Most of the scientific community agrees that time travel is theoretically possible, based on Einstein’s special and general theories of relativity. However, world-famous cosmologist and physicist Stephen Hawking published a 1992 paper, “Chronology Protection Conjecture,” in which he stated the laws of physics do not allow the appearance of closed timelike curves (i.e., time travel to the past). Since its publication, the chronology protection conjecture has been significantly criticized. Most of the criticism centered on Dr. Hawking’s use of semiclassical gravity, versus using quantum gravity, to make his arguments. Dr. Hawking acknowledged, in 1998, that portions of the criticism are valid.

However, not to take sides on this issue, I feel compelled to point out that the two fundamental pillars of modern science, namely, general relativity and quantum mechanics, are incompatible. This placed Dr. Hawking in a difficult position regarding the use of gravity in writing the chronology protection conjecture. General relativity and quantum mechanics do not come together to provide a quantum gravity theory. This argues that we still do not have the whole picture, which makes it difficult to completely rule out Dr. Hawking’s chronology protection conjecture.

Currently, there is no widespread consensus on any theory that unifies general relativity with quantum mechanics. If such a theory existed, it would be the theory of everything (TOE) and would provide us with a quantum gravity theory. Highly regarded physicists, such as Stephen Hawking, believe M-theory (i.e., membrane theory), which is the most comprehensive string theory, is a candidate for the theory of everything. However, there is significant disagreement in the scientific community. Many physicists argue that M-theory is not experimentally verifiable, and on that basis is not a valid theory of science. However, to be fair to all sides, Einstein’s special theory of relativity, published in 1905, was also not experimentally verifiable for years. Today, most of the scientific community views the special theory of relativity as science fact, having withstood over one hundred years of scientific investigation. The scientific community, which didn’t really know what to make of the special theory of relativity in 1905, hails it now as the “gold standard” of theories, arguing that other theories must measure up to the same standards of rigorous investigation. I think science is better served by a more moderate position. In this regard, I agree with prominent physicist and author Michio Kaku, who stated in Nina L. Diamond’s Voices of Truth (2000), “The strength and weakness of physicists is that we believe in what we can measure. And if we can’t measure it, then we say it probably doesn’t exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. The Big Bang is an example. That’s one reason why they scoffed at higher dimensions for so many years. Now we realize that there’s no alternative.”

In essence, we need to keep an open mind, regardless of how bizarre a scientific theory may first appear. However, we need to balance our open-mindedness with experimental verification. This, to my mind, is how science advances.