Big Bang Cosmology - Believe it or Not By William Lama Ph.D.

Big Bang Cosmology - Believe it or Not

By William Lama Ph.D.

NASA Galaxies like colorful pieces of candy fill the Hubble Ultra Deep Field 2014.

Have you ever thought about the universe? How big is it? How and when did it begin?  What does it contain? How will it end?  Will it end?  These “cosmic questions” were once the domain of philosophers. Remarkably, in the 20th century, such questions became the purview of science fiction and TV comedies.

But is the Big Bang a theory, or more specifically, a scientific theory? Unlike its vernacular use, theory in science is not an idea or hypothesis. A scientific theory describes reality; it makes predictions than can be tested; it is falsifiable; and it should contain no adjustable parameters.

Like all good science the Big Bang theory relied on measurements. Astronomers including Edwin Hubble at the Mt. Wilson Observatory provided observational data on far flung galaxies and other celestial objects. Here is a modern Hubble diagram for a special type of Supernova.

Hubble Diagram with permission from P.N.A.S. (© National Academy of Sciences, U.S.A.)

Notice the linear relationship between Velocity and Distance.

The proportionality constant (slope of the line) is the Hubble constant (H0). This relationship held for all celestial objects with the same value of H0 (until recently). It was surprising that the furthest galaxies and supernova were moving the fastest. Even more surprising was that all the distant galaxies appeared to be receding from the Earth. Was the Earth the center of the universe? Was Ptolemy right after all? What did it all mean?

Every theory of the course of events in nature is based on some simplification and is to some extent, therefore, a fairy tale. (Sir Napier Shaw)

Newton's law of universal gravitation (1687) was a valid physical theory. It described the motion of an apple falling from a tree and the motion of the Earth around the Sun. The first test of the theory was an experiment by Henry Cavendish in 1798, over 100 years since Newton formulated the law. His gravity law unified phenomena observed on Earth with astronomical behavior. It was a grand success, but Newton was never satisfied with the notion of “action at a distance” that his theory implied. In 1692 he wrote: "That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it."

On the experimental side, Newton's theory did not explain the precise motion (the precession of the perihelion) of the orbits of the planets, especially that of Mercury.

Einstein's theory of General Relativity (1915) supplanted Newton’s gravitation. In Einstein’s theory, instead of gravity being a force propagated between bodies, energy and mass distort space in their vicinity, and other bodies move in trajectories determined by the geometry of space. Einstein believed that his equations would predict a collapsing universe due to the attraction of all the mass in it. Thus he introduced the cosmological constant (a fudge factor) in 1917 to counterbalance the effects of gravity.

Ten years later Georges Lemaitre, a Jesuit priest and physics professor, showed that Einstein’s equations (without the cosmological constant) predicted an expanding universe. He derived the Hubble relationship theoretically in 1927 two years before Hubble published his data.  Lemaitre also proposed the “hypothesis of the primeval atom” that became known as the “Big Bang” theory of the origin of the universe. Einstein refused to accept that the universe was expanding, commenting to Lemaitre: "Your calculations are correct, but your physics is atrocious." Two years later Einstein had to eat his words, but that is the beautiful thing about science. When experimental data disagreed with his theory the most prominent scientist in the 20th century had to admit he was wrong. Einstein called the cosmological constant his “biggest blunder.”

Over the years a model of the universe that explained the uniform homogeneous expansion was developed. In the Standard Cosmological Model the galaxies are all moving away from each other; no galaxy is special.  A simple analogy may help. Imagine that the galaxies are raisins embedded randomly within a loaf of bread that is put into the oven to bake.  As it heats, the bread dough expands and the raisins all move apart.  Any raisin sees all other raisins moving away from it.  Also, raisins farther from the center of the loaf will move faster than those closer to the center as the loaf expands, just like the galaxies. Reversing time and tracing the galaxies backwards inevitably leads to a point where everything began: the Big Bang.

“Cosmologists are often in error, but never in doubt.” Russian physicist Lev Landau

Then things got even stranger. To explain the properties of the universe the measured mass density and energy density were not sufficient. For example, in spiral galaxies like our Milky Way stars orbiting around the centers seem to strongly disobey the predictions.

Milky Way galaxy rotation curve from Wikipedia

Note that the measured velocity profile is unlike that expected from theory. More mass is needed to account for the measured data and the “missing mass” came to be thought of as some sort of unknown “dark matter.”

The evolution of the universe from the Big Bang was full of surprises.

NASA JPL Big Bang Timeline

In 1998 the Hubble Space Telescope observations of distant supernovae showed that the expansion of the universe was actually accelerating.  What was causing it? Perhaps it was the result of Einstein’s long-discarded cosmological constant. Perhaps some kind of field or energy density described by Einstein’s “blunder” creates this cosmic acceleration. We still don’t know what it is but cosmologists have given it a name: “dark energy.”

And now even the Hubble constant is in doubt. As reported in Physics Today, March 2020: The Planck observatory measurements combined with the Standard Cosmological Model, yields the Hubble value H0 = 67.4 ± 0.5 km/s/Mpc. On the other hand measurements of supernova yield a value H0 = 74.0 ± 1.4 km/s/Mpc. These values disagree by more than 4.4 standard deviations. That is troubling.

In 2002 a special issue of Scientific American magazine was devoted to the Cosmos. In the lead article, the cosmologist James Peebles presented a scorecard for the major ideas. Here are his grades.

1. The universe evolved from a much hotter, denser state 13.7 billion years ago (A+)

2. The universe expands as predicted by General Relativity (A-)

3. “Dark matter” made of unknown particles greatly exceeds normal matter (B+)

4. “Dark energy” in the universe greatly exceeds the matter and is causing an acceleration (B-)

In my view, those grades are inflated. After years of searching and theorizing, we still don’t know what dark matter and dark energy really are. And we can’t predict the Hubble constant. And I won’t mention the inflation, wormholes and the multiverse. Still, it’s the Big Bang model – believe it or not.

Dr. William Lama - PhD in physics from the University of Rochester. Taught physics in college and worked at Xerox as a principle scientist and engineering manager. Upon retiring, joined the PVIC docents; served on the board of the RPV Council of Home Owners Associations; served as a PV Library trustee for eight years; served on the PV school district Measure M oversight committee; was president of the Malaga Cove Homeowner's Association. Writes about science, technology and politics, mostly for his friends.

email: wlama@outlook.com