Monday, May 29, 2017

Some Proposals about the Beginning of our Universe

The theoretical physicist from Caltech, Sean Carroll gave a talk to the American Astronomical Society in January 2017 on the topic of what we know and don't know about the beginning of the universe. He has generously posted a copy of his presentation on his blog, In this talk, Dr. Carroll speculates about how the gaps in what we don't know may be filled in by presenting a systematic classification of the main ideas developed over the last few years about what may have occurred before our universe began and brought our universe into existence. (Dr. Carroll does point out that to say our universe "came into existence" sounds like a process within time, but that time as we know it actually had a beginning with our universe.) In previous posts I have already discussed many of the things Dr. Carroll covers in his talk including (1) that our universe was in a state with very low entropy at its beginning, (2) that something like the Big Bang occurred about 13.8 billion years ago but we don't know what actually happened in the first trillionth of a trillionth of a trillionth of a second because (3) we don't have a quantum theory of gravity which may describe the initial conditions of our universe, even though (4) the equations of classical general relativity predict that our universe had an actual beginning.

Let's review what we do know: (1) About 13.8 billion years ago the universe was very hot and dense and was expanding rapidly while decelerating; (2) classical general relativity predicts that there was an actual beginning of our universe in a singularity; and (3) our early universe was in a very low entropy state which is quite hard to explain since low entropy is associated with an ordered, and improbable state. The last point presents tremendous challenges for any naturalistic proposal about how our universe came into existence.

In regards to what we don't know, Dr. Carroll presents four different classes of models about the space-time origin of our universe: (1) a bouncing model, (2) a cyclic model, (3) a hibernating model, or (4) a reproducing model.

Sunday, May 21, 2017

Extraordinary Claims and Extraordinary Evidence

"Extraordinary claims require extraordinary evidence" is a phrase that was popularized by Carl Sagan but has its roots from at least the 18th century Enlightenment when the miracles of Christianity were being questioned by certain intellectual thinkers of the day. The most famous Enlightenment critic of Christianity was probably David Hume who wrote an essay called Of Miracles in 1748 where he states, "Suppose, for instance, that the fact, which the testimony endeavours to establish, partakes of the extraordinary and the marvellous; in that case, the evidence, resulting from the testimony, admits of a diminution, greater or less, in proportion as the fact is more or less unusual."

At first this statement may sound reasonable. For instance, I am more likely to believe you if you tell me you had breakfast this morning than I would believe you if you told me that you levitated off the ground this morning without anything holding you up. But does the fact that I believe you if you say you did something ordinary and I don't believe you if you say you did something extraordinary support the statement that "Extraordinary claims require extraordinary evidence?" Actually, it doesn't. Although I may believe that you ate breakfast this morning, I must obtain supporting evidence if I want to actually determine whether or not that fact is true. If you have cleaned up your kitchen, such evidence may be hard to find. I might have to pump out the contents of your stomach, for instance to see what you ate and when you ate it. It is one thing to say that I believe you ate breakfast because it is an "ordinary" event, but it is quite another to actually find enough evidence to validate your claim. My point is that actual validation of any event requires sufficient evidence.