S4F: Do You Know the Time?

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by David Siegel Bernstein, PhD

Science fiction writers get a lot of mileage driving their characters through the space-time continuum. In most cases, the protagonist manages it without the benefit of a TARDIS (I really need to get one of those). But, what is time? Physicists know how to measure it (time as a metric, i.e., a clock), what direction it flows (Arrow of Time) and how to bend it (General Relativity). I will go over each of these, but for the record, none of them actually tells us what time is. Most ideas on that subject reside in the realm of speculation. And who are best at speculating? Writers and readers of science fiction—of course.

Let’s begin with what’s known: occasionally something happens. This is an observation, for example me catching you reading this post. If it happens again, we have an interval that can be measured (and hopefully a habit of you reading my stuff). Order, interval, and regularity are the characteristics of a clock. A clock can be heartbeats, planet rotation, or the ticking of a mechanical device. Any of these can be used to measure time, except in doing so we get the problem of whose clock is right. Is there a master clock—a single absolute time that flows uniformly as assumed by Newton? I’ll answer in the next post of Science for Fiction.

Now let’s return to the halcyon days when classical physics ruled and the study of thermodynamics was cutting edge. It is from the second law thermodynamics we derive our old friend entropy, the measure of disorder within an isolated system. For example, think of your bedroom. If you make no effort to clean it, it will gradually (dare I say quickly?) mess up. The only way to prevent this is by regularly cleaning it. In physics, this is the equivalent to pumping energy into a system, the only way to slow down or reverse entropy. However in an isolated system such as our universe, energy can not be added, so entropy will continue increasing. This means, if no universal housekeeper pops in (maybe in science fiction) everything, everywhere in our universe will gradually fall into disarray. The general rise in entropy—disarray—gives us a sequence (direction) of events, what physicists call the “Arrow of Time.”

Here are a few of interesting tidbits to keep in mind about entropy:

  1. Entropy does not tell us the past leads to the future, only it goes from order to disorder. This is an important distinction.
  2. Entropy cannot increase forever. When it reaches its maximum the Arrow of Time will break. Is this the end of time? Speculate. I dare you.
  3. Because we need stuff to get messed up, we need matter for entropy to exist. So until a particle somewhere decides to decay, there is no way to determine time using entropy. Does it mean without matter time doesn’t exit?

I glance at my time-keeping device.  Oh, it looks like I’m out of time for this post.  Rumor has it things will get weird in the next posting of Science for Fiction because we will find out what Einstein has to say on the subject of time—at least what he might have said if he were alive and contributing to this blog, but he’s not so you’ll get my take. After that, we can finally discuss what fiction writers really want from reading this: how can we travel through time?

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3 Responses to “S4F: What’s the Matter with Antimatter?”

  1. William Haloupek Says:
    March 8th, 2012 at 6:43 pm

    Interesting article!

    Stealth is easier than cloaking, and we already have the technology.

  2. David Siegel Bernstein Says:
    March 30th, 2012 at 7:41 am

    William you are absolutely correct. Invisibility (a descendant of Stealth) is not only easier to achieve, but a future topic. I thought I’d go over invisibility first to please those who enjoy Harry Potter, but want to write hard science fiction.

  3. donnagalanti Says:
    April 5th, 2012 at 5:39 am

    Fascinating post. We are so much empty space and mostly water. Amazing to think how we can be beings of intelligence and creativity.

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