As you well know, time goes forward.  We cannot go backwards in time — only forward.  But supposedly the laws of physics also work in reverse.  (I don’t remember that from school, but perhaps I was drawing monster trucks that day.)  So why doesn’t the universe ever run backwards?  Physicists have often wondered why time seems to only go forward.  They call this “the arrow-of-time” mystery.  Lorenzo Maccone, an MIT physicist, has spent time contemplating why it doesn’t happen.  (You’re going to enjoy this one, if your brain doesn’t crash.)

If the universe were to run backwards, a cold cup of coffee might spontaneously heat up, or a broken piece of glass might un-break.   (Hold on to your logic, because we’re only getting started!)  These events are governed by the Second Law of Thermodynamics, which states that the entropy (degree of disorder) of a closed system never decreases.  Regardless of the fancy scientific terms, things work the way they’re supposed to — in forward motion.

However, Maccone’s “solution” is that “entropy-decreasing events occur all the time”, so there’s really no mystery about the arrow-of-time.  So why don’t we witness these things?   After all, wouldn’t you notice if certain events started running backwards?  I think everyone would.  So how does Maccone explain this?  He says that according to quantum mechanics, if you ever do witness an “entropy-decreasing event”, those memories of the event “will have been erased by necessity”.

Just to clarify, Maccone says you actually have the memories, but then they are subsequently erased.   He says this happens because of “quantum entanglement“.   Basically, you and “the system” have become entangled and cannot properly be described separately.  Obviously, you can’t have this entanglement, so there’s a disentangling process.  Maccone says, “the disentangling operation will erase this entanglement, namely the observer’s memory”.  (Why isn’t the actual event ever erased, where we remember something backwards that once happened but then never happened?)  Anyway, Maccone published a paper that explained his conclusion mathematically.  (I was unable to reach the same conclusion mathematically, unless I multiplied by the page number a few times.)

In layman’s terms, Maccone thinks that because of symmetry, if there are transformations that increase entropy (and there are), then there must be transformations that decrease entropy.  (Is that like saying because a star blows up, then it should eventually unexplode?)

Unfortunately for Maccone, there is no proof of these backward events, because he cannot remember them.  🙂

Not everyone in this field of study agree with Maccone (which is not surprising).  Huw Price, head of the Centre for Time at the University of Sydney, thinks Maccone is simply trading one mystery for another: “The proposal to explain the thermodynamic arrow in terms of the [quantum] effects of observers has an obvious flaw.  It doesn’t explain why all observers have the same orientation in time. … Why don’t some observers remember what we call the future, and accumulate information towards what we call the past?”  See, I can explain that, and even with common sense!   The past has already happened, but the future hasn’t happened yet.  Is it really that simple?

In the last sentence of the article about this, the writer said, “Whether or not Maccone has solved the mystery of the arrow of time is unclear.”  I can answer that one, too, without even drawing upon the vast reserves of knowledge accumulated from collegiate study.  The answer, in one word, is NO.