The name Einstein is synonymous with “someone who is really smart.” His name crops up frequently in pop culture and perhaps even more in scientific discussions about the nature of matter, energy, space and time. As someone with a science background (evolutionary biology and ecology) and a deep curiosity about how our universe works, I began to dive into the world of Einstein about six years ago. I’ve been pretty surprised by what I discovered and this little essay is about my own personal journey and some thoughts on modern physics and the nature of time specifically.
I’m scientifically literate but my physics math isn’t well developed so after seeing Einstein’s popular book, Relativity: The Special and the General Theories at the bookstore in the SFO airport I snapped this little tome up and was pleasantly surprised to find it quite accessible and interesting to read. It was also a nice introduction to his technical papers on his theories.
I learned in his little book about Einstein’s two relativity theories. The first, special relativity, was proposed by Einstein in 1905; the second, general relativity, in 1915. I’m going to focus on Special Relativity in this essay.
Special Relativity was Einstein’s first foray into upending our long-standing notions on the nature of space and time. Counter-intuitively, Special Relativity holds that both space and time are malleable and the speed of light is absolute (i.e., constant for all observers, no matter what their speed). In our normal life, of course, space and time seem pretty absolute in a physical sense. Yes, time can seem to pass more quickly or more slowly based on our mental state but generally we realize that this feeling is psychological and not indicative of an actual change in the passage of time in the world around us.
Einstein’s “time dilation” was not, however, merely psychological. He suggested that time dilation was real and is a function of the speed of the observer. The faster you go the more time slows down. “Moving clocks run slow” is the shorthand for this phenomenon. If a person in a spaceship were able somehow to get to the speed of light, time would literally stop. This isn’t actually possible in Special Relativity because the mass of the spaceship increases the closer it is to the speed of light, requiring more and more energy to go even faster. So massive things can never reach the speed of light. Only massless particles, like photons and neutrinos, can travel at the speed of light.
Similarly, “length contraction” is a function of the speed of an object. This means that what you would measure as a one-meter stick when the stick is at rest would be measured as shorter than one meter when it is in motion. And if that stick were accelerated to almost the speed of light it would be very short indeed when measured by you as a stationary observer.
Why do these things happen? Well, Einstein describes it very clearly in his little book: it all comes down to his choices in defining simultaneity. As described also in Peter Galison’s excellent book, Einstein’s Clocks; Poincaré’s Maps: Empires of Time, clock synchronization was a big issue when Einstein was writing on relativity. Railroads, map-making, colonization and other economic activities all depended in various ways on the ability to synchronize clocks. This is what is meant by simultaneity: how do we know when two events occur at the same time? Einstein chose to define simultaneity operationally, that is, by how we can measure it, rather than as a more abstract notion about when events are “really” simultaneous. Einstein’s approach was part of a tendency toward “positivism,” the scientific choice of focusing only on what can be measured, and downplaying or eliminating entirely those concepts that can’t be measured directly.
Einstein suggested that simultaneity should be defined operationally as the perception of simultaneous events, and this perception would include an assumption that the information being perceived traveled at the same speed no matter where it came from. The example he gives relies on a passenger on a moving train. If the passenger sees two lightning strikes at the same time, one in front and one in the rear of the train (using mirrors if necessary in order to see both ways), they will be considered simultaneous.
But for a person on the embankment next to the moving train these same two lightning flashes would not be simultaneous because of the time it takes for those flashes of light to reach each observer. This is because the train is moving toward one flash and away from the other. But that’s not the case, of course, for the person on the embankment. In this way, simultaneity becomes relative and depends on the motion of the observer. This is a key point and is literally the origin of the entire structure of Einstein’s relativity theories and the strange relativistic effects of time dilation and length contraction.
There is a remarkable and telling passage in Einstein’s little book where he explains his reasoning for his proposed definition of simultaneity (p. 27 of the 1952 edition, emphasis in the original):
“There is only one demand to be made of the definition of simultaneity, namely, that in every real case it must supply us with an empirical decision as to whether or not the conception that has to be defined is fulfilled. That my definition satisfies this demand is indisputable. That light requires the same time to traverse the path [from the first lightning flash in front of the train and from the second lightning flash behind the train] is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own free will in order to arrive at a definition of simultaneity.”
Einstein is, then, stating his view that he’s simply assuming (stipulating) that the speed of light is constant for all observers, no matter their speed, and then seeing where this assumption takes us. A key consequence of the relativity of simultaneity is the idea of a “block universe” in which past, present and future all in some manner exist already. As Einstein stated in a 1952 letter: “The distinction between past, present and future is a stubbornly persistent illusion.”
Einstein’s ideas became widespread after his theory of general relativity was spectacularly confirmed in 1919 by Sir Arthur Eddington’s scientific expedition to Sao Tomé and Principe during a solar eclipse. Eddington found that light did indeed appear to bend around the sun during the eclipse and by the amount Einstein predicted in his general theory. The rest is history.
But not so fast. Once I understood what Einstein had done in crafting his special theory, I objected to his logical moves. When I read and re-read the passage above, I objected to his statement that there is “only one demand” to be made of the definition of simultaneity: that the empirical demand of judging simultaneity in each case is fulfilled. There is also a need to avoid contradiction and to avoid contravening empirical facts. I’m going to focus here on the latter item: contravening empirical facts.
Here’s my beef with Einstein: Special Relativity leads to the idea that the flow of time we know intimately is actually an illusion, as suggested by the Einstein quote above. Even though in every moment of our experience time proceeds from moment to moment, with each present becoming a new present, Special Relativity says this flow is an illusion. And even though the past is, based on our common experience of time, only memory, and the future only imagined, Special Relativity says that the past and future co-exist in some manner with the present “in block.” Moreover, if the past, present and future are all in some manner already in existence then there is no room for free will. As with the flow of time, I sure feel like I have free will so there is an empirical issue when a theory suggests otherwise.
What are we to do?
What do we do when a widely accepted theory seems to clash so directly with our direct evidence of the world around us, particularly with our experience of the flow of time? Falsification is the gold standard of good science and this simply means that experiments that disprove (falsify) a prediction of a theory should lead to rejection of that theory. Now, with our experience of the passage of time there’s no experiment even required for a certain kind of falsification of Special Relativity. We can simply look around us and look to the heavens and see that there is indeed an arrow of time and a flow of time, everywhere we see. This isn’t a trivial issue for Special Relativity. Reconciling time’s arrow and the flow of time with special and general relativity remains a serious issue in physics today.
When asked by my colleague Jonathan Schooler how he reconciled the illusory nature of time in relativity theory with our experience of the flow of time, the physicist Brian Greene said that he sees a psychiatrist. This moment of humor highlights the very real problem that modern physics faces in reconciling the flow of time with our best physical theories about time. Lee Smolin’s 2013 book Time Reborn, examines these issues in detail and he asserts that perhaps relativity theory isn’t the last word about time. He suggests a number of ways in which time may be reclaimed.
We are, then, in a new era of debate about the nature of time. I’ve written a number of short essays challenging the completeness or accuracy of the interpretations of relativity theory that render time illusory and these are included in my book, Eco, Ego, Eros: Essays on Philosophy, Spirituality, and Science. My book also includes an interview with Smolin about his ideas.
Back to the present moment. I’m writing this little essay on a train to Seattle on the winter solstice. I’ve seen no lightning. Yet. Night has just fallen on this, the longest night of the year, a nice reminder of the historical importance of the passage of time and of the seasons.
It turns out that my ongoing interest in Einstein’s theories has led me to chairing a panel on these issues at a conference next June in Helsinki, Finland. Part of the Toward a Science of Consciousness conference, our panel will look at “The physics and metaphysics of time in relation to consciousness.” More interestingly, my colleague, Jonathan Schooler, who I mentioned above, will be joining me on that panel.
Not only that, Schooler is on the same train with me now and we’ve been discussing the implications and alternatives to relativity theory for some time. There was a nice synchronicity in our discovering that we’d be on the same train. It’s the first time for both of us to take Amtrak from Santa Barbara to Seattle. My family is in Seattle and Jonathan’s girlfriend’s family is too. I only found out that he’d be on the train with me a few days ago, after we’d been discussing for a matter of months the Helsinki conference panel and our respective presentations. What’s even weirder about this particular synchronicity is that I got my days wrong with respect to when I was actually supposed to board my train. I boarded the train a day too early! I was able to avoid getting kicked off the train by calling Amtrak and changing my ticket. So the synchronicity of being on the same train with Schooler was even more striking because I wasn’t actually going to be on the same train until I made the mistake of thinking my train left on Sunday when it actually left on Monday.
Anyway, I bring up this personal anecdote because it relates directly to the nature of time and our experience of time. Synchronicities (“same-time”) are all about strange and meaningful coincidences. What do they mean? That’s for each of us to decide. But for now, I’m going to continue to take it as a cue from the universe that I’m on the right (train?) track in continuing to examine the nature of time in relation to consciousness. That’s my story and I’m sticking to it.
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