Scientists hunting the elusive subatomic "Higgs" particle will unveil findings that take them nearer to understanding how the Big Bang at the dawn of time gave rise to stars, planets and even life.
Physicists who have been smashing particles together at near light-speed at the CERN laboratory near Geneva have already seen tantalising glimpses of the "Higgs boson", the missing piece of the fundamental theory of physics known as the Standard Model.
The world of science now awaits a mass of evidence big enough to be deemed a formal discovery.
The secrecy surrounding Wednesday's announcement has fuelled speculation that nearly 40 years of research have reached a climax.
CERN accidentally released a video on its website briefly overnight announcing a "new particle" had been observed, but its representatives declined to comment on whether that was what would be announced later in the day.
"This video was released due to a technical glitch on our side here at CERN. The final results have not yet been released," CERN press officer Renilde Vanden Broeck said in Melbourne.
She said the organisation had prepared several videos for a range of outcomes for Wednesday's announcement.
A CERN physicist who knows what will be announced said the discovery was not necessarily definitive.
"This is not a black and white answer which you should expect. This is an important stepping stone," Peter Jenni, former spokesman for the ATLAS collaboration, one part of the CERN research organisation, told Reuters news agency on Wednesday.
Data harvested from CERN's Large Hadron Collider, the biggest particle accelerator in the world, could also shed light on the make-up of the poorly understood "dark matter" and "dark energy" that make up 96 per cent of the universe. It may even point the way to research into the possibility of parallel universes.
CERN is planning to beam the announcement live around the world to a physics conference in Melbourne, Australia. Related events are planned in countries involved in the project, including Britain.
Big news in store
The unusual level of stage management has fuelled the sense that big news is in store.
On Monday, US physicists said they had found the strongest evidence yet of the existence of the Higgs in a mass of data collected from the now-mothballed Tevatron particle accelerator, run by the Fermi National Accelerator Lab outside Chicago.
"It will be interesting to see how it lines up with CERN's results on Wednesday," said CERN spokesman James Gillies.
Some scientists working on the project have told Reuters they expect the unveiling of a formal discovery while others expect it to fall just short.
With thousands of physicists involved, divided into two separate teams called Atlas and CMS, CERN insists the full picture will not be clear to anyone until a seminar shortly before Wednesday's announcement.
"Even CERN's director general won't know much before the seminar reveals the exact results," said Pauline Gagnon, a Canadian particle physicist working on Atlas. "They are being finalised at the last minute after much scrutiny."
The Higgs particle, although crucial for understanding how the universe was formed, remains theoretical.
It is the last undiscovered piece of the Standard Model that describes the fundamental make-up of the universe. The model is for physicists what the theory of evolution is for biologists.
Scientists say the existence of dark matter and dark energy suggests the Standard Model, if validated by a Higgs discovery, is just the first layer of a more complex theory that includes the vast bulk of the universe that is now poorly understood.
"The Standard Model has a few major flaws; the Higgs boson discovery would only fix one of them," said Gagnon.
"We still have no clue regarding what makes 96 per cent of the content of the universe. This should keep us physicists busy for a few more decades."