Fjordman: A History of Astrophysics — Part 5

The fifth and final installment of Fjordman’s history of astrophysics has been published at Vlad Tepes.

Earlier installments are: Part 1, Part 2, Part 3, and Part 4.

Some excerpts from Part 5 are below:

Despite all this progress, countless questions remain unanswered. As Alan Guth notes, even if the present form of the Big Bang theory with inflation should turn out to be correct, it says next to nothing about exactly what “banged,” what caused it to bang or what happened before this event. “I actually find it rather unattractive to think about a universe without a beginning. It seems to me that a universe without a beginning is also a universe without an explanation.”

Another major question is whether the expansion that our universe appears to be experiencing at the moment will continue indefinitely, or whether there is enough mass to slow it down and eventually reverse it, causing the universe to collapse onto itself in a “Big Crunch.” The Swiss astronomer Fritz Zwicky already in 1933 stumbled upon observations indicating that there is more than visible matter out there and that this “dark matter” affects the behavior of galaxies.

In the 1970s the American astrophysicist Jerry Ostriker (born 1937) along with James Peebles discovered that the visible mass of a galaxy is not sufficient to keep it together. The astronomer Vera Rubin (born 1928) studied under Richard Feynman, Hans Bethe, George Gamow and other prominent scholars in the United States. She became a leading authority on the rotation of galaxies. She teamed up with astronomer Kent Ford (born 1931) and began making Doppler observations of the orbital speeds of spiral galaxies. Her calculations based on this empirical evidence showed that galaxies must contain ten times as much mass as can be accounted for by visible stars. She realized that she had discovered evidence for Zwicky’s proposed “ dark matter,” and her work brought the subject to the forefront of astrophysical research. Rubin is an observant Jew and sees no conflict between science and religion.

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In the 1990s, two competing groups began observing a certain type of supernovas as a way to study the expansion of the universe. In 1998 a team led by Saul Perlmutter (born 1959) at Lawrence Berkeley National Laboratory in California completed a search for type Ia supernovas, supplemented by a second team led by Brian P. Schmidt (born 1967) and Adam Riess (born 1969). To everyone’s surprise, their observations indicated that the expansion was not slowing down due to gravitational attraction, as many had suspected, but was speeding up. Further results have confirmed that the expansion of the universe appears to be accelerating.

Astronomers currently estimate that out of the total mass-energy budget in our universe, a meager 4% consists of ordinary matter that makes up everything we can see, such as stars and planets, whereas 21% is dark matter. A full 75% consists of “dark energy,” an even more mysterious entity than dark matter. The US cosmologist Michael S. Turner coined the term “dark energy” to describe the mysterious force which seems to work like anti-gravity.

Petr Horava is a Czech string theorist who is currently a professor of physics at the University of California, Berkeley, and co-author with Edward Witten on articles about string and M-theory. He has proposed a modified theory of gravity, with applications in quantum gravity and cosmology. “I’m going back to Newton’s idea that time and space are not equivalent,” Horava says. At low energies, general relativity emerges from this underlying framework and the fabric of spacetime restitches. He likens this emergence to the way some exotic substances change phase. For example, at low temperatures liquid helium’s properties change dramatically into a “superfluid.” Cosmologist Mu-In Park of Chonbuk National University in Korea believes that this gravity could be behind the accelerated expansion of the universe.

A few scientists have controversially proposed resurrecting the discredited light-bearing ether of nineteenth century physics. Niayesh Afshordi, an Iranian-born USA-based physicist, suggests a model where space is filled with an invisible fluid — ether — as predicted by some proposed quantum theories of gravity such as Horava’s. Black holes may give off feeble radiation, as suggested by many quantum theories of gravity. Afshordi calculates that this radiation could heat the ether and, like bringing a pot of water to a boil, generate a negative pressure of “anti-gravity” throughout the cosmos. This would have the consequence of speeding up cosmic expansion, but it took billions of years for black holes to heat up the ether sufficiently. Another, less exotic alternative theory called Modified Newtonian Dynamics has been introduced by the Israeli astrophysicist Professor Mordehai Milgrom. This proposal has received the backing of some notable scientists, but so far only a minority of them.

Perhaps “dark matter” will turn out to be a new class of particles and matter that behave very differently from the kind of matter we are most familiar with. Perhaps we still don’t know enough about the nature of gravity or the age of the universe and that “dark energy” will in hindsight turn out to be a fancy name for something that does not actually exist, a twenty-first equivalent of phlogiston. Or perhaps we will discover new insights that will fundamentally alter our understanding of the very fabric of spacetime. Whatever the truth turns out to be, the terms “dark matter” and “dark energy” are reminders that scientists cannot yet fully explain some of the observed properties of the visible universe according to known physical laws.

In the late 1800s, many European scholars sincerely believed that they understood almost all of the basic laws of physics. They had reason for this optimism as the previous century had indeed produced enormous progress, culminating in the new science of thermodynamics and the electromagnetic theories of Maxwell. Max Planck was once told by one of his teachers not to study physics since all of the major discoveries in that field had allegedly been made. Lucky for us he didn’t heed this advice but went on to initiate the quantum revolution. We have far greater knowledge today than people had back then, but maybe also greater humility: We know how little we truly understand of the universe, and that is probably a good thing.

Read the rest at Vlad Tepes.