From PI: “The sky as a limit”

Perimeter Institute
Perimeter Institute

January 11, 2016

Eamon O’Flynn
Manager, Media Relations
(519) 569-7600 x5071

Perimeter researchers show how the largest possible structure – the curvature of the universe as a whole – can be used as a lens onto the smallest objects observable today, elementary particles.

Elliot Nelson (left) and Niayesh Afshordi. No image credit found.

Perimeter Associate Faculty member Niayesh Afshordi and postdoctoral fellow Elliot Nelson recently won a third-place Buchalter Cosmology Prize for uncovering an entirely new way cosmology can shed light on the future of particle physics.

Hubble Goes to the eXtreme to Assemble Farthest-Ever View of the Universe

Like photographers assembling a portfolio of best shots, astronomers have assembled a new, improved portrait of mankind’s deepest-ever view of the universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field.

NASA Hubble Telescope

The XDF is a small fraction of the angular diameter of the full moon. The Hubble Ultra Deep Field is an image of a small area of space in the constellation Fornax, created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over many hours of observation, it revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the universe ever taken at that time. The new full-color XDF image is even more sensitive, and contains about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see. Magnificent spiral galaxies similar in shape to our Milky Way and the neighboring Andromeda Galaxy appear in this image, as do the large, fuzzy red galaxies where the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years. Peppered across the field are tiny, faint, more distant galaxies that were like the seedlings from which today’s magnificent galaxies grew. The history of galaxies — from soon after the first galaxies were born to the great galaxies of today, like our Milky Way — is laid out in this one remarkable image.

Hubble pointed at a tiny patch of southern sky in repeat visits (made over the past decade) for a total of 50 days, with a total exposure time of 2 million seconds. More than 2,000 images of the same field were taken with Hubble’s two premier cameras: the Advanced Camera for Surveys [ACS] and the Wide Field Camera 3 [WFC3], which extends Hubble’s vision into near-infrared light.


NASA Hubble WFC3

“The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. XDF allows us to explore further back in time than ever before”, said Garth Illingworth of the University of California at Santa Cruz, principal investigator of the Hubble Ultra Deep Field 2009 (HUDF09) program.

The universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together. The early universe was a time of dramatic birth for galaxies containing brilliant blue stars extraordinarily brighter than our sun. The light from those past events is just arriving at Earth now, and so the XDF is a “time tunnel into the distant past.” The youngest galaxy found in the XDF existed just 450 million years after the universe’s birth in the big bang.

Before Hubble was launched in 1990, astronomers could barely see normal galaxies to 7 billion light-years away, about halfway across the universe. Observations with telescopes on the ground were not able to establish how galaxies formed and evolved in the early universe.

Hubble gave astronomers their first view of the actual forms and shapes of galaxies when they were young. This provided compelling, direct visual evidence that the universe is truly changing as it ages. Like watching individual frames of a motion picture, the Hubble deep surveys reveal the emergence of structure in the infant universe and the subsequent dynamic stages of galaxy evolution.

The infrared vision of NASA’s planned James Webb Space Telescope [JWST] will be aimed at the XDF.

NASA Webb Telescope

The Webb telescope will find even fainter galaxies that existed when the universe was just a few hundred million years old. Because of the expansion of the universe, light from the distant past is stretched into longer, infrared wavelengths. The Webb telescope’s infrared vision is ideally suited to push the XDF even deeper, into a time when the first stars and galaxies formed and filled the early “dark ages” of the universe with light.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy, Inc., in Washington.
Date 29 June 2012
Photographer NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team

Andromeda Galaxy. Adam Evans

Their work begins with the knowledge that space is flat. While there are local wrinkles, they are wrinkles in a flat space, not wrinkles in curved space. The universe as a whole is within one percent of flat.

The problem is that it shouldn’t be. The vacuum of space is not empty; it is filled with fields that may be weak but cannot be zero – nothing quantum can ever be zero, because quantum things wiggle. According to general relativity, such fluctuations should cause spacetime to curve. In fact, a straightforward calculation of how much the vacuum should curve predicts a universe so tightly wound that the moon would not fit inside it.

Cosmologists have typically worked around this problem – that the universe should be curved, but looks flat – by assuming there is some antigravity that exactly offsets the tendency of the vacuum to curve. This set of off-base predictions and unlikely corrections is known as the cosmological constant problem, and it has been dogging cosmology for more than half a century.

In this paper, Nelson and Afshordi make no attempt to solve it, but where other cosmologists invoked an offsetting constant and moved on, Nelson and Afshordi went on to ask one more question: Does adding such a constant to cancel the vacuum’s energy guarantee a flat spacetime? Their answer: not quite.

The vacuum is still filled with quantum fields, and it is the nature of quantum fields to fluctuate. Even if they are perfectly offset such that their average value is zero, they will still fluctuate around that zero point. Those fluctuations should (again) cause space to curve – just not as much.

In this scenario, the amount of curve created by the known fields – the electromagnetic field, for example, or the Higgs field – is too small to be measured, and is therefore allowed. But any unknown field would have to be weak enough that its fluctuations would not cause an observable curve in the universe. This sets a maximum energy for unknown fields.

A theoretical maximum on a theoretical field may not sound groundbreaking – but the work opens a new window in an unexpected place: particle physics.

A particle, quantum mechanics teaches us, is just an excitation of a field. A photon is an excitation of the electric field, for example, and the newly discovered Higgs boson is an excitation of Higgs field. It’s roughly similar to the way a wave is an excitation of the ocean. And just as the height of a breaking wave can tell us something about the depth of the water, the mass of a particle depends on the strength of its corresponding field.

New kinds of quantum fields are often associated with proposals to extend the Standard Model of particle physics.

The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

If Afshordi and Nelson are right, and there can be no such fields whose fluctuations have enough energy to noticeably curve space, there can be no unknown particles with a mass of more than 35 TeV. The authors predict that if there are new fields and particles associated with an extension to the Standard Model, they will be below that range.

For generations, particle physics has made progress from the bottom up: building more and more powerful colliders to create – then spot and study – heavier and heavier particles. It is as if we started from the ground floor and built up, discovering more particles at higher altitudes as we went. What Nelson and Afshordi have done is lower the sky.

There is a great deal of debate in particle physics about whether we should build increasingly powerful accelerators to search for heavier unknown particles. Right now, the most powerful accelerator in the world, the Large Hadron Collider [LHC], runs at a top energy of about 14 TeV; a proposed new super accelerator in China would run at about 100 TeV.

CERN LHC Grand Tunnel
CERN LHC particles

As this debate unfolds, this new work could be particularly useful in helping experimentalists decide which energy levels – which skyscraper heights – are the most interesting.

The sky does indeed have a limit, this research suggests – and we are about to hit it.

Read the original prize-winning paper from by Afshordi and Nelson

See the full article here .

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About Perimeter

Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.