Unexplainable astronomy? Part 2: Of pigeons and cosmic uniformity

By Sam Jarman

Ask just about any scientist, and they will tell you that the very best discoveries they can make are the ones which force us to change how we think about the world completely. That’s exactly what happened in 1923, when Edwin Hubble looked out at a small, hazy nebula from his mountaintop telescope in California.

Without Henrietta Leavitt’s work, we might still think of galaxies like Andromeda as funny-looking nebulae which don’t make any sense | Image: NASA

Based on previous research by Henrietta Leavitt, Hubble was looking for Cepheid variable stars in the nebula, which would tell him exactly how far away it was. He managed to find a variable star easily enough, but it revealed a pretty big problem. The star showed Hubble that the nebula he was looking at was not even a nebula after all, but a vast cluster of stars situated very, very far away.

The distance was greater than any we had thought possible for thousands of years. For scientists, that meant that we needed to completely rethink our model for the structure of the universe. With the discovery of the Andromeda galaxy, the fundamental idea of billions of galaxies occupying a vast, ever-expanding universe was born. It was a lot for the world of astronomy to take in.

In the decades following Hubble’s discovery, theoretical physicists struggled to discern the scientific rules which could possibly govern such a newly colossal, mysterious universe. Some of their theories seemed promising, but In the meantime, the imaginations of the media and the public ran wild. If our understanding of the universe could be so shaken by one discovery like Hubble’s, they reasoned, what other revelations could be hiding in plain sight? And, of course, the biggest question: could intelligent life be out there somewhere?

Apprehension had grown strong by the 60s. Theoretical physicists had some convincing ideas about the nature of the universe, but at the time, technology just wasn’t sophisticated enough to prove experimentally which were correct, and which were misguided. Their ideas so often disagreed with each other that it seemed like no-one had really got anywhere at all. But change was coming. Improved telescopes meant that by 1964, mysterious signals, the likes of which would make or break previously speculative cosmological theories, began to come in.

A dodgy radio receiver? 

Pigeons. It had to be. Since making their home in the cosy hovel that was the Holmdel Horn Antenna, the birds had been busy and painting the walls with the remains of their dinner, which was giving off who knows what kind of radiation. How else could radio astronomers Arno Penzias and Robert Woodrow Wilson explain the uniform, unwanted microwave signal, which wouldn’t go away no matter where in the sky they pointed the telescope?

Whenever you’re feeling down, just remember that a sad metal toilet in New Jersey once became one of the most important telescopes of the 20th century| Image: NASA

The pair cleared out the avian intruders, and scrubbed the inner surface of the antenna clean. They checked the equipment thoroughly yet again, making sure the receiver was still cooled to just above absolute zero, minimising any interference from within the telescope. But still, the low, intense noise hindering their experiment persisted. Clearly, the radiation was originating from something more interesting than pigeon droppings. Something, they realised, beyond our own galaxy.

Coinciding with Penzias and Wilson’s predicament, a group of astrophysicists at Princeton University were working on a theory they believed could explain what was happening in the earliest moments of the universe’s existence. Based on earlier work by cosmologist Ralph Alpher, their idea hinged on the concept that the universe had all started with a rapid, high-energy expansion from a single point: a Big Bang. They proposed that if the Big Bang had really happened, it must have released a colossal surge of radiation, still observable to this day with the right equipment. The radiation would have cooled significantly by now, but if its remnants were detected, it would be definitive proof that the scientists’ notion was correct.

The idea was in direct conflict with the earlier-proposed Steady State theory, which suggested that the universe had no beginning, meaning no Big Bang, at all. Instead, the universe had existed for an eternity beforehand, and had never changed significantly. The two theories were radically different, and both appeared to have equal weight. But without any hard evidence, neither could be validated over the other. That all changed in 1964, when Penzias and Wilson caught word of the Princeton scientists’ research.

The Colossal Clang and Tremendous Toot were also considered, but never really caught on| Image: NASA/WMAP Science Team

Through a friend, Penzias got access to a preview of the Princeton paper. What he read astounded him: using first principles, the astrophysicists had argued that a surge of electromagnetic radiation had permeated the entire universe following the Big Bang. As the universe expanded, so too did the wavelength of the radiation, until reaching its current wavelength of 7.35 cm. That was the very same radiation Penzias and Wilson had attributed to pigeon poop – almost exactly. The pair got in touch with the Princeton scientists as soon as they could.

The rest of the story is history. The two groups teamed up to publish not only a theory of how the Big Bang could have hypothetically played out, but indisputable experimental proof of the Big Bang itself on top of it. The Steady State theory had been disproved, and was consigned to history. In 1975, Penzias and Wilson earned a Nobel Prize for their ground-breaking discovery.

Decades later, the radiation observed for the first time by Penzias and Wilson – now known as Cosmic Background Radiation – has been studied in meticulous detail. It has been found to be incredibly uniform, but not perfectly so. In the very earliest moments of the universe, some regions emerged where matter was densely clumped together, whereas it was sparser in others. As the regions formed, the surge of radiation created by the Big Bang was slightly distorted by the clumps of matter.

Of all the scientific results which were first thought to be literally crap, the Cosmic Microwave Background has got to be the most impressive | Image: NASA

Billions of years later, the denser regions have become areas abundant in galaxies, while the sparser regions are now vast, empty voids in space. The Cosmic Microwave Background has retained the distortion it underwent at the very start. By picking up the subtle variations in the radiation, we can now create maps of the structure of the universe with detail which must have been unthinkable just a few decades ago.

So from a mysterious error first attributed to pigeons with poor housekeeping skills, came another fundamental theory in cosmology. But the 60s weren’t over, and there were yet to be more discoveries which would prove to shake up our understanding of how the universe works. In 1967 came another bizarre signal, this time with a somewhat more exciting misguided idea about where it came from.

Space is Big

By Jonathan Farrow from the Thoughtful Pharaoh

I didn’t grow up by the sea, so every time I’m faced with an ocean, I get a true sense of awe. The sheer magnitude of the thing in front of me leaves me speechless. I look out and it’s just water, as far as the eye can see.

Image my own

On a clear day, the horizon for an average person standing by the sea is about 5 kilometres.

So if looking out 5 kilometres in every direction is enough to impress me (and I’m pretty sure I’m not the only one), you can imagine why I love looking through telescopes so much.

The moon, an easy target for amateur astronomers like myself, is nearly a hundred thousand times further away than that horizon (384000 kilometres on average). When you look at it through a telescope, you can see start to identify craters and “seas”, just like Galileo did 400 years ago.

Full moon.jpg
Image by Gregory Revera via Wikimedia

And that’s the closest non-Earthly object in the Universe. It only gets further from there.

Light, travelling at the speed limit of the universe, takes about one second to reach us from the Moon. The Sun, which by coincidence is the same apparent size as the moon when viewed from Earth, is 400 times further away. Light takes 8 minutes to reach us from its tumultuous, fusion-fuelled surface.

It takes light 4 hours to get from the Sun to Neptune, the edge of the Solar System (sorry Pluto, you don’t count anymore). Light travelling for 4 years will just about get to the nearest star (Proxima Centauri) and to get to the edge of the Milky Way from its centre takes light more than a thousand human generations (50000 years +).

While those distances are starting to get mind-boggling, the Milky Way is only one very tiny part of the Universe. Sure, it contains a billion stars and the only known way that the Universe knows itself, but we’re learning that we’re even smaller than we thought.

The next closest galaxy to the Milky Way is called Andromeda, and together with 52 other mini-galaxies, we live in the Local Group.

Image by Antonio Ciccolella via Wikimedia

The Local Group, in turn, is part of a supercluster of galaxies called Virgo. And that was it – our Universal address was Earth, Solar System, Milky Way, Local Group, Virgo Supercluster.

But in 2014, astronomers redrew the map of the local Universe by looking at where galaxies were moving. It turns out that we’re part of a much larger supercluster called Laniakea. The name is apt, meaning ‘immeasurable heaven’ in Hawaiian.

Another recent discovery has shed new light on the size of the universe. In October 2016, astronomers from the University of Nottingham and the University of Edinburgh used data from a new set of Hubble images called Frontier Fields to recount the number of galaxies in the Universe.

The original Hubble Deep Field images, released in 1996, reached further away (and therefore further back in time) than anything previously available. They glimpsed 12-billion-year-old galaxies from the very early Universe.

These Deep Field images had thousands of galaxies in them, so when astronomers extrapolated that out to the whole sky, 120 billion was the agreed number of galaxies in the Universe.

The original Hubble Deep Field from 1996, Nasa via Wikimedia

But 120 billion galaxies don’t weigh enough, so astronomers suspected that might be a miscount. This new study uses images that go back 13 billion years and used a mass distribution approach to arrive at a new number that would include galaxies too faint to actually observe.

Their results show that there are 2 trillion galaxies in the Universe, 10 times more than previous thought.

Or, at least, there were 2 trillion galaxies. Many of the small, early galaxies will have merged with others in the intervening 13 billion years, but the light from those mergers hasn’t reached up yet.

With astronomers not only redrawing the map but also doing another census, it turns out space was bigger and fuller than we thought.

What does that mean for the awestruck boy by the sea? I’m not entirely sure, but I think it means that even though he’s smaller than he thought, he should keep wondering and keep seeking to understand his place in the Universe. I take a lot of inspiration from Carl Sagan, so I’ll leave you with this, from Cosmos:

“In a cosmic perspective, most human concerns seem insignificant, even petty. And yet our species is young and curious and brave and shows much promise. In the last few millennia, we have made the most astonishing and unexpected discoveries about the Cosmos and our place within it, explorations that are exhilarating to consider. They remind us that humans have evolved to wonder, that understanding is a joy, that knowledge is a prerequisite to survival. I believe our future depends powerfully on how well we understand this Cosmos in which we float like a mote of dust in the morning sky.”