The March of Time

Time is a mystery to physicists.  The Newtonian notion of absolute time, that is, all clocks run at the same rate, was demolished by Einstein’s relativity theory.  Despite the fact that we know clocks in different reference frames can run at different rates, we don’t know what exactly time is.  Does time run continuously or in discrete packets?  Can one travel backwards in time?  Why don’t the laws of physics tell us what time is?  An intriguing book, Now by Richard Muller, gives us some paths to seek these answers.

During the Victorian age, time was considered a constant for everyone.  A conductor’s watch on the way to London would run at the same rate as the station master’s clock.  Perhaps this is why Big Ben is the perfect symbol for that era.  Einstein proved this notion wrong.  The conductor’s pocket watch will run slower than the motionless station master’s clock.  Given the speeds we travel, the difference is too small to discern.  Einstein’s genius was to follow a theory to its natural conclusion and not allowing false intuition to lead him astray.  Clocks run slower the faster you go.  Gravity also slows the rate of time.  Once you hit the speed of light, or enter the infinitely deep gravity well of a black hole, time stands still.

The question remained, why does time always flow forward?  The most common response to that has been quoting the 2nd law of thermodynamics.  This is the only law in physics that suggests a flow of time.  It states that entropy of the universe always increases with time.  More specifically, a closed system, one which energy cannot enter or leave, must become more disordered over time.  An open system, like the Earth which receives a constant stream of energy from the Sun, can experience a decrease in entropy and an increase in ordered states.  The universe, as far as we know, is a closed system.  This argument was first advanced by Arthur Eddington, but Richard Muller proceeds to poke some holes in it.

Eddington was one of the most accomplished astronomers of the early 20th Century.  One of the first to grasp Einstein’s relativity theory, Eddington led an expedition to the island of Príncipe off the west coast of Africa to observe the solar eclipse of 1919.  Eddington was able to measure the bending of starlight by the Sun as predicted by Einstein.  Once this result was reported by the media, Einstein became the most famous scientist in the world.  Eddington was also what we would call today a populizer of science.  His hypothesis that entropy mandates the flow of time was published in his book The Nature of the Physical World, written in a manner for the general public to enjoy.

However, as Muller notes, clocks do not run slower in local regimes where entropy is decreasing.  A recent experiment verified that, at least on a quantum level, heat can run from a cold to warmer object.  This is a violation of the 2nd law of thermodynamics where energy runs from hot to cold objects.  Some of the news articles on this experiment also claim this has reversed the arrow of time.  Muller considers entropy and time to be two separate concepts.  Rather than rely on entropy, Muller’s hypothesis on time is tied into one of the most asked questions I receive from my students.

When going over the Big Bang, I am often asked what existed before then?  The answer is…nothing.  Space did not exist before the Big Bang.  And neither did time.  Muller speculates that just as space is being created with the expansion of the universe, so is time.  And it is this expansion that gives us the flow of time and a sense of now.  Unlike Eddington’s entropy argument, Muller provides a means of falsifying his theory.

The idea of falsifying a theory might seem odd as we are taught in grade school that experiments prove a theory right.  That’s not quite correct.  As Richard Feynman would say, we don’t prove a theory correct, only that it is not wrong.  Newton’s law of gravity was not wrong for a couple of centuries.  It predicts the motion of most celestial objects quite well.  By the late 1800’s, observations came in that Newton’s laws could not predict, specifically the precession of Mercury’s orbit.  Einstein’s relativity theory provided accurate predictions in two areas Newton could not, when an object is near a large gravity well like the Sun and when an object moves at velocities near the speed of light.

When Einstein realized his theory predicted Mercury’s orbit correctly, he was so excited he suffered from heart palpitations.  For a hundred years, Einstein’s theory has been proven not wrong.  It may take a unification of quantum mechanics and relativity to change that.

Muller speculates that as dark energy is accelerating the expansion of the universe, it must also accelerate time.  That is, time runs faster now than in the past.  To detect this, we must look at galaxies at least 8 billion light years away and make highly precise measurements of their red shifts.  Any excess in the red shift not predicted by space expansion would be caused by time expansion.  At this time, we do not have instruments to make this precise a measurement.  It’s not unusual for theory to race ahead of experimental ability.  After all, it took one hundred years to prove gravitational waves predicted by Einstein actually exist.

Is there any way to falsify relativity or quantum mechanics? To date, both have held up to rigorous testing.  One possibility is the simultaneous collapse of the quantum probability curve upon observation.  With the Copenhagen interpretation of quantum mechanics, atomic particles exist in all possible states along a probability curve.  Once observed, the probability curve collapses instantaneously to its exact state.  As Muller notes, this is in direct odds with relativity where nothing, not even information, can exceed the speed of light.  Perhaps, this can provide a crack in the theory that can lead to a unification of the physics of atoms and of large-scale objects.

Muller’s exploration of time delves into other topics, often Star Trek related. In the case of the transporter, Muller questions if the person assembled at the other end is the same person or a duplicate with the original destroyed.  I thought this was interesting as it follows the plot of James Blish’s one off Star Trek novel Spock Must Die.  Published in 1970, the opening chapter involves a rec room conversation between Scotty and Dr. McCoy, where McCoy frets over the possibility he is no longer his original self.  That is, the transporter destroyed the original McCoy the first time he used it and constructed a replicate each time afterward.  Scotty is nonplussed – “a difference that makes no difference is no difference.”

Would it make a difference?

As Muller notes, our bodies are mostly made of different atoms and cells than it was years ago, yet we maintain our sense of self.  The only thing that does change is the sense of now.  So, when I bought Spock Must Die in the mid-70’s, the body of atoms that searched through department and stationery store bookshelves, is markedly different than the body of atoms that purchased Now online.  In that sense, I am a replicate of my childhood self.  Yet, throughout that whole time, my mind has maintained a continuous state of consciousness.

That brings me back to an argument made in a college philosophy class.  If you take a boat, and replace each plank of wood over time, is it still the original boat?  Boats do not experience the sensation of time, it takes a mind to do that.  The brain, in some regions, does replace neurons throughout life and this may lead to memory loss.  For other regions, it appears not to replicate.  This may explain our continuity of consciousness, but as many a journal article has ended, more research is required in this area.

In the same philosophy class, our professor discussed how we lack access to each other’s state of consciousness.  Unless we could perform a mind meld a la Mr. Spock, our life experience and sense of time is locked up within each individual.  So, is time a matter that can be solved by physics alone?  Or does in require an interdisciplinary approach?  My instinct is that time is a problem for physics to solve.  We require eyes to see light and the mind to interpret it, but the electromagnetic waves that create light was solved by physics.  Until some evidence based results come in, we’ll have to keep an open mind. Many a time instincts have led a scientist astray.  How will this story end?

I honestly don’t know.  Only time will tell.

*Image atop post is a Munich clock store.  Credit:  Gregory Pijanowski