From Astrobites : “The Origin of the Origin of the Universe”

From Astrobites

2.4.23
Katherine Lee

Title: Measurement of the Cosmic Microwave Background Spectrum by the COBE FIRAS Instrument

Authors: J. C. Mather, E. S. Cheng, D. A. Cottingham, R. E. Eplee Jr., D. J. Fixsen, T. Hewagama, R. B. Isaacman, K. A. Jensen, S. S. Meyer, P. D. Noerdlinger, S. M. Read, L. P. Rosen, R. A. Shafer, E. L. Wright, C. L. Bennett, N. W. Boggess, M. G. Hauser, T. Kelsall, S. H. Moseley Jr., R. F. Silverberg, G. F. Smoot, R. Weiss, and D. T. Wilkinson

First Author’s Institution: NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Status: published in ApJ [open access]

Back in the mid-20th century, there were two competing theories about the origin of the Universe. Scientists, including Edwin Hubble and Georges Lemaître, had already established that space was expanding.

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Edwin Hubble

Edwin Hubble looking through the 100-inch Hooker telescope at Mount Wilson in Southern California(US), 1929 discovers the Universe is Expanding. Credit: Margaret Bourke-White/Time & Life Pictures/Getty Images.

Mount Wilson Hooker 100in Telescope interior.

Mt Wilson 100 inch Hooker Telescope, perched atop the San Gabriel Mountains outside Los Angeles, CA, Altitude 1,742 m (5,715 ft).

Edwin Hubble Cepheid variable with Messier 31 at the 100 inch Hooker telescope on Mt Wilson, California.

Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope Credit: Emilio Segre Visual Archives/AIP/SPL.

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Caltech Palomar Samuel Oschin 48 inch Telescope, located in San Diego County, California, altitude 1712 m (5617 ft). Credit: Caltech.

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Some argued that if you run this expansion back in time, it implies a beginning when everything must have been compressed into a hot, dense singularity, exploding outward from that point in a “Big Bang”. Other astronomers, however, were uncomfortable with the idea that the Universe even had an origin at all. These scientists, most notably Fred Hoyle, argued instead for a cosmology in which the Universe had always existed and had always been expanding, with new galaxies springing up periodically to fill in the gaps. This picture of our Universe is referred to as the “Steady State Theory”.

These two theories predict fundamentally different things about the background temperature of the Universe. If matter in the Universe does not originate from a single point, as in the Steady State picture, then we would expect the background radiation to be chaotic in nature; there would be no reason for different unconnected regions of spacetime to look the same as each other.

However, if everything in the Universe comes from the same initial conditions, then everything should be roughly the same temperature. This can also be expressed as the idea that the Universe should be in thermodynamic equilibrium on large scales, and that if you measure the intensity of background radiation at all frequencies, you should see a blackbody spectrum—the characteristic spectrum of an object in equilibrium, dependent only on the object’s temperature. Thus, a key prediction of the Big Bang theory is that the temperature should be nearly constant over the entire sky, with the differences (called anisotropies) from this constant average temperature being extremely small—around one part in 100,000!

COBE comes to the rescue

Big Bang cosmologists in the 1960s believed that the peak of the Universe’s blackbody spectrum should be in the microwave frequency range, defined as between 300 MHz and 300 GHz. This would be expected from a massive explosion of energy at the Big Bang, the light from which would have been redshifted into the microwave range as it traveled through the expanding universe. So, if the Big Bang theory is true, we should expect to see a constant source of background radiation coming from all directions in the microwave sky: a so-called Cosmic Microwave Background, or CMB.

The detection of this CMB radiation in 1965 by Arno Penzias and Robert Woodrow Wilson, as well as the cosmological interpretation of that detection by Robert Dicke, Jim Peebles, Peter Roll, and David Wilkinson, laid the groundwork for modern cosmology, and was the beginning of the end for the idea that the Universe had no origin.

Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA, with the Holmdel horn antenna, first caught the faint echo of the Big Bang.

However, Penzias and Wilson’s discovery was not an accurate measurement of the CMB’s temperature or spectrum. No anisotropies had been detected, and there was still debate over whether or not the CMB spectrum was truly a blackbody. The goal of the Cosmic Background Explorer (COBE) satellite, launched by NASA in 1989, was to answer these lingering questions.

COBE was split into three instruments: the Differential Microwave Radiometer (DMR), the Far-InfraRed Absolute Spectrophotometer (FIRAS), and the Diffuse Infrared Background Experiment (DIRBE). DMR measured the CMB anisotropies, while DIRBE mapped infrared radiation from foreground dust.

igure 1: A diagram of the FIRAS instrument, taken from Figure 1a of Mather et. al. (1999).

FIRAS, meanwhile, was designed to measure the CMB spectrum. It scanned the entire sky multiple times in order to minimize errors, and measured the temperature over a wide range of frequencies between 30 and FIRAS, meanwhile, was designed to measure the CMB spectrum. It scanned the entire sky multiple times in order to minimize errors and measured the temperature over a wide range of frequencies between 30 and nearly 3000 GHz. After eliminating known sources of interference such as cosmic rays, as well as subtracting the effects of light from the Milky Way galaxy and of the Doppler shift caused by the movement of the Earth through space, these scans were then averaged together to create direct measurements of the CMB intensity at various frequencies.

Figure 2: The cosmic microwave background spectrum, as measured by FIRAS. It shows a near-perfect blackbody, with any deviations from total thermodynamic equilibrium being much too small to see. This plot is taken from Figure 4 of Fixsen et al. (1996), which notes that “uncertainties are a small fraction of the line thickness.”line thickness.”

The authors found that the background radiation in our universe is in fact extremely close to being a perfect bThe authors of today’s paper found that the background radiation in our Universe is in fact extremely close to being a perfect blackbody! The final temperature found by FIRAS was reported by Mather et al. (1999) to be 2.725 K, with an uncertainty of just 0.002 K! This is an incredibly high-precision measurement and represents the final nail in the coffin for cosmologies other than the Big Bang. John C. Mather received the Nobel Prize in 2006 for his work as FIRAS’s project lead.

Figure 3: A comparison of the abilities of the COBE [above], WMAP, and Planck satellites to resolve tiny fluctuations in the CMB temperature, called anisotropies. Image: NASA/JPL-Caltech/ESA (Wikimedia Commons)

National Aeronautics Space AgencyCosmic Background Explorer COBE 1989 to 1993.

COBE image of the CMB, the earliest image of the CMB

NASA/Wilkinson Microwave Anisotropy Probe (WMAP) 2001 to 2010 annotated.

Cosmic Microwave Background NASA/WMAP

The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganization](EU) Planck microwave telescope 2009 to 2013.

CMB per European Space Agency(EU) Planck.

Today, cosmologists use the CMB and its anisotropies to characterize the early history of the universe, find galaxy clusters in the later universe, and even look for new physics! The COBE measurements represented the dawn of a new era in cosmology, and laid the groundwork for modern CMB measurements. The science we do toToday, cosmologists use the CMB and its anisotropies to characterize the early history of the Universe, find galaxy clusters in the later Universe, and even look for new physics! Later full-sky measurements taken by the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck satellite added never-before-seen levels of precision to our ability to study the structure and content of the Universe, and future missions like LiteBIRD will continue to improve our ability to study the CMB even more closely, building on COBE’s groundbreaking data. These experiments still rely upon the CMB temperature established by FIRAS, which remains the definitive result even 23 years after its publication.

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Inflation

In physical cosmology, cosmic inflation, cosmological inflation is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10^−36 seconds after the conjectured Big Bang singularity to some time between 10^−33 and 10^−32 seconds after the singularity. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago).

Inflation theory was developed in the late 1970s and early 80s, with notable contributions by several theoretical physicists, including Alexei Starobinsky at Landau Institute for Theoretical Physics, Alan Guth at Cornell University, and Andrei Linde at Lebedev Physical Institute. Alexei Starobinsky, Alan Guth, and Andrei Linde won the 2014 Kavli Prize “for pioneering the theory of cosmic inflation.” It was developed further in the early 1980s. It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe. Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.

The detailed particle physics mechanism responsible for inflation is unknown. The basic inflationary paradigm is accepted by most physicists, as a number of inflation model predictions have been confirmed by observation; however, a substantial minority of scientists dissent from this position. The hypothetical field thought to be responsible for inflation is called the inflaton.

In 2002 three of the original architects of the theory were recognized for their major contributions; physicists Alan Guth of M.I.T., Andrei Linde of Stanford, and Paul Steinhardt of Princeton shared the prestigious Dirac Prize “for development of the concept of inflation in cosmology”. In 2012 Guth and Linde were awarded the Breakthrough Prize in Fundamental Physics for their invention and development of inflationary cosmology.

Alan Guth, from M.I.T., who first proposed Cosmic Inflation.

Lambda Cold Dark Matter Expansion ΛCDM of the Universe. Credit Alex Mittelmann Coldcreation.

Alan Guth’s notes:
Alan Guth’s original notes on inflation.
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Nobel Prize in Physics for 2011 Expansion of the Universe

Saul Perlmutter (center) [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt (right) and Adam Riess (left) [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

4 October 2011

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2011

with one half to

Saul Perlmutter
The Supernova Cosmology Project
The DOE’s Lawrence Berkeley National Laboratory and The University of California-Berkeley,

and the other half jointly to

Brian P. SchmidtThe High-z Supernova Search Team, The Australian National University, Weston Creek, Australia.

and

Adam G. Riess

The High-z Supernova Search Team,The Johns Hopkins University and The Space Telescope Science Institute, Baltimore, MD.

Written in the stars

“Some say the world will end in fire, some say in ice…” *

What will be the final destiny of the Universe? Probably it will end in ice, if we are to believe this year’s Nobel Laureates in Physics. They have studied several dozen exploding stars, called supernovae, and discovered that the Universe is expanding at an ever-accelerating rate. The discovery came as a complete surprise even to the Laureates themselves.

In 1998, cosmology was shaken at its foundations as two research teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role.

The research teams raced to map the Universe by locating the most distant supernovae. More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors (CCD, Nobel Prize in Physics in 2009), opened the possibility in the 1990s to add more pieces to the cosmological puzzle.

The teams used a particular kind of supernova, called Type 1a supernova. It is an explosion of an old compact star that is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy. All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected – this was a sign that the expansion of the Universe was accelerating. The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.

For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.

The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma – perhaps the greatest in physics today. What is known is that dark energy constitutes about three quarters of the Universe. Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.

*Robert Frost, Fire and Ice, 1920
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From Astronomy Magazine: “The Steady State: When astronomers tried to overthrow the Big Bang”

From Astronomy Magazine

January 6, 2020
Mara Johnson-Groh

Some astronomers didn’t like the religious implications of a universe with a beginning. Their alternative was the so-called “steady state model.”

NASA/ESA/S. Beckwith(STScI) and The HUDF Team

It all started with a Big Bang. Or maybe it didn’t. In the mid-20th century, most physicists were split on how the universe began — or if it even had a beginning at all. Today, scientists agree that the Big Bang theory best describes the birth of our universe nearly 14 billion years ago. The idea now has a lot of observational evidence, but in the 1940s and ’50s it was still widely debated.

The Big Bang theory roused the public and religious realms perhaps even more than the scientific community, which had previously accepted an idea called the steady state model. “It was not only a scientific controversy, it also included some broader aspects, ideological and religious aspects. And that was one reason why it was so publicly controversial,” says Helge Kragh, a science historian and professor emeritus at the Niels Bohr Institute. “The steady state theory was, especially in England, often associated with atheism, and the Big Bang theory with Christian theism.” If the universe had a creation point, then it probably had a creator, the thinking went.

Beginnings of Cosmology

Humans have always held ideas about how the universe originated. But it wasn’t until advances in the 20th century, including Albert Einstein’s theories of relativity, that astronomers could really form educated ideas about how the universe formed.

Alexander Friedmann, a Russian physicist, was the first to realize that applying the rules of relativity across large scales described a universe that changed over time. With a mathematical approach, he showed the universe could have started small before expanding over enormous distances and, in some cases, eventually collapsing back in on itself.

Observations carried outby Lowell Observatory’s V.M. Slipher and, later, Edwin Hubble, showed that the universe was in fact expanding.

Edwin Hubble looking through a 100-inch Hooker telescope at Mount Wilson in Southern California, 1929 discovers the Universe is Expanding

Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope, (credit: Emilio Segre Visual Archives/AIP/SPL)

And this helped confirm these initial ideas of the Big Bang. Two years later, the Belgian physicist Georges Lemaître published a paper describing how the expanding universe had started as a tiny, hot, dense speck, which he called the “primeval atom.” Ordained as a Catholic priest, Lemaître reported the finding as a happy coincidence of cosmology and theology in an early draft of the paper, though the comment was removed for the final publication of the paper.

Two decades later, George Gamow would develop theories on the fallout of a hot-birthed universe — namely, how it would create neutrons and protons — and published a popular book on the subject. It even caught the eye of Pope Pius XII, who was taken by the parallels between the scripture of Genesis and the scientific theory.

Unlike the church, Einstein wasn’t initially happy with the idea of a changing universe, preferring one invariable on large scales. British astronomer Fred Hoyle wasn’t happy, either. Along with two other scientists, he developed a counter-theory — the steady state model. The steady state model suggested that the universe had no beginning and had always been expanding. To explain why the universe looks identical in all directions, it proposed tiny traces of matter, too small to be experimentally measured, were continually being created.

This model initially garnered support of around half of the scientific community — albeit one that was very small at the time — and became the Big Bang theory’s biggest rival.

“This [debate between theories] was not in the mainstream of physics research,” says David Kaiser, science historian and physics professor at MIT. “Basically no one paid attention or very little attention, even among professional physicists and astronomers.”

But as evidence started gathering, that would change.

New Evidence

Observations of distant ultra-bright galaxies in the 1950s suggested the universe was changing, and measurements of the helium content in the universe didn’t match the steady state model’s predictions. In 1964, the monumental discovery of the cosmic microwave background radiation [CMB] — direct evidence of a young, hot universe — would deal the final deathblow to the steady state model.

CMB per ESA/Planck

ESA/Planck 2009 to 2013

Cosmic Background Radiation per Planck

“It really seems to suggest … the universe had very different conditions in early times than today,” Kaiser says. “And that was just not what the steady state model suggests.”

In an ironic twist, Hoyle used the term “Big Bang” in an attempt to dismiss the theory in a BBC interview. Though his own theory would be largely lost to history, the irreverent name would stick.

To his death, Hoyle would never submit to the Big Bang theory. A small subset of cosmologists still work on resurrecting a steady state model; but, on the whole, the community overwhelmingly supports the Big Bang theory.

“There are a couple of other puzzles, so cosmologists don’t think we’re done, but they’re now kind of patching or filling in some holes to the original Big Bang models — certainly not replacing it,” Kaiser says.

Saul Perlmutter [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt and Adam Riess [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

See the full article here .

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Astronomy is a magazine about the science and hobby of astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy and those who want to know about sky events, observing techniques, astrophotography, and amateur astronomy in general.

Astronomy was founded in 1973 by Stephen A. Walther, a graduate of the University of Wisconsin–Stevens Point and amateur astronomer. The first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained astrophotos and illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at the University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age. Although even in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would ever be able to earn a living. However he graduated in Journalism from the University of Wisconsin Stevens Point, and as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition.[citation needed]. He died in 1977.