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Our future, our universe, and other weighty topics


Saturday, September 23, 2017

His Big Bang Redefinition Is Confusing and Insubstantial

The latest post by cosmologist Ethan Siegel (published by Forbes.com) seems to offer a dramatic announcement. It is entitled, “The Big Bang Wasn't the Beginning, After All.”

For decades astronomers have told us that the Big Bang that occurred about 13 billion years ago was the beginning of the universe. We have been told that the universe began in this event, in which the universe began expanding from an infinitely dense point, with incredible heat and density in its first seconds. Has something new been discovered to overturn this view?

No, not at all. It's just Ethan Siegel playing redefinition games in a very confusing fashion. There is no substance at all in Siegel's announcement, and nothing new has been discovered about the universe's beginning.

Here's what's going on. About 15 years after getting the best evidence for the Big Bang (the discovery of the cosmic background radiation), scientists began to make a speculation about something that may have happened when the universe was about a trillionth of a trillionth of a trillionth of a second old. This speculation is called the cosmic inflation theory. It is speculated that when the universe was only about 10-35 second old, it underwent for a fraction of a second a period of exponential expansion, and then returned to the normal, linear rate of expansion we now observe. This strange speculation is called the cosmic inflation theory.

That name is one of the most confusing labels ever put on a science theory. When discussing this cosmic inflation theory, you must not fall into the trap of thinking that the universe's expansion at, say, 10 seconds after the Big Bang was an example of “cosmic inflation.” You must remember that this term “cosmic inflation” refers only to something that supposedly went on during the first second of the universe's history.

Now Siegel wants to introduce a new confusion. He wishes to redefine the term “Big Bang” so that it only refers to what happened after this alleged period of cosmic inflation that supposedly occurred in the universe's first second. So Siegel wants us to start thinking: first there was the cosmic inflation, and then there was the Big Bang. Redefining the term "Big Bang," he says, "The hot Big Bang definitely happened, but doesn't extend to go all the way back to an arbitrarily hot and dense state." 

By making this attempt at redefining the Big Bang (as something that did not occur at the very beginning), Siegel is out on his own. This is not the way the majority of cosmologists speak, and this is not the way they have been speaking about the Big Bang for the past 50 years. For 50 years cosmologists have been talking about the Big Bang as if that term means: what happened at the very beginning of our universe.

For example, in the visual below from a NASA web site, we see the Big Bang referred to as something occurring before the alleged period of cosmic inflation, not after it (Siegel proposes the opposite order, that we think of the Big Bang as occurring after cosmic inflation). 

big bang


What would motivate a cosmologist to try to redefine the term “Big Bang” so that it does not refer to the very beginning of the universe? It is easy to think of a motivation. For 50 years cosmologists have been troubled by the fact that they have no explanation for the Big Bang at the universe's beginning. But if a cosmologist redefines the term “Big Bang” so that it doesn't refer to the very beginning, he can then say that he has an explanation for the Big Bang. If I redefine “Big Bang” to mean something that began when the universe was one second old, then I can claim to have an explanation for that state by referring to the previous second. So the motivation may be: the redefinition may help a cosmologist place a laurel wreath on his head, allowing him to say, “Clever me, I explained the Big Bang.”

Siegel has been pushing this attempt to redefine the Big Bang for quite a while, but there is little evidence that other cosmologists are following him in this matter. Most cosmologists continue to use the term “Big Bang” as they have done for the past 50 years, to mean the event that started the universe. The majority of cosmologists continue to speak as if the Big Bang began at the very beginning, Time Zero, not some time after Time Zero. They mainly continue to speak as if the Big Bang was the very beginning of time.

There is no substance behind any attempt to redefine the Big Bang as something that began later than the very beginning. Nature does nothing to support such a redefinition. The cosmic inflation theory (that there was some special period of exponential expansion during the universe's first second) is unproven, very farfetched, and not supported by any compelling evidence. There are good reasons for rejecting such a theory, discussed by Paul Steinhardt at Princeton University, and in this post and this post. Among the reasons is that the theory conflicts with findings about anomalies in the cosmic background radiation. 

Were we to redefine the Big Bang so that it does not refer to the very beginning, it would be a kind of arbitrary semantic silliness similar to redefining the word “human” so that it does not refer to people with very dark skin. Whenever such a very arbitrary redefinition is proposed, we should ask: who is attempting to help himself or his kind by proposing such a redefinition? Just as a politician might wish to redefine “human” to make things easier for his own kind, a cosmologist might wish to redefine “Big Bang” to make it easier to place a triumphal gold medal around his own neck. But explanatory triumphs are not earned by arbitrary redefinition. 

Postscript: Theoretical physicist Sabine Hossenfelder has a post entitled "Is the Inflationary Universe a Scientific Theory? Not Anymore."  She states this:

It is this abundance of useless models that gives rise to the criticism that inflation is not a scientific theory. And on that account, the criticism is justified. It’s not good scientific practice. It is a practice that, to say it bluntly, has become commonplace because it results in papers, not because it advances science. 

Post-postscript: Siegel has a new errant post entitled "The Multiverse Is Inevitable, and We're Living in It."  He states the following:

Rather, the Multiverse is a theoretical prediction that comes out of the laws of physics as they’re best understood today. It’s perhaps even an inevitable consequence of those laws: if you have an inflationary Universe governed by quantum physics, this is something you’re pretty much destined to wind up with. 

This is extremely erroneous. The "inflationary universe" is not at all "the laws of physics as they're best understood today," but instead a family of speculative cosmological theories, not well supported by evidence. 

Later on in the post he admits that it could be "our ideas about inflation are completely wrong" and that in that case "the existence of a Multiverse isn't a foregone conclusion."  You do not substantiate one speculation by pointing out it is implied by some another speculation.