Our Expanding Universe, the Cold Dark Night Sky, and Us

Part 1: The astronomy and physics underlying what I call “an undying drive for the best that is in us.”

The Milky Way

Our Unbounded, Expanding Universe

“Olbers’ Paradox”

German astronomer Heinrich Olbers (1758 - 1840), and others before him, asked a question about something so taken for granted and commonplace that no one normally gives it a second thought: Why is the night sky dark?

The reasoning goes like this: If the Universe we inhabit is infinitely old and infinitely large, then every line of sight must end in a star (no matter how long it took light to get here), and the sky must be as bright as the average of all the stars. In other words, the whole sky should be as bright, roughly, as our sun, and all matter would be in some kind of gaseous or plasma form; nothing solid or liquid at all; no Earth; no us.

Astronomical Red Shift

The work of several astronomers (with Edwin Hubble most well known) established that the farther away a galaxy is, the redder its light is. Why and how?

Recessional motion subtracts energy from the light waves emitted (stretches out the wave—photon, actually—as it is emitted). Longer waves mean lower frequencies, and the energy of a photon varies with the square of its frequency.

Thus for example, red light has roughly half the frequency and thus 1/4 the energy* of far blue (actually, violet) light. Hence the term “red shift” has been adopted to express this loss of energy, which was detected in the spectral lines (see below) of stars and galaxies observed.

• * Having so much more energy is why far-blue light can harm eyes unless diets contain lutein, zeaxanthin, and other nutrients to filter it out.

You can hear the same effect of how wavelength changes with motion when a speeding car’s horn, or a train’s horn, goes from a higher pitch approaching you to a much lower pitch when going away (even though light photons don’t propagate the same way sound waves do).

This change in wavelength and frequency associated with a source coming toward you or away from you is called the Doppler effect.

The “Big Bang” and the Expanding Universe

Two main theories developed to explain the astronomical red shift. One, “the steady state,” assumed that matter and space are continually entering—or being created in—our Universe, pushing space and matter outward. The second, “the Big Bang,” assumed the Universe began in one huge explosion billions of years ago, and the expansion from the explosion explains the expansion observed today of the Universe. Resolution of this debate came this way:

Arno Penzias and Robert Woodrow Wilson, working at AT&T’s Bell Labs, Holmdel, NJ, were trying to find the source of a particular radio-wave noise that AT&T’s telecom system, with its globe-spanning connections, was picking up. (Before the Bell System was broken up.)

These radio waves had an electromagnetic frequency much lower—and therefore colder—than light and X-rays, which are higher-energy examples of EMFs. And they were detected coming from all directions. They are now called “cosmic background radiation” and are, of course, invisible to the naked eye.

Physicist/astronomer Robert H. Dicke postulated they could be the background radiation stemming from the Big Bang. That view now prevails: The Universe began in a big explosion providing all the matter and energy in the Universe, and it has been expanding in all directions ever since.

Penzias and Wilson were awarded a Nobel Prize for their discovery in 1978.

The cosmic background radiation corresponds to a temperature of -454.76 Fahrenheit and -270.42 Celsius [F = 32 + (9/5)(C) = 32 + 1.8C]. That is just 2.725 degrees above absolute zero, which is -459.67 degrees Fahrenheit, or -273.15 degrees Celsius.

Astronomers and astrophysicists conventionally estimate that the Big Bang occurred about 13.8 billion years ago. One estimate goes as far back as 26.7 billion years. And astronomers recently have come to think that the expansion is increasing in speed.

Consequently, beyond a given distance, stars in galaxies are receding from us so fast that their light has lost most of its energy and we don’t see them at all. This also explains why the night sky is dark and very, very cold.

Estimating Distances and Motions of Stars and Galaxies

Our sun and planets reside in one of the arms of a spiral galaxy we call the Milky Way, which is visible on a clear night in a good location (absent human light) as a rich elongated field of stars (pictured above). American astronomer Edwin Hubble is credited with discovering that many indistinct nebulae in the sky are actually other galaxies.

You may ask, How do we know distances to stars and galaxies? It’s such a good fundamental question that I’ll take the time to elaborate the answer here:

The distance to regional stars can be gotten using trigonometry: take a sighting of a star from two locations with a known separation, which provides two angles and a base. Taking sightings at opposite ends of the diameter of the Earth’s orbit (6 months apart)—triangulation—can give a large enough base (186 million miles, 300 million kilometers) to measure some pretty distant stars.

Within this range from Earth, astronomers have noticed that some stars, called Cepheid variables, have absolute brightness that correlates with such things as temperature and periods of variability.

Because visible brightness varies from absolute brightness as the inverse of the square of the distance, observed brightness on Earth enables Cepheid variables to be used as a longer yardstick for estimating distances. They are sufficiently bright that they can be seen and used to estimate distances to parts of the Milky Way too far to be triangulated, and to neighboring galaxies.

Other stars can get much brighter, temporarily, than Cepheid variables. Novas flare in brightness periodically. Supernovas are one-time huge explosions that can become brighter than whole galaxies. Astronomers have found ways to characterize such stars and their absolute brightnesses. Combining this with a nova’s or supernova’s brightness as seen from Earth, astronomers can estimate distances to stars in galaxies much farther from Earth.

The amount of the red shift itself is used to estimate distances to the farthest visible galaxies.

These estimates, it must be kept in mind, are well founded but subject to some significant margins of error and reinterpretation. After all, we can’t really measure the absolute brightness of stars, which also means that astronomy, cosmology, and astrophysics are not hard sciences, which require multiple experiments producing the same exact result each and every time, within an acceptable margin of error. Rather, astronomy et al are, at best, disciplined studies that use known scientific facts and draw deductions from their observations.

As for observing the Red Shift:

The light of stars has spectral lines corresponding to light radiated or absorbed at specific frequencies by electrons moving between well defined orbital states in atoms.

That is, when a photon of the right specific energy hits and gets absorbed by an electron, the electron gets kicked up to a higher-energy “orbit.” At some point, the electron reradiates a photon and falls to a lower energy orbit.

(With enough energy absorbed, the electron gets kicked out of the atom entirely. This is the photo-electric effect that Einstein explained, for which he was awarded a Nobel Prize, and that is the basis of various light-sensitive devices.)

The faster a star or galaxy is moving away from us, the more these spectral lines are shifted to the red.

Preview:

Part 2 develops cosmic consequences of the cold dark night sky. (Hint: it drains off entropy and allows information to rise, from which we can build so much that, under capitalism, it pays to “do good to those who hate you.” Hence, I call it an undying drive for the best that is in us.)