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Posts Tagged ‘expansion of the 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


As the time for our camera’s first light approaches, workload and excitement increase exponentially among the Dark Energy Survey collaborators and it is about time we start sharing the latter. Beginning today, you will find here at Quantum Diaries an insider’s account of our fast progress, frequently updated as we countdown to first light.

So, here we go. If you haven’t heard of us yet, DES is an experiment designed to investigate dark energy, one of the most trending topics of the last 30 years, featured among the top priorities in the world-wide scientific agenda despite a recent funding blow up. DES will image an area of 5,000-square degrees (nearly 1/8 of the sky) using five optical-bands, obtaining detailed measurements of about 300 million galaxies. With this data we can shed light on the mystery of cosmic acceleration by analyzing four complementary probes: supernovae, baryonic acoustic oscillations, galaxy clusters and weak lensing.

DES will use its own powerful new instrument, the Dark Energy Camera, or DECam, which is under construction at  Fermilab.  Building an entirely new system to answer a specific question is a growing trend in astrophysics, probably a consequence of developing close ties with the field of high energy physics.

This 570-megapixel, giant camera is being tested on a telescope simulator (the yellow and red rings that you see in the video) until the end of this month. As a Fermilab postdoc, I am heavily involved in these tests, together with a team that keeps up the fast pace even during the blizzard last week.

Check out this time-lapse video of the DECam construction:

We are now getting ready for a simulated observing run, a comprehensive integration test of the full system. We will use a star projector to simulate the sky and the goal is to take one night’s worth of data. The atmosphere here at the lab is of stress and excitement as this is our last test of the full system before we bring DECam down from the telescope simulator. The results of this test will be very important to guiding us through the next steps.

So here is where we stand nine months before first light. Stay tuned for more updates here or follow us on Facebook. Leave a message in the comments if you want to know more or would like to visit us while the camera is still up on the simulator.

–Marcelle Soares-Santos