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Posts Tagged ‘accelerating universe’

What fills space?

Wednesday, July 25th, 2012

This article first appeared in Fermilab Today on July 25.

If you follow the news about physics, you might think that physicists don’t know what they are talking about when it comes to space.

I am not talking about the mysteries of outer space, or cataclysms like black holes. I mean ordinary space itself, the inner space between particles everywhere—what we used to call empty space or vacuum. What’s in it? Sometimes we hear that atoms are “mostly empty space.” Now we read in the papers that the newly discovered Higgs field “fills all of space” and “gives particles mass,” that it acts like a kind of space-filling “molasses,” or that it’s like a space-filling crowd of groupies hanging on as a celebrity’s posse.

On the other hand, astronomers tell us that space is expanding. Last year, the Nobel Prize in physics was awarded for the discovery that the cosmic expansion is speeding up. Scientists think that this acceleration is propelled by what they call “dark energy,” which fills and refills that ever-expanding void of intergalactic space. Cosmological space is said to be expanding in some places (between galaxies) and not expanding in others (such as Brooklyn, to choose Woody Allen’s example).

It gets even worse if you dig deeper. For example, the Higgs field is much weirder than the comparisons with molasses or crowds suggest, since it does not actually drag or impede particles, but still somehow shares its mass with them.

Stranger still, consider another space-filling field that also adds mass to everyday substances, in a way different from the Higgs field. The gluons of the strong nuclear force field create most of the mass of atoms through the energy of their incessant motion inside tiny bubbles of space that we call protons and neutrons. Since the mass-giving gluons are immune to the Higgs field, they have no mass themselves, but only add energy because of their motion. Moreover, they are held inside those bubbles by a gluon field that fills empty space everywhere between the bubbles…in just those places in space where the added mass isn’t.

Space is the first concept of physics we all learn as little kids, yet it is entangled with some of the deepest mysteries confronting physics. Confusing, koan-like paradoxes about space are not just pablum: They reflect a real and profound disparity of descriptions, at a deep level of mathematics, about what defines a vacuum, a position, a particle or a time.

It may be that all the space of the universe began, and may end, dominated by the energy of the vacuum, an expanding space devoid of particles. It may be that when examined over very short time intervals, space as we know it does not even exist, but dissolves into a cloud of quantum indeterminacy: It may never sit still, but constantly seethe in microscopic motion. It may be that space has many more than three dimensions on very small scales, while there may be only two truly independent dimensions on large scales. It may even be that all of these exotic possibilities actually apply in the real world.

At Fermilab, we are working on experiments including the Dark Energy Survey, the Holometer and the CMS experiment at the Large Hadron Collider that will probe these ideas in very different ways. If you want to find out more—watch this space!

—Craig Hogan, Director of Fermilab’s Center for Particle Astrophysics

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 To celebrate its 30th anniversary, Discover magazine created a list of the The 12 Most Important Trends in Science Over the Past 30 Years. High-energy particle physics and Fermilab played a part in three of these 12 game-changing research break throughs. Here’s a look at these Discover-selected trends and Fermilab’s contributions to them.

 Trend: The Web Takes Over

Pictured is Fermilab's 2001 home page, which was designed in 1996. Twenty years ago, Fermilab helped to pioneer the URL. It launched one of the first Web sites in the country in 1992. Credit: Fermilab

The first concept for what would become the World Wide Web was proposed by a high-energy particle physicist in 1989 to help physicists on international collaborations share large amounts of data. The first WWW system was created for high-energy physicists in 1991 under the guidance of CERN. 

A year later, Fermilab became the second institution in the United States to launch a website. It also helped initiate the switch easy-to-remember domain name addresses rather than Internet Protocol addresses, which are a string of numbers. This switch helped spur the growth of the Internet and WWW.

Particle physics also secured a place in sports history through its computing savvy. A softball club at CERN, composed of mostly visiting European and American physicists, many connected to Fermilab, was the first ball club in the world to have a page on the World Wide Web, beating out any team from Major League Baseball.

Trend: Universe on a Scale

The field of cosmology has advanced and created a more precise understanding of the evolution and nature of the universe. This has brought high-energy particle physics, cosmology and astronomy closer together. They have begun to overlap in the key areas of dark energy, dark matter and the evolution of the universe.  Discover magazine cites as being particularly noteworthy in these areas the first precise measurement of cosmic microwave background, or CMB, radiation left over from the Big Bang and the discovery with the aid of supernovas that the  expansion of the universe is accelerating.

Dark Energy Camera under construction at Fermilab. Credit: Fermilab

Fermilab physicists study the CMB with the Q/A Imaging Experiment, or QUIET. They study dark energy with several experiments, most notably the long-running Sloan Digital Sky Survey , the Dark Energy Survey, which will be operational at the end of the year, and the Large Synoptic Survey Telescope, potentially operating at the end of the decade or mid-next decade.  

Trend: Physics Seeks the One

During the last few decades the particle physics community has sought to build a mammoth international machine that can probe the tiniest particles of matter not seen in nature since just after the time of the Big Bang.

Initially, this machine was planned for the United States and named the Superconducting Super Collider. Scientists and engineers from Fermilab help with the design and science suite of experiments for the SSC, which was under construction in Texas until it was canceled in 1993.

A similar machine, the Large Hadron Collider in Switzerland, did take shape, starting operation in 2008. Fermilab played a key role in the design, construction and R&D of the accelerator with expertise garnered through the Tevatron accelerator construction, cutting-edge superconducting magnet technology and project managers.

The U.S. CMS remote operation center at Fermilab. Credit: Fermilab

Fermilab now serves as a remote operation center for CMS, one of the two largest experiments at the LHC. Many physicists work on CMS as well as one of the Tevatron’s detector teams, DZero and CDF.  The United States has the largest national contingent within CMS, accounting for more than 900 physicists in the 3,600-member collaboration.

 Fermilab’s computing division serves as one of two “Tier-1” computing distributions centers in the United States for LHC data. In this capacity, Fermilab provides storage and processing capacity for data collected at the LHC that is analyzed by physicists at Fermilab and sent to U.S. universities for analysis there.

Discover magazine cited as a goal of the LHC the search for the Higgs boson, a theorized particle thought to endow other particles with mass, which allows gravity to act upon them so they can form together to create everything in the visible world, such as people, planets and plants. The LHC and the Tevatron are racing to find the Higgs first. The Tevatron has an advantage searching in the lower mass range and the LHC in the higher mass range. Theorists suspect the Higgs lives in the lower mass range. So far, the Tevatron has greatly narrowed the possible hiding places for the Higgs in this range.

— Tona Kunz

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