July 4th is the big day! And not only because of fireworks. It's the day of a press conference at which it is widely anticipated that CERN (the giant European particle physics laboratory) will announce that the Higgs boson---that much-touted particle needed to make the Standard Model of Physics complete---has been found at the Large Hadron Collider. Or at least, that something that looks very much like it has been observed. What's the Higgs, you say? You've been living under a rock? Well, here is the best explanation we've seen of what the Higgs is and why it's important, courtesy The Guardian's Ian Sample: Normally, we would not be writing anything suggesting the Higgs had been found until the proof was in our hot little hands. Rumors schrumors, we say---many a CERN press conference has ended in disappointment. But this morning, Kate Travis, an editor at ScienceNews, found a leaked CERN video in which a spokesperson all but announces the discovery of a new particle. "We have quite strong evidence that there's something there," Joe Incandela, the spokesperson for the relevant LHC experiment, says on the (now-removed) video, which you can see reposted here. "Its properties are still going to take us a little bit of time. But we can see that it decays to two photons, for example, which tells us it's a boson, it's a particle with integer spin. And we know its mass is roughly 100 times the mass of the proton. And this is very significant. This is the most massive such particle that exists, if we confirm all of this, which I think we will." That sounds very much like the the Higgs predicted by the Standard Model, the theory of subatomic particles assembled by physicists in the 20th century. CERN's media office has stated that the leaked video is just one of several videos made to reflect several different scenarios, and it may be that this video will not be the one that is played at the conference tomorrow. Make of that what you will. The bloggers of Discover's Cosmic Variance who are attending the affair will be live-blogging here, starting at 3 am Eastern time. But whatever is officially announced tomorrow, it now seems likely that it will be significant news. The Higgs has been the focus of a tremendous amount of hype, for better---it's safe to that particle physics was not exactly dinner table conversation before people started calling the Higgs "the God Particle"---or for worse. The Higgs discovery, if that is indeed what they are announcing, will cement a great deal of 20th-century physics work and validate the Standard Model of Physics, but it will also be the end of an era. As one physicist said to me a few minutes ago, "unless it has some very weird properties, it's like the closing of a book, rather than an opening. We've done that--we've dotted the 'i's and crossed the 't's. But it doesn't open new vistas. It's the end of something. We're not going to build another accelerator."