Time Travel: A History by James Gleick

There are two principal topics in this book: time travel and time. Since time travel is fiction, the history of time travel presented in the book is the history of ideas about time travel, mostly ideas expressed in novels like H. G. Wells’s The Time Machine, short stories like Robert Heinlein’s “By His Bootstraps” and movies like The Terminator. Time travel can be fun to think about, and ideas about time travel are suggestive of what people have thought about time, but I quickly lost interest in the topic. So I ended up skimming those sections of the book.

On the other hand, Gleick’s discussion of time itself was worth reading. He covers both physics and philosophy, and does an excellent job explaining complex, competing ideas about time. For example:

You can say Einstein discovered that the universe is a four-dimensional space-time continuum. But it’s better to say, more modestly, Einstein discovered that we can describe the universe as a four-dimensional space-time continuum and that such a model enables physicists to calculate almost everything, with astounding exactitude, in certain limited domains. Call it space-time for the convenience of reasoning….

You can say the equations of physics make no distinction between past and future, between forward and backward in time. But if you do, you are averting your gaze from the phenomena dearest to our hearts. You leave for another day or another department the puzzles of evolution, memory, consciousness, life itself. Elementary processes may be reversible; complex processes are not. In the world of things, time’s arrow is always flying.

It’s an interesting question whether the calculations of the physicists are so accurate because the universe really is a four-dimensional space-time continuum. And is the passage of time some kind of illusion, like many physicists believe? Gleick leans toward time being quite real and physicists taking their models a bit too seriously. I think this would have been a better book if he spent more time on the physics and philosophy and less time on the fiction.

Time Flies and Stuff Happens

Jim Holt has written a nice article on that eternally perplexing subject: the nature of time. As expected, it left me properly perplexed.

Consider this passage:

Events judged to be in the past by one observer may still lie in the future of another; therefore, past and present must be equally definite, equally “real.” In place of the fleeting present, we are left with a vast frozen timescape—a four-dimensional “block universe”… Nothing is “flowing” from one event to another. As the mathematician Hermann Weyl memorably put it, “The objective world simply is; it does not happen. Einstein, through his theory of relativity, furnished a scientific justification for a philosophical view of time [called] “eternalism.” Time, according to this view, belongs to the realm of appearance, not reality. The only objective way to see the universe is as God sees it: sub specie aeternitatis [“under the aspect of eternity”].

But wait (if it’s appropriate to use that term). What is the ultimate fate of the universe?

Ever since its birth in the Big Bang, some 13.82 billion years ago, the universe has been expanding. If this expansion continues forever … the stars will burn out; black holes will evaporate; atoms and their subatomic constituents will decay. In the deep future, the remaining particles … will spread out into the void, becoming so distant from one another that they will cease to interact. Space will become empty except for the merest hint of “vacuum energy”. Yet in this future wasteland of near nothingness, time will go on; random events will continue to occur; things will “fluctuate” into existence, thanks to the magic of quantum uncertainty, only to disappear again into the void….But there is another possible cosmic fate. By and by, at some point in the far future, the expansion that the universe is currently undergoing might be arrested—maybe by gravity, maybe by some force that is currently unknown. Then all the hundreds of billions of galaxies will begin to collapse back on themselves, eventually coming together in a fiery all-annihilating implosion.

Well, you might ask, which is it? Does time belong to the realm of appearance, not reality? Or has the universe been expanding for 13.82 billion years?

Is it correct to say the “objective world simply is; it does not happen”? Or should we say that stuff happens all the time?

Holt is probably correct when he says that “most physicists … agree with Einstein that time’s passage is an illusion; they are eternalists.” Here’s how the “Time” article in the Stanford Encyclopedia of Philosophy defines eternalism:

Eternalism says that objects from both the past and the future exist just as much as present objects. According to eternalism, non-present objects like Socrates and future Martian outposts exist…, even though they are not currently present. We may not be able to see them at the moment, on this view, and they may not be in the same space-time vicinity that we find ourselves in …, but they should nevertheless be on the list of all existing things.

The idea here is that the history of the universe may be thought of as a series of events on a continuum that stretches from the past to the future, but which never includes a moment that is “now”. We can say that one event is earlier or later than another (e.g. the Big Bang is about 14 billion years earlier than December 1, 2014), but it’s wrong to think that the moment you or I perceive as “now” has any special significance, so far as the universe is concerned.

It’s as if the timeline of the universe were a long, straight line between points A and B. Between A and B there are many other points, but none of them is more real than any other. Instead, each point on the line and each moment in the history of the universe (and every object that has ever existed or ever will) exists in the very same way.

Nevertheless, as Holt goes on to say, some physicists are “presentists”. So are some philosophers (as well as most “normal” people who have ever thought about the issue). Presentists believe that “now is a special moment that really advances…; this would still be true, they believe, even if there were no observers like us in the universe”. In the words of the Stanford Encyclopedia:

Presentism is the view that only present objects exist. … According to Presentism, if we were to make an accurate list of all the things that exist … there would be not a single non-present object on the list. Thus, you and the Taj Mahal would be on the list, but neither Socrates nor any future Martian outposts would be included.  

I confess that I find presentism much easier to understand than eternalism. In fact, eternalism sounds sufficiently crazy that there must be extremely good reasons for very smart people to believe it.

Is every object and every event in the history of the universe equally real, so that the biggest triceratops who ever lived and the dinner you’re going to have next New Year’s Eve are just as real as the chair you’re sitting on? Holt says Einstein answered that question and the answer is “Yes!”:

What Einstein [showed] was that there is no universal “now.” Whether two events are simultaneous is relative to the observer. And once simultaneity goes by the board, the very division of moments into “past,” “present,” and “future” becomes meaningless. Events judged to be in the past by one observer may still lie in the future of another; therefore, past and present must be equally definite, equally “real.” In place of the fleeting present, we are left with a vast frozen timescape—a four-dimensional “block universe.”

Maybe that’s the conclusion to be drawn from the scientific evidence. On the other hand, quoting the Stanford Encyclopedia again:

Perhaps it can be plausibly argued that while relativity entails that it is physically impossible to observe whether two events are absolutely simultaneous, the theory nevertheless has no bearing on whether there is such a phenomenon as absolute simultaneity.

Thinking about what might be the case beyond our powers of observation may qualify as metaphysics rather than physics, but it seems to me that change is a fundamental feature of the universe, time is the rate of change, and wherever and whenever changes occur, time is passing. My “now” is different from your “now” in the same way that my “here” is different from your “here”. But each “now” marks a real point in time (a point in the overall history of the universe), just like each “here” marks a real point in space (the universe’s overall expanse).

Eternalism, however, treats time as if it’s one more spatial dimension, a dimensioin in which all locations are equally real. I don’t think time is like that at all. Some moments (or temporal locations) were real, some will be real, and when a moment becomes real, it’s now. Not merely from our perspective, but in reality.

Anyway, that’s my opinion. If you and I aren’t more real than Socrates or the 75th President of the United States (whoever she turns out to be) in a very significant sense, meaning that we exist and they sure don’t, well, this isn’t a universe I want to spend time in.

A Brief History of the Philosophy of Time by Adrian Bardon

Someone thought it would be a good idea to call this book A Brief History of the Philosophy of Time, no doubt as an allusion to Stephen Hawking’s A Brief History of Time. The book’s focus isn’t historical, however. It’s a brief introduction to the philosophy of time, with chapters devoted to the nature of time, its direction, its passage, and a few other standard topics. Professor Bardon’s explanations of the issues are almost always clear and the book is relatively easy to read.

The most interesting aspect of the book is Bardon’s strong preference for the “static theory of time”. That’s the counter-intuitive view that the apparent passage of time is an illusion, or, more precisely, that it’s merely the result of our human perspective. The static theory isn’t new. The Greek philosopher Parmenides argued for it 2,500 years ago. J. M. E. McTaggart unhelpfully gave the name “B-series” to this conception of time, distinguishing it from the more familiar “A-series” or “dynamic theory of time” that most people accept, according to which time passes as events move from the future to the past:

The static theorist believes in change, but only understood in a way that doesn’t commit one to the passage of time: Change, on the static theory, is to be understood as merely referring to the world being timelessly one way and timelessly another way at a subsequent moment.  

The B-series places every event in the history of the universe on an unchanging timeline. On this view, it‘s appropriate to describe every event as either earlier than, later than or simultaneous with every other event. But there is no special significance to the present moment (the “now”). It’s no more descriptive to say that an event is happening “now” than to say that a location is “here” or a direction is “up”. The idea that some events are in the past or future compared to the present moment is an illusion. So far as our “block universe” is concerned, all moments in time are equally real, not just the present one.

The static view of time isn’t universally accepted, but it’s popular among physicists and philosophers. One reason Bardon accepts it is that he thinks McTaggart’s arguments for the static theory and against the passage of time are “devastating”.

I think they’re confused. For example, McTaggart and Bardon hold that it’s self-contradictory to say that an event like the 1960 World Series used to be in the future and is now in the past, since by doing so we are attributing contradictory properties (being past and being future) to the same thing (a particular event). But being past or future are relational properties that vary with time. Saying an event was future and is now past is akin to saying a person was married and is now divorced, hardly a contradiction.

Bardon also presents Einstein’s theory of special relativity as a reason for doubting that time passes. Physicists have confirmed that two observers moving at great speed relative to each other will perceive time differently. For this reason, there is no place in physics for saying that two events are truly simultaneous, or which of two events happened first, except from a particular point of view: 

If there is no privileged vantage point from which to determine the “truth” of the matter – and the whole point of relativity is that there is not – then temporal properties like past, present and future cannot possibly be aspects of reality as it is in itself. They must be subjective and perspectival in nature.

Yet the theory of relativity pertains to how events can be observed or measured, given the constant speed of light. It doesn’t tell us how reality is “in itself”; it tells us how reality is perceived. Just because we can’t always know when two events occurred doesn’t mean there is no truth to the matter. A truth can be unknowable.

Furthermore, if relativity implies that there is no objective A-series past or future, it also implies that there is no objective B-series “earlier” or “later”. Bardon tries to draw a distinction between relativity’s implications for the dynamic and static theories of time, but it isn’t convincing. Perhaps the book would have been better if Bardon hadn’t so clearly taken sides.

Getting Down to the Truly Nitty Gritty

I live near one of the research centers that used to be known as Bell Labs, the place where scientists found evidence of the Big Bang; invented the transistor and the laser; and developed the UNIX operating system and C programming language. A friend once suggested that I try to get a job there, since they would always need janitors.

Nevertheless, even with my weak qualifications, I enjoy reading about theoretical physics. I didn’t understand much of the article below, but it’s good to know that physicists are trying to understand where space and time come from. You might think space and time are fundamental, but there appears to be more to the story.

If you follow the link to the article, you can click on this diagram and make it bigger (spatially, not temporally).

quantum-gravity-nature-online

http://www.nature.com/news/theoretical-physics-the-origins-of-space-and-time-1.13613

Time Reborn: From the Crisis in Physics to the Future of the Universe by Lee Smolin

The theoretical physicist Lee Smolin has written 4 books. I’ve read 3 1/2 of them.

His first book, The Life of the Cosmos, applied the theory of evolution to cosmology. Smolin suggested that our universe might be a good home for life because universes breed new universes, which differ somewhat from their parents. Over time, a universe with lots of black holes will generate a number of new universes with lots of black holes, and universes with lots of black holes tend to be hospitable for life, since their fundamental constants (like the strength of their subatomic forces) have values that permit life to evolve.

His next book, Three Roads to Quantum Gravity, was too technical for me, but I did finish his 3rd book, The Trouble With Physics. In that one, he argued that string theory is much too popular among physicists, since it isn’t a proper scientific theory. It’s too speculative and might never generate testable predictions.

Now there is Time Reborn. This is a kind of sequel to Smolin’s earlier books. He still subscribes to the evolutionary views presented in The Life of the Cosmos, but his principal thesis now is that time is real. In fact, time is more real than space. This contradicts the common view among physicists and philosophers that space and time are the four dimensions that make up “spacetime”. The standard view among physicists is that all events, whether past, present or future, are equally real. There is nothing special about the present moment. In fact, our perception that time passes is an illusion.

Smolin argues that this consensus view of the universe as a “block universe”, in which all moments are the same, is a mistake. He agrees that the laws of physics and the equations that express them can run forwards or backwards, but only on scales smaller than the universe as a whole. The planets could revolve the other way around the sun, just like clocks can run in reverse. But the universe as a whole has a history that is real and a future that isn’t determined. Smolin thinks that treating time as real might help resolve certain issues in physics, such as the “arrow of time”, i.e., the fact that certain processes always go in one direction (entropy tends to increase in isolated systems).

Professor Smolin tries to explain how his view of time fits with Einstein’s special theory of relativity (in which temporal properties are relative to an observer) and how something can act like a particle and a wave at the same time (as shown by the famous “double-slit” experiment). I don’t know if those explanations or some of his other technical explanations make sense. But it was reassuring to read a book by a reputable physicist who believes that time is real, physicists have overemphasized the importance of mathematics in understanding the universe, and there is a reality beyond what we can observe. Smolin also believes that there are probably more fundamental, deterministic laws that underlie quantum mechanics. I believe that’s what Einstein thought too.

Time Reborn veers into philosophy at times. There is much discussion of the Principles of Sufficient Reason and the Identity of Indiscernibles. The book concludes with some comments on subjects that aren’t physics, like the nature of consciousness. Smolin’s philosophical remarks are relatively unsophisticated. I assume his physics is better.

Even if he’s wrong about the reality of time, however, I enjoyed the book. For one thing, I can now see how two particles at opposite ends of the universe could be “entangled”, such that a change to one would automatically result in an immediate change to the other. Space might have more dimensions than we recognize. In another spatial dimension, the two entangled particles might be very close neighbors, making what Einstein called “spooky action at a distance” (“spukhafte Fernwirkung“) less mysterious. That makes me feel a lot better.