Posted on 06/09/2003 6:11:13 AM PDT by andy224
Atlas holds key to scientists' map of Universe By Mark Henderson A vast cavern is the stage for tests to find the 'God particle'
SCIENTISTS have taken a step closer to finding the “God particle” that is thought to shape the Universe. In a concrete cavern 130ft deep and bigger than the nave of Canterbury Cathedral, they will mimic the high-energy conditions that existed fractions of a second after the Big Bang to study a beam of energy a quarter of the thickness of a human hair.
The vast Atlas cavern, which was completed last week at Cern, the European nuclear physics laboratory on the Franco-Swiss border, will house parts of a giant atom-smasher that is expected to solve the most elusive riddle in physics.
When the £1.5 billion Large Hadron Collider (LHC) is switched on in 2007, it will determine once and for all whether the Higgs boson, a mysterious fundamental particle held to give matter its mass, really exists. If the machine finds the boson, proposed by Professor Peter Higgs of Edinburgh University in 1964, it will prove that the Standard Model for the nature of the Universe is correct. If not, the maxims of modern physics will be thrown into disarray.
The boson was nicknamed the “God particle” by the Nobel laureate Leon Lederman for its centrality to the cosmos. Although it will be so small that its presence can only be calculated, not seen, the search for it requires some of the largest and most advanced scientific instruments designed.
The LHC itself is a ring 17 miles (27km) in circumference, buried up to 100m (330ft) underground, through which streams of protons will be bent by the world’s most powerful magnets and smashed into each other at close to the speed of light.
The new cavern, which will house the Atlas detector for tracking the Higgs and other particles, is 40m (130ft) deep, 55m (180ft) long and 35m (115ft) wide.
However, the proton beam that runs through both devices measures just 10 microns in diameter: less than a quarter of the thickness of the average human hair. Roger Cashmore, a British physicist and Cern’s director of research, said: “It is an astonishing feat of engineering. The consultants were on the verge of saying it was impossible to build. But the Atlas cavern is finished, the biggest of its kind in the world, and these experiments are going to tell us whether we’re right about the Universe.”
The current best guide to the nature of the Universe is the Standard Model, an elegant theory that describes how most particles and forces interact. The Higgs boson is its missing keystone: without it, there is no good explanation for why matter has mass and therefore exists.
According to the theory, the Universe is permeated by a field of Higgs bosons, which consist of mass but very little else. As particles move through the field, they interact with it like a ball dropped into a tub of treacle, getting slower, stickier and heavier. Their ultimate mass depends on the strength of the interaction.
Though mathematics predicts its existence, the Higgs boson has never been detected. It is so heavy that the biggest atom-smashers, Cern’s Large Electron-Positron collider (LEP) and the Tevatron at Fermilab in Illinois, have been unable to generate the high energy collisions needed to reveal it, although they have found hints that it is probably there. This is where the LHC comes in. It is 70 times as powerful as the LEP and seven times stronger than the Tevatron, covering all the energy values at which the Higgs might exist. If it is there, it will find it.
What is more, if the “God particle” proves to be a false deity, the LHC will unlock the secret of what is out there instead. “If it doesn’t find the Higgs, it will find what substitutes for it,” Dr Cashmore said.
Jim Virdee, Professor of Physics at Imperial College, London, and a leading Cern researcher, said: “There has to be something else, beyond what we have found already, that explains mass. We believe it’s the Higgs, but Nature may be smarter than us. Either way, the results will tell us what is the right road.”
The atom-smasher will accelerate protons so close to the speed of light that they become 7,000 times heavier than normal. The beams are bent into a circle by superconducting magnets, cooled by liquid helium at -271.4C, almost a degree colder than outer space.
When the protons collide, they are destroyed in a huge burst of energy. This energy coalesces into very heavy particles, one of which scientists hope will be the Higgs.
As the boson is unstable, it will quickly decay, scattering a characteristic signature of smaller particles and energy. These will be picked up by the LHC’s eyes — the Atlas and a sister detector — which surround the collision points.
The detectors, which stand 22m (72ft) and 15m (49ft) tall respectively, are “giant microscopes” built like onions, with several layers of instruments that track particles and measure energy.
The experiments will generate enormous quantities of data, much of it unwanted. “Colliding two protons is like colliding two oranges,” Dr Lyn Evans, director of the LHC project, said. “You’ll occasionally get a collision between two pips, the interesting bits, but you’ll get a lot of pulp. We need to reject an enormous amount of data to pick out the important bits.” Professor Virdee said that the data generated in one second was the equivalent of what all the world’s telecommunications generated in one year.
Even if this wealth of information proves the existence of the Higgs boson, the LHC will continue to serve scientific knowledge for decades.
“Let’s say we have the Higgs,” Dr Cashmore said. “I’d feel warm and content for a few microseconds, then I’d be asking new questions. Why does it affect different particles in different ways? “It would be spectacularly good to find it — I’m not trying to knock it — but it will pose a whole new set of problems. If we are an inquisitive society, these are the things we ought to be doing."
Sore though the temptation is, I will attempt to restrain myself--if I lapse, I hope you will be kind enough to remind me.
I acquiesce to your request.
Ah, if you mean the matter that is embedded in the space, it gets a "free" ride, so to speak. THe key point is that no force acts on the matter, hence it isn't accelerated, hence it's kinetic energy and momentum don't change. The objects (matter) aren't in motion per se; space is just getting bigger.
Free ride or not, the force between 2 particles that were nanometers apart at T0 and "light years" apart at T1 is changed substantially.
First, I'm not sure what "force" you are referring to, and second, the Inflationary epoch was so short that nothing was "light years" apart when it ended. My recollection is that at the end of the Inflationary epoch the Universe was something on the order of the size of a grapefruit.
Fairytales
Maybe someone should ask Vade for the last post on that thread.......after all, it was his.
G'nite
Yes; that's a 2-D illustration of expansion of the Universe.
Technically, Inflation is a sort of short-lived "Hyper-expansion," but AFAIK, the principles are the same, though the mechanism is different.
Any that we know about.
I placed the light years in quotations, because, if I recall correctly, it could be that large although I also am familiar with the grapefruit size of the universe. The change would still apply.
Reference for the big size
In order for inflation to solve the horizon problem, this causal region must be blown up to at least the size of the observable universe today
The ballon is considered a 2-D analogy because the location of any point on its surface can be uniquely defined by only 2 co-ordinates (e.g., Latitude and longitude on the surface of the earth).
I'm pretty sure they mean that the region AT THE TIME OF INFLATION must TODAY be at least the size of the observable Universe, which is exactly what 13 billion years of normal non-inflationary expansion does to to the Universe.
I still don't see what the point is that you are raising; can you cut to the chase -- time is running out for tonight's session.
"Here the extra factor a(ti) / a(t0) accounts for the expansion between the end of inflation Ti ~ 1015 GeV and today, T0 ~ 10-4 eV."
IOW, most of the "scale change" that they are talking about takes place AFTER the inflation stops, that is to say, it occurs through the normal non-inflationary expansion of the universe, as I opined in my previous reply.
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