Tag: Cosmic Microwave Background

Arno A. Penzias, co-discoverer of the Cosmic Microwave Background (CMB), the first evidence for the Big Bang has died at the age of 90.

Most people I suppose have never heard of Arno A. Penzias, but everyone has heard of the Big Bang Theory, the idea that about 14 billion years ago, give or take a couple hundred million, the entire Universe underwent an unimaginable explosion and the expansion caused by that explosion continues today. Well it was Doctor Penzias, along with his colleague Robert W. Wilson who provided the first actual evidence that the Big Bang really happened.

Robert W. Wilson, left, and Arno Penzias, Bell Lab employees who won the 1978 Nobel Prize in physics, are shown standing in front of their microwave antenna at Bell Labs in Holmdel, N.J., Oct. 17, 1978. (AP Photo)

The story of Doctor Penzias contains within it several of the themes that often occur in both science and human history at large. Arno Penzias was born in 1933 in Munich, Germany to Jewish parents. If you can imagine a worse place and time for a Jewish boy to enter the world, well I can’t. Arno was lucky however for he and his brother were part of a British program that brought 10,000 Jewish children out of Nazi Germany just before World War 2 began. Later Arno’s parents also succeeded in escaping Germany and the whole family arrived in America in 1940. Arno was therefore one of the very large number of talented scientists who came to America and who made their discoveries here after fleeing Nazi tyranny.

From Left, Neils Bohr, James Franck, Albert Einstein and Isidor Rabi. Four Nobel Physicists who came to America to escape persecution in Europe. Actually Rabi’s parents fled to America, he was born here but you get the idea! (Credit: Arkiv.org)

Interested in science from an early age Arno first intended to become a chemist but switched majors to Physics while attending the City College of New York. Arno would eventually receive his Ph.D. in 1962. Even before becoming a Doctor however, in 1961 Arno accepted a job on the project that would lead to his greatest discovery.

After WW2 the GI Bill and a booming economy allowed a huge increase in the number of young Americans who attended college. (Credit: Old Magazine Articles)

In the early 1960s Bell Labs in Holmdel, New Jersey was one of the centers for ‘space age’ technology. The transistor had been invented there, as had the Laser. Communications satellites were the next big thing and indeed Telstar; the first communications satellite was built at Bell Labs. The engineers who were designing Telstar needed to know, once their satellite was up in orbit, what kind of radio sources there were in the Universe at large that could cause static interference with Telstar.

Bell Labs in Holmdel N.J. circa 1060 when Arno Penzias would have started working there. (Credit: Reddit)

That was the job that Arno Penzias and his colleague Robert Wilson were assigned, survey the entire sky at microwave frequencies and catalogue all of the radio sources that could cause problems for communications satellites. To accomplish their task Penzias and Wilson used the brand new Holmdel Horn antenna, especially designed for communicating with satellites and at the time one of the largest radio antennas on Earth. With such a powerful instrument in their hands the two physicists were determined to not just survey and catalogue radio sources, but to study them as well.

In the early days of Radio Astronomy measurements were used to develop contour maps of radio sources like this one of the center of the Milky Way. (Credit: ResearchGate)

As the two men carried out their survey they quickly ran up against an annoying, so they thought, little problem. No matter where they pointed their antenna, no matter when, there was always a persistent background hiss that they couldn’t get rid of. The hiss didn’t come from any source, it was everywhere, so they initially thought it had to be man made noise from something nearby. Working methodically the two men eliminated radar from nearby airports as the cause, noise from many sources coming from nearby New York City even the possibility of radiation from nuclear tests. One of their efforts to eliminate the noise has become something of a anecdote in physics departments. Noticing that several pigeons were nesting inside the big horn antenna they wondered if the bird’s droppings could be the cause of the hiss so they gave the entire horn a through clean out. No good, the noise remained.

In our modern world there are all sorts of things, both natural and man-made, that can generate radio noise that will interfere with communications. (Credit: IQS Directory)

Looking through the literature for some idea as to what could be going on they came across a paper written by physicists George Gamow and Ralph Alpher about how the Big Bang, if it had actually happened, should have left behind a measurable amount of heat, the way a frying pan on your stove stays warm for a while after you turn off the burner. After billions of years Gamow and Alpher calculated that residual heat would now be observable in the microwave region, just where Penzias and Wilson’s hiss was. (For more information on George Gamow and the prediction of the CMB see my post of 30 October 2021.)

The first prediction of a Cosmic Microwave Background (CMB) in the November 1948 issue of the journal Nature. (Credit: TheCuriousAstronomer)

Since Gamow and Alpher were teaching in Colorado and Texas respectively Penzias and Wilson decided to contact physicist Robert Dicke at nearby Princeton University. In another of those coincidences that no one could ever imagine Dicke and his students were actually planning on looking for the CMB and were gathering up the equipment they’d need to look for it. As remembered by Nobel Prize winner James Peebles, a graduate student of Dicke’s at that time he was in his mentor’s office when the call came from Wilson. “We’ve been scooped!” Dicke said as he put down the phone.

From right, Robert Dicke, Jim Peebles along with physicist David Wilkinson in their lab at Princeton University. (Credit: Nobel Prize)

That was in 1964 and the news of the discovery of the CMB spread quickly turning the subject of cosmology from a few people working on a few ideas to a major study on which thousands of researchers around the world are working. Penzias and Wilson were awarded with the 1978 Nobel Prize for their discovery. The moral of this story is to keep alert, if some unknown factor is effecting your measurements don’t just ignore it, find out what it is. Like Rontgen and the discovery of X-rays, sometimes that unknown factor is more important than the thing you started out trying to study. In both cases the scientists became famous for discovering something they never even planned on looking for.

Penzias and Wilson saw the CMB as a constant everywhere they looked but today’s measurements, from the Planck satellite, show a very small variation in the temperature. These variations form the seeds out of which today’s galaxies and stars would form. (Credit: New Scientist)

Arno A. Penzias died on the 22nd of January at an assisted living facility in San Francisco. His death was due to complications from Alzheimer’s disease. There were a huge number of major scientific discoveries made during the 20th Century; Arno A. Penzias’ discovery that ‘the Universe began, not with a whimper but with Bang’ may have been the biggest.  

Stephen Hawking Final Paper and Final Resting Place.

Stephen Hawking

Famed physicist Stephen Hawking passed away on the 14th of March at the age of 76 after more than 50 years of suffering from the dehabilitating effects of the motor neural disease ALS. Professor Hawking’s ashes are to be interred in Westminster Cathedral not far from the remains of Sir Isaac Newton.

I do not intend to attempt a biography of Professor Hawking or a review of his work. See links below for a few websites that do a better job than I ever could. Instead I’ll just try to describe a bit of Stephen Hawking’s last paper, which I downloaded from the web a couple of days ago.

http://www.hawking.org.uk/about-stephen.html

http://www.bbc.com/news/science-environment-43499024

The paper is called ‘A Smooth Exit from External Inflation” and Hawking co-wrote the paper with Thomas Hertog of the Institute for Theoretical Physics at the University of Leuven in Leuven Belgium. To even understand the title I’m going to have to talk a little bit about the history of the ‘Big Bang Theory’ going back to 1965 and the discovery of the Cosmic Microwave Background (CMB).

Prior to 1965 the observations by Carl Hubble that the Universe was expanding led several physicists to suggest that in the distant past the entire Universe had exploded outward from an incredibly dense initial condition, and I do mean incredibly dense. One physicist named George Gamow then calculated that the leftover heat of that initial Big Bang should still be observable as a uniform background of microwave radiation. This CMB was discovered in 1965 by Penzias and Wilson at Bell Labs in Holmdel New Jersey. Penzias and Wilson were a pair of radio engineers who were actually trying to measure the amount of interference that cosmic radio sources would cause the new communications satellites and instead discovered the birth cries of our Universe. The image below shows the CMB as observed by the Planck satellite.

The Cosmic Microwave Background as seen by the Planck Satellite (Credit: ESA)

With the discovery of the CMB physicists began to take a really detailed look at what the conditions in the early Universe, just a tiny fraction of a second after the Big bang, must have been like. It was quickly realized that most of the possible initial conditions would lead to a Universe vastly different than the one we see.

Half of all of these possible Universes would be so dense that gravity would make them immediately collapse back upon themselves, these were Universes that never really get started. The other half of the possible Universes would be just the opposite, they would fly apart so fast that no structure could form, a great big empty Universe. Our Universe, that has survived for billions of years but has billions of galaxies, existed on a knife’s edge between the two. Physicists regarded that as too precise to occur naturally and wanted to find some reason for such fine tuning.

It was a physicist named Alan Guth who would in the 1970s would provide a solution to the problem, although it’s a solution that has caused many problems of its own. Guth proposed that a tiny fraction of a second after the big bang (10-30 seconds or thereabout) the Universe underwent a period of inflation, it expanded at many times the speed of light smoothing itself out and leaving virtually all possible Universes looking just like ours.

Alan Guth (Credit: Alamy)

Before long observations from satellites studying the CMB confirmed many of the predictions of Guth’s inflationary model and today nearly every cosmologist accepts the need for some sort of inflation in the early Universe.

Now at first Guth did not proposed a mechanism of what caused his inflation, he would later work on several alternatives, he simply pointed out that inflation whatever caused it would generate a Universe like the one we see. Back when I was taking Cosmology the energy needed to cause inflation was assumed to come from the symmetry breakdown of a Unified Force Field into the four Forces we’re familiar with, Gravity, Electro-Magnetism and the Strong and Weak Nuclear Forces.

Today however Unified Field Theories are having a hard time of it and it has been suggested, based on clues from quantum field theory, that inflating space might be the norm and a Universe like ours is really nothing but a bubble in sitting inside an ever inflating reality. In that case there are undoubtedly infinitely many other bubbles making a Multiverse of infinite Universes.

Is there a Multiverse? (Credit: Smithsonian)

Is your brain hurting yet, because I’m just getting to Hawking’s last paper. What Hawking and his former student have done is to develop a mathematical model of an inflating Universe where inflation comes to a soft end, a smooth exit as Hawking and Hertog put it. This generates a single Universe not an infinite number of Universes in a Multiverse.

Now all of this is just a mathematical model, the only observable prediction that the paper makes is that there should have been gravity waves produced during the inflation period, an observation that may soon be tested. However many other theories of the early Universe make the same prediction so the discovery of such gravity waves will only be weak support for Hawking’s model.

Progress in cosmology is slow but I have seen quite a bit in my time, I can barely remember when the Big Bang was still just a hypothesis. I do hope that in the next few years we get a better understanding of what triggered inflation as well as what brought it to a halt. If and when we do I’m certain that the answer will be something that Stephen Hawking would have found fascinating!