The Universe is Expanding

More Background - The Messier Catalogue

Okay, so you were just told that Slipher found the "nebulae" of the Milky Way are really vast collections of stars that are not within our galaxy, but outside of it. His discovery was shared with Ed Hubble and the two worked to test for the reality of this new finding. Because the implications were expected to be controversial, they spent years collecting and analyzing data. Here is a history of the events that led up to the famous announcement in 1929.

During the mid-1700's, Charles Messier, using an 8-inch mirror telescope, made a list of 110 deep-sky objects that did not look like stars. He was an avid astronomer and comet-hunter, and too often he would become initially excited about a new comet, only to discover that the object has been there for a long time already. By compiling a list of these 110 objects, and including a description and celestial coordinate location, Messier and others after him would know that their new "discovery" was either something not yet seen, or just an object already in the catalogue.

 

 

 

 

Most of these Messier Objects are fuzzy patches in the sky that look like tiny wispy clouds. They were given the name "nebulae" which is Latin for "cloud." We now know that many of these nebulae are indeed entire galaxies, but because they are so far from us, and because the telescopes of the early years of Astronomy lacked good resolving power, they looked like little clouds to Messier. Astronomers knew that the Milky Way was an immense spiral structure containing countless stars and many nebulae. Up until 1920, astronomers thought the Milky Way WAS the entire Universe, and that all of the Messier Objects were within the confines of the Galaxy. Below is a photographic collection of the Messier Objects.

Background Continues with William Herschel

During the 18th Century, German-born, English astronomer William Herschel became the world's most renowned astronomer. He discovered the planet Uranus, built very large telescopes, comparable to those built today, including one with a 48" mirror. Herschel was the first to systematically attempt to ascertain the size and structure of the universe. Using his telescope that had four times the light gathering power of Messier's, Herschel expected to find many more nebulae that Messier missed, and indeed, he found over 2,000 objects that he named:

 

 

 

 

island universes - any galaxy that could not be resolved into aggregations of stars must be so far away that it is an island universe

globular clusters - small, spherical collections of stars

planetary nebulae - gaseous clouds that look like small rogue planets.

The result of Herschel's work was the conclusion that there is a lot more stuff out there than just stars and 110 Messier Objects.

Henrietta Leavitt

During the very last part of the 19th and first part of the 20th Century, Henrietta Swan Leavitt (a member of "Pickering's Harem") made tremendous contributions. Leavitt was totally deaf and quietly reserved, but extremely brilliant, and she joined the Harvard team in 1892 as a volunteer research assistant. By 1902, she was head of a department specializing in measuring magnitudes of stars, and by 1908, she had compiled a list of over 1000 Cepheid Variables in the Small Magellanic Cloud. Sixteen appeared on enough plates for her to establish their period, and she noticed, the longer the period, the brighter the star. By 1912, she had established the periods of 25 Cepheids and found a strict linear relationship between period length and intrinsic brightness. This offered astronomers a means to measure distances due to the inverse- square law: a star, like any other light source, will look a quarter as bright if its distance from the observer is doubled, a sixteenth as bright if the distance is quadrupled, etc. By looking for such Cepheid Variables in Messier and Herschel's "nebulae" it should be possible to determine their relative distance.

In 1913 Enjar Hertzsprung studied 13 close Cepheids to determine their distance and thus their brightness and attempted to measure the distance to the Small Magellanic Cloud. He proposed a distance of 3,000 ly, but there were a few problems with his technique. He dropped a zero from his calculations. He photographed local Cepheids in red-light sensitive film and did not properly measure their apparent magnitude properly. Leavitt had used blue-light sensitive film, so the two photographs could not be properly compared. Therefore, nobody knew how much in error the attempt was! A raging debate ensued - was the Milky Way 300,000 ly across or 30,000 ly across? Were there island universes beyond us, or was all this stuff part of us?

Edwin Hubble, a Missouri-born and English-trained astronomer, returned from England and practiced law, but began studying astronomy as a hobby. He joined the University of Chicago, working with a group at Yerkes Observatory. Hale invited him to work in California atop Mt Wilson on the 100" scope there, but 1917 came by and Hubble went off to war. He returned in 1919 and accepted the position at Mt Wilson. He spent his time studying spiral galaxies - Andromeda in particular - looking for Novae - occasionally brightening stars, and found one that was Cepheid - A VARIABLE. From the period-luminosity relationship he calculated the distance to Andromeda at 900,000 ly - far enough to be considered a full-fledged galaxy.

Edwin Hubble began a serious study of other deep-sky objects at the Mt. Wilson Observatory in California. He began compiling a series of spectroscopic photographs of the deep-sky objects and was astonished to discover that the Hydrogen absorption lines, as well as all of the other classic absorption lines of a typical stellar spectrum were not in the expected locations.

 

 

 

The following powerpoint slides relate his story and startling discovery. The spectra in the slides are highly simplified so you can understand the process.

Hubble has found that everything on a large scale is expanding away from us and each other. Einstein is forced to admit trying to make the Universe fit his ideas. The reality for the world was that the Universe is getting bigger. The farther away the objects are from here, the faster they are moving in their recession! The perspective for any large-scale structure in the Universe is that every other similar structure is moving away from it ... no matter where you are in the Universe. It all looks the same everywhere. Things are moving away. This is illustrated in the three diagrams below.

 

What I want you students to grasp is the use of the term "red shift" when describing the expansion of the Universe. The red-shift is not being caused by the "Doppler Effect" as it applies to sound, but by the very stretching of space itself. Galaxies are not running away, but rather the entire Universe is inflating like the giant balloon analogy and the light from these galaxies are being strecthed. When such light is stretched, the wavelength moves from one higher energ level to a lower energy level. You will learn more about this in the next chapter, The Big Bang.

Conclusion:

1. Everywhere you look in space, galaxies or their associations are moving apart from each other.

2. The more an object is red-shifted, the farther away it is, and the faster it is moving away from us.

3. Some deep-space objects are so far away, and moving so fast that their light has been stretched into the Infrared, Micro, and even Radio wavelengths.

4. If the Universe is expanding, then what was it like in the past?

5. If the Universe is expanding, then what will happen to it in the future?

The implications of this discovery are huge, and it is my personal contention that no other discovery in the 20th Century compares to this expansion of the Universe discovery by Hubble. The result was the development of a new model to explain the origin of everything.

Big Bang Theory in brief form

The Big Bang is not a bang, or explosion, but a sudden expansion of material from a point of infinite density, infinite energy, and zero volume into everything that we see today. The entire process has been laid out by nuclear physicists who study the properties of subatomic particles, going back all the way to the first 10^-43 seconds. Part of the expansion process happened at superlight speeds (Era of Inflation), while the rest of the time the Universe is believed to have expanded at a more constant rate. Einstein has demonstrated the ability of energy to be converted into mass, and mass into energy, and this fundamental theory where E = mc^2 provides the basis for this law. The initial point from which the Big Bang originated cooled from its state of infinite energy to a state where matter formed ... first as subatomic particles that make up protons, electrons, and neutrons, then into those atomic particles. The greater the Universe expanded, the farther apart these particles moved from each other and the cooler the temperatures. This resulted in the ability for electrons to associate with protons and form actual atoms. At some later time, giant clouds of Hydrogen and Helium gas (the only two elements really formed from the Big Bang) collapsed into stars and galaxies.

The basis for this theory is the evidence of the expanding Universe demonstrated by Edwin Hubble. It is reasonable to conclude that if the Universe is expanding today, it must have been smaller in size yesterday. It must have been even smaller last year, 1000 years ago, and billions of years ago. In fact, it is reasonable to conclude that the Universe must have been extremely small in size in the distant past, and perhaps so small that all of it could be contained within a singularity!

To learn more about this theoretical Big Bang, please move forward to The Big Bang, or return to Red-Shifting, or the Cosmology Introduction, or go to the Syllabus .


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