"Reality Check" in Skeptical Briefs September, 2003
Since I have been writing a column called "Reality Check" for several years now, perhaps it is time for me to say what I think is really real. The best definition I can think of is inspired by a comment made by Samuel Johnson in 1763. As described in Boswell's Life of Johnson,
We stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I shall never forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, "I refute it thus."
So, I define something as real when it kicks back after you kick it. In simple terms, this describes the processes of everyday observations, but also the most sophisticated scientific experiments. When we look at an object with our naked eyes, light from some source bounces off the object into our eyes. Or, the object itself may emit light. In either case, the object and the light receptors in our eyes recoil from the momentum that is transferred in the process and generates an electrical signal that is analyzed by our brains.
Scientific observations are basically the same. Not only visible light, but the whole electromagnetic spectrum from radio waves to gamma rays are available to joggle reality, along with sensors far more precise than the human eye to detect the jiggles that are returned. What's more, other particles, such as electrons and neutrinos, are also available as probes and computers are utilized to supplement the analytic capability of our brains. In short, science is not some special method of learning about the world. It is an enhancement of the only method by which we humans, in fact, learn about the world--empirical observation. The stuff of reality that kicks back when you kick it is called matter. And, that's all there is.
In the 1930s, Edward Milne described a procedure by which we can make observations using only a clock to provide quantitative measurements aboutwhatever is out there in reality. This procedure implements the notion that objective reality responds to our probing and that our familiar space-time model of reality is basically a description of this process, a model we have built to describe the data.
Suppose we have a device that can emit a sequence of electromagnetic pulses (tightly grouped bunches of photons) with a fixed time intervalor period controlled by the ticks of a clock. We can think of them as radar pulses, but, in principle, any part of the electromagnetic spectrum can be utilized. Further suppose that we have a device that will detect any electromagnetic pulses returned to us and we use the clock to measure their period along with the time interval between the first pulse transmitted and the first returned.
Consider the case where we observe returning pulses with the same period as the emitted pulses but delayed by a certain amount. We can then make a model to describe this observation. We imagine that "out there" is an object that reflected the pulses back to us. We further imagine that the object is separated from us by a dimension called space. The pulses are pictured as "traveling through space," taking a certain time to reach the object and return.The object is modeled as being separated from us by a "distance" equal to half the observed time delay, multiplied by an arbitrary constant c called the "speed of light." The only purpose of this constant is to allow us the flexibility of expressing distance with different units than time, a rather silly idea.
Next consider the case where the period of the returned pulses has a larger value fromthose transmitted. We model this by saying that the object is "moving" away from us and so the reflected pulses arrive at a lower rate as each succeeding pulse must travel a greater distance. Specifically, we hypothesize that the object is moving away at a speed v along the line between us, which can be calculated from the transmitted and received pulse periods (homework exercise).
Similarly, in the case where the returned pulse rate is lower, we say that the object is "moving" toward us. Of course, this is just the familiar Doppler effect. However, note how we have not presumed a concept if space but introduced it as an operational element of a model that describes observations.
We can extend the picture to two and three spatial dimensions by aiming our sender and receiver in various directions. In this way we measure the vector velocity whose magnitude is the speed. Accelerations can also be measured as the time rate of change of velocity.
This illustrates how space, time, and motion are human constructs, defined operationally in terms of clock measurements. They are not real. They do not kick back. In fact, one does not quite know how to kick them. Still, somethings out there are real, as evidenced by the fact that they do kick back when you kick them. But whether they are really localized objects moving around in space, or something entirely different that can still be modeled that way, we will never know,
Vic Stenger's latest book is Has Science Found God: The Latest Results in the Search for Purpose in the Universe. His web site is at http://spot.colorado.edu/~vstenger.