematics, he predicted there should be a new planet - now called Neptune. Newton wasn't debunked at all and Airy took some short term flak for causing England to miss out on the discovery, though he has been defended aggressively on this matter by his biographers and he also graciously accepted getting beat and did a lot of other terrific things, so none of this is a slap to him.
Urbain Jean Joseph Le Verrier
And so it goes with complex explanations sometimes taking the place of simple ones. In very large motion physics today, nothing makes sense in the universe unless some mystery force/energy/gravity/matter exists - the indirect approach says it must be so. The LHC will, the mass media claims, find the Higgs boson and also solve everything we can want to know. The one benefit to having breakdowns and delays are that people will get tired of hearing about it and physics can get back to business that goes beyond the hype - because the LHC may find nothing at all and I can contend that might actually be better than finding something and calling it a God particle.
Is finding nothing worth spending billions of dollars? Well, yeah. Of course, it's also European money, American congressmen not being willing to underwrite projects in physics that have no definable result, which makes it a little more palatable to many in America like me. Finding nothing in the LHC that can be called a 'Higgs mass' will mean a lot more for discovery than the canned, easy-to-label approach taken in getting the CERN project funded - even Sean Carroll at Cosmic Variance, who should know better, once predicted a 95% chance of finding the Higgs boson with the LHC, though that may just mean someone having to rationalize the budget so they will find something - anything - and call it just that.
So even scientists can get caught up in the promise of high energy physics.
But most scientists won't unless it is legitimate and that will be good, both for the LHC and for low energy physics too. I just knocked the indirect approach and now I am going to defend it because I have no loyalty at all to supersymmetry or Higgs but I have loyalty to finding answers. Sometimes the best answers arrive when you can't find that must be there - and the planet Vulcan(3) is an example.
Vulcan was theorized by Le Verrier, our discoverer of the mystery of the orbit of Uranus, because it had to exist. Mercury, like Uranus, was not moving as it should and followed up when an amateur astronomer claimed to have found something he originally thought was a sunspot; but sunspots don't orbit the sun every 20 days so a planet had to be somewhere in the vicinity of Mercury. Even experienced astronomers such as professor James Craig Watson of the Ann Arbor Observatory and Lewis Swift, who had multiple successes between them, confirmed seeing something they thought was a planet, though in a different place. So most astronomers still doubted the mystery planet despite the fact that nothing made sense about Mercury without one.
The indirect approach which had worked so successfully with Neptune was not as convincing with Mercury. Stating that Mercury's orbit could not exist if what we know about planetary motion is correct was not holding water any more - science had matured since Neptune so astronomers knew the science had to change.
Neptune's rings as taken by Voyager 2
Change it did. In 1915 Einstein explained the odd perturbations of Mercury using special relativity. The effect of the Sun's gravitational field was working on all planets but to a lesser degree farther away.
Had Vulcan been found, we would still have special relativity but with one less example of its awesome power.(4) So I am more interested in what will happen if we don't find this magic bullet of physics in the ground underneath Switzerland. It won't mean the money has been wasted, it will mean that we have a chance to break even more new ground with what we do know.
Likewise, there is a lot left to learn in low energy physics. Fermi lab's Project X, for example, is just the kind of thing that can be done using lower energy physics, just by upgrading the booster - in those physics frontiers of energy and intensity and cosmology, intensity can still add a lot to our understanding of the universe.
Either way, physics wins because we learn a lot about the universe even by discovering that something that should exist doesn't exist. And if something key is found using the LHC, it will require the future ILC to do precision studies of whatever that new thing is, so physics wins there too.
(1) It had been detected before but was assumed to be a star - first name 34 Tauri.
(2) It's also the only one to be named after a Greek God. The rest are Roman.
(3) It is unlikely Spock's homeworld was named after this mystery planet but that would be pretty cool.
(4) Mistakes can also make science better by optimizing it or even inspiring it. In 1846, Frederic Petit, director of the observatory of Toulouse, stated that a second moon of the Earth had been discovered - something Le Verrier did not like hearing much because of the lack of a way to account for air resistance. But Jules Verne inspired generations of scientists just the same and the hunt was on.
- Classical Gravity, Part 1: The Problems
- Sorry Vulcan, Kerberos and Styx Know All The Right People
- Uranus Elsewhere: Ice Giant Planet Discovered 25,000 Light Years Away
- "Imaginary Bullshit Planet" Nibiru- Lens Flares, Sun Mirages, Hoaxes & Just Plain Silly
- Why An Extra Planet Can't Be Hidden Behind The Sun Or Above The South Pole